Sample records for active comet nuclei
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The study of the physics of cometary nuclei
NASA Technical Reports Server (NTRS)
Whipple, F. L.
1983-01-01
On the basis of the icy conglometate model of cometary nuclei various observations demonstrate the spotted nature of many or most nuclei, i.e., regions of unusual activity, either high or low. Rotation periods, spin axes and even precession of the axes have been determined. Narrow dust jets near the nuclei of some bright comets require that small sources be embedded in larger active areas. Certain evidence suggests that very dusty areas and very dusty comets may be less active, respectively, than surrounding areas or other comets.
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What if chondritic porous interplanetary dust particles are not the real McCoy
NASA Astrophysics Data System (ADS)
Rietmeijer, Frans J. M.
To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.
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What if chondritic porous interplanetary dust particles are not the real McCoy
NASA Technical Reports Server (NTRS)
Rietmeijer, Frans J. M.
1989-01-01
To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.
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The study of the physics of cometary nuclei
NASA Technical Reports Server (NTRS)
Whipple, F. L.; Marsden, B. G.; Sekanina, Z.
1976-01-01
A semiannual progress report describing the work completed during the period 1 September 1975 to 29 February 1976 on the physics of cometary nuclei was given. The following items were discussed: (1) a paper entitled ""A speculation about comets and the earth'', (2) a chapter entitled"" The physics of comets'' for ""Reviews of Astronomy and Astrophysics'', (3) continuing work on split comets, and (4) results dealing with a new application of nongravitational solar-radial forces as a measure of comet nucleus dimensions and activity.
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Physical Characteristics of Asteroid-like Comet Nucleus C/2001 OG108 (LONEOS)
NASA Technical Reports Server (NTRS)
Abell, P. A.; Fernandez, Y. R.; Pravec, P.; French, L. M.; Farnham, T. L.; Gaffey, M. J.; Hardersen, P. S.; Kusnirak, P.; Sarounova, L.; Sheppard, S. S.
2003-01-01
For many years several investigators have suggested that some portion of the near-Earth asteroid population may actually be extinct cometary nuclei. Evidence used to support these hypotheses was based on: observations of asteroid orbits and associated meteor showers (e.g. 3200 Phaethon and the Geminid meteor shower); low activity of short period comet nuclei, which implied nonvolatile surface crusts (e.g. Neujmin 1, Arend-Rigaux); and detections of transient cometary activity in some near-Earth asteroids (e.g. 4015 Wilson-Harrington). Recent investigations have suggested that approximately 5-10% of the near- Earth asteroid population may be extinct comets. However if members of the near-Earth asteroid population are extinct cometary nuclei, then there should be some objects within this population that are near their final stages of evolution and so should demonstrate only low levels of activity. The recent detections of coma from near-Earth object 2001 OG108 have renewed interest in this possible comet-asteroid connection. This paper presents the first high quality ground-based near-infrared reflectance spectrum of a comet nucleus combined with detailed lightcurve and albedo measurements.
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On observing comets for nuclear rotation
NASA Astrophysics Data System (ADS)
Whipple, F. L.
1981-10-01
The prevalent non-gravitational motions among comets demonstrate that the sublimination does not reach a maximum at the instant of maximum insolation on the nucleus. The occurrence of halos or "parabolic" envelopes in the comae of some comets and of jets, rays, fans, streamers and similar phenomena very near the nucleus in the brightest comets demonstrates that the sublimation process is not uniform over the nuclei. In other words, the nuclei of many comets contain relatively small active regions which provide much or most of the sublimation when these areas are turned toward the Sun. The period of rotation can be determind by measurement of the diameters of the halos or of the latus recta of the "parabolic" envelopes, if the expansion velocities are averaged from observations as a function of solar distance. Experience from analyses of some 80 well observed comets shows that the nuclei are "spotted" for more than a third of all comets, regardless of the "age" as measured by the original inverse semimajor axis including correction for planetary perturbations.
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P/2006 HR30 (Siding Spring): A Low-activity Comet in Near-Earth Space
NASA Technical Reports Server (NTRS)
Hicks, Michael D.; Bauer, James M.
2007-01-01
The low cometary activity of P/2006 HR30 (Siding Spring) allowed a unique opportunity to study the nucleus of a periodic comet while near perihelion. P/2006 HR30 was originally targeted as a potential extinct comet, and we measured spectral reflectance and dust production using long-slit CCD spectroscopy and wide-field imaging obtained at the Palomar Mountain 200 inch telescope on 2006 August 3 and 4. The dust production Afp = 19.7 +/- 0.4 cm and mass-loss rate Q(dust) 4.1 +/- 0.1 kg/sec of the comet were approximately 2 orders of magnitude dust less than 1P/Halley at similar heliocentric distance. The VRI colors derived from the spectral reflectance were compared to Kuiper Belt objects, Centaurs, and other cometary nuclei. We found that the spectrum of P/2006 HR30 was consistent with other comets. However, the outer solar system bodies have a color distribution statistically distinct from cometary nuclei. It is our conjecture that cometary activity, most likely the reaccretion of ejected cometary dust, tends to moderate and mute the visible colors of the surface of cometary nuclei.
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The mass disruption of Jupiter Family comets
NASA Astrophysics Data System (ADS)
Belton, Michael J. S.
2015-01-01
I show that the size-distribution of small scattered-disk trans-neptunian objects when derived from the observed size-distribution of Jupiter Family comets (JFCs) and other observational constraints implies that a large percentage (94-97%) of newly arrived active comets within a range of 0.2-15.4 km effective radius must physically disrupt, i.e., macroscopically disintegrate, within their median dynamical lifetime. Additional observational constraints include the numbers of dormant and active nuclei in the near-Earth object (NEO) population and the slope of their size distributions. I show that the cumulative power-law slope (-2.86 to -3.15) of the scattered-disk TNO hot population between 0.2 and 15.4 km effective radius is only weakly dependent on the size-dependence of the otherwise unknown disruption mechanism. Evidently, as JFC nuclei from the scattered disk evolve into the inner Solar System only a fraction achieve dormancy while the vast majority of small nuclei (e.g., primarily those with effective radius <2 km) break-up. The percentage disruption rate appears to be comparable with that of the dynamically distinct Oort cloud and Halley type comets (Levison, H.F., Morbidelli, A., Dones, L., Jedicke, R., Wiegert, P.A., Bottke Jr., W.F. [2002]. Science 296, 2212-2215) suggesting that all types of comet nuclei may have similar structural characteristics even though they may have different source regions and thermal histories. The typical disruption rate for a 1 km radius active nucleus is ∼5 × 10-5 disruptions/year and the dormancy rate is typically 3 times less. We also estimate that average fragmentation rates range from 0.01 to 0.04 events/year/comet, somewhat above the lower limit of 0.01 events/year/comet observed by Chen and Jewitt (Chen, J., Jewitt, D.C. [1994]. Icarus 108, 265-271).
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Structure and density of cometary nuclei
NASA Astrophysics Data System (ADS)
Weissman, Paul R.; Lowry, Stephen C.
2008-09-01
Understanding the nature of the cometary nucleus remains one of the major problems in solar system science. Whipple’s (1950) icy conglomerate model has been very successful at explaining a range of cometary phenomena, including the source of cometary activity and the nongravitational orbital motion of the nuclei. However, the internal structure of the nuclei is still largely unknown. We review herein the evidence for cometary nuclei as fluffy aggregates or primordial rubble piles, as first proposed by Donn et al. (1985) and Weissman (1986). These models assume that cometary nuclei are weakly bonded aggregations of smaller, icy- onglomerate planetesimals, possibly held together only by self-gravity. Evidence for this model comes from studies of the accretion and subsequent evolution of material in the solar nebula, from observations of disrupted comets, and in particular comet Shoemaker-Levy 9, from measurements of the ensemble rotational properties of observed cometary nuclei, and from recent spacecraft missions to comets. Although the evidence for rubble pile nuclei is growing, the eventual answer to this question will likely not come until we can place a spacecraft in orbit around a cometary nucleus and study it in detail over many months to years. ESA’s Rosetta mission, now en route to comet 67P/Churyumov- Gerasimenko, will provide that opportunity.
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Analytical study of comet nucleus samples
NASA Technical Reports Server (NTRS)
Albee, A. L.
1989-01-01
Analytical procedures for studying and handling frozen (130 K) core samples of comet nuclei are discussed. These methods include neutron activation analysis, x ray fluorescent analysis and high resolution mass spectroscopy.
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The Diversity of Carbon in Cometary Refractory Dust Particles
NASA Technical Reports Server (NTRS)
Wooden, D. H.
2018-01-01
When comparing the dark icy surfaces of outer solar system small bodies and the composition of carbonaceous chondrites derived from dark asteroids we find a significant discrepancy in the assessed amounts of elemental carbon: up to 80% amorphous carbon is used to model the dark surfaces of Kuiper Belt Objects and Centaurs whereas at most 5% of elemental carbon is found in carbonaceous chondrites. If we presume that regimes of comet nuclei formation are analogous to disk regimes where other outer solar system ice-rich bodies formed then we can turn to comet dust to gain insights into the diversity in the concentration and forms of carbon available in the outer disk. Comet dust offers important insights into the diversity in the amounts and forms of carbon that were incorporated into aggregate dust particles in the colder parts of the protoplanetary disk out of which comet nuclei accreted. Comet nuclei are amongst the most primitive bodies because they have remained cold and unequilibrated. Comet dust particles reveal the presence of forms of elemental carbon and of soluble and insoluble organic matter, and in a great diversity of concentrations from very little, e.g., Stardust samples of comet 81P/Wild 2, to 80% by volume for Ultra Carbonaceous Antarctic Micro Meteorites (UCAMMs). Cometary outbursts and/or jet activity also demonstrate variations in the concentration of carbon in the grains at different grain sizes within a single comet. We review the diversity of carbon-bearing dust grains in cometary samples, flyby measurements and deduced from remote-sensing to enrich the discussion about the diversity of carbonaceous matter available in the outer ice-rich disk at the time of comet nuclei formation.
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Cometary Evolution: Clues on Physical Properties from Chondritic Interplanetary Dust Particles
NASA Technical Reports Server (NTRS)
Rietmeijer, Frans J. M.; Mackinnon, Ian D. R.
1989-01-01
The degree of diversity or similarity detected in comets depends primarily on the lifetimes of the individual cometary nuclei at the time of analysis. It is inherent in our understanding of cometary orbital dynamics and the seminal model of comet origins by Oort that cometary evolution is the natural order of events in our Solar System. Thus, predictions of cometary behaviour in terms of bulk physical, mineralogical or chemical parameters should contain an appreciation of temporal variation(s). Previously, Rietmeijer and Mackinnon developed mineralogical bases for the chemical evolution of cometary nuclei primarily with regard to the predominantly silicate fraction of comet nuclei. We suggested that alteration of solids in cometary nuclei should be expected and that indications of likely reactants and products can be derived from judicious comparison with terrestrial diagenetic environments which include hydrocryogenic and low-temperature aqueous alterations. In a further development of this concept, Rietmeijer provides indirect evidence for the formation of sulfides and oxides in comet nuclei. Furthermore, Rietmeijer noted that timescales for hydrocryogenic and low-temperature reactions involving liquid water are probably adequate for relatively mature comets, e.g. P/comet Halley. In this paper, we will address the evolution of comet nuclei physical parameters such as solid particle grain size, porosity and density. In natural environments, chemical evolution (e.g. mineral reactions) is often accompanied by changes in physical properties. These concurrent changes are well-documented in the terrestrial geological literature, especially in studies of sediment diagenesis and we suggest that similar basic principles apply within the upper few meters of active comet nuclei. The database for prediction of comet nuclei physical parameters is, in principle, the same as used for the proposition of chemical evolution. We use detailed mineralogical studies of chondritic interplanetary dust particles (IDPS) as a guide to the likely constitution of mature comets traversing the inner Solar System. While there is, as yet, no direct proof that a specific sub-group or type of chondritic IDP is derived from a specific comet, it is clear that these particles are extraterrestrial in origin and that a certain portion of the interplanetary flux received by the Earth is cometary in origin. Two chondritic porous (CP) MPs, sample numbers W7010A2 and W7029Cl, from the Johnson Space Center Cosmic Dust Collection have been selected for this study of putative cometary physical parameters. This particular type of particle is considered a likely candidate for a cometary origin on the basis of mineralogy, bulk composition and morphology. While many IDPs have been subjected to intensive study over the past decade, we can develop a physical parameter model on only these two CP IDPs because few others have been studied in sufficient detail.
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Cometary Evolution: Clues on Physical Properties from Chondritic Interplanetary Dust Particles
NASA Technical Reports Server (NTRS)
Reitmeijer, Frans J. M.; Mackinnon, Ian D. R.
1997-01-01
The degree of diversity or similarity detected in comets depends primarily on the lifetimes of the individual cometary nuclei at the time of analysis. It is inherent in our understanding of cometary orbital dynamics and the seminal model of comet origins that cometary evolution is the natural order of events in our Solar System. Thus, predictions of cometary behaviour in terms of bulk physical, mineralogical or chemical parameters should contain an appreciation of temporal variation(s). Previously, Rietmeijer and Mackinnon [1987] developed mineralogical bases for the chemical evolution of cometary nuclei primarily with regard to the predominantly silicate fraction of comet nuclei. We suggested that alteration of solids in cometary nuclei should be expected and that indications of likely reactants and products can be derived from judicious comparison with terrestrial diagenetic environments which include hydrocryogenic and low-temperature aqueous alterations. In a further development of this concept, Rietmeijer [1988] provides indirect evidence for the formation of sulfides and oxides in comet nuclei. Furthermore, Rietmeijer [1988] noted that timescales for hydrocryogenic and low-temperature reactions involving liquid water are probably adequate for relatively mature comets, e.g. P/comet Halley. In this paper, we will address the evolution of comet nuclei physical parameters such as solid particle grain size, porosity and density. In natural environments, chemical evolution (e.g. mineral reactions) is often accompanied by changes in physical properties. These concurrent changes are well-documented in the terrestrial geological literature, especially in studies of sediment diagenesis and we suggest that similar basic principles apply within the upper few meters of active comet nuclei. The database for prediction of comet nuclei physical parameters is, in principle, the same as used for the proposition of chemical evolution. We use detailed mineralogical studies of chondritic interplanetary dust particles (IDPS) as a guide to the likely constitution of mature comets traversing the inner Solar System. While there is, as yet, no direct proof that a specific sub-group or type of chondritic IDP is derived from a specific comet, it is clear that these particles are extraterrestrial in origin and that a certain portion of the interplanetary flux received by the Earth is cometary in origin. Two chondritic porous (CP) IDPS, sample numbers W701OA2 and W7029CI, from the Johnson Space Center Cosmic Dust Collection have been selected for this study of putative cometary physical parameters. This particular type of particle is considered a likely candidate for a cometary origin on the basis of mineralogy, bulk composition and morphology. While many IDPs have been subjected to intensive study over the past decade, we can develop a physical parameter model on only these two CP IDPs because few others have been studied in sufficient detail.
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Infrared Observations of Cometary Dust and Nuclei
NASA Technical Reports Server (NTRS)
Lisse, Carey
2004-01-01
This bibliography lists citations for publications published under the grant. Subjects of the publications include cometary dust, instellar and interplanetary dust, comet nuclei and comae, Comet Hale-Bopp, infrared observations of comets, mass loss, and comet break-up.
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NASA Technical Reports Server (NTRS)
A'Hearn, Michael F.; Belton, Michael J. S.; Delamere, W. Alan; Feaga, Lori M.; Hampton, Donald; Kissel, Jochen; Klaasen, Kenneth P.; McFadden, Jessica M.; Meech, Karen J.; Melosh, H. Jay;
2011-01-01
Understanding how comets work, i,e., what drives their activity, is crucial to using comets to study the early solar system. EPOXI flew past comet 103P/Hartley 2, one with an unusually small but very active nucleus. taking both images and spectra. Unlike large, relatively inactive nuclei, this nncleus is outgassing primarily due to CO2, which drags chnnks of ice out of the nnclens. It also shows significant differences in the relative abundance of volatiles from various parts of the nucleus.
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Comet nuclei and Trojan asteroids - A new link and a possible mechanism for comet splittings
NASA Technical Reports Server (NTRS)
Hartmann, William K.; Tholen, David J.
1990-01-01
Relatively elongated shapes, implied by recent evidence of a greater incidence of high amplitude lightcurves for comet nuclei and Trojan asteroids than for similarly scaled main belt asteroids, are suggested to have evolved among comet nuclei and Trojans due to volatile loss. It is further suggested that such an evolutionary course may account for observed comet splitting; rotational splitting may specifically occur as a result of evolution in the direction of an elongated shape through sublimation. Supporting these hypotheses, the few m/sec separation velocities projected for rotationally splitting elongated nuclei are precisely in the observed range.
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NASA Technical Reports Server (NTRS)
Belton, Michael J. S.; Mueller, Beatrice
1991-01-01
The scientific objectives were as follows: (1) to construct a well sampled photometric time series of comet Halley extending to large heliocentric distances both post and pre-perihelion passage and derive a precise ephemeris for the nuclear spin so that the physical and chemical characteristics of individual regions of activity on the nucleus can be determined; and (2) to extend the techniques in the study of Comet Halley to the study of other cometary nuclei and to obtain new observational data.
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NASA Astrophysics Data System (ADS)
Kulyk, I.; Rousselot, P.; Korsun, P. P.; Afanasiev, V. L.; Sergeev, A. V.; Velichko, S. F.
2018-03-01
Context. The systematic investigation of comets in a wide range of heliocentric distances can contribute to a better understanding of the physical mechanisms that trigger activity at large distances from the Sun and reveals possible differences in the composition of outer solar system bodies belonging to various dynamical groups. Aims: We seek to analyze the dust environment of the selected nearly isotropic comets with a perihelion distance between 4.5 and 9.1 au, where sublimation of water ice is considered to be negligible. Methods: We present results of multicolor broadband photometric observations for 14 distant active objects conducted between 2008 and 2015 with various telescopes. Images obtained with broadband filters were used to investigate optical colors of the cometary comae and to quantify physical activity of the comet nuclei. Results: The activity level was estimated with Afρ parameters ranging between 95 ± 10 cm and 9600 ± 300 cm. Three returning comets were less active than the dynamically new comets. Dust production rates of the comet nuclei were estimated between 1 and 100 kg s-1 based on some assumptions about the physical properties of dust particles populating comae. The measured colors point out reddening of the continuum for all the comets. The mean values of a normalized reflectivity gradient within the group of the comets amount to 14 ± 2% per 1000 Å and 3 ± 2% per 1000 Å in the BV and VR spectral domains, respectively. The comae of the dynamically new comets, which were observed on their inbound legs, may be slightly redder in the blue spectral interval than comae of the comets observed after the perihelion passages. The dynamically new comets observed both pre- and post-perihelion, seem to have higher production rates post-perihelion than pre-perihelion for similar heliocentric distances.
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Implications of the Small Spin Changes Measured for Large Jupiter-Family Comet Nuclei
NASA Astrophysics Data System (ADS)
Kokotanekova, R.; Snodgrass, C.; Lacerda, P.; Green, S. F.; Nikolov, P.; Bonev, T.
2018-06-01
Rotational spin-up due to outgassing of comet nuclei has been identified as a possible mechanism for considerable mass-loss and splitting. We report a search for spin changes for three large Jupiter-family comets (JFCs): 14P/Wolf, 143P/Kowal-Mrkos, and 162P/Siding Spring. None of the three comets has detectable period changes, and we set conservative upper limits of 4.2 (14P), 6.6 (143P) and 25 (162P) minutes per orbit. Comparing these results with all eight other JFCs with measured rotational changes, we deduce that none of the observed large JFCs experiences significant spin changes. This suggests that large comet nuclei are less likely to undergo rotationally-driven splitting, and therefore more likely to survive more perihelion passages than smaller nuclei. We find supporting evidence for this hypothesis in the cumulative size distributions of JFCs and dormant comets, as well as in recent numerical studies of cometary orbital dynamics. We added 143P to the sample of 13 other JFCs with known albedos and phase-function slopes. This sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos. Partly based on findings from recent space missions to JFCs, we hypothesise that this correlation corresponds to an evolutionary trend for JFCs. We propose that newly activated JFCs have larger albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this could be used to analyse surface erosion from ground and to distinguish between dormant comets and asteroids.
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THE NEOWISE-DISCOVERED COMET POPULATION AND THE CO + CO{sub 2} PRODUCTION RATES
DOE Office of Scientific and Technical Information (OSTI.GOV)
Bauer, James M.; Stevenson, Rachel; Kramer, Emily
2015-12-01
The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO{sub 2} production. We present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 μm band excess. We find a possible relation between dust and CO + CO{sub 2} production, as well as possible differences in the sizes of long and short period comet nuclei.
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Disintegration of comet nuclei
NASA Astrophysics Data System (ADS)
Ksanfomality, Leonid V.
2012-02-01
The breaking up of comets into separate pieces, each with its own tail, was seen many times by astronomers of the past. The phenomenon was in sharp contrast to the idea of the eternal and unchangeable celestial firmament and was commonly believed to be an omen of impending disaster, especially for comets with tails stretching across half the sky. It is only now that we have efficient enough space exploration tools to see comet nuclei and even - in the particular case of small comet Hartley-2 in 2010 - to watch their disintegration stage. There are also other suspected candidates for disintegration in the vast family of comet nuclei and other Solar System bodies.
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The bare nucleus of comet Neujmin 1
NASA Technical Reports Server (NTRS)
Campins, Humberto; A'Hearn, Michael F.; Mcfadden, Lucy-Ann
1987-01-01
Simultaneous visible and infrared observations of comet P/Neujmin 1 1984c are presented which show that the comet has a large (mean radius 10 km), dark (geometric albedo 2-3 percent) nucleus with a surface which is mostly inert material but which still shows a low level of gaseous activity. This is the first physical evidence that cometary nuclei can leave behind an inert body after the coma activity ceases. No asteroid or asteroid class has been found to match the reflectance and albedo of this comet except possibly some D asteroids.
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A Spitzer Search for Activity in Dormant Comets
NASA Astrophysics Data System (ADS)
Mommert, Michael; Trilling, David; Hora, Joseph; Smith, Howard
2018-05-01
Dormant comets are inactive cometary nuclei hiding in the asteroid populations. Due to their cometary origin, it is possible that volatiles are still retained in their interiors. This hypothesis is supported by the case of near-Earth asteroid Don Quixote, which had been known as an asteroid for 30 yr before activity was discovered in this team's prior Spitzer observations. Interestingly, Don Quixote showed outgassing of CO or CO2, but no dust activity. This significant observation was repeated in 2017 with the same result, suggesting that Don Quixote is continuously outgassing - and still an active comet. Don Quixote's case suggests that other dormant comets might be outgassing with low dust production rates, concealing their activity to optical surveys. The implication of this scenario is that the volatile inventory of the asteroid populations might be significantly larger than currently assumed. We propose 48.8 hr of deep IRAC observations of eight dormant comets in search of faint activity in them. For each target, we will (1) measure (or provide upper limits on) gas and dust production rates from our IRAC CH1 and CH2 observations, (2) derive the diameters and albedos of five of our targets using asteroid thermal modeling, (3) measure the near-infrared spectral slope between CH1 and CH2 for three of our targets, and (4) obtain lightcurve observations of the nuclei of all of our targets. Our observations, which are combined with ground-based observations as part of a NASA-funded program, will provide important constraints on the volatile content of the asteroid population, as well as the origin, evolution, and physical properties of cometary nuclei.
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Alvarez-Moya, C; Santerre-Lucas, A; Zúñiga-González, G; Torres-Bugarín, O; Padilla-Camberos, E; Feria-Velasco, A
2001-01-01
To assess the genotoxic activity of N-nitroso diethylamine (NDEA), maleic hydrazide (MH), and ethyl methane sulfonate (EMS) using two systems: the comet assay on nuclei from Tradescantia, and the pink mutation test on Tradescantia staminal hairs (clone 4430). Tradescantia cups was obtained from Laboratorio de Citogenética y Mutagénesis del Centro de Ciencias de la Atmósfera de la Universidad Nacional Autónoma de México and treated with: N-nitroso diethylamine (NDEA) at 1, 5, 10 mM, maleic hydrazide (MH) at 1, 5, 10 mM and ethyl methane sulfonate (EMS) at 15, 30 and 45 mM; and used in both pink mutation assay and comet assay using cellular nuclei from Tradescantia staminal hairs. The observation of staminal hair was realized along eight days (6-14) after treatment), flowers produced day 14 after treatment were utilized done according to Underbrink. In previous reports on plants, were comet assay was used, breaking cellular wall and separating by centrifugation gradient are necessary. Here, nuclei from staminal hairs were obtained by squashing the cells (is not necessary to utilize to break special procedure cellular wall), collected using a nylon mesh of 80 Mm and next the comet assay was applied. Student's T test was the statistical test used for analyzing the comet assay data. Both assays showed a great sensitivity to the studied mutagens. A relationship between the dose-pink event and the dose-tail length was evident. Even though the Tradescantia mutation assay is a sensitive test with MH and EMS, low doses of NDEA were not able to induce a significant increase in the pink event frequencies; however, the comet assay was able to detect the mutagenic effect of NDEA at the same dose. Thus, it is clear that the comet assay is highly sensitive to the lowest dose of chemical mutagens. The comet assay on nuclei from Tradescantia staminal hairs is a useful tool to monitor genotoxic agents; it is simple, highly sensitive, and faster than the pink mutation test.
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Evaluation of genetic damage induced by glyphosate isopropylamine salt using Tradescantia bioassays.
Alvarez-Moya, Carlos; Silva, Mónica Reynoso; Arámbula, Alma Rosa Villalobos; Sandoval, Alfonso Islas; Vasquez, Hugo Castañeda; González Montes, Rosa María
2011-01-01
Glyphosate is noted for being non-toxic in fishes, birds and mammals (including humans). Nevertheless, the degree of genotoxicity is seriously controversial. In this work, various concentrations of a glyphosate isopropylamine salt were tested using two methods of genotoxicity assaying, viz., the pink mutation assay with Tradescantia (4430) and the comet assay with nuclei from staminal cells of the same plant. Staminal nuclei were studied in two different forms, namely nuclei from exposed plants, and nuclei exposed directly. Using the pink mutation assay, isopropylamine induced a total or partial loss of color in staminal cells, a fundamental criterion utilized in this test. Consequently, its use is not recommended when studying genotoxicity with agents that produce pallid staminal cells. The comet assay system detected statistically significant (p < 0.01) genotoxic activity by isopropylamine, when compared to the negative control in both the nuclei of treated plants and directly treated nuclei, but only the treated nuclei showed a dose-dependent increase. Average migration in the nuclei of treated plants increased, when compared to that in treated nuclei. This was probably due, either to the permanence of isopropylamine in inflorescences, or to the presence of secondary metabolites. In conclusion, isopropylamine possesses strong genotoxic activity, but its detection can vary depending on the test systems used.
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Evaluation of genetic damage induced by glyphosate isopropylamine salt using Tradescantia bioassays
Alvarez-Moya, Carlos; Silva, Mónica Reynoso; Arámbula, Alma Rosa Villalobos; Sandoval, Alfonso Islas; Vasquez, Hugo Castañeda; González Montes, Rosa María
2011-01-01
Glyphosate is noted for being non-toxic in fishes, birds and mammals (including humans). Nevertheless, the degree of genotoxicity is seriously controversial. In this work, various concentrations of a glyphosate isopropylamine salt were tested using two methods of genotoxicity assaying, viz., the pink mutation assay with Tradescantia (4430) and the comet assay with nuclei from staminal cells of the same plant. Staminal nuclei were studied in two different forms, namely nuclei from exposed plants, and nuclei exposed directly. Using the pink mutation assay, isopropylamine induced a total or partial loss of color in staminal cells, a fundamental criterion utilized in this test. Consequently, its use is not recommended when studying genotoxicity with agents that produce pallid staminal cells. The comet assay system detected statistically significant (p < 0.01) genotoxic activity by isopropylamine, when compared to the negative control in both the nuclei of treated plants and directly treated nuclei, but only the treated nuclei showed a dose-dependent increase. Average migration in the nuclei of treated plants increased, when compared to that in treated nuclei. This was probably due, either to the permanence of isopropylamine in inflorescences, or to the presence of secondary metabolites. In conclusion, isopropylamine possesses strong genotoxic activity, but its detection can vary depending on the test systems used. PMID:21637555
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NASA Technical Reports Server (NTRS)
Sekanina, Z.
1979-01-01
A quantitative test of splitting for comets with suspected multiple nuclei has been formulated using a model which assumes the motions of cometary fragments to be due primarily to outgassing. The model expresses the relative motion of the cometary fragments in terms of the time of splitting and the differential force, which are determined by measurements of the position angle and the separation distance between fragments. The test is applied to 18 comets suspected of having multiple nuclei, of which the comets Sawerthal 1888 I, Campbell 1914 IV, Whipple-Fedtke-Tevzadze 1943 I, Honda 1955 V, Wild 1968 III and Tago-Sato-Kosaka 1969 IX were found to be clear cases of split comets and Davidson 1889 IV and Periodic Giacobini 1896 V were judged to be likely candidates. At least three of the secondary nuclei confirmed can be classified as short-lived companions, while only two appear to be persistent.
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The volatile composition of comets
NASA Technical Reports Server (NTRS)
Weaver, H. A.
1988-01-01
Comets may be our best probes of the physical and chemical conditions in the outer regions of the solar nebula during that crucial period when the planets formed. The volatile composition of cometary nuclei can be used to decide whether comets are the product of a condensation sequence similar to that invoked to explain the compositions of the planets and asteroids, or if comets are simply agglomerations of interstellar grains which have been insignificantly modified by the events that shaped the other bodies in the solar system. Although cometary nuclei are not generally accessible to observation, observations of cometary comae can illuminate at least some of the mysteries of the nuclei provided one has a detailed knowledge of the excitation conditions in the coma and also has access to basic atomic and molecular data on the many species present in comets. Examined here is the status of our knowledge of the volatile composition of cometary nuclei and how these data are obtained.
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The constitution of cometary nuclei
NASA Technical Reports Server (NTRS)
Whipple, F. L.
1977-01-01
The nongravitational term in the expression for the total force acting on a comet is calculated, and an upper limit is obtained for the product of the radial nongravitational term times the radius times the square root of the albedo. This condition is satisfied for ten periodic comets with q no greater than 1.5 AU, and the activity of these comets is consistent with control by H2O ice. Some of the comets must be spotty to account for their low albedo values. The effect of cosmic rays on comets, leading to frosting of their surface, is discussed.
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Strategy for infrared photometry of comets with ISO
NASA Astrophysics Data System (ADS)
Solc, M.; Vanysek, V.; Gruen, E.
1994-07-01
The launch of the ISO (Infrared Satellite Observatory) by the European Space Agency is scheduled for autumn 1995. Photometry and spectrophotometry observing programs of comets in the wavelength range 2.5-200 microns for the onboard spectrophotometer ISOPHOT is now under final preparation. Technical details for preparing propasals are given. Phenomena in comets to be studied are surface properties of bare cometary nuclei at large heliocentric distances, onset of coma activity, and coma dust and gas emission (in inner solar system). Dust production, dust/gas mass ratio, dust distribution in coma, and their temporal variability are important for understanding the physical processes on nuclei, and spectrophotometry in the range of 2.5-12 microns could provide us with data of the chemical composition of cometary dust. Several active comets expected for the 18-month lifetime of ISO in 1995-1997 were selected for the ISO Central Program according to their orbital and physical parameters: P/Schwassman-Wachmann 1, P/Encke, P/d'Arrest, P/Honda-Mrkos-Pajdusakova, P/Churyumov-Gerasimenko, P/Kopff, P/IRAS, P/Wirtanen, P/Wild 2, P/Grigg-Skjellerup, P/Schwassman-Wachmann 3, P/Machholz, and (2060) Chiron. Four of them match well various constraints put on the observations by the technical arrangement of the satellite and instrument. A simple four-parameter model (size, albedo, rotation, optical thickness)was developed to estimate the temperatures and thermal fluxes of both solid nuclei and dust coma.
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Physical characteristics of Comet Nucleus C/2001 OG 108 (LONEOS)
NASA Astrophysics Data System (ADS)
Abell, Paul A.; Fernández, Yanga R.; Pravec, Petr; French, Linda M.; Farnham, Tony L.; Gaffey, Michael J.; Hardersen, Paul S.; Kušnirák, Peter; Šarounová, Lenka; Sheppard, Scott S.; Narayan, Gautham
2005-12-01
A detailed description of the Halley-type Comet C/2001 OG 108 (LONEOS) has been derived from visible, near-infrared, and mid-infrared observations obtained in October and November 2001. These data represent the first high-quality ground-based observations of a bare Halley-type comet nucleus and provide the best characterization of a Halley-type comet other than 1P/Halley itself. Analysis of time series photometry suggests that the nucleus has a rotation period of 57.2±0.5 h with a minimum nuclear axial ratio of 1.3, a phase-darkening slope parameter G of -0.01±0.10, and an estimated H=13.05±0.10. The rotation period of C/2001 OG 108 is one of the longest observed among comet nuclei. The V- R color index for this object is measured to be 0.46±0.02, which is virtually identical to that of other cometary nuclei and other possible extinct comet candidates. Measurements of the comet's thermal emission constrain the projected elliptical nuclear radii to be 9.6±1.0 km and 7.4±1.0 km, which makes C/2001 OG 108 one of the larger cometary nuclei known. The derived geometric albedo in V-band of 0.040±0.010 is typical for comet nuclei. Visible-wavelength spectrophotometry and near-infrared spectroscopy were combined to derive the nucleus's reflectance spectrum over a 0.4 to 2.5 μm wavelength range. These measurements represent one of the few nuclear spectra ever observed and the only known spectrum of a Halley-type comet. The spectrum of this comet nucleus is very nearly linear and shows no discernable absorption features at a 5% detection limit. The lack of any features, especially in the 0.8 to 1.0 μm range such as are seen in the spectra of carbonaceous chondrite meteorites and many low-albedo asteroids, is consistent with the presence of anhydrous rather than hydrous silicates on the surface of this comet. None of the currently recognized meteorites in the terrestrial collections have reflectance spectra that match C/2001 OG 108. The near-infrared spectrum, the geometric albedo, and the visible spectrophotometry all indicate that C/2001 OG 108 has spectral properties analogous to the D-type, and possibly P-type asteroids. Comparison of the measured albedo and diameter of C/2001 OG 108 with those of Damocloid asteroids reveals similarities between these asteroids and this comet nucleus, a finding which supports previous dynamical arguments that Damocloid asteroids could be composed of cometary-like materials. These observations are also consistent with findings that two Jupiter-family comets may have spectral signatures indicative of D-type asteroids. C/2001 OG 108 probably represents the transition from a typical active comet to an extinct cometary nucleus, and, as a Halley-type comet, suggests that some comets originating in the Oort cloud can become extinct without disintegrating. As a near-Earth object, C/2001 OG 108 supports the suggestion that some fraction of the near-Earth asteroid population consists of extinct cometary nuclei.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Kim, Yoonyoung; Ishiguro, Masateru; Usui, Fumihiko
We investigated the population of asteroids in comet-like orbits using available asteroid size and albedo catalogs of data taken with the Infrared Astronomical Satellite, AKARI, and the Wide-field Infrared Survey Explorer on the basis of their orbital properties (i.e., the Tisserand parameter with respect to Jupiter, T{sub J}, and the aphelion distance, Q). We found that (1) there are 123 asteroids in comet-like orbits by our criteria (i.e., Q > 4.5 AU and T{sub J} < 3), (2) 80% of them have low albedo, p{sub v} < 0.1, consistent with comet nuclei, (3) the low-albedo objects among them have amore » size distribution shallower than that of active comet nuclei, that is, the power index of the cumulative size distribution is around 1.1, and (4) unexpectedly, a considerable number (i.e., 25 by our criteria) of asteroids in comet-like orbits have high albedo, p{sub v} > 0.1. We noticed that such high-albedo objects mostly consist of small (D < 3 km) bodies distributed in near-Earth space (with perihelion distance of q < 1.3 AU). We suggest that such high-albedo, small objects were susceptible to the Yarkovsky effect and drifted into comet-like orbits via chaotic resonances with planets.« less
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Autonomous Onboard Science Data Analysis for Comet Missions
NASA Technical Reports Server (NTRS)
Thompson, David R.; Tran, Daniel Q.; McLaren, David; Chien, Steve A.; Bergman, Larry; Castano, Rebecca; Doyle, Richard; Estlin, Tara; Lenda, Matthew
2012-01-01
Coming years will bring several comet rendezvous missions. The Rosetta spacecraft arrives at Comet 67P/Churyumov-Gerasimenko in 2014. Subsequent rendezvous might include a mission such as the proposed Comet Hopper with multiple surface landings, as well as Comet Nucleus Sample Return (CNSR) and Coma Rendezvous and Sample Return (CRSR). These encounters will begin to shed light on a population that, despite several previous flybys, remains mysterious and poorly understood. Scientists still have little direct knowledge of interactions between the nucleus and coma, their variation across different comets or their evolution over time. Activity may change on short timescales so it is challenging to characterize with scripted data acquisition. Here we investigate automatic onboard image analysis that could act faster than round-trip light time to capture unexpected outbursts and plume activity. We describe one edge-based method for detect comet nuclei and plumes, and test the approach on an existing catalog of comet images. Finally, we quantify benefits to specific measurement objectives by simulating a basic plume monitoring campaign.
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The Physics of Cometary Nuclei
NASA Technical Reports Server (NTRS)
Whipple, Fred L.
1997-01-01
The recent developments in cometary studies suggest rather low mean densities and weak structures for the nuclei. They appear to be accumulations of fairly discrete units loosely bound together, as deduced from the observations of Comet Shoemaker-Levy 9 during its encounter with Jupiter. The compressive strengths deduced from comet splitting by Opik and Sekanina are extremely low. These values are confirmed by theory developed here. assuming that Comet P/Holmes had a companion that collided with it in 1892. There follows a short discussion that suggests that the mean densities of comets should increase with comet dimensions. The place of origin of short-period comets may relate to these properties.
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NASA Astrophysics Data System (ADS)
Kelley, Michael; Feaga, Lori; Bodewits, Dennis; McKay, Adam; Snodgrass, Colin; Wooden, Diane
2014-12-01
Spacecraft missions to comets return a treasure trove of details of their targets, e.g., the Rosetta mission to comet 67P/Churyumov-Gerasimenko, the Deep Impact experiment at comet 9P/Tempel 1, or even the flyby of C/2013 A1 (Siding Spring) at Mars. Yet, missions are rare, the diversity of comets is large, few comets are easily accessible, and comet flybys essentially return snapshots of their target nuclei. Thus, telescopic observations are necessary to place the mission data within the context of each comet's long-term behavior, and to further connect mission results to the comet population as a whole. We propose a large Cycle 11 project to study the long-term activity of past and potential future mission targets, and select bright Oort cloud comets to infer comet nucleus properties, which would otherwise require flyby missions. In the classical comet model, cometary mass loss is driven by the sublimation of water ice. However, recent discoveries suggest that the more volatile CO and CO2 ices are the likely drivers of some comet active regions. Surprisingly, CO2 drove most of the activity of comet Hartley 2 at only 1 AU from the Sun where vigorous water ice sublimation would be expected to dominate. Currently, little is known about the role of CO2 in comet activity because telluric absorptions prohibit monitoring from the ground. In our Cycle 11 project, we will study the CO2 activity of our targets through IRAC photometry. In conjunction with prior observations of CO2 and CO, as well as future data sets (JWST) and ongoing Earth-based projects led by members of our team, we will investigate both long-term activity trends in our target comets, with a particular goal to ascertain the connections between each comet's coma and nucleus.
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Cometary Jet Collimation Without Physical Confinement
NASA Astrophysics Data System (ADS)
Steckloff, Jordan; Melosh, H.
2012-10-01
Recent high-resolution images of comet nuclei reveal that gases and dust expelled by the comet are organized into narrow jets. Contemporary models postulate that these jets collimate when the expanding gases and dust pass through a physical aperture or nozzle [1]. However, recent high-resolution spacecraft observations fail to detect such apertures on cometary surfaces [2]. Additionally, observations of comet nuclei by visiting spacecraft have observed that jet activity is tied to the diurnal rotation of the comet. This suggests that jet emissions are driven by the sun, and therefore must emanate from close to the surface of the comet (order of 10 cm.) Here we describe a simplified computer model of jets emanating from Comet Tempel 1. We approximate the active areas (vents) of the comet as a region of smooth, level terrain on the order of 10 m in width. We assume that each element of the active area is emitting gas molecules with the same spatial distribution, and integrate over the active area in order to calculate the gas drag force. We consider two angular emission profiles (isotropic and lambertian), and assume plane-strain geometry. Uniformly sized particles are placed randomly on the surface of the vent, and their positions in time are tracked. For our simulation, spherical particles with radii of 1 µm to 1 cm were considered. We observe that the overwhelming majority of the particles remain close to the central axis of the active area, forming a well-collimated jet, with particles reaching escape velocity. This mechanism may explain cometary jets, given the physical and observational constraints. References: [1] Yelle R.V. (2004) Icarus 167, 30-36. [2] A’Hearn M.F. et al. (2011) Science 332, 1396-1400. [3] Belton M.J.S. and Melosh H.J. (2009) Icarus 200, 280-291. Acknowledgements: This research is supported by NASA grant PGG NNX10AU88G.
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Current ideas on the nature of comets
NASA Technical Reports Server (NTRS)
Rahe, J.
1984-01-01
The chemical composition, emission and line spectra, and structure of comet nuclei, cometary atmospheres, and comet tails are discussed. The role of ultraviolet and infrared astronomy in defining comets is examined.
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NASA Technical Reports Server (NTRS)
Ahearn, Michael F.
1988-01-01
The IUE was used to study comets including the first dynamically new comet to approach closer than 3 AU. Differences between old and new comets are studied. Results relevant to the nature of cometary nuclei are discussed. Identification of species in the spectra; relative abundances; variability of comets; and comet mass are considered.
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Evidence for geologic processes on comets
NASA Astrophysics Data System (ADS)
Sunshine, Jessica M.; Thomas, Nicolas; El-Maarry, Mohamed Ramy; Farnham, Tony L.
2016-11-01
Spacecraft missions have resolved the nuclei of six periodic comets and revealed a set of geologically intriguing and active small bodies. The shapes of these cometary nuclei are dominantly bilobate reflecting their formation from smaller cometesimals. Cometary surfaces include a diverse set of morphologies formed from a variety of mechanisms. Sublimation of ices, driven by the variable insolation over the time since each nucleus was perturbed into the inner Solar System, is a major process on comets and is likely responsible for quasi-circular depressions and ubiquitous layering. Sublimation from near-vertical walls is also seen to lead to undercutting and mass wasting. Fracturing has only been resolved on one comet but likely exists on all comets. There is also evidence for mass redistribution, where material lifted off the nucleus by subliming gases is deposited onto other surfaces. It is surprising that such sedimentary processes are significant in the microgravity environment of comets. There are many enigmatic features on cometary surfaces including tall spires, kilometer-scale flows, and various forms of depressions and pits. Furthermore, even after accounting for the differences in resolution and coverage, significant diversity in landforms among cometary surfaces clearly exists. Yet why certain landforms occur on some comets and not on others remains poorly understood. The exploration and understanding of geologic processes on comets is only beginning. These fascinating bodies will continue to provide a unique laboratory for examining common geologic processes under the uncommon conditions of very high porosity, very low strength, small particle sizes, and near-zero gravity.
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Chaotic dynamics around cometary nuclei
NASA Astrophysics Data System (ADS)
Lages, José; Shevchenko, Ivan I.; Rollin, Guillaume
2018-06-01
We apply a generalized Kepler map theory to describe the qualitative chaotic dynamics around cometary nuclei, based on accessible observational data for five comets whose nuclei are well-documented to resemble dumb-bells. The sizes of chaotic zones around the nuclei and the Lyapunov times of the motion inside these zones are estimated. In the case of Comet 1P/Halley, the circumnuclear chaotic zone seems to engulf an essential part of the Hill sphere, at least for orbits of moderate to high eccentricity.
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Physical Properties of Cometary Nucleus Candidates
NASA Technical Reports Server (NTRS)
Jewitt, David; Hillman, John (Technical Monitor)
2003-01-01
In this proposal we aim to study the physical properties of the Centaurs and the dead comets, these being the precursors to, and the remnants from, the active cometary nuclei. The nuclei themselves are very difficult to study, because of the contaminating effects of near-nucleus coma. Systematic investigation of the nuclei both before they enter the zone of strong sublimation and after they have depleted their near-surface volatiles should neatly bracket the properties of these objects, revealing evolutionary effects.
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CCD-photometry of comets at large heliocentric distances
NASA Technical Reports Server (NTRS)
Mueller, Beatrice E. A.
1992-01-01
CCD imaging and time series photometry are used to determine the state of activity, nuclear properties and eventually the rotational motion of cometary nuclei. Cometary activity at large heliocentric distances and mantle evolution are not yet fully understood. Results of observations carried out at the 2.1 telescope on Kitt Peak April 10-12 and May 15-16, 1991 are discussed. Color values and color-color diagrams are presented for several comets and asteroids. Estimations of nuclear radii and shapes are given.
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The study of the physics of cometary nuclei
NASA Technical Reports Server (NTRS)
Whipple, F. L.; Marsden, B. G.; Sekanina, Z.
1975-01-01
Research in the area of split and hyperbolic comets, orbital calculations, and interstellar comets is discussed. Other topics discussed include the role of comets in galactic chemistry, gamma ray bursts, and predicted favorable visibility conditions for anomalous tails of comets.
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Hubble Space Telescope observations of comet P/Shoemaker-Levy 9 (1993e)
Weaver, H.A.; Feldman, P.D.; A'Hearn, M.F.; Arpigny, C.; Brown, R.A.; Helin, E.F.; Levy, D.H.; Marsden, B.G.; Meech, K.J.; Larson, S.M.; Noll, K.S.; Scotti, J.V.; Sekanina, Z.; Shoemaker, C.S.; Shoemaker, E.M.; Smith, T.E.; Storrs, A.D.; Yeomans, D.K.; Zellner, B.
1994-01-01
The Hubble Space Telescope observed the fragmented comet P/Shoemaker-Levy 9 (1993e) (P indicates that it is a periodic comet) on 1 July 1993. Approximately 20 individual nuclei and their comae were observed in images taken with the Planetary Camera. After subtraction of the comae light, the 11 brightest nuclei have magnitudes between ~23.7 and 24.8. Assuming that the geometric albedo is 0.04, these magnitudes imply that the nuclear diameters are in the range ~2.5 to 4.3 kilometers. If the density of each nucleus is 1 gram per cubic centimeter, the total energy deposited by the impact of these 11 nuclei into Jupiter's atmosphere next July will be ~4 x 1030 ergs (~108 megatons of TNT). This latter number should be regarded as an upper limit because the nuclear magnitudes probably contain a small residual coma contribution. The Faint Object Spectrograph was used to search for fluorescence from OH, which is usually an excellent indicator of cometary activity. No OH emission was detected, and this can be translated into an upper limit on the water production rate of ~2 x 1027 molecules per second.
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NASA Technical Reports Server (NTRS)
Whipple, F. L.; Huebner, W. F.
1976-01-01
The paper discusses physical processes in comets which involve solar and nuclear radial forces that affect the motions of gases and icy grains, gas-phase chemistry very close to the nuclei of large comets near the sun, sublimation of icy grains, dissociation of parent molecules into radicals and of radicals into atoms, and ionization by sunlight and collisions. The composition and dimensions of nuclei are examined along with variations in intrinsic brightness, the nature of volatiles, gas production rates in the coma, characteristics of icy grains in the coma, and the structure of streamers, ion tails, and dust tails. The structure of the coma is described in detail on the basis of spectroscopic observations of several comets. The origin of comets is briefly reviewed together with the relation of comets to earth, the interplanetary complex, and the interstellar medium. Desirable future observations are noted, especially by space missions to comets.
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Comets: Gases, ices, grains and plasma
NASA Technical Reports Server (NTRS)
Wilkening, L. L.
1981-01-01
The program and abstracts of the 97 papers delivered at the colloquium are presented. Cometary nuclei, comet dust, the coma, ion tails, several comet missions, and cometary origin and evolution were discussed.
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Workshop on Analysis of Returned Comet Nucleus Samples
NASA Technical Reports Server (NTRS)
1989-01-01
This volume contains abstracts that were accepted by the Program Committee for presentation at the workshop on the analysis of returned comet nucleus samples held in Milpitas, California, January 16 to 18, 1989. The abstracts deal with the nature of cometary ices, cryogenic handling and sampling equipment, origin and composition of samples, and spectroscopic, thermal and chemical processing methods of cometary nuclei. Laboratory simulation experimental results on dust samples are reported. Some results obtained from Halley's comet are also included. Microanalytic techniques for examining trace elements of cometary particles, synchrotron x ray fluorescence and instrument neutron activation analysis (INAA), are presented.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Jewitt, David, E-mail: jewitt@ucla.edu
Most comets are volatile-rich bodies that have recently entered the inner solar system following long-term storage in the Kuiper belt and the Oort cloud reservoirs. These reservoirs feed several distinct, short-lived “small body” populations. Here, we present new measurements of the optical colors of cometary and comet-related bodies including long-period (Oort cloud) comets, Damocloids (probable inactive nuclei of long-period comets) and Centaurs (recent escapees from the Kuiper belt and precursors to the Jupiter family comets). We combine the new measurements with published data on short-period comets, Jovian Trojans and Kuiper belt objects to examine the color systematics of the comet-relatedmore » populations. We find that the mean optical colors of the dust in short-period and long-period comets are identical within the uncertainties of measurement, as are the colors of the dust and of the underlying nuclei. These populations show no evidence for scattering by optically small particles or for compositional gradients, even at the largest distances from the Sun, and no evidence for ultrared matter. Consistent with earlier work, ultrared surfaces are common in the Kuiper belt and on the Centaurs, but not in other small body populations, suggesting that this material is hidden or destroyed upon entry to the inner solar system. The onset of activity in the Centaurs and the disappearance of the ultrared matter in this population begin at about the same perihelion distance (∼10 AU), suggesting that the two are related. Blanketing of primordial surface materials by the fallback of sub-orbital ejecta, for which we calculate a very short timescale, is the likely mechanism. The same process should operate on any mass-losing body, explaining the absence of ultrared surface material in the entire comet population.« less
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CCD Photometry of Cometary Nuclei, I: Observations from 1990-1995
NASA Astrophysics Data System (ADS)
Licandro, Javier; Tancredi, Gonzalo; Lindgren, Mats; Rickman, Hans; Hutton, Ricardo Gil
2000-09-01
CCD photometry of 18 Jupiter family comets, observed at medium and large heliocentric distances, was carried out between April 1990 and July 1995. This is part of a long-term observational program designed to obtain their nuclear magnitudes. The observations were made with the 1.54-m Danish Telescope at ESO La Silla, the 2.5-m Nordic Optical Telescope (NOT) at Observatorio del Roque de los Muchachos (La Palma), the 2.0-m telescope at Pic du Midi, and the 2.15-m telescope at CASLEO, Argentina. Our estimates of the absolute nuclear magnitudes are discussed in comparison with previous determinations. Estimates (sometimes upper limits) for the effective radius ( R) of the nuclei are computed considering a typical geometric albedo pv=0.04. The lowest radius found is the one of 37P/Forbes ( R=1.0 km) while the largest corresponds to 65P/Gunn ( R=11.0 km), but in this case the comet was observed very active. Wherever possible, cometary image profiles are compared with stellar profiles, in order to determine the existence of a faint coma. Seven of the comets were active, six of them at heliocentric distances larger than 4 AU. This unexpected activity is also discussed. We find a strong correlation between activity at large heliocentric distances and recent downward jumps in perihelion distance.
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Physical properties of asteroids in comet-like orbits in the infrared asteroidal survey catalogs
NASA Astrophysics Data System (ADS)
Kim, Y.; Ishiguro, M.; Usui, F.
2014-07-01
Dormant comet and Infrared Asteroidal Survey Catalogs. Comet nucleus is a solid body consisting of dark refractory material and ice. Cometary volatiles sublimate from subsurface layer by solar heating, leaving behind large dust grains on the surface. Eventually, the appearance could turn into asteroidal rather than cometary. It is, therefore, expected that there would be ''dormant comets'' in the list of known asteroids. Over past decade, several ground-based studies have been performed to dig out such dormant comets. One common approach is applying a combination of optical and dynamical properties learned from active comet nucleus to the list of known asteroids. Typical comet nucleus has (i) Tisserand parameter with respect to Jupiter, T_{J}<3, (ii) low geometric albedo, p_{v}<0.1 and (iii) reddish or neutral spectra, similar to P, D, C-type asteroids. Following past ground-based surveys, infrared space missions gave us an opportunity to work on further study of dormant comets. To the present, three infrared asteroidal catalogs taken with IRAS[1], AKARI[2] and WISE[3] are available, providing information of sizes and albedos which are useful to study the physical properties of dormant comets as well as asteroids. Usui et al. (2014) merged three infrared asteroidal catalogs with valid sizes and albedos into single catalog, what they called I-A-W[4]. We applied a huge dataset of asteroids in I-A-W to investigate the physical properties of asteroids in comet-like orbits (ACOs, whose orbits satisfy Q>4.5 au and T_{J}<3). Here we present a study of ACOs in infrared asteroidal catalogs taken with AKARI, IRAS and WISE. In this presentation, we aim to introduce albedo and size properties of ACOs in infrared asteroidal survey catalogs, in combination with orbital and spectral properties from literature. Results and Implications. We summarize our finding and implication as followings: - are 123 ACOs (Q>4.5 au and T_J<3) in I-A-W catalog after rejection of objects with large orbital uncertainties. - Majority (˜80 %) of ACOs have low albedo (p_{v}<0.1), showing similar albedo distribution to active comet nuclei. - Low-albedo ACOs have the cumulative size distribution shallower than that of active comet nuclei. - High-albedo (p_{v}≥0.1) ACOs consist of small (D<3 km) bodies are concentrated in near-Earth space. - We suggest that such high-albedo, small near-Earth asteroids are susceptible to Yarkovsky effect and injected into comet-like orbits.
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Agarwal, Jessica; Jewitt, David; Mutchler, Max; Weaver, Harold; Larson, Stephen
2017-09-20
Asteroids are primitive Solar System bodies that evolve both collisionally and through disruptions arising from rapid rotation. These processes can lead to the formation of binary asteroids and to the release of dust, both directly and, in some cases, through uncovering frozen volatiles. In a subset of the asteroids called main-belt comets, the sublimation of excavated volatiles causes transient comet-like activity. Torques exerted by sublimation measurably influence the spin rates of active comets and might lead to the splitting of bilobate comet nuclei. The kilometre-sized main-belt asteroid 288P (300163) showed activity for several months around its perihelion 2011 (ref. 11), suspected to be sustained by the sublimation of water ice and supported by rapid rotation, while at least one component rotates slowly with a period of 16 hours (ref. 14). The object 288P is part of a young family of at least 11 asteroids that formed from a precursor about 10 kilometres in diameter during a shattering collision 7.5 million years ago. Here we report that 288P is a binary main-belt comet. It is different from the known asteroid binaries in its combination of wide separation, near-equal component size, high eccentricity and comet-like activity. The observations also provide strong support for sublimation as the driver of activity in 288P and show that sublimation torques may play an important part in binary orbit evolution.
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Comet Wild 2 and the two kinds of cometary sub-nuclei population
NASA Astrophysics Data System (ADS)
Illes-Almar, E.
On the 2nd January 2004 Stardust encountered the nucleus of comet Wild 2 by 240 km. 72 images have been collected - among them the up-till-now best views of a cometary nucleus. The "pockmarked" surface of the comet is peculiar as the "craters" are not normal craters: neither in shape nor in cross section. Their shapes are rather irregular and generally not central or axisymmetric. Furthermore they have flat bottoms and very steep walls that seem almost perpendicular to the surface. One has the feeling that they are not impact craters. In the framework of our `two kinds of cometary sub-nuclei population' hypothesis (Illés-Almár, 1995, 2002) the cavities can be explained by the stronger sublimation where the loose sub-nuclei are exposed to the surface. The almost vertical walls resemble to the vertical walls of the sublimated CO2 ice on the South polar cap of Mars. References: Illés-Almár, E.: On two different populations of cometary sub-nuclei. Antarctic Meteorites XX. June 6-8, 1995, Tokyo. Abstracts pp. 93-94, 1995. Illés-Almár, E.: Comet Borrelly and the two kinds of cometary sub-nuclei population. (submitted to Adv. Sp. Res. in 2002)
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The morphology of cometary nuclei
NASA Astrophysics Data System (ADS)
Keller, H. U.; Jorda, L.
The sudden appearance of a bright comet stretching over a large part of the night sky must have been one of the most awesome phenomena for early humans watching the sky. The nature of comets remained obscure well into the Middle Ages. Only with the introduction of astronomical techniques and analyses in Europe was the parallax of a comet determined by Tycho Brahe for the first time. He proved that comets are not phenomena of the Earth's atmosphere but are farther away than the Moon; in other words they are interplanetary objects. Later Kepler first predicted that comets follow straight lines, then Hevelius suggested parabolic orbits roughly a hundred years later. It was Halley who suggested that the comets of the years 1531, 1607 and 1682 were apparitions of one and the same comet that would return again in 1758. The success of this prediction made it clear that comets are members of our Solar System. While it was now established that periodic comets are objects of the planetary system, their origin and nature continued to be debated. Were they formed together with the planets from the solar nebula (Kant) or were they of extrasolar origin as suggested by Laplace? This debate lasted for 200 years until well into the second half of the last century. Öpik (1932) suggested that a cloud of comets surrounded our Solar System. This hypothesis was quantified and compared to the observed distribution of orbital parameters (essentially the semi-major axes) of new comets by Oort (1950) (Section 2.1). Comets are scattered into the inner Solar System by perturbations caused by galactic tides, passing stars and large molecular clouds. The Oort cloud would have a radius of 2 105AU, a dimension comparable to the distances of stars in our neighbourhood. The lifetime (limited by decay due to activity and by perturbations caused by encounters with planets) even of the new comets on almost parabolic orbits and typical periods of the order of 106 years is short compared to the age of the planetary system (4.5 Gy). Therefore, observed comets could only recently have arrived on their orbits dipping inside the inner Solar System. This reservoir of comets must have been established during the formation process of the planetary system itself. Cometesimals were agglomerated from interstellar/interplanetary gas and dust and scattered out of the inner Solar System by the giant outer planets (Section 2.3). This scheme implies that a central part of a comet, its nucleus, is stable enough to survive these perturbations. It must also be stable enough to pass the vicinity of the sun for many times in the case of a short-period comet. Comets are bright and large when they are close to the sun and fade quickly when they recede beyond about 2AU. Only with the advent of photography and large astronomical telescopes could a comet be followed until it becomes a starlike point source. What makes comets active near the Sun, blowing their appearances up to the order of 105 km? Bright comets often develop tails two orders of magnitude longer. In an attempt to explain the cometary appearance, Bredichin (1903) introduced a mechanical model where repulsive forces drive the particles away from a central condensation. Spectroscopy revealed that dust grains reflect the solar irradiation. In addition, simple molecules, radicals and ions were found as constituents of the cometary coma and tail. The nature of the central condensation remained mysterious for a long time because of the observational dilemma. When the comet is close to the Earth and therefore to the Sun the dense coma obscures the view into its centre. When activity recedes the comet is too far away and too dim for detailed observations of its central condensation. During the middle of the nineteenth century the connection between comets and meteor streams was established. Schiaparelli (1866) calculated the dispersion of cometary dust within the orbital plane. From this time on the perception that the central condensations of comets were agglomerations of dust particles prevailed for about a century. The gas coma was explained by desorption of molecules from dust particles with large surfaces (Levin 1943). The storage of highly reactive radicals (most observed species (CN, CH, NH2, etc.) were of this category) posed a major difficulty to be explained. The inference that these radicals should be dissociation products of stable parent molecules (such as (CN)2, CH4, NH3, etc.) by Wurm (1934, 1935, 1943) led to our present understanding that these molecules are stored as ices within the central nucleus of a comet. Whipple (1950a,b) combined the astrometrical observations of changes of the orbital periods of comets with the existence of an icy cometary nucleus. The sublimation of ices cause reactive (rocket) non-gravitational forces that increase or decrease the orbital period of an active comet according to the sense of rotation of its nucleus. Evidence in support of the icy conglomerate nucleus became more and more compelling by the derived high gas production rates that could not be stored by adsorption on dust grains (Biermann and Trefftz 1964, Huebner 1965, Keller 1976a,b) and by the same account by the large quantities of dust moving into the cometary tail (Finson and Probstein 1968b). The `sand bank' model (Lyttleton 1953) was clearly dismissed in favour of a solid icy nucleus. Its formation and origin could now be explored. While there was some knowledge about the chemical composition of the nucleus, its physical properties, even the basic ones like size, shape and mass, remained largely unknown because the nucleus could not be observed. Early attempts to derive the nucleus size from the `nuclear' magnitudes of comets at large heliocentric distances while they are inactive (Roemer 1966a,b) led to a systematic overestimation of the size because their residual activity could not be eliminated. The advent of modern detectors and large ground-based telescopes revealed that most comets display residual activity or clouds of dust grains around their nuclei. Taking the residual signal into account (mostly using simple models for the brightness distribution) the size estimates of the nuclei could be improved. The (nuclear) magnitude of a comet depends on the product of its albedo and cross-section. Only in a few cases could the albedo and size of a cometary nucleus be separated by additional observation of its thermal emission at infrared wavelengths. By comparison with outer Solar System asteroids Cruikshank et al. (1985) derived a surprisingly low albedo of about 0.04. A value in clear contradiction to the perception of an icy surface but fully confirmed by the first resolved images of a cometary nucleus during the flybys of the Vega and Giotto spacecraft of comet Halley (Sagdeev et al. 1986, Keller et al. 1986). The improvements of radar techniques led to the detection of reflected signals and finally to the derivation of nuclear dimensions and rotation rates. The observations, however, are also model dependent (rotation and size are similarly interwoven as are albedo and size) and sensitive to large dust grains in the vicinity of a nucleus. As an example, Kamoun et al. (1982) determined the radius of comet Encke to 1.5 (2.3, 1.0) km using the spin axis determination of Whipple and Sekanina (1979). The superb spatial resolution of the Hubble Space Telescope (HST) is not quite sufficient to resolve a cometary nucleus. The intensity distribution of the inner coma, however, can be observed and extrapolated toward the nucleus based on models of the dust distribution. If this contribution is subtracted from the central brightness the signal of the nucleus can be derived and hence its product of albedo times cross-section (Lamy and Toth 1995, Rembor 1998, Keller and Rembor 1998; Section 4.3). It has become clear that cometary nuclei are dark, small, often irregular bodies with dimensions ranging from about a kilometre (comet Wirtanen, the target of the Rosetta comet rendezvous mission) to about 50 km (comet Hale- Bopp, comet P/Schwassman-Wachmann 1). Their albedos are very low, about 0.04. Their shapes are irregular, axes ratios of 2:1 are often derived. Even though comets are characterized by their activity, in most cases only a small fraction of the nuclear surface (in some cases less than 1%) is active. An exception seems to be comet P/Wirtanen where all its surface is required to be active in order to explain its production rates (Rickman and Jorda 1998). The detection of trans-Neptunian objects (TNOs) in the Kuiper belt (Jewitt and Luu 1993) reveals a new population of cometary bodies with dimensions an order of magnitude bigger (100 km and larger) than the typical comet observed in the inner planetary system. Little is known about the extent, density, size distribution and physical characteristics of these objects. This region is supposedly the reservoir for short-period comets, manly those controlled by Jupiter (Jupiter family comets). Our present concept of a cometary nucleus has been strongly influenced by the first pictures of the nucleus of comet Halley achieved during the Giotto flyby in 1986. While this revelation seems to be confirmed as typical by modern observations it carries the danger of prototyping new observational results and inferences. Missions and spacecraft are already on their way (Deep Space, Contour, Stardust, Deep Impact) or in preparation (Rosetta) to diversify our knowledge. The morphology of cometary nuclei is determined by their formation process in the early solar nebula, their dynamics and evolution. The physics of the processes leading to their apparent activity while approaching the Sun are still obscure in many details but determine the small- and intermediate-scale morphology. The large-scale morphology, the shape, of a cometary nucleus is determined by its fragility and inner structure and by its generally complex rotational state. These topics will be reviewed in the following sections. Chemical and compositional aspects will be only discussed where they are important in the framework of the physical evolution of cometary nuclei. More details are given in Chapter 53. A brief survey of the current modelling efforts is given. The fate of cometary nuclei and their decay products follows. A summary and outlook ends this chapter on the morphology of cometary nuclei.
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Thermal evolution of cometary nuclei
NASA Astrophysics Data System (ADS)
Prialnik, D.
2014-07-01
Thermal modeling of comet nuclei and similar objects involves the solution of conservation equations for energy and masses of the various components over time. For simplicity, the body is generally, but not necessarily, assumed to be of spherical shape. The processes included in such calculations are heat transfer, gas flow, dust drag, phase transitions, internal heating by various sources, internal structure alterations, surface sublimation. Physical properties --- such as the thermal conductivity, permeability, material strength, and porous structure --- are assumed, based on the best available estimates from laboratory experiments and space-mission results. Calculations employ various numerical procedures and require significant computational power, data analysis, and often sophisticated methods of graphical presentation. They start with a body of given size, mass, and composition, as well as a given orbit. The results yield properties and activity patterns that can be confronted with observations. Initial parameters may be adjusted until agreement is achieved. A glimpse into the internal structure of the object, which is inaccessible to direct observation, is thus obtained. The last decade, since the extensive overview of the subject was published (Modeling the structure and activity of comet nuclei, Prialnik, D.; Benkhoff, J.; Podolak, M., in Comets II, M. C. Festou, H. U. Keller, and H. A. Weaver, eds., University of Arizona Press, Tucson, p.359-387), thermal modeling has significantly advanced. This was prompted both by new properties and phenomena gleaned from observations, one example being main-belt comets, and the continual increase in computational power and performance. Progress was made on two fronts. On the computational side, multi-dimensional models have been developed, adaptive-grid and moving-boundaries techniques have been adopted, and long-term evolutionary calculations have become possible, even spanning the lifetime of the Solar System. On the chemo-physical side, additional chemical processes like serpentinization, and formation and decompositions of clathrates have been investigated. Special efforts have been devoted to related classes of objects: main-belt comets, Centaurs, Kuiper-belt objects and also to other ice-rich bodies, such as icy satellites. Since some of these objects are sufficiently large for hydrostatic pressure to become important, hydrostatic equilibrium was introduced into the modeling. This required the addition of an appropriate equation of state. Interesting new results have thus been obtained: retention of ice in the deep interior of main-belt comets over the age of the Solar System, differentiation between core and mantle in the larger Kuiper-belt objects, and complex patterns of outburst for active comets, simulating observed ones.
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Comets, Asteroids, Meteorites, and the Origin of the Biosphere
NASA Technical Reports Server (NTRS)
Hoover, Richard B.
2006-01-01
During the past few decades, the delivery of water, organics, and prebiotic chemicals to the Biosphere of Earth during the Hadean (4.5-3.8 Ga) period of heavy bombardment by comets and asteroids has become more widely accepted. Comets are still largely regarded as frigid, pristine bodies of protosolar nebula material that are devoid of liquid water and therefore unsuitable for life. Complex organic compounds have been observed in comets and on the water-rich asteroid 1998 KY26 and near IR observations have indicated the presence of crystalline water ice and ammonia hydrate on the large Kuiper Belt object (50000) Quaoar that has resurfacing suggesting cryovolcanic outgassing. Spacecraft observations of the chemical compositions and characteristics of the nuclei of several comets (Halley, Borrelly, Wild 2, and Tempel 1) have shown that comets contain complex organic chemicals; that water is the predominant volatile; and that extremely high temperatures (approx. 350-400 K) can be reached on the surfae of the very black (albedo approx. 0.03) nuclei of comets when they approach the Sun. Impact craters and pinnacles observed on comet Wild 2 suggest a thick crust. Episodic outbursts and jets from the nuclei of several comets indicate that localized regimes of liquid water and water vapor can periodically exist beneath the comet crust. The Deep Impact mission found the temperature of the nucleus of comet Tempel 1 at 1.5 AU varied from a minimum of 280 plus or minus 8 K the 330K (57 C) on the sunlit side. In this paper it is argued that that pools and films of liquid water exist (within a wide range of temperatures) in cavities and voids just beneath the hot, black crust. The possibility of liquid water existing over a wide range of temperatures significantly enhances the possibility that comets might contain niches suitable for the growth of microbial communities and ecosystems. These regimes would be ideal for the growth of psychrophilic, mesophilic, and thermophilic photoautotrophs and chemolithotrophs such as the motile filamentous cyanobacteria (e.g., Calothrix, Oscillatoria, Phormidium, and Spirulina) that grow in geothermal springs and geysers of Earth at temperatures ranging fiom 320K to 345K and are also found growing in cold polar desert soils. The mineralized remains of morphotypes of all of these cyanobacteria have also been found in the Orgueil CI1 and the Murchison CN2 carbonaceous meteorites that may derive from cometary parent bodies. Observational results that support the hypothesis that liquid water can in active regions just beneath the surface of comets and that comets, carbonaceous meteorites, and asteroids may have played a significant role in the origin and evolution of the Biosphere and in the distribution of microbial life throughout the Solar System.
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Episodic Aging and End States of Comets
NASA Technical Reports Server (NTRS)
Sekanina, Zdenek
2008-01-01
It is known that comets are aging very rapidly on cosmic scales, because they rapidly shed mass. The processes involved are (i) normal activity - sublimation of ices and expulsion of dust from discrete emission sources on and/or below the surface of a comet's nucleus, and (ii) nuclear fragmentation. Both modes are episodic in nature, the latter includes major steps in the comet's life cycle. The role and history of dynamical techniques used are described and results on mass losses due to sublimation and dust expulsion are reviewed. Studies of split comets, Holmes-like exploding comets, and cataclysmically fragmenting comets show that masses of 10 to 100 million tons are involved in the fragmentation process. This and other information is used to investigate the nature of comets' episodic aging. Based on recent advances in understanding the surface morphology of cometary nuclei by close-up imaging, a possible mechanism for large-scale fragmentation events is proposed and shown to be consistent with evidence available from observations. Strongly flattened pancake-like shapes appear to be required for comet fragments by conceptual constraints. Possible end states are briefly examined.
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Figure Caption for pair of images of 'Comet Nucleus Q
NASA Technical Reports Server (NTRS)
2002-01-01
Figure Caption for pair of images of 'Comet Nucleus Q'. 21Jul94 Last Look at the Q-nuclei First image - March 30, 1994. Two Q-nuclei and a split nucleus, P. Second image - July 20, 1994. at T - 10 hours. Both nuclei still show no sign of further fragmentation, although the coma near each is being stretched out along the direction of motion. Both images were taken with the WFPC2 Planetary Camera using a red filter. Credit: H. A. Weaver and T. E. Smith
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NASA Technical Reports Server (NTRS)
Sekanina, Zdenek
1991-01-01
One of the more attractive among the plausible scenarios for the major emission event recently observed on Comet Halley at a heliocentric distance of 14.3 AU is activation of a source of ejecta driven by an icy substance much more volatile than water. As prerequisite for the forthcoming detailed analysis of the imaging observations of this event, a simple model is proposed that yields the sublimation rate versus time at any location on the surface of a rotating cometary nucleus for two candidate ices: carbon monoxide and carbon dioxide. The model's variable parameters are the comet's heliocentric distance r and the Sun's instantaneous zenith angle z.
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Asteroids, Comets, Meteors 1991
NASA Technical Reports Server (NTRS)
Harris, Alan W. (Editor); Bowell, Edward (Editor)
1992-01-01
Papers from the conference are presented and cover the following topics with respect to asteroids, comets, and/or meteors: interplanetary dust, cometary atmospheres, atmospheric composition, comet tails, astronomical photometry, chemical composition, meteoroid showers, cometary nuclei, orbital resonance, orbital mechanics, emission spectra, radio astronomy, astronomical spectroscopy, photodissociation, micrometeoroids, cosmochemistry, and interstellar chemistry.
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Comets, Asteroids, and the Origin of the Biosphere
NASA Technical Reports Server (NTRS)
Hoover, Richard B.
2006-01-01
During the past few decades, the role of comets in the delivery of water, organics, and prebiotic chemicals to the Biosphere of Earth during the Hadean (4.5-3.8 Ga) period of heavy bombardment has become more widely accepted. However comets are still largely regarded as frigid, pristine bodies of protosolar nebula material that are entirely devoid of liquid water and consequently unsuitable for life in any form. Complex organic compounds have been observed comets and on the water rich asteroid 1998 KY26, which has color and radar reflectivity similar to the carbonaceous meteorites. Near infrared observations have indicated the presence of crystalline water ice and ammonia hydrate on the large Kuiper Belt object (50000) Quaoar with resurfacing that may indicate cryovolcanic outgassing and the Cassini spacecraft has detected water-ice geysers on Saturn s moon Enceladus. Spacecraft observations of the chemical compositions and characteristics of the nuclei of several comets (Halley, Borrelly, Wild 2, and Tempel 1) have now firmly established that comets contain a suite of complex organic chemicals; water is the predominant volatile; and that extremely high temperatures (approx.350-400 K) can be reached on the surface of the very black (albedo-0.03) nuclei when the comets are with 1.5 AU from the Sun. Impact craters and pinnacles observed on comet Wild 2 suggest a thick crust and episodic outbursts and jets observed on the nuclei of several comets are interpreted as indications that localized regimes of liquid water and water vapor can periodically exist beneath the crust of some comets. The Deep Impact observations indicate that the temperature on the nucleus of of comet Tempel 1 at 1.5 AU varied from 330K on the sunlit side to a minimum of 280+/-8 K. It is interesting that even the coldest region of the comet surface was slightly above the ice/liquid water phase transition temperature. These results suggest that pools and films of liquid water can exist in a wide range of temperatures in cavities and voids at different depths just beneath the crust of a comet. The possibility that liquid water may exist over a wide range of temperatures on comets significantly enhances the possibility that these bodies may harbor niches suitable for microbial communities and ecosystems. Such niches would by ideal for the growth of psychrophilic, mesophilic, and possibly even thermophilic chemolithotrophs and photoautotrophs such as the motile filamentous cyanobacteria (e.g., Calothrix, Oscillatoria, Phormidium, and Spirulina) that can grow in geothermal springs and geysers at temperatures ranging from 320K to 345K and in cold polar desert soils. This paper reviews the observational data in support of the hypothesis that liquid water can exist in permafrost-like active regions just beneath the surface of comets when near perihelion and provides additional arguments in support of the hypothesis that comets, carbonaceous meteorites, and asteroids may have played a significant role in the origin and evolution of the Biosphere and in the distribution of microbial life throughout the Solar System.
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Constraining the Compositional Heterogeneity in CO-Dominated Comet C/2016 R2 (PanSTARRS)
NASA Astrophysics Data System (ADS)
McKay, Adam; Kelley, Michael; DiSanti, Michael; Womack, Maria; Wierzchos, Kacper; Biver, Nicolas; de Val-Borro, Miguel; Cordiner, Martin; Dello Russo, Neil; Feaga, Lori; Bauer, James; Cochran, Anita; Harrington Pinto, Olga
2018-05-01
Comets exhibit a primitive volatile composition, making them invaluable tools for understanding the formation of the Solar System. Constraining the compositional heterogeneity of cometary nuclei is vital for interpreting cometary composition in terms of the physical conditions operating in the protosolar disk at the time of planet formation. Some comets exhibit variability in observed coma composition over the course of their orbit. This could be indicative of a heterogeneous nucleus consisting of cometesimals formed in different parts of the protosolar nebula under differing conditions. Alternatively, the observed heterogeneity could be post-formation evolution. We propose to use Spitzer IRAC observations of CO2 in the atypically CO-rich comet C/2016 R2 (PanSTARRS) to better understand the compositional heterogeneity of cometary nuclei.
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Epoxi Has Its Sights On Hartley; Our Sights Are On Education And Public Outreach
NASA Astrophysics Data System (ADS)
Feaga, Lori M.; EPOXI E/PO Team
2010-10-01
The Deep Impact eXtended Investigation (DIXI) of NASA's EPOXI Discovery Program continues its thematic investigation of comets with a flyby of comet 103P/Hartley 2 on November 4, 2010. During the approach, encounter, and departure phase of the mission, the remaining instruments on the Deep Impact spacecraft will further explore the properties of comets. Ultimately, the planetary science community wants to better understand the diversity between comets and how these protoplanetary building blocks have evolved throughout their history in the Solar System. A goal of EPOXI Education and Public Outreach (E/PO) is to share in the excitement of comet science and their potential to preserve details of our origins. The DIXI E/PO team has been publicizing the flyby at many events across the US. The E/PO program is focused on a hands-on approach to learning about comets and their place in the Solar System. Many of the activities available on our website (epoxi.umd.edu) have been adapted from existing education materials and encompass results from several cometary missions. A newly developed and released educational activity called Comparing Comets has been implemented successfully in classrooms. The activity encourages students to make observations, interpretations and think like scientists for the day. The activity guides students through a scientific comparative analysis of two previously visited cometary nuclei, Tempel 1 and Wild 2, a process similar to that which the DIXI science team members will be undertaking when the spacecraft arrives at Hartley 2 and captures images of another comet. Comparing Comets includes audio files from scientists that gives the students and educators insight into the type of data that can be obtained by a mission and the methods that observational astronomers employ when deriving real scientific results from data.
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The crash of P/Shoemaker-Levy 9 into Jupiter and its implications for comet bombardment on Earth
NASA Technical Reports Server (NTRS)
Shoemaker, E. M.; Shoemaker, C. S.
1994-01-01
Periodic Comet Shoemaker/Levy 9 will impact Jupiter in late July 1994. The comet, which broke into more than 20 telescopically detectable fragments when it passed with the Roche lobe of Jupiter on July 8, 1992, is captured in a highly eccentric orbit about Jupiter. The 21 recognized nuclei will be spread out in a train of the order 7 x 10(exp 6) km long at the time of impact, and the impacts will be spread in time over about 5 1/2 days centered on about July 21.2 UT. In addition to the train of recognized bright nuclei, the comet consists of 'wings' of unresolved bodies that are the source of a very broad composite dust tail. The linear extent of the wings is about an order of magnitude greater than that of the train of recognized discrete nuclei. Collision of the wings will be spread in time over several months. Thus the impact of P/S-L 9 with Jupiter will be an event of appreciable duration.
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The Amazing Apparition of 73P/Schwassmann-Wachmann 3 in 2006
NASA Astrophysics Data System (ADS)
Weaver, Harold A.
2006-09-01
Most comets may meet their ultimate demise as a result of catastrophic fragmentation events, and that process was prominently displayed during the 2006 apparition of comet 73P/Schwassmann-Wachmann 3 (73P/SW3). This Jupiter-family comet with an orbital period of 5.4 yr was discovered when it passed within 0.06 AU of the Earth during the spring of 1930. However, it was subsequently lost until 1979 when it arrived at perihelion about 5 weeks later than predicted, probably owing to a close approach to Jupiter in 1965. Several remarkable outbursts in dust and gas activity were observed during the 1995 apparition, and four separate fragments were clearly detected and followed for several months. The solar elongation angle was unfavorably small, and the geocentric distance rather large, throughout the 2000-2001 apparition, and only two fragments were definitely detected then. Thus, it was with considerable uncertainty that cometary researchers approached the 2006 apparition, when the geometry would be nearly as favorable as for the discovery apparition with the comet passing within 0.08 AU during May 2006. Owing to the extremely fragile nature of cometary nuclei in general, and the previously recorded breakup of 73P/SW3, there was no guarantee that any fragment would return this year. To the delight of professional and amateur astronomers alike, the 2006 apparition of 73P/SW3 was nothing short of spectacular, as over 60 new fragments were detected and monitored during the late-winter and spring. Ground-based and space-based observatories, large and small, intensively monitored 73P/SW3 to document the disintegration of its nuclei and to measure the composition of its larger fragments. This paper will review the scientific results obtained during the 2006 apparition of 73P/SW3 and reflect on what the disintegration of this comet reveals about the nature of cometary nuclei.
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A Post-Stardust Mission View of Jupiter Family Comets
NASA Technical Reports Server (NTRS)
Zolensky, M.
2011-01-01
Before the Stardust Mission, many persons (including the mission team) believed that comet nuclei would be geologically boring objects. Most believed that comet nucleus mineralogy would be close or identical to the chondritic interplanetary dust particles (IDPs), or perhaps contain mainly amorphous nebular condensates or that comets might even be composed mainly of preserved presolar material [1]. Amazingly, the results for Comet Wild 2 (a Jupiter class comet) were entirely different. Whether this particular comet will ultimately be shown to be typical or atypical will not be known for a rather long time, so we describe our new view of comets from the rather limited perspective of this single mission.
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Mid-infrared spectra of comet nuclei
NASA Astrophysics Data System (ADS)
Kelley, Michael S. P.; Woodward, Charles E.; Gehrz, Robert D.; Reach, William T.; Harker, David E.
2017-03-01
Comet nuclei and D-type asteroids have several similarities at optical and near-IR wavelengths, including near-featureless red reflectance spectra, and low albedos. Mineral identifications based on these characteristics are fraught with degeneracies, although some general trends can be identified. In contrast, spectral emissivity features in the mid-infrared provide important compositional information that might not otherwise be achievable. Jovian Trojan D-type asteroids have emissivity features strikingly similar to comet comae, suggesting that they have the same compositions and that the surfaces of the Trojans are highly porous. However, a direct comparison between a comet and asteroid surface has not been possible due to the paucity of spectra of comet nuclei at mid-infrared wavelengths. We present 5-35 μm thermal emission spectra of comets 10P/Tempel 2, and 49P/Arend-Rigaux observed with the Infrared Spectrograph on the Spitzer Space Telescope. Our analysis reveals no evidence for a coma or tail at the time of observation, suggesting the spectra are dominated by the comet nucleus. We fit each spectrum with the near-Earth asteroid thermal model (NEATM) and find sizes in agreement with previous values. However, the NEATM beaming parameters of the nuclei, 0.74-0.83, are systematically lower than the Jupiter-family comet population mean of 1.03 ± 0.11, derived from 16- and 22-μm photometry. We suggest this may be either an artifact of the spectral reduction, or the consequence of an emissivity low near 16 μm. When the spectra are normalized by the NEATM model, a weak 10-μm silicate plateau is evident, with a shape similar to those seen in mid-infrared spectra of D-type asteroids. A silicate plateau is also evident in previously published Spitzer spectra of the nucleus of comet 9P/Tempel 1. We compare, in detail, these comet nucleus emission features to those seen in spectra of the Jovian Trojan D-types (624) Hektor, (911) Agamemnon, and (1172) Aneas, as well as those seen in the spectra of seven comet comae. The comet comae present silicate features with two distinct shapes, either trapezoidal, or more rounded, the latter apparently due to enhanced emission near 8 to 8.5 μm. The surfaces of Tempel 2, Arend-Rigaux, and Hektor best agree with the comae that present trapezoidal features, furthering the hypothesis that the surfaces of these targets must have high porosities in order to exhibit a spectrum similar to a comet coma. An emissivity minimum at 15 μm, present in the spectra of Tempel 2, Arend-Rigaux, Hektor, and Agamemnon, is also described, the origin of which remains unidentified. The compositional similarity between D-type asteroids and comets is discussed, and our data supports the hypothesis that they have similar origins in the early Solar System.
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The enigmatic object 2201 Oljato - Is it an asteroid or an evolved comet?
NASA Technical Reports Server (NTRS)
Mcfadden, Lucy A.; Cochran, Anita L.; Barker, Edwin S.; Cruikshank, Dale P.; Hartmann, William K.
1993-01-01
The orbital properties of near-earth object 2201 have been associated with meteor showers, and its modeled orbital evolution is chaotic - a property which might indicate a history related to comets. Telescopic observations of its visible and near-infrared spectral reflectance, broad-band visible and near-infrared photometry, infrared radiometric measurements, and radar echoes are reported here from two apparitions, 1979 and 1983. This asteroid has a high radiometric albedo, a property not associated with comet nuclei. In certain wavelength regimes it is classified as an S-type asteroid, in others, an E-type, but its overall spectral reflectance is not typical of either taxonomic type, and neither type is thought of as cometlike. Unexpectedly high ultraviolet reflectance at the 1979 apparition was suggested to be the result of residual outgassing as in a comet. The UV photometric data are modeled as fluorescent emission from neutral species found in comets. The resulting calculations indicate a plausible value for OH and CN emission at 0.3085 and 0.38 micron relative to the observed range of active comets.
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How pristine is the interior of the comet 67P/Churyumov-Gerasimenko?
NASA Astrophysics Data System (ADS)
Capria, Maria Teresa; Capaccioni, Fabrizio; Filacchione, Gianrico; Tosi, Federico; De Sanctis, Maria Cristina; Mottola, Stefano; Ciarniello, Mauro; Formisano, Michelangelo; Longobardo, Andrea; Migliorini, Alessandra; Palomba, Ernesto; Raponi, Andrea; Kührt, Ekkehard; Bockelée-Morvan, Dominique; Erard, Stéphane; Leyrat, Cedric; Zinzi, Angelo
2017-07-01
Comets are usually considered to be the most primitive bodies in the Solar System. The level of truth of this paradigm, however, is a matter of debate, especially if by primitive we mean that they represent a sample of intact, unprocessed material. We now have the possibility of analysing the comet 67P/Churyumov-Gerasimenko with an unprecedented level of detail, but its interior remains largely unprobed and unknown. The questions we address in this paper concern the depth of the processed layers, and whether the comet nucleus, under these processed layers, is really representative of the original material. We applied the Rome model for the thermal evolution and differentiation of nuclei to give an estimation of the evolution and depth of the active layers and of the interplay between the erosion process and the penetration of the heat wave. In order to characterize the illumination regime and the activity on the nucleus, two locations with very different illumination histories were chosen for the simulation. For both locations, the bulk of the activity tends to be concentrated around the perihelion time, giving rise to a high erosion rate. As a consequence, the active layers tend to remain close to the surface, and the interior of the comet, below a layer of few tens of centimetres, can be considered as pristine.
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NASA Astrophysics Data System (ADS)
Greenberg, J. M.
The density of typical comet nuclei is estimated on the basis of published empirical and theoretical density data on meteors. The nuclei are assumed to consist of aggregated interstellar dust (silicate cores with complex organic refractory mantles) as proposed by Greenberg (1982 and 1983) and Van de Bult et al. (1985). The theoretical density (0.5 g/cu cm) of a compact nucleus of this type is contrasted with the observed densities of meteors associated with short-period comets (0.2 g/cu cm) and the Draconids associated with comet Giacobini-Zinner (0.01 g/cu cm), and it is inferred that the original comet debris was less than fully packed. A birdsnest structure comprising elongated crystals and about 60 percent empty space is proposed; its albedo is estimated as about 0.05 (in the range predicted by observations); and it is shown to undergo much less internal heating by the sun than a solid ice nucleus. The mean density of reconstituted cometary matter is found to be in the range 0.54-0.03 g/cu cm, consistent with the estimates (0.1 g/cu cm) of Lin (1966) and Donn (1963).
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HUBBLE SEES MINI-COMET FRAGMENTS FROM COMET LINEAR
NASA Technical Reports Server (NTRS)
2002-01-01
[lower right] In one stunning Hubble picture the fate of the mysteriously vanished solid nucleus of Comet LINEAR has been settled. The Hubble picture shows that the comet nucleus has been reduced to a shower of glowing 'mini-comets' resembling the fiery fragments from an exploding aerial firework. This is the first time astronomers have ever gotten a close-up look at what may be the smallest building blocks of cometary nuclei, the icy solid pieces called 'cometesimals', which are thought to be less than 100 feet across. The farthest fragment to the left, which is now very faint, may be the remains of the parent nucleus that fragmented into the cluster of smaller pieces to the right. The comet broke apart around July 26, when it made its closest approach to the Sun. The picture was taken with Hubble's Wide Field Planetary Camera 2 on August 5, 2000, when the comet was at a distance of 64 million miles (102 million kilometers) from Earth. Credit: NASA, Harold Weaver (the Johns Hopkins University), and the HST Comet LINEAR Investigation Team [upper left] A ground-based telescopic view (2.2-meter telescope) of Comet LINEAR taken on August 5, at nearly the same time as the Hubble observations. The comet appears as a diffuse elongated cloud of debris without any visible nucleus. Based on these images, some astronomers had concluded that the ices in the nucleus had completely vaporized, leaving behind a loose swarm of dust. Hubble's resolution was needed to pinpoint the remaining nuclei (inset box shows HST field of view as shown in lower right). Credit: University of Hawaii
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Report of the Comet Science Working Group
NASA Technical Reports Server (NTRS)
1979-01-01
General scientific questions and measurement objectives that can be addressed on a first comet mission relate to: (1) the chemical nature and the physical structure of comet nuclei as well as the changes that occur as functions of time and orbital position; (2) the chemical and physical nature of the atmospheres and ionospheres of comets, the processes which occur in them, and the development of these atmospheres and ionospheres as functions of time and orbital position; and (3) the nature of comet tails, the processes by which they are formed, and the interaction of comets with the solar wind. Capabilities of the various instruments required are discussed.
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NASA Astrophysics Data System (ADS)
Shustov, B.; Sachkov, M.; Gómez de Castro, A. I.; Vallejo, J. C.; Kanev, E.; Dorofeeva, V.
2018-04-01
Comets are important "eyewitnesses" of Solar System formation and evolution. Important tests to determine the chemical composition and to study the physical processes in cometary nuclei and coma need data in the UV range of the electromagnetic spectrum. Comprehensive and complete studies require additional ground-based observations and in situ experiments. We briefly review observations of comets in the ultraviolet (UV) and discuss the prospects of UV observations of comets and exocomets with space-borne instruments. A special reference is made to the World Space Observatory-Ultraviolet (WSO-UV) project.
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NASA Astrophysics Data System (ADS)
Schleicher, David G.; Bair, Allison Nicole
2016-10-01
As remnants from the epoch of early solar system formation, comet nuclei are less processed than any other class of objects currently available for detailed study. Compositional and physical studies can therefore be used to investigate primordial conditions across the region of comet formation and/or subsequent evolutionary effects. With these goals, a long duration program of comet narrowband photometry was begun in 1976 and results for 85 comets were published by A'Hearn et al. (1995; Icarus 118, 223). Observations continued and we performed a new set of analyses of data obtained through mid-2011. Following a hiatus due to lack of funding and other competing priorities, we have now resumed our efforts at completing this project while also incorporating the most recent five years of data. The database now includes 191 comets obtained over 848 nights. A restricted subset of 116 objects were observed multiple times and are considered well-determined; these form the basis of our compositional studies. Using a variety of taxonomic techniques, we identified seven compositional classes for the data up to 2011 and anticipate no changes with the newest additions. Several classes are simply sub-groups of the original carbon-chain depleted class found by A'Hearn et al.; all evidence continues to indicate that carbon-chain depletion reflects the primordial composition at the time and location of cometary accretion and is not associated with evolution. Another new class contains five comets depleted in ammonia but not depleted in carbon-chain molecules; it is unclear if this group is primordial or not. In comparison, clear evidence for evolutionary effects are seen in the active fractions for comet nuclei -- decreasing with age -- and with the dust-to-gas ratio -- decreasing with age and perihelion distance, implying an evolution of the surface of the nucleus associated with the peak temperature attained and how often such temperatures have been reached. Updates of these and other results including data from the last five years will be presented. Support was provided by NASA Planetary Atmospheres grant NNX08AG19G.
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NASA Technical Reports Server (NTRS)
Saunders, R. S.; Parker, T. J.; Stephens, J. B.; Fanale, F. P.; Sutton, S.
1986-01-01
Results are reported from experimental studies of the formation of ice mixed with mineral particles in an effort to simulate similar processes on natural surfaces such as at the Martian poles, on comet nuclei and on icy satellites. The study consisted of low-pressure, low-temperature sublimations of water ice from dilutions of water-clay (montmorillonite and Cabosil) dispersions of various component ratios. Liquid dispersions were sprayed into liquid nitrogen to form droplets at about -50 C. Both clay-water dispersions left a filamentary residue on the bottom of the Dewar after the water ice had sublimated off. The residue was studied with optical and SEM microscopy, the latter method revealing a high electrical conductivity in the residue. The results suggest that the sublimation of the water ice can leave a surface crust, which may be analogous to processes at the Martian poles and on comet nuclei. The process could proceed by the attachment of water molecules to salt crystals during the hottest part of the Martian year. The residue remaining was found to remain stable up to 370 C, be porous, and remain resilient, which could allow it to insulate ice bodies such as comets in space.
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NASA Technical Reports Server (NTRS)
Luna, Michael E.; Collins, Steven M.
2011-01-01
On November 4, 2010 the former "Deep Impact" spacecraft, renamed "EPOXI" for its extended mission, flew within 700km of comet 103P/Hartley 2. In July 2005, the spacecraft had previously imaged a probe impact of comet Tempel 1. The EPOXI flyby was the fifth close encounter of a spacecraft with a comet nucleus and marked the first time in history that two comet nuclei were imaged at close range with the same suite of onboard science instruments. This challenging objective made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby.As part of the spacecraft flyby preparations, the ADCS operations team had to perform meticulous sequence reviews, implement complex spacecraft engineering and science activities and perform numerous onboard calibrations. ADCS contributions included design and execution of 10 trajectory correction maneuvers, the science calibration of the two telescopic instruments, an in-flight demonstration of high-rate turns between Earth and comet point, and an ongoing assessment of reaction wheel health. The ADCS team was also responsible for command sequences that included updates to the onboard ephemeris and sun sensor coefficients and implementation of reaction wheel assembly (RWA) de-saturations.
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Planetary research at Lowell Observatory
NASA Technical Reports Server (NTRS)
Baum, William A.
1988-01-01
Scientific goals include a better determination of the basic physical characteristics of cometary nuclei, a more complete understanding of the complex processes in the comae, a survey of abundances and gas/dust ratios in a large number of comets, and measurement of primordial (12)C/(13)C and (14)N/(15)N ratios. The program also includes the observation of Pluto-Charon mutual eclipses to derive dimensions. Reduction and analysis of extensive narrowband photometry of Comet Halley from Cerro Tololo Inter-American Observatory, Perth Observatory, Lowell Observatory, and Mauna Kea Observatory were completed. It was shown that the 7.4-day periodicity in the activity of Comet Halley was present from late February through at least early June 1986, but there is no conclusive evidence of periodic variability in the preperihelion data. Greatly improved NH scalelengths and lifetimes were derived from the Halley data which lead to the conclusion that the abundance of NH in comets is much higher than previously believed. Simultaneous optical and thermal infrared observations were obtained of Comet P/Temple 2 using the MKO 2.2 m telescope and the NASA IRTF. Preliminary analysis of these observations shows that the comet's nucleus is highly elongated, very dark, and quite red.
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DNA Strand Breaks in Mitotic Germ Cells of Caenorhabditis elegans Evaluated by Comet Assay
Park, Sojin; Choi, Seoyun; Ahn, Byungchan
2016-01-01
DNA damage responses are important for the maintenance of genome stability and the survival of organisms. Such responses are activated in the presence of DNA damage and lead to cell cycle arrest, apoptosis, and DNA repair. In Caenorhabditis elegans, double-strand breaks induced by DNA damaging agents have been detected indirectly by antibodies against DSB recognizing proteins. In this study we used a comet assay to detect DNA strand breaks and to measure the elimination of DNA strand breaks in mitotic germline nuclei of C. elegans. We found that C. elegans brc-1 mutants were more sensitive to ionizing radiation and camptothecin than the N2 wild-type strain and repaired DNA strand breaks less efficiently than N2. This study is the first demonstration of direct measurement of DNA strand breaks in mitotic germline nuclei of C. elegans. This newly developed assay can be applied to detect DNA strand breaks in different C. elegans mutants that are sensitive to DNA damaging agents. PMID:26903030
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The study of the physics of cometary nuclei
NASA Technical Reports Server (NTRS)
Whipple, F. L.
1985-01-01
The development and utilization of an optimized computer program to analyze orbital stabilization by repeated calculations is presented. The stability of comets in the Opik-Oort Cloud about the Sun against perturbations by the Galactic center involve the same basic type of calculation. The supposed persistence of these bodies in orbits over the life of the solar system, depends upon the stability of bodies of negligible mass in orbits around a body whose mass is small compared to the central mass about which they revolve. The question remains of preferential orientation of extremely eccentric comet orbits, possibly to explain the asymmetry observed among new comet motions. A third application of the computing programs is suited to meteoroids that may exist in orbits about asteroids and that may endanger science spacecraft making flybys too near to asteroids. As in the double-comet case, solar activity and solar gravitational perturbations limit the attendance to an asteroid by small meteroids in their orbits. It is found that the mass distances planned for asteroid fly-bys are adequate.
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NASA Technical Reports Server (NTRS)
Meech, Karen J.
1991-01-01
The question of physical aging in cometary nuclei is addressed in order to elucidate the relationship between the past conditions in the protosolar nebula and the present state of the cometary nucleus, and to understand the processes that will physically and chemically alter the nucleus as a function of time. Attention is given to some of the processes that might be responsible for causing aging in comets, namely, radiation damage in the upper layers of the nucleus during the long residences in the Oort cloud, processing from heating and collisions within the Oort cloud, loss of highly volatile species from the nucleus on the first passage through the inner solar system, buildup of a dusty mantle, which can eventually prohibit further sublimation, and a change in the porosity, and hence the thermal properties, of the nucleus. Recent observations suggest that there are distinct differences between 'fresh' Oort cloud comets and thermally processed periodic comets with respect to intrinsic brightness and rate of change of activity as a function of distance.
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Massive stars: flare activity due to infalls of comet-like bodies
NASA Astrophysics Data System (ADS)
Ibadov, Subhon; Ibodov, Firuz S.
2015-01-01
Passages of comet-like bodies through the atmosphere/chromosphere of massive stars at velocities more than 600 km/s will be accompanied, due to aerodynamic effects as crushing and flattening, by impulse generation of hot plasma within a relatively very thin layer near the stellar surface/photosphere as well as ``blast'' shock wave, i.e., impact-generated photospheric stellar/solar flares. Observational manifestations of such high-temperature phenomena will be eruption of the explosive layer's hot plasma, on materials of the star and ``exploding'' comet nuclei, into the circumstellar environment and variable anomalies in chemical abundances of metal atoms/ions like Fe, Si etc. Interferometric and spectroscopic observations/monitoring of young massive stars with dense protoplanetary discs are of interest for massive stars physics/evolution, including identification of mechanisms for massive stars variability.
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From Kuiper Belt to Comet: The Shapes of the Nuclei
NASA Astrophysics Data System (ADS)
Jewitt, D.; Sheppard, S.; Fernandez, Y.
2003-05-01
It is widely believed that escaped objects from the Kuiper Belt are the source of both the Centaurs and the nuclei of the Jupiter Family Comets (JFCs). If the JFC nuclei are produced by collisional breakup of parent objects in the Kuiper Belt, then it is reasonable to expect that their shape distribution should be consistent with those of fragments produced in disintegrative laboratory experiments, or with the small main-belt asteroids (which are produced collisionally). We test this idea using a sample of eleven well-observed cometary nuclei. Our main result is that the nuclei are, on average, much more elongated than either the collisionally produced small main-belt asteroids or the fragments created in laboratory impact experiments. Several interpretations of this systematic shape difference are possible (including the obvious one that the JFC nuclei are not, after all, produced collisionally in the Kuiper Belt). Our preferred explanation, however, is that the asphericities of the nuclei have been modified by one or more processes of mass loss. An implication of this interpretation is that the JFC nuclei in our sample are highly evolved, having lost a major part of their original mass. In turn, this implies that the angular momenta of the nuclei are also non-primordial: the JFC nuclei are highly physically evolved objects. We will discuss the evidence supporting these conclusions. This work has been recently published in Astronomical Journal, 125, 3366-3377 (2003).
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NASA Astrophysics Data System (ADS)
Vincent, J.; Oklay, N.; Marchi, S.; Höfner, S.; Sierks, H.
2014-07-01
This paper reviews the observations of crater-like features on cometary nuclei. ''Pits'' have been observed on almost all cometary nuclei but their origin is not fully understood [1,2,3,4]. It is currently assumed that they are created mainly by the cometary activity with a pocket of volatiles erupting under a dust crust, leaving a hole behind. There are, however, other features which cannot be explained in this way and are interpreted alternatively as remnants of impact craters. This work focusses on the second type of pit features: impact craters. We present an in-depth review of what has been observed previously and conclude that two main types of crater morphologies can be observed: ''pit-halo'' and ''sharp pit''. We extend this review by a series of analysis of impact craters on cometary nuclei through different approaches [5]: (1) Probability of impact: We discuss the chances that a Jupiter Family Comet like 9P/Tempel 1 or the target of Rosetta 67P/Churyumov-Gerasimenko can experience an impact, taking into account the most recent work on the size distribution of small objects in the asteroid Main Belt [6]. (2) Crater morphology from scaling laws: We present the status of scaling laws for impact craters on cometary nuclei [7] and discuss their strengths and limitations when modeling what happens when a rocky projectile hits a very porous material. (3) Numerical experiments: We extend the work on scaling laws by a series of hydrocode impact simulations, using the iSALE shock physics code [8,9,10] for varying surface porosity and impactor velocity (see Figure). (4) Surface processes and evolution: We discuss finally the fate of the projectile and the effects of the impact-induced surface compaction on the activity of the nucleus. To summarize, we find that comets do undergo impacts although the rapid evolution of the surface erases most of the features and make craters difficult to detect. In the case of a collision between a rocky body and a highly porous cometary nucleus, two specific crater morphologies can be formed: a central pit surrounded by a shallow depression, or a pit, deeper than typical craters observed on rocky surfaces. After the impact, it is likely that a significant fraction of the projectile will remain in the crater. During its two years long escort of comet 67P/Churyumov-Gerasimenko, ESA's Rosetta mission should be able to detect specific silicate signatures on the bottom of craters or crater-like features, as evidence of this contamination. For large craters, structural changes in the impacted region, in particular, compaction of material, will affect the local activity. The increase of tensile strength can stop the activity by preventing the gas from lifting up dust grains. On the other hand, material compaction can help the heat flux to travel deeper in the nucleus, potentially reaching unexposed pockets of volatiles, and therefore increasing the activity [11]. Ground truth data from Rosetta will help us infer the relative importance of those two effects.
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The natural history of Halley's comet
NASA Astrophysics Data System (ADS)
McLaughlin, W. I.
1981-07-01
The 1986 apparition of Halley's comet will be the subject of numerous space probes, planned to determine the chemical nature and physical structure of comet nuclei, atmospheres, and ionospheres, as well as comet tails. The problems of cometary origin remain inconclusive, with theories ranging from a purely interstellar origin to their being ejecta from the Galilean satellites of Jupiter. Comets can be grouped into one of two classes, depending on their periodicity, and statistical mechanics of the entire Jovian family of comets can be examined under the equilibrium hypothesis. Comet anatomy estimations have been determined, and there is speculation that comet chemistry may have been a factor in the origin of life on earth. Halley's comet was first noted using Newton's dynamical methods, and Brady (1972) attempted to use the comet as a gravitational probe in search of a trans-Plutonian planet. Halley's orbit is calculated by combination of ancient observations and modern scientific methods.
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Comparative study of icy patches on comet nuclei
NASA Astrophysics Data System (ADS)
Oklay, Nilda; Pommerol, Antoine; Barucci, Maria Antonietta; Sunshine, Jessica; Sierks, Holger; Pajola, Maurizio
2016-07-01
Cometary missions Deep Impact, EPOXI and Rosetta investigated the nuclei of comets 9P/Tempel 1, 103P/Hartley 2 and 67P/Churyumov-Gerasimenko respectively. Bright patches were observed on the surfaces of each of these three comets [1-5]. Of these, the surface of 67P is mapped at the highest spatial resolution via narrow angle camera (NAC) of the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS, [6]) on board the Rosetta spacecraft. OSIRIS NAC is equipped with twelve filters covering the wavelength range of 250 nm to 1000 nm. Various filters combinations are used during surface mapping. With high spatial resolution data of comet 67P, three types of bright features were detected on the comet surface: Clustered, isolated and bright boulders [2]. In the visible spectral range, clustered bright features on comet 67P display bluer spectral slopes than the average surface [2, 4] while isolated bright features on comet 67P have flat spectra [4]. Icy patches observed on the surface of comets 9P and 103P display bluer spectral slopes than the average surface [1, 5]. Clustered and isolated bright features are blue in the RGB composites generated by using the images taken in NIR, visible and NUV wavelengths [2, 4]. This is valid for the icy patches observed on comets 9P and 103P [1, 5]. Spectroscopic observations of bright patches on comets 9P and 103P confirmed the existence of water [1, 5]. There were more than a hundred of bright features detected on the northern hemisphere of comet 67P [2]. Analysis of those features from both multispectral data and spectroscopic data is an ongoing work. Water ice is detected in eight of the bright features so far [7]. Additionally, spectroscopic observations of two clustered bright features on the surface of comet 67P revealed the existence of water ice [3]. The spectral properties of one of the icy patches were studied by [4] using OSIRIS NAC images and compared with the spectral properties of the active regions observed on comet 67P. Additionally jets rising from the same clustered bright feature were detected visually [4]. We analyzed bright patches on the surface of comets 9P, 103P and 67P using multispectral data obtained by the high-resolution instrument (HRI), medium- resolution instrument (MRI) and OSIRIS NAC using various spectral analysis techniques. Clustered bright features on comet 67P have similar visible spectra to the bright patches on comets 9P and 103P. The comparison of the bright patches includes the published results of the IR spectra. References: [1] Sunshine et al., 2006, Science, 311, 1453 [2] Pommerol et al., 2015, A&A, 583, A25 [3] Filacchione et al., 2016, Nature, 529, 368-372 [4] Oklay et al., 2016, A&A, 586, A80 [5] Sunshine et al. 2012, ACM [6] Keller et al., 2007, Space Sci. Rev., 128, 433 [7] Barucci et al., 2016, COSPAR, B04
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Evolution of carbonaceous chondrite parent bodies: Insights into cometary nuclei
NASA Technical Reports Server (NTRS)
Mcsween, Harry Y., Jr.
1989-01-01
It is thought that cometary samples will comprise the most primitive materials that are able to be sampled. Although parent body alteration of such samples would not necessarily detract from scientists' interest in them, the possibility exists that modification processes may have affected cometary nuclei. Inferences about the kinds of modifications that might be encountered can be drawn from data on the evolution of carbonaceous chondrite parent bodies. Observations suggest that, of all the classes of chondrites, these meteorites are most applicable to the study of comets. If the proportion of possible internal heat sources such as Al-26 in cometary materials are similar to those in chondrites, and if the time scale of comet accretion was fast enough to permit incorporation of live radionuclides, comets might have had early thermal histories somewhat like those of carbonaceous chondrite parent bodies.
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Silva, M R; Alvarez, C M; García, P M; Ruiz, M A
2014-12-12
The genus Lupinus is widely distributed. Its seeds are used for animal and human food, and Lupinus possesses pharmacological potential because of its high content of quinolizidine alkaloids and flavonoids; however, there is little available information about its genotoxicity. We used the comet assay and staminal nuclei of Tradescantia (clone 4430) to evaluate the in vitro genotoxicity of 4 concentrations (0.01, 0.1, 0.5, and 1.0 mM) of alkaloid extracts of Lupinus mexicanus and Lupinus montanus, flavonoids of L. mexicanus, and commercial sparteine; nitrosodiethylamine was used as a positive control and untreated nuclei were used as a negative control. All concentrations of L. mexicanus and L. montanus showed significant genotoxic activity (P ≤ 0.05). A similar behavior was observed for flavonoid extracts of L. montanus except the 1.0 mM concentration. Sparteine showed genotoxic activity only at 0.5 mM. The order of genotoxicity of the compounds studied was as follows: L. mexicanus > L. montanus > flavonoids of L. montanus > sparteine. There is evident genotoxic activity in the compounds that were studied, particularly at lower concentrations (0.01 and 0.1 mM). Given the limited information about the genotoxicity of the compounds of L. mexicanus and L. montanus, further studies are necessary.
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NASA Astrophysics Data System (ADS)
Belton, Michael J. S.; Thomas, Peter; Veverka, J.; Schultz, Peter; A'Hearn, Michael F.; Feaga, Lori; Farnham, Tony; Groussin, Olivier; Li, Jian-Yang; Lisse, Casey; McFadden, Lucy; Sunshine, Jessica; Meech, Karen J.; Delamere, W. Alan; Kissel, Jochen
2007-03-01
We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441-446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230-238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253-263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136-2160; 1999a. Astron. J. 118, 1101-1119; 1999b. Astrophys. J. 526, 465-470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255-1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220-229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670-1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193-204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or "layered pile" model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects.
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NASA Astrophysics Data System (ADS)
Belton, Michael J. S.; Thomas, Peter; Veverka, J.; Schultz, Peter; A'Hearn, Michael F.; Feaga, Lori; Farnham, Tony; Groussin, Olivier; Li, Jian-Yang; Lisse, Casey; McFadden, Lucy; Sunshine, Jessica; Meech, Karen J.; Delamere, W. Alan; Kissel, Jochen
We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441 446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230 238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253 263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136 2160; 1999a. Astron. J. 118, 1101 1119; 1999b. Astrophys. J. 526, 465 470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255 1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220 229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670 1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193 204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or “layered pile” model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects.
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Formation environment of cometary nuclei in the primordial solar nebula
NASA Astrophysics Data System (ADS)
Yamamoto, T.
1985-01-01
The formation environment of comets in the primordial solar nebula is investigated from the point of view of the chemical composition of the ices of cometary nuclei. A sublimation sequence for various species of possible constituents of the nuclear ice, which would have condensed on the grain surface in the parent interstellar cloud was obtained by calculating the temperature of grains in the solar nebula. On this basis, an allowed range of the nebular temperature in the formation region of cometary nuclei is obtained from a condition for retention of the ices of the nuclear composition. Combining this result with models of the solar nebula, the region for the formation of cometary nuclei in the solar nebula is discussed. It is shown that cometary nuclei formed at least beyond the region between the formation regions of Saturn and Uranus. Finally, an upper limit is estimated for the grain temperature in the region of comet formation at an earlier stage of the solar nebula. The grain temperature is shown to be less than 60 K at this stage.
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Cometary activity and nucleus modelling: a new approach
NASA Astrophysics Data System (ADS)
Möhlmann, D.
1996-06-01
The phenomena of comet splittings with an average frequency of about one splitting per 100 years and comet (Chen and Jewitt, Icarus108, 265-271, 1994), and the restriction of cometary activity to well-defined small areas at the almost passive and mantle covered surface (Keller et al., ESA SP-250, Vol. II, pp. 363-364, 1986) are at present driving challenges to models of structure and evolution of comet nuclei. Extending the presently discussed models by incorporating lateral subsurface transport of sublimed volatiles, there appears the possibility that the places of sublimation are different from those of activity (the so-called active areas). Then, there is no necessity to distinguish between different surface properties at active and passive areas, assuming, e.g. an uncovered icy surface at active areas. Active areas are simply the very local "source sites" where the accumulated subsurface flows from distant regions reach the surface. The pressure driven subsurface flows of volatiles may not only leave the comet at its surface, they may penetrate via cracks, etc. also deeply into the nucleus. There they can cause a further growth of cracks and also new cracks. This can be a cause for the observed regular splittings. Furthermore, actual models (Kührt and Keller, Icarus109, 121-132, 1994; Skorov and Rickman, Planet. Space Sci.43, 1587-1594, 1995) of the gas transport through porous comet surface crusts can be interpreted as to give first indications for thermodynamical parameters in heat conducting and porous cometary crusts which are appropriate for 1 AU conditions to permit the temporary existence of a layer with fluid subsurface water within these crusts. This exciting result of the possible temporary existence of subsurface warm water in comets which approach the Sun within about 1 AU makes a cometary subsurface chemistry much more efficient than expected hitherto.
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Anticipated results from dust experiments on cometary missions
NASA Technical Reports Server (NTRS)
Kissel, J.; Fechtig, H.; Grun, E.
1981-01-01
The major scientific objectives of a mission are: to determine the chemical nature and physical structure of comet nuclei, and to characterize the changes that occur as a function of time orbital position; to characterize the chemical and physical nature of the atmospheres and ionospheres of comets as well as the processes that occur in them, and to characterize the development of the atmospheres and ionospheres as functions of time and orbital position; and to determine the nature of comet tails and processes by which they are formed, and to characterize the interaction of comets with the solar wind. Since dust is a major constituent of a comet, the achievement of these goals requires the intensive study of the paticulate emission from a comet.
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Modelling the evolution of a comet subsurface: implications for 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Guilbert-Lepoutre, Aurélie; Rosenberg, Eric D.; Prialnik, Dina; Besse, Sébastien
2016-11-01
Modelling the evolution of comets is a complex task aiming at providing constraints on physical processes and internal properties that are inaccessible to observations, although they could potentially bring key elements to our understanding of the origins of these primitive objects. This field has made a tremendous step forward in the post-Giotto area, owing to detailed space- and ground-based observations, as well as detailed laboratory simulations of comet nuclei. In this paper, we review studies that we believe are significant for interpreting the observations of 67P/Churyumov-Gerasimenko by the ESA/Rosetta mission, and provide new calculations where needed. These studies hold a strong statistical significance, which is exactly what is needed for this comet with an orbital evolution that cannot be traced back accurately for more than hundreds of years. We show that radial and lateral differentiation may have occurred on 67P's chaotic path to the inner Solar system, and that internal inhomogeneities may result in an erratic activity pattern. Finally, we discuss the origins of circular depressions seen on several comets including 67P, and suggest that they could be considered as evidence of the past processing of subsurface layers.
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NASA Technical Reports Server (NTRS)
Whipple, Fred L.
1991-01-01
Comments on the nature of cometary nuclei, some problems regarding cometary origin, and some correlations among cometary data are presented. Comparisons with an earlier report on cometary nuclei are noted, and most of the earlier advances in concept are substantiated. The mean density of the Halley nucleus may have been underestimated, while the nature of the rotation remains uncertain. The dust/gas ratio apparently needs to be increased by as much as two times, perhaps to unity or higher. CHON grains appear to be important sources of gas. Evidence is presented to support the thesis that aging among long-period comets increases statistically as the periods decrease. Data on the orientation of cometary axes with respect to the Galaxy and the properties of clusters defined by these axes are presented.
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Modeling of meteoroid streams: The velocity of ejection of meteoroids from comets (a review)
NASA Astrophysics Data System (ADS)
Ryabova, G. O.
2013-05-01
An analytical review of the models of ejection of meteoroids from cometary nuclei is presented. Different formulas for the ejection velocity of meteoroids and the corresponding parameters are discussed and compared with the use of comet Halley and the Geminids meteoroid stream as examples. The ejection velocities obtained from observations of the dust trails of comets are discussed, and the values for comets 2P/Encke, 4P/Faye, 17P/Holmes, 22P/Kopff, and 67P/Churyumov-Gerasimenko are compared to the velocities yielded by Whipple's model. The uncertainty intervals of the results are estimated.
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Cratering time scales for the Galilean satellites
NASA Technical Reports Server (NTRS)
Shoemaker, E. M.; Wolfe, R. F.
1982-01-01
An attempt is made to estimate the present cratering rate for each Galilean satellite within the correct order of magnitude and to extend the cratering rates back into the geologic past on the basis of evidence from the earth-moon system. For collisions with long and short period comets, the magnitudes and size distributions of the comet nuclei, the distribution of their perihelion distances, and the completeness of discovery are addressed. The diameters and masses of cometary nuclei are assessed, as are crater diameters and cratering rates. The dynamical relations between long period and short period comets are discussed, and the population of Jupiter-crossing asteroids is assessed. Estimated present cratering rates on the Galilean satellites are compared and variations of cratering rate with time are considered. Finally, the consistency of derived cratering time scales with the cratering record of the icy Galilean satellites is discussed.
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Velocity of Ejection of Meteor Particle from the Nucleus of Comets
NASA Astrophysics Data System (ADS)
Safarov, Abduljalol; Ibadinov, Khursand
2016-07-01
The time and velocity of dust particles of anomalous tail of comets was determine. Velocity ejection of dust particles from the nuclei of comets C/1851 U1, C/1877 G1, C/1921 E1, C/1925 V1, C/1962 C1, C/1969 T1, C/1975 V2, 2P/1924 and 26P/1927 F1 reaching up to 0.4 km/s can be attributed to the removal of large dust particles from the surface of the icy nucleus of comet sublimating molecules. In comets C/1823 Y1, C/1844 Y1, C/1882 R1, C/1883 D1, C/1888 R1, C/1892 E1, D/1894 F1, C/1910 A1, C/1921 E1, C/1922 U1, C/1930 D1, C/1930 O1, C/1931 P1, C/1932 M1, C/1935 A1, C/1954 O1, C/1961 O1, C/1963 A1, C/1968 H1, C/1973 E1, C/1980 P1, C/1984 N2, C/1987 P1, C/1995 O1, C/1999 H1, C/1999 T2, C/1999 S4, C/2002 T7, C/2004 F4, C/2004 Q2, 6P/1950, 7P/1869 G1, 7P/1933, 10P/1930, 19P/1918, 34P/1938 J1, 35P/1939, 67P/1982, 73P/1930 J1, 96P/1986 J1 and 109P/1862 O1 ejection velocity (up to a few km/s) of the particles of anomalous tail from the nuclei significantly exceed the thermal velocity of the molecules sublimating ice nuclei. Such velocity may be explained by the removal of particles from the surface of the nucleus after the collision of the comet nucleus with meteoroids
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Comet Dust: The Story of Planet Formation as Told by the Tiniest of Particles
NASA Technical Reports Server (NTRS)
Wooden, D. H.
2005-01-01
Our planetary system formed out of a gas-rich disk-shaped nebula with the early Sun at its center. Many small icy bodies were consumed by the formation of the giant planets. However, many km-size icy bodies were tossed out of the giant-planet region to the cold, distant reaches of our solar system. Comets remained in their places of cold storage until perturbed into orbits that carry them into the inner solar system where they pass relatively close to the Sun. Comets are warmed by the Sun and shed material from their outer layers. The ices and gases shed by comets reveal simple and complex organic molecules were present at the time and in the region of the formation of the giant planets. Where the Earth was forming was too hot and had too intense sunlight for many of these ices and molecules to survive. The dust shed by comets tells us that some stardust survived unaltered but much of the dust was heated and crystallized before becoming part of the comet. Therefore, comet dust grains tell of large radial migrations from the cold outer reaches near Neptune into the hot regions near the forming Sun, and then back out to the cold regions where icy comets were accreting and forming. On 2005 July 4, the NASA Deep Impact Mission hit a comet and ejected primitive materials fiom its interior. These materials were not released into the comet s coma during normal activity. Despite the many passages of this comet close to the Sun, these primitive volatile gases and dust grains survived in its interior. Comet dust grains show that cold and hot materials were mixed into the same tiny particle very early in the formation of the solar system, and these aggregate dust grains never saw high temperatures again. The survival of primitive materials in comet nuclei suggests comets could have delivered organic molecules and primitive dust grains to early Earth.
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NASA Technical Reports Server (NTRS)
Russell, Ray W.
1988-01-01
Laboratory studies related to cometary grains and the nuclei of comets can be broken down into three areas which relate to understanding the spectral properties, the formation mechanisms, and the evolution of grains and nuclei: (1) Spectral studies to be used in the interpretation of cometary spectra; (2) Sample preparation experiments which may shed light on the physical nature and history of cometary grains and nuclei by exploring the effects on grain emissivities resulting from the ways in which the samples are created; and (3) Grain processing experiments which should provide insight on the interaction of cometary grains with the environment in the immediate vicinity of the cometary nucleus as the comet travels from the Oort cloud through perihelion, and perhaps even suggestions regarding the relationship between interstellar grains and cometary matter. A summary is presented with a different view of lab experiments than is found in the literature, concentrating on measurement techniques and sample preparations especially relevant to cometary dust.
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The infrared spectral properties of frozen volatiles. [in cometary nuclei
NASA Technical Reports Server (NTRS)
Fink, U.; Sill, G. T.
1982-01-01
Since Whipple's dirty snowball model of comet nuclei, it has been generally accepted that volatile ices help to explain cometary phenomena. The infrared spectral properties of many substances that are potential candidates for frozen volatiles in the solar system are being pursued; indeed some of these frozen materials have been found in the solar system: H2O, CO2, and SO2. A review of laboratory spectra in the range 1 to 20 microns of H2O, CO2, SO2, CH4, NH3, H2S, CO, NH4HS and NH3.H2O is presented. Both reflection spectra of thick frosts and transmission spectra of thin films are shown, and their main characteristics are described. Hydrates, clathrates, and composite spectra are discussed. When it is possible to observe the nuclei of comets at close range, it may be possible to identify frozen volatiles by their infrared spectra.
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Rapid evolution of the spin state of comet 41P/Tuttle-Giacobini-Kresak
NASA Astrophysics Data System (ADS)
Bodewits, Dennis; Farnham, Tony; Knight, Matthew M.; Kelley, Michael S.
2017-10-01
Comet nuclei are small, dynamic objects influenced strongly by their individual history, orbit, rotation and inhomogeneity. Mass loss due to sublimation can exert a profound influence on the physical nature of the cometary nucleus, changing the shape, size, and rotation (Jewitt, in Comets II, 2004). The Rosetta mission to comet 67P showed that these effects are all interrelated (Sierks et al., Science 347, 2015).Comet 41P/Tuttle-Giacobini-Kresak passed Earth as close as 0.142 au in April 2017, allowing observations of the inner coma and an assessment of the rotational state of the nucleus. We acquired observations of comet 41P between March and May 2017 using the 4.3-m Discovery Channel Telescope and the UltraViolet-Optical Telescope (UVOT) on board the Earth-orbiting Swift Gamma Ray Burst Mission.Using CN narrowband imaging and aperture photometry we found that the apparent rotation period of comet 41P more than doubled between March and May 2017, increasing from 20 hours to 50 hours. Measurements of the periodicity in late-March by Knight et al. (CBET 4377, 2017) are consistent with this rate of increase. Comet 41P is the ninth comet for which a rotation period change has been observed (c.f. Samarasinha et al., in Comets II, 2004), but both the fractional change and the rate of change of the period far exceed those observed in the other comets. It is presumably the combination of a long rotation period, high surface activity, and a small nucleus that makes 41P highly susceptible to changes in its rotational state.Extrapolating the comet’s rotation period using its current gas production rates and a simple activity model suggests that the nucleus will continue to spin down, possibly leading to an excited spin state in the next few apparitions. Finally, 41P is known for its large outbursts, and our extrapolation suggest that the comet’s rotation period may have been close to the critical period for splitting in 2001, when it exhibited two significant outbursts.
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NASA Technical Reports Server (NTRS)
Schleicher, David G.
1991-01-01
The physical properties of comets were studied by applying a wide variety of observational techniques. Emphasis is on simultaneous or coordinated observations in different spectral regions (e.g., visible and thermal IR or visible and far UV) or with different instrumentation (imaging, spectroscopy, and photometry). The aim was to: (1) measure the basic properties of cometary nuclei by studying comets whose comae are so anemic that the signal from the nucleus can be extracted; (2) investigate the group characteristics of comets by narrowband photometry applied uniformly to a large sample of comets; (3) understand the detailed physics and chemistry occurring in cometary comae through wide-field charge coupled device (CCD) imaging using narrow filters and through long-slit CCD spectroscopy; and (4) investigate the rotational states of comets through time-resolution photometry.
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NASA Astrophysics Data System (ADS)
Churyumov, K. I.; Kleshchonok, V. V.
Observations of the Jupiter satellites within the program for investigation of the comet D/SL-9 Jupiter collision were held with the electrophotometer installed on the AZT-14 (D = 0.48 m) telescope at the Lisnyki Station of the Kiev University Astronomical Observatory. Circumstances for observations did not reveal changes in the satellite brightnesses which could be linked with the reflection of light of a fireball in the Jupiter atmosphere, with the exception of the A and Q2 nucleus fall down. Here, three events that can be tied with the outburst during the nuclei fall down were found out.
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Abstracts for the International Conference on Asteroids, Comets, Meteors 1991
NASA Technical Reports Server (NTRS)
1991-01-01
Topics addressed include: chemical abundances; asteroidal belt evolution; sources of meteors and meteorites; cometary spectroscopy; gas diffusion; mathematical models; cometary nuclei; cratering records; imaging techniques; cometary composition; asteroid classification; radio telescopes and spectroscopy; magnetic fields; cosmogony; IUE observations; orbital distribution of asteroids, comets, and meteors; solar wind effects; computerized simulation; infrared remote sensing; optical properties; and orbital evolution.
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CCD scanning for asteroids and comets
NASA Technical Reports Server (NTRS)
Gehrels, T.; Mcmillan, R. S.
1986-01-01
A change coupled device (CCD) is used in a scanning mode to find new asteroids and recover known asteroids and comet nuclei. Current scientific programs include recovery of asteroids and comet nuclei requested by the Minor Planet Center (MPC), discovery of new asteroids in the main belt and of unusual orbital types, and follow-up astrometry of selected new asteroids discovered. The routine six sigma limiting visual magnitude is 19.6 and slightly more than a square degree is scanned three times every 90 minutes of observing time during the fortnight centered on New Moon. Semiautomatic software for detection of moving objects is in routine use; angular speeds as low as 11.0 arcseconds per hour were distinguished from the effects of the Earth's atmosphere on the field of view. A typical set of three 29-minute scans near the opposition point along the ecliptic typically nets at least 5 new main-belt asteroids down to magnitude 19.6. In 18 observing runs (months) 43 asteroids were recovered, astrometric and photometric data on 59 new asteroids were reported, 10 new asteroids with orbital elements were consolidated, and photometry and positions of 22 comets were reported.
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NASA Technical Reports Server (NTRS)
Lowry, Stephen C.; Weissman, Paul R.; Sykes, Mark V.; Reach, William T.
2003-01-01
We are conducting an observational program designed to determine the overall distributions of size, shape, rotation period, and surface characteristics of cometary nuclei. Here, we present results from a study of the Jupiter- family comet 2P/Encke based on observations from Steward Observatory's 2.3m Bok Telescope at Kitt Peak. This comet has been observed extensively in the past and was one of the primary flyby targets of the recently failed CONTOUR mission.
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The Nucleus of 10 Short-Period Comets
NASA Astrophysics Data System (ADS)
Lamy, P. L.; Toth, I.; Weaver, H. A.; Delahodde, C. E.; Jorda, L.; A'Hearn, M. F.
2001-11-01
We report on the successful detection and extensive characterization of the nuclei of 10 short-period comets with the Hubble Space Telescope: 47P/Ashbrook-Jackson, 61P/Shajn-Schaldach, 70P/Kojima, 74P/Smirnova-Chernikh, 76P/West-Kohoutek-Ikemura, 82P/Gehrels 3, 86P/Wild 3, 87P/Bus, 110P/Hartley 3, 147P/Kushida-Muramatsu. The observations were performed with the Planetary Camera of WFPC2 during cycle 9, between July 2000 and June 2001. Each comet was observed eight times over a time span of about 12 hours through different filters, up to three (V, R, I) for the brightest ones. The sizes were determined assuming a geometric albedo of 0.04 for the R band and a phase law of 0.04 mag/deg. We confirm our past findings that cometary nuclei are generally extremely small; the radius of 147P/Kushida-Muramatsu was only 0.13 km. We also present the results for the colors and the lightcurves of the nuclei and discuss the implications for their shape and rotational state. This work was supported by grants from the Universite de Provence, from C.N.E.S., C.N.R.S. (France), from the Hungarian Academy of Science and from NASA through grant HST-GO-08699.01-A from the STScI.
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Numerical Simulations of Lightcurves of Non-principal Axis Rotators
NASA Astrophysics Data System (ADS)
Mueller, Beatrice E. A.; Samarasinha, N. H.
2012-10-01
Theory predicts that most short-period comets should be in non-principal axis (NPA) rotational states (Jewitt 1997) due to torques caused by outgassing from the nuclei. However the fraction that is currently observed to be in such a state is small (less than 15%; Samarasinha et al 2004, and references therein). This suggests that NPA states naturally occurring as a consequence of cometary jetting are more rapidly damped because comets are structurally far weaker than has been assumed. However, there is a serious question whether this discrepancy is real or an artifact of interpreting lightcurve observations. We will present initial results of our numerical simulation of the observational manifestation of lightcurves over the range of possible NPA rotation states and determine the effects of observing geometry, signal-to-noise, and sampling. References: Jewitt, D. 1997. Cometary Rotation: An Overview. Earth, Moon, and Planets 79, 35-53. Samarasinha, N.H., B.E.A. Mueller, M.J.S. Belton,L. Jorda 2004. Rotation of Cometary Nuclei. In Comets II, pp. 281-299.
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NASA Astrophysics Data System (ADS)
Lamy, P. L.; Toth, I.; Weaver, H. A.; A'Hearn, M. F.; Jorda, L.
2011-04-01
We report on our on-going effort to detect and characterize cometary nuclei with the Hubble Space Telescope (HST). During cycle 9 (2000 July to 2001 June), we performed multi-orbit observations of 10 ecliptic comets with the Wide Field Planetary Camera 2. Nominally, eight contiguous orbits covering a time interval of ˜11 h were devoted to each comet but a few orbits were occasionally lost. In addition to the standard R band, we could additionally observe four of them in the V band and the two brightest ones in the B band. Time series photometry was used to constrain the size, shape and rotational period of the 10 nuclei. Assuming a geometric albedo of 0.04 for the R band, a linear phase law with a coefficient of 0.04 mag deg-1 and an opposition effect similar to that of comet 19P/Borrelly, we determined the following mean values of the effective radii 47P/Ashbrook-Jackson: 2.86±0.08 km, 61P/Shajn-Schaldach: 0.62±0.02 km, 70P/Kojima: 1.83±0.05 km, 74P/Smirnova-Chernykh: 2.23±0.04 km, 76P/West-Kohoutek-Ikemura: 0.30±0.02 km, 82P/Gehrels 3: 0.69±0.02 km, 86P/Wild 3: 0.41±0.03 km, 87P/Bus: 0.270.01 km, 110P/Hartley 3: 2.15±0.04 km and 147P/Kushida-Muramatsu: 0.21±0.01 km. Because of the limited time coverage (˜11 h), the rotational periods could not be accurately determined, multiple solutions were sometime found and three periods were not constrained at all. Our estimates range from ˜5 to ˜32 h. The lower limits for the ratio a/b of the semi-axis of the equivalent spheroids range from 1.10 (70P) to 2.20 (87P). The four nuclei for which we could measure (V-R) are all significantly redder than the Sun, with 86P/Wild 3 (V-R) = 0.86 ± 0.10 appearing as an ultrared object. We finally determined the dust activity parameter Afρ of their coma in the R band, the colour indices and the reflectivity spectra of four of them. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-26555.
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Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Hässig, M.; Altwegg, K.; Balsiger, H.; Bar-Nun, A.; Berthelier, J. J.; Bieler, A.; Bochsler, P.; Briois, C.; Calmonte, U.; Combi, M.; De Keyser, J.; Eberhardt, P.; Fiethe, B.; Fuselier, S. A.; Galand, M.; Gasc, S.; Gombosi, T. I.; Hansen, K. C.; Jäckel, A.; Keller, H. U.; Kopp, E.; Korth, A.; Kührt, E.; Le Roy, L.; Mall, U.; Marty, B.; Mousis, O.; Neefs, E.; Owen, T.; Rème, H.; Rubin, M.; Sémon, T.; Tornow, C.; Tzou, C.-Y.; Waite, J. H.; Wurz, P.
2015-01-01
Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.
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Spectral mapping of comet 67P/Churyumov-Gerasimenko with VLT/MUSE and SINFONI
NASA Astrophysics Data System (ADS)
Guilbert-Lepoutre, Aurelie; Besse, Sebastien; Snodgrass, Colin; Yang, Bin
2016-10-01
Comets are supposedly the most primitive objects in the solar system, preserving the earliest record of material from the nebula out of which our Sun and planets were formed, and thus holding crucial clues on the early phases of the solar system formation and evolution. For most small bodies in the solar system we can only access the surface properties, whereas active comet nuclei lose material from their subsurface, so that understanding cometary activity represents an unique opportunity to assess their internal composition, and by extension the composition, the temperature and pressure conditions of the protoplanetary disk at their place of formation.The ESA/Rosetta mission is performing the most thorough investigation of a comet ever made. Rosetta is measuring properties of comet 67P/Churyumov-Gerasimenko at distances between 5 and hundreds of km from the nucleus. However, it is unable to make any measurement over the thousands of km of the rest of the coma. Fortunately, the outer coma is accessible from the ground. In addition, we currently lack an understanding of how the very detailed information gathered from space-based observations can be extrapolated to the many ground-based observations that we can potentially perform. Combining parallel in situ observations with observations from the ground therefore gives us a great opportunity, not only to understand the behavior of 67P, but also to other comets observed exclusively from Earth. As part of the many observations taken from the ground, we have performed a spectral mapping of 67's coma using two IFU instruments mounted on the VLT: MUSE in the visible, and SINFONI in the near-infrared. The observations, carried out in March 2016, will be presented and discussed.
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NASA Technical Reports Server (NTRS)
Jewitt, D. C.; Soifer, B. T.; Neugebauer, G.; Matthews, K.; Danielson, G. E.
1982-01-01
The paper reports combined visual imagery and spectroscopy, near-infrared spectroscopy, and broadband infrared photometry of comets P/Stephan-Oterma (1980g), Bowell (1980b), and Panther (1980u) at intermediate heliocentric distances. The visual data indicate the existence of solid grains in extended halos around the nuclei of the three comets. Broadband near-infrared and thermal infrared measurements of Comet Panther suggest the presence of 2-4-micron-radius particles in the coma which most likely contain molecules incorporating the N-H bond, but which are more complex and less volatile than NH3. Such molecules can be produced in the grains by cosmic-ray reprocessing. Near infrared spectral features identical to those seen in comet Panther similary suggest the presence of a molecule incorporating the N-H bond in comet Bowell.
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NASA Astrophysics Data System (ADS)
Jewitt, D. C.; Soifer, B. T.; Neugebauer, G.; Matthews, K.; Danielson, G. E.
1982-12-01
The paper reports combined visual imagery and spectroscopy, near-infrared spectroscopy, and broadband infrared photometry of comets P/Stephan-Oterma (1980g), Bowell (1980b), and Panther (1980u) at intermediate heliocentric distances. The visual data indicate the existence of solid grains in extended halos around the nuclei of the three comets. Broadband near-infrared and thermal infrared measurements of Comet Panther suggest the presence of 2-4-micron-radius particles in the coma which most likely contain molecules incorporating the N-H bond, but which are more complex and less volatile than NH3. Such molecules can be produced in the grains by cosmic-ray reprocessing. Near infrared spectral features identical to those seen in comet Panther similary suggest the presence of a molecule incorporating the N-H bond in comet Bowell.
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The population, magnitudes, and sizes of Jupiter family comets
NASA Astrophysics Data System (ADS)
Fernández, J. A.; Tancredi, G.; Rickman, H.; Licandro, J.
1999-12-01
We analyze the sample of measured nuclear magnitudes of the observed Jupiter family (JF) comets (taken as those with orbital periods P < 20 years and Tisserand parameters T > 2). We find a tendency of the measured nuclear magnitudes to be fainter as JF comets are observed with CCD detectors attached to medium- and large-size telescopes (e.g. Spacewatch Telescope). However, a few JF comets observed very far from the Sun (4-7 AU) show a wide dispersion of their derived absolute nuclear magnitudes which suggests that either these JF comets keep active all along the orbit, so the reported unusually bright distant magnitudes were strongly contaminated by a coma, or some of the measured ``nuclear magnitudes'' were grossly overestimated (i.e. their brightness underestimated). The cumulative mass distribution of JF comets is found to follow a power-law of index s = - 0.88 +/- 0.08, suggesting a distribution significantly steeper than that for both small main-belt asteroids and near-Earth asteroids. The cumulative mass distribution of JF comets with q < 2 AU tends to flatten for absolute (visual) nuclear magnitudes H_N > 16, which is probably due to incompleteness of discovery of fainter comets and/or a real scarcity of small comets due, perhaps, to much shorter physical lifetimes. In particular, no JF comets fainter than H_N ~ 19.5 are found in the sample, suggesting that the critical size for a comet to be still active may be of about 0.4 km radius for an assumed geometric albedo of 0.04. Possibly, smaller comet nuclei disintegrate very quickly into meteor streams. Most absolute nuclear magnitudes are found in the range 15-18, corresponding to nuclear radii in the range 0.8-3.3 km (for the same geometric albedo). We find that a large majority of JF comets with perihelion distances q > 2.5 AU are brighter than absolute nuclear magnitude H_N = 16, suggesting that only a very small fraction (a few percent) of the population of the JF comets with large q has so far been detected. A similar trend is noted for the corresponding absolute total magnitudes H_T taken from Kresák & Kresáková's (1994) catalog. By analyzing the H_N and H_T data, and trends in the discovery rate of JF comets as a function of their perihelion distances, the overall population of JF comets within Jupiter's region (q < 5.2 AU) up to an absolute nuclear magnitude H_N = 18.5 is estimated to be from several thousand to about 104 members. The q-distribution of JF comets shows a steep increase with q, which is consistent with JF comets coming from a flat intermediate source in the Jupiter-Saturn region.
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Could life have evolved in cometary nuclei
NASA Technical Reports Server (NTRS)
Bar-Nun, A.; Lazcano-Araujo, A.; Oro, J.
1981-01-01
The suggestion by Hoyle and Wickramasinghe (1978) that life might have originated in cometary nuclei rather than directly on the earth is discussed. Factors in the cometary environment including the conditions at perihelion passage leading to the ablation of cometary ices, ice temperatures, the absence of an atmosphere and discrete liquid and solid surfaces, weak cometary structure incapable of supporting a liquid core, and radiation are presented as arguments against biopoesis in comets. It is concluded that although the contribution of cometary and meteoritic matter was significant in shaping the earth environment, the view that life on earth originally arose in comets is untenable, and the proposition that the process of interplanetary infection still occurs is unlikely in view of the high specificity of host-parasite relationships.
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The 67P/Churyumov-Gerasimenko nucleus spectroscopic properties and their evolution over time
NASA Astrophysics Data System (ADS)
Fornasier, S.
2016-11-01
Comets are primitive small bodies witness of the Solar System formation. Our knowledge on cometary nuclei and on their evolution over time is very limited because they are dark, small, and thus faint objects, spatially unresolved by groundbased telescopes and masked by their atmosphere when they become brighter close to the Sun. Before the Rosetta mission, only 5 cometary nuclei have been directly imaged and investigated by space missions during relatively short fly-bys, catching thus a small fraction of the comet lifetime in its orbit. The Rosetta mission is orbiting around the 67P/Churyumov-Gerasimenko comet since August 2014, and provides the unique opportunity to continuously investigate the 67P nucleus during about 2 years, from large heliocentric distances (about 4 AU) to its perihelion passage (1.24 AU) and beyond. The OSIRIS cameras and VIRTIS spectrometer have shown that the 67P nucleus has a red spectral behavior with spectral properties similar to those of bare cometary nuclei, of primitive D-type asteroids like the Jupiter Trojans, and of the moderately red Transneptunians population (Sierks et al., 2015, Capaccioni et al., 2015). The surface is globally dominated by dehydrated and organic-rich refractory materials (Capaccioni et al., 2015), and shows some color heterogeneities. Three kind of terrains, from the spectrally bluer and water ice enriched terrains to the redder ones, associated mostly to dusty regions, have been identified by visible spectrophotometry from the first resolved images acquired in July-August 2014 (Fornasier et al., 2015), covering mostly the northern hemisphere of the nucleus. The southern hemisphere has become visible from Rosetta only since March 2015, and it shows a lack of spectrally red regions compared to the northern one, associated to the absence of wide spread smooth or dust covered terrains. Although water is the dominant volatile observed in the coma, exposed water ice has been detected only in small amounts in different regions of the comet (Pommerol et al., 2015; De Sanctis et al., 2015; Filacchione et al., 2016; Barucci et al. 2016). Thanks to the unprecedented spatial resolution, VIRTIS and OSIRIS instruments have detected the occurrence of water frost close to the morning shadows, putting in evidence the diurnal cycle of water. Seasonal color and spectral variations have also been observed when the comet approached perihelion, indicating that the increasing activity had progressively shed the surface dust, partially showing the underlying ice-rich layer. I will present an overview of the spectroscopic properties of the 67P nucleus and of their diurnal and seasonal variations over time and heliocentric distance.
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Are comets connected to the origin of life
NASA Technical Reports Server (NTRS)
Delsemme, A. H.
1981-01-01
Possible connections between comets and the origin of life on earth are discussed. The orbital evolution of comets and their origin are considered within a framework for the origin of the solar system, with particular attention given to the origin of the biosphere, and the origin of the Oort cloud. Evidence suggesting that cometary nuclei are undifferentiated throughout is considered, and a model of the average composition of a mean new comet is obtained from observational data which is similar to that of an interstellar frost. The chemistry of the model composition giving rise to the species observed in cometary spectra is considered, as well as the relations of cometary to cosmic abundances of oxygen, carbon and sulfur. The characteristics of possible sites for prebiotic chemistry, including interstellar clouds, the protosolar nebula, comets in the Oort cloud, periodic comets and the primitive earth, are examined, and a possible role of comets in bringing the interstellar prebiotic chemistry to earth is suggested.
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Exploring the fission and reconfiguration cycle of comet 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Scheeres, Daniel J.; Hirabayashi, Masatoshi; Chesley, Steven R.; McMahon, Jay W.
2016-10-01
In Hirabayashi et al. (Nature, 2016) the nucleus of comet 67P/Churyumov-Gerasimenko (67P) is studied with a focus on the straight cracks observed on the Hapi region. These cracks were shown to have formed during a period of fast rotation and led to a proposed evolutionary scenario in which the nuclei may eventually split into two components and recombine to create a new bilobate configuration. Other bilobate nuclei should be subject to such a reconfiguration process, based on the relative sizes of the components, suggesting that this evolutionary scenario may be common for bilobate nuclei which comprise the majority of comet nuclei observed at high spatial resolution. Such reconfigurations could explain the observed occurrence of comet nucleus splitting and brightening events, which still lack a definitive geophysical understanding. Motivated by the proposed theory in Hirabayashi et al., the current work explores the dynamics of the 67P nucleus' rotation rate, fission limits, and subsequent dynamics. One aspect of the theory posits that the comet's distant Jupiter flybys will cause the latitude of the sub-solar point at perihelion to vary chaotically, leading to periods of net positive and negative torques and causing the nucleus to spin-up and spin-down in a random fashion. We analyze the current 67P nucleus shape and orbit to estimate the characteristic time-scale of this rotational evolution, providing an estimate of the current nucleus lifetime in its current configuration. Once the nucleus reaches a spin period shorter than ~7 hours the components will fission into a bound orbit, with the components subsequently reimpacting at speeds less than local escape speed (about 0.4 m/s). The current study extends Hirabayashi et al., explicitly modeling the mutual gravity and orbital dynamics of the head and body, assuming that the head and body rest on each other with the current shape of the 67P nucleus. The results show that when the components are released at a spin period between 6.5 hr and 7 hr, the components will separate and subsequently collide with a low impact speed. The orbital and rotational dynamics of the system components after fission are explored as a function of the initial spin rate at fission.
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Dynamics of landslides on comets of irregular shape
NASA Astrophysics Data System (ADS)
Czechowski, Leszek
2017-04-01
Landslides were observed on a few comet's nuclei, e.g. [1], [2]. The mechanism of their origin is not obvious because of very low gravity. According to [2] fluidization and multiphase transport of cometary material could be an explanation. We investigate here motion of the mass on a comet of irregular shape. The mechanism responsible for the low friction is not considered here. In fact, mass motion often occurs without contact with the surface. The motion could be triggered by meteoroids impacts or by the tidal forces. Comets nuclei are believed to be built of soft materials like snow and dust. The landing of Philae on the comet 67P/Czuriumow-Gierasimienko indicates a different situation. According to [1]: "thermal probe did not fully penetrate the near-surface layers, suggesting a local resistance of the ground to penetration of >4 megapascals, equivalent to >2 megapascal uniaxial compressive strength". Here we assume that elastic properties of comet's nuclei could be similar to elastic properties of dry snow, namely Young modulus is assumed to be 1 - 100 MPa, see [3] and [4]. We consider nucleus of the shape of 67P/Churyumov-Gerasimenko with density 470 kg/m3. The impact or tidal forces result in changing of rotation of the comet. In general, the vector of angular velocity will be a subject to nutation that results in changing of centrifugal force, and consequently could be a factor triggering landslides. Note that nucleus' shape does not resemble the shape of surface of constant value of gravitational potential (i.e. 'geoid'). Our numerical models indicate the parts of the nucleus where landslides start and other parts where landslides stop. Of course, the regolith from the first type of regions would be removed to the regions of the second class. The motion of the mass is often complicated because of complicated distribution of the gravity and complicated shape of the nucleus. Acknowledgement: The research is partly supported by Polish National Science Centre NCN) (decision 2014/15/B/ST 10/02117) References [1] T. Spohn, et al. (2015) Thermal and mechanical properties of the near-surface layers of comet 67P/Churyumov- Gerasimenko. Science 31 July 2015: Vol. 349 no. 6247 DOI: 10.1126/science.aab0464 [2] Belton M. J.S., Melosh J. (2009). Fluidization and multiphase transport of particulate cometary material as an explanation of the smooth terrains and repetitive outbursts on 9P/Tempel 1. Icarus 200 (2009) 280-291 [3] Reuter B. (2013) On how to measure snow mechanical properties relevant to slab avalanche release. International Snow Science Workshop Grenoble - Chamonix Mont-Blanc - 2013 007 [4] Ball A.J. (1997) Ph. D. Thesis: Measuring Physical Properties at the Surface of a Comet Nucleus, Univ.of Kent U.K.
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NASA Astrophysics Data System (ADS)
Fernandez, Yanga R.; Weaver, Harold A.; Lisse, Casey M.; Meech, Karen Jean; Lowry, Stephen C.; Bauer, James M.; Fitzsimmons, Alan; Snodgrass, Colin
2016-01-01
Cometary nuclei are some of the least reflective natural objects in the Solar System, although the number of comets for which the reflectivity has heretofore actually been measured is small due to the difficulty of the requisite measurements. When no other information is present, it is common to assume a geometric albedo of 4%, and this is consistent with the limited number of known albedos. However the true average albedo, median albedo, and spread of the distribution are not well constrained. Knowing the ensemble properties of cometary albedos would aid in understanding the surface scattering properties as well as the interior thermal evolution and surface evolution of the population. We present here a preliminary estimate of the distribution of geometric albedos among the Jupiter-family comet (JFC) population. We make use of and build on the results of the Survey of Ensemble Physical Properties of Cometary Nuclei (SEPPCoN), in which we obtained new and independent estimates of the radii of 89 JFCs [1,2]. We will present our preliminary albedo estimates for ~50 JFC nuclei (by far the most ever obtained), and we will discuss the implications of the ensemble of the results. These JFCs were all observed in R-band, and were all observed at relatively large heliocentric distances (usually >4 AU from the Sun) where the comets appeared inactive, thus minimizing coma contamination. We acknowledge the support of NASA grant NNX09AB44G, of NSF grant AST-0808004, and of the Astrophysical Research Consortium/Apache Point Observatory for this work. References: [1] Y. R. Fernandez et al., 2013, Icarus 226, 1138. [2] M. S. Kelley et al., 2013, Icarus 225, 475.
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CRAF Mission: An opportunity for exobiology
NASA Technical Reports Server (NTRS)
Neugebauer, Marcia; Weissman, Paul
1992-01-01
The Halley missions of 1986 gave us a first, quick glimpse of a comet nucleus and the first in situ measurements of cometary gas and dust. Many of our basic ideas about cometary nuclei were confirmed while a number of startling new discoveries were also made. However, in many respects the very fast Halley flybys raised more questions than they answered. We learned, for example, that comets contain a large amount of organic material but we were unable to determine precisely which organic molecules were present. We learned, too, that the nucleus of a comet is a dark, irregularly shaped body, but we could determine very little about the physical state and structure of the ices and grains within the comet nucleus.
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Are 2P/Encke, the Taurid complex NEOs and CM chondrites related?
NASA Astrophysics Data System (ADS)
Tubiana, C.; Snodgrass, C.; Michelsen, R.; Haack, H.; Fitzsimmons, A.; Williams, I.; Boehnhardt, H.
2013-09-01
Comet 2P/Encke is a short-period comet that was discovered in 1786 and has been extensively observed and studied for more than 200 years. It has an orbital period of 3.3 years and its orbit is dynamically decoupled from Jupiter's control due to gravitational interaction with terrestrial planets [6]. It is the only comet known on such an orbit, making it unique. Capture from the outer solar system onto its current orbit is very unlikely and even a continuous smooth dynamical evolution has a low probability as this requires a continuous period when it is dormant in order to avoid the volatiles from the nucleus becoming exhausted and making the current observed activity impossible. An origin in the asteroid belt is a possibility especially in view of the recently discovered main belt comets. The nucleus of 2P/Encke is dark (geometric albedo of 0.047 ± 0.023 [3]), has an effective radius of 2.4 ± 0.3 km [3] and it has polarimetric properties that are unique compared to other measured types of solar system objects, such as asteroids, TNOs, cometary dust, Centaurs [2]. The colors of 2P/Encke's nucleus are typical for comets, but no spectra of the nucleus in the visible wavelength range exist so far. The Taurid meteoroid stream has long been linked with 2P/Encke, but the activity of the comet is not strong enough to explain the number of observed meteors. It has been suggested that the meteoroid stream was caused by the break up of a larger parent body, which left comet 2P/Encke and other various small bodies along with a stream of dust. Various small near-Earth objects (NEOs) have been discovered with orbits that can be linked with 2P/Encke and the Taurid meteoroid stream [1]. Though many of the associations are spurious due to the low inclination of 2P/Encke's orbit, many NEO's have evolved in a similar way to 2P/Encke overa period of 5000 years [8] suggesting some relationship. In addition to dynamical properties, common taxonomic properties can also provide an indication of a common origin for small bodies in the solar system. Taxonomic properties are poorly known for cometary nuclei and only few comets have measurements in the visible wavelength range. The existing spectra of bare nuclei are generally featureless and display different reddening slopes. Given the poor S/N ratio that is usually obtained in observations, more subtle features, such as ones from hydrated minerals, are beyond the detection limit in most cases. If the Taurid complex NEOs are fragments of the same body as 2P/Encke, we expect them to have the same spectral properties as the comet nucleus. Furthermore, it would be reasonable to expect that these NEOs could show cometary activity. Maribo is a type CM carbonaceous chondrite that fell in Denmark on 17 January 2009 [5]. The preatmospheric orbit of the object places it in the middle of the Taurid meteor stream [4], which raises the intriguing possibility that comet 2P/Encke could be the parent body of CM chondrites, meaning that these meteorites are potentially samples of cometary material we can study in the laboratory. CM chondrites show signs of extensive aqueous alteration, which suggest that the parent body was an icy body that was at least partially molten at some point. It is therefore possible that the parent body of the CM chondrites is a comet [7]. In order to investigate whether a relationship between comet 2P/Encke, the Taurid complex associated NEOs and CM chondrites exists, spectroscopic studies of these objects were performed. Here we present ground-based observations, in the visible wavelength range, of 2P/Encke and 12 candidate Taurid NEOs obtained on 2 August 2011 at the ESO-VLT in Chile, using the FORS2 instrument. We obtained the first optical spectrum of the inactive nucleus of comet 2P/Encke and optical spectra of the selected candidate Taurid NEOs. In addition we obtained deep images in the R filter of each NEO to search for activity and of 2P/Encke to confirm that the comet was not active at the time of the observation. Preliminary analysis shows that 2P/Encke has a starlike profile, confirming that no cometary activity was present at the time of the observation. Its spectrum is flat and does not show any obvious absorption or mission feature in the wavelength range 400 - 950 nm. The spectra of the 12 Taurid NEOs are featureless as well and two of them show moderate reddening. Using deep R-filter images we will investigate the presence of weak activity around the asteroids. We will look for similarities between the spectrum of 2P/Encke and the ones of the selected NEOs to test the link between the comet and the Taurid complex associated NEOs. Moreover, a comparison between chondritic meteorite spectra and that of 2P/Encke will provide information about the possible link between 2P/Encke and CM chondrites.
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NASA Astrophysics Data System (ADS)
Steckloff, Jordan K.; Graves, Kevin; Hirabayashi, Masatoshi; Melosh, H. Jay; Richardson, James E.
2016-07-01
Comet 103P/Hartley 2 has diurnally controlled, CO2-driven activity on the tip of the small lobe of its bilobate nucleus. Such activity is unique among the comet nuclei visited by spacecraft, and suggests that CO2 ice is very near the surface, which is inconsistent with our expectations of an object that thermophysically evolved for ∼45 million years prior to entering the Jupiter Family of comets. Here we explain this pattern of activity by showing that a very plausible recent episode of rapid rotation (rotation period of ∼11 [10-13] h) would have induced avalanches in Hartley 2's currently active regions that excavated down to CO2-rich ices and activated the small lobe of the nucleus. At Hartley 2's current rate of spindown about its principal axis, the nucleus would have been spinning fast enough to induce avalanches ∼3-4 orbits prior to the DIXI flyby (∼1984-1991). This coincides with Hartley 2's discovery in 1986, and implies that the initiation of CO2 activity facilitated the comet's discovery. During the avalanches, the sliding material would either be lofted off the surface by gas activity, or possibly gained enough momentum moving downhill (toward the tip of the small lobe) to slide off the tip of the small lobe. Much of this material would have failed to reach escape velocity, and would reimpact the nucleus, forming debris deposits. The similar size frequency distribution of the mounds observed on the surface of Hartley 2 and chunks of material in its inner coma suggest that the 20-40 m mounds observed by the DIXI mission on the surface of Hartley 2 are potentially these fallback debris deposits. As the nucleus spun down (rotation period increased) from a period of ∼11-18.34 h at the time of the DIXI flyby, the location of potential minima, where materials preferentially settle, migrated about the surface, allowing us to place relative ages on most of the terrains on the imaged portion of the nucleus.
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Water ice grains in comet C/2013 US10 (Catalina)
NASA Astrophysics Data System (ADS)
Protopapa, Silvia; Kelley, Michael S. P.; Yang, Bin; Woodward, Charles E.; Sunshine, Jessica M.
2017-10-01
Knowledge of the the physical properties of water ice in cometary nuclei is critical in determining how the Solar System was formed. While it is difficult to directly study the properties of water ice in comet nuclei, we can study comet interiors through their comae. Cometary activity makes the interiors of these objects available for characterization. However, the properties (grain size, abundance, purity, chemical state) of water-ice grains detected in the coma do not necessarily represent the characteristics of the water ice on the surface and/or in the interior of the nucleus. This is due to the potential physical and chemical evolution of the emitted material. Once in the coma, water-ice grains are heated by sunlight, and if temperatures are warm enough, they sublime. In this case, their sizes and potentially their ice-to-dust fractions are reduced.We present IRTF/SpeX measurements of the Oort cloud comet C/2013 US10 (Catalina), which reached perihelion in Nov 2015 at a heliocentric distance Rh=0.822 AU. Observations of US10 were acquired on UT 2014-08-13, 2016-01-12, and 2016-08-13 (Rh=5.9, 1.3, and 3.9 AU). This set of measurements, spanning a broad range in Rh, are rare and fundamental for estimating how ice grains evolve in the coma. The spectrum obtained close to perihelion is featureless and red sloped, which is consistent with a dust-dominated coma. Conversely, the spectra acquired on August 2014 and 2016 display neutral slopes and absorption bands at 1.5 and 2.0 μm, consistent with the presence of water-ice grains. These variations in water ice with heliocentric distance are correlated with sublimation rates. Additionally, the measurements obtained at 5.8 AU and 3.9 AU are nearly identical, suggesting that water-ice grains, once in the coma, do not sublime significantly. Therefore, the properties of these long-lived water-ice grains may represent their state in the nucleus or immediately after insertion into the coma. We will present radiative transfer models of the data and interpret the results in the context of spacecraft data of cometary nuclei, and of our on-going compositional survey of water-ice grain halos in cometary comae.This work was funded by NASA SSO, NASA PAST and NASA SOFIA grants.
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Secular orbital evolution of Jupiter family comets
NASA Astrophysics Data System (ADS)
Rickman, H.; Gabryszewski, R.; Wajer, P.; Wiśniowski, T.; Wójcikowski, K.; Szutowicz, S.; Valsecchi, G. B.; Morbidelli, A.
2017-02-01
Context. The issue of the long term dynamics of Jupiter family comets (JFCs) involves uncertain assumptions about the physical evolution and lifetimes of these comets. Contrary to what is often assumed, real effects of secular dynamics cannot be excluded and therefore merit investigation. Aims: We use a random sample of late heavy bombardment cometary projectiles to study the long-term dynamics of JFCs by a Monte Carlo approach. In a steady-state picture of the Jupiter family, we investigate the orbital distribution of JFCs, including rarely visited domains like retrograde orbits or orbits within the outer parts of the asteroid main belt. Methods: We integrate 100 000 objects over a maximum of 100 000 orbital revolutions including the Sun, a comet, and four giant planets. Considering the steady-state number of JFCs to be proportional to the total time spent in the respective orbital domain, we derive the capture rate based on observed JFCs with small perihelia and large nuclei. We consider a purely dynamical model and one where the nuclei are eroded by ice sublimation. Results: The JFC inclination distribution is incompatible with our erosional model. This may imply that a new type of comet evolution model is necessary. Considering that comets may live for a long time, we show that JFCs can evolve into retrograde orbits as well as asteroidal orbits in the outer main belt or Cybele regions. The steady-state capture rate into the Jupiter family is consistent with 1 × 109 scattered disk objects with diameters D > 2 km. Conclusions: Our excited scattered disk makes it difficult to explain the JFC inclination distribution, unless the physical evolution of JFCs is more intricate than assumed in standard, erosional models. Independent of this, the population size of the Jupiter family is consistent with a relatively low-mass scattered disk.
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Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse.
Vincent, Jean-Baptiste; Bodewits, Dennis; Besse, Sébastien; Sierks, Holger; Barbieri, Cesare; Lamy, Philippe; Rodrigo, Rafael; Koschny, Detlef; Rickman, Hans; Keller, Horst Uwe; Agarwal, Jessica; A'Hearn, Michael F; Auger, Anne-Thérèse; Barucci, M Antonella; Bertaux, Jean-Loup; Bertini, Ivano; Capanna, Claire; Cremonese, Gabriele; Da Deppo, Vania; Davidsson, Björn; Debei, Stefano; De Cecco, Mariolino; El-Maarry, Mohamed Ramy; Ferri, Francesca; Fornasier, Sonia; Fulle, Marco; Gaskell, Robert; Giacomini, Lorenza; Groussin, Olivier; Guilbert-Lepoutre, Aurélie; Gutierrez-Marques, P; Gutiérrez, Pedro J; Güttler, Carsten; Hoekzema, Nick; Höfner, Sebastian; Hviid, Stubbe F; Ip, Wing-Huen; Jorda, Laurent; Knollenberg, Jörg; Kovacs, Gabor; Kramm, Rainer; Kührt, Ekkehard; Küppers, Michael; La Forgia, Fiorangela; Lara, Luisa M; Lazzarin, Monica; Lee, Vicky; Leyrat, Cédric; Lin, Zhong-Yi; Lopez Moreno, Josè J; Lowry, Stephen; Magrin, Sara; Maquet, Lucie; Marchi, Simone; Marzari, Francesco; Massironi, Matteo; Michalik, Harald; Moissl, Richard; Mottola, Stefano; Naletto, Giampiero; Oklay, Nilda; Pajola, Maurizio; Preusker, Frank; Scholten, Frank; Thomas, Nicolas; Toth, Imre; Tubiana, Cecilia
2015-07-02
Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments and models cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts. Alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.
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NASA Technical Reports Server (NTRS)
Thomas, Paul J. (Editor)
1992-01-01
Papers are presented on comets and the formation of biochemical compounds on the primitive earth; the cometary origin of carbon, nitrogen, and water on the earth; comets as a possible source of prebiotic molecules; comet impacts and chemical evolution on the bombarded earth; and cometary supply of terrestrial organics (lessons from the K/T and the present epoch). Other papers are on a computational study of radiation chemical processing in comet nuclei, the origin of the polycyclic aromatic hydrocarbons in meteorites, the fate of organic matter during planetary accretion (preliminary studies of the organic chemistry of experimentally shocked Murchison meteorite), recent observations of interstellar molecules (detection of CCO and a limit on H2C3O), terrestrial and extraterrestrial sources of molecular monochirality, and dark matter in the solar system (hydrogen cyanide polymers).
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Cometary science. Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko.
Hässig, M; Altwegg, K; Balsiger, H; Bar-Nun, A; Berthelier, J J; Bieler, A; Bochsler, P; Briois, C; Calmonte, U; Combi, M; De Keyser, J; Eberhardt, P; Fiethe, B; Fuselier, S A; Galand, M; Gasc, S; Gombosi, T I; Hansen, K C; Jäckel, A; Keller, H U; Kopp, E; Korth, A; Kührt, E; Le Roy, L; Mall, U; Marty, B; Mousis, O; Neefs, E; Owen, T; Rème, H; Rubin, M; Sémon, T; Tornow, C; Tzou, C-Y; Waite, J H; Wurz, P
2015-01-23
Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface. Copyright © 2015, American Association for the Advancement of Science.
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NASA Technical Reports Server (NTRS)
Mumma, Michael J.; Charnley, Steven B.
2012-01-01
The question of exogenous delivery of water and organics to Earth and other young planets is of critical importance for understanding the origin of Earth's volatiles, and for assessing the possible existence of exo-planets similar to Earth. Viewed from a cosmic perspective, Earth is a dry planet, yet its oceans are enriched in deuterium by a large factor relative to nebular hydrogen and analogous isotopic enrichments in atmospheric nitrogen and noble gases are also seen. Why is this so? What are the implications for Mars? For icy Worlds in our Planetary System? For the existence of Earth-like exoplanets? An exogenous (vs. outgassed) origin for Earth's atmosphere is implied, and intense debate on the relative contributions of comets and asteroids continues - renewed by fresh models for dynamical transport in the protoplanetary disk, by revelations on the nature and diversity of volatile and rocky material within comets, and by the discovery of ocean-like water in a comet from the Kuiper Belt (cf., Mumma & Charnley 2011). Assessing the creation of conditions favorable to the emergence and sustenance of life depends critically on knowledge of the nature of the impacting bodies. Active comets have long been grouped according to their orbital properties, and this has proven useful for identifying the reservoir from which a given comet emerged (OC, KB) (Levison 1996). However, it is now clear that icy bodies were scattered into each reservoir from a range of nebular distances, and the comet populations in today's reservoirs thus share origins that are (in part) common. Comets from the Oort Cloud and Kuiper Disk reservoirs should have diverse composition, resulting from strong gradients in temperature and chemistry in the proto-planetary disk, coupled with dynamical models of early radial transport and mixing with later dispersion of the final cometary nuclei into the long-term storage reservoirs. The inclusion of material from the natal interstellar cloud is probable, for comets formed in the outer solar system.
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Comets and nongravitational forces. IV.
NASA Technical Reports Server (NTRS)
Marsden, B. G.; Sekanina, Z.
1971-01-01
Orbital elements and nongravitational parameters are derived from observations at every apparition of the periodic comets Honda-Mrkos-Pajdusakova, Faye, Tempel 2, Biela, Brorsen, and Tempel-Swift. For all except the first comet, the observations go back a century and more, although the last three comets have failed to reappear for some considerable time. The circumstances of the splitting of P/Biela are studied, and it is shown that the motion of the primary component was scarcely affected; it is also demonstrated that, if the primary still exists, it may pass only 0.05 AU from the earth in November 1971. An up-to-date list of mass-loss rates from comets is presented. It is found that, while most of the reliable determinations indicate that the cometary nongravitational effects decrease with time, there are a few cases where the effects increase slightly. The former situation is discussed in terms of a nuclear core-mantle model, implying that these comets will eventually evolve into inert, asteroidal objects, while the nuclei of the other comets are interpreted as coreless, eventually to disappear completely (or almost completely).
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Rosetta/VIRTIS-M spectral data: Comet 67P/CG compared to other primitive small bodies.
NASA Astrophysics Data System (ADS)
De Sanctis, M. C.; Capaccioni, F.; Filacchione, G.; Erard, S.; Tosi, F.; Ciarniello, M.; Raponi, A.; Piccioni, G.; Leyrat, C.; Bockelée-Morvan, D.; Drossart, P.; Fornasier, S.
2014-12-01
VIRTIS-M, the Visible InfraRed Thermal Imaging Spectrometer, onboard the Rosetta Mission orbiter (Coradini et al., 2007) acquired data of the comet 67P/Churyumov-Gerasimenko in the 0.25-5.1 µm spectral range. The initial data, obtained during the first mission phases to the comet, allow us to derive albedo and global spectral properties of the comet nucleus as well as spectra of different areas on the nucleus. The characterization of cometary nuclei surfaces and their comparison with those of related populations such as extinct comet candidates, Centaurs, near-Earth asteroids (NEAs), trans-Neptunian objects (TNOs), and primitive asteroids is critical to understanding the origin and evolution of small solar system bodies. The acquired VIRTIS data are used to compare the global spectral properties of comet 67P/CG to published spectra of other cometary nuclei observed from ground or visited by space mission. Moreover, the spectra of 67P/Churyumov-Gerasimenko are also compared to those of primitive asteroids and centaurs. The comparison can give us clues on the possible common formation and evolutionary environment for primitive asteroids, centaurs and Jupiter-family comets. Authors acknowledge the funding from Italian and French Space Agencies. References: Coradini, A., Capaccioni, F., Drossart, P., Arnold, G., Ammannito, E., Angrilli, F., Barucci, A., Bellucci, G., Benkhoff, J., Bianchini, G., Bibring, J. P., Blecka, M., Bockelee-Morvan, D., Capria, M. T., Carlson, R., Carsenty, U., Cerroni, P., Colangeli, L., Combes, M., Combi, M., Crovisier, J., De Sanctis, M. C., Encrenaz, E. T., Erard, S., Federico, C., Filacchione, G., Fink, U., Fonti, S., Formisano, V., Ip, W. H., Jaumann, R., Kuehrt, E., Langevin, Y., Magni, G., McCord, T., Mennella, V., Mottola, S., Neukum, G., Palumbo, P., Piccioni, G., Rauer, H., Saggin, B., Schmitt, B., Tiphene, D., Tozzi, G., Space Science Reviews, Volume 128, Issue 1-4, 529-559, 2007.
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Comet nuclear magnitudes and a new size distribution using archived NEAT data.
NASA Astrophysics Data System (ADS)
Bambery, R. J.; Hicks, M. D.; Pravdo, S. H.; Helin, E. F.; Lawrence, K. J.
2002-09-01
A reliable estimate of the size distribution of cometary nuclei provides important constraints on the formation and dynamical/physical evolution of these bodies as well as their relative proportions in the near-Earth population. The basic data of nuclear sizes has been difficult to obtain, due to the shroud of dust that envelopes the nucleus across a wide range of heliocentric distances. Only two comets, P/Halley and P/Borrelly, have had direct imaging of their nuclei from spacecraft encounters, though high spatial-resolution imaging by the Hubble Space Telescope has also yielded very reliable diameters [1]. Other observers have recently used ground-based photometry to obtain cumulative size-frequency distributions which are not in agreement [2,3]. One possible source of error is the need to include data from a wide range of telescopes and reduction techniques. We shall obtain a new estimate of the size-frequency distribution using a self-consistent data-set. The Near-Earth Asteroid Tracking (NEAT) Program at the Jet Propulsion laboratory remotely operates two 1.2-meter telescopes at widely geographically separated locations on a near-nightly basis. All NEAT data is archived and publically available through the SKYMORPH website (http:/skyview.gsfc.nasa.gov/skymorph/skymorph.html) Though optimized to discover near-Earth asteroids, we have obtained over 300 CCD images of approximately 40 short and long-period comets over the last 15 months. Though we model coma contamination for all images, we shall concentrate on the fraction of comets at heliocentric distances greater than 3 AU. Our data will be used to derive an independent comet size-frequency distribution .
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Physical Processing of Cometary Nuclei
NASA Technical Reports Server (NTRS)
Weissman, Paul R.; Stern, S. Alan
1997-01-01
Cometary nuclei preserve a cosmo-chemical record of conditions and processes in the primordial solar nebula, and possibly even the interstellar medium. However, that record is not perfectly preserved over the age of the solar system due to a variety of physical processes which act to modify cometary surfaces and interiors. Possible structural and/or internal processes include: collisional accretion, disruption, and reassembly during formation; internal heating by long and short-lived radionuclides; amorphous to crystalline phase transitions, and thermal stresses. Identified surface modification processes include: irradiation by galactic cosmic rays, solar protons, UV photons, and the Sun's T Tauri stage mass outflow; heating by passing stars and nearby supernovae; gardening by debris impacts; the accretion of interstellar dust and gas and accompanying erosion by hypervelocity dust impacts and sputtering; and solar heating with accompanying crust formation. These modification processes must be taken into account in both the planning and the interpretation of the results of a Comet Nucleus Sample Return Mission. Sampling of nuclei should be done at as great a depth below the surface crust as technically feasible, and at vents or fissures leading to exposed volatiles at depth. Samples of the expected cometary crust and near-surface layers also need to be returned for analysis to achieve a better understanding of the effects of these physical processes. We stress that comets are still likely less modified dm any other solar system bodies, but the degree of modification can vary greatly from one comet to the next.
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Cometary Jet Collimation Without Physical Confinement
NASA Astrophysics Data System (ADS)
Steckloff, J. K.; Melosh, H. J.
2012-12-01
Recent high-resolution images of comet nuclei reveal that gases and dust expelled by the comet are organized into narrow jets. Contemporary models postulate that these jets collimate when the expanding gases and dust pass through a physical aperture or nozzle. However, recent high-resolution spacecraft observations fail to detect such apertures on cometary surfaces. Furthermore, these models do not explain why cometary jets appear to be directed normal to the local gravitational potential, and/or appear to originate on the faces of scarps. Additionally, observations of comet nuclei by visiting spacecraft have observed that jet activity is tied to the diurnal rotation of the comet. This suggests that jet emissions are powered by the sun, and therefore must emanate from close to the surface of the comet due to a thermal skin depth on the order of ~10 cm. Here we describe a simplified computer model of jets emanating from Comet Tempel 1. Our novel mechanism is based on the occurrence of fluidized flows, which have gained observational support from the Deep Impact and Stardust-NExT flyby missions We approximate the vents of the comet as a region of smooth terrain on the order of ~10 m in width. We assume that each element of the active area is emitting gas molecules with the same spatial distribution function, and integrate over the active area in order to calculate the gas drag force due to the vent. We consider two angular emission profiles (isotropic and lambertian), and assume plane-strain geometry. The vent surfaces were modeled at various angles with respect to the gravitational potential. To approximate scarps, we modeled a non-venting region located above the vent and at the same angle as the vent. The size of this non-venting region was allowed to vary. We assumed that the scarp face, which is composed of the vent and non-venting regions, eroded uniformly. Particles of a constant size are placed randomly on the surface of the vent, and their positions in time are tracked. After a set time interval, the particles are allowed to split in half. The particles are assumed to be ice grains emitting H2O molecules isotropically. The resulting repulsive drag force was modeled as a one-time impulse. For our simulation, spherical particles with radii of 1 μm to 1 cm were considered. We observe that, when the vent is level, the overwhelming majority of the particles remain close to the central axis of the active area, forming a well-collimated jet. When the vent was at an angle, the particles emanating from the vent itself rose normal to the vent, with smaller particles reaching escape velocity in this direction while larger particles fell out of the jet and impacted the surface. Material from the non-venting region slumped down the slope, hit the upslope edge of the vent, which then ejected this material in a well-collimated cone roughly normal to the gravitational potential. The calculated opacity from this material overwhelmed the opacity of the material originating from the vent. The degree and angle of collimation depended on the initial particle size and time between splitting events. This mechanism may explain cometary jets, given the physical and observational constraints.
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Structure and origin of cometary nuclei
NASA Technical Reports Server (NTRS)
Donn, B.; Rahe, J.
1981-01-01
There is strong evidence that a comet nucleus consists of a single object whose basic structure is Whipple's icy conglomerate. A number of cometary phenomena indicate that the nucleus is a low density, fragile object with a large degree of radial uniformity in structure and composition. Details of the ice-dust pattern are more uncertain. A working model is proposed which is based on theories of accumulation of larger objects from grains. This nucleus is a distorted spherical aggregate of a hierarchy of ice-dust cometesimals. These cometesimals retain some separate identity which lead to comet fragmentation when larger components break off. The outer layers of new comets were modified by cosmic ray irradiation in the Oort Cloud. The evidence for meteorite-comet association is steill controversial. Current dynamical studies do not seem to require a cometary source of meteorites.
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Several twilight bolides over Kiev in 2013-2015 - fragments of comets nuclei
NASA Astrophysics Data System (ADS)
Churyumov, K. I.; Steklov, A. F.; Vidmachenko, A. P.; Dashkiev, G. N.
2016-06-01
During the short period of our observations (from March 2013 to 2015), was fixed falling at least a dozen fragments of cometary nuclei, at least five of sufficiently large and dozens of smaller fragments of meteoroids. The results of our observations also showed that during the morning and evening twilight over Kiev clearly visible the plume of aerosols of technical nature from the plants, factories and other production facilities.
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New Application of the Comet Assay
Cortés-Gutiérrez, Elva I.; Dávila-Rodríguez, Martha I.; Fernández, José Luís; López-Fernández, Carmen; Gosálbez, Altea; Gosálvez, Jaime
2011-01-01
The comet assay is a well-established, simple, versatile, visual, rapid, and sensitive tool used extensively to assess DNA damage and DNA repair quantitatively and qualitatively in single cells. The comet assay is most frequently used to analyze white blood cells or lymphocytes in human biomonitoring studies, although other cell types have been examined, including buccal, nasal, epithelial, and placental cells and even spermatozoa. This study was conducted to design a protocol that can be used to generate comets in subnuclear units, such as chromosomes. The new technique is based on the chromosome isolation protocols currently used for whole chromosome mounting in electron microscopy, coupled to the alkaline variant of the comet assay, to detect DNA damage. The results show that migrant DNA fragments can be visualized in whole nuclei and isolated chromosomes and that they exhibit patterns of DNA migration that depend on the level of DNA damage produced. This protocol has great potential for the highly reproducible study of DNA damage and repair in specific chromosomal domains. PMID:21540337
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Secular light curves of comets, II: 133P/Elst Pizarro, an asteroidal belt comet
NASA Astrophysics Data System (ADS)
Ferrín, Ignacio
2006-12-01
We present the secular light curve (SLC) of 133P/Elst-Pizarro, and show ample and sufficient evidence to conclude that it is evolving into a dormant phase. The SLC provides a great deal of information to characterize the object, the most important being that it exhibits outburst-like activity without a corresponding detectable coma. 133P will return to perihelion in July of 2007 when some of our findings may be corroborated. The most significant findings of this investigation are: (1) We have compiled from 127 literature references, extensive databases of visual colors (37 comets), rotational periods and peak-to-valley amplitudes (64 comets). 2-Dimensional plots are created from these databases, which show that comets do not lie on a linear trend but in well defined areas of these phase spaces. When 133P is plotted in the above diagrams, its location is entirely compatible with those of comets. (2) A positive correlation is found between cometary rotational periods and diameters. One possible interpretation suggest the existence of rotational evolution predicted by several theoretical models. (3) A plot of the historical evolution of cometary nuclei density estimates shows no trend with time, suggesting that perhaps a consensus is being reached. We also find a mean bulk density for comets of <ρ>=0.52±0.06 g/cm. This value includes the recently determined spacecraft density of Comet 9P/Tempel 1, derived by the Deep Impact team. (4) We have derived values for over 18 physical parameters, listed in the SLC plots, Figs. 6-9. (5) The secular light curve of 133P/Elst-Pizarro exhibits a single outburst starting at +42±4 d (after perihelion), peaking at LAG=+155±10 d, duration 191±11 d, and amplitude 2.3±0.2 mag. These properties are compatible with those of other low activity comets. (6) To explain the large time delay in maximum brightness, LAG, two hypothesis are advanced: (a) the existence of a deep ice layer that the thermal wave has to reach before sublimation is possible, or (b) the existence of a sharp polar active region pointing to the Sun at time = LAG, that may take the form of a polar ice cap, a polar fissure or even a polar crater. The diameter of this zone is calculated at ˜1.8 km. (7) A new time-age is defined and it its found that T-AGE = 80 cy for 133P, a moderately old comet. (8) We propose that the object has its origin in the main belt of asteroids, thus being an asteroid-comet hybrid transition object, an asteroidal belt comet (ABC), proven by its large density. (9) Concerning the final evolutionary state of this object, to be a truly extinct comet the radius must be less than the thermal wave depth, which at 1 AU is ˜250 m (at the perihelion distance of 133P the thermal wave penetrates only ˜130 m). Comets with radius larger than this value cannot become extinct but dormant. Thus we conclude that 133P cannot evolve into a truly extinct comet because it has too large a diameter. Instead it is shown to be entering a dormant phase. (10) We predict the existence of truly extinct comets in the main belt of asteroids (MBA) beginning at absolute magnitude ˜21.5 (diameter smaller than ˜190 m). (11) The object demonstrates that a comet may have an outburst of ˜2.3 mag, and not show any detectable coma. (12) Departure from a photometric R law is a more sensitive method (by a factor of 10) to detect activity than star profile fitting or spectroscopy. (13) Sufficient evidence is presented to conclude that 133P is the first member of a new class of objects, an old asteroidal belt comet, ABC, entering a dormant phase.
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Osman, Alaa G M; Mekkawy, Imam A; Verreth, Johan; Wuertz, Sven; Kloas, Werner; Kirschbaum, Frank
2008-12-01
Increasing lead contamination in Egyptian ecosystems and high lead concentrations in food items have raised concern for human health and stimulated studies on monitoring ecotoxicological impact of lead-caused genotoxicity. In this work, the alkaline comet assay was modified for monitoring DNA strand breakage in sensitive early life stages of the African catfish Clarias gariepinus. Following exposure to 100, 300, and 500 microg/L lead nitrate, DNA strand breakage was quantified in embryos at 30, 48, 96, 144, and 168 h post-fertilization (PFS). For quantitative analysis, four commonly used parameters (tail % DNA, %TDNA; head % DNA, %HDNA; tail length, TL; tail moment, TM) were analyzed in 96 nuclei (in triplicates) at each sampling point. The parameter %TDNA revealed highest resolution and lowest variation. A strong correlation between lead concentration, time of exposure, and DNA strand breakage was observed. Here, genotoxicity detected by comet assay preceded the manifested malformations assessed with conventional histology. Qualitative evaluation was carried out using five categories are as follows: undamaged (%TDNA < or = 10%), low damaged (10% < %TDNA < or = 25%), median damaged (25 < %TDNA < or = 50%), highly damaged (50 < %TDNA < or = 75%), and extremely damaged (%TDNA > 75%) nuclei confirming a dose and time-dependent shift towards increased frequencies of highly and extremely damaged nuclei. A protective capacity provided by a hardened chorion is a an interesting finding in this study as DNA damage in the prehatching stages 30 h-PFS and 48 h-PFS was low in all treatments (qualitative and quantitative analyses). These results clearly show that the comet assay is a sensitive tool for the detection of genotoxicity in vulnerable early life stages of the African catfish and is a method more sensitive than histological parameters for monitoring genotoxic effects. 2008 Wiley Periodicals, Inc.
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NASA Astrophysics Data System (ADS)
Dykhuis, Melissa J.; Samarasinha, N. H.; Mueller, B. E. A.; Storm, S. P.
2012-10-01
Observations of temporal variations in the dust and gas morphology of comet nuclei can be used to infer the rotation states of the nuclei. The rotation of component C of Comet 73P/Schwassmann-Wachmann 3 is of particular interest, as it could place constraints on the damping timescale for non-principal axis rotation following the comet's breakup event of 1995 (Crovisier et al. 1995, IAU Circ., 6227). We obtained narrowband H-B and broadband R images of component C from May 3-10, 2006 UT, near the comet's perigee passage, using the 4-meter Mayall telescope on Kitt Peak. We identified the morphological features in the images using the enhancement method of division by azimuthal average. In addition, we binned the data to alleviate issues related to poor guiding and to increase the signal-to-noise. A new method for quantifying measurements of the features allowed for the development of a more robust statistic to evaluate the results, which yielded different period constraints than those found previously in Storm et al. (2007). Analysis of the dust morphology suggests a minimum periodicity of repeatability of the features of about 15 hours. This value is consistent with the lower limit of 10 hours determined from radar data (Nolan et al. 2006, BAAS 38, 504); however, it does not agree with the values around 3-4 hours determined using HST lightcurves and HCN morphology (Toth et al. 2006, BAAS 38, 489; Drahus et al. 2010, A&A 510, respectively). MJD's work was supported by a National Science Foundation Graduate Research Fellowship. NHS and BEAM were supported by the NASA Planetary Atmospheres Program.
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Cometary Nuclei and Tidal Disruption: The Geologic Record of Crater Chains on Callisto and Ganymede
NASA Technical Reports Server (NTRS)
Schenk, Paul M.; Asphaug, Erik; McKinnon, William B.; Melosh, H. J.; Weissman, Paul R.
1996-01-01
Prominent crater chains on Ganymede and Callisto are most likely the impact scars of comets tidally disrupted by Jupiter and are not secondary crater chains. We have examined the morphology of these chains in detail in order to place constraints on the properties of the comets that formed them and the disruption process. In these chains, intercrater spacing varies by no more than a factor of 2 and the craters within a given chain show almost no deviation from linearity (although the chains themselves are on gently curved small circles). All of these crater chains occur on or very near the Jupiter-facing hemisphere. For a given chain, the estimated masses of the fragments that formed each crater vary by no more than an order of magnitude. The mean fragment masses for all the chains vary by over four orders of magnitude (W. B. McKinnon and P. M. Schenk 1995, Geophys. Res. Lett. 13, 1829-1832), however. The mass of the parent comet for each crater chain is not correlated with the number of fragments produced during disruption but is correlated with the mean mass of the fragments produced in a given disruption event. Also, the larger fragments are located near the center of each chain. All of these characteristics are consistent with those predicted by disruption simulations based on the rubble pile cometary nucleus model (in which nuclei are composed on numerous small fragments weakly bound by self-gravity), and with those observed in Comet D/Shoemaker-Levy 9. Similar crater chains have not been found on the other icy satellites, but the impact record of disrupted comets on Callisto and Ganymede indicates that disruption events occur within the Jupiter system roughly once every 200 to 400 years.
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Arrhenius reconsidered: astrophysical jets and the spread of spores
NASA Astrophysics Data System (ADS)
Sheldon, Malkah I.; Sheldon, Robert B.
2015-09-01
In 1871, Lord Kelvin suggested that the fossil record could be an account of bacterial arrivals on comets. In 1903, Svante Arrhenius suggested that spores could be transported on stellar winds without comets. In 1984, Sir Fred Hoyle claimed to see the infrared signature of vast clouds of dried bacteria and diatoms. In 2012, the Polonnaruwa carbonaceous chondrite revealed fossilized diatoms apparently living on a comet. However, Arrhenius' spores were thought to perish in the long transit between stars. Those calculations, however, assume that maximum velocities are limited by solar winds to ~5 km/s. Herbig-Haro objects and T-Tauri stars, however, are young stars with jets of several 100 km/s that might provide the necessary propulsion. The central engine of bipolar astrophysical jets is not presently understood, but we argue it is a kinetic plasma instability of a charged central magnetic body. We show how to make a bipolar jet in a belljar. The instability is non-linear, and thus very robust to scaling laws that map from microquasars to active galactic nuclei. We scale up to stellar sizes and recalculate the viability/transit-time for spores carried by supersonic jets, to show the viability of the Arrhenius mechanism.
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Application of DNA comet assay for detection of radiation treatment of grams and pulses.
Khan, Hasan M; Khan, Ashfaq A; Khan, Sanaullah
2011-12-01
Several types of whole pulses (green lentils, red lentils, yellow lentils, chickpeas, green peas, cowpeas and yellow peas) and grams (black grams, red grams and white grams) have been investigated for the identification of radiation treatment using microgel electrophoresis of single cells (DNA comet assay). Pulses and grams were exposed to the radiation doses of 0.5, 1.0 and 5 kGy covering the legalized commercial dose range for protection from insect/pest infestations. All irradiated samples showed comet like stretching of fragmented DNA toward anode, which is expected for irradiated samples. Unirradiated samples showed many intact cells/nuclei in form of round stains or with short faint tails, which is typical for unirradiated food samples. The study shows that DNA comet assay can be used as a rapid, inexpensive and highly effective screening test for the detection of radiation treatment of foods, like pulses and grams.
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Ways of Changing the Number and Size Distribution of Ecliptic Comets
NASA Astrophysics Data System (ADS)
Dones, Henry C. Luke; Womack, Maria; Alvarellos, Jose; Bierhaus, Edward B.; Bottke, William; Hamill, Patrick; Nesvorny, David; Robbins, Stuart J.; Zahnle, Kevin
2017-06-01
The existence of the Kuiper Belt was proposed because of the need for a low-inclination source for the Jupiter-family comets (JFCs). Indeed, the Kuiper Belt is thought to be the main reservoir of ecliptic comets (ECs), which include the JFCs and Centaurs. Ironically, we still do not know whether the belt, specifically its Scattered Disk, provides an adequate source for the ECs (Volk and Malhotra 2008). ECs are also thought to be the main source of Sun-orbiting impactors on the regular moons of the giant planets (Zahnle et al. 2003 [Z03]). Some models of the cometary orbital distribution used by Z03 and others to estimate impact rates assume comets are indestructible; in fact, many cometssplit, sometimes far from the Sun (Fernández 2009). Assuming shatterproof comets may lead to incorrect results for cometary orbital distributions. Other models impose a physical lifetime for bodies that approach within ~3 AU of the Sun, where sublimation of water ice begins, after which a comet is assumed to be dormant or disrupted (Nesvorný et al. 2017). In reality, some comets (e.g., 29P, Hale-Bopp) are active due to volatiles such as CO and CO2 beyond the orbit of Jupiter (Womack et al. 2017). 174P/Echeclus underwent a 7-magnitude outburst 13 AU from the Sun (Rousselot et al. 2016), and CO emission was recently detected from Echeclus at 6 AU (Wierzchos et al. 2017). We will estimate the effects of several mechanisms on the number and size distribution of comet nuclei as a function of distance from the Sun, including cometary activity and spontaneous disruption; tidal disruption by a giant planet, as happened for Shoemaker-Levy 9; and tidal disruption of binaries, which are numerous among "cold classical" Kuiper Belt Objects (Fraser et al. 2017). We thank the Cassini Data Analysis Program for support.Fernández Y (2009). Planet. Space. Sci. 57, 1218.Fraser WC, et al. (2017). Nat. Astron. 1, 0088.Nesvorný D, et al. (2017). In preparation.Rousselot P, et al. (2016). MNRAS 462, S432.Volk K, Malhotra R (2008). Astrophys. J. 687, 714.Wierzchos K, Womack M, Sarid G. (2017). Astron. J., in press.Womack M, Sarid G, Wierzchos, K (2017). Publ. Astron. Soc. Pac. 129, 031001.Zahnle K, et al. (2003). Icarus 163, 263.
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The colors of cometary nuclei and other primitive bodies
NASA Astrophysics Data System (ADS)
Toth, I.; Lamy, P. L.
2005-12-01
Primitive minor objects like Kuiper-belt objects (KBOs), Centaurs, cometary nuclei and low-albedo asteroids contain a considerable amount of information regarding the formation of early solar system planetesimals and some of the primordial processes. Broadband colors by themselves offer limited insight into surface composition but correlations either between different color indices or with other (e.g., orbital) parameters can shed some light on the questions of the composition and the evolution of the minor objects. Furthermore, a systematic comparison of the color indices of various populations may provide clues on their relationships, and concur along with dynamical studies, to establish a scenario of their formation and evolution in the solar system. We present new color results on cometary nuclei obtained with the Hubble Space Telescope (HST) whose superior resolution enables us to accurately isolate the nucleus signals from the surrounding comae. By combining with scrutinized available data obtained with ground-based telescopes, we accumulated a sample of 39 cometary nuclei, 34 ecliptic comets (ECs) and 5 nearly-isotropic comets (NICs) using the nomenclature of Levison (1996). We analyze color distributions and color-color correlations as well as correlations with other physical parameters. We present our own compilation of colors of 282 objects in the outer solar system, separately considering the different dynamical populations, classical KBOs in low and high-inclination orbits, resonant KBOs (practically Plutinos), scattered-disk objects (SDOs) and Centaurs. We perform a systematic analysis of color distributions of all plausible parent-child combinations and conclude by synthesizing the implications of the colors for the origin of ecliptic comets. We acknowledge the support of the French "Programme National de Planétologie", jointly funded by CNRS and CNES, and of the bilateral French--Hungarian cooperation program. I. Toth further acknowledges the support of the Université de Provence, of the Hungarian Academy of Sciences through grant No. 9871.
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NASA Technical Reports Server (NTRS)
Hoover, R.; Hoyle, F.; Wallis, M. K.; Wickramasinghe, N. C.
1986-01-01
The fossil record of the microscopic algae classified as diatoms suggests they were injected to earth at the Cretaceous boundary. Not only could diatoms remain viable in the cometary environment, but also many species might replicate in illuminated surface layers or early interior layers of cometary ice. Presumably they reached the solar system on an interstellar comet as an already-evolved assemblage of organisms. Diatoms might cause color changes to comet nuclei while their outgassing decays and revives around highly elliptical orbits. Just as for interstellar absorption, high-resolution IR observations are capable of distinguishing whether the 10-micron feature arises from siliceous diatom material or mineral silicates. The 10-30-micron band and the UV 220-nm region can also provide evidence of biological material.
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Manufactured Porous Ambient Surface Simulants
NASA Technical Reports Server (NTRS)
Carey, Elizabeth M.; Peters, Gregory H.; Chu, Lauren; Zhou, Yu Meng; Cohen, Brooklin; Panossian, Lara; Green, Jacklyn R.; Moreland, Scott; Backes, Paul
2016-01-01
The planetary science decadal survey for 2013-2022 (Vision and Voyages, NRC 2011) has promoted mission concepts for sample acquisition from small solar system bodies. Numerous comet-sampling tools are in development to meet this standard. Manufactured Porous Ambient Surface Simulants (MPASS) materials provide an opportunity to simulate variable features at ambient temperatures and pressures to appropriately test potential sample acquisition systems for comets, asteroids, and planetary surfaces. The original "flavor" of MPASS materials is known as Manufactured Porous Ambient Comet Simulants (MPACS), which was developed in parallel with the development of the Biblade Comet Sampling System (Backes et al., in review). The current suite of MPACS materials was developed through research of the physical and mechanical properties of comets from past comet missions results and modeling efforts, coordination with the science community at the Jet Propulsion Laboratory and testing of a wide range of materials and formulations. These simulants were required to represent the physical and mechanical properties of cometary nuclei, based on the current understanding of the science community. Working with cryogenic simulants can be tedious and costly; thus MPACS is a suite of ambient simulants that yields a brittle failure mode similar to that of cryogenic icy materials. Here we describe our suite of comet simulants known as MPACS that will be used to test and validate the Biblade Comet Sampling System (Backes et al., in review).
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Searches for comet-induced solar flares
NASA Astrophysics Data System (ADS)
Ibadov, Subhon; Ibodov, Firuz
During the last decade we have carried out analytical consideration of the impacts of comets with the Sun: the study of passage of cometary nuclei through the solar chromosphere and photosphere was carried out taking into account aerodynamic crushing of the nucleus, transversal expansion of the crushed mass and aerodynamic deceleration of the flattening structure. The results indicate that the stopping of the hypervelocity, more than 600 km/s, comet matter near the photosphere has essentially "explosive" character and will be accompanied by generation of a strong "blast" shock wave as well as ejection of a hot plasma from a relatively very thin,"exploding", near-photosphere layer. Observational manifestations of these processes, comet-induced solar flares, CISF, will be anomalous line emission of metal atoms/ions like Fe, Si, etc. from chromosphere/corona regions and continuum emission of a high-temperature, around 10^6-10^7 K, plasma cloud near the solar surface. Space observations of the phenomena by solar telescopes, including future out-of-ecliptic ones, are of interest for the physics/prognosis of solar flares as well as physics of comets.
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NASA Astrophysics Data System (ADS)
Guliyev, Ayyub; Nabiyev, Shaig
2017-07-01
This paper presents the results of a statistical analysis of the dynamic parameters of 300 comets that have osculating hyperbolic orbits. It is shown that such comets differ from other comets by their large perihelion distances and by a predominance of retrograde motion. It is shown that the values of i, the inclination of the hyperbolic comets, are in comparative excess over the interval 90-120°. The dominance by q, the perihelion distance, renders it difficult to suggest that the excess hyperbolic velocity of these comets can be the result of physical processes that take place in their nuclei. Aspects of the following working hypothesis, that the hyperbolic excess of parameter e might be formed after comets pass through meteoroid streams, are also studied. To evaluate this hypothesis, the distribution of the orbits of hyperbolic comets relative to the plane of motion of 112 established meteoroid streams are analyzed. The number (N) of orbit nodes for hyperbolic comets with respect to the plane of each stream at various distances is calculated. To determine the degree of redundancy of N, a special computing algorithm was applied that provided the expected value nav as well as the standard deviation σ for the number of cometary nodes at the plane of each stream. A comparative analysis of the N and nav values that take σ into account suggests an excess in 40 stream cases. This implies that the passage of comets through meteoroid streams can lead to an acceleration of the comets' heliocentric velocity.
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Accretion of Cometary Nuclei in the Solar Nebula: Boulders, Not Pebbles
NASA Astrophysics Data System (ADS)
Weissman, Paul R.; A'Hearn, Michael
2015-11-01
Comets are the most primitive bodies in the solar system. They retain a largely unprocessed record of conditions in the primordial solar nebula 4.56 Gyr ago, including the initial accretion of dust and ice particles into macroscopic bodies. Current accretion theory suggests that ice and dust aggregates grew to pebble (cm) sizes before streaming instabilities and gravitational collapse brought these pebble swarms together as km-sized (or larger) bodies. Recent imaging of the nucleus of comet 67P/Churyumov-Gerasimenko by the Rosetta OSIRIS camera team has revealed the existence of “goose bump” terrain on the nucleus surface and lining the interior walls of large, ~200 m diameter and 180 m deep cylindrical pits. These pits are believed to be sinkholes, formed when near-surface materials collapse into voids within the nucleus, revealing the fresh comet interior on the walls of the pits. The goose bump terrain consists of 3-4 m diameter “boulders” randomly stacked one on top of another. We propose that these boulders, likely with an icy-conglomerate composition, are the basic building blocks of cometary nuclei. This is the first observational confirmation of current accretion theories, with the caveat that rather than pebbles, the preferred size range is 3-4 m boulders for objects formed in the giant planets region of the solar system. The presence of icy grains beyond the solar nebula snow-line and the large heliocentric range of the giant planets region likely contribute to the formation of these larger boulders, before they are incorporated into cometary nuclei. This work was supported by NASA through the U.S. Rosetta Project.
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Can Ecliptic Comets Be Created En Route from the Kuiper Belt?
NASA Astrophysics Data System (ADS)
Dones, Henry C. Luke; Womack, Maria; Nesvorny, David; Bierhaus, Edward B.; Zahnle, Kevin; Robbins, Stuart J.; Bottke, William; Alvarellos, Jose; Hamill, Patrick
2017-10-01
The Kuiper Belt is thought to be the reservoir of ecliptic comets (ECs), which include the Jupiter-family comets (JFCs) and Centaurs. ECs are also the main source of Sun-orbiting impactors on the regular moons of the giant planets (Zahnle et al. 2003). Ironically, we still do not know whether the belt, specifically its Scattered Disk, provides enough ECs (Volk and Malhotra 2008). We are investigating whether cometary breakup in the planetary region (Fernández 2009) can substantially increase the number of ECs. In support of this idea, the Kreutz sungrazers may derive from a hierarchical series of fragmentation events of a progenitor long-period comet (e.g., Sekanina and Chodas 2007), and the JFCs 42P and 53P appear to be fragments of a comet that split in 1845 (Kresák et al. 1984). On the other hand, although 16P was tidally disrupted by Jupiter in 1886, only one fragment survives.Models of the cometary orbital distribution ignore activity or apply a physical lifetime based on the number of passages within 2 or 3 AU of the Sun, where sublimation of water ice occurs (Nesvorný et al. 2017). In reality, some comets (e.g., 29P, Hale-Bopp) are active beyond Jupiter due to volatiles such as CO and CO2 (Womack et al. 2017). 174P/Echeclus underwent a 7-magnitude outburst at 13 AU (Rousselot et al. 2016), and CO emission was detected from Echeclus at 6 AU (Wierzchos et al. 2017). We will estimate how the number and size distribution of comet nuclei change with distance from the Sun due to cometary activity and spontaneous disruption, tidal disruption by a giant planet, and tidal disruption of binaries (Fraser et al. 2017).We thank the Cassini Data Analysis Program for support.Fernández Y (2009). Planet. Space. Sci. 57, 1218.Fraser WC, et al. (2017). Nat. Astron. 1, 0088.Kresák L, et al. (1984). IAU Circular 3940.Nesvorný D, et al. (2017). arXiv:1706.07447.Rousselot P, et al. (2016). MNRAS 462, S432.Sekanina, Z, Chodas, PW (2007). Astrophys. J. 663, 657.Volk K, Malhotra R (2008). Astrophys. J. 687, 714.Wierzchos K, Womack M, Sarid G. (2017). Astron. J. 153, id 230.Womack M, Sarid G, Wierzchos, K (2017). Publ. Astron. Soc. Pac. 129,031001.Zahnle K, et al. (2003). Icarus 163, 263.
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The Comet Radar Explorer Mission
NASA Astrophysics Data System (ADS)
Asphaug, Erik; Belton, Mike; Bockelee-Morvan, Dominique; Chesley, Steve; Delbo, Marco; Farnham, Tony; Gim, Yonggyu; Grimm, Robert; Herique, Alain; Kofman, Wlodek; Oberst, Juergen; Orosei, Roberto; Piqueux, Sylvain; Plaut, Jeff; Robinson, Mark; Sava, Paul; Heggy, Essam; Kurth, William; Scheeres, Dan; Denevi, Brett; Turtle, Elizabeth; Weissman, Paul
2014-11-01
Missions to cometary nuclei have revealed major geological surprises: (1) Global scale layers - do these persist through to the interior? Are they a record of primary accretion? (2) Smooth regions - are they landslides originating on the surface? Are they cryovolcanic? (3) Pits - are they impact craters or sublimation pits, or rooted in the interior? Unambiguous answers to these and other questions can be obtained by high definition 3D radar reflection imaging (RRI) of internal structure. RRI can answer many of the great unknowns in planetary science: How do primitive bodies accrete? Are cometary nuclei mostly ice? What drives their spectacular activity and evolution? The Comet Radar Explorer (CORE) mission will image the detailed internal structure of the nucleus of 10P/Tempel 2. This ~16 x 8 x 7 km Jupiter Family Comet (JFC), or its parent body, originated in the outer planets region possibly millions of years before planet formation. CORE arrives post-perihelion and observes the comet’s waning activity from safe distance. Once the nucleus is largely dormant, the spacecraft enters a ~20-km dedicated Radar Mapping Orbit (RMO). The exacting design of the RRI experiment and the precise navigation of RMO will achieve a highly focused 3D radar reflection image of internal structure, to tens of meters resolution, and tomographic images of velocity and attenuation to hundreds of meters resolution, tied to the gravity model and shape. Visible imagers will produce maps of the surface morphology, albedo, color, texture, and photometric response, and images for navigation and shape determination. The cameras will also monitor the structure and dynamics of the coma, and its dusty jets, allowing their correlation in 3D with deep interior structures and surface features. Repeated global high-resolution thermal images will probe the near-surface layers heated by the Sun. Derived maps of thermal inertia will be correlated with the radar boundary response, and photometry and texture, probing surface materials attainable by future robotic excavation missions. Thermal images will reveal areas of sublimation cooling around vents and pits, and the secular response of the outer meters as the nucleus moves farther from the Sun.
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NASA Astrophysics Data System (ADS)
Miles, Richard
2016-07-01
This paper is a continuation of Miles et al. (2015) [Icarus] and Miles (2015b) [Icarus], which detail new observations of Comet 29P/Schwassmann‒Wachmann, characterise its rotational period (∼57 d), and identify the presence of discrete sources of outburst on its nucleus: the latter ruling out amorphous-to-crystalline H2O ice transitions as the cause of its outbursts. Summary data are presented for 29P and a further 16 non-fragmenting comets which exhibit outbursts of >2 magnitudes. A comprehensive physicochemical mechanism is postulated to account for major outbursts based on melting of cometary ices and the exothermic dissolution of gases, especially CO and CO2 at pressures of 10‒200 kPa. The thermodynamics of enthalpy heating are described and heats of solution are calculated from gas-liquid solubility data yielding -6 kJ mol-1 for CO in CH4, and -15 kJ mol-1 for CO2 in CH3OH close to their freezing point. Heats of solution are ∼6 times greater (per mole) than the enthalpy of fusion of the pure CH4 and CH3OH ices, enabling gas pressures of >∼80 kPa to continually melt these ices. Supervolatile O2 and N2 gases may also participate by dissolving exothermically in liquid CH4 and other hydrocarbons potentially reaching high mixing ratios. H2S and NH3 gases dissolve exothermically in CH3OH liberating up to 20 kJ mol-1 and 13 kJ mol-1, respectively, and all three hydrophilic species facilitate sintering of H2O ice in the near-surface of comets. Localised melting and consolidation is favoured in slowly-rotating cometary nuclei of intermediate dust/gas ratios, at pressures of ∼1 kPa, and temperatures as low as 50‒65 K where O2 and N2 are abundant. Nyctogenic processes on the night-time side of the nucleus restock desiccated surface layers, reseal the crust, enabling fractionation of solutes in sub-crustal liquid phases via fractional sublimation/distillation of non-polar, hydrophobic CH4 and other hydrocarbons; and by fractional crystallisation of polar, hydrophilic phases rich in aqueous CH3OH and other organic oxygenates, e.g. CH2O, able to form low melting point eutectic mixtures. A generalised outburst mechanism is described involving the containment of gases as solutes in cryomagma beneath consolidated surface crustal regions. Disruption of the crust and associated pressure loss render the cryomagma supersaturated, and the concomitant explosive exsolution of gases provokes a cometary outburst. The CO gas-exsolution mechanism operates at ∼65 to 95 K and accounts for activity of 29P and other distant comets up to rh = ∼15 AU. A similar mechanism can operate at ∼150 to 200 K driven by CO2 in aqueous CH3OH and may account for rare outbursts of Jupiter-family comets such as 17P/Holmes. At least 10-15% of all periodic comets may be subject to gas-exsolution outbursts, the majority of which are weak and go undetected. Possible surface morphologies of the nucleus of Comet 29P are discussed. The mechanism may also explain the phenomenon of strong cometary outbursts triggering secondary events, as observed for 17P, 29P and 41P.
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Landslide on comets as a result of impacts
NASA Astrophysics Data System (ADS)
Czechowski, Leszek
2016-04-01
Introduction: Landslides were observed on a few comet's nuclei, e.g. [1], [2]. The mechanism of their origin is not obvious because of very low gravity. According to [2] fluidization and multiphase transport of cometary material could be an explanation. We consider another option, namely, earthquakes resulted from meteoroids impacts as a trigging mechanism. Material of comets: Comets nuclei are believed to built of soft materials like snow and dust. The recent landing of Philae on the comet 67P/Czuriumow-Gierasimienko indicates a different situation. According to [1]: "thermal probe did not fully penetrate the near-surface layers, suggesting a local resistance of the ground to penetration of >4 megapascals, equivalent to >2 megapascal uniaxial compressive strength". Here we assume that elastic properties of comet's nuclei could be similar to elastic properties of dry snow, namely Young modulus is assumed to be 106 - 108Pa, see [3] and [4]. The model and results: We consider cometary nucleus in the shape of two spheres (with radius 1400 m each) connected by a cylinder (with radius of 200 m and length of 200 m). Density is 470 kg m-3. This shape corresponds approximately to shapes of some comets (e.g. 67P/Churyumov- Gerasimenko [1], 103P/Hartley 2 [5]) A few vibration modes of such body are possible. In present research we consider 3 modes: bending, lengthening-shortening along axis of symmetry, and torsion. We calculated periods of basic oscillation in each of these modes for different values of Young modulus - Table 1. Table 1 Basic results of calculations Young modulus [MPa]Periods [s] of vibrationMaximum acceleration [m s-2] 4 110 - 950 0.0001- 0.0004 40 38 - 290 0.0004- 0.0014 400 12 - 92 0.0012- 0.0045 Rotation and nutation: the impact results in changing of rotation of the comet. In general, the vector of angular velocity will be a subject to nutation that results in changing of centrifugal force, and consequently could be an additional factor triggering landslides. Discussion: Let assume that the comet are hit by small meteoroid of the mass of 1 kg and velocity 20 km s-1. The mode of excited vibrations and their amplitudes depends on many factors. Of course, the energy of vibration cannot exceed energy released during impact. Generally a few modes of vibration are excited but for some special place of impact and the special velocity vector of the impactor one mode could take most of the energy and this mode will prevail. In calculations for Table 1 we assume that only one mode is generated. The maximum values of acceleration of the surface resulting from the impact are given in Table 1. The acceleration of the cometary surface could be vertical, horizontal or inclined with respect to local gravity or local normal to the surface. Note that acceleration is often higher than acceleration of the gravity of the comet. Consequently, the vibrations could throw loose material into space that could lead to massive instability of loose material, i.e. to landslides. It could be alternative mechanism to that presented in [2] (i.e. fluidization). Acknowledgement: The research is partly supported by Polish National Science Centre NCN) (decision 2014/15/B/ST 10/02117) References [1] T. Spohn, et al. (2015) Thermal and mechanical properties of the near-surface layers of comet 67P/Churyumov- Gerasimenko. Science 31 July 2015: Vol. 349 no. 6247 DOI: 10.1126/science.aab0464 [2] Belton M. J.S., Melosh J. (2009). Fluidization and multiphase transport of particulate cometary material as an explanation of the smooth terrains and repetitive outbursts on 9P/Tempel 1. Icarus 200 (2009) 280-291 [3] Reuter B. (2013) On how to measure snow mechanical properties relevant to slab avalanche release. International Snow Science Workshop Grenoble - Chamonix Mont-Blanc - 2013 007 [4] Ball A.J. (1997) Ph. D. Thesis: Measuring Physical Properties at the Surface of a Comet Nucleus, Univ.of Kent U.K. [5] Thomas P.C. et al.(2013) Shape, density, and geology of the nucleus of Comet 103P/Hartley 2. Icarus 222 (2013) 550-558
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3D radar wavefield tomography of comet interiors
NASA Astrophysics Data System (ADS)
Sava, Paul; Asphaug, Erik
2018-04-01
Answering fundamental questions about the origin and evolution of small planetary bodies hinges on our ability to image their surface and interior structure in detail and at high resolution. The interior structure is not easily accessible without systematic imaging using, e.g., radar transmission and reflection data from multiple viewpoints, as in medical tomography. Radar tomography can be performed using methodology adapted from terrestrial exploration seismology. Our feasibility study primarily focuses on full wavefield methods that facilitate high quality imaging of small body interiors. We consider the case of a monostatic system (co-located transmitters and receivers) operated in various frequency bands between 5 and 15 MHz, from a spacecraft in slow polar orbit around a spinning comet nucleus. Using realistic numerical experiments, we demonstrate that wavefield techniques can generate high resolution tomograms of comets nuclei with arbitrary shape and complex interior properties.
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3200 Phaethon, Asteroid or Comet Nucleus?
NASA Astrophysics Data System (ADS)
Boice, Daniel C.; Benkhoff, Johannes
2015-08-01
Physico-chemical modeling is central to understand the important physical processes in small solar system bodies. We have developed a computer simulation, SUISEI, that includes the physico-chemical processes relevant to comets within a global modeling framework. Our goals are to gain valuable insights into the intrinsic properties of cometary nuclei so we can better understand observations and in situ measurements. SUISEI includes a 3-D model of gas and heat transport in porous sub-surface layers in the interior of the nucleus.We present results on the application of SUISEI to the near-Sun object, Phaethon. Discovered in 1983 and classified as an asteroid, it has recently exhibited an active dust coma. Phaethon has long been associated as the source of the Geminids meteor shower so the dust activity provides a clear link to the meteor shower. The observed dust activity would traditionally lead to Phaethon being also classified as a comet (e.g., 2060-95P/Chiron, 133P/Elst-Pizarro). This is unusual since the orbit of Phaethon has a perihelion of 0.14 AU, resulting in surface temperatures of more than 1025K, much too hot for water ice or other volatiles to exist near the surface and drive the activity. This situation and others such as the “Active Asteroids” necessitates a revision of how we understand and classify these small asteroid-comet transition objects.We conclude the following for Phaethon:1. It is likely to contain relatively pristine volatiles in its interior despite repeated near perihelion passages of 0.14 AU during its history in its present orbit,2. Steady water gas fluxes at perihelion and throughout its orbit are insufficient to entrain the currently observed dust production,3. Thermal gradients into the surface as well as those caused by diurnal rotation are consistent with the mechanism of dust release due to thermal fracture,4. The initial large gas release during the first perihelion passage may be sufficient to produce enough dust to explain the entire meteor stream.Acknowledgements: We greatly appreciate support from the NSF Planetary Astronomy Program under Grant No. 0908529 and the ESA/ESTEC Visiting Scientist Program.
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Spectral properties of the nucleus of short-period comets
NASA Astrophysics Data System (ADS)
Toth, I.; Lamy, P. L.
2000-10-01
Comets, Edgeworth-Kuiper-Belt Objects (EKBOs), Centaurs and low albedo asteroids contain a considerable amount of information regarding some of the primordial processes that governed the formation of the early Solar System planetesimals. Opportunities to determine the colors of cometary nuclei are rare and relevant ground-based observations are difficult to perform. Color diversities and similarities between different types of small bodies have already been considered ([1] and references therein). We pursue this analysis further by introducing new BVRI colors obtained from our survey of cometary nuclei with the Hubble Space Telescope [2] as well as recent data obtained on EKBOs. We present preliminary results on the distribution of the BVRI colors (histograms, two-color diagrams) and possible relationships between the colors and orbital elements as well as the determined body sizes. The mean colors of the selected sample of the short-period (s-p) comets are: < (B-V) > = 0.91, < (V-R) > = 0.52, and < (V-I) > = 0.84. Pearson's linear correlation analysis of the (B-V) versus (V-R) and (V-R) versus (V-I) colors show significant correlations for the EKBOs+Centaurs sample while the s-p sample seems to be uncorrelated, with a few outliers. The linear regression lines of the EKBOs+Centaurs sample crosses through the sample of the s-p comets. There are no correlations of the colors versus perihelion distances, effective radii and perihelion distances as well as the (a,sin(i)) diagrams. This work was supported by grants from CNRS and CNES, France and partially by the the Hungarian Research Foundation OTKA T025049. [1] Luu, J., 1993. Icarus 104, 138. [2] Lamy, P.L. et al., this conference
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NASA Astrophysics Data System (ADS)
Ksanfomality, L. V.
2017-05-01
On March 6 and 9, 1986, for the first time in the history of science, the Russian spacecraft Vega-1 and -2 approached the nucleus of comet 1P/Halley and flew by at a small distance. A while later, on March 14, 1986, the Giotto spacecraft (European Space Agency (ESA)) followed them. Together with the Japanese spacecraft Suisei (Japan Aerospace Exploration Agency (JAXA)), they obtained spaceborne investigations of cometary nuclei. Direct studies of cometary bodies that bear traces of the Solar System formation were continued in the next missions to comets. Starting from 2014 and up to 2016 September, the Rosetta spacecraft (ESA), being in a low orbit around the nucleus of comet 67P/Churyumov-Gerasimenko, has performed extremely sophisticated investigations of this comet. Here, we compare some results of these missions. The paper is based on the reports presented at the memorial conference dedicated to the 30th anniversary of the Vega mission, which took place at the Space Research Institute of the Russian Academy of Sciences in March, 2016, and does not pretend to comprehensively cover the problems of cometary physics.
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NASA Astrophysics Data System (ADS)
Ksanfomality, L. V.
2017-06-01
On March 6 and 9, 1986, for the first time in the history of science, the Russian spacecraft Vega-1 and Vega-2 approached and closely passed by the nucleus of Halley’s comet (1P/Halley). A few days later, on March 14, 1986, the same was done by the European Space Agency’s (ESA) Giotto spacecraft. These missions, together with the Japanese Suisei (JAXA), marked a successful start to spacecraft exploration of cometary nuclei. Subsequent missions to other comets have been aimed at directly studying cometary bodies carrying signs of the formation of the Solar System. The Rosetta spacecraft, inserted into a low orbit around the nucleus of the 67P/Churyumov-Gerasimenko comet, performed its complex measurements from 2014 to September 2016. In this review, some of the data from these missions are compared. The review draws on the proceedings of the Vega 30th anniversary conference held at the Space Research Institute (IKI) of the Russian Academy of Sciences in March 2016 and is not meant to be exhaustive in describing mission results and problems in the physics of comets.
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The 3.4 micron emission in comets
NASA Technical Reports Server (NTRS)
Brooke, Tim Y.; Knacke, Roger F.; Owen, T. C.; Tokunaga, Alan T.
1989-01-01
Emission features near 3.4 microns were detected in comet Bradfield (1987s) on 17 Nov. 1987 UT, and, marginally, on two earlier dates, with the Cooled Grating Array Spectrometer at the NASA Infrared Radio Telescope Facility (IRTF) (Brooke et al., 1988b). The central wavelength (3.36 microns) and width (approx. 0.15 microns) of the strongest feature coincide with those observed in comet Halley. A weaker emission feature at 3.52 microns and a strong feature extending shortward of 2.9 microns were also detected. This brings the number of comets in which these three features have been seen to three, two new (Bradfield, Wilson) and one old (Halley). It seems almost certain that the 3.4 micron features are emissions by C-H groups in complex molecules. Based on the similarity of the 3.4 micron features in comets Halley and Wilson, the authors suggest that a particular set of organic compounds may be common to all comets (Brooke et al. 1988a). The absence of the feature in some comets could then be due to photodestruction or evaporation of the organics when the comet approaches the sun, in combination with a predominance of thermal emission from non C-H emitting grains. Detection of the 3.4 micron emission feature in comet Bradfield at 4 = 0.9 AU provides support for this argument. Complex organics in comets could have been formed by particle irradiation of parent ices in the nucleus or been incorporated as grains at the time the comets formed. Since the most heavily irradiated layers of Halley would have been lost in its hundreds of perihelion passages, the authors believe the more likely explanation is that the 3.4 micron emitting material was incorporated in comet nuclei at the time of formation. The 3.4 micron comet feature resembles, but is not identical to, the interstellar 3.29 micron (and longer wavelength) emission features and the broad 3.4 micron feature seen in absorption toward the Galactic center. Detailed comparisons of cometary and interstellar organics will require comet spectra with signal-to-noise and spectral resolution comparable to that available in spectra of the interstellar medium. Such observations are currently being planned.
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NASA Technical Reports Server (NTRS)
Mcfadden, Lucy-Ann
1988-01-01
Photometric and spectrophotometric studies of asteroids and comets are in progress to address questions about the mineralogical relationship between asteroids near the 3:1 Kirkwood gap and ordinary chondrite meteorites and between cometary nuclei and the surface of asteroids. Progress was made on a method to convert the measured excess UV flux in the spectrum of 2201 Oljato to column abundance of OH and CN. Spectral reflectance measurements of large asteroids near the 3:1 Kirkwood gap, which is expected to be the source of ordinary chondrite meteorites, were briefly examined and show no spectral signatures that are characteristic of ordinary chondrite meteorite powders measured in the lab.
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Asteroid and comet flux in the neighborhood of the earth
NASA Technical Reports Server (NTRS)
Shoemaker, Eugene M.; Shoemaker, Carolyn S.; Wolfe, Ruth F.
1988-01-01
Significant advances in the knowledge and understanding of the flux of large solid objects in the neighborhood of Earth have occurred. The best estimates of the collision rates with Earth of asteroids and comets and the corresponding production of impact craters are presented. Approximately 80 Earth-crossing asteroids were discovered through May 1988. Among 42 new Earth-crossing asteroids found in the last decade, two-thirds were discovered from observations at Palomar Observatory and 15 were discovered or independently detected in dedicated surveys with the Palomar Observatory and 15 were discovered or independently detected in dedicated surveys with the Palomar 46 cm Schmidt. Probabilities of collision with Earth have been calculated for about two-thirds of the known Earth-crossing asteroids. When multiplied by the estimated population of Earth-crossers, this yields an estimated present rate of collision about 65 pct higher than that previously reported. Spectrophotometric data obtained chiefly in the last decade show that the large majority of obvserved Earth-crossers are similar to asteroids found in the inner part of the main belt. The number of discovered Earth-crossing comets is more than 4 times greater than the number of known Earth-crossing asteroids, but reliable data on the sizes of comet nuclei are sparse. The flux of comets almost certainly was highly variable over late geologic time, owing to the random perturbation of the Oort comet cloud by stars in the solar neighborhood.
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NASA Technical Reports Server (NTRS)
Luu, Jane X.
1992-01-01
Activity in distant comets remains a mystery in the sense that we still have no complete theory to explain the various types of activity exhibited by different comets at large distances. This paper explores the factors that should play a role in determining activity in a distant comet, especially in the cases of comet P/Tempel 2, comet Schwassmann-Wachmann 1, and 2060 Chiron.
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A continuing controversy: Has the cometary nucleus been resolved?
NASA Technical Reports Server (NTRS)
Sekanina, Z.
1976-01-01
Evidence is presented for classifying cometary nuclei into two basic types, described by core mantle and coreless models. Mass loss related nongravitational effects in a comet's motion as a function of time are included in considering gradual evaporation of an icy envelope surrounding the meteoric matrix in the core of the nucleus.
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NASA Technical Reports Server (NTRS)
Allton, Judith H.; Gooding, James L.
1991-01-01
Although results from the Giotto and Vega spacecraft flybys of comet P/Halley indicate a complex chemistry for both the ices and dust in the nucleus, carbonaceous chondrite meteorites are still regarded as useful analogs for the rocky components. Carbonaceous chondrites mixed with water enable simulation of water/rock interactions which may occur in cometary nuclei. Three general types of interactions can be expected between water and minerals at sub-freezing temperatures: heterogeneous nucleation of ice by insoluble minerals; adsorption of water vapor by hygroscopic phases; and freezing and melting point depression of liquid water sustained by soluble minerals. Two series of experiments were performed in a differential scanning calorimeter (DSC) with homogenized powders of the following whole-rock meteorites and comparison samples: Allende (CV3), Murchison (CM2), Orgueil (CI), Holbrook (L6), and Pasamonte (eucrite) meteorites as well as on peridotite (PCC-1, USGS), saponite (Sap-Ca-1, CMS), montmorillonite (STx-1, CMS), and serpentine (Franciscan Formation, California). Results are briefly discussed.
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The presence of clathrates in comet 67P/Churyumov-Gerasimenko
Luspay-Kuti, Adrienn; Mousis, Olivier; Hässig, Myrtha; Fuselier, Stephen A.; Lunine, Jonathan I.; Marty, Bernard; Mandt, Kathleen E.; Wurz, Peter; Rubin, Martin
2016-01-01
Cometary nuclei are considered to most closely reflect the composition of the building blocks of our solar system. As such, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. Recent measurements of the time variation of major and minor volatile species in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko (67P) by the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument onboard Rosetta provide insight into the possible origin of this comet. The observed outgassing pattern indicates that the nucleus of 67P contains crystalline ice, clathrates, and other ices. The observed outgassing is not consistent with gas release from an amorphous ice phase with trapped volatile gases. If the building blocks of 67P were formed from crystalline ices and clathrates, then 67P would have agglomerated from ices that were condensed and altered in the protosolar nebula closer to the Sun instead of more pristine ices originating from the interstellar medium or the outskirts of the disc, where amorphous ice may dominate. PMID:27152351
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The presence of clathrates in comet 67P/Churyumov-Gerasimenko.
Luspay-Kuti, Adrienn; Mousis, Olivier; Hässig, Myrtha; Fuselier, Stephen A; Lunine, Jonathan I; Marty, Bernard; Mandt, Kathleen E; Wurz, Peter; Rubin, Martin
2016-04-01
Cometary nuclei are considered to most closely reflect the composition of the building blocks of our solar system. As such, comets carry important information about the prevalent conditions in the solar nebula before and after planet formation. Recent measurements of the time variation of major and minor volatile species in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko (67P) by the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument onboard Rosetta provide insight into the possible origin of this comet. The observed outgassing pattern indicates that the nucleus of 67P contains crystalline ice, clathrates, and other ices. The observed outgassing is not consistent with gas release from an amorphous ice phase with trapped volatile gases. If the building blocks of 67P were formed from crystalline ices and clathrates, then 67P would have agglomerated from ices that were condensed and altered in the protosolar nebula closer to the Sun instead of more pristine ices originating from the interstellar medium or the outskirts of the disc, where amorphous ice may dominate.
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Nucleus Characterization of Main-Belt Comet P/Garradd
NASA Astrophysics Data System (ADS)
Hsieh, Henry H.; Kaluna, Heather; Meech, Karen J.
2012-02-01
We seek SOAR time to physically characterize the nucleus of main- belt comet (MBC) P/2008 R1 (Garradd). Our primary objectives include determination of P/Garradd's rotation period, shape, and colors. MBCs are mysterious objects that exhibit cometary activity yet are dynamically indistinguishable from main-belt asteroids. Studying these apparently icy objects so close to the Sun is important for understanding the distribution of volatile material in our solar system as well as the origin of Earth's water. Five MBCs are currently known: only two have well-characterized nuclei, while the others have only been partially characterized. With so little known about this population, it is crucial to obtain the best possible physical characterizations for as many of the few currently known MBCs as possible. This information will aid us in developing a global understanding of the population's characteristics, such as the level of diversity as well as any commonalities. This will then help answer larger scientific questions such as how abundant MBCs may be and what they can tell us about the past and present distribution of ice in the inner solar system.
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I. T. - R. O. C. K. S. Comet Nuclei Sample Return Mission
NASA Astrophysics Data System (ADS)
Dalcher, N.
2009-04-01
Ices, organics and minerals recording the chemical evolution of the outer regions of the early solar nebula are the main constituents of comets. Because comets maintain the nearly pristine nature of the cloud where they formed, the analyses of their composition, structure, thermodynamics and isotope ratios will increase our understanding of the processes that occurred in the early phases of the solar system as well as the Interstellar Medium (ISM) Cloud that predated the formation of the solar nebula [1]. While the deep impact mission aimed at determining the internal structure of comet Temple1's nuclei [e.g. 3], the stardust mission sample return has dramatically increased our understanding of comets. Its first implications indicated that some of the comet material originated in the inner solar system and was later transported outward beyond the freezing line [4]. A wide range of organic compounds identified within different grains of the aerogel collectors has demonstrated the heterogeneity in their assemblages [5]. This suggests either many histories associated with these material or possibly analytical constraints imposed by capture heating of Wild2 material in silica aerogel. The current mission ROSETTA, will further expand our knowledge about comets considerably through rigorous in situ analyses of a Jupiter Family Comet (JFC). As the next generation of comet research post ROSETTA, we present the comet nuclei sample return mission IT - ROCKS (International Team - Return Of Comet's Key Samples) to return several minimally altered samples from various locations of comet 88P/Howell, a typical JFC. The mission scenario includes remote sensing of the comet's nucleus with onboard instruments similar to the ROSETTA instruments [6, 7, 8] (VIS, IR, Thermal IR, X-Ray, Radar) and gas/dust composition measurements including a plasma science package. Additionally two microprobes [9] will further investigate the physical properties of the comet's surface. Retrieving of the samples will be performed by touch and go manoeuvres and a penetrator device [10]. Solar arrays are used as energy source and additional cooling is required to keep the samples at low temperatures (<135K) to prevent them from alteration during return [11]. The return of the samples will be performed by a re-entry capsule similar to that used in the stardust mission. A combined propulsion method of solar electric and chemical propulsion was chosen and an Ariane 5 ECB will be used as launching vehicle due to the payload of nearly 5.5 tons. The overall mission time is about 9 years and it will operate after 2025. The total costs will exceed 2000 million Euro. The amount of material returned (at least 15 g in total) will enable a wide range of scientific analyses techniques. For future analyses on Earth, in laboratories capable of more sophisticated techniques, a certain amount (1/4 of total mass) of the samples will be stored under a sufficient protective environment which includes cooling systems, clean rooms and high vacuum conditions. Different experimental techniques non-, semi-, and completely destructive will be applied to the samples including XRD, IR-VIS spectroscopy for mineralogical analysis, X-Ray tomography for physical properties, SEM, TEM for imaging, TOF-SIMS, Nano-SIMS for isotopic composition and Nano-SIMS, Raman-Spectroscopy for organic analyses . This will aid us with understanding the nature of comets, the isotopic composition of presolar grains and the role comets played in delivering water and organics to Earth [2] and other celestial bodies. [1] Irvine W. and Lunine J., The cycle of matter in the galaxy. In Comets II (M. Festou et al., eds.), p. 25. University of Arizona, Tucson (2005). [2] Sagan C. And Druyan A., Comets, revised. First Ballantine Books Edition (1997). [3] The shape, topography, and geology of Tempel 1 from Deep Impact observations Thomas P.C., Veverka J., Belton M.J.S., Hidy A., A'Hearn M.F., Farnham T.L., Groussin O., Li J.-Y., McFadden L.A., Sunshine J., Wellnitz D., Lisse C., Schultz P., Meech K. J., Delamere W. A. Icarus 187,4-15 (2007). [4] Simon S.B., Joswiak D.J., Ishii H.A., Bradley J.P., Chi M., Grossman L., Aléon J., Brownlee D.E., Fallon S., Hutcheon I.D., Matrajt G., Mckeegan K.D.: Refractory Inclusion Returned by Stardust from Comet P81/Wild 2. Meteoritics and Planetary Science (2007). [5] George D. Cody, Harald Ade, Conel M. O'D. Alexander, Tohru Araki, Anna Butterworth, Holger Fleckenstein, George Flynn, Mary K. Gilles, Chris Jacobsen, A.L. D. Kilcoyne, Keiko Messenger, Scott A. Sandford, Tolek Tyliszczak, Andrew J.Westphal4, Susan Wirick, and Hikaru Yabuta. Quantitative Organic and Light Element analysis of Comet 81P/Wild 2 particles using C-, N-, and O- µ-XANES, Meteoretics and Planetary Science: In Press. [6] Stern, S. et al. Alice: The Rosetta Ultraviolet Imaging Spectrograph. Space Science Reviews 128, 507-527 (2007). [7] Balsiger, H. et al. Rosina-Rosetta Orbiter Spectrometer for Ion and Neutral Analysis. Space Science Reviews 128, 745-801 (2007). [8] Colangeli, L. et al. The Grain Impact Analyser and Dust Accumulator (GIADA) Experiment for the Rosetta Mission: Design, Performances and First Results. Space Science Reviews 128, 803-821 (2007). [9] Yoshimitsu, T., Kubota, T., Nakatani, I., Adachi, T. & Saito, H. Micro-hopping robot for asteroid exploration. Acta Astronautica 52, 441-446 (2003). [10] Lorenz, R. et al. Demonstration of comet sample collection by penetrator. ESA SP-542, 387-393 (2003). [11] Küppers et al. Triple F—a comet nucleus sample return mission. Experimental Astronomy, Online First (2008).
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Collisional Processing of Olivine and Pyroxene in Cometary Dust
NASA Technical Reports Server (NTRS)
Lederer, S. M.; Cintala, M. J.; Olney, R. D.; Keller, L. P.; Nakamura-Messenger, K.; Zolensky, M.
2008-01-01
According to the nebular theory of solar-system formation, collisions between bodies occurred frequently early in the solar system s history and continue at a lower rate even today. Collisions have reworked the surface compositions and structures of cometary nuclei, though to an unknown degree. The majority of the collisional history of a typical Jupiter-family comet takes place while it resides in the Kuiper Belt. Impacts occur on the surfaces of small bodies over a large range of velocities by impactors of all sizes, but typical encounter speeds within the Kuiper Belt are 1.5 to 2.0 km/s[1]. Durda and Stern suggest that the interiors of most cometary nuclei with diameters <5 km have been heavily damaged by collisions [2]. They estimate that over a period of 3.5 Gy, a nucleus with a diameter of 2 km and an orbit between 35-45 AU will experience 90-300 collisions with objects greater than 8 m in diameter. In this same time interval, collisions between a typical Trans-Neptunian Object (TNO) 200 km in diameter and objects with d > 8 m would rework up to one-third of that TNO s surface. In fact, it has been proposed that most short-period comets from the Kuiper Belt (90%) are collisional fragments from larger TNOs - not primordial objects themselves [3] - and that most short-period comets from the Kuiper Belt will be collisionally processed both on their surfaces as well as in their interiors.
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Comets, Carbonaceous Meteorites, and the Origin of the Biosphere
NASA Technical Reports Server (NTRS)
Hoover, Richard B.
2005-01-01
The biosphere comprises the Earth s crust, atmosphere, oceans, and ice caps and the living organisms that survive within this habitat. The discoveries of barophilic chemolithoautotrophic thermophiles living deep within the crust and in deep-sea hydrothermal vents, and psychrophiles in permafrost and deep within the Antarctic Ice Sheet indicate the Earth s biosphere is far more extensive than previously recognized. Molecular biomarkers and Bacterial Paleontology provide evidence that life appeared very early on the primitive Earth and the origin of the biosphere is closely linked with the emergence of life. The role of comets, meteorites, and interstellar dust in the delivery of water, organics and prebiotic chemicals has long been recognized. Deuterium enrichment of seawater and comets indicates that comets delivered oceans to the early Earth. Furthermore, the similarity of the D/H ratios and the chemical compositions of CI carbonaceous meteorites and comets indicate that the CI meteorites may be remnants of cometary nuclei with most volatiles removed. Comets, meteorites, and interstellar dust also contain complex organic chemicals, amino acids, macromolecules, and kerogen-like biopolymers and may have played a crucial role in the delivery of complex organics and prebiotic chemicals during the Hadean (4.5-3.8 Gyr) period of heavy bombardment. The existence of indigenous microfossils of morphotypes of cyanobacteria in the CI and CM carbonaceous meteorites suggests that the paradigm that life originated endogenously in the primitive oceans of early Earth may require re-consideration. Recent data on the hot (300-400 K) black crust on comet P/Halley and Stardust images of P/Wild 2 showing depressions, tall cliffs, and pinnacles, indicate the presence of thick, durable, dark crusts on comets. If cavities within the ice and crust sustain vapor pressures in excess of 10 millibar, then localized pools of liquid water and brines could exist within the comet. Since life exists on Earth wherever there is liquid water, it is suggested that comets might also harbour viable and/or cryopreserved microbiota.
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Composition and Cosmogonic Parameters of the Chemically Distinct Comet C/2007 N3 (Lulin)
NASA Astrophysics Data System (ADS)
Gibb, Erika L.; Villanueva, G. L.; Bonev, B. P.; DiSanti, M. A.; Mumma, M. J.; Radeva, Y. L.
2012-10-01
Comets are remnants from the early solar system that retain the volatiles (ices) from the cold outer proto-planetary disk (beyond 5 AU) where they formed. Comet nuclei were among the first objects to accrete in the early solar nebula and many of them were subsequently incorporated into the growing giant planets. Gravitational scattering redistributed the remaining comet population by either sending them to the inner solar system, where they may have enriched the early biosphere, or scattering them into their present-day dynamical reservoirs. Since this early time, comets have been orbiting the Sun relatively untouched by processing mechanisms, until their orbits are perturbed towards the inner solar system. As such, they are believed to be among the most primitive objects in the solar system and may be representative of the material from which the solar system formed. Of particular interest is their icy volatile composition since other solar system objects have either lost or have had significant modifications to their volatile compositions since their formation. Many of the volatiles observed in comets are also important prebiotic species. For example, H2CO is a chemical precursor to sugars and HCN and NH3 are precursors of amino acids. Studying comets is therefore a vital link to understanding the origin and evolution of our planetary system and life on Earth. We obtained high-resolution, near-infrared spectroscopic observations of Comet C/2007 N3 (Lulin) on 30 January - 1 February 2009 with NIRSPEC on Keck II. Lulin is an Oort Cloud comet with a very large aphelion distance, suggesting that it may have been dynamically new. We report production rates of H2O, C2H6, HCN, C2H2, CH4, NH3, H2CO, CH3OH, and CO. We also report two cosmogonic parameters: D/H ratio in H2O and CH4, and isomeric spin temperatures. The implications for comet formations scenarios are discussed.
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Infrared Spectroscopy of Parent Volatiles in Comets: Implications for Astrobiology
NASA Technical Reports Server (NTRS)
DiSanti, Michael A.
2010-01-01
Current cometary orbits provide information on their recent dynamical history. However, determining a given comet's formation region from its current dynamical state alone is complicated by radial migration in the proto-planetary disk and by dynamical interactions with the growing giant planets. Because comets reside for long periods of time in the outer Solar System, the ices contained in their nuclei (native ices) retain a relatively well-preserved footprint of when and where they formed, and this in turn can provide clues to conditions in the formation epoch. As a comet approaches the Sun, sublimation of its native ices releases parent volatiles into the coma where they can be measured spectroscopically. The past to - 15 years have seen the advent of infrared spectrometers with high sensitivity between about 2.8 and 5.0 micron, enabling a taxonomy among comets based on abundances of parent volatiles (e.g., H2O, CO, CH4, C2H6, HCN, CH30H, H2CO, NH3). Such molecules are of keen interest to Astrobiology, as they include important pre-biotic species that likely were required for the emergence of life on Earth and perhaps elsewhere. Approximately 20 comets have thus far been characterized, beginning with C/1996 82 (Hyakutake) in 1996. Molecular production rates are established through comparison of observed emission line intensities with those predicted by quantum mechanical fluorescence models. Abundances of parent volatiles (relative to H2O) vary among even the relatively small number of comets sampled, with the most volatile species (CO and CH4) displaying the largest variations. Techniques developed for measuring parent volatile abundances in comets will be discussed, as will possible implications for their formation.
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HUBBLE DETECTION OF COMET NUCLEUS AT FRINGE OF SOLAR SYSTEM
NASA Technical Reports Server (NTRS)
2002-01-01
This is sample data from NASA's Hubble Space Telescope that illustrates the detection of comets in the Kuiper Belt, a region of space beyond the orbit of the planet Neptune. This pair of images, taken with the Wide Field Planetary Camera 2 (WFPC2), shows one of the candidate Kuiper Belt objects found with Hubble. Believed to be an icy comet nucleus several miles across, the object is so distant and faint that Hubble's search is the equivalent of finding the proverbial needle-in-haystack. Each photo is a 5-hour exposure of a piece of sky carefully selected such that it is nearly devoid of background stars and galaxies that could mask the elusive comet. The left image, taken on August 22, 1994, shows the candidate comet object (inside circle) embedded in the background. The right picture, take of the same region one hour forty-five minutes later shows the object has apparently moved in the predicted direction and rate of motion for a kuiper belt member. The dotted line on the images is a possible orbit that this Kuiper belt comet is following. A star (lower right corner) and a galaxy (upper right corner) provide a static background reference. In addition, other objects in the picture have not moved during this time, indicating they are outside our solar system. Through this search technique astronomers have identified 29 candidate comet nuclei belonging to an estimated population of 200 million particles orbiting the edge of our solar system. The Kupier Belt was theorized 40 years ago, and its larger members detected several years ago. However, Hubble has found the underlying population of normal comet-sized bodies. Credit: A. Cochran (University of Texas) and NASA
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Parametric Dielectric Model of Comet Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Heggy, E.; Palmer, E. M.; Kofman, W. W.; Clifford, S. M.; Righter, K.; Herique, A.
2012-12-01
In 2014, the European Space Agency's Rosetta mission is scheduled to rendezvous with Comet 67P/Churyumov-Gerasimenko (Comet 67P). Rosetta's CONSERT experiment aims to explore the cometary nucleus' geophysical properties using radar tomography. The expected scientific return and inversion algorithms are mainly dependent on our understanding of the dielectric properties of the comet nucleus and how they vary with the spatial distribution of geophysical parameters. Using observations of comets 9P/Tempel 1 and 81P/Wild 2 in combination with dielectric laboratory measurements of temperature, porosity, and dust-to-ice mass ratio dependencies for cometary analog material, we have constructed two hypothetical three-dimensional parametric dielectric models of Comet 67P's nucleus to assess different dielectric scenarios of the inner structure. Our models suggest that dust-to-ice mass ratios and porosity variations generate the most significant measurable dielectric contrast inside the comet nucleus, making it possible to explore the structural and compositional hypotheses of cometary nuclei. Surface dielectric variations, resulting from temperature changes induced by solar illumination of the comet's faces, have also been modeled and suggest that the real part of the dielectric constant varies from 1.9 to 3.0, hence changing the surface radar reflectivity. For CONSERT, this variation could be significant at low incidence angles, when the signal propagates through a length of dust mantle comparable to the wavelength. The overall modeled dielectric permittivity spatial and temporal variations are therefore consistent with the expected deep penetration of CONSERT's transmitted wave through the nucleus. It is also clear that changes in the physical properties of the nucleus induce sufficient variation in the dielectric properties of cometary material to allow their inversion from radar tomography.
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NASA Astrophysics Data System (ADS)
Rietmeijer, F.
The good news is that the original, typically non-chondritic, presolar dust had an extremely simple mineralogy of predominantly Mg-rich olivines and -pyroxenes, pyrrhotite (Fe7 S8 ), Fe-o xides and Fe,Ni-metal. This unique property is preserved in the least modified protoplanets for in situ sampling (e.g. STARDUST, MUSES-C) and in their debris in the form of stratospheric IDPs and MMs. The corollary is that mineralogical complexity in all extraterrestrial materials is an evolved secondary property. The earliest stages of solar system evolution were defined by hierarchical dust accretion whereby the accreting dust was recycled prior to the formation of the final surviving protoplanets. This recycling concentrated initially minor elements so they could form new minerals , e.g. alkali-feldspars and plagioclase. The least- modified protoplanets are comet nuclei, i.e. random mixtures of rubble piles and dirty snowballs, and the icy (ultra)carbonaceous asteroids. Second best are the dormant, extinct and rare active comet nuclei among the near-Earth asteroids that are relatively easy to access by sample return missions. Third are the anhydrous CO/CV carbonaceous chondrites and the low metamorphic grade, unequilibrated ordinary chondrites from the main asteroid belt. Lithification of the original rubble piles in these asteroids erased all structural properties but not the mineralogy and chemistry of the accreted entities, i.e. matrix, chondrules and CAIs.Consequently , returned samples of small chips, fragments or powders from the surface of undifferentiated protoplanets will amply suffice for a full mineralogical and chemical characterization of these small bodies, including modifications from interactions with the space environment, e.g. space weathering, regolith formation and the black mantle on icy-protoplanets. Major improvements in the sensitivity of available micro-analytical tools means that in situ acquired samples can be analyzed at scales of individual, n m-s i z e d constituents to determine the major rock-forming and minor element abundances , isotopic compositions, the nature of and chemical bonds in organic matter. The nature of solid s , crystalline or amorphous, can be identified and the solid-state modification as a function of composition. Measurements of noble gas abundances and isotopes and the physical properties (e.g. density) require samples of only a few nano-grams. Sample site selection on rubble piles is critical. For example, boulders and pebbles in comet nuclei might be proto- CI material that is the most pristine, anhydrous lithified rock in the solar system.
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The study of the physics of cometary nuclei
NASA Technical Reports Server (NTRS)
Whipple, Fred L.
1987-01-01
The numerical calculations of stability for many possible orbits of the double nucleus for P/Holmes showed that the likelihood of such a precollision history was quite high. A number of investigations were made of hypothetical orbits for particles about the asteroid Amphitrite to test for stability. The purpose was to establish more favorable fly-by orbits close to the asteroid for the Galileo missions en-route to Jupiter, reducing the collisional hazards. A statistical study was made of the orbits of long-period comets with small original semi-major axes recently perturbed from the great Opik-Oort Cloud. The results from the space missions to Halley's comet are partially reported in the two papers in the appendices.
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Water/rock interactions in experimentally simulated dirty snowball and dirty iceball cometary nuclei
NASA Technical Reports Server (NTRS)
Gooding, James L.; Allton, Judith H.
1991-01-01
In the dirty snowball model for cometary nuclei, comet-nucleus materials are regarded as mixtures of volatile ices and relatively non-volatile minerals or chemical compounds. Carbonaceous chondrite meteorites are regarded as useful analogs for the rocky component. To help elucidate the possible physical geochemistry of cometary nuclei, preliminary results are reported of calorimetric experiments with two-component systems involving carbonaceous chondrites and water ice. Based on collective knowledge of the physics of water ice, three general types of interactions can be expected between water and minerals at sub-freezing temperatures: (1) heterogeneous nucleation of ice by insoluble minerals; (2) adsorption of water vapor by hygroscopic phases; and (3) freezing- and melting-point depression of liquid water sustained by soluble minerals. The relative and absolute magnitude of all three effects are expected to vary with mineral composition.
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Detection of radiation treatment of beans using DNA comet assay
NASA Astrophysics Data System (ADS)
Khan, Ashfaq A.; Khan, Hasan M.; Delincée, Henry
2002-03-01
A simple technique of microgel electrophoresis of single cells (DNA Comet Assay) enabled a quick detection of radiation treatment of several kinds of leguminous beans (azuki, black, black eye, mung, pinto, red kidney and white beans). Each variety was exposed to radiation doses of 0.5, 1 and 5kGy covering the permissible limits for insect disinfestation. The cells or nuclei from beans were extracted in cold PBS, embedded in agarose on microscope slides, lysed between 15 and 60min in 2.5% SDS and electrophoresis was carried out at a voltage of 2V/cm for 2-2.5min. After silver staining, the slides were evaluated through an ordinary transmission microscope. In irradiated samples, fragmented DNA stretched towards the anode and the damaged cells appeared as a comet. The density of DNA in the tails increased with increasing radiation dose. However, in non-irradiated samples, the large molecules of DNA remained relatively intact and there was only minor or no migration of DNA; the cells were round or had very short tails only. Hence, the DNA comet assay provides an inexpensive, rapid and relatively simple screening method for the detection of irradiated beans.
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ACTIVITY OF 50 LONG-PERIOD COMETS BEYOND 5.2 au
DOE Office of Scientific and Technical Information (OSTI.GOV)
Sárneczky, K.; Szabó, Gy. M.; Csák, B.
2016-12-01
Remote investigations of ancient matter in the solar system have traditionally been carried out through observations of long-period (LP) comets, which are less affected by solar irradiation than their short-period counterparts orbiting much closer to the Sun. Here we summarize the results of our decade-long survey of the distant activity of LP comets. We found that the most important separation in the data set is based on the dynamical nature of the objects. Dynamically new comets are characterized by a higher level of activity on average: the most active new comets in our sample can be characterized by Afρ valuesmore » >3–4, higher than those for our most active returning comets. New comets develop more symmetric comae, suggesting a generally isotropic outflow. In contrast to this, the comae of recurrent comets can be less symmetrical, ocassionally exhibiting negative slope parameters, which suggest sudden variations in matter production. The morphological appearance of the observed comets is rather diverse. A surprisingly large fraction of the comets have long, tenuous tails, but the presence of impressive tails does not show a clear correlation with the brightness of the comets.« less
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The gravitational potential of a homogeneous polyhedron or don't cut corners
NASA Technical Reports Server (NTRS)
Werner, Robert A.
1994-01-01
A polyhedron can model irregularly shaped objects such as asteroids, comet nuclei, and small planetary satellites. With minor effort, such a model can incorporate important surface features such as large craters. Here we develop closed-form expressions for the exterior gravitational potential and acceleration components due to a constant-density polyhedron. An equipotential surface of Phobos is illustrated.
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Comets: Dirty snowballs or icy dirtballs
NASA Astrophysics Data System (ADS)
Keller, H. U.
1989-12-01
The observations of comet Halley show that the non-volatile (dust) component of the cometary nucleus has become more dominant if compared to the perception based on the icy conglomerate nucleus. The in-situ observations on the Giotto spacecraft revealed an excess of large dust particles that dominate the mass distribution. Even larger particles were derived from the attitude changes of the spacecraft bridging the gap to the cloud of particles observed by radar techniques. A dust to gas ratio larger than one was derived for comet Halley. The importance of dust for the structure of the nucleus is corroborated by the amount of particles and their lifetime in meteor streams. Fireballs show that large (meter size) objects separate from the nucleus and are stable enough to survive hundreds of orbital periods. From the various lines of evidence it is concluded that the structure of cometary nuclei is determined by the non-volatile component rather than by ice or snow. Laboratory models based on icy agglomerations do not seem realistic as nucleus analogs.
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Milkovic, Durdica; Garaj-Vrhovac, Vera; Ranogajec-Komor, Mária; Miljanic, Saveta; Gajski, Goran; Knezevic, Zeljka; Beck, Natko
2009-01-01
The aim of this work is to assess DNA damage in peripheral blood lymphocytes of children prior to and following airway X-ray examinations of the chest using the alkaline comet assay and to compare data with the measured absorbed dose. Twenty children with pulmonary diseases, between the ages of 5 and 14 years, are assessed. Absorbed dose measurements are conducted for posterior-anterior projection on the forehead, thyroid gland, gonads, chest, and back. Doses are measured using thermoluminescent and radiophotoluminescent dosimetry systems. Differences between tail lengths, tail intensity, and tail moments as well as for the long-tailed nuclei before and after exposures are statistically significant and are dependent on the individual. The results demonstrate the usefulness of the comet assay as a measure of X-ray damage to lymphocytes in a clinical setting. Doses measured with both dosimeters show satisfactory agreement (0.01 mSv) and are suitable for dosimetric measurements in X-ray diagnostics.
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On the evolution and activity of cometary nuclei.
Prialnik, D; Bar-Nun, A
1987-02-15
The thermal evolution of a spherical cometary nucleus (initial radius of 2.5 km), composed initially of very cold amorphous ice and moving in comet Halley's orbit, is simulated numerically for 280 revolutions. It is found that the phase transition from amorphous to crystalline ice constitutes a major internal heat source. The transition does not occur continuously, but in five distinct rounds, during the following revolutions: 1, 7, 40-41, 110-112, and 248-252. Due to the (slow) heating of the amorphous ice between crystallization rounds, the phase transition front advances into the nucleus to progressively greater depths: 36 m on the first round, and then 91 m, 193 m, 381 m, and 605 m respectively. Each round of crystallization starts when when the boundary between amorphous and crystalline ice is brought to approximately 15 m below the surface, as the nucleus radius decreases due to sublimation. At the time of crystallization, the temperature of the transformed ice rises to 180 K. According to experimental studies of gas-laden amorphous ice, a large fraction of the gas trapped in the ice at low temperatures is released. Whereas some of the released gas may find its way out through cracks in the crystalline ice layer, the rest is expected to accumulate in gas pockets that may eventually explode, forming "volcanic calderas." The gas-laden amorphous ice thus exposed may be a major source of gas and dust jets into the coma, such as those observed on comet Halley by the Giotto spacecraft. The activity of new comets and, possibly, cometary outbursts and splits may also be explained in terms of explosive gas release following the transition from amorphous to crystalline ice.
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The evolution of volatile production in C/2009 P1 (Garradd) during its 2011-2012 apparition
NASA Astrophysics Data System (ADS)
Gicquel, A.; Milam, S.; Cordiner, M.; Villanueva, G.; Charnley, S.; Coulson, I.; Remijan, A.; DiSanti, M.; Mumma, M.; Szutowicz, S.
2014-07-01
Comets are likely to be the most pristine objects in our Solar System. They provide a record of the physical and chemical conditions in the protosolar nebula between about 5 and 40 au during the epoch when the distinct cometary populations were being assembled (Festou et al. 2004; Jewitt 2004; Mumma & Charnley 2011). Cometary nuclei today reside in (at least) two distinct reservoirs, the Oort Cloud (OC) and the Kuiper Belt (KB). Past observations have shown that comets appear to contain a mixture of products from both interstellar and nebular chemistries and could also have been important for initiating prebiotic chemistry on the early Earth (Ehrenfreund & Charnley 2000). Although there are some differences, the volatile composition of cometary ices is generally similar to the inventory of molecules detected in the ices and gas of dense molecular clouds. Given the gradient in physical conditions expected across the proto-Solar nebula, chemical diversity in the comet population is to be expected. Here we report an analysis of long-term ground-based radio observations towards comet C/2009 P1 (Garradd). Comet C/2009 P1 Garradd is an OC comet that reached perihelion (at heliocentric distance R_h = 1.55 au) in late December 2011 and had its closest approach to the Earth on 5 March 2012. Like C/1995 O1 (Hale-Bopp) at 7.2 au, Garradd exhibited unusual activity at large R_h (8.68 au), displaying a 15'' diameter circular coma (IAUC 9062). It is well known that some comets exhibit volatile activity at large heliocentric distances, where water ice cannot sublime efficiently. Infrared (IRTF/CSHELL, Keck 2/NIRSPEC, and VLT/CRIRES) spectroscopy of Garradd showed clear CO (R1 & R2) emission near λ = 4.7 μ m (2150 cm^{-1}), as well as a suite of molecules (e.g., C_2H_6, CH_4, CH_3OH, H_2CO, HCN, C_2H_2, NH_3) that were also detected near or beyond R_h = 2 au (Villanueva et al. 2012; Paganini et al. 2012; DiSanti et al. 2014). We monitored the abundance of parent volatiles in Garradd at multiple epochs around the time of its closest approach to the Earth, using multiple facilities: the Arizona Radio Observatory's 12-m telescope, Kitt Peak, the SubMillimeter Telescope, the James Clerk Maxwell Telescope, and the Greenbank 100-m telescope (GBT), covering wavelengths of 20 cm, 3 cm, and 0.8-3 mm. Observations were taken between 28 December 2011 (R_h = 1.55 au, Δ = 1.97 au) and 28 November 2012 (R_h = 4.27 au, Δ = 4.26 au). GBT monitored OH as a proxy for H_2O activity, while the other facilities were used to study the primary volatiles (e.g., CH_3OH, H_2CO, HCN, HNC, CS, CO). The full analysis of these data, including the determination of the rotational temperatures, abundances, and the variation of given species with time, will be presented. Also, comparisons with other comets will be shown in order to constrain the chemical history on comets and add to the statistics for a taxonomic classification of these objects.
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Carbajal-López, Yolanda; Gómez-Arroyo, Sandra; Villalobos-Pietrini, Rafael; Calderón-Segura, María Elena; Martínez-Arroyo, Amparo
2016-02-01
The aim of this study was to evaluate the genotoxic effect of pesticides in exfoliated buccal cells of workers occupationally exposed in Guerrero, Mexico, using the comet assay and the micronucleus test. The study compared 111 agricultural workers in three rural communities (Arcelia 62, Ajuchitlan 13, and Tlapehuala 36), with 60 non-exposed individuals. All the participants were males. The presence of DNA damage was investigated in the exfoliated buccal cells of study participants with the comet assay and the micronucleus (MN) test; comet tail length was evaluated in 100 nuclei and 3000 epithelial cells of each individual, respectively; other nuclear anomalies such as nuclear buds, karyolysis, karyorrhexis, and binucleate cells were also evaluated. Study results revealed that the tail migration of DNA and the frequency of MN increased significantly in the exposed group, which also showed nuclear anomalies associated with cytotoxic or genotoxic effect. No positive correlation was noted between exposure time and tail length and micronuclei frequencies. No significant effect on genetic damage was observed as a result of age, smoking, and alcohol consumption. The MN and comet assay in exfoliated buccal cells are useful and minimally invasive methods for monitoring genetic damage in individuals exposed to pesticides. This study provided valuable data for establishing the possible risk to human health associated with pesticide exposure.
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A new activity index for comets
NASA Technical Reports Server (NTRS)
Whipple, Fred L.
1992-01-01
An activity index, AI, is derived from observational data to measure the increase of activity in magnitudes for comets when brightest near perihelion as compared to their inactive reflective brightness at great solar distances. Because the observational data are still instrumentally limited in the latter case and because many comets carry particulate clouds about them at great solar distances, the application of the activity index is still limited. A tentative application is made for the comets observed by Max Beyer over a period of nearly 40 years, providing a uniform magnitude system for the near-perihelion observations. In all, 32 determinations are made for long-period (L-P) comets and 15 for short-period (S-P). Although the correlations are scarcely definitive, the data suggest that the faintest comets are just as active as the brightest and that the S-P comets are almost as active as those with periods (P) exceeding 10(exp 4) years or those with orbital inclinations of i less than 120 deg. Comets in the range 10(exp 2) less than P less than 10(exp 4) yr. or with i greater than 120 deg appear to be somewhat more active than the others. There is no evidence to suggest aging among the L-P comets or to suggest other than a common nature for comets generally.
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Mid-infrared observations of sungrazing comet C/2012 S1 (ISON) with the Subaru Telescope
NASA Astrophysics Data System (ADS)
Ootsubo, T.; Usui, F.; Takita, S.; Watanabe, J.; Yanamandra-Fisher, P.; Honda, M.; Kawakita, H.; Furusho, R.
2014-07-01
Comets are the frozen reservoirs of the early solar nebula and are made of ice and dust. The determination of the properties for cometary dust provides us insight into both the early-solar-nebula environment and the formation process of the planetary system. A silicate feature is often observed in comet spectra in the mid-infrared region and may be used for probing the early history of the solar system. In most cases, the feature shows the existence of crystalline silicate (for example, 11.3 microns) together with amorphous silicate [1,2]. Since the crystallization of silicates from amorphous ones generally requires high-temperature annealing above 800 K (e.g., [3,4]), it is believed that the crystalline silicate grains produced at the inner part of the disk were transported to the outer cold regions where the comet nuclei formed. Comet C/2012 S1 (ISON) is a long-period Oort Cloud comet, discovered in September 2012. In particular, comet ISON is a sungrazing comet, which was predicted to pass close by the Sun and the Earth and becoming a bright object. Mid-infrared observations of this new comet and investigation of the 10-micron silicate feature help us understand the formation of crystalline silicate grains in the early solar nebula. We conducted observations of comet ISON in the mid-infrared wavelength region with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru Telescope on Mauna Kea, Hawaii [5,6,7]. The observation of comet ISON was carried out on 2013 October 19 and 21 UT. Since the weather conditions were not so good when we observed, we carried out N-band imaging observations (8.8 and 12.4 microns) and N-band low-resolution spectroscopy. The spectrum of comet ISON can be fit with the 260--265-K blackbody spectrum when we use the regions of 7.8--8.2 and 12.4--13.0 microns as the continuum. The spectrum has only a weak silicate excess feature, which may be able to attribute to small amorphous olivine grains. We could not detect a clear crystalline silicate feature in the spectrum of our observations. We will compare the spectrum with other Oort Cloud comets, such as comets C/2011 L4 (PanSTARRS) and C/2013 R1 (Lovejoy), and discuss the dust properties and the birthplace of comet ISON.
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The cometary and asteroidal origins of meteors
NASA Technical Reports Server (NTRS)
Kresak, L.
1973-01-01
A quantitative examination of the gravitational and nongravitational changes of orbits shows that for larger interplanetary bodies the perturbations by Jupiter strongly predominate over all other effects, which include perturbations by other planets, splitting of comet nuclei and jet effects of cometary ejections. The structure of meteor streams, indicates that the mutual compensation of the changes in individual elements entering the Jacobian integral, which is characteristic for the comets, does not work among the meteoroids. It appears that additional forces of a different kind must exert appreciable influence on the motion of interplanetary particles of meteoroid size. Nevertheless, the distribution of the Jacobian constant in various samples of meteor orbits furnishes some information on the type of their parent bodies and on the relative contribution of individual sources.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Harker, David E.; Woodward, Charles E.; Kelley, Michael S.
2011-01-15
We present mid-infrared spectra and images from the Gemini-N (+ Michelle) observations of fragments SW3-[B] and SW3-[C] of the ecliptic (Jupiter family) comet 73P/Schwassmann-Wachmann 3 pre-perihelion. We observed fragment B soon after an outburst event (between 2006 April 16-26 UT) and detected crystalline silicates. The mineralogy of both fragments was dominated by amorphous carbon and amorphous pyroxene. The grain size distribution (assuming a Hanner-modified power law) for fragment SW3-[B] has a peak grain radius of a{sub p} {approx} 0.5 {mu}m, and for fragment SW3-[C], a{sub p} {approx} 0.3 {mu}m; both values are larger than the peak grain radius of themore » size distribution for the dust ejected from ecliptic comet 9P/Tempel 1 during the Deep Impact event (a{sub p} = 0.2 {mu}m). The silicate-to-carbon ratio and the silicate crystalline mass fraction for the submicron to micron-sized portion of the grain size distribution on the nucleus of fragment SW3-[B] were 1.341{sup +0.250}{sub -0.253} and 0.335{sup +0.089}{sub -0.112}, respectively, while on the nucleus of fragment SW3-[C] they were 0.671{sup +0.076}{sub -0.076} and 0.257{sup +0.039}{sub -0.043}, respectively. The similarity in mineralogy and grain properties between the two fragments implies that 73P/Schwassmann-Wachmann 3 is homogeneous in composition. The slight differences in grain size distribution and silicate-to-carbon ratio between the two fragments likely arise because SW3-[B] was actively fragmenting throughout its passage while the activity in SW3-[C] was primarily driven by jets. The lack of diverse mineralogy in the fragments SW3-[B] and SW3-[C] of 73P/Schwassmann-Wachmann 3 along with the relatively larger peak in the coma grain size distribution suggests that the parent body of this comet may have formed in a region of the solar nebula with different environmental properties than the natal sites where comet C/1995 O1 (Hale-Bopp) and 9P/Tempel 1 nuclei aggregated.« less
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Infrared Imaging, Spectroscopic, and Photometric Studies of Comets
NASA Technical Reports Server (NTRS)
Gehrz, Robert D.
1997-01-01
We have continued our program of infrared (IR) photometric, imaging, spectroscopic, and polarimetric temporal observations of comets to study the properties of comet dust and comet nuclei. During the first two years we digitized our IR data base on P/Halley and other recent comets to facilitate further analysis and comparison with other data bases, and found compelling evidence for the emission of a burst of small grains from P/Halley's nucleus at perihelion. We reported imaging and photometric observations of Comets Austin 1990 V and Swift-Tuttle 1992. The Swift-Tuttle 1992t observations included IR photometry, several 7-14 micron long-slit spectra of the coma and a time-sequence of more than 150 10 micron broadband images of the coma. An analysis of near-IR images of the inner coma of P/Halley obtained on three consecutive nights in 1986 March showed sunwardjets. We completed our analysis of IR imaging spectrosco-photometric data on comets. We also obtained observations of Comets Hyakutake 1996 B2 and Hale/Bopp 1995 01. We obtained infrared imaging, photometric, spectroscopic and polarimetric temporal observations of bright comets using a network of five telescopes, with emphasis on simultaneous observations of comets at many wavelengths with different instruments. Our program offers several unique advantages: 1) rapid observational response to new comets with dedicated infrared telescopes; 2) observations within a few degrees of the sun when comets are near perihelion and 3) access to advanced infrared array imagers and spectrometers. In particular, reduction, analysis, publication and archiving of our Jupiter/sl-9 and Comet Hyakutake infrared data received special emphasis. Instrumentation development included installation of the latest version of the innovative FORTH telescope control and a data acquisition system that enables us to control three telescopes remotely by telephone from anywhere in the world for comet observations in broad daylight. We have acquired more than 3000 256x256 images totaling nearly two gigabytes of data detailing the near-IR development of the impact sites of the S-L9 fragments on Jupiter. These data were obtained using the University of Rochester Imaging IR Camera at the cassegrain focus of the 92" at WIRO. The WIRO data set covers 8 days and is, to our knowledge, one of the most extensive observational records of the S-L/Jupiter encounter obtained by any ground-based telescope. This program benefitted from the compilation during these last few months of an upgrade to the data acquisition program at WIRO with support of this NASA contract.
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NASA Technical Reports Server (NTRS)
Oberbeck, Verne R.; Marshall, John; Shen, Thomas
1991-01-01
The chemical evolution hypothesis of Woese (1979), according to which prebiotic reactions occurred rapidly in droplets in giant atmospheric reflux columns was criticized by Scherer (1985). This paper proposes a mechanism for prebiotic chemistry in clouds that answers Scherer's concerns and supports Woese's hypothesis. According to this mechanism, rapid prebiotic chemical evolution was facilitated on the primordial earth by cycles of condensation and evaporation of cloud drops containing clay condensation nuclei and nonvolatile monomers. For example, amino acids supplied by, or synthesized during entry of meteorites, comets, and interplanetary dust, would have been scavenged by cloud drops containing clay condensation nuclei and would be polymerized within cloud systems during cycles of condensation, freezing, melting, and evaporation of cloud drops.
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Deflection and fragmentation of near-earth asteroids
NASA Technical Reports Server (NTRS)
Ahrens, Thomas J.; Harris, Alan W.
1992-01-01
The collision with earth of near-earth asteroids or comet nuclei poses a potential threat to mankind. Objects about 100 m in diameter could be diverted from an earth-crossing trajectory by the impact of a rocket-launched mass, but for larger bodies nuclear explosions seem to be the only practical means of deflection. Fragmentation of the body by nuclear charges is less efficient or secure.
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Rotational Spin-up Caused CO2 Outgassing on Comet 103P/Hartley 2
NASA Astrophysics Data System (ADS)
Steckloff, Jordan; Graves, Kevin; Hirabayashi, Masatoshi; Richardson, James
2015-11-01
The Deep Impact spacecraft’s flyby of comet 103P/Hartley 2 on November 4, 2010 revealed its nucleus to be a small, bilobate, and highly active world [1] [2]. The bulk of this activity is driven by CO2 sublimation, which is enigmatically restricted to the tip of the small lobe [1]. Because Hartley 2's CO2 production responds to the diurnal cycle of the nucleus [1], CO2 ice must be no deeper than a few centimeters below the surface of the small lobe. However the high volatility of CO2 would suggest that its sublimation front should recede deep below the surface, such that diurnal volatile production is dominated by more refractory species such as water ice, as was observed at comet Tempel 1 [3].Here we show that both the near surface CO2 ice and its geographic restriction to the tip of the small lobe suggest that Hartley 2 recently experienced an episode of fast rotation. We use the GRAVMAP code to compute the stability of slopes on the surface of Hartley 2 as a function of spin period. We determine that the surface of the active region of Hartley 2’s small lobe becomes unstable at a rotation period of ~10-12 hours (as opposed to its current spin period of ~ 18 hours [1]), and will flow toward the tip of the lobe, excavating buried CO2 ice and activating CO2-driven activity. However, the rest of the surface of the nucleus is stable at these spin rates, and will therefore not exhibit CO2 activity. We additionally use Finite Element Model (FEM) analysis to demonstrate that the interior of Hartley 2’s nucleus is structurally stable (assuming a cohesive strength of at least 5 Pa) at these spin rates.The uncommonly high angular acceleration of Hartley 2, which has changed the nucleus spin period by two hours in three months [4], suggests that this episode of fast rotation may have existed only a few years or decades ago. Thus, Hartley 2 may provide an excellent case study into the reactivation of quiescent comet nuclei via rotational spin up, as would result from weak homogeneous gas emissions via the SYORP Effect.References: [1] A'Hearn et al. Science 332, 1396 (2011) [2] Thomas et al. Icarus 222, 550 (2013) [3] Feaga et al. Icarus 190, 345 (2007) [4] Samarasinha & Mueller. Ap. J. 775:L10 (2013)
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Cometary ephemerides - needs and concerns
NASA Technical Reports Server (NTRS)
Yeomans, D. K.
1981-01-01
With the use of narrow field-of-view instrumentation on faint comets, the accuracy requirements upon computed ephemerides are increasing. It is not uncommon for instruments with a one arc minute field-of-view to be tracking a faint comet that is not visible without a substantial integration time. As with all ephemerides of solar syste objects, the computed motion and reduction of these observations, the computed motion of a comet is further depenent upon effects related to the comet's activity. Thus, the ephemeris of an active comet is corrupted by both observational errors and errors due to the comet's activity.
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Assessment of toxicity in fresh water fish Labeo rohita treated with silver nanoparticles
NASA Astrophysics Data System (ADS)
Khan, Muhammad Saleem; Qureshi, Naureen Aziz; Jabeen, Farhat
2017-06-01
Silver nanoparticles (17.78 ± 12.12 nm) were synthesized by the reduction of 0.5 M silver nitrate using formaldehyde as reducing and triethylamine as promoting and stabilizing agent. The particles were grain like agglomerates with spherical, centered-face cubic and crystalline in nature. The sample was highly pure with amine (NH) as associated and capping molecules. Further, the genotoxicity and oxidative stress of these particles were evaluated using Labeo rohita ( L. rohita) as genetic model exposed (10-55 mg L-1 dose) through aquatic medium for 28 days. The cells were produced with micronuclei, fragmented, lobed and buds nuclei in dose dependent manner. The highest incidence of comet was recoded (27.34 ± 5.68) at 55 mg L-1 Ag-NPs and 14 days treatment. Then frequency was decreased to 22.65 ± 6.66% after 28 days due to complex repair mechanism. Moreover, the treatment also produces the oxidative stress and disturbs the level of GST in gill and liver tissue. There was a sharp decline in the activities of GST and this decrease of activity increase the MDA content. Further, the elevated level of GSH represents that the liver has started defensive mechanism against oxyraidcals. This study concluded, Ag-NPs are genotoxic in nature and produce micronuclei, comet cells and also induces oxidative stress in aquatic organisms.
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Valencia, Laura Carolina; García, Adriana; Ramírez-Pinilla, Martha Patricia; Fuentes, Jorge Luis
2011-01-01
The aim of this study was to use the Comet assay to assess genetic damage in the direct-developing frog Eleutherodactylus johnstonei. A DNA diffusion assay was used to evaluate the effectiveness of alkaline, enzymatic and alkaline/enzymatic treatments for lysing E. johnstonei blood cells and to determine the amount of DNA strand breakage associated with apoptosis and necrosis. Cell sensitivity to the mutagens bleomycin (BLM) and 4-nitro-quinoline-1-oxide (4NQO) was also assessed using the Comet assay, as was the assay reproducibility. Alkaline treatment did not lyse the cytoplasmic and nuclear membranes of E. johnstonei blood cells, whereas enzymatic digestion with proteinase K (40 μg/mL) yielded naked nuclei. The contribution of apoptosis and necrosis (assessed by the DNA diffusion assay) to DNA damage was estimated to range from 0% to 8%. BLM and 4NQO induced DNA damage in E. johnstonei blood cells at different concentrations and exposure times. Dose-effect curves with both mutagens were highly reproducible and showed consistently low coefficients of variation (CV ≤ 10%). The results are discussed with regard to the potential use of the modified Comet assay for assessing the exposure of E. johnstonei to herbicides in ecotoxicological studies. PMID:22215974
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Valencia, Laura Carolina; García, Adriana; Ramírez-Pinilla, Martha Patricia; Fuentes, Jorge Luis
2011-10-01
The aim of this study was to use the Comet assay to assess genetic damage in the direct-developing frog Eleutherodactylus johnstonei. A DNA diffusion assay was used to evaluate the effectiveness of alkaline, enzymatic and alkaline/enzymatic treatments for lysing E. johnstonei blood cells and to determine the amount of DNA strand breakage associated with apoptosis and necrosis. Cell sensitivity to the mutagens bleomycin (BLM) and 4-nitro-quinoline-1-oxide (4NQO) was also assessed using the Comet assay, as was the assay reproducibility. Alkaline treatment did not lyse the cytoplasmic and nuclear membranes of E. johnstonei blood cells, whereas enzymatic digestion with proteinase K (40 μg/mL) yielded naked nuclei. The contribution of apoptosis and necrosis (assessed by the DNA diffusion assay) to DNA damage was estimated to range from 0% to 8%. BLM and 4NQO induced DNA damage in E. johnstonei blood cells at different concentrations and exposure times. Dose-effect curves with both mutagens were highly reproducible and showed consistently low coefficients of variation (CV ≤ 10%). The results are discussed with regard to the potential use of the modified Comet assay for assessing the exposure of E. johnstonei to herbicides in ecotoxicological studies.
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Outbursts of H2O in Comet P/Halley
NASA Astrophysics Data System (ADS)
Larson, H. P.; Hu, H.-Y.; Mumma, M. J.; Weaver, H. A.
1990-07-01
Comet Halley gas-production monitoring efforts in March 1986 with the NASA Kuiper Airborne Observatory's Fourier transform spectrometer have indicated rapid temporal variations in H2O emissions; a continuous record of an H2O outburst was thus obtained. The event, in which H2O brightness increased by a factor of 2.2 in less than 10 min, is ascribable to an energetic process in the nucleus whose character may have been that of amorphous H2O ice crystallization, chemical explosion, thermal stress, or a compressed gas pocket. The timing and energy of the event appear to require an internal energy source; amorphous ice crystallization is held to be most consistent with compositional and thermal models of cometary nuclei as well as the observations.
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Preliminary studies of electromagnetic sounding of cometary nuclei
NASA Technical Reports Server (NTRS)
Gabriel, A.; Warne, L.; Bednarczyk, S.; Elachi, C.
1978-01-01
The internal structure of a comet could be determined with a spacecraft borne electromagnetic sounder. A dielectric profile of the comet could be produced in direct analogy with terrestrial glacier and ice sheet sounding experiments. This profile would allow the detection of a rocky core or ice layers if they exist, just as layers in the ice and the bedrock interface have been clearly observed through the Greenland ice sheet. It would also provide a gross estimate of the amount of dust in the icy region. Models for the response of the nucleus and cometary plasma to electromagnetic sounding are developed and used to derive experimental parameters. A point system design was completed. Preliminary engineering study results indicate that the sounder is well within the bounds of current space technology.
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Elemental, isotopic and molecular abundances in comets
NASA Technical Reports Server (NTRS)
Delsemme, A. H.
1986-01-01
The chemical composition of comet nuclei and the factors affecting it are discussed, summarizing the results of recent theoretical, experimental, and observational investigations. Consideration is given to the evidence supporting the view that the nucleus is radially differentiation (except for a thin outer layer), surface differentiation by heat processing and outgassing, and mantle buildup on an undifferentiated core. The nature of the refractory and volatile components is examined, and the elemental and isotopic compositions are given in tables and characterized. The uncertain (except for H2O) molecular composition of the volatile fraction is considered, and it is suggested that some oxides or aldehydes (such as CO, CO2, and H2CO), but no large amounts of fully hydrogenated compounds (such as CH4 and NH3) are included.
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NASA Technical Reports Server (NTRS)
Whipple, Fred L.
1992-01-01
The variations in total brightness of a comet when it is most active, near perihelion, are presently used as the bases of a volatility index (VI) for short-period (SP) and long-period (LP) comets. Volatility does not correlate with period among the LP comets, and thereby shows no 'aging' effect; similarly, the VI measurements are the same for SP and for LP comets and exhibit no correlation with (1) absolute magnitude near perihelion, (2) orbital inclination, or (3) activity index measuring the intrinsic brightness change from great solar distances to the maximum near perihelion. Active comets are shown to be basically alike irrespective of their orbits or 'ages'.
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Rotational behavior of comet nuclei under gravitational perturbations
NASA Technical Reports Server (NTRS)
Oberti, Pascal; Bois, E.; Froeschle, Claude
1992-01-01
A dynamical qualitative study of the rotational motion for cometary-type bodies submitted to gravitational perturbations has been performed by numerical simulations, including the Sun and Jupiter's disturbing torques in the model. Results show small gravitational disturbing effects from the Sun on Halley-type orbits, as well as from Jupiter on most close-approach configurations. Only a very close-approach induces notable effects, presenting then some interesting sensitivity to initial conditions.
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Mustapha, Nadia; Bouhlel, Inès; Chaabane, Fadwa; Bzéouich, Imèn Mokdad; Ghedira, Kamel; Hennebelle, Thierry; Chekir-Ghedira, Leila
2014-02-01
The present study was carried out to characterize the cellular antioxidant effect of the aqueous extract of Crataegus azarolus and its antigenotoxic potential using human myelogenous cells, K562. The antioxidant capacity of this extract was evaluated by determining its cellular antioxidant activity (CAA) in K562 cells. Also, preceding antigenotoxicity assessment, its eventual genotoxicity property was investigated by evaluating its capacity to induce the DNA degradation of treated cell nuclei. As no genotoxicity was detected at different exposure times, its ability to protect cell DNA against H2O2 oxidative effect was investigated, using the "comet assay." It appears that 800 μg/mL of extract inhibited the genotoxicity induced by H2O2 with a rate of 41.30 %, after 4 h of incubation. In addition, this extract revealed a significant cellular antioxidant capacity against the reactive oxygen species in K562 cells.
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PHOTO ILLUSTRATION OF COMET P/SHOEMAKER-LEVY 9 and PLANET JUPITER
NASA Technical Reports Server (NTRS)
2002-01-01
This is a composite photo, assembled from separate images of Jupiter and comet P/Shoemaker-Levy 9, as imaged by the Wide Field and Planetary Camera-2 (WFPC-2), aboard NASA's Hubble Space Telescope (HST). Jupiter was imaged on May 18, 1994, when the giant planet was at a distance of 420 million miles (670 million km) from Earth. This 'true-color' picture was assembled from separate HST exposures in red, blue, and green light. Jupiter's rotation between exposures creates the blue and red fringe on either side of the disk. HST can resolve details in Jupiter's magnificent cloud belts and zones as small as 200 miles (320 km) across (wide field mode). This detailed view is only surpassed by images from spacecraft that have traveled to Jupiter. The dark spot on the disk of Jupiter is the shadow of the inner moon Io. This volcanic moon appears as an orange and yellow disk just to the upper right of the shadow. Though Io is approximately the size of Earth's Moon (but 2,000 times farther away), HST can resolve surface details. When the comet was observed on May 17, its train of 21 icy fragments stretched across 710 thousand miles (1.1 million km) of space, or 3 times the distance between Earth and the Moon. This required six WFPC exposures along the comet train to include all the nuclei. The image was taken in red light. The apparent angular size of Jupiter relative to the comet, and its angular separation from the comet when the images were taken, have been modified for illustration purposes. Credit: H.A. Weaver, T.E. Smith (Space Telescope Science Institute) and J.T. Trauger, R.W. Evans (Jet Propulsion Laboratory), and NASA
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What's Causing the Activity on Comet 67P?
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2015-09-01
Comet 67P/ChuryumovGerasimenko made famous by the explorations of the Rosetta mission has been displaying puzzling activity as it hurtles toward the Sun. However, recent modeling of the comet by a group of scientists from the Cte dAzur University may now explain whats causing 67Ps activity.Shadowed ActivityA model of comet 67P, with the colors indicating the rate of change of the temperature on the comets surface. The most rapid temperature changes are seen at the comets neck, in the same locations as the early activity seen in the Rosetta images. [Al-Lagoa et al. 2015] Between June and September of 2014, Rosetta observed comet 67P displaying early activity in the form of jets of dust emitted from near the neck of the comet (its narrowest point). Such activity is usually driven by the sublimation of volatiles from the comets surface as a result of sun exposure. But the neck of the comet is frequently shadowed as the comet rotates, and it receives significantly less sunlight than the rest of the comet. So why would the early activity originate from the comets neck?The authors of a recent study, led by Victor Al-Lagoa, hypothesize that its precisely because the neck is receiving alternating sunlight/shadows that its displaying activity. They suggest that thermal cracking of the surface of the comet is happening faster in this region, due to the rapid changes in temperature that result from the shadows cast by the surrounding terrain. The cracking exposes subsurface ices in the neck faster than in other regions, and the ensuing sublimation of that ice is what creates the activity were seeing.Temperature Models: To test their hypothesis, the authors study the surface temperatures on comet 67P by means of a thermophysical model a model used to calculate the temperatures on an airless body, both on and below the surface. The model takes into account factors like thermal inertia (how quickly the bodys temperature responds to changes in the incident energy), shadowing, and self-heating between parts of the surface in contact.Plot of the modeled temperature of two typical surfaces on the comet: one from the neck region (solid line) and one from the head region (dashed line). Unlike the head, the neck displays drastic drops in temperature as a result of shadowing. [Al-Lagoa et al. 2015]Using this model, the authors find that the temperatures behaved as they predicted: the shadows falling on the comets neck causes this region to experience very rapid temperature changes relative to the rest of the body. The authors also found a definite correlation between the regions of most rapid temperature variations and the regions of the comet that show signs of activity in Rosetta images. This provides strong evidence that thermal cracking is indeed taking place in the shadowed regions of the neck, gradually eroding away the surface.Should this model prove correct, its a step toward understanding the evolution of comets like 67P. In addition, the results from this study imply that thermal cracking might happen faster than previously estimated in shadowed regions of other atmosphereless bodies, both near Earth and in the asteroid belt.CitationV. Al-Lagoa et al 2015 ApJ 810 L22. doi:10.1088/2041-8205/810/2/L22
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OORT-Cloud and Kuiper-Belt Comets
NASA Technical Reports Server (NTRS)
Whipple, Fred L.
1998-01-01
This paper follows the broadly accepted theory that Oort-Cloud Comets originated in the Solar Nebula in the general region where the major planets, Jupiter and Saturn, were formed while the Kuiper-Belt Comets originated farther out where the temperatures were lower. The Oort-Cloud Comets are identified orbitally by long periods and random inclinations and, including the Halley-type comets, comets with a Tisserand Criterion less than 2.0. Kuiper-Belt comets are identified by short periods, usually much less than 200 years, and small inclinations to the ecliptic. Here two criteria for comet activity are found to separate the two classes of comets. These quantities NG1 and NG2, were intended to measure theoretical nongravitaional effects on comet orbits. They are only, mildly successful in correlations with observed cases of measured non-gravitational forces. But, in fact, their variations with perihelion distance separate the two classes of comets. The results are consistent with the theory that the activity or intrinsic brightness of Oort-Cloud Comets fall off faster with increasing perihelion distance that does the intrinsic brightness of short-period Kuiper-Belt Comets.
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The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
NASA Astrophysics Data System (ADS)
Jones, Geraint H.; Knight, Matthew M.; Battams, Karl; Boice, Daniel C.; Brown, John; Giordano, Silvio; Raymond, John; Snodgrass, Colin; Steckloff, Jordan K.; Weissman, Paul; Fitzsimmons, Alan; Lisse, Carey; Opitom, Cyrielle; Birkett, Kimberley S.; Bzowski, Maciej; Decock, Alice; Mann, Ingrid; Ramanjooloo, Yudish; McCauley, Patrick
2018-02-01
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun's centre, equal to half of Mercury's perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics.
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Comet Kohoutek, 1973-1974, A Teachers' Guide with Student Activities.
ERIC Educational Resources Information Center
Chapman, Robert D.
This teacher's guide provides background information, curriculum source materials, and suggested class activities for class discussion and study. Information related to the discovery of the comet is presented as well as photographic and schematic pictures showing the sky through which the comet travels. Historical data regarding comets of the past…
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Observations of CO2 in Comets C/2012 S1 ISON and C/2012 K1 PANSTARRS
NASA Astrophysics Data System (ADS)
McKay, Adam; Kelley, Michael; DiSanti, Michael; Cochran, Anita; Dello Russo, Neil; Lisse, Carey; Chanover, Nancy
2013-10-01
Comets have undergone very little thermal evolution in their lifetimes, resulting in a primitive composition. This primitive composition makes observations of comets very important tools for understanding the origin of the Solar System. The ices H2O, CO2, and CO are the primary ices present in cometary nuclei, and constraining their abundances has tremendous implications for the formation and evolutionary history of comets. Of these ices, H2O and CO can be observed from the ground, while CO2 cannot. A potentially effective tracer for CO2 in comets that is accessible from the ground is atomic oxygen. However, the relationship between these ices and atomic oxygen is only understood at a qualitative level. We propose to use Spitzer observations in IRAC's 4.5 micron band pass to observe the CO2 v3 band at 4.26 microns in comets C/2012 S1 ISON and C/2012 K1 PANSTARRS. These observations will be coordinated with observations of atomic oxygen obtained at Apache Point Observatory and McDonald Observatory and observations of H2O and CO at Keck and IRTF. These observations of H2O, CO2, and atomic oxygen in a cometary coma will increase our understanding of the link between these primary ices and atomic oxygen. With a complete understanding of the relationship between atomic oxygen and the primary ices on the nucleus, observations of atomic oxygen can serve as a powerful proxy for the production of CO2. In addition, ISON is the target of an extensive observing campaign led by NASA, and the proposed Spitzer observations fill a vital niche as the only observatory that can observe CO2 during both the near-perihelion time frame and significantly (months) after perihelion. Understanding the evolution of the CO2 abundance over the apparition is a key piece to understanding how the volatile compostion of the comet changes over the apparition.
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Comets, Carbonaceous Meteorites, and the Origin of the Biosphere
NASA Technical Reports Server (NTRS)
Hoover, Richard B.
2007-01-01
Evidence for indigenous microfossils in carbonaceous meteorites suggests that the paradigm of the endogenous origin of life on Earth should be reconsidered. It is now widely accepted that comets and carbonaceous meteorites played an important role in the delivery of water, organics and life critical biogenic elements to the early Earth and facilitated the origin and evolution of the Earth's Biosphere. However; the detection of embedded microfossils and mats in carbonaceous meteorites implies that comets and meteorites may have played a direct role in the delivery of intact microorganisms and that the Biosphere may extend far into the Cosmos. Recent space observations have found the nuclei of comets to have very low albedos (approx.0.03) and. these jet-black surfaces become very hot (T approx. 400 K) near perihelion. This paper reviews recent observational data-on comets and suggests that liquid water pools could exist in cavities and fissures between the internal ices and rocks and the exterior carbonaceous crust. The presence of light and liquid water near the surface of the nucleus enhances the possibility that comets could harbor prokaryotic extremophiles (e.g., cyanobacteria) capable of growth over a wide range of temperatures. The hypothesis that comets are the parent bodies of the CI1 and the CM2 carbonaceous meteorites is advanced. Electron microscopy images will be presented showing forms interpreted as indigenous-microfossils embedded' in freshly. fractured interior surfaces of the Orgueil (CI1) and Murchison (CM2) meteorites. These forms are consistent in size and morphologies with known morphotypes of all five orders of Cyanobacteriaceae: Energy Dispersive X-ray Spectroscopy (EDS) elemental data shows that the meteoritic forms have anomalous C/O; C/N; and C/S as compared with modern extremophiles and cyanobacteria. These images and spectral data indicate that the clearly biogenic and embedded remains cannot be interpreted as recent biological contaminants and'therefore are indigenous'microfossils in the meteorites.
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The study of the physics of cometary nuclei
NASA Technical Reports Server (NTRS)
Whipple, F. L.
1984-01-01
The observations of comet P/Holmes 1892III, exhibiting two 8 to 10 magnitude bursts, were carefully analyzed. The phenomena are consistent with the grazing encounter of a small satellite with the nucleus. The grazing encounter produced, besides the first great burst, an active area on the nucleus, which was rotating retrograde with a period of 16.3 hr and inclination nearly 180 deg. After the final encounter, the spin period was essentially unchanged, but two areas became active, separated some 164 deg in longitude on the nucleus. After the first burst the total magnitude fell less than two magnitudes, while the nuclear region remained diffuse or complex, rarely if ever showing a stellar appearance. The fading was much more rapid after the second burst (barely naked eye at maximum) while the nucleus frequently stellar after the first day. It seems reasonable to conclude that the grazing encounter distributed a volume of large chunks in the neighborhood of the nucleus, maintaining activity for weeks.
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NASA Astrophysics Data System (ADS)
Jewitt, David
2017-08-01
Disintegration may be the leading cause of the demise of cometary nuclei yet is rarely observed and not well understood. We propose to use an amazing but largely unpublished archival dataset on comet 73P/Schwassmann-Wachmann 3 from HST in order to characterize the breakup of this body, focussing on components 73-B, 73-C and 73-G from GO 8699, 10625 and 10992. We will measure the number, sizes, velocities and (short-term) photometric variability of the fragments in 73-B and 73-G and derive the ejection speeds and times. A nucleus/coma convolution model will be used to extract the best estimates of fragment and nucleus size. The size distributions and integral masses will be compared to the parent body masses to estimate lifetimes. Lightcurves will be determined to the test the possibility that disintegration is due to rotational instability.
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Electron beam analysis of particulate cometary material
NASA Technical Reports Server (NTRS)
Bradley, John
1989-01-01
Electron microscopy will be useful for characterization of inorganic dust grains in returned comet nucleus samples. The choice of instrument(s) will depend primarily on the nature of the samples, but ultimately a variety of electron-beam methods could be employed. Scanning and analytical (transmission) electron microscopy are the logical choise for morphological, mineralogical, and bulk chemical analyses of dust grains removed from ices. It may also be possible to examine unmelted ice/dust mixtures using an environmental scanning electron microscope equipped with a cryo-transfer unit and a cold stage. Electron microscopic observations of comet nuclei might include: (1) porosities of dust grains; (2) morphologies and microstructures of individual mineral grains; (3) relative abundances of olivine, pyroxene, and glass; and (4) the presence of phases that might have resulted from aqueous alteration (layer silicates, carbonates, sulfates).
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Probing the presently tenuous link between comets and the origin of life
NASA Technical Reports Server (NTRS)
Hobbs, R. W.; Hollis, J. M.
1982-01-01
The possibilities of using millimeter-wave technology to probe the subsurface processes of comets to investigate links between cometary materials and the origins of life are explored. It is noted that current theories hold that the necessities for life to begin comprise a fairly uniform temperature, the presence of a solvent to give materials mobility, and the presence of atoms which can form long chains of molecules. Consideration is given to two cometary nuclei models: a core with an equal amount of liquid water and lunar material, and a nucleus with equal amounts of frozen water ice and lunar material. Solutions to the radiative transfer equation for the two models are presented to characterize identifiable emissions using radiometric spectrometer instrumentation on a spacecraft. Particular species such as OH, CN, HCN, and glycine are expected to be detectable if present.
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Landslides and impacts on comets.
NASA Astrophysics Data System (ADS)
Czechowski, Leszek
2016-07-01
The recent landing of Philae on the comet 67P/Czuriumow-Gierasimienko indicates that elastic properties of comet's nuclei could be similar to elastic properties of dry snow, namely Young modulus is assumed to be 106 - 108 Pa. We considered a simple model of two spheres (with radius 1400 m each) connected by cylinder (with radius of 200 m and length of 200 m). Density is 470 kg m-3. This shape corresponds approximately to shape of some comets. A few vibration modes are possible. In present research we consider 3 modes: bending, lengthening-shortening along axis of symmetry, and torsion. Let assume that comets are hit by small meteoroid of the mass of 1 kg and velocity 20 km s-1. The maximum values of acceleration of the surface resulting from this impact are given in Table 1. Note that these values are higher than acceleration of the gravity of the comet. Consequently, these vibrations could be an important factor of surface evolution, e.g. they could trigger landslides. It could be alternative mechanism to that presented in [4] (i.e. fluidization). Acknowledgement: The research is partly supported by Polish National Science Centre (decision 2014/15/B/ST 10/02117) References [1] T. Spohn, J. Knollenberg, A. J. Ball, M. Ba-naszkiewicz, J. Benkhoff, M. Grott, J. Gry-gorczuk, C. Hüttig, A. Hagermann, G. Kargl, E. Kaufmann, N. Kömle, E. Kührt, K. J. Kossacki, W. Marczewski, I. Pelivan, R. Schrödter, K. Seiferlin. (2015) Thermal and mechanical properties of the near-surface layers of comet 67P/Churyumov- Gera-simenko Science 31 July 2015: Vol. 349 no. 6247 DOI: 10.1126/science.aab0464 [2] Reuter B. (2013) On how to measure snow mechanical properties relevant to slab avalanche release. International Snow Science Workshop Grenoble - Chamonix Mont-Blanc - 2013 007 [3] Ball A.J. (1997) Ph. D. Thesis: Measuring Physical Properties at the Surface of a Comet Nu-cleus, Univ.of Kent U.K. [4] Belton M. J.S., Melosh J. (2009). Fluidization and multiphase transport of particulate cometary material as an explanation of the smooth terrains and repetitive outbursts on 9P/Tempel 1. Icarus 200 (2009) 280-291
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Spin-dependent μ → e conversion
Cirigliano, Vincenzo; Davidson, Sacha; Kuno, Yoshitaka
2017-05-22
The experimental sensitivity to μ→e conversion on nuclei is expected to improve by four orders of magnitude in coming years. Here, we consider the impact of μ→e flavour-changing tensor and axial-vector four-fermion operators which couple to the spin of nucleons. Such operators, which have not previously been considered, contribute to μ→e conversion in three ways: in nuclei with spin they mediate a spin-dependent transition; in all nuclei they contribute to the coherent (A 2-enhanced) spin-independent conversion via finite recoil effects and via loop mixing with dipole, scalar, and vector operators. Furthermore, we estimate the spin-dependent rate in Aluminium (the targetmore » of the upcoming COMET and Mu2e experiments), show that the loop effects give the greatest sensitivity to tensor and axial-vector operators involving first-generation quarks, and discuss the complementarity of the spin-dependent and independent contributions to μ→e conversion.« less
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Spin-dependent μ → e conversion
DOE Office of Scientific and Technical Information (OSTI.GOV)
Cirigliano, Vincenzo; Davidson, Sacha; Kuno, Yoshitaka
The experimental sensitivity to μ→e conversion on nuclei is expected to improve by four orders of magnitude in coming years. Here, we consider the impact of μ→e flavour-changing tensor and axial-vector four-fermion operators which couple to the spin of nucleons. Such operators, which have not previously been considered, contribute to μ→e conversion in three ways: in nuclei with spin they mediate a spin-dependent transition; in all nuclei they contribute to the coherent (A 2-enhanced) spin-independent conversion via finite recoil effects and via loop mixing with dipole, scalar, and vector operators. Furthermore, we estimate the spin-dependent rate in Aluminium (the targetmore » of the upcoming COMET and Mu2e experiments), show that the loop effects give the greatest sensitivity to tensor and axial-vector operators involving first-generation quarks, and discuss the complementarity of the spin-dependent and independent contributions to μ→e conversion.« less
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Singing comet changes its song
NASA Astrophysics Data System (ADS)
Volwerk, M.; Goetz, C.; Delva, M.; Richter, I.; Tsurutani, B. T.; Eriksson, A.; Odelstad, E.; Meier, P.; Nilsson, H.; Glassmeier, K.-H.
2017-09-01
The singing comet was discovered at the beginning of the Rosetta mission around comet 67P/Churyumov-Gerasimenko. Large amplitude compressional waves with frequencies between 10 and 100 mHz were observed. When the comet became more active this signal was no longer measured. During the so-called tail excursion, late in the mission after perihelion, with again a less active comet, the singing was observed again and interestingly, going from 26 March to 27 March 2016 the character of the singing changed.
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Spacewatch Survey of the Solar System
NASA Technical Reports Server (NTRS)
McMillan, Robert S.
2000-01-01
The purpose of the Spacewatch project is to explore the various populations of small objects throughout the solar system. Statistics on all classes of small bodies are needed to infer their physical and dynamical evolution. More Earth Approachers need to be found to assess the impact hazard. (We have adopted the term "Earth Approacher", EA, to include all those asteroids, nuclei of extinct short period comets, and short period comets that can approach close to Earth. The adjective "near" carries potential confusion, as we have found in communicating with the media, that the objects are always near Earth, following it like a cloud.) Persistent and voluminous accumulation of astrometry of incidentally observed main belt asteroids MBAs will eventually permit the Minor Planet Center (MPQ to determine the orbits of large numbers (tens of thousands) of asteroids. Such a large body of information will ultimately allow better resolution of orbit classes and the determinations of luminosity functions of the various classes, Comet and asteroid recoveries are essential services to planetary astronomy. Statistics of objects in the outer solar system (Centaurs, scattered-disk objects, and Trans-Neptunian Objects; TNOs) ultimately will tell part of the story of solar system evolution. Spacewatch led the development of sky surveying by electronic means and has acted as a responsible interface to the media and general public on this discipline and on the issue of the hazard from impacts by asteroids and comets.
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The cometary and asteroidal impactor flux at the earth
NASA Technical Reports Server (NTRS)
Weissman, Paul R.
1988-01-01
The cratering records on the Earth and the lunar maria provide upper limits on the total impactor flux at the Earth's orbit over the past 600 Myr and the past 3.3 Gyr, respectively. These limits can be compared with estimates of the expected cratering rate from observed comets and asteroids in Earth-crossing orbits, corrected for observational selection effects and incompleteness, and including expected temporal variations in the impactor flux. Both estimates can also be used to calculate the probability of large impacts which may result in biological extinction events on the Earth. The estimated cratering rate on the Earth for craters greater than 10 km-diameter, based on counted craters on dated surfaces is 2.2 + or - 1.1 x 10 to the minus 14th power km(-2) yr(-1) (Shoemaker et al., 1979). Using a revised mass distribution for cometary nuclei based on the results of the spacecraft flybys of Comet Halley in 1986, and other refinements in the estimate of the cometary flux in the terrestrial planets zone, it is now estimated that long-period comets account for 11 percent of the cratering on the Earth (scaled to the estimate above), and short-period comets account for 4 pct (Weissman, 1987). However, the greatest contribution is from large but infrequent, random cometary showers, accounting for 22 pct of the terrestrial cratering.
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Science Benefits of Onboard Spacecraft Navigation
NASA Technical Reports Server (NTRS)
Cangahuala, Al; Bhaskaran, Shyam; Owen, Bill
2012-01-01
Primitive bodies (asteroids and comets), which have remained relatively unaltered since their formation, are important targets for scientific missions that seek to understand the evolution of the solar system. Often the first step is to fly by these bodies with robotic spacecraft. The key to maximizing data returns from these flybys is to determine the spacecraft trajectory relative to the target body-in short, navigate the spacecraft- with sufficient accuracy so that the target is guaranteed to be in the instruments' field of view. The most powerful navigation data in these scenarios are images taken by the spacecraft of the target against a known star field (onboard astrometry). Traditionally, the relative trajectory of the spacecraft must be estimated hours to days in advance using images collected by the spacecraft. This is because of (1)!the long round-trip light times between the spacecraft and the Earth and (2)!the time needed to downlink and process navigation data on the ground, make decisions based on the result, and build and uplink instrument pointing sequences from the results. The light time and processing time compromise navigation accuracy considerably, because there is not enough time to use more accurate data collected closer to the target-such data are more accurate because the angular capability of the onboard astrometry is essentially constant as the distance to the target decreases, resulting in better "plane-of- sky" knowledge of the target. Excellent examples of these timing limitations are high-speed comet encounters. Comets are difficult to observe up close; their orbits often limit scientists to brief, rapid flybys, and their coma further restricts viewers from seeing the nucleus in any detail, unless they can view the nucleus at close range. Comet nuclei details are typically discernable for much shorter durations than the roundtrip light time to Earth, so robotic spacecraft must be able to perform onboard navigation. This onboard navigation can be accomplished through a self- contained system that by eliminating light time restrictions dramatically improves the relative trajectory knowledge and control and subsequently increases the amount of quality data collected. Flybys are one-time events, so the system's underlying algorithms and software must be extremely robust. The autonomous software must also be able to cope with the unknown size, shape, and orientation of the previously unseen comet nucleus. Furthermore, algorithms must be reliable in the presence of imperfections and/or damage to onboard cameras accrued after many years of deep-space operations. The AutoNav operational flight software packages, developed by scientists at the Jet Propulsion Laboratory (JPL) under contract with NASA, meet all these requirements. They have been directly responsible for the successful encounters on all of NASA's close-up comet-imaging missions (see Figure !1). AutoNav is the only system to date that has autonomously tracked comet nuclei during encounters and performed autonomous interplanetary navigation. AutoNav has enabled five cometary flyby missions (Table!1) residing on four NASA spacecraft provided by three different spacecraft builders. Using this software, missions were able to process a combined total of nearly 1000 images previously unseen by humans. By eliminating the need to navigate spacecraft from Earth, the accuracy gained by AutoNav during flybys compared to ground-based navigation is about 1!order of magnitude in targeting and 2!orders of magnitude in time of flight. These benefits ensure that pointing errors do not compromise data gathered during flybys. In addition, these benefits can be applied to flybys of other solar system objects, flybys at much slower relative velocities, mosaic imaging campaigns, and other proximity activities (e.g., orbiting, hovering, and descent/ascent).
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Time-dependent evolution of the near nuclear coma of cometary nuclei during their rotational motion
NASA Astrophysics Data System (ADS)
Szego, K.; Crifo, J.-F.; Fulle, M.; Rodionov, A. V.
2003-04-01
The new physical model of Rodionov et al. (Planetary and Space Sci., 50, 983, 2002) that describes the cometary activity based on a 3-d collisional gas dynamical model has been successfully applied to account for the dust features observed by the cameras flying onboard of the VEGA and Giotto probes during the encounter with comet Halley. This indicates, in particular, that these structures are dominantly controlled by the nucleus topography. An upgraded version of this model has been recently developed and is being applied to the vast body of data gathered in 1986 on comet Halley. This new version is tridimensional as previously, and, in addition, time-dependent. This allows the exact, self-consistent computation of the whole coma structure (primary and daughter molecules, dust), allowing to study its dependence upon nucleus shape, composition, and rotation. The results presented here assume that the coma is formed by solar-driven sublimation of a homogeneous dusty-ice nucleus with shape and rotational state derived for P/Halley. The results are, however, of quite general significance -- in particular they remain valid for different shapes and for inhomogeneous nucleus. This presentation focuses on the time dependence of the dust and gas features obtained around the nucleus. Movies will summarize the results of the calculations exhibiting the time development of the dust and gas coma and its relation to the surface orography for a rotating nucleus. The effect of nucleus activity on its rotational motion, and possible constraints hampering the observation of the activity will be also analyzed.
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2010-11-04
This montage from NASA EPOXI mission shows the only five comets imaged up close with spacecraft. The comets vary in shape and size. Comet Hartley 2 is by far the smallest and the most active of small comets.
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An analysis of the BVRI colors of 22 active comets
NASA Astrophysics Data System (ADS)
Betzler, A. S.; Almeida, R. S.; Cerqueira, W. J.; Araujo, L. A.; Prazeres, C. J. M.; Jesus, J. N.; Bispo, P. A. S.; Andrade, V. B.; Freitas, Y. A. S.; Betzler, L. B. S.
2017-08-01
Our aim was to analyze the variation of Johnson-Kron-Cousins BVRI color indexes of a sample with 22 active comets of various dynamic groups with the time, geometrical, observational and dynamical parameters. We performed photometric observations of 16 comets between 2010 and 2014, using robotic telescopes in three continents. In addition to the sample, we used data of six comets available in the literature. A statistical comparison between the distributions of color indexes was performed using the Kruskal-Wallis H-test. The color indexes of active comets can vary a few tenths up to a magnitude on time scales that range from hours to weeks. Using the B-V colors of the observed comets, we generated a relationship that correlates the cometary visual and CCD magnitudes. We did not identify any relationship between B-V and V-R colors with heliocentric distance and phase angle. The color B-V is correlated with the photometric aperture that can be described by a logarithmic function. We did not identify any differences in the distribution of B-V color among the comets analyzed at a confidence level equal to or greater than 95%. The mean color of active comets are B-R = 1.20 ± 0.24 , B-V = 0.76 ± 0.16 and V-R = 0.42 ± 0.16 . Active comets with V-R colors outside the three standard deviation interval can be considered objects with unusual physical characteristics.
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Gamma-ray burst constraints on the galactic frequency of extrasolar Oort Clouds
NASA Technical Reports Server (NTRS)
Shull, J. Michael; Stern, S. Alan
1995-01-01
With the strong Compton Gamma-Ray Observatory/Burst and Transient Source Experiment (CGRO/BATSE) evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approx. equals 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NSs penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequence stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on time scales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating, events. Comparing these estimates to the 3-4 soft gamma-ray repeater sources detected by BATSE, one is forced to conclude that (1) comet impacts on NSs are inefficient at producing gamma rays; or (2) the gamma rays from such events are highly beamed; or (3) the fraction of stars in the galaxy with Oort Clouds like our own is not higher than a few percent.
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Gamma-ray burst constraints on the galactic frequency of extra-solar Oort clouds
NASA Technical Reports Server (NTRS)
Shull, J. Michael; Stern, S. Alan
1994-01-01
With the strong CGRO/BATSE evidence that most gamma-ray bursts do not come from galactic neutron stars, models involving the accretion of a comet onto a neutron star (NS) no longer appear to be strong contenders for explaining the majority of bursts. If this is the case, then it is worth asking whether the lack of an observed galactic gamma-ray burst population provides a useful constraint on the number of comets and comet clouds in the galaxy. Owing to the previously unrecognized structural weakness of cometary nuclei, we find the capture cross sections for comet-NS events to be much higher than previously published estimates, with tidal breakup at distances R(sub b) approximately equals to 4 x 10(exp 10) cm from the NS. As a result, impacts of comets onto field NS's penetrating the Oort Clouds of other stars are found to dominate all other galactic NS-comet capture rates by a factor of 100. This in turn predicts that if comet clouds are common, there should be a significant population of repeater sources with (1) a galactic distribution, (2) space-correlated repetition, and (3) a wide range of peak luminosities and luminosity time histories. If all main sequences stars have Oort Clouds like our own, we predict approximately 4000 such repeater sources in the Milky Way at any time, each repeating on timescales of months to years. Based on estimates of the sensitivity of the CGRO/BATSE instrument and assuming isotropic gamma-ray beaming from such events, we estimate that a population of approximately 20-200 of these galactic NS-Oort Cloud gamma-ray repeater sources should be detectable by CGRO. In addition, if giant planet formation is common in the galaxy, we estimate that the accretion of isolated comets injected to the interstellar medium by giant planet formation should produce an additional source of galactic, nonrepeating events. Comparing these estimates to the three to four soft gamma-ray repeater sources detected by BATSE, one is forced to conclude that (1) comet impacts on NS's are inefficient at producing gamma-rays; or (2) the gamma-rays from such events are highly beamed; or (3) the fraction of stars in the galaxy with Oort Cloud like our own is not higher than a few percent.
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Vega-Giotto flyby missions and cometary cosmogony
NASA Technical Reports Server (NTRS)
Lang, Bruno
1989-01-01
The most important implication of the Vega/Giotto flyby missions to Halley's Comet for cometary cosmogony is the opportunity to absorb the results of the in-situ measurements as made onboard the spacecrafts. Unfortunately the exploration of ejecta form the nucleus was unable to provide an unambiguous definition of the chemical-mineralogical nature of the nucleus: it failed to provide information comparable to that which was expected from a sample return mission. However, the obtained results are significant enough to affect and redirect cosmogonical thinking. Accordingly, the understanding of the cometary-matter dichotomy is modified as deduced from the distiction of water-dominated volitiles and silicate-based non-volitiles. Organic carbon compounds emerge as a major constituent of cometary nuclei. Presently, it is likely that the revision of Whipple's classic concept of the icy conglomerate cannot be avoided. Affected by the Vega/Giotto flyby missions to Hally's Comet, cometary cosmogony seems to enter a new conceptual period. The results of the in-situ measurements (mass spectrometric, UV spectroscopic, and IR spectroscopic) appear to be of basic importance. A chemical explanation is employed to explain the occurrence inside the nuclei of the variety of species, as inferred from the mass spectrometric data, to predict the results of the processes possibly involved. A cosmochemical factor is postulated to operate behind the observed cometary phenomena. The chemistry of the interstellar medium, covering the circumstellar and interstellar dust, advances cometary cosmogony.
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A Survey of Rotation Lightcurves of Small Jovian Trojan Asteroids in the L4 Cloud
NASA Astrophysics Data System (ADS)
French, Linda M.; Stephens, Robert; Warner, Brian; James, David; Rohl, Derrick; Connour, Kyle
2017-10-01
Jovian Trojan asteroids are of interest both as objects in their own right and as possible relics of Solar System formation. Several lines of evidence support a common origin for, and possible hereditary link between, Jovian Trojan asteroids and cometary nuclei. Asteroid lightcurves give information about processes that have affected a group of asteroids including their density. Due to their distance and low albedos, few comet-sized Trojans have been studied. We have been carrying out a survey of Trojan lightcurve properties comparing small Trojan asteroids with comets (French et al 2015). We present new lightcurve information for 39 Trojans less than about 35 km in diameter. We report our latest results and compare them with results from the sparsely-sampled lightcurves from the Palomar Transient Factory (Waszazak et al., Chang et al. 2015). The minimum densities for objects with complete lightcurves are estimated and are found to becomparable to those measured for cometary nuclei. A significant fraction (~40%) of thisobserved small Trojan population rotates slowly (P > 24 hours), with measured periods as over 500 hours (Waszczak et al 2015). The excess of slow rotators may be due to the YORP effect. Results of the Kolmogorov-Smirnov test suggest that the distribution of Trojan rotation rates is dissimilar to those of Main Belt Asteroids of the same size.
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NASA Astrophysics Data System (ADS)
Churyumov, K. I.; Steklov, A. F.; Vidmachenko, A. P.; Dashkiev, G. N.; Steklov, E. A.; Slipchenko, A. S.; Romaniuk, Ya. O.
2016-10-01
1. Reasons for the creation of modern services of terrestrial space monitoring. In recent years, an increasingly important role in an observation of traces of invasions fireball in an Earth's atmosphere, playing artificial earth satellites at low and medium orbits. But the time between such registrations - is about one and a half hours. And consequently, many types of traces of invasions of small fragments of nuclei of comets, asteroids and meteoroids - remain outside of the data. In the interest of safety of large and medium-sized cities need to create a special small basic observatories of terrestrial aerospace monitoring services. 2. Four types of dangerous viruses that may be present in traces of all kinds of dangerous invasions into the sky over our cities. In modern times the most dangerous commonly believed the cosmic viruses in the nuclei of comets and their fragments; orbital recurrent-mutant viruses, bacteria, fungi in an components of Space Debris (for example, in the fragments of space station "Mir"); as well as modern modified and synthetic viruses, that are easy and very effective is possible to apply in the invasion of simple, and suborbital unmanned aerial vehicles, especially with the function of self-destruction, in order to the invasion able to remain latent, secret, poorly registrable. 3. Our plans on criteria experimentation for active operations with a specialized astronomical aviation of special purpose. Essence of the method according to the ideas is very simple; but there are difficulties in its practical implementation. Organizational, registration of tracks of all kinds of dangerous invasions, is carried out from stationary, mobile and aircraft (quadrocopters, drones, unmanned aerial vehicles) astronomical observatories of terrestrial aerospace monitoring services. Registered by us at daytime and twilight traces can be seen from a few minutes, sometimes up to two hours [1, 2, 4, 6-10].
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Drobyshevski, E M; Chesnakov, V A; Sinitsyn, V V
1995-01-01
Many moonlike bodies (M approximately or = 1 Moon) beyond the Martian orbit contain large amounts of dirty ice (approximately 50%) forming thick mantle with the solid phase thermal convection. When a body moves through the inter- or nearplanetary magnetized plasma, electric current is generated in the body and its environment. The current passing through a dirty ice containing up to 10% of organic admixtures produces a lot of electrochemical effects which have a profound impact on its composition. At this stage one can hardly say something definite concerning changes experienced by organics. The changes must occur inevitably and can be of a rather unexpected and far-reaching nature, so deserving a close study. Another obvious effect is a volumetric electrolysis of ice containing alien inclusions. The electrolysis products accumulate in ice in the form of a solid solution which is capable of detonation at 15-20 wt.% of 2H2 + O2. If M > or = 1 Moon (Galilean satellites, Titan), the body loses in explosion a part of its mass in the form of vapor and ice fragments (=short-period comet nuclei), whereas if M < or = 0.2 Moon, the body breaks up totally (the Main Belt asteroids origin approximately 3.9 Byr ago). 2H2 + O2 containing cometary nuclei are capable of burning or suffer new explosions when receiving an additional energy. The combustion in the sublimation products containing also light organics and 2H2 + O2 explains unexpected energetics and nearnuclear chemistry of Comet P/Halley (e.g. great abundances of negative and positive ions, atomic carbon, CO over CO2, origin of CHON particles etc) and its distant outbursts correlated, possibly, with the Solar activity. Thus the electrochemical processes in the dirty ice with organics, along with its subsequent thermal, radiative etc. processing, open up new potentials for explanation and prediction of quite unexpected discoveries.
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NASA Astrophysics Data System (ADS)
Levasseur-Regourd, Anny-Chantal; Agarwal, Jessica; Cottin, Hervé; Engrand, Cécile; Flynn, George; Fulle, Marco; Gombosi, Tamas; Langevin, Yves; Lasue, Jérémie; Mannel, Thurid; Merouane, Sihane; Poch, Olivier; Thomas, Nicolas; Westphal, Andrew
2018-04-01
This review presents our understanding of cometary dust at the end of 2017. For decades, insight about the dust ejected by nuclei of comets had stemmed from remote observations from Earth or Earth's orbit, and from flybys, including the samples of dust returned to Earth for laboratory studies by the Stardust return capsule. The long-duration Rosetta mission has recently provided a huge and unique amount of data, obtained using numerous instruments, including innovative dust instruments, over a wide range of distances from the Sun and from the nucleus. The diverse approaches available to study dust in comets, together with the related theoretical and experimental studies, provide evidence of the composition and physical properties of dust particles, e.g., the presence of a large fraction of carbon in macromolecules, and of aggregates on a wide range of scales. The results have opened vivid discussions on the variety of dust-release processes and on the diversity of dust properties in comets, as well as on the formation of cometary dust, and on its presence in the near-Earth interplanetary medium. These discussions stress the significance of future explorations as a way to decipher the formation and evolution of our Solar System.
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A population of comets in the main asteroid belt.
Hsieh, Henry H; Jewitt, David
2006-04-28
Comets are icy bodies that sublimate and become active when close to the Sun. They are believed to originate in two cold reservoirs beyond the orbit of Neptune: the Kuiper Belt (equilibrium temperatures of approximately 40 kelvin) and the Oort Cloud (approximately 10 kelvin). We present optical data showing the existence of a population of comets originating in a third reservoir: the main asteroid belt. The main-belt comets are unlike the Kuiper Belt and Oort Cloud comets in that they likely formed where they currently reside and may be collisionally activated. The existence of the main-belt comets lends new support to the idea that main-belt objects could be a major source of terrestrial water.
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NASA Technical Reports Server (NTRS)
Broderick, Daniel
2010-01-01
A computational model calculates the excitation of water rotational levels and emission-line spectra in a cometary coma with applications for the Micro-wave Instrument for Rosetta Orbiter (MIRO). MIRO is a millimeter-submillimeter spectrometer that will be used to study the nature of cometary nuclei, the physical processes of outgassing, and the formation of the head region of a comet (coma). The computational model is a means to interpret the data measured by MIRO. The model is based on the accelerated Monte Carlo method, which performs a random angular, spatial, and frequency sampling of the radiation field to calculate the local average intensity of the field. With the model, the water rotational level populations in the cometary coma and the line profiles for the emission from the water molecules as a function of cometary parameters (such as outgassing rate, gas temperature, and gas and electron density) and observation parameters (such as distance to the comet and beam width) are calculated.
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The Internal Structure of Jupiter Family Comet Nuclei: The Talps or Layered Pile Model
NASA Astrophysics Data System (ADS)
Belton, Michael J.; Members of theDeep Impact Science Team
2006-09-01
The characteristics of layered structures seen on the nucleus of Tempel 1 in the Deep Impact images, and also seen on Wild 2 and Borrelly are noted. We consider the implications of the hypothesis that such structures are ubiquitous on Jupiter Family Comets and is an essential element of their internal stucture. If correct this hypothesis implies that the internal structure of JFCs are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for possible compositional changes, is essentially as it was when they were formed. This hypothesis has implications for their place of origin and their subsequent collisional evolution. Current models of the latter are in conflict with this hypothesis. Possible resolutions of this conflict are noted. A new conceptual model of the interior of a typical JFC called the Talps or "layered pile" model is presented.
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Gas Dynamics and Kinetics in the Cometary Coma: Theory and Observations
NASA Technical Reports Server (NTRS)
Combi, Michael R.; Harris, Walter M.; Smyth, William H.
2005-01-01
Our ability to describe the physical state of the expanding coma affects fundamental areas of cometary study both directly and indirectly. In order to convert measured abundances of gas species in the coma to gas production rates, models for the distribution and kinematics of gas species in the coma are required. Conversely, many different types of observations, together with laboratory data and theory, are still required to determine coma model attributes and parameters. Accurate relative and absolute gas production rates and their variations with time and from comet to comet are crucial to our basic understanding of the composition and structure of cometary nuclei and their place in the solar system. We review the gas dynamics and kinetics of cometary comae from both theoretical and observational perspectives, which are important for understanding the wide variety of physical conditions that are encountered.
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Comet rendezvous mission study
NASA Technical Reports Server (NTRS)
Friedlander, A. L.; Wells, W. C.
1971-01-01
Four periodic comets with perihelia between 1980 and 1986 (Encke, d'Arrest, Kipff, and Halley) are used as candidates for the comet rendezvous mission study. All these comet apparitions are especially favorable for rendezvous missions, because of early earth-based comet recovery, good opportunities to view their activity from earth, and reasonable launch vehicle and trajectory requirements for nominal payloads.
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Reis, Gabriela Barreto Dos; Andrade-Vieira, Larissa Fonseca; Moraes, Isabella de Campos; César, Pedro Henrique Souza; Marcussi, Silvana; Davide, Lisete Chamma
2017-08-01
Comet assay is an efficient test to detect genotoxic compounds based on observation of DNA damage. The aim of this work was to compare the results obtained from the comet assay in two different type of cells extracted from the root tips from Lactuca sativa L. and human blood. For this, Spent Pot Liner (SPL), and its components (aluminum and fluoride) were applied as toxic agents. SPL is a solid waste generated in industry from the aluminum mining and processing with known toxicity. Three concentrations of all tested solutions were applied and the damages observed were compared to negative and positive controls. It was observed an increase in the frequency of DNA damage for human leukocytes and plant cells, in all treatments. On human leukocytes, SPL induced the highest percentage of damage, with an average of 87.68%. For root tips cells of L. sativa the highest percentage of damage was detected for aluminum (93.89%). Considering the arbitrary units (AU), the average of nuclei with high levels of DNA fragmentation was significant for both cells type evaluated. The tested cells demonstrated equal effectiveness for detection of the genotoxicity induced by the SPL and its chemical components, aluminum and fluoride. Further, using a unique method, the comet assay, we proved that cells from root tips of Lactuca sativa represent a reliable model to detect DNA damage induced by genotoxic pollutants is in agreement of those observed in human leukocytes as model. So far, plant cells may be suggested as important system to assess the toxicological risk of environmental agents. Copyright © 2017 Elsevier Inc. All rights reserved.
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1994-07-07
This is a composite photo, assembled from separate images of Jupiter and Comet P/Shoemaker-Levy 9 as imaged by the Wide Field & Planetary Camera-2 (WFPC-2), aboard NASA's Hubble Space Telescope (HST). Jupiter was imaged on May 18, 1994, when the giant planet was at a distance of 420 million miles (670 million KM) from Earth. This 'true-color' picture was assembled from separate HST exposures in red, blue, and green light. Jupiter's rotation between exposures creates the blue and red fringe on either side of the disk. HST can resolve details in Jpiter's magnifient cloud belts and zones as small as 200 miles (320 km) across (wide field mode). This detailed view is only surpassed by images from spacecraft that have traveled to Jupiter. The dark spot on the disk of Jupiter is the shadow of the inner moon Io. This volcanic moon appears as an orange and yellow disk just to the upper right of the shadow. Though Io is approximately the size of Earth's Moon (but 2,000 times farther away), HST can resolve surface details. When the comet was observed on May 17, its train of 21 icy fragments stretched across 710 thousand miles (1.1 million km) of space, or 3 times the distance between Earth and the Moon. This required six WFPC exposures along the comet train to include all the nuclei. The image was taken in red light. The apparent angular size of Jupiter relative to the comet, and its angular separation from the comet when the images were taken, have been modified for illustration purposes. CREDIT: H.A. Weaver, T.E. Smith (Space Telescope Science Institute (STSI)) and J.T. Tranuger, R.W. Evans (Jet Propulsion Laboratory (JPL)) and NASA. (HST ref: STSci-PR94-26a)
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Mineral abundances of comet 17P/Holmes derived from the mid-infrared spectrum
NASA Astrophysics Data System (ADS)
Shinnaka, Yoshiharu; Yamaguchi, MItsuru; Ootsubo, Takafumi; Kawakita, Hideyo; Sakon, Itsuki; Honda, Mitsuhiko; Watanabe, Jun-ichi
2017-10-01
Dust grains of crystalline silicate, which is rarely presented in an interstellar space, were found in cometary nuclei (Messenger et al. 1996, LPI, 27, 867; Wooden et al. 1999, ApJ, 517, 1058, references therein). It is thought that these crystalline silicates had formed by annealing or condensations of amorphous grains near the Sun in the solar nebula, and incorporated into a cometary nucleus in a cold region (farther than formation regions of the crystalline silicates) by radial transportation in the solar nebula. It is considered that transportation mechanisms to outside of the solar nebula were turbulent and/or X-wind. An abundance of the crystalline dust grains was therefore expected to be smaller as far from the Sun (Gail, 2001, A&A, 378, 192; Bockelée-Morvan et al. 2002, A&A, 384, 1107). Namely, the abundance ratio of the crystalline silicate in cometary dust grains relates a degree of mass transportation and a distance from the Sun when cometary nucleus formed in the Solar nebula. The mass ratio of crystalline silicates of dust grains is determined from by Si-O stretching vibrational bands of silicate grains around 10 μm using difference of spectral band features between crystalline and amorphous grains. We present the crystalline-to-amorphous mass ratio of silicate grains in the comet 17P/Holmes by using the thermal emission mode of the dust grains (Ootsubo et al. 2007, P&SS, 55, 1044) applied to the mid-infrared spectra of the comet. These spectra were taken by the COMICS mounted on the Subaru Telescope on 2007 October 25, 26, 27 and 28 immediately after the great outburst of the comet (started on October 23). We discuss about formation conditions of the nucleus of the comet based on the derived mass ratio of silicate grains of the comet.
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Structure and Formation of Comets: Updates from Post-Rosetta Solid Fraction Analyses
NASA Astrophysics Data System (ADS)
Levasseur-Regourd, A. C.; Bentley, M. S.; Kofman, W. W.; Brouet, Y.; Ciarletti, V.; Hadamcik, E.; Herique, A.; Lasue, J.; Mannel, T.; Schmied, R.
2016-12-01
The combination of investigations of 67P/C-G by Rosetta, theoretical and experimental studies, and remote observations allowed unprecedented insight into the structure and formation of comets. Rosetta mission has provided ground-truth for the low-density and high porosity of the nucleus, without heterogeneities larger than a few meters in its small lobe [1,2]. Further studies related to CONSERT experiment now suggest that the porosity increases inside the nucleus [3,4]. Rosetta has also provided ground-truth for the aggregated structure of dust particles within a wide range of sizes in the inner coma [e.g. 5-7]. Such discoveries confirm previous interpretations of remote observations of solar light scattered by dust in cometary comae. Differences in structure between the two parts of the nucleus, strongly suspected from previous high-resolution images of the surface [8] and possibly suggested from some remote observations in fragmenting sub-nuclei [9], might be pointed out from data obtained shortly before Rosetta controlled descent in September 2016. Further analyses by MIDAS of dust particles morphology at submicron-sizes [7,10], as well as compilations of remote observations of solar light scattered by 67P/C-G [11], are presently taking place. We will discuss how such results could lead to a better understanding of dust growth processes during the formation, specifically of 67P/C-G, and more generally, thanks to the link now provided between structural properties of dust and remote polarimetric observations, of comet's nuclei in the early Solar System. References. 1 Kofman et al. Science 2015. 2 Pätzold et al. Nature 2016. 3 Ciarletti et al. A&A 2015. 4 Brouet et al. MNRAS 2016 (under revision). 5. Rotundi et al. Science 2015. 6 Langevin et al. Icarus 2016. 7 Bentley et al. Nature 2016. 8 Massironi et al. Nature 2016. 9 Hadamcik et al. A&A 2016. 10. Mannel et al. Leiden symposium 2016. 11 Hadamcik et al. Leiden symposium 2016.
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Modeling Subsidence-Like Events on Cometary Nuclei
NASA Astrophysics Data System (ADS)
Rosenberg, Eric; Prialnik, Dina
2017-10-01
There is ample evidence, particularly from the Rosetta mission, that cometary nuclei have very low tensile strength. Consequently, morphological changes are expected to occur, caused by buildup of pressure due to gas release in the interior of the nucleus. Such changes have been observed on the surface of comet 67P/Churyumov-Gerasimenko, as reported for example by Groussin et al.(2015). A mechanism for explaining comet surface depressions has been recently proposed by Prialnik & Sierks (2017). Here we report on a numerical study, elaborating on this mechanism. Essentially, the model considers a cometary nucleus composed of a low-density mixture of ice and dust, assuming that the ice is amorphous and traps volatile gasses, such as CO and CO2. The model assumes that the tensile strength of the subsurface material is low and that the surface is covered by a thin crust of low permeability. As the comet evolves, the amorphous ice crystallizes, and the crystallization front recedes from the surface, releasing the trapped gasses, which accumulate beneath the surface, building up pressure. The gas pressure weakens the material strength, but sustains the gas-filled layer against hydrostatic pressure. Eventually, the gas will break its way through the outer crust in an outburst. The rapid pressure drop may cause the collapse of the gas depleted layer, as seen on the nucleus of 67P/Churyumov-Gerasimenko. This mechanism is similar to subsidence events in gas fields on earth.We have performed quasi-3D numerical simulations in an attempt to determine the extent of the area that would be affected by such a mechanism. The frequency of such subsidence events and the depth of the collapse are investigated as functions of solar angle and spin axis inclination. The necessary conditions for outburst-induced collapse are determined and confronted with observations.References:Groussin, O., Sierks, H., et al. 2015, A&A, 583, A35Prialnik, D. & Sierks, H., 2017, MNRAS, in press
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Cometary coma ions. [which occur when water is the major constituent
NASA Technical Reports Server (NTRS)
Aikin, A. C.
1974-01-01
For comets whose nuclei are composed of water ice conglomerates it is shown that the ion H3O(+) can predominate to distances of 5000 km in the subsolar direction. Beyond this distance H2O(+) is the most important ion. The crossover point is a sensitive function of the rate of evaporation from the nucleus. The presence of ammonia or metals such as sodium, in concentrations greater than 0.1% H2O, can lead to NH4(+) and Na(+) ions.
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Modeling the Thermodynamic Properties of the Inner Comae of Comets
NASA Astrophysics Data System (ADS)
Boice, Daniel C.
2017-10-01
Introduction: Modeling is central to understand the important properties of the cometary environment. We have developed a comet model, SUISEI, that self-consistently includes the relevant physicochemical processes within a global modeling framework, from the porous subsurface layers of the nucleus to the interaction with the solar wind. Our goal is to gain valuable insights into the intrinsic properties of cometary nuclei so we can better understand observations and in situ measurements. SUISEI includes a multifluid, reactive gas dynamics simulation of the dusty coma (ComChem) and a suite of other coupled numerical simulations. This model has been successfully applied to a variety of comets in previous studies over the past three decades. We present results from a quantitative study of the thermodynamic properties and chemistry of cometary comae as a function of cometocentric and heliocentric distance to aid in interpretation of observations and in situ measurements of comets.Results and Discussion: ComChem solves the fluid dynamic equations for the mass, momentum, and energy of three neutral fluids (H, H2, and the heavier bulk fluid), ions, and electrons. In the inner coma, the gas expands, cools, accelerates, and undergoes many photolytic and gas-phase chemical reactions tracking hundreds of sibling species. The code handles the transition to free molecular flow and describes the spatial distribution of species in the coma of a comet. Variations of neutral gas temperature and velocity with cometocentric distance and heliocentric distance for a comet approaching the Sun from 2.5 to 0.3 AU are presented. Large increases in the gas temperatures (>400 K) due to photolytic heating in the coma within ~0.5 AU are noted, with dramatic effects on the chemistry, optical depth, and other coma properties. Results are compared to observations when available.Conclusions: SUISEI has proven to be a unique and valuable model to understand the relevant physical processes and properties of small Solar System bodies, including near-Sun comets and asteroids.Acknowledgments: This work was supported by FAPESP under Grant No. 2015/03176-8 and the National Science Foundation Planetary Astronomy Program Grant No. 0908529.
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The gas production rate of periodic comet d'Arrest
NASA Technical Reports Server (NTRS)
Festou, Michel C.; Feldman, Paul D.; Ahearn, Michael F.
1992-01-01
Comet P/d'Arrest is a potential target for a rendezvous mission to a short period comet. Its light curve is rather peculiar, the comet being active only after perihelion passage. One apparition out of two is easy to observe from the ground. The 1995 apparition of the comet will offer a unique opportunity to characterize the outgassing properties of its nucleus.
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High-molecular-weight organic matter in the particles of comet 67P/Churyumov-Gerasimenko.
Fray, Nicolas; Bardyn, Anaïs; Cottin, Hervé; Altwegg, Kathrin; Baklouti, Donia; Briois, Christelle; Colangeli, Luigi; Engrand, Cécile; Fischer, Henning; Glasmachers, Albrecht; Grün, Eberhard; Haerendel, Gerhard; Henkel, Hartmut; Höfner, Herwig; Hornung, Klaus; Jessberger, Elmar K; Koch, Andreas; Krüger, Harald; Langevin, Yves; Lehto, Harry; Lehto, Kirsi; Le Roy, Léna; Merouane, Sihane; Modica, Paola; Orthous-Daunay, François-Régis; Paquette, John; Raulin, François; Rynö, Jouni; Schulz, Rita; Silén, Johan; Siljeström, Sandra; Steiger, Wolfgang; Stenzel, Oliver; Stephan, Thomas; Thirkell, Laurent; Thomas, Roger; Torkar, Klaus; Varmuza, Kurt; Wanczek, Karl-Peter; Zaprudin, Boris; Kissel, Jochen; Hilchenbach, Martin
2016-10-06
The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley. Such matter is generally thought to have originated in the interstellar medium, but it might have formed in the solar nebula-the cloud of gas and dust that was left over after the Sun formed. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization. Many gaseous organic molecules, however, have been observed; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov-Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites' parent bodies. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.
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NASA Technical Reports Server (NTRS)
Lindstrom, David J.; Lindstrom, Richard M.
1989-01-01
Prompt gamma activation analysis (PGAA) is a well-developed analytical technique. The technique involves irradiation of samples in an external neutron beam from a nuclear reactor, with simultaneous counting of gamma rays produced in the sample by neutron capture. Capture of neutrons leads to excited nuclei which decay immediately with the emission of energetic gamma rays to the ground state. PGAA has several advantages over other techniques for the analysis of cometary materials: (1) It is nondestructive; (2) It can be used to determine abundances of a wide variety of elements, including most major and minor elements (Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Co, Ni), volatiles (H, C, N, F, Cl, S), and some trace elements (those with high neutron capture cross sections, including B, Cd, Nd, Sm, and Gd); and (3) It is a true bulk analysis technique. Recent developments should improve the technique's sensitivity and accuracy considerably.
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EVIDENCE FOR FRESH FROST LAYER ON THE BARE NUCLEUS OF COMET HALE-BOPP AT 32 AU DISTANCE
DOE Office of Scientific and Technical Information (OSTI.GOV)
Szabo, Gyula M.; Kiss, Laszlo L.; Pal, Andras
2012-12-10
Here, we report that the activity of comet Hale-Bopp ceased between late 2007 and 2009 March, at about 28 AU distance from the Sun. At that time, the comet resided at a distance from the Sun that exceeded the freeze-out distance of regular comets by an order of magnitude. A Herschel Space Observatory PACS scan was taken in mid-2010, in the already inactive state of the nucleus. The albedo has been found to be surprisingly large (8.1% {+-} 0.9%), which exceeds the value known for any other comets. With re-reduction of archive Hubble Space Telescope images from 1995 and 1996,more » we confirm that the pre-perihelion albedo resembled that of an ordinary comet and was smaller by a factor of two than the post-activity albedo. Our further observations with the Very Large Telescope also confirmed that the albedo increased significantly by the end of the activity. We explain these observations by proposing gravitational redeposition of icy grains toward the end of the activity. This is plausible for such a massive body in a cold environment, where gas velocity is lowered to the range of the escape velocity. These observations also show that giant comets are not just the upscaled versions of the comets we know but can be affected by processes that are yet to be fully identified.« less
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Rosetta/VIRTIS investigation of the chemistry and activity of comet 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Bockelee-Morvan, Dominique; Drossart, Pierre; Piccioni, Giuseppe; Migliorini, Alessandra; Erard, Stéphane; Capaccioni, Fabrizio; Filacchione, Gianrico; Fougere, Nicolas; Leyrat, Cedric; Crovisier, Jacques; Capaccioni, Fabrizio
2016-07-01
The composition of cometary ices inside cometary nuclei provides clues to the chemistry of the protoplanetary disk where they formed, 4.6 Gyr ago. These ices sublimate when the body approches the Sun, so that the coma molecular species give insights on the nucleus surface and sub-surface composition. So far, most investigations of the coma chemical composition were performed from telescopic observations from the ground or space plateforms. Since August 2014, the ESA/Rosetta spacecraft has been investigating the nucleus and inner coma of 67P/Churyumov-Gerasimenko. This talk will present an overview of the results obtained by the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument onboard Rosetta, focussing on observations of molecular species. VIRTIS is composed of two channels. The VIRTIS-M channel is a spectro-imager covering the 0.27-5.1 microns range, which allowed us to map the spatial distribution of H2O and CO2 (Migliorini et al. 2016, A&A in press). VIRTIS-H is a high-spectral resolution spectrometer covering the 2-5 microns range. Spectra obtained with VIRTIS-H show signatures of H2O, CO2 (both fundamental and hot bands), 13CO2, CH4 and other C-H bearing species (Bockelee-Morvan et al. A&A, 583, A6,2015). VIRTIS is a key instrument to investigate regional, diurnal and seasonal variations of the comet outgassing.
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Linking surface morphology, composition and activity on the 67P/Churyumov-Gerasimenko’s nucleus
NASA Astrophysics Data System (ADS)
Fornasier, Sonia; Hoang, Van Hong; Hasselmann, Pedro H.; Barucci, Maria Antonieta; Feller, Clement; Prasanna Deshapriya, Jasinghege Don; Keller, Horst Uwe; OSIRIS Team
2017-10-01
The Rosetta mission orbited around the comet 67P/Churyumov-Gerasimenko for more than 2 years, getting an incredible amount of unique data of the comet nucleus and inner coma. This has enabled us to study its activity continuously from 4 AU inbound to 3.6 AU outbound, including the perihelion passage at 1.25 AU.This work focuses on the identification of the regions sources of faint jets and outbursts, and on the study of their spectrophotometric properties, from observations acquired with the OSIRIS/NAC camera during the July-October 2015 period, i.e. close to perihelion. More than 150 jets of different intensities were identified directly on the nucleus from NAC color sequences acquired in 7-11 filters covering the 250-1000 nm wavelength range, and their spectrophotometric properties studied for the first time. Some spectacular outbursts appear dominated by water ice particles, while fainter jets often show colors redder than the nucleus and appear dominated by dusty particles. Some jets are very faint and were identified on the nucleus thanks to the unprecedented spatial and temporal resolution of the ROSETTA/OSIRIS observations. Some of them have an extremely short lifetime, appearing on the cometary surface during the color sequence observations, reaching their peak in flux and then vanishing in less than a couple of minutes.We will present the results on the location, duration, and colors of active sources on the 67P nucleus from the relatively low resolution (i.e. 6-10 m/pixel) images acquired close to the perihelion passage. Some of this active regions were observed and investigated in higher resolution (up to few dm per pixel) during other phases of the mission. These observations allow us to study the morphological and spectral evolution of the regions found to be active and to further investigate the link between morphology, composition, and activity on cometary nuclei.
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The Uncertain Nature of Cometary Motions
NASA Technical Reports Server (NTRS)
Yeomans, Donald K.
1997-01-01
The number of active short- and long-periodic comets crossing the Earth's orbit each year is less than 10 percent of the corresponding number of asteroids crossing the Earth's orbit. However, the higher relative velocities of comets with respect to the Earth and the uncertainties associated with accurately computing their future trajectories can cause considerable problems when assessing the risks of Earth-crossing objects. Unlike asteroids, the motions of active comets are often affected by so-called nongravitational (outgassing) forces that are imperfectly modeled. In addition, the astrometric optical observations that are used to refine a comet's orbit are often imprecise because a comet's center of mass can be hidden by atmospheric gas and dust. For long-period comets, there is the additional problem of having to base orbital solutions on relatively short observational data intervals. Long-term numerical integrations extending two centuries into the future have been carried out to investigate upcoming Earth-close approaches by known periodic comets. Error analyses and impact probabilities have been computed for those comets that will pass closest to the Earth. Although there are no known comets that will make dangerously close Earth approaches in the next two centuries, there are a few objects that warrant future monitoring.
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The Chandra X-Ray Observatory and its Role for the Study of Ionized Plasmas
NASA Technical Reports Server (NTRS)
Weisskopf, Martin C.
2010-01-01
NASA's Chandra X-Ray Observatory was launched in July of 1999. Featuring a 1000cm2-class X-ray telescope with sub-arcsecond angular resolution, the Observatory has observed targets from the solar system including the earth s moon, comets, and planets to the most distant galaxy clusters and active galactic nuclei. Capable of performing moderate energy resolution image-resolved spectroscopy using its CCD detectors, and high-resolution grating spectroscopy, the Observatory has produced, and continues to produce, valuable data and insights into the emission mechanisms of the ionized plasmas in which the X-rays originate. We present a brief overview of the Observatory to provide insight as to how to use it for your investigations. We also present an, admittedly brief and biased, overview of some of the results of investigations performed with Chandra that may be of interest to this audience.
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Asteroids, Comets, Meteors 2014
NASA Astrophysics Data System (ADS)
Muinonen, K.; Penttilä, A.; Granvik, M.; Virkki, A.; Fedorets, G.; Wilkman, O.; Kohout, T.
2014-08-01
Asteroids, Comets, Meteors focuses on the research of small Solar System bodies. Small bodies are the key to understanding the formation and evolution of the Solar System, carrying signals from pre-solar times. Understanding the evolution of the Solar System helps unveil the evolution of extrasolar planetary systems. Societally, small bodies will be important future resources of minerals. The near-Earth population of small bodies continues to pose an impact hazard, whether it be small pieces of falling meteorites or larger asteroids or cometary nuclei capable of causing global environmental effects. The conference series entitled ''Asteroids, Comets, Meteors'' constitutes the leading international series in the field of small Solar System bodies. The first three conferences took place in Uppsala, Sweden in 1983, 1985, and 1989. The conference is now returning to Nordic countries after a quarter of a century. After the Uppsala conferences, the conference has taken place in Flagstaff, Arizona, U.S.A. in 1991, Belgirate, Italy in 1993, Paris, France in 1996, Ithaca, New York, U.S.A. in 1999, in Berlin, Germany in 2002, in Rio de Janeiro, Brazil in 2005, in Baltimore, Maryland, U.S.A. in 2008, and in Niigata, Japan in 2012. ACM in Helsinki, Finland in 2014 will be the 12th conference in the series.
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Dimensions and Fragmentation of the Nuclei of Comet Shoemaker-Levi 9
NASA Technical Reports Server (NTRS)
Sekanina, Zdenek
1994-01-01
Central regions on the digital maps of 13 nuclear condensations of Comet Shoemaker-Levi 9, obtained with the Planetary Camera of the Hubble Space Telescope on January 27, March 30, and July 4, 1994, have been analyzed with the aim to identify the presence of distinct, major fragments in each condensation, to deconvolve their contributions to the signal that also includes the contribution from a surrounding cloud of dust (modeled as an extended source, using two different laws), to estimate the dimensions of the fragments and to study their temporal variations, and to determine the spatial distributions of the fragments as projected on to the plane of the sky. The deconvolution method applied is described and the results of the analysis are summarized, including the finding that sizable fragments did survive until the time of atmospheric entry. This result does not contradict evidence of the comet's continuing, apparently spontaneous fragmentation, which still went on long after the extremely close approach to Jupiter in July 1992 and which, because of the Jovian tidal effects, may have intensified in the final days before the crash on Jupiter. Since the developed approach is based on certain premises and involves approximations, the results should be viewed as preliminary and the problem should be the subject of further investigation.
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Primary DNA damage in chrome-plating workers.
Gambelunghe, A; Piccinini, R; Ambrogi, M; Villarini, M; Moretti, M; Marchetti, C; Abbritti, G; Muzi, G
2003-06-30
In order to evaluate the primary DNA damage due to occupational exposure to chromium (VI), DNA strand-breaks and apoptosis in peripheral lymphocytes were measured in a group of 19 chrome-plating workers. DNA strand-breaks was assessed by alkaline (pH>13) single-cell microgel electrophoresis ('comet') assay, while apoptosis was measured by flow-cytometry after propidium iodide staining of the cells. Concentrations of chromium in urine, erythrocytes and lymphocytes were investigated as biological indicators of exposure. A group of 18 hospital workers (control group I) and another 20 university personnel (control group II) without exposure to chromium were also studied as controls. The results of the study show that chrome-plating workers have higher levels of chromium in urine, erythrocytes and lymphocytes than unexposed workers. Comet tail moment values, assumed as index of DNA damage, are increased in chromium-exposed workers and results are significantly correlated to chromium lymphocyte concentrations. No difference emerged in the percentage of apoptotic nuclei in exposed and unexposed workers. The study confirms that measurements of chromium in erythrocytes and lymphocytes may provide useful information about recent and past exposure to hexavalent chromium at the workplace. The increase in DNA strand-breaks measured by comet assay suggests this test is valid for the biological monitoring of workers exposed to genotoxic compounds such as chromium (VI).
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A Model for the Breakup of Comet Linear (C/1999 S4)
NASA Technical Reports Server (NTRS)
Samarasinha, Nalin H.
2001-01-01
We propose a mechanism based on the rubble-pile hypothesis of the cometary nucleus (Weissman 1986) to explain the catastrophic breakup of comet LINEAR (C/1999 S4) observed during July-August 2000. We suggest that a solid nucleus made up of 10-100 m "cometesimals" (Weidenschilling 1997) contains a network of inter-connected voids in the inter-cometesimal regions. The production of super-volatile (i.e., species more volatile than water) gases into these voids occurs due to the thermal wave propagating through the nucleus and associated phase transitions of water ice. The network of voids provides an efficient pathway for rapid propagation of these gases within the nucleus resulting in gas pressure caused stresses over a wide regime of the nucleus. This provides a mechanism for catastrophic breakups of small cometary nuclei such as comet LINEAR (C/1999 S4) as well as for some observed cometary outbursts including those that occur at large heliocentric distances (e.g., West et al. 1991). We emphasize the importance of techniques such as radar reflection tomography and radiowave transmission tomography (e.g., Kofman et al. 1998) aboard cometary missions to determine the three dimensional structure of the nucleus in particular the extent of large scale voids.
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Observational Search for Cometary Aging Processes
NASA Technical Reports Server (NTRS)
Meech, Karen J.
1997-01-01
The scientific objectives of this study were (i) to search for physical differences in the behavior of the dynamically new comets (those which are entering the solar system for the first time from the Oort cloud) and the periodic comets, and (ii) to interpret these differences, if any, in terms of the physical and chemical nature of the comets and the evolutionary histories of the two comet groups. Because outer solar system comets may be direct remnants of the planetary formation processes, it is clear that the understanding of both the physical characteristics of these bodies at the edge of the planet forming zone and of their activity at large heliocentric distances, r, will ultimately provide constraints on the planetary formation process both in our Solar System and in extra-solar planetary systems. A combination of new solar system models which suggest that the protoplanetary disk was relatively massive and as a consequence comets could form at large distances from the sun (e.g. from the Uranus-Neptune region to the vicinity of the Kuiper belt), observations of activity in comets at large r, and laboratory experiments on low temperature volatile condensation, are dramatically changing our understanding of the chemical'and physical conditions in the early solar nebula. In order to understand the physical processes driving the apparent large r activity, and to address the question of possible physical and chemical differences between periodic, non-periodic and Oort comets, the PI has been undertaking a long-term study of the behavior of a significant sample of these comets (approximately 50) over a wide range of r to watch the development, disappearance and changing morphology of the dust coma. The ultimate goal is to search for systematic physical differences between the comet classes by modelling the coma growth in terms of volatile-driven activity. The systematic observations for this have been ongoing since 1986, and have been obtained over the course of approximately 300 nights using the telescopes on Mauna Kea, Kitt Peak, Cerro Tololo, the European Southern Observatory, and several other large aperture facilities. A greater than 2 TB database of broad band comet images has been obtained which follows the systematic development and fading of the cometary coma for the comets in the database. The results to date, indicate that there is a substantial difference in the brightness and the amount of dust as a function of r between the two comet classes. In addition to this major finding, the program has been responsible for several exciting discoveries, including: the P/Halley outburst at r = 14.3 AU, the discovery of Chiron's coma and modelling and observations of the gravitationally bound component, observational evidence that activity continues out beyond r = 17 AU for many dynamically new comets
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Combi, M. R.; Aptekar, G.; Bertaux, J.-L.
2014-06-01
Comets C/2011 L4 (PanSTARRS) and C/2012 F6 (Lemmon) were observed throughout their 2012-2013 apparitions with the Solar Wind Anisotropies (SWAN) all-sky hydrogen Lyα camera on board the Solar and Heliosphere Observatory (SOHO) satellite. SOHO has been in a halo orbit around the L1 Earth-Sun Lagrange point since early 1996 and has been observing the interplanetary medium and comets beginning with C/1996 B2 (Hyakutake). The global water production from these comets was determined from an analysis of the SWAN Lyα camera observations. Comet C/2011 L4 (PanSTARRS), which reached its perihelion distance of 0.302 AU on 2013 March 10.17, was observed onmore » 50 days between 2013 January 29 and April 30. Comet C/2012 F6 (Lemmon), which reached its perihelion distance of 0.731 AU on 2013 March 24.51, was observed on 109 days between 2012 November 29 and 2013 June 31. The maximum water production rates were ∼1 × 10{sup 30} molecules s{sup –1} for both comets. The activities of both comets were asymmetric about perihelion. C/2011 L4 (PanSTARRS) was more active before perihelion than after, but C/2012 F6 (Lemmon) was more active after perihelion than before.« less
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NASA Technical Reports Server (NTRS)
Wooden, D. H.; Woodward, C. E.; Harker, D. E.
2002-01-01
We report on observations and analysis of HIFOGS 10 microns spectrophotometry of short period comet 19P/Borrelly on 2003 October 13, 15 UT at the NASA IRTF. 19P/Borrelly is one of two short period comets, comet 4PIFaye being the other, to have a silicate feature detected. During Borrelly s perihelion passage in 1994 December, a silicate feature was present with a flux-to-continuum ratio of 0.25. Two apparitions later in 2003 October, the silicate feature is absent. Thermal emission modeling using amorphous olivine and amorphous carbon shows that a slight increase in grain size accounts for the disappearance of the silicate feature. Analysis of 19P/Borrelly suggests grain size, and not the absence of olivine minerals, may be responsible for the absence of silicate features in most short period comets. 19P/Borrelly is one of the more active short period comets. However, short period comets as a family are less active than long period comets. Short period comets probably originated in the Kuiper Belt and suffered collisions while in residence in the outer solar system. Upon evolution into orbits that take them through the inner solar system, the surfaces of short period comets are exposed to sunlight through their many perihelion passages. This is in contrast to long period comets which probably originated near Jupiter and were expelled to the Oort cloud where they have existed and been exposed to cosmic ray processing. By studying the grain properties in short period comets and comparing to long period comets, we compare the effects on the grain populations of different parent body evolution histories. Upcoming opportunities to study short and long period comets will be advertised.
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DYNAMIC DEUTERIUM ENRICHMENT IN COMETARY WATER VIA ELEY–RIDEAL REACTIONS
DOE Office of Scientific and Technical Information (OSTI.GOV)
Yao, Yunxi; Giapis, Konstantinos P., E-mail: giapis@cheme.caltech.edu
2017-01-20
The deuterium-to-hydrogen ratio (D/H) in water found in the coma of Jupiter family comet (JFC) 67P/Churyumov–Gerasimenko was reported to be (5.3 ± 0.7) × 10{sup −4}, the highest among comets and three times the value for other JFCs with an ocean-like ratio. This discrepancy suggests the diverse origins of JFCs and clouds the issue of the origin of Earth’s oceanic water. Here we demonstrate that Eley–Rideal reactions between accelerated water ions and deuterated cometary surface analogs can lead to instantaneous deuterium enrichment in water scattered from the surface. The reaction proceeds with H{sub 2}O{sup +} abstracting adsorbed D atoms, formingmore » an excited H{sub 2}DO* state, which dissociates subsequently to produce energetic HDO. Hydronium ions are also produced readily by the abstraction of H atoms, consistent with H{sub 3}O{sup +} detection and abundance in various comets. Experiments with water isotopologs and kinematic analysis on deuterated platinum surfaces confirmed the dynamic abstraction mechanism. The instantaneous fractionation process is independent of the surface temperature and may operate on the surface of cometary nuclei or dust grains, composed of deuterium-rich silicates and carbonaceous chondrites. The requisite energetic water ions have been detected in the coma of 67P in two populations. This dynamic fractionation process may temporarily increase the water D/H ratio, especially as the comet gets closer to the Sun. The magnitude of the effect depends on the water ion energy-flux and the deuterium content of the exposed cometary surfaces.« less
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Observational evidence of aging processes in comets
NASA Astrophysics Data System (ADS)
Meech, Karen J.
1991-10-01
Emphasis was on searching for systematic differences among two groups of comets: periodic comets which spend most of their time in the vicinity of the inner Solar System and the new comets which are believed to be passing through the inner Solar System for the first time. Such differences are expected, but have never been observed, in part because there has never been a systematic observational program aimed at addressing this question. Understanding possible physical and compositional differences between these two groups will lead to a better understanding of the cometary formation conditions in the early Solar System. The employed method studies the activity in the comets as a function of distance by obtaining charge coupled device (CCD) observations of the comets at frequent intervals on both the pre- and post-perihelion legs of their orbits in order to ascertain the distances at the onset and turn-off of activity through comparison with sublimation models.
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Getting Reactions to Chemistry.
ERIC Educational Resources Information Center
Smith, Walter S.
1983-01-01
"COMETS on Careers" describes science-related careers, introduces activities illustrating a science concept being studied, and encourages use of professional persons as activity leaders. Several COMETS chemistry activities are described. These activities, which can be performed in school or at home, focus on colloids, acid/base…
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From the Vega mission to comet Halley to the Rosetta mission to comet 67/P Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Zelenyi, L. M.; Ksanfomality, L. V.
2016-12-01
The data acquired by the Vega and Giotto spacecraft, while investigating comet 1P/Halley in 1986, are compared to the results of the first phase of exploration of the nucleus of comet 67P/Churyumov-Gerasimenko performed with the Rosetta and Philae modules. The course of the Rosetta mission activity and the status of the modules after the Philae probe landing on the comet's nucleus are overviewed. Since some elements of the touchdown equipment failed, a number of in-situ experiments on the comet's nucleus were not carried out.
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NASA Technical Reports Server (NTRS)
Southworth, R. B.; Mccrosky, R. E.
1970-01-01
An overview of research on radio and radar meteors accomplished during the past decade is presented, and the work of the past year is highlighted. Velocity distribution and mass flux data are obtained for meteors in the range 10 to 0.0001 g, the size believed to be the principal hazard to space missions. The physical characteristics of mass, structure and density, luminosity, and ablation are briefly described, and the formulation of a theory for interactions of ionization and excitation during collision of atomic particles is mentioned. Five classes of meteoroids are identified, including the two of iron and stone meteorites. Stream meteors associated with known comets are Classes A or C, and parent comets of Class B streams are not observed. Class A meteoroids are identified with the core of a cometary nucleus, Class C with less dense surface of the nucleus after sublimation of ices, and Class B with less dense cores of smaller cometary nuclei. Atmospheric meteor phenomena associated with winds and gravity waves, density and temperature, atomic oxygen, and meteor rate changes are mentioned.
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On LAM's and SAM's for Halley's rotation
NASA Technical Reports Server (NTRS)
Peale, Stanton J.
1992-01-01
Non principal axis rotation for comet Halley is inferred from dual periodicities evident in the observations. The modes where the spin axis precesses around the axis of minimum moment of inertia (long axis mode or LAM) and where it precesses around the axis of maximum moment of inertia (short axis mode or SAM) are described from an inertial point of view. The currently favored LAM model for Halley's rotation state satisfies observational and dynamical constraints that apparently no SAM can satisfy. But it cannot reproduce the observed post perihelion brightening through seasonal illumination of localized sources on the nucleus, whereas a SAM can easily produce post or pre perihelion brightening by this mechanism. However, the likelihood of a LAM rotation for elongated nuclei of periodic comets such as Halley together with Halley's extreme post perihelion behavior far from the Sun suggest that Halley's post perihelion brightening may be due to effects other than seasonal illumination of localized sources, and therefore such brightening may not constrain its rotation state.
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Thermal modeling of cometary nuclei
NASA Astrophysics Data System (ADS)
Weissman, P. R.; Kieffer, H. H.
1981-09-01
A model of the sublimation of volatile ices from a cometary nucleus is presented which includes the effects of (1) diurnal heating and cooling, (2) rotation period and pole orientation, (3) the thermal properties of the ice and subsurface layers, and (4) the contributions from coma opacity, scattering and thermal emission where the properties of the coma are derived from the integrated rate of volatile production by the nucleus. In applying the model to the case of the 1986 apparition of Halley's comet, it is found that the generation of a cometary dust coma increases the total energy reaching the Halley nucleus due to the greater geometrical cross-section of the coma as compared with the bare nucleus. The calculated coma opacity of Halley is about 0.2 at 1 AU from the sun and 1.2 at perihelion. Possible consequences of the results obtained for the generation of nongravitational forces, volatile production rates for comets and cometary lifetimes against sublimation are discussed.
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Modeling the surface and interior structure of comet nuclei using a multidisciplinary approach
NASA Technical Reports Server (NTRS)
Odell, C. R.; Dakoulas, Panos C.; Pharr, George M.
1991-01-01
The goal was to investigate the structural properties of the surface of comet nucleus and how the surface should change with time under effect of solar radiation. The basic model that was adopted was that the nucleus is an aggregate of frosty particles loosely bound together, so that it is essentially a soil. The nucleus must mostly be composed of dust particles. The observed mass ratios of dust to gas in the coma is never much greater than unity, but this ratio is probably a much lower limit than that of the nucleus because it is vastly easier to remove the gaseous component by sublimation than by carrying off the dust. Therefore the described models assumed that the particles in the soil were frost covered grains of submicron basic size, closely resembling the interstellar grains. The surface properties of such a nucleus under the effects of heating and cooling as the nucleus approaches and recedes from the Sun generally characterized.
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Trapping of N 2, CO and Ar in amorphous ice—Application to comets
NASA Astrophysics Data System (ADS)
Bar-Nun, A.; Notesco, G.; Owen, T.
2007-10-01
Recent attempts using high resolution spectra to detect N +2 in several comets were unsuccessful [Cochran, A.L., Cochran, W.D., Baker, E.S., 2000. Icarus 146, 583-593; Cochran, A.L., 2002. Astrophys. J. 576, L165-L168]. The upper limits on N +2 in comparison with the positively detected CO + for Comets C/1995 O1 Hale-Bopp, 122P/1995 S1 de Vico and 153P/2002 C1 Ikeya-Zhang range between N2+/CO<(0.65-5.4)×10. Ar was not detected in three recent comets [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95-L98], with upper limits of Ar/CO<(3.4-7.8)×10 for Comets C/1999 T1 McNaught-Hartley, C/2001 A2 LINEAR and C/2000 WM1 LINEAR. The Ar detected by Stern et al. [Stern, S.A., Slater, D.C., Festou, M.C., Parker, J.Wm., Gladstone, G.R., A'Hearn, M.F., Wilkinson, E., 2000. Astrophys. J. 544, L169-L172] for Comet C/1995 O1 Hale-Bopp, gives a ratio Ar/CO=7.25×10, which was not confirmed by Cosmovici et al. [Cosmovici, C.B., Bratina, V., Schwarz, G., Tozzi, G., Mumma, M.J., Stalio, R., 2006. Astrophys. Space Sci. 301, 135-143]. Trying to solve the two problems, we studied experimentally the trapping of N+CO+Ar in amorphous water ice, at 24-30 K. CO was found to be trapped in the ice 20-70 times more efficiently than N 2 and with the same efficiency as Ar. The resulting Ar/CO ratio of 1.2×10 is consistent with Weaver et al.'s [Weaver, H.A., Feldman, P.D., Combi, M.R., Krasnopolsky, V., Lisse, C.M., Shemansky, D.E., 2002. Astrophys. J. 576, L95-L98] non-detection of Ar. However, with an extreme starting value for N 2/CO = 0.22 in the region where the ice grains which agglomerated to produce comet nuclei were formed, the expected N 2/CO ratio in the cometary ice should be 6.6×10, much higher than its non-detection limit.
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Coma in Comet C/2012 S1 (ISON) at ~4 au
NASA Astrophysics Data System (ADS)
Videen, Gorden; Zubko, Evgenij; Hines, Dean C.; Shkuratov, Yuriy; Kaydash, Vadym; Muinonen, Karri; Knight, Matthew W.; Sitko, Michael L.; Lisse, Carrey M.; Mutchler, Max; Wooden, Diane H.; Li, Jian-Yang; Kobayashi, Hiroshi
2015-11-01
We analyze HST observations of Comet ISON (C/2012 S1) at heliocentric distance ~4 au and phase angle ~12-14 degree. The inner coma (< 5000 km) reveals two polarimetric features, positive degree of linear polarization P = (2.48 ± 0.45)% at projected distances less than 236 km and negative polarization P = - (1.6 ± 0.45)% at 1000 - 5000 km [Hines et al. 2014: ApJL 780, L32]. At these projected distances, average color slope was found to be ~6% per 100 nm [Li et al. 2013: ApJL 779, L3]. When considered simultaneously, these two features place significant constraint on the physical and chemical properties of dust particles [Zubko et al. 2015: Planet. Space Sci., http://dx.doi.org/10.1016/j.pss.2015.08.002].We model this response with agglomerated debris particles, having highly irregular morphology and density of constituent material being consistent with in situ studies of comets. We consider particles of 28 different refractive indices that correspond to in situ studies of comets and plausible assumptions on chemical composition of cometary dust and ices. What emerges from our analysis is that the ISON coma was chemically heterogeneous at the epoch of observation. The positive polarization at small projected distances suggests a high spatial concentration of highly absorbing materials, such as amorphous carbon and/or organics highly irradiated with UV radiation. At larger distances, the negative polarization P = - (1.6 ± 0.45)% and color slope ~6% per 100 nm appear consistent with organics slightly processed with UV radiation, tholins, Mg-Fe silicates, and Mg-rich silicates contaminated with ~10% (by volume) amorphous carbon. A significant abundance of pure water-ice particles and/or pure Mg-rich silicates must be ruled out in this region. These materials have been found in situ in other comets and also detected with imaging polarimetry in the circumnucleus halo regions. Analyses of polarimetric images suggest that Mg-rich silicates could originate from a refractory surface layer on the surface of cometary nuclei [Zubko et al. 2012: A&A 544, L8]. A depletion of such particles in Comet ISON could imply an absence of such a layer on its nucleus.
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103P/Hartley 2: ground-based monitoring of the EPOXI flyby comet
NASA Astrophysics Data System (ADS)
Tubiana, C.; Snodgrass, C.; Vincent, J.-B.; Barrera, L.; Nowajewski, P.; Retamales, G.; Lister, T.; Boehnhardt, H.
2011-10-01
Comet 103P/Hartley 2 was the fly-by target of the NASA EPOXI mission. Observations of this comet during its previous perihelion passage [1] and in 2008 when it was in its aphelion arc [2, 3] revealed a small and very active nucleus. We observed 103P from March 2010 to January 2011 using the 4m SOAR telescope located at Cerro Pachon, Chile. We took images in UBVRI filters using the SOAR Optical Imager (SOI). In addition, we made use of the large collection of (mostly BVR) images taken of the comet by school pupils using the two robotic 2m Faulkes Telescopes, which cover the same period. At the time of the observations, the comet was moving from 2.8 AU pre-perihelion to 1.6 AU post-perihelion heliocentric distance, when the comet was expected to display the most activity. The main purpose of our observations was the characterization of the activity of comet 103P and its evolution along the perihelion arc. We searched for the presence of dust coma structures and their evolution with changing heliocentric distance and determined gas and dust production rates, the dust color and the variation in these quantities as the comet passed perihelion. While no coma structures were detected between March and July 2010, a clear anisotropy in the coma in the anti-tail direction was detected in images obtained in November 2011 (Fig. 1). At the same place, the Laplace filter detects what might be a jet.
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Physical mechanism of comet outbursts - An experimental result
NASA Technical Reports Server (NTRS)
Hartmann, William K.
1993-01-01
Attention is given to an experimental investigation of the physical mechanism of comet outbursts which is consistent with the general picture of mantle presence on comets and clarifies the relation of mantles to eruptive activity. The experiment and closeup observation of Comet P/Halley suggest a result different from most mathematical models in that the release of gas pressure does not occur only from uniform gas flow out of the entire surface. In some active comets near perihelion within a few AU of the sun, gas production rates and disturbance of the surface may be so high that the outflow is nearly continuous, with the regolith being entirely stripped away, as in many of the models. The present model provides a cyclic eruption and recharge mechanism which is lacking in most other models.
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NASA Astrophysics Data System (ADS)
Combi, M. R.; Mäkinen, T. T.; Bertaux, J.-L.; Quémerais, E.; Ferron, S.; Avery, M.; Wright, C.
2018-01-01
Nine recently discovered long-period comets were observed by the Solar Wind Anisotropies (SWAN) Lyman-alpha all-sky camera on board the Solar and Heliosphere Observatory (SOHO) satellite during the period of 2013 to 2016. These were C/2012 K1 (PanSTARRS), C/2013 US10 (Catalina), C/2013 V5 (Oukaimeden), C/2013 R1 (Lovejoy), C/2014 E2 (Jacques), C/2014 Q2 (Lovejoy), C/2015 G2 (MASTER), C/2014 Q1 (PanSTARRS) and C/2013 XI (PanSTARRS). Of these 9 comets 6 were long-period comets and 3 were possibly dynamically new. Water production rates were calculated from each of the 885 images using our standard time-resolved model that accounts for the whole water photodissociation chain, exothermic velocities and collisional escape of H atoms. For most of these comets there were enough observations over a broad enough range of heliocentric distances to calculate power-law fits to the variation of production rate with heliocentric distances for pre- and post-perihelion portions of the orbits. Comet C/2014 Q1 (PanSTARRS), with a perihelion distance of only ∼0.3 AU, showed the most unusual variation of water production rate with heliocentric distance and the resulting active area variation, indicating that when the comet was within 0.7 AU its activity was dominated by the continuous release of icy grains and chunks, greatly increasing the active sublimation area by more than a factor of 10 beyond what it had at larger heliocentric distances. A possible interpretation suggests that a large fraction of the comet's mass was lost during the apparition.
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The Activity of Comet 67P/Churyumov-Gerasimenko as Seen by Rosetta/OSIRIS
NASA Astrophysics Data System (ADS)
Sierks, H.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Rickman, H.; Koschny, D.
2015-12-01
The Rosetta mission of the European Space Agency arrived on August 6, 2014, at the target comet 67P/Churyumov-Gerasimenko. OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) is the scientific imaging system onboard Rosetta. OSIRIS consists of a Narrow Angle Camera (NAC) for the nucleus surface and dust studies and a Wide Angle Camera (WAC) for the wide field gas and dust coma investigations. OSIRIS observed the coma and the nucleus of comet 67P/C-G during approach, arrival, and landing of PHILAE. OSIRIS continued comet monitoring and mapping of surface and activity in 2015 with close fly-bys with high resolution and remote, wide angle observations. The scientific results reveal a nucleus with two lobes and varied morphology. Active regions are located at steep cliffs and collapsed pits which form collimated gas jets. Dust is accelerated by the gas, forming bright jet filaments and the large scale, diffuse coma of the comet. We will present activity and surface changes observed in the Northern and Southern hemisphere and around perihelion passage.
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Non-gravitational acceleration in the trajectory of 1I/2017 U1 ('Oumuamua).
Micheli, Marco; Farnocchia, Davide; Meech, Karen J; Buie, Marc W; Hainaut, Olivier R; Prialnik, Dina; Schörghofer, Norbert; Weaver, Harold A; Chodas, Paul W; Kleyna, Jan T; Weryk, Robert; Wainscoat, Richard J; Ebeling, Harald; Keane, Jacqueline V; Chambers, Kenneth C; Koschny, Detlef; Petropoulos, Anastassios E
2018-06-27
'Oumuamua (1I/2017 U1) is the first known object of interstellar origin to have entered the Solar System on an unbound and hyperbolic trajectory with respect to the Sun 1 . Various physical observations collected during its visit to the Solar System showed that it has an unusually elongated shape and a tumbling rotation state 1-4 and that the physical properties of its surface resemble those of cometary nuclei 5,6 , even though it showed no evidence of cometary activity 1,5,7 . The motion of all celestial bodies is governed mostly by gravity, but the trajectories of comets can also be affected by non-gravitational forces due to cometary outgassing 8 . Because non-gravitational accelerations are at least three to four orders of magnitude weaker than gravitational acceleration, the detection of any deviation from a purely gravity-driven trajectory requires high-quality astrometry over a long arc. As a result, non-gravitational effects have been measured on only a limited subset of the small-body population 9 . Here we report the detection, at 30σ significance, of non-gravitational acceleration in the motion of 'Oumuamua. We analyse imaging data from extensive observations by ground-based and orbiting facilities. This analysis rules out systematic biases and shows that all astrometric data can be described once a non-gravitational component representing a heliocentric radial acceleration proportional to r -2 or r -1 (where r is the heliocentric distance) is included in the model. After ruling out solar-radiation pressure, drag- and friction-like forces, interaction with solar wind for a highly magnetized object, and geometric effects originating from 'Oumuamua potentially being composed of several spatially separated bodies or having a pronounced offset between its photocentre and centre of mass, we find comet-like outgassing to be a physically viable explanation, provided that 'Oumuamua has thermal properties similar to comets.
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Geomorphology of comet 67P/Churyumov–Gerasimenko
Birch, Samuel P. D.; Tang, Y.; Hayes, A. G.; Kirk, Randolph L.; Bodewitz, D.; Campins, H.; Fernandez, Y.; de Freitas Bart, R.; Kutsop, N. W.; Sierks, H.; Soderblom, J. M.; Squyres, S. W.; Vincent, J.-B.
2017-01-01
We present a global geomorphological map of comet 67P/Churyumov–Gerasimenko (67P/C-G) using data acquired by the Rosetta Orbiter’s OSIRIS Narrow Angle Camera. The images used in our study were acquired between 2014 August and 2015 May, before 67P/C-G passed through perihelion. Imagery of the Southern hemisphere was included in our study, allowing us to compare the contrasting hemispheres of 67P/C-G in a single study. Our work also puts into greater context the morphologies studied in previous works, and also the morphologies observed on previously visited cometary nuclei. Relative to other nuclei, 67P/C-G appears most similar to 81P/Wild 2, with a topographically heterogeneous surface dominated by smooth-floored pits. Our mapping describes the landscapes of 67P/C-G when they were first observed by Rosetta, and our map can be used to detect changes in surface morphologies after its perihelion passage. Our mapping reveals strong latitudinal dependences for emplaced units and a highly heterogeneous surface. Layered bedrock units that represent the exposed nucleus of 67P/C-G are dominant at southern latitudes, while topographically smooth, dust covered regions dominate the Northern hemisphere. Equatorial latitudes are dominated by smooth terrain units that show evidence for flow structures. We observe no obvious differences between the comet’s two lobes, with the only longitudinal variations being the Imhotep and Hatmehit basins. These correlations suggest a strong seasonal forcing on the surface evolution of 67P/C-G, where materials are transported from the Southern hemisphere to Northern hemisphere basins over multiple orbital time-scales.
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The COMET Initiative database: progress and activities update (2015).
Gargon, E; Williamson, P R; Altman, D G; Blazeby, J M; Tunis, S; Clarke, M
2017-02-03
This letter describes the substantial activity on the Core Outcome Measure in Effectiveness Trials (COMET) website in 2015, updating our earlier progress reports for the period from the launch of the COMET website and database in August 2011 to December 2014. As in previous years, 2015 saw further increases in the annual number of visits to the website, the number of pages viewed and the number of searches undertaken. The sustained growth in use of the website and database suggests that COMET is continuing to gain interest and prominence, and that the resources are useful to people interested in the development of core outcome sets.
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Cortés-Eslava, Josefina; Gómez-Arroyo, Sandra; Risueño, Maria C; Testillano, Pilar S
2018-05-02
The ubiquity of pollutants, such as agrochemicals and heavy metals, constitute a serious risk to human health. To evaluate the induction of DNA damage and programmed cell death (PCD), root cells of Allium cepa and Vicia faba were treated with two organophosphate insecticides (OI), fenthion and malathion, and with two heavy metal (HM) salts, nickel nitrate and potassium dichromate. An alkaline variant of the comet assay was performed to identify DNA breaks; the results showed comets in a dose-dependent manner, while higher concentrations induced clouds following exposure to OIs and HMs. Similarly, treatments with higher concentrations of OIs and HMs were analyzed by immunocytochemistry, and several structural characteristics of PCD were observed, including chromatin condensation, cytoplasmic vacuolization, nuclear shrinkage, condensation of the protoplast away from the cell wall, and nuclei fragmentation with apoptotic-like corpse formation. Abiotic stress also caused other features associated with PCD, such as an increase of active caspase-3-like protein, changes in the location of cytochrome C (Cyt C) toward the cytoplasm, and decreases in extracellular signal-regulated protein kinase (ERK) expression. Genotoxicity results setting out an oxidative via of DNA damage and evidence the role of the high affinity of HM and OI by DNA molecule as underlying cause of genotoxic effect. The PCD features observed in root cells of A. cepa and V. faba suggest that PCD takes place through a process that involves ERK inactivation, culminating in Cyt C release and caspase-3-like activation. The sensitivity of both plant models to abiotic stress was clearly demonstrated, validating their role as good biosensors of DNA breakage and PCD induced by environmental stressors. Copyright © 2018 Elsevier Ltd. All rights reserved.
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Infrared Spectroscopy of HR 4796A's Bright Outer Cometary Ring + Tenuous Inner Hot Dust Cloud
NASA Astrophysics Data System (ADS)
Lisse, C. M.; Sitko, M. L.; Marengo, M.; Vervack, R. J., Jr.; Fernandez, Y. R.; Mittal, T.; Chen, C. H.
2017-11-01
We have obtained new NASA/IRTF SpeX spectra of the HR 4796A debris ring system. We find a unique red excess flux that extends out to ˜9 μm in Spitzer IRS spectra, where thermal emission from cold, ˜100 K dust from the system’s ring at ˜75 au takes over. Matching imaging ring photometry, we find the excess consists of NIR reflectance from the ring, which is as red as that of old, processed comet nuclei, plus a tenuous thermal emission component from close-in, T ˜ 850 K circumstellar material evincing an organic/silicate emission feature complex at 7-13 μm. Unusual, emission-like features due to atomic Si, S, Ca, and Sr were found at 0.96-1.07 μm, likely sourced by rocky dust evaporating in the 850 K component. An empirical cometary dust phase function can reproduce the scattered light excess and 1:5 balance of scattered versus thermal energy for the ring with optical depth < τ > ≥slant 0.10 in an 8 au wide belt of 4 au vertical height and M dust > 0.1-0.7 M Mars. Our results are consistent with HR 4796A, consisting of a narrow shepherded ring of devolatilized cometary material associated with multiple rocky planetesimal subcores and a small steady stream of dust inflowing from this belt to a rock sublimation zone at ˜1 au from the primary. These subcores were built from comets that have been actively emitting large, reddish dust for >0.4 Myr at ˜100 K, the temperature at which cometary activity onset is seen in our solar system.
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NASA Astrophysics Data System (ADS)
Wooden, D. H.; Woodward, C. E.; Harker, D. E.
2003-05-01
We report on observations and analysis of HIFOGS 10 \\micron \\ spectrophotometry of short period comet 19P/Borrelly on 2003 October 13, 15 UT at the NASA IRTF. 19P/Borrelly is one of two short period comets, comet 4P/Faye being the other, to have a silicate feature detected (Hanner et al. 1996, Icarus, 124, 344). During Borrelly.s perihelion passage in 1994 December, a silicate feature was present with a flux-to-continuum ratio of 0.25. Two apparitions later in 2003 October, the silicate feature is absent. Thermal emission modeling (cf. Harker et al. 2002, ApJ, 580, 579) using amorphous olivine and amorphous carbon shows that a slight increase in grain size accounts for the disappearance of the silicate feature. Analysis of 19P/Borrelly suggests grain size, and not the absence of olivine minerals, may be responsible for the absence of silicate features in most short period comets. 19P/Borrelly is one of the more active short period comets. However, short period comets as a family are less active than long period comets. Short period comets probably originated in the Kuiper Belt and suffered collisions while in residence in the outer solar system. Upon evolution into orbits that take them through the inner solar system, the surfaces of short period comets are exposed to sunlight through their many perihelion passages. This is in contrast to long period comets which probably originated near Jupiter and were expelled to the Oort cloud where they have existed and been exposed to cosmic ray processing. By studying the grain properties in short period comets and comparing to long period comets, we compare the effects on the grain populations of different parent body evolution histories. Upcoming opportunities to study short and long period comets will be advertised. This research is supported in part by an NSF Grant to the University of Minnesota.
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Activity of Comet Hale-Bopp (1995 01) Beyond 6 AU From the Sun
NASA Technical Reports Server (NTRS)
Sekanina, Z.
1996-01-01
The physical evolution of comet Hale-Bopp is investigated along the preperihelic arc of its orbit at heliocentric distances larger than 6 AU. The comet's considerable intrinsic brightness and activity are explained by the existence of a relatively larg area on its nucleus surface that is a resevoir of both carbon monoxide and dust particulates. Three recuring dust emission events observed in August-October 1995 are studied in some detail.
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NASA Astrophysics Data System (ADS)
Pozuelos, F. J.; Moreno, F.; Aceituno, F.; Casanova, V.; Sota, A.; López-Moreno, J. J.; Castellano, J.; Reina, E.; Climent, A.; Fernández, A.; San Segundo, A.; Häusler, B.; González, C.; Rodriguez, D.; Bryssinck, E.; Cortés, E.; Rodriguez, F. A.; Baldris, F.; García, F.; Gómez, F.; Limón, F.; Tifner, F.; Muler, G.; Almendros, I.; de los Reyes, J. A.; Henríquez, J. A.; Moreno, J. A.; Báez, J.; Bel, J.; Camarasa, J.; Curto, J.; Hernández, J. F.; González, J. J.; Martín, J. J.; Salto, J. L.; Lopesino, J.; Bosch, J. M.; Ruiz, J. M.; Vidal, J. R.; Ruiz, J.; Sánchez, J.; Temprano, J.; Aymamí, J. M.; Lahuerta, L.; Montoro, L.; Campas, M.; García, M. A.; Canales, O.; Benavides, R.; Dymock, R.; García, R.; Ligustri, R.; Naves, R.; Lahuerta, S.; Pastor, S.
2014-11-01
Aims: This paper is a continuation of the first paper in this series, where we presented an extended study of the dust environment of a sample of short-period comets and their dynamical history. On this occasion, we focus on comets 81P/Wild 2 and 103P/Hartley 2, which are of special interest as targets of the spacecraft missions Stardust and EPOXI. Methods: As in the previous study, we used two sets of observational data: a set of images, acquired at Sierra Nevada and Lulin observatories, and the Afρ data as a function of the heliocentric distance provided by the amateur astronomical association Cometas-Obs. The dust environment of comets (dust loss rate, ejection velocities, and size distribution of the particles) was derived from our Monte Carlo dust tail code. To determine their dynamical history we used the numerical integrator Mercury 6.2 to ascertain the time spent by these objects in the Jupiter family Comet region. Results: From the dust analysis, we conclude that both 81P/Wild 2 and 103P/Hartley 2 are dusty comets, with an annual dust production rate of 2.8 × 109 kg yr-1 and (0.4-1.5) × 109 kg yr-1, respectively. From the dynamical analysis, we determined their time spent in the Jupiter family Comet region as ~40 yr in the case of 81P/Wild 2 and ~1000 yr for comet 103P/Hartley 2. These results imply that 81P/Wild 2 is the youngest and the most active comet of the eleven short-period comets studied so far, which tends to favor the correlation between the time spent in JFCs region and the comet activity previously discussed.
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NASA Astrophysics Data System (ADS)
Womack, M.; Sarid, G.; Wierzchos, K.
2017-03-01
The activity of most comets near the Sun is dominated by the sublimation of frozen water, the most abundant ice in comets. Some comets, however, are active well beyond the water-ice sublimation limit of ˜3 au. Three bodies dominate the observational record and modeling efforts for distantly active comets: the long-period comet C/1995 O1 (Hale-Bopp), and the short-period comets (with Centaur orbits) 29P/Schwassmann-Wachmann 1 and 2060 Chiron. We summarize what is known about these three objects with an emphasis on their gaseous comae. We calculate their CN/CO and CO2/CO production rate ratios from the literature and discuss implications, such as HCN and CO2 outgassing are not significant contributors to their comae. Using our own data we derive CO production rates, Q(CO), for all three objects to examine whether there is a correlation between gas production and different orbital histories and/or size. The CO measurements of Hale-Bopp (4-11 AU) and 29P are consistent with a nominal production rate of Q(CO) = 3.5 × 1029 r-2 superimposed with sporadic outbursts. The similarity of Hale-Bopp CO production rates for pre- and post-perihelion suggests that thermal inertia was not very important and therefore most of the activity is at or near the surface of the comet. We further examine the applicability of existing models in explaining the systematic behavior of our small sample. We find that orbital history does not appear to play a significant role in explaining 29P’s CO production rates. 29P outproduces Hale-Bopp at the same heliocentric distance, even though it has been subjected to much more solar heating. Previous modeling work on such objects predicts that 29P should have been devolatilized over a fresher comet like Hale-Bopp. This may point to 29P having a different orbital history than current models predict, with its current orbit acquired more recently. On the other hand, Chiron’s CO measurements are consistent with it being significantly depleted over its original state, perhaps due to increased radiogenic heating made possible by its much larger size or its higher processing due to orbital history. Observed spectral line profiles for several volatiles are consistent with the development and sublimation of icy grains in the coma at about 5-6 au for 29P and Hale-Bopp, and this is probably a common feature in distantly active comets, and an important source of volatiles for all comets within 5 au. In contrast, the narrow CO line profiles indicate a nuclear, and not extended, origin for CO beyond ˜4 au.
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Discovery of Main-Belt Comet P/2006 VW139 by Pan-STARRS1
NASA Astrophysics Data System (ADS)
Hsieh, H. H.; Yang, B.; Haghighipour, N.; Kaluna, H. M.; Fitzsimmons, A.; Denneau, L.; Novakovic, B.; Jedicke, R.; Wainscoat, R. J.; Armstrong, J. D.; Duddy, S. R.; Lowry, S. C.; Trujillo, C. A.; Micheli, M.; Keane, J. V.; Urban, L.; Riesen, T.; Meech, K. J.; Abe, S.; Cheng, Y. C.; Chen, W. P.; Granvik, M.; Grav, T.; Ip, W. H.; Kinoshita, D.; Kleyna, J.; Lacerda, P.; Lister, T.; Milani, A.; Tholen, D. J.; Veres, P.; Lisse, C. M.; Kelley, M. S.; Fernandez, Y. R.; Bhatt, B. C.; Sahu, D. K.; Kaiser, N.; Chambers, K. C.; Hodapp, K. W.; Magnier, E. A.; Price, P. A.; Tonry, J. L.
2012-05-01
We describe the discovery of comet-like activity in main-belt asteroid (300163) 2006 VW139 (later re-designated as Comet P/2006 VW139) by Pan-STARRS1. We also detail follow-up photometric, spectroscopic, and dynamical analyses of the object.
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NASA Technical Reports Server (NTRS)
Wooden, Diane H.; Lindsay, Sean S.
2011-01-01
Crystalline silicates in comets are a product of the condensation in the hot inner regions (T > or approx. equals 1400 K [1]) of our proto-planetary disk or annealing at somewhat lower temperatures (T > or approx. equals 1000-1200 K) [2, 3, 4] in shocks coupled with disk evolutionary processes that include radial transport of crystals from their formation locations out to the cold outer regions where comet nuclei formed. The grain shape of forsterite (crystals) could be indicative of their formation pathways at high temperatures through vapor-solid condensation or at lower temperatures through vapor-liquid-solid formation and growth [5, 6, 7]. Experiments demonstrate that crystals that formed from a rapidly cooled highly supersaturated silicate vapor are characterized by bulky, platy, columnar/needle and droplet shapes for values of temperature and supersaturation, T and sigma, of 1000-1450 C and < 97, 700-1000 C and 97-161, 580-820 C and 131-230, and <500 C and > 230, respectively [7]. The experimental columnar/needle shapes, which form by vapor-liquid-solid at lower temperatures (<820 C), are extended stacks of plates, where the extension is not correlated with an axial direction: columnar/needles may be extended in the c-axis or a-axis direction, can change directions, and/or are off-kilter or a bit askew extending in a combination of the a- and c-axis direction.
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Comet nucleus sample return mission
NASA Technical Reports Server (NTRS)
1983-01-01
A comet nucleus sample return mission in terms of its relevant science objectives, candidate mission concepts, key design/technology requirements, and programmatic issues is discussed. The primary objective was to collect a sample of undisturbed comet material from beneath the surface of an active comet and to preserve its chemical and, if possible, its physical integrity and return it to Earth in a minimally altered state. The secondary objectives are to: (1) characterize the comet to a level consistent with a rendezvous mission; (2) monitor the comet dynamics through perihelion and aphelion with a long lived lander; and (3) determine the subsurface properties of the nucleus in an area local to the sampled core. A set of candidate comets is discussed. The hazards which the spacecraft would encounter in the vicinity of the comet are also discussed. The encounter strategy, the sampling hardware, the thermal control of the pristine comet material during the return to Earth, and the flight performance of various spacecraft systems and the cost estimates of such a mission are presented.
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Exposed water ice on the nucleus of comet 67P/Churyumov-Gerasimenko.
Filacchione, G; De Sanctis, M C; Capaccioni, F; Raponi, A; Tosi, F; Ciarniello, M; Cerroni, P; Piccioni, G; Capria, M T; Palomba, E; Bellucci, G; Erard, S; Bockelee-Morvan, D; Leyrat, C; Arnold, G; Barucci, M A; Fulchignoni, M; Schmitt, B; Quirico, E; Jaumann, R; Stephan, K; Longobardo, A; Mennella, V; Migliorini, A; Ammannito, E; Benkhoff, J; Bibring, J P; Blanco, A; Blecka, M I; Carlson, R; Carsenty, U; Colangeli, L; Combes, M; Combi, M; Crovisier, J; Drossart, P; Encrenaz, T; Federico, C; Fink, U; Fonti, S; Ip, W H; Irwin, P; Kuehrt, E; Langevin, Y; Magni, G; McCord, T; Moroz, L; Mottola, S; Orofino, V; Schade, U; Taylor, F; Tiphene, D; Tozzi, G P; Beck, P; Biver, N; Bonal, L; Combe, J-Ph; Despan, D; Flamini, E; Formisano, M; Fornasier, S; Frigeri, A; Grassi, D; Gudipati, M S; Kappel, D; Mancarella, F; Markus, K; Merlin, F; Orosei, R; Rinaldi, G; Cartacci, M; Cicchetti, A; Giuppi, S; Hello, Y; Henry, F; Jacquinod, S; Reess, J M; Noschese, R; Politi, R; Peter, G
2016-01-21
Although water vapour is the main species observed in the coma of comet 67P/Churyumov-Gerasimenko and water is the major constituent of cometary nuclei, limited evidence for exposed water-ice regions on the surface of the nucleus has been found so far. The absence of large regions of exposed water ice seems a common finding on the surfaces of many of the comets observed so far. The nucleus of 67P/Churyumov-Gerasimenko appears to be fairly uniformly coated with dark, dehydrated, refractory and organic-rich material. Here we report the identification at infrared wavelengths of water ice on two debris falls in the Imhotep region of the nucleus. The ice has been exposed on the walls of elevated structures and at the base of the walls. A quantitative derivation of the abundance of ice in these regions indicates the presence of millimetre-sized pure water-ice grains, considerably larger than in all previous observations. Although micrometre-sized water-ice grains are the usual result of vapour recondensation in ice-free layers, the occurrence of millimetre-sized grains of pure ice as observed in the Imhotep debris falls is best explained by grain growth by vapour diffusion in ice-rich layers, or by sintering. As a consequence of these processes, the nucleus can develop an extended and complex coating in which the outer dehydrated crust is superimposed on layers enriched in water ice. The stratigraphy observed on 67P/Churyumov-Gerasimenko is therefore the result of evolutionary processes affecting the uppermost metres of the nucleus and does not necessarily require a global layering to have occurred at the time of the comet's formation.
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A survey of possible missions to the periodic comets in the interval 1974 - 2010
NASA Technical Reports Server (NTRS)
Bender, D. F.
1974-01-01
Catalogs are developed to survey the mission possibilities for the short period comets. In the first the physical and pertinent orbital characteristics are given for 65 short period comets. The second catalog is one containing the predicted perihelia for each of the 65 comets between 1974 and 2010. Geometry is included to indicate feasibility of Earth-based observation and sighting within 100 days of perihelion. The comets are divided on the basis of size and activity into three groups from the data in the first catalog: primary, secondary and low interest. The perihelia are separated into two groups: satisfactory and not satisfactory on the basis of earth-comet distance.
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The outbursts of the comet 29P/Schwassmann-Wachmann 1: A new approach to the old problem
NASA Astrophysics Data System (ADS)
Gronkowski, P.
2014-02-01
As far as outbursts activity is concerned, the 29P/Schwassmann-Wachmann 1 is the exceptional comet. This Centaur object shows quasi-regular flares with periodicities of 50 days eriodicity (Trigo-Rodriguez et al. 2010). In the introductory part of the presented paper the most well-known hypotheses which try to explain this cometary behaviour are reviewed. The second, actual part of this paper presents the new model for the outburst activity of this comet. The model is based on the idea of Ipatov (2012), according to which there are large cavities %%in comets %%with material under gas pressure, below a considerable fraction of the comet's surface containing material under high gas pressure. In favourite conditions the surface layers over the cavities are thrown away and the interior of these cavities is exposed. Consequently, an outburst of the comet's brightness may be observed. The main characteristics of an outburst of this comet, the brightness jump, %%in its brightness is calculated. Numerical simulations were carried out for wide range of possible cometary parameters. The obtained results are in good agreement with the real observations.
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Rapid evolution of the spin state of comet 41P/Tuttle-Giacobini-Kresak
NASA Astrophysics Data System (ADS)
Bodewits, Dennis; Farnham, Tony; Kelley, Michael S. P.; Manning Knight, Matthew
2018-01-01
Cometary outgassing can produce torques that change the spin state of the nucleus, influencing the evolution and lifetimes of comets. If these torques spin up the rotation to the point that centripetal forces exceed the material strength of the nucleus, the comet may fragment. Comet 41P/Tuttle-Giacobini-Kresak passed Earth as close as 0.142 au in April 2017, allowing observations of the inner coma and an assessment of the rotational state of the nucleus. We acquired observations of comet 41P between March and May 2017 using the 4.3-m Discovery Channel Telescope and the UltraViolet-Optical Telescope (UVOT) on board the Earth-orbiting Swift Gamma Ray Burst Mission.We combined CN narrowband imaging and aperture photometry and found that the apparent rotation period of comet 41P more than doubled between March and May 2017, increasing from 20 hours to over 46 hours. Measurements of the periodicity in late-March by Knight et al. (CBET 4377, 2017) are consistent with this rate of increase. Comet 41P is the ninth comet for which a rotation period change has been observed (c.f. Samarasinha et al., in Comets II, 2004), but both the fractional change and the rate of change of the period far exceed those observed in the other comets. It is the combination of a slow rotation, high activity, and a small nucleus that contribute to the rapid changes of the rotation state of 41P. In addition, the active regions on the surface of 41P are likely oriented in a way such that its torques are highly optimized in comparison to many other comets.Extrapolating the comet’s rotation period using its current gas production rates and a simple activity model suggests that the nucleus will continue to spin down, possibly leading to an excited spin state in the next apparitions. Finally, 41P is known for its large outbursts, and our extrapolation suggest that the comet’s rotation period may have been close to the critical period for splitting in 2001, when it exhibited two significant outbursts.
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Van Wezel, I L; Dharmarajan, A M; Lavranos, T C; Rodgers, R J
1999-06-01
Granulosa cell death is an early feature of atresia; however, there are many apparent contradictions in the literature concerning the mode of granulosa cell death. We have therefore examined this process in bovine healthy and atretic antral follicles, using a variety of established techniques. Light and electron microscopic observations indicated the presence of pyknotic or shrunken nuclei in both the membrana granulosa and the antrum. In the membrana granulosa, these nuclei were frequently crescent shaped and uniformly electron dense and were approximately the same size as healthy nuclei, all of which are typical of early apoptosis. However, these nuclei were within the membranes of a healthy granulosa cell, suggesting that phagocytosis by a neighboring granulosa cell is an unusually early event in the apoptotic pathway of granulosa cells. In the membrana granulosa, pyknotic nuclei stained intensely with hematoxylin but weakly with the DNA-intercalating stain propidium iodide. A percentage of these pyknotic nuclei stained by TUNEL (terminal deoxy-UTP nick end-labeling). However, in the antrum, the pyknotic nuclei and larger globules of DNA stained intensely with both hematoxylin and propidium iodide, but were not TUNEL positive. The comet assay of cell death produced a streak tail of randomly nicked DNA, rather than the plume of low mol wt apoptotic DNA. Globules collected from fresh follicular fluid stained intensely with propidium iodide and were shown by PAGE to contain DNA, the majority of which was high mol wt. In conclusion, granulosa cells within the membrana granulosa die by apoptosis, with phagocytosis by a neighboring cell preceding any potential budding of the nucleus or cell itself. Granulosa cells near the antrum are sloughed off into the antrum, and their death has features more consistent with that of other cell types that undergo death as a result of terminal differentiation.
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Comments on the Rotational State and Non-Gravitational Forces of Comet 46/WIRTANEN. Revised
NASA Technical Reports Server (NTRS)
Samarasinha, Nalin H.; Mueller, Beatrice E. A.; Belton, Michael J. S.
1995-01-01
We apply our experience of modeling the rotational state and non-gravitational forces of comet 1 P/Halley and other comets to comet 46P/Wirtanen. While the paucity of physical data on 46P/Wirtanen makes this process somewhat speculative, this comet's place as target for the important Rosetta mission gives significance to such a study. Our arguments are based on the summary of observational data provided by Jorda and Rickman (1995) and a comparative study of the behavior of other periodic comets. We find 46P/Wirtanen to have a level of surface activity relative to its mass that is dynamically more akin to that found in comet 1 P/Halley than in a typical periodic comet. We show through an illustrative numerical example that this apparent fact should likely lead to an excited spin state for this comet and that significant changes in the spin period could occur in a single pass through perihelion. We argue that the available observations are not sufficient to substantiate the claim of Jorda and Rickman (1995) that the nucleus is undergoing retrograde rotation and it is possible that the rotation is either prograde as well as retrograde. The substantial requirements that must be placed on any future observing program necessary to determine the precise rotational state are outlined. We advocate an extended (approx. two month) southern hemisphere observing campaign to determine the nuclear rotational state in 1996 if possible before activity turns on.
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Once a myth, now an object of study - How the perception of comets has changed over the centuries
NASA Astrophysics Data System (ADS)
2004-02-01
In February 2004, Rosetta will be setting off on its long journey through our solar system to meet up with Comet Churyumov-Gerasimenko. It will take the European Space Agency (ESA) space probe ten years to reach its destination. The comet, which moves in an elliptical orbit around the Sun, will at rendezvous be some 675 million kilometres from the Sun, near the point in its orbit farthest from the Sun. The meeting point was not chosen at random: at this point the comet is still barely active, it is still in fact a frozen lump of ice and interplanetary dust, in all probability the matter from which our solar system emerged four and a half billion years ago. Rosetta’s job is to find out more about these strange bodies that travel through our solar system. As it moves on, the comet will begin to change. As it approaches the Sun, it will - like all comets - become active: in the warmth of the Sun’s rays, the ices evaporate, tearing small dust particles from the surface. This produces the comet head (the coma) and tail. Only these two phenomena are visible from Earth. The comet nucleus itself is far too tiny - Churyumov-Gerasimenko measures about 4 kilometres across - to be viewed from Earth. As Dr Uwe Keller of the Max Planck Institute for Aeronomy in Kaltenburg-Lindau, the scientist responsible for the Osiris camera carried by Rosetta, explains, “Formation of the coma and tail during solar flyby skims several metres of matter off the comet’s surface. In the case of a small comet like Churyumov-Gerasimenko, the shrinkage is a good 1% each time round.” As it flies past the Sun every 6.6 years it can look forward to a short future, especially on a cosmic timescale. Comets - a mystical view Visible cometary phenomena have fascinated human beings from time immemorial - and frightened them too. Even today mystical explanations prevail among some of the Earth’s peoples. The Andaman islanders, a primitive people living in the Gulf of Bengal, see comets as burning torches hurled into the air by forest spirits - the more easily to detect humans foolish enough to stay out at night. For some Australian aborigines, comets are flaming sticks ridden by mighty shamans. Efforts to provide a scientific explanation of the ‘cometa aster’ (‘hairy star’) phenomenon stretch back to ancient times. A widely held view was that comets were in some way connected with processes at work in the atmosphere. In Meteorologica, Aristotle (384-322 BC) described how inflammable gases escape from clefts in rocks, collect in the upper layers of the sub-lunar world (‘world under the Moon’) and ignite. Rapid release of such gases produced a shooting star; when let out slowly, they gave rise to a comet. That was Aristotle’s best shot - and he was well aware of his limited insight into the question. As he himself acknowledged: “As we have no demonstrable basis for assertions about comets, I have to settle for an interpretation that does not conflict with established truths.” Admittedly such truths were thin on the ground at the time. Comets - something of a disaster As the centuries unfolded, what could be called the opposite view - that the comets were responsible for intense heat spells - also gained a considerable audience, though there was just as little truth in it. The natural philosophers went one further. They said comets lead to heat, heat to storms and storms to natural disasters. Pliny the Elder for example (born circa 23 AD) listed twelve cometary phenomena according to their external appearances. And he assigned one natural disaster to each class. The Christian Middle Ages no longer saw cometary phenomena as the blind raging of an even blinder nature, preferring to interpret them as signs from God. Theologians such as Saint Hildegard of Bingen (1098-1179) and Albert Magnus (1200-1280) cited holy scripture. The Book of Jeremiah for example (1:11,12), in which God caused a fearsome “rod of an almond tree” to appear in the sky, a symbol of the prophet’s empowerment. Or again Luke 21:11: “And great earthquakes shall be in divers places, and famines, and pestilences; and fearful sights and great signs shall there be from heaven.” In 1066, Halley’s Comet appeared to many as a harbinger of the Norman conquest of Britain, so vividly portrayed in the Bayeux tapestry, with its scenes from the Battle of Hastings. The decisive step towards overturning the view that comets are atmospheric phenomena was taken in 1577 by Danish astronomer, Tycho Brahe. For two and a half months he observed from his observatory in Uranienburg the progress of a comet across the heavens. Relying on the phenomenon of the daily parallax - an apparent “shuddering” motion of heavenly bodies in fact attributable to the observer’s position on the revolving Earth - he was able to establish that the comet had to be located beyond the lunar orbit. Halley discovers an elliptical orbit The scientific description of comets took another major step forward in 1705 thanks to the work of the British astronomer and physicist, Edmond Halley, a friend and patron of Isaac Newton. Investigating recorded comet measurements, he observed that the orbits of a number of bright comets were very similar: his own calculation of the orbit of a comet observed in 1682 coincided with the data recorded by Johannes Kepler in 1607 and by Apianus in 1531. He concluded that various comet observations were attributable to one and the same comet. Halley was proved right when in December 1758, the comet whose return he had predicted, thenceforth named after him, did indeed make a repeat appearance. This confirmed his theory that apparently parabolic comet orbits were in fact “simply” sections of one enormous elliptical orbit. Since then observations recorded in China in 240 BC have been identified as relating to a sighting of Halley’s comet, the oldest known document dealing with this phenomenon. What was described in the Bible as a sign from God was seen by Fred Hoyle, the British astrophysicist, as a possible explanation for the great hiatal breaks in history. He took the view that such extraordinary developments as the extinction of the mammoth were attributable to strikes by comet fragments. His views incorporated the theory advanced by British astronomers Victor Clube and Bill Napier in 1982 that a giant comet was trapped by our solar system 15000 years ago. With the return of that comet every 1600 years, the accompanying debris - so the argument goes - prompted some of the world’s great turning points. This might also be an explanation for such legends as the Flood. A lump of icy sludgew So what does the actual nucleus of a comet look like? One answer was supplied by the Giotto space probe in a mission masterminded by ESA. The probe was named after the major Italian painter Giotto di Bondone, who, in the early 14th century, portrayed a comet in his fresco in the Scrovegni Chapel in Padua. On 14 March 1986, the probe succeeded in taking 100-metre-resolution pictures of the nucleus of Halley’s Comet from only 600 kilometres away. In the words of Uwe Keller: “The mission forced us to revisit our long-standing image of a comet nucleus as a ‘dirty snowball’. The pictures showed that it was more like a lump of icy sludge. The solid part of the nucleus is much larger than the icy part.” Bur hardly had Giotto trained its electronic eye on the heavenly body than the photo opportunity was already over; a dust particle measuring about a millimetre hit the probe. As the velocity differential between probe and comet was at that point 68.4 km per second, the force of the involuntary encounter was enough to put paid to any further snapshots. All the same, despite the damage to the camera, it proved possible to go on with the mission. Following two periods of “hibernation”, Giotto achieved a successful flyby of the Grigg-Skjellerup comet on 10 July 1992. Rosetta should now bring us entirely new knowledge about comet nuclei. It will orbit the comet and deposit a small lander probe on its surface. So for the first time in history a comet travelling sunwards will be investigated from close quarters. For further information on Rosetta and ESA projects, please consult our portal at : http://www.esa.int/science or http:// www.esa.int/rosetta
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Dust Activity of Comet Hale-Bopp (C/1995 O1) at Rh ~ 3 AU
NASA Astrophysics Data System (ADS)
Tozzi, G. P.; Mannucci, F.; Stanga, R.; Testi, L.
1997-07-01
Observations of comet Hale-Bopp (C/1995 O1) have been performed in the infrared (J, H, K bands) at the Nordic Optical Telescope (NOT), located on Canary islands, with the ARNICA (ARcetri Near Infrared CAmera). The comet was observed during two periods, at the beginning and the end of September 1996, when the comet was at heliocentric distances rh of ~ 3.3 and 2.9 AU, respectively. The data show a relatively large activity of the comet with production of some outbursts, the largest of which happened some time before the start of the second run (24.8 Sept.) and which may be the further evolution of the outburst detected by the HST (Weaver et al., 1997, Science 275, 1900). Here we present the analysis of the data with particular attention to the evolution of the outbursts and the photometric IR color index of the dust released.
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The Extremely Low Activity Comet 209P/LINEAR During Its Extraordinary Close Approach in 2014
NASA Astrophysics Data System (ADS)
Schleicher, David G.; knight, Matthew m.
2016-10-01
We present results from our observing campaign of Comet 209P/LINEAR during its exceptionally close approach to Earth during 2014 May, the third smallest perigee of any comet in two centuries. These circumstances permitted us to pursue several studies of this intrinsically faint object, including measurements of gas and dust production rates, searching for coma morphology, and direct detection of the nucleus to measure its properties. Indeed, we successfully measured the lowest water production rates of an intact comet in over 35 years and a corresponding smallest active area, ∼0.007 km2. When combined with the nucleus size found from radar, this also yields the smallest active fraction for any comet, ∼0.024%. In all, this strongly suggests that 209P/LINEAR is on its way to becoming an inert object. The nucleus was detected but could not easily be disentangled from the inner coma due to seeing variations and changing spatial scales. Even so, we were able to measure a double-peaked lightcurve consistent with the shorter of two viable rotational periods found by Hergenrother. Radial profiles of the dust coma are quite steep, similar to that observed for some other very anemic comets, and suggest that vaporizing icy grains are present.
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Comprehensive model for the nucleus of Periodic Comet Tempel 2 and its activity
NASA Technical Reports Server (NTRS)
Sekanina, Zdenek
1991-01-01
A comprehensive synergistic physical model for the nucleus of Periodic Comet Tempel 2 was developed on the basis of observations carried out in 1988. The model includes the best possible estimates of the comet's bulk properties (including the dimensions and the approximate shape), information on its state of rotation, and the characterization of its activity. The model is shown to be consistent with all lines of evidence that are currently available, including relevant information from earlier apparitions.
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ESO's VLT Helps ESA's Rosetta Spacecraft Prepare to Ride on a Cosmic Bullet
NASA Astrophysics Data System (ADS)
2002-02-01
New Images of Comet Wirtanen's Nucleus [1] Summary New images of Comet Wirtanen's 1-km 'dirty snowball' nucleus have been obtained with the ESO Very Large Telescope at Paranal (Chile). They show this object at a distance of approx. 435 million km from the Sun, about the same as when the Rosetta spacecraft of the European Space Agency (ESA) arrives in 2011. The new observations indicate that the comet has a very low degree of activity at this point in its orbit - almost no material is seen around the nucleus. This means that there will not be so much dust near the nucleus as to make the planned landing dramatically difficult. PR Photo 06a/02 : The Nucleus of Comet Wirtanen (composite photo). PR Photo 06b/02 : Comet Wirtanen's motion in the sky (animated). A distant target ESO PR Photo 06a/02 ESO PR Photo 06a/02 [Preview - JPEG: 400 x 445 pix - 120k] [Normal - JPEG: 800 x 890 pix - 1.1M] ESO PR Photo 06b/02 ESO PR Photo 06b/02 [Animated GIF: 400 x 420 pix - 312k] Caption : PR Photo 06a/02 shows a (false-colour) composite image of the nucleus of Comet Wirtanen (the point of light at the centre), recorded on December 9, 2001, with the FORS2 multi-mode instrument at the 8.2-m VLT YEPUN Unit Telescope. It is based on four exposures and since the telescope was set to track the motion of the comet in the sky, the images of stars in the field are seen as four consecutive trails. The measured brightness and the fact that the image of the comet's 'dirty snowball' nucleus is almost star-like indicates that it is surrounded by a very small amount of gas or dust. The diameter of the nucleus is about 1 km and the distance to the comet from the Earth was approx. 534 million km. In PR Photo 06b/02 , the four exposures have been combined to show the motion of the comet during the four exposures. Technical information about the photos is available below. Chase a fast-moving comet, land on it and 'ride' it while it speeds up towards the Sun: not the script of a science-fiction movie, but the very real task of ESA's Rosetta spacecraft. New observations with the ESO Very Large Telescope (VLT) provide vital information about Comet Wirtanen - Rosetta's target - to help ESA reduce uncertainties in the mission, one of the most difficult ever to be performed. Every 5.5 years Comet Wirtanen completes an orbit around the Sun. Wirtanen has been seen during several apparitions since its discovery in 1948, but only recently have astronomers obtained detailed observations that have allowed them to estimate the comet's size and behaviour, cf. ESO PR Photos 27a-b/99. The most recent of these observations was performed in December 2001 with the ESO VLT at the Paranal Observatory in Northern Chile, cf. PR Photos 06a-b/02 , reproduced here. As a result of these observations ESA will be able to refine plans for its Rosetta mission. Good news for Rosetta Rosetta will be launched next year and it will reach Comet Wirtanen in 2011. By that time the comet will be nearly as far from the Sun as Jupiter, charging headlong towards the inner Solar System at speeds of up to 135,000 km/h. To get there and to be able to match the comet's orbit, Rosetta will need to be accelerated by several planetary swing-bys, after which the spacecraft - following a series of difficult manoeuvres - will get close to the comet, enter into orbit around it and release a lander from a height of about 1 km. The VLT observations were planned specifically to investigate the 'activity' of Wirtanen at about the same solar distance as at the time of the landing manoeuvres . Because of this timing requirement, they had to be carried out at a certain moment - unfortunately, when the comet was low in the twilight evening sky and descending rapidly towards the western horizon. However, even though the exposures therefore had to be quite short, the VLT with its superb light-gathering capability and opto-mechanical perfection was still able to produce excellent images of this rather faint, moving object (about 6 million times fainter than what can be perceived with the unaided eye). These observations have now confirmed that - at the same distance from the Sun at which the landing will take place (about 450 million km from the Sun) - the activity on Wirtanen is very low, cf. PR Photo 06a/02 . This is very good news for the mission, because it means that there will not be so much dust near the nucleus as to make the landing dramatically difficult . Landing on a 1-km snowball Cometary nuclei are small frozen bodies made of ice and dust ('dirty snowballs'). When they get close to the Sun the heat causes ices on the surface to 'evaporate'. Gas and dust grains are ejected into the surrounding space forming the comet's atmosphere (coma) and the tail. In addition to dropping a lander on Wirtanen's nucleus for detailed in-situ observations, Rosetta's task is to investigate the evolution of the comet on its way to the Sun: in fact, Rosetta will keep orbiting around Wirtanen up to the end of the mission in July 2013, at which time the comet is at its closest approach to the Sun, at about 160 million km from it. These and earlier VLT observations have also provided Rosetta mission planners with an accurate measurement of their target's size: Wirtanen's nucleus is only 1.2 km in diameter, a true cosmic bullet . "Rosetta is certainly a very challenging space mission. No one has ever tried to land on a comet before," says Gerhard Schwehm , Rosetta's Project Scientist. "We need to learn as much as possible about our target. The new VLT data will allow us to improve our models and make decisions once we get there." "It is a pleasure to help our colleagues at ESA", says ESO astronomer and comet specialist Hermann Boehnhardt . "We will continue to keep an eye on this comet, in particular when Rosetta is approaching its target. We can then provide the spacecraft controllers and the astronomers with very useful, regular updates, e.g., about the 'cometary weather' at the time of arrival." More about Rosetta Rosetta's prime scientific goal is to unravel the origin of the Solar System. The chemical composition of comets is known to reflect that of the primordial nebula that gave birth to the Solar System - in the planets, that primeval material has gone through complex processing, but not in the comets. Therefore, Rosetta will allow scientists to look back 4.6 billion years, to an epoch when the Solar System formed. Previous studies by ESA's Giotto spacecraft and by ground-based observatories have shown that comets contain complex organic molecules - compounds that are rich in carbon, hydrogen, oxygen and nitrogen. Intriguingly, these are the elements which make up nucleic acids and amino acids, essential ingredients for life as we know it. Did life on Earth begin with the help of comet seeding? Rosetta may help us to find the answer to this fundamental question. Rosetta carries 21 experiments in total. These are provided by scientific consortia from institutes across Europe and the United States. The Wirtanen observations by the VLT fall into a tradition of fruitful collaboration between the European Space Agency (ESA) and the European Southern Observatory (ESO). The two organizations, both members of the EIROFORUM collaboration ( ESO PR 12/01 ), are already combining their efforts in several strategic areas, in order to facilitate the synergy between space and ground facilities, where mutual sharing of technology and procedures can result in substantial gains and savings.
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8- to 13-micron spectroscopy of Comet Levy 1990 XX
NASA Technical Reports Server (NTRS)
Lynch, David K.; Russell, Ray W.; Hackwell, John A.; Hanner, Martha S.; Hammel, Heidi B.
1992-01-01
The results are reported of IR spectroscopy of Comet Levy 1990 XX over a three-day period when the comet was about 1.54 AU from the sun roughly 70 days before perihelion. Comet Levy 1990 XX was bright, and for at least part of its inbound journey toward perihelion, active. At a distance of 1.54 AU from the sun it showed strong structured silicate emission with peaks or shoulders at 9.8 and 11.2 microns. These features resemble those of Comets P/Halley and Bradfield 1987 XXIX. The comet was variable in brightness. Specifically, the contrast of the silicate features changed by a factor of two relative to the continuum level and showed some evidence for a shape change as well.
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Monitoring of comets activity and composition with the TRAPPIST-North telescope
NASA Astrophysics Data System (ADS)
Moulane, Y.; Benkhaldoun, Z.; Jehin, E.; Opitom, C.; Gillon, M.; Daassou, A.
2017-06-01
TRAPPIST-North (TRAnsiting Planets and PlanetesImals Small Telescope) is a 60-cm robotic telescope that was installed in May 2016 at the Oukaimeden Observatory [1]. The project is led by the University of Liège (Belgium) and the Caddi Ayad University of Marrakech (Morocco). This telescope is a twin of the TRAPPIST-South telescope, which was installed at the ESO La Silla Observatory in 2010 [2]. The TRAPPIST telescopes are dedicated to the detection and characterization of planets orbiting stars other than our Sun (exoplanets) and the study of comets and other small bodies in our solar system. For the comets research, these telescopes have very sensitive CCD cameras with complete sets of narrow band filters to measure the production rates of several gases (OH, NH, CN, C3 and C2) and the dust [3]. With TRAPPIST-North we can also observe comets that would not be visible in the southern hemisphere. Therfore, with these two telescopes, we can now observe continuously the comets around their orbit. We project to study individually the evolution of the activity, chemical composition, dust properties, and coma morphology of several comets per year and of different origins (New comets and Jupiter Family comets) over a wide range of heliocentric distances, and on both sides of perihelion. We measure the production rates of each daughter molecules using a Haser model [4], in addition to the Afρ parameter to estimate the dust production in the coma. In this work, we present the first measurements of the production rates of comet C/2013 X1 (PANSTARRS) observed with TN in June 2016, and the measurements of comet C/2013 V5 (Oukaimeden) observed in 2014 with TRAPPIST-South.
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Dynamical and Physical Models of Ecliptic Comets
NASA Astrophysics Data System (ADS)
Dones, L.; Boyce, D. C.; Levison, H. F.; Duncan, M. J.
2005-08-01
In most simulations of the dynamical evolution of the cometary reservoirs, a comet is removed from the computer only if it is thrown from the Solar System or strikes the Sun or a planet. However, ejection or collision is probably not the fate of most active comets. Some, like 3D/Biela, disintegrate for no apparent reason, and others, such as the Sun-grazers, 16P/Brooks 2, and D/1993 F2 Shoemaker-Levy 9, are pulled apart by the Sun or a planet. Still others, like 107P/Wilson Harrington and D/1819 W1 Blanpain, are lost and then rediscovered as asteroids. Historically, amateurs discovered most comets. However, robotic surveys now dominate the discovery of comets (http://www.comethunter.de/). These surveys include large numbers of comets observed in a standard way, so the process of discovery is amenable to modeling. Understanding the selection effects for discovery of comets is a key problem in constructing models of cometary origin. To address this issue, we are starting new orbital integrations that will provide the best model to date of the population of ecliptic comets as a function of location in the Solar System and the size of the cometary nucleus, which we expect will vary with location. The integrations include the gravitational effects of the terrestrial and giant planets and, in some cases, nongravitational jetting forces. We will incorporate simple parameterizations for mantling and mass loss based upon detailed physical models. This approach will enable us to estimate the fraction of comets in different states (active, extinct, dormant, or disintegrated) and to track how the cometary size distribution changes as a function of distance from the Sun. We will compare the results of these simulations with bias-corrected models of the orbital and absolute magnitude distributions of Jupiter-family comets and Centaurs.
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Repeatability of the Dust and Gas Morphological Structures in the Coma of Comet
NASA Astrophysics Data System (ADS)
Lejoly, Cassandra; Samarasinha, N. H.; Ojha, L.; Schleicher, D. G.
2013-10-01
Comet 1P/Halley is the most famous comet in history and has been observed for over two millennia, making it one of the most extensively studied comets. The morphology in the coma of comet 1P/Halley originates due to the activity at the nucleus and could be used as a probe of the nuclear rotation and the activity. We will present the results from a study summarizing the evolution of coma morphology of comet 1P/Halley observed from ground between October 1985 and June 1986. The results to be presented include analysis of dust features as well as gas (CN) features in the coma and comparisons will be made between their spatial and temporal evolution. About 80 CN images and 300 continuum images from the Small Bodies Node of the NASA Planetary Data System were analyzed using image enhancement techniques that were not available n the 1980s. This enables us to see coma structure never observed before in comet 1P/Halley. Because of the comet's proximity to Earth, most of our best signal-to-noise images were taken in the March-April interval of 1986. Despite the limited coverage of preceding and following months, there is a sufficient number of images to monitor morphological evolution over many months. The initial synodic periods as a function of time used to phase the images together were extrapolated from the lightcurves of the active coma (Schleicher et al. 1990, AJ, 100, 896-912). We will present the periods of repeatability of individual coma features measured using the position angle at different spatial distances from the nucleus in adjacent cycles. Separate features appear to have slightly different periods of repeatability, perhaps depending on the corresponding source regions on the nucleus and/or projection effects. The periods of repeatability of coma morphologies will be presented as a function of time from the perihelion. These results will ultimately be used in detailed modeling of the coma morphologies of comet 1P/Halley over the 1985-1986 apparition in order to characterize the activity of the comet. This work is supported by NASA Planetary Atmospheres grant NNX11AD85G and C.L.'s participation at the meeting is supported by a gift to the Lunar and Planetary Laboratory at the University of Arizona.
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Surface Activity Distributions of Comet 67P/Churyumov-Gerasimenko Derived from VIRTIS Images
NASA Astrophysics Data System (ADS)
Fougere, N.; Combi, M. R.; Tenishev, V.; Migliorini, A.; Bockelée-Morvan, D.; Fink, U.; Filacchione, G.; Rinaldi, G.; Capaccioni, F.; Toth, G.; Gombosi, T. I.; Hansen, K. C.; Huang, Z.; Shou, Y.
2017-12-01
The outgassing mechanism of comets still remains a critical question to better understand these objects. The Rosetta mission gave some insight regarding the potential activity distribution from the surface of the nucleus of comet 67P/Churyumov-Gerasimenko, Fougere et al. (2016) used a spherical harmonics inversion scheme with in-situ measurements from the ROSINA instrument to derive mapping of the broad distribution of potential activity at the surface of the nucleus. Marschall et al. (2017) based on the appearance of dust active areas suggested that the so-called "neck" region and regions with fractured cliffs and locally steep slopes show more activity than the rest of comet 67P's nucleus. Using in situ ROSINA measurements from a distance makes it difficult to distinguish between these two scenarios because the fast expansion of the gas and large molecular mean free paths prevents distinguishing small outgassing features even when the spacecraft was in bound orbits within 10 km from the nucleus. In this paper, we present a similar numerical inversion approach using VIRTIS images, which should better probe the very inner coma of comet 67P and give more detailed information about the outgassing activity. Support from contracts JPL #1266314 and #1266313 from the US Rosetta Project and grant NNX14AG84G from the NASA Planetary Atmospheres Program are gratefully acknowledged.
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Water and dust production rates in comet P/Halley derived from ultraviolet and optical observations
NASA Technical Reports Server (NTRS)
Festou, Michel C.
1992-01-01
We evaluate whether the activity of comet P/Halley is due solely to the presence of discrete active areas. We preliminarily conclude that the dark areas of the nucleus contribute to the formation of the coma.
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Ballistic intercept missions to Comet Encke
NASA Technical Reports Server (NTRS)
Mumma, M. (Compiler)
1975-01-01
The optimum ballistic intercept of a spacecraft with the comet Encke is determined. The following factors are considered in the analysis: energy requirements, encounter conditions, targeting error, comet activity, spacecraft engineering requirements and restraints, communications, and scientific return of the mission. A baseline model is formulated which includes the basic elements necessary to estimate the scientific return for the different missions considered. Tradeoffs which have major impact on the cost and/or scientific return of a ballistic mission to comet Encke are identified and discussed. Recommendations are included.
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Determination of the radius of comet 19P/Borrelly in support of the NMP DS1 Flyby
NASA Astrophysics Data System (ADS)
Festou, Michel
1999-07-01
Comet 19P/Borrelly is the ultimate target of the New Mellinium Program {NMP} Deep Space 1 asteroid-comet flyby mission. The size of this comet's nucleus is a critical parameter needed for flyby planning activities. However, as we describe below, P/Borrelly's radius is not well established. We, the NMP DS1 Science Team, request 1 orbit of HST/STIS time in Cycle 8 to refine the nuclear size estimate. This program cannot wait until Cycle 9 because of mission planning constraints and the fact that the comet is likely to be producing a weak but nonetheless enhanced coma by the time of Cycle 9. We therefore propose to observe comet P/Borrelly in Cycle 8 when the activity level of its nucleus is near its minimum, and quite possibly negligible. From a clear separation of the contributions of the coma and the nucleus in the inner part of STIS images, we will extract the cross section of Borrelly's nucleus. In addition to its immediate value for NMP DS1 mission planning, when c oupled to existing data sets, the STIS data will then enable us to model the coma morphology to better infer the effect of the nucleus outgassing on the comet's motion.
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Search for Dormant Comets in Near-Earth Space
NASA Astrophysics Data System (ADS)
Kim, Yoonyoung
2013-06-01
It is considered that comets have been injected into near-Earth space from outer region (e.g. Kuiper-belt region), providing rich volatile and organic compounds to the earth. Some comets are still active while most of them are dormant with no detectable tails and comae. Here we propose to make a multi-band photometric observation of near-Earth objects (NEOs) with comet-like orbits. We select our targets out of infrared asteroidal catalogs based on AKARI and WISE observations. With a combination of taxonomic types by Subaru observation and albedos by AKARI or WISE, we aim to dig out dormant comet candidates among NEOs. Our results will provide valuable information to figure out the dynamical evolution and fate of comets. We would like to emphasize that this is the first taxonomic survey of dormant comets to utilize the infrared data archive with AKARI and WISE.
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Comet Halley returns: A teachers' guide 1985-1986
NASA Technical Reports Server (NTRS)
Chapman, R. D.; Bondurant, R. L.
1985-01-01
This booklet has been put together as an aid for teachers in elementary and secondary schools. It is divided into two distinct parts. The first part is a brief tutorial which introduces some of the most important concepts about comets, including their historical significance. A list of selected readings is provided at the end of the booklet. The second part of the booklet contains a number of suggested activities, built around the comet. These include both classroom exercises and carefully described field work to observe the comet. Guidance is provided on where to look for the comet, how to observe it, and to photograph it.
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Colors of active regions on comet 67P
NASA Astrophysics Data System (ADS)
Oklay, N.; Vincent, J.-B.; Sierks, H.; Besse, S.; Fornasier, S.; Barucci, M. A.; Lara, L.; Scholten, F.; Preusker, F.; Lazzarin, M.; Pajola, M.; La Forgia, F.
2015-10-01
The OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) scientific imager (Keller et al. 2007) is successfully delivering images of comet 67P/Churyumov-Gerasimenko from its both wide angle camera (WAC) and narrow angle camera (NAC) since ESA's spacecraft Rosetta's arrival to the comet. Both cameras are equipped with filters covering the wavelength range of about 200 nm to 1000 nm. The comet nucleus is mapped with different combination of the filters in resolutions up to 15 cm/px. Besides the determination of the surface morphology in great details (Thomas et al. 2015), such high resolution images provided us a mean to unambiguously link some activity in the coma to a series of pits on the nucleus surface (Vincent et al. 2015).
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Dormant Comets in the Near-Earth Asteroid Population
NASA Astrophysics Data System (ADS)
Mommert, Michael; Harris, Alan W.; Mueller, Michael; Hora, Joseph L.; Trilling, David E.; Knight, Matthew; Bottke, William F.; Thomas, Cristina; Delbo', Marco; Emery, Josh P.; Fazio, Giovanni; Smith, Howard A.
2015-11-01
The population of near-Earth objects comprises active comets and asteroids, covering a wide range of dynamical parameters and physical properties. Dormant (or extinct) comets, masquerading as asteroids, have long been suspected of supplementing the near-Earth asteroid (NEA) population. We present a search for asteroidal objects of cometary origin based on dynamical and physical considerations. Our study is based on albedos derived within the ExploreNEOs program and is extended by adding data from NEOWISE and the Akari asteroid catalog. We use a statistical approach to identify asteroids on orbits that resemble those of short-period near-Earth comets using the Tisserand parameter with respect to Jupiter, the aphelion distance, and the minimum orbital intersection distance with respect to Jupiter. We identify a total of 23 near-Earth asteroids from our sample that are likely to be dormant short-period near-Earth comets and, based on a de-biasing procedure applied to the cryogenic NEOWISE survey, estimate both magnitude-limited and size-limited fractions of the NEA population that are dormant short-period comets. We find that 0.3-3.3% of the NEA population with H <= 21, and 9(+2/-5)% of the population with diameters d >= 1 km, are dormant short-period near-Earth comets. We also present an observation program that utilizes the 1.8m Vatican Advanced Technology Telescope (VATT) on Mt. Graham, AZ, to identify dormant comet candidates and search for activity in these objects. Our targets are NEAs on comet-like orbits, based on the dynamical criteria derived in the above study, that are accessible with the VATT (V <= 22). We identify dormant comets based on their optical spectral slope, represented by V-R color measurements, as albedo measurements for most of these objects are not available. For each target we measure and monitor its V magnitude in order to reveal activity outbreaks. We also search for extended emission around our targets using deep imaging and a point-spread-function subtraction technique that allows us to obtain an upper limit on the dust production rate in each target. We present preliminary results from this program. This work is supported in part by funding from the Spitzer Science Center.
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Bi-lobed Shape of Comet 67P from a Collapsed Binary
NASA Astrophysics Data System (ADS)
Nesvorný, David; Parker, Joel; Vokrouhlický, David
2018-06-01
The Rosetta spacecraft observations revealed that the nucleus of comet 67P/Churyumov–Gerasimenko consists of two similarly sized lobes connected by a narrow neck. Here, we evaluate the possibility that 67P is a collapsed binary. We assume that the progenitor of 67P was a binary and consider various physical mechanisms that could have brought the binary components together, including small-scale impacts and gravitational encounters with planets. We find that 67P could be a primordial body (i.e., not a collisional fragment) if the outer planetesimal disk lasted ≲10 Myr before it was dispersed by migrating Neptune. The probability of binary collapse by impact is ≃30% for tightly bound binaries. Most km-class binaries become collisionally dissolved. Roughly 10% of the surviving binaries later evolve to become contact binaries during the disk dispersal, when bodies suffer gravitational encounters with Neptune. Overall, the processes described in this work do not seem to be efficient enough to explain the large fraction (∼67%) of bi-lobed cometary nuclei inferred from spacecraft imaging.
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Meteor stream activity. 2: Meteor outbursts
NASA Technical Reports Server (NTRS)
Jenniskens, P.
1995-01-01
In the past two centuries, alert amateur and professional meteor astronomers have documented 35 outbursts of 17 individual meteor streams well enough to allow the construction of a homogeneous set of activity curves. These curves add to similar profiles of the annual streams in a previous paper (Paper 1). This paper attempts to define the type and range of phenomena that classify as meteor outbursts from which the following is concluded: Outbursts are associated with the return of the comet to perihelion (near-comet type outbursts), but occur also when the parent comet is far from perihelion and far from the Earth (far-comet type). All outbursts of a given type only, depending on encounter geometry. The activity curves, expressed in terms of Zenith Hourly Rates (ZHR), have a shape that is generally well described by: ZHR = ZHR(sub max) 10(sup(-B (the absolute value of lambda (sub dot in a circle) - lambda (sup max) (sub dot in a circle))). The steepness of the slopes varies from an exponent of B = 7 to B = 220 per degree of solar longitude, with a typical value of B = 30. In addition, most near-comet type outbursts have a broader component underlying the main peak with B approximately 1 - 7.The duration Delta t is approximately 1/B of the main peak is almost independent of location near the comet, while the background component varies considerably in duration and relative intensity from one return to another. The two components in the activity curve are due to two distinct structures in the dust distribution near the parent comet, where the main component can be due to a sheet of dust that emanates from the IRAS dust trail. This brings the total number of distinct structures in meteor streams to four, including the two structures from the annual stream activity in Paper 1.
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Further characterization of benzo[a]pyrene diol-epoxide (BPDE)-induced comet assay effects.
Bausinger, Julia; Schütz, Petra; Piberger, Ann Liza; Speit, Günter
2016-03-01
The present study aims to further characterize benzo[a]pyrene diol-epoxide (BPDE)-induced comet assay effects. Therefore, we measured DNA effects by the comet assay and adduct levels by high-performance liquid chromatography (HPLC) in human lymphocytes and A549 cells exposed to (±)-anti-benzo[a]pyrene-7,8-diol 9,10-epoxide [(±)-anti-BPDE] or (+)-anti-benzo[a]pyrene-7,8-diol 9,10-epoxide [(+)-anti-BPDE]. Both, the racemic form and (+)-anti-BPDE, which is the most relevant metabolite with regard to mutagenicity and carcinogenicity, induced DNA migration in cultured lymphocytes in the same range of concentrations to a similar extent in the alkaline comet assay after exposure for 2h. Nevertheless, (+)-anti-BPDE induced significantly enhanced DNA migration after 16 and 18h post-cultivation which was not seen in response to (±)-anti-BPDE. Combination of the comet assay with the Fpg (formamidopyrimidine-DNA glycosylase) protein did not enhance BPDE-induced effects and thus indicated the absence of Fpg-sensitive sites (oxidized purines, N7-guanine adducts, AP-sites). The aphidicolin (APC)-modified comet assay suggested significant excision repair activity of cultured lymphocytes during the first 18h of culture after a 2 h-exposure to BPDE. In contrast to these repair-related effects measured by the comet assay, HPLC analysis of stable adducts did not reveal any significant removal of (+)-anti-BPDE-induced adducts from lymphocytes during the first 22h of culture. On the other hand, HPLC measurements indicated that A549 cells repaired about 70% of (+)-anti-BPDE-induced DNA-adducts within 22h of release. However, various experiments with the APC-modified comet assay did not indicate significant repair activity during this period in A549 cells. The conflicting results obtained with the comet assay and the HPLC-based adduct analysis question the real cause for BPDE-induced DNA migration in the comet assay and the reliability of the APC-modified comet assay for the determination of DNA excision repair activity in response to BPDE in different cell types. © The Author 2015. Published by Oxford University Press on behalf of the UK Environmental Mutagen Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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In-situ investigations of the ionosphere of comet 67P
NASA Astrophysics Data System (ADS)
Eriksson, A. I.; Edberg, N. J. T.; Odelstad, E.; Vigren, E.; Engelhardt, I.; Henri, P.; Lebreton, J.-P.; Galand, M.; Carr, C. M.; Koenders, C.; Nilsson, H.; Broiles, T.; Rubin, M.
2015-10-01
Since arrival of Rosetta at its target comet 67P/Churyumov-Gerasimenko in August 2014, the plasma environment has been dominated by ionized gas emanating from the comet nucleus rather than by solar wind plasma. This was evident early on from the strong modulation seen with Rosetta's position in a reference frame fixed to the rotating nucleus, with higher plasma densities observed when the spacecraft is above the neck region and when the comet exposes maximum area to the sun. In this respect, Rosetta is inside the comet ionosphere, providing excellent in situ investigation opportunities for the instruments of the Rosetta Plasma Consortium (RPC). In contrast to the often modelled scenario for a very active comet, the Langmuir probe instrument (RPC-LAP) finds electron temperatures mainly in the range of tens of thousand kelvin around this less active comet. This can be attributed to the lower density of neutral gas, meaning little cooling of recently produced electrons. A side effect of this is that the spacecraft charges negatively when within about 100 km from the nucleus. Interesting in itself, this also may point to similar charging for dust grains in the coma, with implications for the detection of the smallest particles and possibly for processes like electrostatic fragmentation. The inner coma also proves to be very dynamic, with large variations not only with latitude and longitude in a comet frame, but also with the solar wind and various wave phenomena.
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NASA Astrophysics Data System (ADS)
Volwerk, Martin; Goetz, Charlotte; Richter, Ingo; Delva, Magda; Ostaszewski, Katharina; Schwingenschuh, Konrad; Glassmeier, Karl-Heinz
2018-06-01
Context. The Rosetta Plasma Consortium (RPC) magnetometer (MAG) data during the tail excursion in March-April 2016 are used to investigate the magnetic structure of and activity in the tail region of the weakly outgassing comet 67P/Churyumov-Gerasimenko (67P). Aims: The goal of this study is to compare the large scale (near) tail structure with that of earlier missions to strong outgassing comets, and the small scale turbulent energy cascade (un)related to the singing comet phenomenon. Methods: The usual methods of space plasma physics are used to analyse the magnetometer data, such as minimum variance analysis, spectral analysis, and power law fitting. Also the cone angle and clock angle of the magnetic field are calculated to interpret the data. Results: It is found that comet 67P does not have a classical draped magnetic field and no bi-lobal tail structure at this late stage of the mission when the comet is already at 2.7 AU distance from the Sun. The main magnetic field direction seems to be more across the tail direction, which may implicate an asymmetric pick-up cloud. During periods of singing comet activity the propagation direction of the waves is at large angles with respect to the magnetic field and to the radial direction towards the comet. Turbulent cascade of magnetic energy from large to small scales is different in the presence of singing as without it.
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NASA Technical Reports Server (NTRS)
DiSanti, M. A.; Bonev, B. P.; Vilanueva, G. L.; Paganini, L.; Radeva, Y. L.; Mumma, M. J.; Gibb, E.; Magee-Sauer, K.
2012-01-01
Comets retain relatively primitive icy material remaining from the epoch of Solar System formation, however the extent to which they are modified from their initial state remains a key question in cometary science. High-resolution lR spectroscopy has emerged as a powerful tool for measuring vibrational emissions from primary volatiles (i.e., those contained in the nuclei of comets). With modern instrumentation, most notably NIRSPEC at the Keck II 10-m telescope, we can quantify species of astrobiological importance (e.g., H20, C2H2, CH4, C2H6, CO, H2CO, CH30H, HCN, NH3). In space environments, compounds of keen interest to astrobiology could originate from HCN and NH3 (leading to amino acids), H2CO (leading to sugars), or C2H6 and CH4 (suggested precursors of ethyl- and methylamine). Measuring the abundances of these precursor molecules (and their variability among comets) is a feasible task that contributes to understanding their delivery to Earth's early biosphere and to the synthesis of more complex pre biotic compounds. Over 20 comets have now been measured with IR spectroscopy, and this sample reveals significant diversity in primary volatile compositions. From this, a taxonomic classification scheme is emerging, presumably reflecting the diverse conditions experienced by pre-cometary grains in interstellar and subsequent nebular environs. The importance of H-atom addition to C2H2 on the surfaces of interstellar grains to produce C2H6 was validated by the discovery of abundant ethane in comet C/1996 B2 (Hyakutake) with C2H6/CH4 well above that achievable by gas-phase chemistry , and then in irradiation experiments on laboratory ices at 10 - 50 K. The large abundance ratios C2H6/CH4 observed universally in comets establish H-atom addition as an important and likely ubiquitous process, and comparing C2H6/C2H2 among comets can provide information on its efficiency. The IR is uniquely capable since symmetric hydrocarbons (e.g., C2H2, CH4, C2H6) have no electric dipole moment and thus no allowed pure rotational transitions. CO should also be hydrogenated on grain surfaces. Irradiation experiments on interstellar ice analogs show this to require very low temperatures, the resulting yields of H2CO and CH30H being highly dependent on temperature in the range approx 10 - 25 K. The relative abundances of these chemically-related molecules in comets provide one measure of the efficiency of H-atom addition to CO Oxidation of CO is also important on grain mantles, as evidenced by the widespread presence of C02 ice towards interstellar sources observed with ISO and in a survey of 17 comets observed with AKARI. H-atom addition to C2H2 produces the vinyl radical, and through subsequent oxidation1reduction reactions can lead to vinyl alcohol, acetaldehyde, and ethanol This may have implications for interpreting observed abundance ratios CO/C2H2. We will discuss possible implications regarding formation conditions in the context of measured primary volatile compositions, emphasizing recently observed comets and published results. These are continually providing new insights regarding our taxonomic scheme and also delivery of pre-biological material to the young Earth.
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Shamim, Uzma; Hanif, Sarmad; Ullah, M F; Azmi, Asfar S; Bhat, Showket H; Hadi, S M
2008-08-01
It was earlier proposed that an important anti-cancer mechanism of plant polyphenols may involve mobilization of endogenous copper ions, possibly chromatin-bound copper and the consequent pro-oxidant action. This paper shows that plant polyphenols are able to mobilize nuclear copper in human lymphocytes, leading to degradation of cellular DNA. A cellular system of lymphocytes isolated from human peripheral blood and comet assay was used for this purpose. Incubation of lymphocytes with neocuproine (a cell membrane permeable copper chelator) inhibited DNA degradation in intact lymphocytes. Bathocuproine, which is unable to permeate through the cell membrane, did not cause such inhibition. This study has further shown that polyphenols are able to degrade DNA in cell nuclei and that such DNA degradation is inhibited by neocuproine as well as bathocuproine (both of which are able to permeate the nuclear pore complex), suggesting that nuclear copper is mobilized in this reaction. Pre-incubation of lymphocyte nuclei with polyphenols indicates that it is capable of traversing the nuclear membrane. This study has also shown that polyphenols generate oxidative stress in lymphocyte nuclei which is inhibited by scavengers of reactive oxygen species (ROS) and neocuproine. These results indicate that the generation of ROS occurs through mobilization of nuclear copper resulting in oxidatively generated DNA breakage.
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Education And Public Outreach For NASA's EPOXI Mission
NASA Astrophysics Data System (ADS)
McFadden, Lucy-Ann A.; Warner, E. M.; Crow, C. A.; Ristvey, J. D.; Counley, J.
2008-09-01
NASA's EPOXI mission has two scientific objectives in using the Deep Impact flyby spacecraft for further studies of comets and adding studies of extra-solar planets around other stars. During the Extrasolar Planetary Observations and Characterization (EPOCh) phase of the mission, observations of extrasolar planets transiting their parent stars are observed to further knowledge and understanding of planetary systems. Observations of Earth allow for comparison with Earth-like planets around other stars. A movie of Earth during a day when the Moon passed between Earth and the spacecraft is an educational highlight with scientific significance. The Deep Impact Extended Investigation (DIXI) continues the Deep Impact theme of investigating comets with a flyby of comet Hartley 2 in November 2010 to further explore the properties of comets and their formation. The EPOXI Education and Public Outreach (E/PO) program builds upon existing materials related to exploring comets and the Deep Impact mission, updating and modifying activities based on results from Deep Impact. An educational activity called Comparing Comets is under development that will guide students in conducting analyses similar to those that DIXI scientists will perform after observing comet Hartley 2. Existing educational materials related to planet finding from other NASA programs are linked from EPOXI's web page. Journey Through the Universe at the National Air and Space Museum encourages education in family and community groups and reaches out to underrepresented minorities. EPOXI's E/PO program additionally offers a newsletter to keep the public, teachers, and space enthusiasts apprised of mission activities. For more information visit: http://epoxi.umd.edu.
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Periodicity Signatures of Lightcurves of Active Comets in Non-Principal-Axis Rotational States
NASA Astrophysics Data System (ADS)
Samarasinha, Nalin H.; Mueller, Beatrice E. A.; Barrera, Jose G.
2016-10-01
There are two comets (1P/Halley, 103P/Hartley 2) that are unambiguously in non-principal-axis (NPA) rotational states in addition to a few more comets that are candidates for NPA rotation. Considering this fact, and the ambiguities associated with how to accurately interpret the periodicity signatures seen in lightcurves of active comets, we have started an investigation to identify and characterize the periodicity signatures present in simulated lightcurves of active comets. We carried out aperture photometry of simulated cometary comae to generate model lightcurves and analyzed them with Fourier techniques to identify their periodicity signatures. These signatures were then compared with the input component periods of the respective NPA rotational states facilitating the identification of how these periodicity signatures are related to different component periods of the NPA rotation. Ultimately, we also expect this study to shed light on why only a small fraction of periodic comets is in NPA rotational states, whereas theory indicates a large fraction of them should be in NPA states (e.g., Jewitt 1999, EMP, 79, 35). We explore the parameter space with respect to different rotational states, different orientations for the total rotational angular momentum vector, and different locations on the nucleus for the source region(s). As for special cases, we also investigate potential NPA rotational states representative of comet 103P/Hartley2, the cometary target of the EPOXI mission. The initial results from our investigation will be presented at the meeting. The NASA DDAP Program supports this work through grant NNX15AL66G.
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The activity of C-G at 3.5 AU from the Sun
NASA Astrophysics Data System (ADS)
Rubin, M.; Altwegg, K.
2014-04-01
Starting in early August the ROSINA instrument on board the Rosetta spacecraft (1] saw clearly cometary molecules above the spacecraft background. The COPS sensor, which measures the total density with its nude gauge, registered large density variations in line with the rotation period of the comet. Mapping this to the comet showed that especially the neck of the comet is very active whenever it comes into sunlight. However, the outgassing pattern is more complex. In this talk we give an overview on the measured density profiles along the Rosetta trajectory.
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NASA Astrophysics Data System (ADS)
Zaprudin, B.; Lehto, H. J.; Nilsson, K.; Somero, A.; Pursimo, T.; Snodgrass, C.; Schulz, R.
2017-07-01
Context. 67P/Churyumov-Gerasimenko (67P/C-G) is a short-period Jupiter family comet with an orbital period of 6.55 yr. Being the target comet of ESA's Rosetta mission, 67P/C-G has become one of the most intensively studied minor bodies of the solar system. The Rosetta Orbiter and the Philae Lander have brought us unique information about the structure and activity of the comet nucleus, as well as its activity along the orbit, composition of gas, and dust particles emitted into the coma. However, as Rosetta stayed in very close proximity to the cometary nucleus (less than 500 km with a few short excursions reaching up to 1500 km), it could not see the global picture of a coma at the scales reachable by telescopic observations (103 - 105 km). Aims: In this work we aim to connect in-situ observations made by Rosetta with the morphological evolution of the coma structures monitored by the ground-based observations. In particular, we concentrate on causal relationships between the coma morphology and evolution observed with the Nordic Optical Telescope (NOT) in the Canary Islands, and the seasonal changes of the insolation and the activity of the comet observed by the Rosetta instruments. Methods: Comet 67P/C-G was monitored with the NOT in imaging mode in two colors. Imaging optical observations were performed roughly on a weekly basis, which provides good coverage of short- and long-term variability. With the three dimensional modeling of the coma produced by active regions on the southern hemisphere, we aim to qualify the observed morphology by connecting it to the activity observed by Rosetta. Results: During our monitoring program, we detected major changes in the coma morphology of comet 67P/C-G. These were long-term and long-lasting changes. They do not represent any sudden outburst or short transient event, but are connected to seasonal changes of the surface insolation and the emergence of new active regions on the irregular shaped comet nucleus. We have also found significant deviations in morphological changes from the prediction models based on previous apparitions of 67P/C-G, like the time delay of the morphology changes and the reduced activity in the northern hemisphere. According to our modeling of coma structures and geometry of observations, the changes are clearly connected with the activity in the southern hemisphere observed by the Rosetta spacecraft.
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The Dependence of the Circumnuclear Coma Structure on the Properties of the Nucleus
NASA Astrophysics Data System (ADS)
Crifo, J. F.; Rodionov, A. V.
1997-06-01
A new step of development of the 3-D circumnuclear coma (“CNC”) model described in Crifoet al.(1995) is presented: now the gas and dust production are computed from an explicit dusty-ice sublimation model and a realistic dust mass spectrum is used. For the first time, (1) a clear distinction is made betweennucleus active area fraction gandactive surface icy area fraction f; (2) the dependence of the dusty ice sublimation rate onfand that offon the heliocentric distancerhdue to the evolution of the dust cover are explicitly taken into account; (3) the 3-D structure of the CNC is described thoroughly instead of only in one symmetry plane; (4) the 3-D CNC model is quantitatively fitted to observational data; (5) a detailed comparison is made between the CNC structures resulting from two alternative assumptions concerning the nucleus. The first assumed nucleus is a homogeneous sphere of dusty ice (g= 1). We show that, in this case: (1) The maximum ejectable mass of spherical dust grains has a ∝f(rh) cosz/r2hdependence upon solar zenith anglezand uponrh. (2) The terminal ejected dust velocities have an approximate ∝coszdependence onzand a strong ∝f(rh)/rhdependence onrh. Fitting-for definiteness-the model to the light curve of the weak Comet P/Wirtanen (P/W), target of the future Rosetta mission, we find, assuming an upper limit nucleus radius of 1.4 km, that: (1)fdecreases from about 14% at perihelion to possibly 0.025% atrh= 3 AU; (2) forrh≤ 2.5 AU all or most of the sunward circumnuclear CNC is in fluid regime; (3) for 2.5 ≤rh≤ 3 AU, most of the sunward CNC is in the so-called “transition regime”; (4) due to their dependence uponf, the dust velocities are in absolute value much smaller than expected from the usually accepted algorithms (which assumef≡ 1) and decrease strongly with increasingrh. The physical significance of these results is discussed. The second assumed nucleus fitted to P/W is an inhomogeneous sphere of dusty ice, most of the gas and dust production being due to four identical active areas separated by a background area, and covering a fractiong= 0.43 of the surface. It is found that, up to at least 2 AU, the structure of the CNC is, in such a case complex. (1) Owing to the difference in solar zenith angle, identical active areas produce differing CNC gas and dust distributions: therefore, in an inhomogeneous rotating nucleus, an active region is not characterized by a fixed corotating CNC pattern. (2) As with more productive comets, the interaction between gas issuing from different active regions leads to the formation of three-dimensional quasi stationary shock structures. (3) In particular, the weaker active areas cannot expand freely in the sunward hemisphere, but are surrounded by a low-altitude concave sheath of shocked gas and deflected dust. (4) Near to the shock surfaces, the dust density distribution is characterized, as in more productive comets, by density patterns that mimic dust jets. (5) Over the background areas, and close to the surface, the gas flows transverse to the vertical, and exhibits steepincreasesin density outwards. (6) The results reveal a fast smoothing-out of the CNC near-surface patterns with increasing distance to the surface. The implications of the present results for (1) the general physical characterization of comet nuclei on the basis of their coma-averaged properties, and (2) the assessment of the environmental parameters of future cometary close encounter missions are discussed. In particular, we show that simple, unidimensional heuristic models based on observations of a comet from the Earth are unable to provide relevant predictions concerning the physical conditions near to its nucleus. This conclusion is further enforced by the companion paper-Crifo and Rodionov (1996)-in which anasphericalhomogeneous nucleus is assumed.
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The evolving activity of the dynamically young comet C/2009 P1 (Garradd)
DOE Office of Scientific and Technical Information (OSTI.GOV)
Bodewits, D.; Farnham, T. L.; A'Hearn, M. F.
2014-05-01
We used the Ultraviolet-Optical Telescope on board Swift to observe the dynamically young comet C/2009 P1 (Garradd) from a heliocentric distance of 3.5 AU pre-perihelion until 4.0 AU outbound. At 3.5 AU pre-perihelion, comet Garradd had one of the highest dust-to-gas ratios ever observed, matched only by comet Hale-Bopp. The evolving morphology of the dust in its coma suggests an outburst that ended around 2.2 AU pre-perihelion. Comparing slit-based measurements and observations acquired with larger fields of view indicated that between 3 AU and 2 AU pre-perihelion a significant extended source started producing water in the coma. We demonstrate thatmore » this source, which could be due to icy grains, disappeared quickly around perihelion. Water production by the nucleus may be attributed to a constantly active source of at least 75 km{sup 2}, estimated to be >20% of the surface. Based on our measurements, the comet lost 4 × 10{sup 11} kg of ice and dust during this apparition, corresponding to at most a few meters of its surface. Even though this was likely not the comet's first passage through the inner solar system, the activity of Garradd was complex and changed significantly during the time it was observed.« less
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Observations of the 18-cm lines of the OH radical in comets
NASA Astrophysics Data System (ADS)
Crovisier, J.; Colom, P.; Biver, N.; Bockelée-Morvan, D.
2015-10-01
Since 1973, the 18-cm lines of the OH radical have been systematically observed in selected comets with the 300×40 m radio telescope at Nançay. Up to now, 133 comets have been observed (counting different returns of short-period comets as different comets), totalling about 6000 individual observations (typically one hour per day for each observation).These observations trace the water production rates (through its photodissociation product OH) and the coma expansion velocity. They are precious for statistical investigations of the evolution of the activity of the comets. These observations are also made as a participation to multi-wavelength observing campaigns of dedicated comets and as a support to cometary space missions. The observations are organized in a database which is progressively made publicly available: http://www.lesia.obspm.fr/planeto/ cometes/basecom/ [1]The most recent observations are listed in Table 1. Here are some recent highlights: 103P/Hartley 2 was observed in support to its fly-by by the EPOXI mission and to observations with Herschel. [2] The outbursts of the sungrazing comet C/2012 S1 (ISON), preceding its demise as it approached the Sun at 0.012 AU on 28 November 2013, were observed. [3] Comet C/2013 A1 (Siding Spring) was detected just before it passed at only 0.001 AU from Mars on 19 October 2014, due to enhanced background radiation as the comet was close to the Galactic plane. [4] The Nançay radio telescope actively participated to the multi-wavelength observing campaigns of the bright comets C/2011 L4 (PANSTARRS), C/2012 F6 (Lemmon), C/2012 X1 (LINEAR), C/2013 R1 (Lovejoy) and C/2014 Q2 (Lovejoy) (Fig. 1), especially in coordination with radio observations with IRAM and ALMA. It should be noted that the Rosetta target 67P/Churyumov-Gerasimenko, which was marginally detected at its 1982 passage due to a relatively close approach to Earth (# = 0.39 AU) [1], is unfavourably placed at its present return for observations at Nançay.
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Asteroid Family Associations of Main-Belt Comets
NASA Astrophysics Data System (ADS)
Hsieh, Henry H.; Novakovic, Bojan; Kim, Yoonyoung; Brasser, Ramon
2016-10-01
We present a population-level analysis of the asteroid family associations of known main-belt comets or main-belt comet candidates (which, to date, have largely just been analyzed on individual bases as they have been discovered). In addition to family associations that have already been reported in the literature, we have identified dynamical relationships between 324P/La Sagra and the Alauda family, P/2015 X6 (PANSTARRS) and the Aeolia family, and P/2016 G1 (PANSTARRS) and the Adeona family. We will discuss the overall implications of these family associations, particularly as they pertain to the hypothesis that members of primitive asteroid family members may be more susceptible to producing observable sublimation-driven dust emission activity, and thus becoming main-belt comets. We will also discuss the significance of other dynamical and physical properties of a family or sub-family as they relate to the likelihood of that family containing one or more currently active main-belt comets.
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EPOXI: Comet 103p/Hartley 2 Observations from a Worldwide Campaign
NASA Technical Reports Server (NTRS)
Meech, K. J.; Hearn, M. F. A.; Bauer, J. M.; Bonev, B. P.; Charnley, S. B.; DiSanti, M. A.; Gersch, A.; Immler, S. M.; Kaluna, H. M.; Keane, J. V.;
2011-01-01
Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales. at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P (Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was approximately 16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production.
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NASA Astrophysics Data System (ADS)
Kovalenko, N.; Churyumov, K.; Babenko, Yu.
2002-01-01
Chiron, comet 39P/Oterma and comet 29P/Schwassmann-Wachmann 1 are discussed. The orbital evolutions of chosen objects were traced 1 million years backward and forward from the present time. For numerical integration the program based on the Everhart implicit single sequence methods for integrating orbits was used. perturbations from the giant planets and very chaotic. It is now believed that Centaurs could be captured from the Kuiper Belt and in the future transform into the short-period comets. Currently more then 20 Centaurs are known. The cometary activity in one of them (2060 Chiron) has been detected up to now. simulated the past and future orbital evolution of active Centaur 2060 (95P) Chiron and two distant Jupiter-family comets with similar to Centaurs' perihelia and aphelia - comets 39P/Oterma and 29P/Schwassmann-Wachmann 1. Only our knowledge gathered from the Earth-based observations, orbital evolution investigations and future spacecraft missions will solve this problem.
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Georgieva, Mariyana; Rashydov, Namik M; Hajduch, Martin
2017-02-01
This pilot study was carried out to assess the effect of radio-contaminated Chernobyl environment on plant genome integrity 27 years after the accident. For this purpose, nuclei were isolated from root tips of the soybean seedlings harvested from plants grown in the Chernobyl area for seven generations. Neutral, neutral-alkaline, and methylation-sensitive comet assays were performed to evaluate the induction and repair of primary DNA damage and the epigenetic contribution to stress adaptation mechanisms. An increased level of single and double strand breaks in the radio-contaminated Chernobyl seedlings at the stage of primary root development was detected in comparison to the controls. However, the kinetics of the recovery of DNA breaks of radio-contaminated Chernobyl samples revealed that lesions were efficiently repaired at the stage of cotyledon. Methylation-sensitive comet assay revealed comparable levels in the CCGG methylation pattern between control and radio-contaminated samples with a slight increase of approximately 10% in the latter ones. The obtained preliminary data allow us to speculate about the onset of mechanisms providing an adaptation potential to the accumulated internal irradiation after the Chernobyl accident. Despite the limitations of this study, we showed that comet assay is a sensitive and flexible technique which can be efficiently used for genotoxic screening of plant specimens in natural and human-made radio-contaminated areas, as well as for safety monitoring of agricultural products. Copyright © 2016 Elsevier B.V. All rights reserved.
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Ghaoui, Roula; Sallustio, Benedetta C; Burcham, Philip C; Fontaine, Frank R
2003-05-06
Glucuronidation of a number of carboxyl-containing drugs generates reactive acyl glucuronide metabolites. These electrophilic species alkylate cell proteins and may be implicated in the pathogenesis of a number of toxic syndromes seen in patients receiving the parent aglycones. Whether acyl glucuronides also attack nuclear DNA is unknown, although the acyl glucuronide formed from clofibric acid was recently found to decrease the transfection efficiency of phage DNA and generate strand breaks in plasmid DNA in vitro. To determine if such a DNA damage occurs within a cellular environment, the comet assay (i.e. single-cell gel electrophoresis) was used to detect DNA lesions in the nuclear genome of isolated mouse hepatocytes cultured with clofibric acid. Overnight exposure to 50 microM and higher concentrations of clofibric acid produced concentration-dependent increases in the comet areas of hepatocyte nuclei, with 1 mM clofibrate producing a 3.6-fold elevation over controls. These effects closely coincided with culture medium concentrations of the glucuronide metabolite formed from clofibric acid, 1-O-beta-clofibryl glucuronide. Consistent with a role for glucuronidation in the DNA damage observed, the glucuronidation inhibitor borneol diminished glucuronide formation from 100 microM clofibrate by 98% and returned comet areas to baseline levels. Collectively, these results suggest that the acyl glucuronide formed from clofibric acid is capable of migrating from its site of formation within the endoplasmic reticulum to generate strand nicks in nuclear DNA.
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NASA Astrophysics Data System (ADS)
Tavera Busso, Iván; Vera, Anahí; Mateos, Ana Carolina; Amarillo, Ana Carolina; Carreras, Hebe
2017-10-01
Concentration of fine particulate matter (PM2.5) is one of the most important environmental parameters to estimate health impacts attributable to air pollution. Despite the fact there are many studies regarding PM2.5 effects on human health, most of them were performed under conditions that do not simulate the natural particles interaction with the organism. In the present paper, we studied the effects of mammals' sub-chronic exposure to PM2.5 on the lower respiratory tract, addressing realistic exposure conditions to normal urban air. Thus, we exposed Wistar rats under controlled settings to the same normal urban air, with and without particles. Next, we analyzed chemical composition of PM2.5 and lungs samples, performed a histologic examination and run the comet assay to assess genotoxic effects. We found a strong agreement between lung tissues and PM2.5 elemental composition suggesting that metals found in lungs came from the particles inhaled. Histological analysis showed a mild to moderate infiltration, with a reduction of alveoli lumen and increment of alveolar macrophages and periodic acid-Schiff (PAS) (+) cells in treated animals. We also observed an increase in the number of nuclei with comets, mostly comets type 3, with a high DNA fragmentation as well. These results provide strong evidence that sub-chronic exposure to low particle levels, even below the 24 h WHO standard, can cause injuries in lungs tissues and DNA damage, as well.
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Constraints on Comet 332P/Ikeya-Murakami
NASA Astrophysics Data System (ADS)
Hui, Man-To; Ye, Quan-Zhi; Wiegert, Paul
2017-01-01
Encke-type comet 332P/Ikeya-Murakami is experiencing cascading fragmentation events during its 2016 apparition. It is likely the first splitting Encke-type comet ever observed. A nongravitational solution to the astrometry reveals a statistical detection of the radial and transverse nongravitational parameters, {A}1=(1.54+/- 0.39)× {10}-8 au day‑2 and {A}2=(7.19+/- 1.92)× {10}-9 au day‑2, respectively, which implies a nucleus erosion rate of (9.1+/- 1.7)‰ per orbital revolution. The mass-loss rate likely has to be supported by a much larger fraction of an active surface area than known cases of short-period comets; it may be relevant to the ongoing fragmentation. We failed to detect any serendipitous pre-discovery observations of the comet in archival data from major sky surveys, whereby we infer that 332P used to be largely inactive, and is perhaps among the few short-period comets that have been reactivated from weakly active or dormant states. We therefore constrain an upper limit to the nucleus size as 2.0 ± 0.2 km in radius. A search for small bodies in similar orbits to that of 332P reveals comet P/2010 B2 (WISE) to be the best candidate. From an empirical generalized Jupiter-family (Encke-type included) comet population model, we estimate the likelihood of a chance alignment of the 332P–P/2010 B2 pair to be 1 in 33, a small number indicative of a genetic linkage between the two comets on a statistical basis. The pair possibly originated from a common progenitor, which underwent a disintegration event well before the twentieth century.
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NASA Technical Reports Server (NTRS)
Luna, Michael E.; Collins, Stephen M.
2011-01-01
On November 4, 2010 the already "in-flight" Deep Impact spacecraft flew within 700km of comet 103P/Hartley 2 as part of its extended mission EPOXI, the 5th time to date any spacecraft visited a comet. In 2005, the spacecraft had previously imaged a probe impact comet Tempel 1. The EPOXI flyby marked the first time in history that two comets were explored with the same instruments on a re-used spacecraft-with hardware and software originally designed and optimized for a different mission. This made the function of the attitude determination and control subsystem (ADCS) critical to the successful execution of the EPOXI flyby. As part of the spacecraft team preparations, the ADCS team had to perform thorough sequence reviews, key spacecraft activities and onboard calibrations. These activities included: review of background sequences for the initial conditions vector, sun sensor coefficients, and reaction wheel assembly (RWA) de-saturations; design and execution of 10 trajectory correction maneuvers; science calibration of the two telescope instruments; a flight demonstration of the fastest turns conducted by the spacecraft between Earth and comet point; and assessment of RWA health (given RWA problems on other spacecraft).
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The 67P nucleus composition and temporal variations observed by the OSIRIS cameras onboard Rosetta
NASA Astrophysics Data System (ADS)
Fornasier, Sonia; Barucci, Maria Antonietta; Feller, Clement; Deshapriya, Prasanna J. D.; Pommerol, Antoine; Lara, Luisa; Oklay, Nilda; A'Hearn, Mike; Davidsson, Bjorn; Perna, Davide; Sierks, Holger
2015-11-01
Since August 2014, the comet 67P/Churyumov-Gerasimenko has been mapped by the NAC and WAC cameras of the OSIRIS imaging system in the 250-1000 nm wavelength range. OSIRIS got the most detailed maps at the highest spatial resolution of a comet nucleus surface. Here we report on the colors and spectrophotometry of the whole 67P nucleus from images acquired since the first Rosetta bound orbits in August 2014 up to the comet perihelion passage. Globally, the nucleus shows a red spectral behavior and it has spectrophotometric properties similar to those of bare cometary nuclei, of primitive D-type asteroids such us Jupiter Trojans, and of the moderately red Transneptunians. No clear absorption bands have been identified yet in the UV-VIS-NIR range, except for a potential absorption centered at 290 nm, possibly due to SO2 ice. The nucleus shows an important phase reddening, with disk-averaged spectral slopes increasing from 11%/(100 nm) to 16%/(100 nm) in the 1.3-54° phase angle range. On the basis of the spectral slope, we identified three different groups of regions, characterized by a low, medium, and high spectral slope, respectively. The three groups are distributed everywhere on the nucleus, with no evident distinction between the two lobes of the comet. The comet southern hemisphere, that has been observed by Rosetta since April 2015, shows a lack of spectrally red regions associated to the absence of wide spread smooth or dust covered terrains. Several local bright and spectrally blue patches have been identified on the nucleus and attributed to exposed water ice on the surface. In particular we observed big (> 1500 m2) bright ice rich areas in the southern hemisphere which completely sublimated in a few weeks. We see evidence of very bright patches in the NUV-blue region close to the morning shadows that are compatible with the presence of frosts/ices. These patches disappear when fully illuminated by the Sun indicating that important processes of sublimation and recondensation of volatiles are taking place on the nucleus.
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Interior of 67P/C-G comet as seen by CONSERT bistatic radar on Rosetta
NASA Astrophysics Data System (ADS)
Ciarletti, V.; Kofman, W. W.; Herique, A.; Levasseur-Regourd, A. C.; Lasue, J.; Zine, S.; Plettemeier, D.
2017-12-01
The scientific objectives of the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) aboard ESA spacecraft's Rosetta was to perform an interior characterization of comet 67P/C-G nucleus. This characterization is important to understand the formation and evolution of comets. The measurements were done by means of a bi-static sounding between Philae lander on the nucleus surface and Rosetta orbiter. CONSERT operated during 9 hours after Philae's landing and made measurements through the small lobe (head) of 67P/ C-G. The analyses and interpretation have been done using the shape of the received signals and 3D modeling of the signal propagation. The propagation time inside the nucleus allowed us to derive the average permittivity value (1.27+/- 0.05 ) of the cometary interior. Permittivity data for ices and dust particles were compared with our measurements, providing constraints on the nucleus constituents (ices, silicates and organics) and the bulk porosity (70-85%). The shape of the received signals, very close to the calibration signal's one, showed that no significant scattering by heterogeneities is occurring inside the nucleus. This indicates that the interior is homogeneous at a scale of a few CONSERT's 3-m wavelengths. This conclusion lead to 3D simulations of the signal propagation in non-homogeneous nuclei models, to define the sensitivity of CONSERT to detect potential inhomogeneities and to find constrains on the internal structures in terms of size and composition at a scale commensurate with the wavelength. Given the high bulk porosity of 75% inside the sounded part of the nucleus, a likely model would be obtained by a mixture, at 3m-size scale, of voids (vacuum) and blobs with material made of ices and dust with a porosity above 60%. The absence of any pulse spreading by scattering excludes heterogeneities with higher contrast (0.25) and larger size (3m) (but remaining on the few wavelengths scale, since larger scales can be responsible for multipath propagation). These very important results provide clues to a better understanding of the comet formation processes.
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NASA Astrophysics Data System (ADS)
Koenders, C.; Perschke, C.; Goetz, C.; Richter, I.; Motschmann, U.; Glassmeier, K. H.
2016-10-01
Context. A new type of low-frequency wave was detected by the magnetometer of the Rosetta Plasma Consortium at the comet during the initial months after the arrival of the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. This large-amplitude, nearly continuous wave activity is observed in the frequency range from 30 mHz to 80 mHz where 40 mHz to 50 mHz is the dominant frequency. This type of low frequency is not closely related to the gyrofrequency of newborn cometary ions, which differs from previous wave activity observed in the interaction region of comets with the solar wind. Aims: This work aims to reveal a global view on the wave activity region using simulations of the comet-solar wind interaction region. Parameters, such as wavelength, propagation direction, and propagation patterns, are within the focus of this study. While the Rosetta observations only provide local information, numerical simulations provide further information on the global wave properties. Methods: Standard hybrid simulations were applied to the comet-solar wind interaction scenario. In the model, the ions were described as particles, which allows us to describe kinetic processes of the ions. The electrons were described as a fluid. Results: The simulations exhibit a threefold wave structure of the interaction region. A Mach cone and a Whistler wing are observed downstream of the comet. The third kind of wave activity found are low-frequency waves at 97 mHz, which corresponds to the waves observed by Richter et al. (2015, Ann. Geophys., 33, 1031). These waves are caused by the initial pick-up of the cometary ions that are perpendicular to the solar wind flow and in the interplanetary magnetic field direction. The associated electric current becomes unstable. The simulations show that wave activity is only detectable in the + E hemisphere and that the Mach cone and whistler wings need to be distinguished from the newly found instability driven wave activity. The movie associated to Fig. 10 is available at http://www.aanda.org
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Are There Many Inactive Jupiter-Family Comets among the Near-Earth Asteroid Population?
NASA Astrophysics Data System (ADS)
Fernández, Julio A.; Gallardo, Tabaré; Brunini, Adrián
2002-10-01
We analyze the dynamical evolution of Jupiter-family (JF) comets and near-Earth asteroids (NEAs) with aphelion distances Q>3.5 AU, paying special attention to the problem of mixing of both populations, such that inactive comets may be disguised as NEAs. From numerical integrations for 2×10 6 years we find that the half lifetime (where the lifetime is defined against hyperbolic ejection or collision with the Sun or the planets) of near-Earth JF comets (perihelion distances q<1.3 AU) is about 1.5×10 5 years but that they spend only a small fraction of this time (˜ a few 10 3 years) with q<1.3 AU. From numerical integrations for 5×10 6 years we find that the half lifetime of NEAs in "cometary" orbits (defined as those with aphelion distances Q>4.5 AU, i.e., that approach or cross Jupiter's orbit) is 4.2×10 5 years, i.e., about three times longer than that for near-Earth JF comets. We also analyze the problem of decoupling JF comets from Jupiter to produce Encke-type comets. To this end we simulate the dynamical evolution of the sample of observed JF comets with the inclusion of nongravitational forces. While decoupling occurs very seldom when a purely gravitational motion is considered, the action of nongravitational forces (as strong as or greater than those acting on Encke) can produce a few Enckes. Furthermore, a few JF comets are transferred to low-eccentricity orbits entirely within the main asteroid belt ( Q<4 AU and q>2 AU). The population of NEAs in cometary orbits is found to be adequately replenished with NEAs of smaller Q's diffusing outward, from which we can set an upper limit of ˜20% for the putative component of deactivated JF comets needed to maintain such a population in steady state. From this analysis, the upper limit for the average time that a JF comet in near-Earth orbit can spend as a dormant, asteroid-looking body can be estimated to be about 40% of the time spent as an active comet. More likely, JF comets in near-Earth orbits will disintegrate once (or shortly after) they end their active phases.
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NASA Technical Reports Server (NTRS)
Reme, H.; Mazelle, C.; Sauvaud, J. A.; D'Uston, C.; Froment, F.; Lin, R. P.; Anderson, K. A.; Carlson, C. W.; Larson, D. E.; Korth, A.
1993-01-01
The three-dimensional electron spectrometer of the Reme plasma analyzer-complete positive ion, electron and ram negative ion measurements near comet Halley (RPA-COPERNIC) experiment aboard the Giotto spacecraft, although damaged during the comet Halley encounter in March 1986, has provided very new results during the encounter on July 10, 1992, with the weakly active comet Grigg-Skjellerup (G-S). The main characteristic features of the highly structured interaction region extending from approximately 26,500 km inbound to approximately 37,200 km outbound are presented. These results are compared to the results obtained by the same instrument during the Giotto comet Halley fly-by. Despite the large difference in the size of the interaction regions (approximately 60,000 km for G-S, approximately 2000,000 km for Halley) due to 2 orders of magnitude difference in cometary neutral gas production rate, there are striking similarities in the solar wind interactions with the two comets.
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Will comet 209P/LINEAR generate the next meteor storm?
NASA Astrophysics Data System (ADS)
Ye, Quanzhi; Wiegert, Paul A.
2014-02-01
Previous studies have suggested that comet 209P/LINEAR may produce strong meteor activity on Earth on 2014 May 24; however, exact timing and activity level is difficult to estimate due to the limited physical observations of the comet. Here, we reanalyse the optical observations of 209P/LINEAR obtained during its 2009 apparition. We find that the comet is relatively depleted in dust production, with Afρ at 1 cm level within eight months around its perihelion. This feature suggested that this comet may be currently transitioning from a typical comet to a dormant comet. Syndyne simulation shows that the optical cometary tail is dominated by larger particles with β ˜ 0.003. Numerical simulations of the cometary dust trails confirm the arrival of particles on 2014 May 24 from some of the 1798-1979 trails. The nominal radiant is at RA 122° ± 1°, Dec. 79° ± 1° (J2000) in the constellation of Camelopardalis. Given that the comet is found to be depleted in dust production, we concluded that a meteor storm (ZHR ≥ 1000) may be unlikely. However, our simulation also shows that the size distribution of the arrived particles is skewed strongly to larger particles. Coupling with the result of syndyne simulation, we think that the event, if detectable, may be dominated by bright meteors. We encourage observers to monitor the expected meteor event as it will provide us with rare direct information on the dynamical history of 209P/LINEAR which is otherwise irretrievably lost.
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Behavioral Characteristics and CO+CO2 Production Rates of Halley-Type Comets Observed by NEOWISE
NASA Astrophysics Data System (ADS)
Rosser, Joshua David; Bauer, James M.; Mainzer, Amy K.; Kramer, Emily A.; Masiero, Joseph R.; Nugent, Carrie; Sonnett, Sarah M.; Fernandez, Yanga R.; Wright, Edward L.; WISE, NEOWISE
2017-10-01
From the NEOWISE dataset of comet images, 11 different Halley-Type Comets (HTCs) were identified and analyzed for dust production rates (Afρ), CO+CO2 production rates (QCO2), and nucleus size. The objects considered ranged in heliocentric distance from 1.21 AU to 2.66 AU and were only considered when showing signs of reasonable activity. When multiple epochs were included and when combined with data from previous WISE and NEOWISE studies, our dataset totaled to 21 observations; 13 of which included active comets, and 7 for which we calculated upper limits of production. Comet P/2010 JC81 was removed from consideration due to clear inactivity. For this study, active comets are defined as those which exhibit excess signal of at least 3σ in the 4.6 μm detection band, while comets for which upper limits were calculated demonstrated excess signal of 1σ in the 4.6 μm detection band. Furthermore, we confirmed the nucleus size of 27P, P/2006 HR30, C/2010 L5, P/2012 NJ, C/2016 S1. We found that given the range in heliocentric distance for this sample of HTCs, Afρ ranged from 0.790 ± 0.036 to 2.64 ± 0.14, and QCO2 ranged from 25.08 ± 0.08 to 26.71 ± 0.12. No significant correlation between dust production and heliocentric distance, nor CO+CO2 production with heliocentric distance was found for this population. This poster will display production rates and other physical properties of these HTCs, as well as place the ensemble of HTC production rate properties into context.
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Astronaut George Nelson working on Comet Halley Active monitoring program
1986-01-14
61C-05-026 (14 Jan. 1986) --- Astronaut George D. Nelson smiles for a fellow crew man's 35mm camera exposure while participating in the Comet Halley active monitoring program (CHAMP). Camera equipment and a protective shroud used to eliminate all cabin light interference surround the mission specialist. This is the first of three 1986 missions which are scheduled to monitor the rare visit by the comet. The principal investigators for CHAMP are S. Alan Stern of the Laboratory for Atmospheric and Space Physics at the University of Colorado; and Dr. Stephen Mende of Lockheed Palo Alto Research Laboratory.
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2016-10-07
The European Space Agency's Rosetta mission concluded its study of comet 67P/Churyumov-Gerasimenko on Sept. 30, 2016. NASA's planet-hunting Kepler spacecraft observed the comet during the final month of the Rosetta mission, while the comet was not visible from Earth. This animation is composed of images from Kepler of the comet. From Sept. 7 through Sept. 20, the Kepler spacecraft, operating in its K2 mission, fixed its gaze on comet 67P. From the distant vantage point of Kepler, the comet's nucleus and tail could be observed. The long-range view from Kepler complements the closeup view of the Rosetta spacecraft, providing context for the high-resolution investigation Rosetta performed as it descended closer and closer to the comet. During the two-week period of study, Kepler took a picture of the comet every 30 minutes. The animation shows a period of 29.5 hours of observation from Sept. 17 thru Sept. 18. The comet is seen passing through Kepler's field of view from top right to bottom left, as outlined by the diagonal strip. The white dots represent stars and other regions in space studied during K2's tenth observing campaign. As a comet travels through space it sheds a tail of gas and dust. The more material that is shed, the more surface area there is to reflect sunlight. A comet's activity level can be obtained by measuring the reflected sunlight. Analyzing the Kepler data, scientists will be able to determine the amount of mass lost each day as comet 67P travels through the solar system. An animation is available at http://photojournal.jpl.nasa.gov/catalog/PIA21072
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NASA Astrophysics Data System (ADS)
Mugrauer, M.; Hohle, M. M.; Ginski, C.; Vanko, M.; Freistetter, F.
2009-05-01
We present follow-up observations of comet 17/P Holmes after its extreme outburst in brightness, which occurred end of October 2007. We obtained 58 V-band images of the comet between October 2007 and February 2008, using the Cassegrain-Teleskop-Kamera (CTK) at the University Observatory Jena. We present precise astrometry of the comet, which yields its most recent Keplerian orbital elements. Furthermore, we show that the comet's coma expands quite linearly with a velocity of about 1650 km/s between October and December 2007. The photometric monitoring of comet 17/P Holmes shows that its photometric activity level decreased by about 5.9 mag within 105 days after its outburst. Based on observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.
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A search for the millimetre lines of HCN in Comets Wilson 1987 VII and Machholz 1988 XV
NASA Astrophysics Data System (ADS)
Crouvisier, J.; Despois, D.; Bockelee-Morvan, D.; Gerard, E.; Paubert, G.; Johansson, L. E. B.; Ekelund, L.; Winnberg, A.; Ge, W.; Irvine, W. M.; Kinzel, W. M.; Schloerb, F. P.
1990-08-01
The J(1-0) lines of HCN at 89 GHz were searched for in Comet Wilson 1987 VII, with the FCRAO, the SEST and the IRAM radio telescopes between February and June 1987. There was no firm detection, but significant upper limits were obtained, which put severe constraints on the HCN production rate in that comet. A direct comparison with the observations of P/Halley suggests that the HCN abundance relative to water might be smaller in Comet Wilson by at least a factor of two. The J(1-0) and J(3-2) lines of HCN at 89 and 266 GHz were searched for in Comet Machholz 1988 XV when it was close to perihelion at 0.17 AU from the sun. There was no detection. At that moment, the comet was probably no longer active.
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NASA Astrophysics Data System (ADS)
Lang, A.; Wesely, N.; Soós, B.; Sléber, B.; Majnovics, Z.; Ettingshausen, M.; Bodnár, L.; Németh, A.; Roos, M.
2011-10-01
In our school works a course in robotics where students build and program robots from a LEGO MINDSTORMS kit. We took part in the Hunveyor- Husar project with a Mars rover based on a rover model kit, of which the operating arms are built out of LEGO and controlled by an MINDSTORMS NXT computer. We presented our rover on the EPSC in Rome last September 2010 We presented our rover on the EPSC in Rome in September 2010. At that same conference the "Rosetta's Comet Touchdown" educational kit was officially presented. We were very interested and in conversation with the people from the project, we agreed that our school in Sopron would also participate in testing the kit. . The kit comes with a set of Interdisciplinary Activity Sheets (IAS, downloadable from Vimeo channel1) and a great feature is that the proposed activities in the IAS cover three areas: science, art/history and engineering. The 31 students from our class divided up in groups and each group chose a different topic: History of comets in Hungarian culture; Designing a T-shirt; Research on comets; Hungary in the Rosetta mission; Animation of Rosetta's orbit in space; building a LEGO MINDSTORM model; a film was made of the activities . In this presentation we report in particular the activities of the LEGO building team.
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Surface Activity Distributions of Comet 67P/Churyumov-Gerasimenko Derived from VIRTIS Images
NASA Astrophysics Data System (ADS)
Fougere, Nicolas; Combi, Michael R.; Tenishev, Valeriy; Migliorini, Alessandra; Bockelee-Morvan, Dominique; Fink, Uwe; Filacchione, Gianrico; Rinaldi, Giovanna; Capaccioni, Fabrizio; Toth, Gabor; Gombosi, T. I.; Hansen, Kenneth C.; Huang, Zhenguang; Shou, Yinsi; VIRTIS Team
2017-10-01
The outgassing mechanism of comets still remains a critical question to better understand these objects. The Rosetta mission gave some insight regarding the potential activity distribution from the surface of the nucleus of comet 67P/Churyumov-Gerasimenko, Fougere et al. (2016, Astronomy & Astrophysics, Volume 588, id.A134, 11 pp and Monthly Notices of the Royal Astronomical Society, Volume 462, Issue Suppl_1, p.S156-S169) used a spherical harmonics inversion scheme with in-situ measurements from the ROSINA instrument to derive mapping of the broad distribution of potential activity at the surface of the nucleus. Marschall et al. (2016, Astronomy & Astrophysics, doi: 10.1051/0004-6361/201730849) based on the appearance of dust active areas suggested that the so-called “neck” region and regions with fractured cliffs and locally steep slopes show more activity than the rest of comet 67P’s nucleus. Using in situ ROSINA measurements from a distance makes it difficult to distinguish between these two scenarios because the fast expansion of the gas and large molecular mean free paths prevents distinguishing small outgassing features even when the spacecraft was in bound orbits within 10 km from the nucleus. In this paper, we present a similar numerical inversion approach using VIRTIS images, which should better probe the very inner coma of comet 67P and give more detailed information about the outgassing activity. Support from contracts JPL #1266314 and #1266313 from the US Rosetta Project and grant NNX14AG84G from the NASA Planetary Atmospheres Program are gratefully acknowledged.
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NASA Astrophysics Data System (ADS)
Brouet, Y.; Levasseur-Regourd, A. C.; Encrenaz, P.; Gheudin, M.; Ciarletti, V.; Gulkis, S.; Jambon, A.; Ruffié, G.; Prigent, C.
2012-04-01
The European Rosetta spacecraft (s/c), launched in 2004, will be the first s/c to orbit a comet and place a lander module on its surface. In 2014, the s/c will rendezvous with the comet 67P/Churyumov-Gerasimenko and place the lander on its surface thereby allowing in situ and remote sensing of the comet nucleus. Two radio experiments, one passive (MIRO [1]) and one active (CONSERT [2]), are aboard the Rosetta s/c. MIRO, composed of two radiometers, with center band frequencies at 190 GHz and at 563 GHz to determine the brightness temperatures of the target surfaces and sub-surfaces, has already observed asteroids (2867) Steins [3] and (21) Lutetia [4]. CONSERT will investigate the deep interior of the nucleus using 90 MHz radio-waves transmitted from the orbiter through the nucleus and returned to the orbiter from the lander. To support interpretations of MIRO and CONSERT observations, a program of dielectric properties measurements is under development on a large range of frequencies encompassing those of the above-mentioned experiments. Several instruments for dielectric constant determination are available at IMS laboratory (Bordeaux, France): impedance analyzer, coaxial sensor, resonant cavities (measuring respectively at 100 MHz, 0.5-6 GHz, 1.2-13.4 GHz). Millimeter benches are available at both IMS and LERMA laboratories (measuring respectively at 30-110 GHz and 70-230 GHz). Taking into account the possible presence of regolith layers on the surface of asteroids or nuclei and the very low density of cometary nuclei [5], the dependence of the dielectric constant on the structure and porosity of given granular materials needs also to be investigated (while the thermal and hygrometric conditions are carefully monitored). We have already reported measurements obtained on various meteorites, possibly representative of some asteroid surfaces [6, 7]. We will also report systematic measurements obtained on a large sample of pyroclastic deposits from Etna, providing different sizes distributions (i.e. surface to volume ratios), and possibly porosities. Dielectric constant determination at 190 GHz typically suggests that the real part of dielectric constant slowly increases with grain size: 2.86 ± 0.06, 2.96 ± 0.02 and 3.13 ± 0.05 for sizes respectively lower than 50 µm, between 50 and 160 µm and between 160 and 355 µm. Additional series of measurements on compact and granular samples of meteoritic analogues, such as carbonaceous chondrites are also to take place. [1] Gulkis et al. , Space Sci. Rev., 128, 561-597, 2007. [2] Kofman et al. , Space Sci. Rev., 128, 413-432, 2007. [3] Gulkis et al. , Space. Sci. Rev., 58, 1077-1087, 2010. [4] Gulkis et al. , Space. Sci. Rev., doi: 10.1016/j.pss.2011.12.004, 2011. [5] Levasseur-Regourd et al. , Planet. Space Sci., 57, 221-228, 2009. [6] McFadden et al., 40th LPSC, 2887, 2009. [7] Brouet el al. , EPSC-DPS Joint Meeting, p. 1083, 2011.
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Dust environment and dynamical history of a sample of short-period comets
NASA Astrophysics Data System (ADS)
Pozuelos, F. J.; Moreno, F.; Aceituno, F.; Casanova, V.; Sota, A.; López-Moreno, J. J.; Castellano, J.; Reina, E.; Diepvens, A.; Betoret, A.; Häusler, B.; Gonález, C.; Rodríguez, D.; Bryssinck, E.; Cortés, E.; García, F.; García, F.; Limón, F.; Grau, F.; Fratev, F.; Baldrís, F.; Rodriguez, F. A.; Montalbán, F.; Soldán, F.; Muler, G.; Almendros, I.; Temprano, J.; Bel, J.; Sánchez, J.; Lopesino, J.; Báez, J.; Hernández, J. F.; Martín, J. L.; Ruiz, J. M.; Vidal, J. R.; Gaitán, J.; Salto, J. L.; Aymamí, J. M.; Bosch, J. M.; Henríquez, J. A.; Martín, J. J.; Lacruz, J.; Tremosa, L.; Lahuerta, L.; Reszelsky, M.; Rodríguez, M.; Camarasa, M.; Campas, M.; Canales, O.; Dekelver, P. J.; Moreno, Q.; Benavides, R.; Naves, R.; Dymoc, R.; García, R.; Lahuerta, S.; Climent, T.
2014-08-01
Aims: In this work, we present an extended study of the dust environment of a sample of short-period comets and their dynamical history. With this aim, we characterize the dust tails when the comets are active, and we make a statistical study to determine their dynamical evolution. The targets selected were 22P/Kopff, 30P/Reinmuth 1, 78P/Gehrels 2, 115P/Maury, 118P/Shoemaker-Levy 4, 123P/West-Hartley, 157P/Tritton, 185/Petriew, and P/2011 W2 (Rinner). Methods: We use two different observational data sets: a set of images taken at the Observatorio de Sierra Nevada and, the Afρ curves provided by the amateur astronomical association Cometas-Obs. To model these observations, we use our Monte Carlo dust tail code. From this analysis, we derive the dust parameters, which best describe the dust environment: dust loss rates, ejection velocities, and size distribution of particles. On the other hand, we use a numerical integrator to study the dynamical history of the comets, which allows us to determine with a 90% confidence level the time spent by these objects in the region of Jupiter family comets. Results: From the Monte Carlo dust tail code, we derived three categories according to the amount of dust emitted: weakly active (115P, 157P, and Rinner), moderately active (30P, 123P, and 185P), and highly active (22P, 78P, and 118P). The dynamical studies showed that the comets of this sample are young in the Jupiter family region, where the youngest ones are 22P (~100 yr), 78P (~500 yr), and 118P (~600 yr). The study points to a certain correlation between comet activity and time spent in the Jupiter family region, although this trend is not always fulfilled. The largest particle sizes are not tightly constrained, so that the total dust mass derived should be regarded as a lower limit. Appendices are available in electronic form at http://www.aanda.org
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ERIC Educational Resources Information Center
Noyce, Ruth, Ed.
Twenty-four biographical sketches of women in scientific professions are included in this COMETS Profiles package. Each biography relates to a science topic dealt with in one of the instructional modules of COMETS Science (Career Oriented Modules to Explore Topics in Science). The purpose of these materials is to demonstrate to early adolescents…
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NASA Astrophysics Data System (ADS)
Hadamcik, E.; Levasseur-Regourd, A.-C.
2014-07-01
Remote observations of sunlight scattered by solid particles provide information on the particle properties for a large variety of comets. When comets approach the Sun, solid particles and gases are released from the surface or from the inner layers [1,2]. If the comet is close enough to the Earth, the inner coma may be studied. Different coma regions are observed corresponding to different dust properties, e.g., in jets or fresh ejected dust around the coma. Narrow-band continuum filters or broader-band filters in less contaminated spectral domains (red or near infrared) are currently used to avoid or reduce the contributions from gaseous emission. Comet 73P/Schwassmann-Wachmann 3 is a fascinating fragmenting comet. Different observations in 1995 revealed an increase of activity and at least four fragments of the nucleus. In its 2011 apparition, the fragments were well separated and appeared like small individual comets. In 2006, its apparition was very favorable and allowed high- spatial resolution imaging by different complementary techniques. We observed three fragments of comet 73P/Schwassmann-Wachmann 3 from April 27 to May 3, 2006, by imaging polarimetry with the 80-cm telescope at Observatoire de Haute-Provence. The distance to the Earth was smaller than 0.2 au. Fragment C resembles a classical active comet. Regions of high and lower polarization were observed in the inner coma, appearing to change almost periodically. The variation of polarization in the inner coma was important from one night to the next one, the whole coma polarization being about constant for nucleus distances greater than 2000 km and increasing with the phase angle. Fragment B continued its (sequential) fragmentation, with a region of secondary fragments progressively moving away from the main nucleus in the antisolar direction. The chemical composition has been reported as being similar in all the fragments [3], but differences were observed between them in polarization underlining differences in, e.g., structure or size distribution of the particles during their ejection and fragmentation. The variation of polarization in the coma and around the fragments will be presented. Finally, a comparison to other comets, including split comets observed at small geocentric distances, will be provided.
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Rosetta Comet Spreads its Jets
2014-10-24
This image was taken by the Optical, Spectroscopic, and Infrared Remote Imaging System, Rosetta main onboard scientific imaging system, on Sept. 10, 2014. Jets of cometary activity can be seen along almost the entire body of the comet.
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Diamagnetic region(s): structure of the unmagnetized plasma around Comet 67P/CG
NASA Astrophysics Data System (ADS)
Henri, P.; Vallières, X.; Hajra, R.; Goetz, C.; Richter, I.; Glassmeier, K.-H.; Galand, M.; Rubin, M.; Eriksson, A. I.; Nemeth, Z.; Vigren, E.; Beth, A.; Burch, J. L.; Carr, C.; Nilsson, H.; Tsurutani, B.; Wattieaux, G.
2017-07-01
The ESA's comet chaser Rosetta has monitored the evolution of the ionized atmosphere of comet 67P/Churyumov-Gerasimenko (67P/CG) and its interaction with the solar wind, during more than 2 yr. Around perihelion, while the cometary outgassing rate was highest, Rosetta crossed hundreds of unmagnetized regions, but did not seem to have crossed a large-scale diamagnetic cavity as anticipated. Using in situ Rosetta observations, we characterize the structure of the unmagnetized plasma found around comet 67P/CG. Plasma density measurements from RPC-MIP are analysed in the unmagnetized regions identified with RPC-MAG. The plasma observations are discussed in the context of the cometary escaping neutral atmosphere, observed by ROSINA/COPS. The plasma density in the different diamagnetic regions crossed by Rosetta ranges from ˜100 to ˜1500 cm-3. They exhibit a remarkably systematic behaviour that essentially depends on the comet activity and the cometary ionosphere expansion. An effective total ionization frequency is obtained from in situ observations during the high outgassing activity phase of comet 67P/CG. Although several diamagnetic regions have been crossed over a large range of distances to the comet nucleus (from 50 to 400 km) and to the Sun (1.25-2.4 au), in situ observations give strong evidence for a single diamagnetic region, located close to the electron exobase. Moreover, the observations are consistent with an unstable contact surface that can locally extend up to about 10 times the electron exobase.
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Cosmogenic nuclide production within the atmosphere and long period comets
NASA Astrophysics Data System (ADS)
Overholt, Andrew C.
The Earth is constantly bombarded by cosmic rays. These high energy particles collide with target nuclei, producing a shower of secondary particles. These secondaries contribute significantly to the radiation background at sea level and in the atmosphere, as well as producing rare cosmogenic nuclides. This contribution is variable over long time scales as astrophysical events change the cosmic ray flux incident on the Earth. Our work re-examines a previously proposed climate effect of increased cosmic ray flux due to galactic location. Although our work does not support this effect, cosmic ray secondaries remain a threat to terrestrial biota. We calculate the cosmogenic neutron flux within the atmosphere as a function of primary spectrum. This work is pivotal in determining the radiation dose due to any arbitrary astrophysical event where the primary spectrum is known. Additionally, this work can be used to determine the cosmogenic nuclide production from such an event. These neutrons are the fundamental source of cosmogenic nuclides within our atmosphere and extraterrestrial matter. We explore the idea that excursions in 14C and 10Be abundances in the atmosphere may arise from direct deposition by long-period comet impacts, and those in 26Al from any bolide. We find that the amount of nuclide mass on large long-period comets entering the Earth's atmosphere may be sufficient for creating anomalies in the records of 14C and 10Be from past impacts. In particular, the estimated mass of the proposed Younger Dryas comet is consistent with its having deposited sufficient isotopes to account for recorded nuclide increases at that time. The 26Al/10Be ratio is much larger in extraterrestrial objects than in the atmosphere, and so, we note that measuring this ratio in ice cores is a suitable further test for the Younger Dryas impact hypothesis. This portion of our work may be used to find possible impact events in the geologic record as well as determination of a large bolide impact rate.
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Cometary Defense with Directed Energy
NASA Astrophysics Data System (ADS)
Zhang, Q.; Lubin, P. M.; Hughes, G. B.
2016-12-01
Cometary impacts pose a long-term hazard to humans on Earth. Due to their comparative rarity, most planetary defense schemes neglect the comet threat, choosing instead to focus exclusively on mitigating asteroid impacts. Methods like kinetic impactors may be suitable for deflecting near-Earth asteroids (NEAs) and Jupiter-family comets (JFCs), both of which are characterized by low inclination orbits and short orbital periods which favor early detection—characteristics ideal for an interception mission. In contrast, Halley-type comets (HTCs) and long-period comets (LPCs) are often found in high inclination orbits rarely more than 2 yr prior to reaching Earth's orbit. Unless discovered and identified in a prior apparition—often centuries or millennia earlier, if ever—timely interception of a threatening HTC or LPC is improbable even with preparation, with missions demanding delta-v budgets often in excess of 30 km/s. Active comets, however, are already naturally perturbed from purely gravitational trajectories through solar-driven sublimation of volatiles. Further deflection may be achieved by supplementing the solar radiation with an artificial directed energy source such as by one or more laser arrays positioned on or near Earth. Simulations were developed with models derived from the known solar nongravitational perturbations of typical comets. Results suggest that a diffraction-limited 500 m array operating at 10 GW for 10 min/day may be sufficient to divert a typical active 500 m comet from an impact given 1 yr. A larger 1 km array operating at 100 GW for 100 s/day is similarly effective. Care must be taken to ensure the target remains intact throughout the deflection period due to comets' low compressive strength and resulting propensity for disintegration at high incident flux.
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NASA Astrophysics Data System (ADS)
Elmaarry, M. R.; Groussin, O.; Thomas, N.; Pajola, M.; Auger, A. T.; Davidsson, B. J. R.; Hu, X.; Hviid, S. F.; Joerg, K.; Güttler, C.; Tubiana, C.; Bodewits, D.; Fornasier, S.; Vincent, J. B.; Sierks, H.
2017-12-01
Prior to the Rosetta mission at comet 67P/Churyumov-Gerasimenko (hereinafter referred to as 67P), we had limited snapshots of comets from flyby missions: the only comet other than 67P that showed evidence of long-term or seasonal changes was comet Tempel 1 because it was visited by spacecrafts on two separate occasions. With Rosetta, it was possible to monitor the surface of a comet continuously for approximately two years with high spatial resolution, which led to the discovery of a wide variety of changes that occur on comets, and made it possible to constrain the timing and rates of these changes. Comet 67P showed a variety of changes that affected its consolidated materials such as collapsing cliffs, moving boulders, and propagating fractures, which indicate ongoing weathering and erosion on the surface. Similarly, the comet's smooth and unconsolidated materials also displayed changes. However, these changes were mainly transient or short-lived involving the development of circular features that vary in size with time, textural changes in the "dusty" mantles, and retreating scarps similar in scale to what has been previously observed at Tempel 1. The changes in the smooth terrains are more difficult to explain but appear related to insolation since most of the changes to the surface of the comet occurred at, or close to, perihelion, mainly when the comet was around 2 AU away from the Sun. While many (100s) of changes have been detected so far on the surface, they are nonetheless small-scale, and minimally affecting the overall shape or landscape of the comet. This would suggest that higher activity is likely at the earlier stages of a comet's introduction into the inner solar system when comets possibly possess a higher inventory of volatiles (particularly CO and CO2), and/or amorphous ice.
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Comet Halley: The Curtis Schmidts-Isla de Pascua observations
NASA Technical Reports Server (NTRS)
Miller, Freeman D.; Liller, William
1986-01-01
Halley's comet plasma tail disturbances and attendant tail phenomena were observed. Nearly simultaneous exposures with two telescopes serve to correlate information obtained with the two instruments. Photographs of 14 pre-Halley comets taken on 54 nights were examined with a view to cross-interpretation of phenomena seen in Halley with the earlier comets, as recorded on a homogenous collection of plates taken with the same instrument. The tail of Halley was highly active. This contrasts sharply with pre-Halley comets where undisturbed tails are the rule. During March and April, disturbances appeared in the tail of Halley at an average of 1 new distrubance every 3.7 days. It is considered that 10 of the 11 observed disturbances had common characteristics which allow them to be characterized as disconnections.
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NASA Technical Reports Server (NTRS)
Niedner, Malcolm B., Jr.; Schwingenschuh, Konrad; Hoeksema, J. Todd; Dryer, Murray; Mcintosh, Patrick S.
1987-01-01
The encounters of five spacecraft with Halley's Comet during 6-14 March 1986 offered a unique opportunity to calibrate the solar-wind interaction with cometary plasmas as recorded by remote wide-field and narrow-field/narrowband imaging. Perhaps not generally recognized in the comet community is the additional opportunity offered by the Halley Armada to study the structure of the solar-wind and interplanetary magnetic field (IMF) in three dimensions using five sets of data obtained over similar time intervals and heliocentric distances, but at somewhat different heliolatitudes. In fact, the two problems, i.e., comet physics and the structure of the interplanetary medium, are coupled if one wants to understand what conditions pertained at the comet between the encounters. This relationship is discussed.
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Comet Tempel 1 Went Back to Sleep
NASA Astrophysics Data System (ADS)
2005-07-01
Astronomers Having Used ESO Telescopes Start Analysing Unique Dataset on the Comet Following the Deep Impact Mission Ten days after part of the Deep Impact spacecraft plunged onto Comet Tempel 1 with the aim to create a crater and expose pristine material from beneath the surface, astronomers are back in the ESO Offices in Santiago, after more than a week of observing at the ESO La Silla Paranal Observatory. In this unprecedented observing campaign - among the most ambitious ever conducted by a single observatory - the astronomers have collected a large amount of invaluable data on this comet. The astronomers have now started the lengthy process of data reduction and analysis. Being all together in a single place, and in close contacts with the space mission' scientific team, they will try to assemble a clear picture of the comet and of the impact. The ESO observations were part of a worldwide campaign to observe this unique experiment. During the campaign, ESO was connected by phone, email, and videoconference with colleagues in all major observatories worldwide, and data were freely exchanged between the different groups. This unique collaborative spirit provides astronomers with data taken almost around the clock during several days and this, with the largest variety of instruments, making the Deep Impact observing campaign one of the most successful of its kind, and thereby, ensuring the greatest scientific outcome. From the current analysis, it appears most likely that the impactor did not create a large new zone of activity and may have failed to liberate a large quantity of pristine material from beneath the surface. ESO PR Photo 22/05 ESO PR Photo 22/05 Evolution of Comet Tempel 1 (FORS2/VLT) [Preview - JPEG: 400 x 701 pix - 128k] [Normal - JPEG: 800 x 1401 pix - 357k] ESO PR Photo 22/05 Animated Gif Caption: ESO PR Photo 22/05 shows the evolution of Comet Tempel 1 as observed with the FORS2 instrument on Antu (VLT). The images obtained at the VLT show that after the impact, the morphology of Comet Tempel 1 had changed, with the appearance of a new plume-like structure, produced by matter being ejected with a speed of about 700 to 1000 km/h (see ESO PR Photo 23/05). This structure, however, diffused away in the following days, being more and more diluted and less visible, the comet taking again the appearance it had before the impact. Further images obtained with, among others, the adaptive optics NACO instrument on the Very Large Telescope, showed the same jets that were visible prior to impact, demonstrating that the comet activity survived widely unaffected by the spacecraft crash. The study of the gas in Comet Tempel 1 (see "Looking for Molecules"), made with UVES on Kueyen (UT2 of the VLT), reveals a small flux increase the first night following the impact. At that time, more than 17 hours after the impact, the ejected matter was fading away but still measurable thanks to the large light collecting power of the VLT. The data accumulated during 10 nights around the impact have provided the astronomers with the best ever time series of optical spectra of a Jupiter Family comet, with a total of more than 40 hours of exposure time. This unique data set has already allowed the astronomers to characterize the normal gas activity of the comet and also to detect, to their own surprise, an active region. This active region is not related to the impact as it was also detected in data collected in June. It shows up about every 41 hours, the rotation period of the comet nucleus determined by the Deep Impact spacecraft. Exciting measurements of the detailed chemical composition (such as the isotopic ratios) of the material released by the impact as well as the one coming from that source will be performed by the astronomers in the next weeks and months. Further spectropolarimetric observations with FORS1 have confirmed the surface of the comet to be rather evolved - as expected - but more importantly, that the dust is not coming from beneath the surface. These data constitute another unique high-quality data set on comets. Comet Tempel 1 may thus be back to sleep but work only starts for the astronomers. More information On July 4, 2005, the NASA Deep Impact spacecraft launched a 360 kg impactor onto Comet 9P/Tempel 1. This experiment is seen by many as the first opportunity to study the crust and the interior of a comet, revealing new information on the early phases of the Solar System. ESO actively participated in pre- and post-impact observations. Apart from a long-term monitoring of the comet, for two days before and six days after, all major ESO telescopes - i.e. the four Unit Telescopes of the Very Large Telescope Array at Paranal, as well as the 3.6m, 3.5m NTT and the 2.2m ESO/MPG telescopes at La Silla - have been observing Comet 9P/Tempel 1, in a coordinated fashion and in very close collaboration with the space mission' scientific team. The simultaneous use of all ESO telescopes with all together 10 instruments has an enormous potential, since it allows for observation of the comet at different wavelengths in the visible and infrared by imaging, spectroscopy and polarimetry. Such multiplexing capabilities of the instrumentation do not exist at any other observatory in the world. More information is available at the dedicated Deep Impact at ESO web site.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Muñoz-Gutiérrez, M. A.; Pichardo, B.; Peimbert, A.
With the use of long-term numerical simulations, we study the evolution and orbital behavior of cometary nuclei in cold Kuiper belt–like debris disks under the gravitational influence of dwarf planets (DPs); we carry out these simulations with and without the presence of a Neptune-like giant planet. This exploratory study shows that in the absence of a giant planet, 10 DPs are enough to induce strong radial and vertical heating on the orbits of belt particles. On the other hand, the presence of a giant planet close to the debris disk, acts as a stability agent reducing the radial and verticalmore » heating. With enough DPs, even in the presence of a Neptune-like giant planet some radial heating remains; this heating grows steadily, re-filling resonances otherwise empty of cometary nuclei. Specifically for the solar system, this secular process seems to be able to provide material that, through resonant chaotic diffusion, increase the rate of new comets spiraling into the inner planetary system, but only if more than the ∼10 known DP sized objects exist in the trans-Neptunian region.« less
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How the morphology of dusts influences packing density in small solar system bodies
NASA Astrophysics Data System (ADS)
Zangmeister, C.; Radney, J. G.; Zachariah, M. R.
2014-12-01
Large planetary seedlings, comets, and nanoscale soot particles are made from rigid, aggregated subunits that are compacted under low compression into larger structures spanning over 10 orders of magnitude in dimensional space. Here, we demonstrate that the packing density (Φf) of compacted rigid aggregates is independent of spatial scale for systems under weak compaction, a regime that includes small solar system bodies. The Φf of rigid aggregated structures across 6 orders of magnitude were measured using nanoscale spherical soot aerosol composed of aggregates with ≈ 17 nm monomeric subunits and aggregates made from uniform monomeric 6 mm spherical subunits at the macroscale. We find Φf = 0.36 ± 0.02 at both the nano- and macroscale. These values are remarkably similar to qf observed for comet nuclei and measured values of other rigid aggregated systems across a wide variety of spatial and formative conditions. We present a packing model that incorporates the aggregate morphology and show that Φf is independent of both monomer and aggregate size. These observations suggest thatqf of rigid aggregates is independent of spatial dimension across varied formative conditions ranging from interstellar space to pharmaceutical manufacturing.
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Cartography of asteroids and comet nuclei from low resolution data
NASA Technical Reports Server (NTRS)
Stooke, Philip J.
1992-01-01
High resolution images of non-spherical objects, such as Viking images of Phobos and the anticipated Galileo images of Gaspra, lend themselves to conventional planetary cartographic procedures: control network analysis, stereophotogrammetry, image mosaicking in 2D or 3D, and airbrush mapping. There remains the problem of a suitable map projection for bodies which are extremely elongated or irregular in shape. Many bodies will soon be seen at lower resolution (5-30 pixels across the disk) in images from speckle interferometry, the Hubble Space Telescope, ground-based radar, distinct spacecraft encounters, and closer images degraded by smear. Different data with similar effective resolutions are available from stellar occultations, radar or lightcurve convex hulls, lightcurve modeling of albedo variations, and cometary jet modeling. With such low resolution, conventional methods of shape determination will be less useful or will fail altogether, leaving limb and terminator topography as the principal sources of topographic information. A method for shape determination based on limb and terminator topography was developed. It has been applied to the nucleus of Comet Halley and the jovian satellite Amalthea. The Amalthea results are described to give an example of the cartographic possibilities and problems of anticipated data sets.
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Collapse-driven formation of depressions on comet 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Leliwa-Kopystynski, J.
2018-03-01
The extremely diverse surface of comet 67P/Churyumov-Gerasimenko contains a large number of depressions or craters of very different scales. Among the most prominent are two large roughly circular depressions, each with radii of several hundred meters. In this work a model for the formation of the depressions is proposed. It is based on the theory of the deformation of a thin circular elastic plate under its own weight. The plate covers a circular cavity with a given radius. The resilience of the plate diminishes over time as a result of its thinning which is itself a consequence of sublimation. When the stress limit is achieved, a gravitational collapse occurs: the plate cracks and the remnants fall into the cavity bottom. A formula that links the radius of the plate corresponding to collapse with the plate thickness has been derived. The formula was discussed for the large intervals of the values of parameters that characterize surface layers of cometary nuclei. It was found that the surface above large cavities collapses sooner than one of a similar thickness that covers a smaller cavity. So, if the collapse mechanism theory works, that larger depressions are therefore older than smaller ones.
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Selected configuration tradeoffs of contour optical instruments
NASA Astrophysics Data System (ADS)
Warren, J.; Strohbehn, K.; Murchie, S.; Fort, D.; Reynolds, E.; Heyler, G.; Peacock, K.; Boldt, J.; Darlington, E.; Hayes, J.; Henshaw, R.; Izenberg, N.; Kardian, C.; Lees, J.; Lohr, D.; Mehoke, D.; Schaefer, E.; Sholar, T.; Spisz, T.; Willey, C.; Veverka, J.; Bell, J.; Cochran, A.
2003-01-01
The Comet Nucleus Tour (CONTOUR) is a low-cost NASA Discovery mission designed to conduct three close flybys of comet nuclei. Selected configuration tradeoffs conducted to balance science requirements with low mission cost are reviewed. The tradeoffs discussed focus on the optical instruments and related spacecraft considerations. Two instruments are under development. The CONTOUR Forward Imager (CFI) is designed to perform optical navigation, moderate resolution nucleus/jet imaging, and imaging of faint molecular emission bands in the coma. The CONTOUR Remote Imager and Spectrometer (CRISP) is designed to obtain high-resolution multispectral images of the nucleus, conduct spectral mapping of the nucleus surface, and provide a backup optical navigation capability. Tradeoffs discussed are: (1) the impact on the optical instruments of not using reaction wheels on the spacecraft, (2) the improved performance and simplification gained by implementing a dedicated star tracker instead of including this function in CFI, (3) the improved flexibility and robustness of switching to a low frame rate tracker for CRISP, (4) the improved performance and simplification of replacing a visible imaging spectrometer by enhanced multispectral imaging in CRISP, and (5) the impact on spacecraft resources of these and other tradeoffs.
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On the mechanisms leading to orphan meteoroid streams
NASA Astrophysics Data System (ADS)
Vaubaillon, J.; Lamy, P.; Jorda, L.
2006-08-01
We analyse several mechanisms capable of creating orphan meteoroid streams (OMSs) for which a parent has not been identified. OMSs have been observed as meteor showers since the XIXth century and by the IRAS satellite in the 1980s. We find that the process of close encounters with giant planets (particularly Jupiter) is the most efficient mechanism to create them: only a limited section of the stream is perturbed and follows the parent body on its new orbit, while the majority of the meteoroids remain in their pre-encounter orbit or in an intermediate state, breaking the link with their parent body. Cometary non-gravitational forces can also contribute to the process since they cause the comet to drift away from its stream. However, they are not sufficient by themselves to produce an OMS. Resonances can either split or confine a stream over a long time (>1000 yr). Some meteoroid streams may look like OMSs since their parent comet is dormant or not observable (e.g. long period). Even if new techniques succeed in linking minor objects to meteoroid streams, OMSs will still exist simply because cometary nuclei are subject to complete disruption leading to their disappearance.
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DISINTEGRATING ASTEROID P/2013 R3
DOE Office of Scientific and Technical Information (OSTI.GOV)
Jewitt, David; Li, Jing; Agarwal, Jessica
Splitting of the nuclei of comets into multiple components has been frequently observed but, to date, no main-belt asteroid has been observed to break up. Using the Hubble Space Telescope, we find that main-belt asteroid P/2013 R3 consists of 10 or more distinct components, the largest up to 200 m in radius (assumed geometric albedo of 0.05) each of which produces a coma and comet-like dust tail. A diffuse debris cloud with total mass ∼2 × 10{sup 8} kg further envelopes the entire system. The velocity dispersion among the components, ΔV ∼ 0.2-0.5 m s{sup –1}, is comparable to the gravitational escape speeds ofmore » the largest members, while their extrapolated plane-of-sky motions suggest a break up between 2013 February and September. The broadband optical colors are those of a C-type asteroid. We find no spectral evidence for gaseous emission, placing model-dependent upper limits to the water production rate ≤1 kg s{sup –1}. Breakup may be due to a rotationally induced structural failure of the precursor body.« less
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Thermal infrared and optical photometry of Asteroidal Comet C/2002 CE10
NASA Astrophysics Data System (ADS)
Sekiguchi, Tomohiko; Miyasaka, Seidai; Dermawan, Budi; Mueller, Thomas; Takato, Naruhisa; Watanabe, Junichi; Boehnhardt, Hermann
2018-04-01
C/2002 CE10 is an object in a retrograde elliptical orbit with Tisserand parameter - 0.853 indicating a likely origin in the Oort Cloud. It appears to be a rather inactive comet since no coma and only a very weak tail was detected during the past perihelion passage. We present multi-color optical photometry, lightcurve and thermal mid-IR observations of the asteroidal comet. With the photometric analysis in BVRI, the surface color is found to be redder than asteroids, corresponding to cometary nuclei and TNOs/Centaurs. The time-resolved differential photometry supports a rotation period of 8.19 ± 0.05 h. The effective diameter and the geometric albedo are 17.9 ± 0.9 km and 0.03 ± 0.01, respectively, indicating a very dark reflectance of the surface. The dark and redder surface color of C/2002 CE10 may be attribute to devolatilized material by surface aging suffered from the irradiation by cosmic rays or from impact by dust particles in the Oort Cloud. Alternatively, C/2002 CE10 was formed of very dark refractory material originally like a rocky planetesimal. In both cases, this object lacks ices (on the surface at least). The dynamical and known physical characteristics of C/2002 CE10 are best compatible with those of the Damocloids population in the Solar System, that appear to be exhaust cometary nucleus in Halley-type orbits. The study of physical properties of rocky Oort cloud objects may give us a key for the formation of the Oort cloud and the solar system.
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The 1986 DA and 1986 EB: M-class asteroids in near-Earth orbits
NASA Technical Reports Server (NTRS)
Gradie, Jonathan; Tedesco, Edward
1987-01-01
The Earth-approaching asteroid population is composed of asteroids in orbits with short lifetimes compared with the age of the solar system. These objects which are comprised of Aten, Apollo, and Amor asteroids must be replenished from either cometary or mainbelt asteroid sources since lifetimes against collision with or ejection by a planet are on the order of 10 to 100 million years. The physical study of Earth-approaching asteroids is constrained by the generally long period between favorable apparitions and poorly known orbits. Broadband spectrophotometry on the Johnson UBVR system and the Eight-Color Asteroid Survey system were obtained at Kitt Peak National Observatory and on the Johnson JHK system and at 10 and 20 microns at the NASA Infrared Telescope Facility at Mauna Kea Observatory. These observations were used to determine the absolute visual magnitudes and to derive the visual geometric albedos and diameters on the IRAS system. The spectral reflectance properties and geometric albedos of the M-class asteroids are consistent compositions analogous to the iron nickel meteorites or the enstatite-metal assemblages of the enstatite chondrites. The issue of the source(s) of the near-Earth asteroids population was examined by comparing the classifications on the scheme employed by Gradie and Tedesco of 38 such asteroids. Most of the near-Earth objects is indeed the asteroid belt as the observations suggest, then a method for removing extinct nuclei of short period comets must be found since the rate of production of short period comets from the long period comets is relatively large.
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Hydrogen cyanide polymers, comets and the origin of life.
Matthews, Clifford N; Minard, Robert D
2006-01-01
Hydrogen cyanide polymers--heterogeneous solids ranging in colour from yellow to orange to brown to black--could be major components of the dark matter observed on many bodies of the outer solar system including asteroids, moons, planets and, especially, comets. The presence on cometary nuclei of frozen volatiles such as methane, ammonia and water subjected to high energy sources makes them attractive sites for the ready formation and condensed-phase polymerization of hydrogen cyanide. This could account for the dark crust observed on Comet Halley in 1986 by the Vega and Giotto missions. Dust emanating from its nucleus would arise partly from HCN polymers as suggested by the Giotto detection of free hydrogen cyanide, CN radicals, solid particles consisting only of H, C and N, or only of H, C, N, O, and nitrogen-containing organic compounds. Further evidence for cometary HCN polymers could be expected from in situ analysis of the ejected material from Comet Tempel 1 after collision with the impactor probe from the two-stage Deep Impact mission on July 4, 2005. Even more revealing will be actual samples of dust collected from the coma of Comet Wild 2 by the Stardust mission, due to return to Earth in January 2006 for analyses which we have predicted will detect these polymers and related compounds. In situ results have already shown that nitriles and polymers of hydrogen cyanide are probable components of the cometary dust that struck the Cometary and Interstellar Dust Analyzer of the Stardust spacecraft as it approached Comet Wild 2 on January 2, 2004. Preliminary evidence (January 2005) obtained by the Huygens probe of the ongoing Cassini-Huygens mission to Saturn and its satellites indicates the presence of nitrogen-containing organic compounds in the refractory organic cores of the aerosols that give rise to the orange haze high in the atmosphere of Titan, Saturn's largest moon. Our continuing investigations suggest that HCN polymers are basically of two types: ladder structures with conjugated -C=N- bonds and polyamidines readily converted by water to polypeptides. Thermochemolysis GC-MS studies show that cleavage products of the polymer include alpha-amino acids, nitrogen heterocycles such as purines and pyrimidines, and provide evidence for peptide linkages. Hydrogen cyanide polymers are a plausible link between cosmochemistry and the origin of informational macromolecules. Implications for prebiotic chemistry are profound. Following persistent bolide bombardment, primitive Earth may have been covered by water and carbonaceous compounds, particularly HCN polymers which would have supplied essential components for establishing protein/nucleic acid life.
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The Split Nucleus of Comet Wilson (C/1986 P1 = 1987 VII).
NASA Astrophysics Data System (ADS)
Meech, Karen J.; Knopp, Graham P.; Farnham, Tony L.; Green, Daniel
1995-07-01
We present CCD observations of Comet Wilson (C/1986 P1 = 1987 VII) from 26 nights during the time period 1986 October to 1991 February, which brackets perihelion, During the observing run of 1988 February, the comet was observed to have split into two fragments. Our broadband CCD photometry, along with photometry from the International Cometary Quarterly, shows a steady decline in brightness of Comet Wilson post-perihelion, with an outburst between heliocentric distances r = 2.8 and 3.3 AU during 1987 October and November. By r ≈ 7 AU, the fragment had faded with respect to the parent and was no longer centrally condensed. A brightness limit of mR ≈ 25, when the comet was at r = 12.65 AU, constrains the primary nucleus to have a maximum radius between 5 and 7 km, assuming an albedo of 0.04. The accuracy of direct orbital solutions for the parent body and fragment to determine the time of splitting was limited by the presence of significant nongravitational forces and the limited fragment orbital coverage. We used the relative position of the fragment with respect to the parent to calculate a time of splitting which was consistent with the time of the observed outburst. We discuss the possible causes of the splitting. The coma of Comet Wilson was observed to have a surface-brightness profile which fell off as p-1 (characteristic of a canonical steady-state coma under the influence of radiation pressure) for all of the data with the exception of the data taken during 1987 November when the gradient was p-1.3 . This steeper slope was probably caused by the injection of new material into the coma during the outburst. During 1986 October, there was a break in the surface-brightness profile slope which may be interpreted as the distance at which grains are swept into the tail. The profiles suggested grain velocities of a few x 10 2 to 10 m sec -1 for grains between 1 and a few hundred micrometers. Finson-Probstein dust modeling showed that ejection of grains began preperihelion at r gt; 6 AU, peaking near perihelion with a very rapid decline thereafter, with an outburst occurring roughly 170 days post-perihelion. We found no evidence for the existence of discrete features in the coma. Both the primary and fragment nuclei grew redder with time, with the fragment being redder than the parent, consistent with the picture of smaller grains leaving the field of view of the aperture more quickly than larger grains.
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Sublimation rates of carbon monoxide and carbon dioxide from comets at large heliocentric distances
NASA Technical Reports Server (NTRS)
Sekanina, Zdenek
1992-01-01
Using a simple model for outgassing from a small flat surface area, the sublimation rates of carbon monoxide and carbon dioxide, two species more volatile than water ice that are known to be present in comets, are calculated for a suddenly activated discrete source on the rotating nucleus. The instantaneous sublimation rate depends upon the comet's heliocentric distance and the Sun's zenith angle at the location of the source. The values are derived for the constants of CO and CO2 in an expression that yields the local rotation-averaged sublimation rate as a function of the comet's spin parameters and the source's cometocentric latitude.
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Small is different: RPC observations of a small scale comet interacting with the solar wind
NASA Astrophysics Data System (ADS)
Nilsson, Hans; Burch, James L.; Carr, Christopher M.; Eriksson, Anders I.; Glassmeier, Karl-Heinz; Henri, Pierre; Rosetta Plasma Consortium Team
2016-10-01
Rosetta followed comet 67P from low activity at more than 3 AU heliocentric distance to peak activity at perihelion and then out again. We study the evolution of the dynamic plasma environment using data from the Rosetta Plasma Consortium (RPC). Observations of cometary plasma began in August 2014, at a distance of 100 km from the comet nucleus and at 3.6 AU from the Sun. As the comet approached the Sun, outgassing from the comet increased, as did the density of the cometary plasma. Measurements showed a highly heterogeneous cold ion environment, permeated by the solar wind. The solar wind was deflected due to the mass loading from newly added cometary plasma, with no discernible slowing down. The magnetic field magnitude increased significantly above the background level, and strong low frequency waves were observed in the magnetic field, a.k.a. the "singing comet". Electron temperatures were high, leading to a frequently strongly negative spacecraft potential. In mid to late April 2015 the solar wind started to disappear from the observation region. This was associated with a solar wind deflection reaching nearly 180°, indicating that mass loading became efficient enough to form a solar wind-free region. Accelerated water ions, moving mainly in the anti-sunward direction, kept being observed also after the solar wind disappearance. Plasma boundaries began to form and a collisionopause was tentatively identified in the ion and electron data. At the time around perihelion, a diamagnetic cavity was also observed, at a surprisingly large distance from the comet. In late 2016 the solar wind re-appeared at the location of Rosetta, allowing for studies of asymmetry of the comet ion environment with respect to perihelion. A nightside excursion allowed us to get a glimpse of the electrodynamics of the innermost part of the plasma tail. Most of these phenomena are dependent on the small-scale physics of comet 67P, since for most of the Rosetta mission the solar wind - comet atmosphere interaction region is smaller than the pickup ion gyroradius in the undisturbed solar wind.
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Comets as parent bodies of CI1 carbonaceous meteorites and possible habitats of ice-microbes
NASA Astrophysics Data System (ADS)
Wickramasinghe, N. Chandra; Wickramasinghe, Janaki T.; Wallis, Jamie; Hoover, Richard B.; Rozanov, Alexei Y.
2011-10-01
Recent studies of comets and cometary dust have confirmed the presence of biologically relevant organic molecules along with clay minerals and water ice. It is also now well established by deuterium/hydrogen ratios that the CI1 carbonaceous meteorites contain indigenous extraterrestrial water. The evidence of extensive aqueous alteration of the minerals in these meteorites led to the hypothesis that water-bearing asteroids or comets represent the parent bodies of the CI1 (and perhaps CM2) carbonaceous meteorites. These meteorites have also been shown to possess a diverse array of complex organics and chiral and morphological biomarkers. Stable isotope studies by numerous independent investigators have conclusively established that the complex organics found in these meteorites are both indigenous and extraterrestrial in nature. Although the origin of these organics is still unknown, some researchers have suggested that they originated by unknown abiotic mechanisms and may have played a role in the delivery of chiral biomolecules and the origin of life on Early Earth. In this paper we review these results and investigate the thermal history of comets. We show that permanent as well as transient domains of liquid water can be maintained on a comet under a plausible set of assumptions. With each perihelion passage of a comet volatiles are preferentially released, and during millions of such passages the comet could shed crustal debris that may survive transit through the Earth's atmosphere as a carbonaceous meteorite. We review the current state of knowledge of comets and carbonaceous meteorites. We also present the results of recent studies on the long-term viability of terrestrial ice-microbiota encased in ancient glacial ice and permafrost. We suggest that the conditions which have been observed to prevail on many comets do not preclude either survivability (or even the active metabolism and growth) of many types of eukaryotic and prokaryotic microbial extremophiles-including algae, cyanobacteria, bacteria and archaea. It is argued that the chemical and morphological biomarkers detected on comets and carbonaceous meteorites can be explained by ancient microbial activity without the need to invoke unknown abiotic production mechanisms.
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Comets as Parent Bodies of CI1 Carbonaceous Meteorites and Possible Habitats of Ice-Microbiota
NASA Technical Reports Server (NTRS)
Wickramasinghe, N. Chandra; Wallis, Daryl H.; Rozanov, Alexei Yu.; Hoover, Richard B.
2011-01-01
Recent studies of comets and cometary dust have confirmed the presence of biologically relevant organic molecules along with clay minerals and water ice. It is also now well established by deuterium/hydrogen ratios that the CI1 carbonaceous meteorites contain indigenous extraterrestrial water. The evidence of extensive aqueous alteration of the minerals in these meteorites led to the hypothesis that water-bearing asteroids or comets represent the parent bodies of the CI1 (and perhaps CM2) carbonaceous meteorites. These meteorites have also been shown to possess a diverse array of complex organics and chiral and morphological biomarkers. Stable isotope studies by numerous independent investigators have conclusively established that the complex organics found in these meteorites are both indigenous and extraterrestrial in nature. Although the origin of these organics is still unknown, some researchers have suggested that they originated by unknown abiotic mechanisms and may have played a role in the delivery of chiral biomolecules and the origin of life on Early Earth. In this paper we review these results and investigate the thermal history of comets. We show that permanent as well as transient domains of liquid water can be maintained on a comet under a plausible set of assumptions. With each perihelion passage of a comet volatiles are preferentially released, and during millions of such passages the comet could shed crustal debris that may survive transit through the Earth s atmosphere as a carbonaceous meteorite. We review the current state of knowledge of comets and carbonaceous meteorites. We also present the results of recent studies on the long-term viability of terrestrial ice-microbiota encased in ancient glacial ice and permafrost. We suggest that the conditions which have been observed to prevail on many comets do not preclude either survivability (or even the active metabolism and growth) of many types of eukaryotic and prokaryotic microbial extremophiles-including algae, cyanobacteria, bacteria and archaea. It is argued that the chemical and morphological biomarkers detected on comets and carbonaceous meteorites can be explained by ancient microbial activity without the need to invoke unknown abiotic production mechanisms.
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The age and the probable parent body of the daytime arietid meteor shower
NASA Astrophysics Data System (ADS)
Abedin, Abedin; Wiegert, Paul; Pokorný, Petr; Brown, Peter
2017-01-01
The daytime Arietid meteor shower is active from mid-May to late June and is amongst the strongest of the annual meteor showers, comparable in activity and duration to the Perseids and the Geminids. Due to the daytime nature of the shower, the Arietids have mostly been constrained by radar studies. The Arietids exhibit a long-debated discrepancy in the semi-major axis and the eccentricity of meteoroid orbits as measured by radar and optical surveys. Radar studies yield systematically lower values for the semi-major axis and eccentricity, where the origin of these discrepancies remain unclear. The proposed parent bodies of the stream include comet 96P/Machholz [McIntosh, B.A., 1990. Comet P/Machholz and the Quadrantid meteor stream. Icarus 86, 894 299-304. doi:10.1016/0019-1035(90)90219-Y.] and more recently a member of the Marsden group of sun-skirting comets, P/1999 J6 [Sekanina, Z., Chodas, P.W., 2005. Origin of the Marsden and Kracht Groups of Sunskirting 922 Comets. I. Association with Comet 96P/Machholz and Its Interplanetary Complex. ApJS 923 161, 551-586. doi:10.1086/497374.]. In this work, we present detailed numerical modelling of the daytime Arietid meteoroid stream, with the goal to identifying the parent body and constraining the age of the stream. We use observational data from an extensive survey of the Arietids by the Canadian Meteor Orbit Radar (CMOR), in the period of 2002-2013, and several optical observations by the SonotaCo meteor network and the Cameras for All-sky Meteor Surveillance (CAMS). We find the most plausible scenario to be that the age and the formation mechanism of the Arietids is consistent with continuous cometary activity of 96P/Machholz over a time interval of ≈12,000 years. The sun-skirting comet P/1999 J6 suggested by [Sekanina, Z., Chodas, P.W., 2005. Origin of the Marsden and Kracht Groups of Sunskirting 922 Comets. I. Association with Comet 96P/Machholz and Its Interplanetary Complex. ApJS 923 161, 551-586. doi:10.1086/497374.] may contribute to the shower, but the comet break up prior to 950 CE they propose does not reproduce all the characteristics of the observed shower.
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Gone in a Blaze of Glory: The Demise of Comet C/2015 D1 (SOHO)
NASA Astrophysics Data System (ADS)
Hui, Man-To; Ye, Quan-Zhi; Knight, Matthew; Battams, Karl; Clark, David
2015-11-01
We present studies of C/2015 D1 (SOHO), the first sunskirting comet ever seen from ground stations over the past half century. The Solar and Heliospheric Observatory (SOHO) witnessed its peculiar light curve with a huge dip followed by a flare-up around perihelion: the dip was likely caused by sublimation of olivines, directly evidenced by a coincident temporary disappearance of the tail. The flare-up likely reflects a disintegration event, which we suggest was triggered by intense thermal stress established within the nucleus interior. Photometric data reveal an increasingly dusty coma, indicative of volatile depletion. A catastrophic mass-loss rate of ˜105 kg s-1 around perihelion was seen. Ground-based Xingming Observatory spotted the post-perihelion debris cloud. Our morphological simulations of post-perihelion images find newly released dust grains of size a ≳ 10 μm in radius however, a temporal increase in amin was also witnessed, possibly owing to swift dispersions of smaller grains swept away by radiation forces without replenishment. Together with the fading profile of the light curve, a power-law dust size distribution with index γ = 3.2 ± 0.1 is derived. We detected no active remaining cometary nuclei over ˜0.1 km in radius in post-perihelion images acquired at Lowell Observatory. Applying a radial nongravitational parameter, {{A}}1=≤ft(1.209+/- 0.118\\right)× {10}-6 AU day-2, from an isothermal water-ice sublimation model to the SOHO astrometry significantly reduces residuals and sinusoidal trends in the orbit determination. The nucleus mass ˜108-109 kg and the radius ˜50-150 m (bulk density ρd = 0.4 g cm-3 assumed) before the disintegration are deduced from the photometric data; consistent results were determined from the nongravitational effects.
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Gone in a Blaze of Glory: the Demise of Comet C/2015 D1 (SOHO)
NASA Astrophysics Data System (ADS)
Hui, Man-To; Ye, Quan-Zhi; Manning Knight, Matthew; Battams, Karl; Clark, David
2015-11-01
We present studies of C/2015 D1 (SOHO), the first sunskirting comet ever seen from ground stations over the past half century. The Solar and Heliospheric Observatory (SOHO) witnessed its peculiar light curve with a huge dip followed by a flareup around perihelion: the dip was likely caused by sublimation of olivines, directly evidenced by a coincident temporary disappearance of the tail. The flareup likely reflects a disintegration event, which we suggest was triggered by intense thermal stress established within the nucleus interior. Photometric data reveal an increasingly dusty coma, indicative of volatile depletion. A catastrophic mass loss rate of ~105 kg s-1 around perihelion was seen. Ground-based Xingming Observatory spotted the post-perihelion debris cloud. Our morphological simulations of post-perihelion images find newly released dust grains of size a >~ 15 μm in radius, however, a temporal increase in amin was also witnessed, possibly due to swift dispersions of smaller grains swept away by radiation forces without replenishment. Together with the fading profile of the light curve, a power law dust size distribution with index γ = 3.2 ± 0.1 is derived. We detected no active remaining cometary nuclei over ~0.1 km in radius in post-perihelion images acquired at Lowell Observatory. Applying radial non-gravitational parameter, A1 = (1.209 ± 0.118) × 10-6 AU day-2, from an isothermal water-ice sublimation model to the SOHO astrometry significantly reduces residuals and sinusoidal trends in the orbit determination. The nucleus mass ~108--109 kg, and the radius ~50--150 m (bulk density ρd = 0.4 g cm-3 assumed) before the disintegration are deduced from the photometric data; consistent results were determined from the non-gravitational effects.
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Possible viruses from outer space fall into the Earth's atmosphere
NASA Astrophysics Data System (ADS)
Steklov, A. F.; Dashkiev, G. N.; Vidmachenko, A. P.
2017-05-01
Statistical data show that sometime after the passage of the Earth along its orbit through the tail of a comet, a number of epidemics and pandemics occurred. This indicated a possible invasion of viruses, which could be in cometary dust. K.I. Churyumov proposed to develop special traps. They need to be placed under the wings of high-altitude aircraft. And with their help it is necessary to catch, accumulate and examine in the laboratories those particles, which are captured in traces of invasions. The main purpose of such experiments is to reveal, or prove the absence of cosmic viruses in the tracks from the intrusions of fragments of cometary nuclei.
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Evolution of the P/Shoemaker-Levy 9 'Gang of Four' Region
NASA Technical Reports Server (NTRS)
1994-01-01
This series of eight NASA Hubble Space Telescope 'snapshots' shows the evolution of the P-Q complex, also called the 'gang of four' region, of comet P/Shoemaker-Levy 9.
The eight individual frames chronicle changes in the comet during the 12 months before colliding with Jupiter. The sequence shows that the relative separations of the various cometary fragments, thought to range in size from about 500 meters to almost 4 km (2.5 miles) across, changed dramatically over this period. The apparent separation of Q1 and Q2 was only about 1100 kilometers (680 miles) on 1 July 1993 and increased to 28,000 kilometers (17,400 miles) by 20 July 1994.The P-Q complex demonstrates that further fragmentation occurred after the breakup of the parent body in July 1992. Fragments Q1 and Q2 were probably together at some point in a single body. However, it is not clear how P1 and P2, and the P and Q objects are related.Between 24 January and 30 March 1994, the P2 nucleus broke-up into two separate fragments, one of which disappeared by late June. (It might be present in the mid-May image.) The P1 nucleus had a 'streaked' appearance on 24 January 1994 and then became a barely discernible 'puff' through mid-May. It was not detected in subsequent observations.Throughout the period, most nuclei were within a 4000 kilometer-wide (2500 miles) spherical cloud of dust, called a coma. However, shortly before impact, the coma around each nucleus became highly elongated along the comet's travel path due to 'stretching' by Jupiter's rapidly increasing gravity.This stretching is dramatic in the image of the Q-complex taken on 20 July 1994, just 10 hours before collision. Despite the coma's changes, HST images show that the core of each nucleus always remained concentrated. This shows that the nuclei were probably not catastrophically fragmenting, at least not up to 10 hours before impact.The first HST image was taken on 1 July 1993 with the Planetary Camera before the December 1993 HST servicing mission. All other images were taken with the WFPC-2. (The image taken on 17 May 1994 was taken in 'wide-field' mode and has a lower resolution than the other WFPC-2 images). The images were taken in visible light. The different shades of red are a false-color representation of the different intensities of light reflecting off the comet's dust. Each frame covers a region 90,000 by 30,000 kilometers (56,000 by 18,600 miles).This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL http://oposite.stsci.edu/pubinfo/ -
67P/Churyumov-Gerasimenko: Activity between March and June 2014 as observed from Rosetta/OSIRIS
NASA Astrophysics Data System (ADS)
Tubiana, C.; Snodgrass, C.; Bertini, I.; Mottola, S.; Vincent, J.-B.; Lara, L.; Fornasier, S.; Knollenberg, J.; Thomas, N.; Fulle, M.; Agarwal, J.; Bodewits, D.; Ferri, F.; Güttler, C.; Gutierrez, P. J.; La Forgia, F.; Lowry, S.; Magrin, S.; Oklay, N.; Pajola, M.; Rodrigo, R.; Sierks, H.; A'Hearn, M. F.; Angrilli, F.; Barbieri, C.; Barucci, M. A.; Bertaux, J.-L.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; De Cecco, M.; Debei, S.; Groussin, O.; Hviid, S. F.; Ip, W.; Jorda, L.; Keller, H. U.; Koschny, D.; Kramm, R.; Kührt, E.; Küppers, M.; Lazzarin, M.; Lamy, P. L.; Lopez Moreno, J. J.; Marzari, F.; Michalik, H.; Naletto, G.; Rickman, H.; Sabau, L.; Wenzel, K.-P.
2015-01-01
Aims: 67P/Churyumov-Gerasimenko is the target comet of the ESA's Rosetta mission. After commissioning at the end of March 2014, the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) onboard Rosetta, started imaging the comet and its dust environment to investigate how they change and evolve while approaching the Sun. Methods: We focused our work on Narrow Angle Camera (NAC) orange images and Wide Angle Camera (WAC) red and visible-610 images acquired between 2014 March 23 and June 24 when the nucleus of 67P was unresolved and moving from approximately 4.3 AU to 3.8 AU inbound. During this period the 67P - Rosetta distance decreased from 5 million to 120 thousand km. Results: Through aperture photometry, we investigated how the comet brightness varies with heliocentric distance. 67P was likely already weakly active at the end of March 2014, with excess flux above that expected for the nucleus. The comet's brightness was mostly constant during the three months of approach observations, apart from one outburst that occurred around April 30 and a second increase in flux after June 20. Coma was resolved in the profiles from mid-April. Analysis of the coma morphology suggests that most of the activity comes from a source towards the celestial north pole of the comet, but the outburst that occurred on April 30 released material in a different direction.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Ishiguro, Masateru; Kuroda, Daisuke; Hanayama, Hidekazu
2015-01-10
We report a new observation of the Jupiter family comet 209P/LINEAR during its 2014 return. The comet is recognized as a dust source of a new meteor shower, the May Camelopardalids. 209P/LINEAR was apparently inactive at a heliocentric distance r{sub h} = 1.6 AU and showed weak activity at r{sub h} ≤ 1.4 AU. We found an active region of <0.001% of the entire nuclear surface during the comet's dormant phase. An edge-on image suggests that particles up to 1 cm in size (with an uncertainty of factor 3-5) were ejected following a differential power-law size distribution with index qmore » = –3.25 ± 0.10. We derived a mass-loss rate of 2-10 kg s{sup –1} during the active phase and a total mass of ≈5 × 10{sup 7} kg during the 2014 return. The ejection terminal velocity of millimeter- to centimeter-sized particles was 1-4 m s{sup –1}, which is comparable to the escape velocity from the nucleus (1.4 m s{sup –1}). These results imply that such large meteoric particles marginally escaped from the highly dormant comet nucleus via the gas drag force only within a few months of the perihelion passage.« less
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Ancient Chinese Observations and Modern Cometary Models
NASA Astrophysics Data System (ADS)
Yeomans, D. K.
1995-12-01
Ancient astronomical observations by Chinese, Japanese, and Korean observers represent the only data source for discerning the long-term behavior of comets. The primary source material is derived from Chinese astrologers who kept a vigilant celestial watch in an effort to issue up-to-date astrological forecasts for the reigning emperors. Surprisingly accurate records were kept on cometary apparitions with careful notes being made of an object's position, motion, size, color, and tail length. For comets Halley, Swift-Tuttle, and Tempel-Tuttle, Chinese observations have been used to model their motions over two millennia and to infer their photometric histories. One general result is that active comets must achieve an apparent magnitude of 3.5 or brighter before they become obvious naked-eye objects. For both comets Halley and Swift-Tuttle, their absolute magnitudes and hence their outgassing rates, have remained relatively constant for two millennia. Comet Halley's rocket-like outgassing has consistently delayed the comet's return to perihelion by 4 days so that the comet's spin axis must have remained stable for at least two millennia. Although its outgassing is at nearly the same rate as Halley's, comet Swift-Tuttle's motion has been unaffected by outgassing forces; this comet is likely to be ten times more massive than Halley and hence far more difficult for rocket-like forces to push it around. Although the earliest definite observations of comet Tempel-Tuttle were in 1366, the associated Leonid meteor showers have been identified as early as A.D. 902. The circumstance for each historical meteor shower and storm have been used to guide predictions for the upcoming 1998-1999 Leonid meteor displays.
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Rosetta Comet Spreads its Jets
2014-10-24
This image was taken by the Optical, Spectroscopic, and Infrared Remote Imaging System, Rosetta main onboard scientific imaging system, on Sept. 10, 2014. Jets of cometary activity can be seen along almost the entire body of the comet. http://photojournal.jpl.nasa.gov/catalog/PIA18886
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A search for frosts in Comet Bowell /1980b/
NASA Technical Reports Server (NTRS)
Campins, H.; Lebofsky, L. A.; Rieke, G. H.; Lebofsky, M. J.
1982-01-01
Infrared observations of Comet Bowell represent the first search for frost signatures in a comet beyond 2 AU from the sun. Broad- and narrowband photometry has been obtained as well as CVF spectrophotometry of this comet and there is no evidence for absorption features in the spectral area between 1.25 and 2.3 microns. Models of the coma have been generated which constrain the volatile content of the grains an; are in agreement with the observed albedo. The darkness of the coma particles at large heliocentric distances indicates a low albedo nucleus as well. Brightness variations during the observing period seem to indicate an active nucleus at 4.5 AU from the sun.
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Alkaline Comet Assay for Assessing DNA Damage in Individual Cells.
Pu, Xinzhu; Wang, Zemin; Klaunig, James E
2015-08-06
Single-cell gel electrophoresis, commonly called a comet assay, is a simple and sensitive method for assessing DNA damage at the single-cell level. It is an important technique in genetic toxicological studies. The comet assay performed under alkaline conditions (pH >13) is considered the optimal version for identifying agents with genotoxic activity. The alkaline comet assay is capable of detecting DNA double-strand breaks, single-strand breaks, alkali-labile sites, DNA-DNA/DNA-protein cross-linking, and incomplete excision repair sites. The inclusion of digestion of lesion-specific DNA repair enzymes in the procedure allows the detection of various DNA base alterations, such as oxidative base damage. This unit describes alkaline comet assay procedures for assessing DNA strand breaks and oxidative base alterations. These methods can be applied in a variety of cells from in vitro and in vivo experiments, as well as human studies. Copyright © 2015 John Wiley & Sons, Inc.
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Remote comets and related bodies - VJHK colorimetry and surface materials
NASA Technical Reports Server (NTRS)
Hartmann, W. K.; Cruikshank, D. P.; Degewij, J.
1982-01-01
VJHK colors for a number of asteroids and eight comets at various solar distances and levels of activity were obtained, and the observations are interpreted in terms of a two-component mixing model in which outer solar system interplanetary bodies are viewed as mixtures of ice and dark carbonaceous-type (RD and C) dirt. It is inferred that the observed comets have comae, and perhaps surfaces, of dirty ice or ice dirt grains colored by an RD-dirt component. This inference is supported by systematics of an 'alpha index' based on VJHK colors and empirically correlated with albedo and ice/dirt ratio. Among comets the alpha index correlates with solar distance in a way that suggests comets emit dirty ice grains which are stable at large solar distance but from which the ice component sublimes and leaves dirt grains at small solar distance.
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NEOWISE OBSERVATIONS OF COMET C/2013 A1 (SIDING SPRING) AS IT APPROACHES MARS
DOE Office of Scientific and Technical Information (OSTI.GOV)
Stevenson, R.; Bauer, J. M.; Mainzer, A. K.
The Near-Earth Object Wide-field Infrared Survey Explorer mission observed comet C/2013 A1 (Siding Spring) three times at 3.4 μm and 4.6 μm as the comet approached Mars in 2014. The comet is an extremely interesting target since its close approach to Mars in late 2014 will be observed by various spacecraft in situ. The observations were taken in 2014 January, July, and September when the comet was at heliocentric distances of 3.82 AU, 1.88 AU, and 1.48 AU. The level of activity increased significantly between the January and July visits but then decreased by the time of the observations in September, approximately four weeksmore » prior to its close approach to Mars. In this work, we calculate Afρ values and CO/CO{sub 2} production rates.« less
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A study of ion composition and dynamics at Comet Halley
NASA Technical Reports Server (NTRS)
Shelley, E. G.; Fuselier, S. A.
1991-01-01
This report details the participation by Lockheed co-investigators in the reduction, analysis, and interpretation of data obtained by the Ion Mass Spectrometer onboard the Giotto mission to Comet Halley. The data analysis activities and much of the scientific collaboration was shared by this team. One objective of the effort under this contract was to use data obtained by the Giotto Ion Mass Spectrometer (IMS) during the encounter with comet Halley for the purpose of advancing our understanding of the chemistry and physics of the interaction of the solar wind with comets and obtaining new information on the comet's composition. An additional objective was to make this unique data set available in a format which can be easily used by the reset of the cometary science community for other analysis in the future. The IMS has two sensors: the High Intensity Spectrometer (HIS) and the High Energy Range Spectrometer (HERS).
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Unusual Water Production Activity of Comet C/2012 S1 (ISON): Outbursts and Continuous Fragmentation
NASA Astrophysics Data System (ADS)
Combi, M. R.; Fougere, N.; Mäkinen, J. T. T.; Bertaux, J.-L.; Quémerais, E.; Ferron, S.
2014-06-01
The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyα camera on the SOlar and Heliospheric Observer (SOHO) satellite observed the hydrogen coma of comet C/2012 S1 (ISON) for most of the last month of its activity from 2013 October 24 to November 24, ending just 4 days before perihelion and its final disruption. The water production rate of the comet was determined from these observations. SOHO has been operating in a halo orbit around the Earth-Sun L1 Lagrange point since its launch in late 1995. Most water vapor produced by comets is ultimately photodissociated into two H atoms and one O atom producing a huge hydrogen coma that is routinely observed in the daily SWAN images in comets of sufficient brightness. Water production rates were calculated from 22 images over most of the last month of the pre-perihelion apparition. The water production rate increased very slowly on average from October 24.9 until November 12.9, staying between 1.8 and 3.4 × 1028 s-1, after which it increased dramatically, reaching 1.6 to 2 × 1030 s-1 from November 21.6 to 23.6. It was not detected after perihelion on December 3.7 when it should have been visible. We examine the active surface area necessary to explain the water production rate and its variation and are able to place constraints on the physical size of the original nucleus necessary to account for the large amount of activity from November 12.9 and until just before perihelion.
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NASA Astrophysics Data System (ADS)
Deca, J.; Divin, A. V.; Horanyi, M.; Henri, P.
2016-12-01
We present preliminary results of the first 3-D fully kinetic and electromagnetic simulations of the solar wind interaction with 67P/Churyumov-Gerasimenko at 3 AU, before the comet transitions into its high-activity phase. We focus on the global cometary environment and the electron-kinetic activity of the interaction. In addition to the background solar wind plasma flow, our model includes also plasma-driven ionization of cometary neutrals and collisional effects. We approximate mass loading of cold cometary oxygen and hydrogen using a hyperbolic relation with distance to the comet. We consider two primary cases: a weak outgassing comet (with the peak ion density 10x the solar wind density) and a moderately outgassing comet (with the peak ion density 50x the solar wind density). The weak comet is characterized by the formation of a narrow region containing a compressed solar wind (the density of the solar wind ion population is 3x the value far upstream of the comet) and a magnetic barrier ( 2x to 4x the interplanetary magnetic field). Blobs of plasma are detached continuously from this sheath region. Standing electromagnetic waves are excited in the cometary wake due to a strong anisotropy in the plasma pressure, as the density and the magnetic field magnitude are anti-correlated.The moderate mass-loading case shows more dynamics at the dayside region. The stagnation of the solar wind flow is accompanied by the formation of elongated density stripes, indicating the presence of a Rayleigh-Taylor instability. These density cavities are elongated in the direction of the magnetic field and encompass the dayside ionopause. To conclude, we believe that our results provide vital information to disentangle the observations made by the Rosetta spacecraft and compose a global solar wind - comet interaction model.
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Pant, Kamala; Roden, Nicholas; Zhang, Charles; Bruce, Shannon; Wood, Craig; Pendino, Kimberly
2015-12-01
14-Hydroxycodeinone (14-HC) is an α,β-unsaturated ketone impurity found in oxycodone drug substance and has a structural alert for genotoxicity. 14-HC was tested in a combined Modified and Standard Comet Assay to determine if the slight decrease in % Tail DNA noted in a previously conducted Standard Comet Assay with 14-HC could be magnified to clarify if the response was due to cross-linking activity. One limitation of the Standard Comet Assay is that DNA cross-links cannot be reliably detected. However, under certain modified testing conditions, DNA cross-links and chemical moieties that elicit such cross-links can be elucidated. One such modification involves the induction of additional breakages of DNA strands by gamma or X-ray irradiation. To determine if 14-HC is a DNA crosslinker in vivo, a Modified Comet Assay was conducted using X-ray irradiation as the modification to visualize crosslinking activity. In this assay, 14-HC was administered orally to mice up to 320 mg/kg/day. Results showed a statistically significant reduction in percent tail DNA in duodenal cells at 320 mg/kg/day, with a nonstatistically significant but dose-related reduction in percent tail DNA also observed at the mid dose of 160 mg/kg/day. Similar decreases were not observed in cells from the liver or stomach, and no increases in percent tail DNA were noted for any tissue in the concomitantly conducted Standard Comet Assay. Taken together, 14-HC was identified as a cross-linking agent in the duodenum in the Modified Comet Assay. © 2015 Wiley Periodicals, Inc.
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An early look of comet C/2013 A1 (Siding Spring): Breathtaker or nightmare?
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ye, Quan-Zhi; Hui, Man-To, E-mail: qye22@uwo.ca
The dynamically new comet, C/2013 A1 (Siding Spring), is to make a close approach to Mars on 2014 October 19 at 18:30 UT at a distance of 40 ± 1 Martian radii. Such an extremely rare event offers a precious opportunity for the spacecrafts on Mars to closely study a dynamically new comet itself as well as the planet-comet interaction. Meanwhile, the high-speed meteoroids released from C/Siding Spring also pose a threat to physically damage the spacecrafts. Here we present our observations and modeling results of C/Siding Spring to characterize the comet and assess the risk posed to the spacecraftsmore » on Mars. We find that the optical tail of C/Siding Spring is dominated by larger particles at the time of the observation. Synchrone simulation suggests that the comet was already active in late 2012 when it was more than 7 AU from the Sun. By parameterizing the dust activity with a semi-analytic model, we find that the ejection speed of C/Siding Spring is comparable to comets such as the target of the Rosetta mission, 67P/Churyumov-Gerasimenko. Under a nominal situation, the simulated dust cone will miss the planet by about 20 Martian radii. At the extreme ends of uncertainties, the simulated dust cone will engulf Mars, but the meteoric influx at Mars is still comparable to the nominal sporadic influx, seemly indicating that an intense and enduring meteoroid bombardment due to C/Siding Spring is unlikely. Further simulation also suggests that gravitational disruption of the dust tail may be significant enough to be observable at Earth.« less
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NASA Astrophysics Data System (ADS)
Kohler, Susanna
2015-11-01
High-resolution imagery of comet 67P ChuryumovGerasimenko has revealed that its surface is covered in active pits some measuring hundreds of meters both wide and deep! But what processes caused these pits to form?Pitted LandscapeESAs Rosetta mission arrived at comet 67P in August 2014. As the comet continued its journey around the Sun, Rosetta extensively documented 67Ps surface through high-resolution images taken with the on-board instrument NavCam. These images have revealed that active, circular depressions are a common feature on the comets surface.In an attempt to determine how these pits formed, an international team of scientists led by Olivier Mousis (Laboratory of Astrophysics of Marseille) has run a series of simulations of a region of the comet the Seth region that contains a 200-meter-deep pit. These simulations include the effects of various phase transitions, heat transfer through the matrix of ices and dust, and gas diffusion throughout the porous material.Escaping VolatilesAdditional examples of pitted areas on 67Ps northern-hemisphere surface include the Ash region and the Maat region (both imaged September 2014 by NavCam) [Mousis et al. 2015]Previous studies have already eliminated two potential formation mechanisms for the pits: impacts (the sizes of the pits werent right) and erosion due to sunlight (the pits dont have the right shape). Mousis and collaborators assume that the pits are instead caused by the depletion of volatile materials chemical compounds with low boiling points either via explosive outbursts at the comets surface, or via sinkholes opening from below the surface. But what process causes the volatiles to deplete when the comet heats?The authors simulations demonstrate that volatiles trapped beneath the comets surface either in icy structures called clathrates or within amorphous ice can be suddenly released as the comet warms up. The team shows that the release of volatiles from these two structures can create 200-meter-deep pits within ~800 years and ~2,000 years, respectively. Since comet 67P has been around the inner solar system for about 7,000 years, both of these processes are viable explanations for the pits.The simulations also show that direct sublimation of crystalline ices of water, carbon monoxide, and carbon dioxide can cause deep pits but only in the absence of a surface layer of dust, known as a dust mantle, in that region of the comet. Direct sublimation could be a viable explanation for the pits, then, if dust grains in the area are so small that they are carried away with the released gas, rather than falling back to form a layer on the comets surface.Regardless of the formation mechanism for these pits, the authors conclude that their very existence implies that the physical and chemical properties across the surface and subsurface of the comet cannot be uniform. Further observations from Rosetta will continue to help us understand comet 67P.CitationO. Mousis et al 2015 ApJ 814 L5. doi:10.1088/2041-8205/814/1/L5
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Staring, A B P; van den Berg, D P G; Cath, D C; Schoorl, M; Engelhard, I M; Korrelboom, C W
2016-07-01
Little is known about treating low self-esteem in anxiety disorders. This study evaluated two treatments targeting different mechanisms: (1) Eye Movement Desensitization and Reprocessing (EMDR), which aims to desensitize negative memory representations that are proposed to maintain low self-esteem; and (2) Competitive Memory Training (COMET), which aims to activate positive representations for enhancing self-esteem. A Randomized Controlled Trial (RCT) was used with a crossover design. Group 1 received six sessions EMDR first and then six sessions COMET; group 2 vice versa. Assessments were made at baseline (T0), end of first treatment (T1), and end of second treatment (T2). Main outcome was self-esteem. We included 47 patients and performed Linear Mixed Models. COMET showed more improvements in self-esteem than EMDR: effect-sizes 1.25 versus 0.46 post-treatment. Unexpectedly, when EMDR was given first, subsequent effects of COMET were significantly reduced in comparison to COMET as the first intervention. For EMDR, sequence made no difference. Reductions in anxiety and depression were mediated by better self-esteem. COMET was associated with significantly greater improvements in self-esteem than EMDR in patients with anxiety disorders. EMDR treatment reduced the effectiveness of subsequent COMET. Improved self-esteem mediated reductions in anxiety and depression symptoms. Copyright © 2016 Elsevier Ltd. All rights reserved.
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Exposed bright features on the comet 67P/Churyumov-Gerasimenko: distribution and evolution
NASA Astrophysics Data System (ADS)
Deshapriya, J. D. P.; Barucci, M. A.; Fornasier, S.; Hasselmann, P. H.; Feller, C.; Sierks, H.; Lucchetti, A.; Pajola, M.; Oklay, N.; Mottola, S.; Masoumzadeh, N.; Tubiana, C.; Güttler, C.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Bertaux, J.-L.; Bertini, I.; Bodewits, D.; Boudreault, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B. J. R.; Debei, S.; Cecco, M. De; Deller, J.; Fulle, M.; Groussin, O.; Gutierrez, P. J.; Hoang, H. V.; Hviid, S. F.; Ip, W.; Jorda, L.; Keller, H. U.; Knollenberg, J.; Kramm, R.; Kührt, E.; Küppers, M.; Lara, L.; Lazzarin, M.; Lopez Moreno, J. J.; Marzari, F.; Naletto, G.; Preusker, F.; Shi, X.; Thomas, N.; Vincent, J.-B.
2018-05-01
Context. Since its arrival at the comet 67P/Churyumov-Gerasimenko in August 2014, the Rosetta spacecraft followed the comet as it went past the perihelion and beyond until September 2016. During this time there were many scientific instruments operating on board Rosetta to study the comet and its evolution in unprecedented detail. In this context, our study focusses on the distribution and evolution of exposed bright features that have been observed by OSIRIS, which is the scientific imaging instrument aboard Rosetta. Aims: We envisage investigating various morphologies of exposed bright features and the mechanisms that triggered their appearance. Methods: We co-registered multi-filter observations of OSIRIS images that are available in reflectance. The Lommel-Seeliger disk function was used to correct for the illumination conditions and the resulting colour cubes were used to perform spectrophotometric analyses on regions of interest. Results: We present a catalogue of 57 exposed bright features observed on the nucleus of the comet, all of which are attributed to the presence of H2O ice on the comet. Furthermore, we categorise these patches under four different morphologies and present geometric albedos for each category. Conclusions: Although the nucleus of 67P/Churyumov-Gerasimenko appears to be dark in general, there are localised H2O ice sources on the comet. Cometary activity escalates towards the perihelion passage and reveals such volatile ices. We propose that isolated H2O ice patches found in smooth terrains in regions, such as Imhotep, Bes, and Hapi, result from frost as an aftermath of the cessation of the diurnal water cycle on the comet as it recedes from perihelion. Upon the comet's return to perihelion, such patches are revealed when sublimation-driven erosion removes the thin dust layers that got deposited earlier. More powerful activity sources such as cometary outbursts are capable of revealing much fresher, less contaminated H2O ice that is preserved with consolidated cometary material, as observed on exposed patches resting on boulders. This is corroborated by our albedo calculations that attribute higher albedos for bright features with formations related to outbursts.
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Comet 252P/LINEAR: Born (Almost) Dead?
NASA Astrophysics Data System (ADS)
Ye, Quan-Zhi; Brown, Peter G.; Wiegert, Paul A.
2016-02-01
Previous studies have revealed Jupiter-family comet 252P/LINEAR as a comet that was recently transported into the near-Earth object (NEO) region in ∼1800 AD yet only being weakly active. In this Letter, we examine the “formed (almost) dead” hypothesis for 252P/LINEAR using both dynamical and observational approaches. By statistically examining the dynamical evolution of 252P/LINEAR over a period of 107 years, we find the median elapsed residency in the NEO region to be 4 × 102 years, which highlights the likelihood of 252P/LINEAR as an (almost) first-time NEO. With available cometary and meteor observations, we find the dust production rate of 252P/LINEAR to be on the order of 106 kg per orbit since its entry to the NEO region. These two lines of evidence support the hypothesis that the comet was likely to have formed in a volatile-poor environment. Cometary and meteor observations during the comet's unprecedented close approach to the Earth around 2016 March 21 would be useful for understanding of the surface and evolutionary properties of this unique comet.
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Where are the mini Kreutz-family comets?
DOE Office of Scientific and Technical Information (OSTI.GOV)
Ye, Quan-Zhi; Wiegert, Paul A.; Hui, Man-To
The Kreutz family of sungrazing comets contains over 2000 known members, many of which are believed to be under ∼100 m sizes (mini comets) and have only been studied at small heliocentric distances (r {sub H}) with space-based SOHO/STEREO spacecraft. To understand the brightening process of mini Kreutz comets, we conducted a survey using CFHT/MegaCam at moderate r {sub H} guided by SOHO/STEREO observations. We identify two comets that should be in our search area but are not detected, indicating that the comets have either followed a steeper brightening rate within the previously reported rapid brightening stage (the brightening burst),more » or the brightening burst starts earlier than expected. We present a composite analysis of the pre-perihelion light curves of five Kreutz comets that cover to ∼1 AU. We observe significant diversity in the light curves that can be used to grossly classify them into two types: C/Ikeya-Seki and C/SWAN follow the canonical r{sub H}{sup −4} while the others follow r{sub H}{sup −7}. In particular, C/SWAN seems to have undergone an outburst (Δm > 5 mag) or a rapid brightening (n ≳ 11) between r {sub H} = 1.06 AU and 0.52 AU, and shows hints of structural/compositional differences compared to other bright Kreutz comets. We also find evidence that the Kreutz comets as a population lose their mass less efficiently than the dynamically new comet, C/ISON, and are relatively devoid of species that drive C/ISON's activity at large r {sub H}. Concurrent observations of C/STEREO in different wavelengths also suggest that a blueward species such as CN may be the main driver for brightening bursts, instead of sodium as previously thought.« less
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Rosetta following a living comet
NASA Astrophysics Data System (ADS)
Accomazzo, Andrea; Ferri, Paolo; Lodiot, Sylvain; Pellon-Bailon, Jose-Luis; Hubault, Armelle; Porta, Roberto; Urbanek, Jakub; Kay, Ritchie; Eiblmaier, Matthias; Francisco, Tiago
2016-09-01
The International Rosetta Mission was launched on 2nd March 2004 on its 10 year journey to rendezvous with comet 67P Churyumov-Gerasimenko. Rosetta performed comet orbit insertion on the 6th of August 2014, after which it characterised the nucleus and orbited it at altitudes as low as a few kilometres. In November 2014 Rosetta delivered the lander Philae to perform the first soft landing ever on the surface of a comet. The critical landing operations have been conducted with remarkable accuracy and will constitute one of the most important achievements in the history of spaceflight. After this critical operation, Rosetta began the escort phase of the comet in its journey in the Solar System heading to the perihelion, reached in August 2015. Throughout this period, the comet environment kept changing with increasing gas and dust emissions. A first phase of bound orbits was followed by a sequence of complex flyby segments which allowed the scientific instruments to perform in depth investigation of the comet environment and nucleus. The unpredictable nature of the comet activity forced the mission control team to implement unplanned changes to the flight plan prepared for this mission phase and to plan the whole mission in a more dynamic way than originally conceived. This paper describes the details of the landing operations and of the main comet escort phase. It also includes the mission status as achieved after perihelion and the findings about the evolution of the comet and its environment from a mission operations point of view. The lessons learned from this unique and complex operations phase and the plans for the next mission phases, which include a mission extension into 2016, are also described.
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Early Activity of Cometary Species from ROSINA/DFMS at 67P/ Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Hässig, Myrtha; Fuselier, Stephen A.; Altwegg, Kathrin; Balsiger, Hans; Berthelier, Jean-Jacques; Bieler, André; Calmonte, Ursina; Dhooghe, Frederik; Fiethe, Björn; Gasc, Sébastien; Gombosi, Tamas I.; Jäckel, Annette; Korth, Axel; Le Roy, Léna; Rème, Henri; Rubin, Martin; Tzou, Chia-Yu; Wurz, Peter
2014-11-01
The European Space Agency’s Rosetta spacecraft arrived after a journey of more than 10 years at comet 67P/Churyumov-Gerasimenko. ROSINA is an instrument package on board Rosetta. It consists of two mass spectrometers and a COmetary Pressure Sensor (COPS). The two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron Time of Flight (RTOF) complement each other with high mass resolution (e.g to resolve 13C from CH), high dynamic range (to detect low abundant isotopes and species), high mass range (to detect organics), and high time resolution. ROSINA is designed to measure the neutral gas and plasma composition in the coma of 67P/Churyumov-Gerasimenko in addition to the physical properties of the neutral component of the coma. For the first time, a comet can be observed in situ from its early activity towards and after perihelion. Little is known about what drives initial cometary activity very far from the Sun. Remote sensing observations to date are highly constrained to a limited number of a few bright comets (e.g. Hale-Bopp) and a limited number of species. Rosetta provides the first measurements of the early activity of a comet in situ and detected the first cometary molecules early August. We will focus on early activity of cometary species from the high resolution mass spectrometer ROSINA/DFMS.
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NASA Astrophysics Data System (ADS)
Bacci, P.
2017-12-01
Cometary activity in the asteroid (457175) 2008 GO98 was observed at San Marcello Observatory, highlighting an extended coma and a tail of 36 arcseconds. The asteroid should be classified as a quasi-Hilda comet.
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NASA Astrophysics Data System (ADS)
Kwan, Teiler J.; Bullis, Jeremy; Gustafsson, Annika; Fisher, Robert Scott
2015-01-01
The University of Oregon (UO) owns and operates Pine Mountain Observatory (PMO), located in central Oregon on the summit of Pine Mountain at an elevation of 1980 meters. PMO consists of four telescopes ranging in size from 0.35 - 0.8 meters. The Oregon Observatory Remote Control Center (OORCC) is a remote-observing center within the Department of Physics on the UO campus (~140 miles from the observatory) that has a direct connection to PMO through a dedicated fiber-optic cable. With this facility, we will enable UO undergraduate student researchers, UO faculty, and the non-scientific community to fully control and operate a newly installed robotic telescope on the summit of Pine Mountain from Eugene, or any other authorized site in Oregon. In addition to providing undergraduates with instrumentation and engineering experience, we will implement research by photometrically monitoring bright and variable astronomical sources including main belt comets, Herbig Ae/Be stars, and active galactic nuclei in extragalactic systems. The primary objective with the OORCC is to manage a multifaceted astronomy and astrophysics research facility, extending as a state-wide resource for K-12 STEM activities and public outreach programs. With the OORCC, we intend to bring unique and enriching astronomy exposure to many different groups of people throughout the state of Oregon.
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Rosetta/OSIRIS - Nucleus morphology and activity of comet 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Sierks, Holger; Barbieri, Cesare; Lamy, Philippe; Rickman, Hans; Rodrigo, Rafael; Koschny, Detlef
2015-04-01
ESA's Rosetta mission arrived on August 6, 2014, at target comet 67P/Churyumov-Gerasimenko after 10 years of cruise. OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) is the scientific imaging system onboard Rosetta. It comprises a Narrow Angle Camera (NAC) for nucleus surface and dust studies and a Wide Angle Camera (WAC) for the wide field coma investigations. OSIRIS imaged the nucleus and coma of the comet from the arrival throughout the mapping phase, PHILAE landing, early escort phase and close fly-by. The overview paper will discuss the surface morpholo-gy and activity of the nucleus as seen in gas, dust, and local jets as well as small scale structures in the local topography.
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DOE Office of Scientific and Technical Information (OSTI.GOV)
Bodewits, Dennis; Kelley, Michael S. P.; Farnham, Tony L.
We used the UltraViolet-Optical Telescope on board Swift to systematically follow the dynamically new comet C/2013 A1 (Siding Spring) on its approach to the Sun. The comet was observed from a heliocentric distance of 4.5 AU pre-perihelion to its perihelion at 1.4 AU. From our observations, we estimate that the water production rate during closest approach to Mars was 1.5 ± 0.3 × 10{sup 28} molecules s{sup −1}, that peak gas delivery rates where between 4.5 and 8.8 kg s{sup −1}, and that in total between 3.1 and 5.4 × 10{sup 4} kg cometary gas was delivered to the planet.more » Seasonal and evolutionary effects on the nucleus govern the pre-perihelion activity of comet Siding Spring. The sudden increase of its water production between 2.46 and 2.06 AU suggests the onset of the sublimation of icy grains in the coma, likely driven by CO{sub 2}. As the comet got closer to the Sun, the relative contribution of the nucleus’ water production increased, while CO{sub 2} production rates decreased. The changes in the comet’s activity can be explained by a depletion of CO{sub 2}, but the comet’s high mass loss rate suggests they may reflect primordial heterogeneities in the nucleus.« less
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NASA Astrophysics Data System (ADS)
Stoyan, Ronald; Dunlop, Storm
2015-01-01
Foreword; Using this book; Part I. Introduction: Cometary beliefs and fears; Comets in art; Comets in literature and poetry; Comets in science; Cometary science today; Great comets in antiquity; Great comets of the Middle Ages; Part II. The 30 Greatest Comets of Modern Times: The Great Comet of 1471; Comet Halley 1531; The Great Comet of 1556; The Great Comet of 1577; Comet Halley, 1607; The Great Comet of 1618; The Great Comet of 1664; Comet Kirch, 1680; Comet Halley, 1682; The Great Comet of 1744; Comet Halley, 1759; Comet Messier, 1769; Comet Flaugergues, 1811; Comet Halley, 1835; The Great March Comet of 1843; Comet Donati, 1858; Comet Tebbutt, 1861; The Great September Comet of 1882; The Great January Comet of 1910; Comet Halley, 1910; Comet Arend-Roland, 1956; Comet Ikeya-Seki, 1965; Comet Bennett, 1970; Comet Kohoutek, 1973-4; Comet West, 1976; Comet Halley, 1986; Comet Shoemaker-Levy 9, 1994; Comet Hyakutake, 1996; Comet Hale-Bopp, 1997; Comet McNaught, 2007; Part III. Appendices; Table of comet data; Glossary; References; Photo credits; Index.
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Comet C/2017 K2 (PANSTARRS): Dynamically Old or New?
NASA Astrophysics Data System (ADS)
de la Fuente Marcos, Raúl; de la Fuente Marcos, Carlos
2018-04-01
At discovery time, C/2017 K2 (PANSTARRS) was the second most distant inbound active comet ever observed. It has been argued that this object is in the process of crossing the inner Solar System for the first time, but other authors have concluded that it is dynamically old. We have performed full N-body simulations for 3 Myr into the past using the latest public orbit determination for this object and most of them, 67%, are consistent with a bound and dynamically old Oort cloud comet, but about 29% of the studied orbits are compatible with an interstellar origin. Our independent calculations strongly suggest that C/2017 K2 is not a dynamically new Oort cloud comet.
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Direct Characterization of Comets and Asteroids via Cosmic Dust Analysis from the Deep Space Gateway
NASA Technical Reports Server (NTRS)
Fries, M.; Fisher, K.
2018-01-01
The Deep Space Gateway (DSG) may provide a platform for direct sampling of a large number of comets and asteroids, through employment of an instrument for characterizing dust from these bodies. Every year, the Earth traverses through debris streams of dust and small particles from comets and asteroids in Earth-crossing orbits, generating short-lived outbursts of meteor activity commonly known as "meteor showers" (Figure 1). The material in each debris stream originates from a distinct parent body, many of which have been identified. By sampling this material, it is possible to quantitatively analyze the composition of a dozen or more comets and asteroids (See Figure 2, following page) without leaving cislunar space.
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Interaction of the solar wind with comets: a Rosetta perspective
NASA Astrophysics Data System (ADS)
Glassmeier, Karl-Heinz
2017-05-01
The Rosetta mission provides an unprecedented possibility to study the interaction of comets with the solar wind. As the spacecraft accompanies comet 67P/Churyumov-Gerasimenko from its very low-activity stage through its perihelion phase, the physics of mass loading is witnessed for various activity levels of the nucleus. While observations at other comets provided snapshots of the interaction region and its various plasma boundaries, Rosetta observations allow a detailed study of the temporal evolution of the innermost cometary magnetosphere. Owing to the short passage time of the solar wind through the interaction region, plasma instabilities such as ring-beam and non-gyrotropic instabilities are of less importance during the early life of the magnetosphere. Large-amplitude ultra-low-frequency (ULF) waves, the `singing' of the comet, is probably due to a modified ion Weibel instability. This instability drives a cross-field current of implanted cometary ions unstable. The initial pick-up of these ions causes a major deflection of the solar wind protons. Proton deflection, cross-field current and the instability induce a threefold structure of the innermost interaction region with the characteristic Mach cone and Whistler wings as stationary interaction signatures as well as the ULF waves representing the dynamic aspect of the interaction. This article is part of the themed issue 'Cometary science after Rosetta'.
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NASA Astrophysics Data System (ADS)
Rubin, M.; Altwegg, K.; Balsiger, H. R.; Berthelier, J. J.; Calmonte, U.; De Keyser, J.; Fiethe, B.; Fuselier, S. A.; Gasc, S.; Gombosi, T. I.; Hässig, M.; Jäckel, A.; Le Roy, L.; Mall, U. A.; Rème, H.; Sémon, T.; Tzou, C. Y.; Wurz, P.
2015-12-01
The European Space Agency's Rosetta spacecraft is in close proximity of comet 67P/Churyumov-Gerasimenko for well over a year now. During this time Rosetta followed the comet from almost 3.5 AU through perihelion at 1.25 AU and away from the Sun again. Part of the scientific payload scrutinizing the comet is the ROSINA experiment, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis. The suite of instruments consists of the Double Focusing Mass Spectrometer DFMS, the Reflectron Time-Of-Flight mass spectrometer RTOF, and the COmet Pressure Sensor COPS. From the combined measurements by ROSINA, the composition and dynamics of the volatiles in the coma of the comet are derived. On 13 August 2015, comet 67P/Churyumov-Gerasimenko reached perihelion, the point along its orbits that is closest to the Sun. Furthermore equinox occurred in May 2015 leading to a change in season - the previous summer hemisphere is now in winter and vice versa. One of the goals of ROSINA is to track the activity of the comet during its apparition and to investigate potential changes in the chemical composition as the spacecraft orbits around the nucleus. In this presentation we will summarize some key findings obtained during the first year and a half of the nominal mission and present first results comparing the pre- and post perihelion neutral gas coma. The goal of these observations is to gather information about the formation and the composition of the comet and ultimately our early Solar System.
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The Rosetta mission orbiter science overview: the comet phase
Altobelli, N.; Buratti, B. J.; Choukroun, M.
2017-01-01
The international Rosetta mission was launched in 2004 and consists of the orbiter spacecraft Rosetta and the lander Philae. The aim of the mission is to map the comet 67P/Churyumov–Gerasimenko by remote sensing, and to examine its environment in situ and its evolution in the inner Solar System. Rosetta was the first spacecraft to rendezvous with and orbit a comet, accompanying it as it passes through the inner Solar System, and to deploy a lander, Philae, and perform in situ science on the comet's surface. The primary goals of the mission were to: characterize the comet's nucleus; examine the chemical, mineralogical and isotopic composition of volatiles and refractories; examine the physical properties and interrelation of volatiles and refractories in a cometary nucleus; study the development of cometary activity and the processes in the surface layer of the nucleus and in the coma; detail the origin of comets, the relationship between cometary and interstellar material and the implications for the origin of the Solar System; and characterize asteroids 2867 Steins and 21 Lutetia. This paper presents a summary of mission operations and science, focusing on the Rosetta orbiter component of the mission during its comet phase, from early 2014 up to September 2016. This article is part of the themed issue ‘Cometary science after Rosetta’. PMID:28554981
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Modeling Coma Gas Jets in Comet Hale-Bopp
NASA Technical Reports Server (NTRS)
Lederer, S. M.; Campins, H.
2001-01-01
We present an analysis of OH, CN, and C2 jets observed in Comet Hale-Bopp. The relative contributions from and composition of the coma gas sources, and the parameters describing the active areas responsible for the gas jets will be discussed. Additional information is contained in the original extended abstract.
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NASA Technical Reports Server (NTRS)
2004-01-01
This composite image was taken by the navigation camera during the close approach phase of Stardust's Jan 2, 2004 flyby of comet Wild 2. Several large depressed regions can be seen. Comet Wild 2 is about five kilometers (3.1 miles) in diameter. To create this image, a short exposure image showing tremendous surface detail was overlain on a long exposure image taken just 10 seconds later showing jets. Together, the images show an intensely active surface, jetting dust and gas streams into space and leaving a trail millions of kilometers long.
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Atlas of Secular Light Curves of Comets
NASA Astrophysics Data System (ADS)
Ferrin, Ignacio
2007-12-01
We have completed work on the secular light curves of 30 periodic and non-periodic comets. The objectives and approach of this project has been explained in Ferrin (Icarus, 178, 493-516, 2005). Each comet requires 2 plots. The time plot shows the reduced (to Δ = 1 AU) magnitude of the comet as a function of time, thus displaying the brightness history of the object. The log plot is a reflected double log plot. The reflection takes place at R=1 AU, to allow the determination of the absolute magnitude by extrapolation. 22 photometric parameters are measured from the plots, most of them new. The plots have been collected in a document that constitutes "The Atlas". We have defined a photometric age, P-AGE, that attempts to measure the age of a comet based on its activity. P-AGE has been scaled to human ages to help in its interpretation. We find that comets Hale-Bopp and 29P/SW 1, are baby comets (P-AGE < 3 comet years), while 107P, 162P and 169P are methuselah comets (P-AGE > 100 cy). The secular light curve of 9P/Tempel 1 exhibits sublimation due to H2O and due to CO. Comet 67P/Churyumov-Gerasimento to be visited by the Rossetta spacecraft in 2014 exhibits a photometric anomaly. Comet 65P/Gunn exhibits a lag in maximum brightness of LAG = + 254 days after perihelion. We suggest that the pole is pointing to the sun at that time. The secular light curves will be presented and a preliminary interpretation will be advanced. The secular light curves present complexity beyond current understanding. The observations described in this work were carried out at the National Observatory of Venezuela (ONV), managed by the Center for Research in Astronomy (CIDA), for the Ministry of Science and Technology (MinCyT).
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The friable sponge model of a cometary nucleus
NASA Technical Reports Server (NTRS)
Horanyi, M.; Gombosi, T. I.; Korosmezey, A.; Kecskemety, K.; Szego, K.; Cravens, T. E.; Nagy, A. F.
1984-01-01
The mantle/core model of cometary nuclei, first suggested by Whipple and subsequently developed by Mendis and Brin, is modified and extended. New terms are added to the heat conduction equation for the mantle, which is solved in order to obtain the temperature distribution in the mantle and the gas production rate as a function of mantle thickness and heliocentric distance. These results are then combined with some specific assumptions about the mantle structure (the friable sponge model) in order to make predictions for the variation of gas production rate and mantle thickness as functions of heliocentric distance for different comets. A solution of the time-dependent heat conduction equation is presented in order to check some of the assumptions.
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Garaj-Vrhovac, Verica; Gajski, Goran
2009-03-01
Several studies have reported radioprotective, antimutagenic, anti-inflammatory, antinociceptive, and anticancer effects of bee venom both in the cell and the whole organism. The aim of this study was to assess the effects of a single high dose of 100 microg mL(-1) of whole bee venom in human lymphocytes in vitro over a variety of time spans (from 10 min to 24 h). After the treatment, we used the comet assay and micronucleus test to see the effect of bee venom on the cell. The comet assay confirmed that the venom damaged the DNA molecule. Tail length, tail intensity, tail moment showed a significant increase (P < 0.05). The percentage of long-tailed nuclei (LTN) with the tail length exceeding the 95th percentile also increased in a time-dependent manner. The micronucleus parameters (number of micronuclei, nucleoplasmic bridges, and nuclear buds) also showed a significant time-dependent increase (P < 0.05). This research indicates that high concentrations of bee venom can lead to cellular instability. Further research is needed to understand the mechanism of action of bee venom and its components in human cells and to see if this natural product may find application in medicine.
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Can the comet assay be used reliably to detect nanoparticle-induced genotoxicity?
Karlsson, Hanna L; Di Bucchianico, Sebastiano; Collins, Andrew R; Dusinska, Maria
2015-03-01
The comet assay is a sensitive method to detect DNA strand breaks as well as oxidatively damaged DNA at the level of single cells. Today the assay is commonly used in nano-genotoxicology. In this review we critically discuss possible interactions between nanoparticles (NPs) and the comet assay. Concerns for such interactions have arisen from the occasional observation of NPs in the "comet head", which implies that NPs may be present while the assay is being performed. This could give rise to false positive or false negative results, depending on the type of comet assay endpoint and NP. For most NPs, an interaction that substantially impacts the comet assay results is unlikely. For photocatalytically active NPs such as TiO2 , on the other hand, exposure to light containing UV can lead to increased DNA damage. Samples should therefore not be exposed to such light. By comparing studies in which both the comet assay and the micronucleus assay have been used, a good consistency between the assays was found in general (69%); consistency was even higher when excluding studies on TiO2 NPs (81%). The strong consistency between the comet and micronucleus assays for a range of different NPs-even though the two tests measure different endpoints-implies that both can be trusted in assessing the genotoxicity of NPs, and that both could be useful in a standard battery of test methods. © 2014 Wiley Periodicals, Inc.
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Rotation lightcurves of small jovian Trojan asteroids
NASA Astrophysics Data System (ADS)
French, Linda M.; Stephens, Robert D.; Coley, Daniel; Wasserman, Lawrence H.; Sieben, Jennifer
2015-07-01
Several lines of evidence support a common origin for, and possible hereditary link between, cometary nuclei and jovian Trojan asteroids. Due to their distance and low albedos, few comet-sized Trojans have been studied. We present new lightcurve information for 19 Trojans ≲ 30 km in diameter, more than doubling the number of objects in this size range for which some rotation information is known. The minimum densities for objects with complete lightcurves are estimated and are found to be comparable to those measured for cometary nuclei. A significant fraction (∼40%) of this observed small Trojan population rotates slowly (P > 24 h), with measured periods as long as 375 h (Warner, B.D., Stephens, R.D. [2011]. Minor Planet Bull. 38, 110-111). The excess of slow rotators may be due to the YORP effect. Results of the Kolmogorov-Smirnov test suggest that the distribution of Trojan rotation rates is dissimilar to those of Main Belt Asteroids of the same size. Concerted observations of a large number of Trojans could establish the spin barrier (Warner, B.D., Harris, A.W., Pravec, P. [2009]. Icarus 202, 134-146), making it possible to estimate densities for objects near the critical period.
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Alvarez-Moya, Carlos; Silva, Mónica Reynoso; Ramírez, Carlos Valdez; Gallardo, David Gómez; Sánchez, Rafael León; Aguirre, Alejandro Canales; Velasco, Alfredo Feria
2014-01-01
There is considerable controversy with regard to the genotoxicity of glyphosate, with some reports stating that this compound is non-toxic for fish, birds and mammals. In this work, we used the comet assay to examine the genotoxicity of glyphosate isopropylamine (0.7, 7, 70 and 700 μM) in human lymphocytes, erythrocytes of Oreochromis niloticus and staminal nuclei of Tradescantia (4430) in vitro and in vivo. Cells, nuclei and fish that had and had not been exposed to 5 mM N-nitrosodiethylamine (NDEA) were used as positive and negative controls, respectively. Significant (p < 0.01) genetic damage was observed in vivo and in vitro in all cell types and organisms tested. Human lymphocytes and Tradescantia hairs showed lower genetic damage in vivo compared to in vitro, possibly because of efficient metabolization of the herbicide. In O. niloticus erythrocytes, significant (p < 0.001) genotoxicity was observed at ≥ 7 μM, whereas in vitro, glyphosphate was genotoxic in human lymphocytes and Tradescantia hairs at ≥ 0.7 μM. These results indicate that glyphosate is genotoxic in the cells and organisms studied at concentrations of 0.7–7 μM. PMID:24688297
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Alvarez-Moya, Carlos; Silva, Mónica Reynoso; Ramírez, Carlos Valdez; Gallardo, David Gómez; Sánchez, Rafael León; Aguirre, Alejandro Canales; Velasco, Alfredo Feria
2014-03-01
There is considerable controversy with regard to the genotoxicity of glyphosate, with some reports stating that this compound is non-toxic for fish, birds and mammals. In this work, we used the comet assay to examine the genotoxicity of glyphosate isopropylamine (0.7, 7, 70 and 700 μM) in human lymphocytes, erythrocytes of Oreochromis niloticus and staminal nuclei of Tradescantia (4430) in vitro and in vivo. Cells, nuclei and fish that had and had not been exposed to 5 mM N-nitrosodiethylamine (NDEA) were used as positive and negative controls, respectively. Significant (p < 0.01) genetic damage was observed in vivo and in vitro in all cell types and organisms tested. Human lymphocytes and Tradescantia hairs showed lower genetic damage in vivo compared to in vitro, possibly because of efficient metabolization of the herbicide. In O. niloticus erythrocytes, significant (p < 0.001) genotoxicity was observed at ≥ 7 μM, whereas in vitro, glyphosphate was genotoxic in human lymphocytes and Tradescantia hairs at ≥ 0.7 μM. These results indicate that glyphosate is genotoxic in the cells and organisms studied at concentrations of 0.7-7 μM.
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Understanding the Physical Structure of the Comet Shoemaker-Levy 9 Fragments
NASA Astrophysics Data System (ADS)
Rettig, Terrence
2000-07-01
Images of the fragmented comet Shoemaker-Levy 9 {SL9} as it approached Jupiter in 1994 provided a unique opportunity to {1} probe the comae, {2} understand the structure of the 20 cometary objects, and {3} provide limits on the Jovian impact parameters. The primary cometary questions were: how were the fragments formed and what was their central structure? There still remains a diversity of opinion regarding the structure of the 21 comet-like fragments as well as the specifics of the disruption event itself. We have shown from Monte Carlo modeling of surface brightness profiles that SL9 fragments had unusual dust size distributions and outflow velocities. Further work of a preliminary nature showed some of the central reflecting area excesses derived from surface brightness profile fitting {w/psf} appeared distributed rather than centrally concentrated as would be expected for comet- like objects, some central excesses were negative and also, the excesses could vary with time. With an improved coma subtraction technique we propose to model each coma surface brightness profile, extract central reflecting areas or central brightness excesses for the non-star-contaminated WFPC-2 SL9, to determine the behavior and characteristics of the central excesses as the fragments approached Jupiter. A second phase of the proposal will be to use numerical techniques {in conjunction with D. Richardson} to investigate the various fragment models. This is a difficult modeling process that will allow us to model the structure and physical characteristics of the fragments and thus constrain parameters for the Jovian impact events. The results will be used to constrain the structure of the central fragment cores of SL9 and how the observed dust comae were produced. The results will provide evidence to discriminate between the parent nucleus models {i.e., were the fragments solid objects or swarms of particles?} and provide better constraints on the atmospheric impact models. The physical characteristics of cometary nuclei are not well understood and the SL9 data provides an important opportunity to constrain these parameters.
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New active asteroid 313P/Gibbs
DOE Office of Scientific and Technical Information (OSTI.GOV)
Jewitt, David; Hui, Man-To; Li, Jing
We present initial observations of the newly discovered active asteroid 313P/Gibbs (formerly P/2014 S4), taken to characterize its nucleus and comet-like activity. The central object has a radius ∼0.5 km (geometric albedo 0.05 assumed). We find no evidence for secondary nuclei and set (with qualifications) an upper limit to the radii of such objects near 20 m, assuming the same albedo. Both aperture photometry and a morphological analysis of the ejected dust show that mass-loss is continuous at rates ∼0.2–0.4 kg s{sup −1}, inconsistent with an impact origin. Large dust particles, with radii ∼50–100 μm, dominate the optical appearance. Atmore » 2.4 AU from the Sun, the surface equilibrium temperatures are too low for thermal or desiccation stresses to be responsible for the ejection of dust. No gas is spectroscopically detected (limiting the gas mass-loss rate to <1.8 kg s{sup −1}). However, the protracted emission of dust seen in our data and the detection of another episode of dust release near perihelion, in archival observations from 2003, are highly suggestive of an origin by the sublimation of ice. Coincidentally, the orbit of 313P/Gibbs is similar to those of several active asteroids independently suspected to be ice sublimators, including P/2012 T1, 238P/Read, and 133P/Elst–Pizarro, suggesting that ice is abundant in the outer asteroid belt.« less
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Evolution of H2O, CO, and CO2 production in Comet C/2009 P1 Garradd during the 2011-2012 apparition
NASA Astrophysics Data System (ADS)
McKay, Adam J.; Cochran, Anita L.; DiSanti, Michael A.; Villanueva, Geronimo; Russo, Neil Dello; Vervack, Ronald J.; Morgenthaler, Jeffrey P.; Harris, Walter M.; Chanover, Nancy J.
2015-04-01
We present analysis of high spectral resolution NIR spectra of CO and H2O in Comet C/2009 P1 (Garradd) taken during its 2011-2012 apparition with the CSHELL instrument on NASA's Infrared Telescope Facility (IRTF). We also present analysis of observations of atomic oxygen in Comet Garradd obtained with the ARCES echelle spectrometer mounted on the ARC 3.5-m telescope at Apache Point Observatory and the Tull Coude spectrograph on the Harlan J. Smith 2.7-m telescope at McDonald Observatory. The observations of atomic oxygen serve as a proxy for H2O and CO2. We confirm the high CO abundance in Comet Garradd and the asymmetry in the CO/H2O ratio with respect to perihelion reported by previous studies. From the oxygen observations, we infer that the CO2/H2O ratio decreased as the comet moved towards the Sun, which is expected based on current sublimation models. We also infer that the CO2/H2O ratio was higher pre-perihelion than post-perihelion. We observe evidence for the icy grain source of H2O reported by several studies pre-perihelion, and argue that this source is significantly less abundant post-perihelion. Since H2O, CO2, and CO are the primary ices in comets, they drive the activity. We use our measurements of these important volatiles in an attempt to explain the evolution of Garradd's activity over the apparition.
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Does a continuous solid nucleus exist in comets.
NASA Technical Reports Server (NTRS)
Lyttleton, R. A.
1972-01-01
The implication of actual cometary observations for the physical nature of comets is briefly reviewed, bringing out the complete conflict with observation of the ice-dust solid nucleus model put forward in recent years as representing the fundamental structure of comets. That under increasing solar heat the nucleus develops an expanding atmosphere is inconsistent with the well-established phenomenon that the coma contracts with decreasing distance from the sun. Several comets remaining always beyond Mars have nevertheless been strongly active and produced fine tails. That some comets show at times a star-like point of light is readily explicable on the dust-cloud structure and by no means establishes that a solid nucleus exists. With the nucleus-area corresponding not to a small solid mass but to an optical phenomenon, there would be no reason to expect that it would describe a precise dynamical orbit. On the hypothesis of a nucleus, it is necessary to postulate further some internal jet-propulsion mechanism to account for the orbital deviations.
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Simulating the Solar Wind Interaction with Comet 67P/Churyumov-Gerasimenko: Latest Results
NASA Astrophysics Data System (ADS)
Deca, J.; Divin, A. V.; Henri, P.; Eriksson, A. I.; Markidis, S.; Olshevsky, V.; Goldstein, R.; Myllys, M. E.; Horanyi, M.
2017-12-01
First observed in 1969, comet 67P/Churyumov-Gerasimenko was escorted for almost two years along its 6.45-yr elliptical orbit by ESA's Rosetta orbiter spacecraft. When a comet is sufficiently close to the Sun, the sublimation of ice leads to an outgassing atmosphere and the formation of a coma, and a dust and plasma tail. Comets are critical to decipher the physics of gas release processes in space. The latter result in mass-loaded plasmas, which more than three decades after the Active Magnetospheric Particle Tracer Explorers (AMPTE) space release experiments are still not fully understood. Using a 3D fully kinetic approach, we study the solar wind interaction with comet 67P/Churyumov-Gerasimenko, focusing in particular on the ion-electron dynamics for various outgassing rates. A detailed kinetic treatment of the electron dynamics is critical to fully capture the complex physics of mass-loading plasmas and to describe the strongly inhomogeneous plasma dynamics observed by Rosetta, down to electron kinetic scales.
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SOLANKY, DIPESH; HAYDEL, SHELLEY E.
2012-01-01
This study aimed to determine the mechanism of action of a natural antibacterial clay mineral mixture, designated CB, by investigating the induction of DNA double-strand breaks (DSBs) in Escherichia coli. To quantify DNA damage upon exposure to soluble antimicrobial compounds, we modified a bacterial neutral comet assay, which primarily associates the general length of an electrophoresed chromosome, or comet, with the degree of DSB-associated DNA damage. To appropriately account for antimicrobial-mediated strand fragmentation, suitable control reactions consisting of exposures to water, ethanol, kanamycin, and bleomycin were developed and optimized for the assay. Bacterial exposure to the CB clay resulted in significantly longer comet lengths, compared to water and kanamycin exposures, suggesting that the induction of DNA DSBs contributes to the killing activity of this antibacterial clay mineral mixture. The comet assay protocol described herein provides a general technique for evaluating soluble antimicrobial-derived DNA damage and for comparing DNA fragmentation between experimental and control assays. PMID:22940101
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Rapid Temperature Changes and the Early Activity on Comet 67P/Churyumov-Gerasimenko
NASA Astrophysics Data System (ADS)
Alí-Lagoa, V.; Delbo', M.; Libourel, G.
2015-09-01
The so-called “early activity” of comet 67P/Churyumov-Gerasimenko has been observed to originate mostly in parts of the concave region or “neck” between its two lobes. Since activity is driven by the sublimation of volatiles, this is a puzzling result because this area is less exposed to the Sun and is therefore expected to be cooler on average. We used a thermophysical model that takes into account thermal inertia, global self-heating, and shadowing, to compute surface temperatures of the comet. We found that, for every rotation in the 2014 August-December period, some parts of the neck region undergo the fastest temperature variations of the comet’s surface precisely because they are shadowed by their surrounding terrains. Our work suggests that these fast temperature changes are correlated to the early activity of the comet, and we put forward the hypothesis that erosion related to thermal cracking is operating at a high rate on the neck region due to these rapid temperature variations. This may explain why the neck contains some ice—as opposed to most other parts of the surface—and why it is the main source of the comet’s early activity. In a broader context, these results indicate that thermal cracking can operate faster on atmosphereless bodies with significant concavities than implied by currently available estimates.
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A new model of physical evolution of Jupiter-family comets
NASA Astrophysics Data System (ADS)
Rickman, H.; Szutowicz, S.; Wójcikowski, K.
2014-07-01
We aim to find the statistical physical lifetimes of Jupiter Family comets. For this purpose, we try to model the processes that govern the dynamical and physical evolution of comets. We pay special attention to physical evolution; attempts at such modelling have been made before, but we propose a more accurate model, which will include more physical effects. The model is tested on a sample of fictitious comets based on real Jupiter Family comets with some orbital elements changed to a state before the capture by Jupiter. We model four different physical effects: erosion by sublimation, dust mantling, rejuvenation (mantle blow-off), and splitting. While for sublimation and splitting there already are some models, like di Sisto et. al. (2009), and we only wish to make them more accurate, dust mantling and rejuvenation have not been included in previous, statistical physical evolution models. Each of these effects depends on one or more tunable parameters, which we establish by choosing the model that best fits the observed comet sample in a way similar to di Sisto et. al. (2009). In contrast to di Sisto et. al., our comparison also involves the observed active fractions vs. nuclear radii.
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Early Activity of Churyumov-Gerasimenko: ROSINA/RTOF Results
NASA Astrophysics Data System (ADS)
Wurz, P.; Altwegg, K.; Balsiger, H. R.; Gasc, S.; Galli, A.; Rubin, M.; Jäckel, A.; Le Roy, L.; Calmonte, U.; Tzou, C. Y.; Mall, U. A.; Korth, A.; Fiethe, B.; De Keyser, J. M.; Berthelier, J. J.; Rème, H.; Gombosi, T. I.; Fuselier, S.
2014-12-01
The European Space Agency's Rosetta spacecraft is now close to the comet 67P/Churyumov-Gerasimenko (67P/C-G). On board is the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument suite. ROSINA consists of two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron-type Time-Of-Flight (RTOF), as well as the COmet Pressure Sensor (COPS). The first signal with ROSINA/RTOF of the gaseous environment of the comet was a significant increase in water density observed on DOY 218.1 of 2014 (at 3.5 AU) by RTOF above the gaseous envelope of the Rosetta spacecraft. A similar density increase is observed by COPS at the same time. A preliminary analysis shows that the water density is nH2O ≈ 1012 m-3 at 100 km distance from the comet (located at 3.5 AU from the Sun). This gives a density at the surface of nH2O ≈ 6.4·1015 m-3 and a vertical column density of water of NCH2O ≈ 6.5·1018 m-2. Assuming an active area of 4% we arrive at a production rate of QH2O ≈ 5.8·1024 mole s-1. These values are preliminary and will be refined by forthcoming observations. Other than water, no signal related to cometary activity could be observed above the molecular background from the spacecraft at present, e.g. cometary CO and CO2 are not observed in the RTOF data so far. This hints at a possible deficiency of carbon bearing compounds in the comet.
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Cytotoxic and genotoxic characterization of aluminum and silicon oxide nanoparticles in macrophages.
Hashimoto, Masanori; Imazato, Satoshi
2015-05-01
Although aluminum oxide and silicon oxide nanoparticles are currently available as dental materials, there is a lack of basic information concerning their biocompatibility. This study evaluates the biological responses of cultured macrophages (RAW264) to aluminum oxide (Al2O3NPs) and silicon oxide nanoparticles (SiO2NPs) by analyzing cytotoxicity and genotoxicity. The nanoparticles are amorphous and spherical, with diameters of 13 nm for the Al2O3NPs and 12 nm for the SiO2NPs. The cultured RAW264 are exposed to the nanoparticles (NPs) and examined for cytotoxicity using the WST-8 cell viability and Hoechst/PI apoptosis assay, for genotoxicity by micronucleus analysis, for changes in nuclear shape (deformed nuclei) and for comet assay using confocal microscopy, and micromorphological analysis is done using scanning and transmission electron microscopes. Nuclei and DNA damage because of exposure to both types of NPs is observed by inmunostaining genotoxicity testing. The cytotoxicity and genotoxicity are well correlated in this study. Numerous NPs are observed as large aggregates in vesicles, but less or nonexistent NP internalization is seen in the nucleus or cytoplasm. These morphological results suggest that a primary cause of cell disruption is the chemical changes of the NPs in the low pH of vesicles (i.e., ionization of Al2O3 or SiO2) for both types of oxide NPs. Although further research on the elution of NP concentrations on cell or tissue activity under simulated clinical conditions is required, NP concentrations over 200 μg/mL are large enough to induce cytotoxic and genotoxic effects to cells. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
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Human sperm sex chromosome disomy and sperm DNA damage assessed by the neutral comet assay.
McAuliffe, M E; Williams, P L; Korrick, S A; Dadd, R; Marchetti, F; Martenies, S E; Perry, M J
2014-10-10
Is there an association between human sperm sex chromosome disomy and sperm DNA damage? An increase in human sperm XY disomy was associated with higher comet extent; however, there was no other consistent association of sex chromosome disomies with DNA damage. There is limited published research on the association between sex chromosome disomy and sperm DNA damage and the findings are not consistent across studies. We conducted a cross-sectional study of 190 men (25% ever smoker, 75% never smoker) from subfertile couples presenting at the Massachusetts General Hospital Fertility Clinic from January 2000 to May 2003. Multiprobe fluorescence in situ hybridization for chromosomes X, Y and 18 was used to determine XX, YY, XY and total sex chromosome disomy in sperm nuclei using an automated scoring method. The neutral comet assay was used to measure sperm DNA damage, as reflected by comet extent, percentage DNA in the comet tail, and tail distributed moment. Univariate and multiple linear regression models were constructed with sex chromosome disomy (separate models for each of the four disomic conditions) as the independent variable, and DNA damage parameters (separate models for each measure of DNA damage) as the dependent variable. Men with current or past smoking history had significantly greater comet extent (µm: regression coefficients with 95% CI) [XX18: 15.17 (1.98, 28.36); YY18: 14.68 (1.50, 27.86); XY18: 15.41 (2.37, 28.45); Total Sex Chromosome Disomy: 15.23 (2.09, 28.38)], and tail distributed moment [XX18: 3.01 (0.30, 5.72); YY18: 2.95 (0.24, 5.67); XY18: 3.04 (0.36, 5.72); Total Sex Chromosome Disomy: 3.10 (0.31, 5.71)] than men who had never smoked. In regression models adjusted for age and smoking, there was a positive association between XY disomy and comet extent. For an increase in XY disomy from 0.56 to 1.47% (representing the 25th to 75th percentile), there was a mean increase of 5.08 µm in comet extent. No other statistically significant findings were observed. A potential limitation of this study is that it is cross-sectional. Cross-sectional analyses by nature do not lend themselves to inference about directionality for any observed associations; therefore we cannot determine which variable is the cause and which one is the effect. A small sample size may be a further limitation. Comparison of these findings to other studies is limited due to methodological differences. Although consistent associations across sex chromosome disomies or DNA damage measures were not observed, this study highlights the need to explore etiologies of sperm DNA damage and sex chromosome disomy to better understand the potential mechanistic overlaps between the two. This work was supported by NIOSH Grant T42 OH008416, and NIH/NIEHS Grants ES 009718, ES 000002, and R01 ES017457. During the study M.E.M. was affiliated with the Department of Environmental Health at the Harvard School of Public Health. N/A. © The Author 2014. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
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Human sperm sex chromosome disomy and sperm DNA damage assessed by the neutral comet assay
McAuliffe, M.E.; Williams, P.L.; Korrick, S.A.; Dadd, R.; Marchetti, F.; Martenies, S.E.; Perry, M.J.
2014-01-01
STUDY QUESTION Is there an association between human sperm sex chromosome disomy and sperm DNA damage? SUMMARY ANSWER An increase in human sperm XY disomy was associated with higher comet extent; however, there was no other consistent association of sex chromosome disomies with DNA damage. WHAT IS KNOWN ALREADY There is limited published research on the association between sex chromosome disomy and sperm DNA damage and the findings are not consistent across studies. STUDY DESIGN, SIZE, AND DURATION We conducted a cross-sectional study of 190 men (25% ever smoker, 75% never smoker) from subfertile couples presenting at the Massachusetts General Hospital Fertility Clinic from January 2000 to May 2003. PARTICIPANTS/MATERIALS, SETTING, METHODS Multiprobe fluorescence in situ hybridization for chromosomes X, Y and 18 was used to determine XX, YY, XY and total sex chromosome disomy in sperm nuclei using an automated scoring method. The neutral comet assay was used to measure sperm DNA damage, as reflected by comet extent, percentage DNA in the comet tail, and tail distributed moment. Univariate and multiple linear regression models were constructed with sex chromosome disomy (separate models for each of the four disomic conditions) as the independent variable, and DNA damage parameters (separate models for each measure of DNA damage) as the dependent variable. MAIN RESULTS AND THE ROLE OF CHANCE Men with current or past smoking history had significantly greater comet extent (µm: regression coefficients with 95% CI) [XX18: 15.17 (1.98, 28.36); YY18: 14.68 (1.50, 27.86); XY18: 15.41 (2.37, 28.45); Total Sex Chromosome Disomy: 15.23 (2.09, 28.38)], and tail distributed moment [XX18: 3.01 (0.30, 5.72); YY18: 2.95 (0.24, 5.67); XY18: 3.04 (0.36, 5.72); Total Sex Chromosome Disomy: 3.10 (0.31, 5.71)] than men who had never smoked. In regression models adjusted for age and smoking, there was a positive association between XY disomy and comet extent. For an increase in XY disomy from 0.56 to 1.47% (representing the 25th to 75th percentile), there was a mean increase of 5.08 µm in comet extent. No other statistically significant findings were observed. LIMITATIONS, REASONS FOR CAUTION A potential limitation of this study is that it is cross-sectional. Cross-sectional analyses by nature do not lend themselves to inference about directionality for any observed associations; therefore we cannot determine which variable is the cause and which one is the effect. A small sample size may be a further limitation. Comparison of these findings to other studies is limited due to methodological differences. WIDER IMPLICATIONS OF THE FINDINGS Although consistent associations across sex chromosome disomies or DNA damage measures were not observed, this study highlights the need to explore etiologies of sperm DNA damage and sex chromosome disomy to better understand the potential mechanistic overlaps between the two. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by NIOSH Grant T42 OH008416, and NIH/NIEHS Grants ES 009718, ES 000002, and R01 ES017457. During the study M.E.M. was affiliated with the Department of Environmental Health at the Harvard School of Public Health. TRIAL REGISTRATION NUMBER N/A. PMID:25069502
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Education and Public Outreach for NASA's EPOXI Mission.
NASA Astrophysics Data System (ADS)
McFadden, Lucy-Ann A.; Crow, C. A.; Behne, J.; Brown, R. N.; Counley, J.; Livengood, T. A.; Ristvey, J. D.; Warner, E. M.
2009-09-01
NASA's EPOXI mission is reusing the Deep Impact (DI) flyby spacecraft to study comets and extra-solar planets around other stars. During the Extrasolar Planetary Observations and Characterization (EPOCh) phase of the mission extrasolar planets transiting their parent stars were observed to gain further knowledge and understanding of planetary systems. Observations of Earth also allowed for characterization of Earth as an extrasolar planet. A movie of a lunar transit of the Earth created from EPOCh images and links to existing planet finding activities from other NASA missions are available on the EPOXI website. The Deep Impact Extended Investigation (DIXI) continues the Deep Impact theme of investigating comet properties and formation by observing comet Hartley 2 in November 2010. The EPOXI Education and Public Outreach (E/PO) program is both creating new materials and updating and modifying existing Deep Impact materials based on DI mission results. Comparing Comets is a new educational activity under development that will guide students in conducting analyses of comet surface features similar to those the DIXI scientists will perform after observing comet Hartley 2. A new story designed to stimulate student creativity was developed in alignment with national educational standards. EPOXI E/PO also funded Family Science Night (FSN), a program bringing together students, families, and educators for an evening at the National Air and Space Museum in Washington, DC. FSN events include time for families to explore the museum, a presentation by a space scientist, and an astronomy themed IMAX film. Nine events were held during the 2008-2009 school year with a total attendance of 3,145 (attendance since inception reached 44,732). Half of attendance is reserved for schools with high percentages of underrepresented minorities. EPOXI additionally offers a bi-monthly newsletter to keep the public, teachers, and space enthusiasts updated on current mission activities. For more information visit: http://epoxi.umd.edu/index.shtml.
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Dust Trails of SP/Tuttle and the Unusual Outbursts of the Ursid Shower
NASA Technical Reports Server (NTRS)
Jenniskens, Peter; Lyytinen, E.; deLignie, M. C.; Johannink, C.; Jobse, K.; Schievink, R.; Langbroek, M.; Koop, M.; Gural, P.; Wilson, M.;
2001-01-01
Halley-type comets tend to have a series of dust trails that remain spatially correlated for extended periods of time, each dating from a specific return of the comet. Encounters with 1 - 9 revolution old individual dust trails of 55P/Tempel-Tuttle have led to well recognized Leonid shower maxim, the peak time of which was well predicted by recent models. Now. we used the same model to calculate the position of dust trails of comet Shuttle, a Halley-type comet in an (approximately) 13.6 year orbit passing just outside of Earth's orbit. We discovered that the meteoroids tend to be trapped in the 14:12 mean motion resonance with Jupiter, while the comet librates in a slightly shorter period orbit around the 13:15 resonance. It takes six centuries to change the orbit enough to intersect Earth's orbit. During that time, the meteoroids and comet separate in mean anomaly by six years. thus explaining the unusual aphelion occurrences of Ursid outbursts. The resonances also prevent dispersion, so that the dust trail encounters (specifically, from dust trails of AD 1378 - 1405) occur only in one year in each orbit. We predicted enhanced activity on December 22, 2000, at around 7:29 and 8:35 UT (universal time) from dust trails dating to the 1405 and 1392 return, respectively. This event was observed from California using video and photographic techniques. At the same time, five Global-MS-Net stations in Finland, Japan and Belgium counted meteors using forward meteor scatter. The outburst peaked at 8:06:07 UT, December 22, at Zenith Hourly Rate (approx.) 90 per hour. The Ursid rates were above half peak intensity during 4.2 hours. This is only the second Halley type comet for which a meteor outburst can be dated to a specific return of the parent comet, and traces their presence back form 9 to at least 45 revolutions of the comet. New orbital elements of Ursid meteoroids are presented. We find that most orbits do scatter around the anticipated positions, confirming the link with comet Shuttle and the epoch of ejection. The 1405 and.1392 dust trails appear to have contributed similar amounts to the activity profile. Some orbits provide a hint of much older debris being present as well. Some of the dispersion in the radiant position may reflect a true variation in inclinations, with two groupings at low and high values, which is not understood at present.
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Khairnar, Krishna; Sanmukh, Swapnil; Chandekar, Rajshree; Paunikar, Waman
2014-07-01
The comet assay is the widely used method for in vitro toxicity testing which is also an alternative to the use of animal models for in vivo testing. Since, its inception in 1984 by Ostling and Johansson, it is being modified frequently for a wide range of application. In spite of its wide applicability, unfortunately there is no report of its application in bacteriophages research. In this study, a novel application of comet assay for the detection of bacteriophage mediated bacterial cell lysis was described. The conventional methods in bacteriophage research for studying bacterial lysis by bacteriophages are plaque assay method. It is time consuming, laborious and costly. The lytic activity of bacteriophage devours the bacterial cell which results in the release of bacterial genomic material that gets detected by ethidium bromide staining method by the comet assay protocol. The objective of this study was to compare efficacy of comet assay with different assay used to study phage mediated bacterial lysis. The assay was performed on culture isolates (N=80 studies), modified comet assay appear to have relatively higher sensitivity and specificity than other assay. The results of the study showed that the application of comet assay can be an economical, time saving and less laborious alternative to conventional plaque assay for the detection of bacteriophage mediated bacterial cell lysis. Copyright © 2014 Elsevier B.V. All rights reserved.
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Long-period comet impact risk mitigation with Earth-based laser arrays
NASA Astrophysics Data System (ADS)
Zhang, Qicheng; Lubin, Philip M.; Hughes, Gary B.
2017-09-01
Long-period comets (LPCs) frequently transit the inner solar system, and like near-Earth asteroids (NEAs), pose a continued risk of impact with Earth. Unlike NEAs, LPCs follow nearly parabolic trajectories and approach from the distant outer solar system where they cannot be observed. An LPC on an Earth-impact trajectory is unlikely to be discovered more than a few years in advance of its arrival, even with significant advancements in sky survey detection capabilities, likely leaving insufficient time to develop and deliver an interception mission to deflect the comet. However, recent proposals have called for the development of one or more large ˜ 1 km laser arrays placed on or near Earth primarily as a means for photon propulsion of low-mass spacecraft at delta-v above what would be feasible by traditional chemical or ion propulsion methods. Such a laser array can also be directed to target and heat a threatening comet, sublimating its ices and activating jets of dust and vapor which alter the comet's trajectory in a manner similar to rocket propulsion. Simulations of directed energy comet deflection were previously developed from astrometric models of nongravitational orbital perturbations from solar heating, an analogous process that has been observed in numerous comets. These simulations are used together with the distribution of known LPC trajectories to evaluate the effect of an operational Earth-based laser array on the LPC impact risk.
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2004-03-18
This composite image was taken by the navigation camera during the close approach phase of Stardust's Jan 2, 2004 flyby of comet Wild 2. Several large depressed regions can be seen. Comet Wild 2 is about five kilometers (3.1 miles) in diameter. To create this image, a short exposure image showing tremendous surface detail was overlain on a long exposure image taken just 10 seconds later showing jets. Together, the images show an intensely active surface, jetting dust and gas streams into space and leaving a trail millions of kilometers long. http://photojournal.jpl.nasa.gov/catalog/PIA05578
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Interaction of the solar wind with comets: a Rosetta perspective
2017-01-01
The Rosetta mission provides an unprecedented possibility to study the interaction of comets with the solar wind. As the spacecraft accompanies comet 67P/Churyumov–Gerasimenko from its very low-activity stage through its perihelion phase, the physics of mass loading is witnessed for various activity levels of the nucleus. While observations at other comets provided snapshots of the interaction region and its various plasma boundaries, Rosetta observations allow a detailed study of the temporal evolution of the innermost cometary magnetosphere. Owing to the short passage time of the solar wind through the interaction region, plasma instabilities such as ring--beam and non-gyrotropic instabilities are of less importance during the early life of the magnetosphere. Large-amplitude ultra-low-frequency (ULF) waves, the ‘singing’ of the comet, is probably due to a modified ion Weibel instability. This instability drives a cross-field current of implanted cometary ions unstable. The initial pick-up of these ions causes a major deflection of the solar wind protons. Proton deflection, cross-field current and the instability induce a threefold structure of the innermost interaction region with the characteristic Mach cone and Whistler wings as stationary interaction signatures as well as the ULF waves representing the dynamic aspect of the interaction. This article is part of the themed issue ‘Cometary science after Rosetta’. PMID:28554976
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Shoemaker-Levy 9/JUPITER Collision Update
NASA Astrophysics Data System (ADS)
1994-05-01
There are many signs that the upcoming collision between comet Shoemaker-Levy 9 and giant planet Jupiter is beginning to catch the imagination of the public. Numerous reports in the various media describe the effects expected during this unique event which according to the latest calculations will start in the evening of July 16 and end in the morning of July 22, 1994. (The times in this Press Release are given in Central European Summer Time (CEST), i.e., Universal Time (UT) + 2 hours. The corresponding local time in Chile is CEST - 6 hours.) Astronomers all over the world are now preparing to observe the associated phenomena with virtually all major telescopes. There will be no less than 12 different investigations at the ESO La Silla observatory during this period. This Press Release updates the information published in ESO PR 02/94 (27 January 1994) and provides details about the special services which will be provided by ESO to the media around this rare astronomical event. SCIENTIFIC EXPECTATIONS The nucleus of comet Shoemaker-Levy 9 broke into many smaller pieces during a near passage of Jupiter in July 1992. They are now moving in parallel orbits around this planet and recent calculations show with close to 100 % certainty that they will all collide with it, just two months from now. At some time, more than 20 individual nuclei were observed. This Press Release is accompanied by a photo that shows this formation, the famous "string of pearls", as it looked like in early May 1994. Both Jupiter and these nuclei have been extensively observed during the past months. A large, coordinated observing programme at La Silla has been active since early April and the first results have become available. However, while we now possess more accurate information about the comet's motion and the times of impact, there is still great uncertainty about the effects which may actually be observed at the time of the impacts. This is first of all due to the fact that it has not been possible to measure the sizes and masses of the individual cometary nuclei and thereby to estimate the amount of energy which will be liberated at the collisions. The first object (nucleus "A"; indicated on the photo) will hit the Jovian atmosphere somewhat later than earlier predicted; the best estimate is now at about 22:00 CEST in the evening of Saturday, 16 July, 1994. The second ("B") will follow the next morning at about 05:00. These two nuclei are comparatively faint and therefore presumably also rather small, and it is at this moment still uncertain whether these impacts will actually be observed. The first, relatively large nuclei ("E") will hit Jupiter around 17:00 on 17 July. The brightest nucleus ("Q"; actually a double object, as seen on images obtained with the Hubble Space Telescope) is expected to arrive just before 22:00 on 20 July, and the last in the train ("W") should collide with the planet at about 10:20 on 22 July. The timing uncertainty varies from impact to impact; in the best cases, there is at present a 95% chance that the collision will happen between 40 minutes before and 40 minutes after the indicated time. Further positional observations are being obtained, also at ESO, and it is hoped that this margin can be reduced to about +-15 minutes or better. Despite intensive spectroscopic observations, no gas has yet been detected in any of the nuclei. We only see dust around the nuclei which are completely hidden from our view within these clouds. The amount of the dust has been steadily decreasing; this is because the dust production from the individual nuclei -- which began when the parent body broke up at the time of the near-collision with Jupiter in July 1992 -- is slowly diminishing with time. Some of the smaller nuclei have recently disappeared from view, probably because they have ceased to produce dust. It is not clear, however, whether this also implies that they no longer exist at all, or whether they are just too small to be seen with available telescopes. THE ESO COORDINATED PROGRAMME Together with their colleagues all over the world, several groups of astronomers in the ESO member states are now getting ready to observe this event with the La Silla telescopes. The observers at ESO participate in a coordinated programme and will profit from the simultaneous observations with many different telescopes and observing techniques at one site. Altogether, there are 12 individual programmes at all the major telescopes, including the 3.6-m, the NTT, the SEST, the 2.2-m MPI/ESO, the 1.4-m CAT and the Danish 1.54-m telescopes. It is clear that these observations will be difficult, in particular because of the relatively short time that Jupiter and the comet will be well above the horizon at La Silla, at most a few hours each evening. When Jupiter is very low in the sky, the viewing conditions are less favourable, since the light must traverse a longer distance through the turbulent and absorbing terrestrial atmosphere. However, since Jupiter will be south of the celestial equator, observing conditions will be even worse from observatories located in the Northern hemisphere. To record the best possible data (images, spectra, light curves, etc.), the telescopes must follow the motion of Jupiter very accurately. Due to its orbital motion in the solar system, Jupiter moves rather rapidly in the sky, and the telescope motion must be precisely offset to continuously track the planet without "smearing" the images. This is not a simple task, also since the planet's rate of motion changes with time and new corrections must be made several times each hour. All in all, the observers face a difficult task and must be extremely alert, especially around the predicted moments of impact. This will demand very high concentration and necessitate "training runs" before the real observations begin. Some of these have already taken place -- not surprisingly, various technical problems were uncovered and are now in the process of being resolved. ESO'S SERVICES TO THE MEDIA In view of the unique nature of this event and the associated astronomical observations, ESO has decided to provide special services to the media. In particular, it is the intention to ensure that the media will be able to follow the developments at La Silla closely and in near-real time, and at the same time will be kept informed about the observational results at other observatories all over the world. This service will be available from the ESO Headquarters in Garching near Munich, Germany, but special arrangements will also be made for the media in Chile. Kindly note that in view of the complex and critical nature of these observations, it is not possible to arrange direct access to the La Silla observatory during the observing period. ESO will obtain all new information directly from the observers at La Silla via the permanent satellite link to the ESO Headquarters in Garching (Germany). For this, ESO is setting up the necessary internal communication lines at La Silla which will allow this transfer to be done at the shortest possible notice. While the observers cannot be disturbed during the actual observations, they will communicate their results and observational progress at regular intervals, and very quickly, if and when "dramatic" events are observed. ESO furthermore has complete and permanent access to the world-wide communication net between all observers of this event, especially set up for this purpose. The information available from this source will first of all serve to alert the observers about the results in other places and to warn them about new and unexpected developments. Moreover, the Space Telescope European Coordinating Facility, the ESA/ESO group that is responsible for the Hubble Space Telescope use by European astronomers and which is housed at the ESO Headquarters, will contribute with information regarding the observations with this major observational facility. With these important sources of information at its disposal, ESO will therefore be in a prime position to inform about and comment on the latest developments at the shortest possible notice. SPECIFIC ARRANGEMENTS In practical terms, ESO's service to the media will have the following elements: - Background material in the form of text and images, as well as related video clippings (broadcast quality) will be available at request, 7 - 10 days before the first impact takes place on 16 July. - Beginning a few days before this date, ESO will issue daily bulletins with the latest predictions and other news, related to the preparations of observations at La Silla and elsewhere in the world. - ESO will arrange a Press Conference at the ESO Headquarters in Garching at 20:00 (CEST) on Saturday 16 July, 1994. This will be just before the first impact is expected to happen and will provide an excellent opportunity to inform the media about the very latest developments. Following this in-depth briefing, media representatives are welcome to pass the night at the ESO Headquarters and to follow the first observations at La Silla at distance (food and beverages will be provided). Unexpected and "spectacular" events, should they happen, will be announced and commented as quickly as possible. We will also attempt to contact the La Silla observers by phone immediately after the end of their observations (in the early morning hours at Garching) and request live commentaries about the intial results. At the same time, the latest images will be transferred and made available. - There will be a Press Conference each day at 11:00 (CEST) on 17 - 22 July 1994, summarizing the previous night's results. Selected images obtained at ESO the night before will be available on these occasion. Media representatives, who are interested in participating in the Press Conference in the evening of July 16 and who would like to stay at ESO during the following night, are kindly requested to soonest contact Mrs. E. Voelk of the ESO Information Service (Tel.: +4989-32006276; Fax: +4989-3202362), to obtain a personal invitation. ESO is preparing special arrangements for the Chilean media; they will soon be announced directly to the involved. PHOTO CAPTION ESO PR PHOTO 10/94-1: PORTRAIT OF A DOOMED COMET These two photos from the ESO La Silla observatory show the individual nuclei of comet Shoemaker-Levy 9, now headed for collision with Jupiter on 16 - 22 July 1994. The wide-field photo (below, left) was obtained by Klaus Jockers and Galina Chernova (Max-Planck-Institute fur Aeronomie, Katlenburg, Lindau, Germany) on May 1, 1994. For this 5 min exposure in red light they used a CCD camera at the MPIfAe/Hoher List focal reducer at the ESO 1-metre telescope. The entire nuclear train (the "string of pearls") is very well seen, together with the sunlight-reflecting dust from the nuclei, all on one side. On this date, the comet was 654 million km from the Earth and the angular extension of the train was about 5.3 arcmin, corresponding to a projected length of just over 1 million km. A 15 min CCD image was obtained for astrometric purposes on May 11, 1994, by Jean-Francois Claeskens at the Danish 1.5 m telescope at La Silla; it is here reproduced in close-up to show well the individual nuclei, in particular the fainter ones. The bright object to the upper right is a 10th mag star. Note that the stars in the field are somewhat trailed, since the telescope was set to follow the motion of the comet. The first nucleus to hit Jupiter will be "A", here seen 42 mm from the left edge and 33 mm below the upper edge of the large picture. The last is "W", 43 mm above the lower edge and 9 mm from the right edge. The comet was 657 million km from the Earth and the train was somewhat longer, 5.8 arcmin, i.e. the projected length was now 1.1 million km. Technical information: Wide-Field: pixel size 1.5 arcsec; scale on photo: 5.1 arcsec/mm; field size: 12.2 x 6.6 arcmin; 5 min exposure; gunn-r filtre. Close-Up: pixel size 0.38 arcsec; scale on photo: 1.3 arcsec/mm; field size: 6.4 x 4.4 arcmin; 15 min exposure; V-filtre. On both photos, North is up and East is to the left; both were obtained during moderate seeing conditions.
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NASA Astrophysics Data System (ADS)
Brownlee, D. E.
2003-12-01
Comets are surviving members of a formerly vast distribution of solid bodies that formed in the cold regions of the solar nebula. Cometary bodies escaped incorporation into planets and ejection from the solar system and they have been stored in two distant reservoirs, the Oort cloud and the Kuiper Belt, for most of the age of the solar system. Observed comets appear to have formed between 5 AU and 55 AU. From a cosmochemical viewpoint, comets are particularly interesting bodies because they are preserved samples of the solar nebula's cold ice-bearing regions that occupied 99% of the areal extent of the solar nebula disk. All comets formed beyond the "snow line" of the nebula, where the conditions were cold enough for water ice to condense, but they formed from environments that significantly differed in temperature. Some formed in the comparatively "warm" regions near Jupiter where the nebular temperature may have been greater than 120 K and others clearly formed beyond Neptune where temperatures may have been less than 30 K (Bell et al., 1997). Although comets are the best-preserved materials from the early solar system, they should be a mix of nebular and presolar materials that accreted over a vast range of distances from the Sun in environments that differed in temperature, pressure, and accretional conditions such as impact speed.Comets, by conventional definition, are unstable near the Sun; they contain highly volatile ices that vigorously sublime within 2-3 AU of the Sun. When heated, they release gas and solids due to "cometary activity," a series of processes usually detected from afar by the presence of a coma of gas and dust surrounding the cometary nucleus and or elongated tails composed of dust and gas. Active comets clearly have not been severely modified by the moderate to extreme heating that has affected all other solar system materials, including planets, moons, and even the asteroids that produced the most primitive meteorites. Comets have been widely described as the most primitive solar system materials, preserved at cryogenic temperature and low pressure since the formation of the Sun. This is likely to be true, in general, but there is a growing body of recent evidence suggesting that comets are both more physically complex and have had more complex histories than formerly believed. They formed over an order of magnitude range of distances from the Sun; some are fragments of relatively large bodies and collisional effects must have processed at least some comets, as they have processed asteroids (McSween and Weissman, 1989).Comet-like materials are presumed to be the building blocks of Uranus and Neptune (the ice giants); they may have played a role in the formation of Jupiter and Saturn (the gas giants) and they also played some role in transporting outer solar system volatile materials to inner planets (Delsemme, 2000). The inner solar system flux of comets may have been much higher in the past and comets may have played a role in producing the late heavy bombardment on terrestrial planets ( Levison et al., 2001). Comets also exist outside the solar system and there is good evidence that they orbit a major fraction of Sun-like stars. Circumstellar dust, which appears to have been generated by comets, is detected as thermal infrared emission and sometimes as scattered starlight ( Backman et al., 1997; Weissman, 1984; Jewitt and Luu, 1995). It is particularly interesting that the amount of dust around stars declines with stellar age and is highest around stars younger than a few hundred million years. The common presence of what appears to be comet-generated dust around other stars suggests that comet formation is a normal and common consequence of star formation ( Figure 1). (6K)Figure 1. The ratio of infrared excess/stellar luminosity is a measure of the fraction of starlight absorbed by circumstellar dust and re-radiated in the infrared. The plot from Spangler et al. (2001) shows the temporal decline of dust around "Vega-like" stars (points) and stars in clusters with measured ages (circles). At least for the longer ages, the dust is most probably generated by comets.
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Possible Dust Models for C/2012 S1
NASA Astrophysics Data System (ADS)
Yanamandra-Fisher, P. A.
2014-12-01
Comet C/2012 S1 (ISON) provided a great opportunity to study a dynamically new Oort-cloud comet on its initial and only passage through the inner solar system. Contrary to expectations, the comet's activity fluctuated from high through a quiescent phase, and a major outburst days before its perihelion passage, ending in a dramatic race to complete disintegration on perihelion day, 28 November 2013. Amateur observations to professional ground-based, sub-orbital telescopes indicate the various changes of visible factors such as Afrho, a proxy for dust activity, and the measured production rates for water, consistent with the disintegration of the nucleus. Hines et al. (2013; ApJ Lett. 780) detected positive polarization in the inner coma and negative polarization in the outer coma, indicative of a jet, independently confirmed by Li et al. (2013, ApJ Lett., 779). Thermal emission observations of the comet pre-perihelion from NAOJ/Subaru/COMICS, a mid-infrared spectrometer, indicated a body with an equivalent brightness temperature of 265K (Ootsubo et al., 2013, ACM, Helsinki,FI); thermal observations acquired at the NASA/Infrared Telescope Facility (IRTF) with The Aerospace Corporation spectrometer (BASS, PI. R. Russell), before and after the November 12, 2013 outburst observed by the CIOC_ISON amateur network, indicates a brightness temperature of 330K and the presence, albeit weak, of the 11.3-micron crystalline silicate feature (Sitko et al., 2014, LPI abstract 1537). A Monte Carlo comet dust tail model, applied to extract the dust environment parameters of comet C/2012 S1 (ISON) from both Earth-based and Solar and Heliospheric Observatory (SOHO) calibrated observations, performed from about 6 AU (inbound), to right after perihelion passage, when just a small portion of the original comet nucleus survived in the form of a cloud of tiny particles, indicates that particles underwent disintegration and fragmentation (Moreno et al., 2014, ApJ Lett., 791). Ongoing work on possible dust models that incorporate both the observed polarization and thermal emission will be discussed.
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Meteor activity from 2001XQ on 2-3 December 2016?
NASA Astrophysics Data System (ADS)
Roggemans, Paul
2016-04-01
The minor shower 66 Draconid (541 SDD) which was discovered by the Croatian Meteor Network has a mean orbit based on 43 meteors, similar to the orbit of 2001 XD. The asteroid 2001 XD has an orbit typical for Jupiter family comets and therefore may be a dormant comet. The shower activity ranges from November 23 until December 21. All meteor observers are encouraged to pay attention to any possible meteors from this source, although no outburst or any anything spectacular has to be expected.
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David Levy's Guide to Observing and Discovering Comets
NASA Astrophysics Data System (ADS)
Levy, David H.
2003-05-01
Preface; Part I. Why Observe Comets?: 1. Of history, superstition, magic, and science; 2. Comet science progresses; Part II. Discovering Comets: 3. Comet searching begins; 4. Tails and trails; 5. Comet searching in the twentieth century; 6. How I search for comets; 7. Searching for comets photographically; 8. Searching for comets with CCDs; 9. Comet hunting by reading; 10. Hunting for sungrazers over the Internet; 11. What to do when you think you've found a comet; Part III. A New Way of Looking at Comets: 12. When comets hit planets; 13. The future of visual comet hunting; Part IV. How to Observe Comets: 14. An introduction to comet hunting; 15. Visual observing of comets; 16. Estimating the magnitude of a comet; 17. Taking a picture of a comet; 18. Measuring where a comet is in the sky; Part V. Closing Notes: 19. My passion for comets.
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Triple F - A Comet Nucleus Sample Return Mission
NASA Technical Reports Server (NTRS)
Kueppers, Michael; Keller, Horst Uwe; Kuhrt, Ekkehard; A'Hearn, Michael; Altwegg, Kathrin; Betrand, Regis; Busemann, Henner; Capria, Maria Teresa; Colangeli, Luigi
2008-01-01
The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA s Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would extract three samples of the upper 50 cm from three locations on a cometary nucleus and return them cooled to Earth for analysis in the laboratory. The simple mission concept with a touch-and-go sampling by a single spacecraft was proposed as an M-class mission in collaboration with the Russian space agency ROSCOSMOS.
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Triple F - A Comet Nucleus Sample Return Mission
NASA Technical Reports Server (NTRS)
Kueppers, Michael; Keller, H. U.; Kuehrt, E.; A'Hearn, M. F.; Altwegg, K.; Bertrand, R.; Busemann, H.; Capria, M. T.; Colangeli, L.; Davidsson, B.;
2008-01-01
The Triple F (Fresh From the Fridge) mission, a Comet Nucleus Sample Return, has been proposed to ESA's Cosmic Vision program. A sample return from a comet enables us to reach the ultimate goal of cometary research. Since comets are the least processed bodies in the solar system, the proposal goes far beyond cometary science topics (like the explanation of cometary activity) and delivers invaluable information about the formation of the solar system and the interstellar molecular cloud from which it formed. The proposed mission would extract three sample cores of the upper 50 cm from three locations on a cometary nucleus and return them cooled to Earth for analysis in the laboratory. The simple mission concept with a touch-andgo sampling by a single spacecraft was proposed as an M-class mission in collaboration with the Russian space agency ROSCOSMOS.
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Sublimation-Driven Activity in Main-Belt Comet 313p/Gibbs
NASA Astrophysics Data System (ADS)
Hsieh, Henry H.; Hainaut, Olivier; Novaković, Bojan; Bolin, Bryce; Denneau, Larry; Fitzsimmons, Alan; Haghighipour, Nader; Kleyna, Jan; Kokotanekova, Rosita; Lacerda, Pedro; Meech, Karen J.; Micheli, Marco; Moskovitz, Nick; Schunova, Eva; Snodgrass, Colin; Wainscoat, Richard J.; Wasserman, Lawrence; Waszczak, Adam
2015-02-01
We present an observational and dynamical study of newly discovered main-belt comet 313P/Gibbs. We find that the object is clearly active both in observations obtained in 2014 and in precovery observations obtained in 2003 by the Sloan Digital Sky Survey, strongly suggesting that its activity is sublimation-driven. This conclusion is supported by a photometric analysis showing an increase in the total brightness of the comet over the 2014 observing period, and dust modeling results showing that the dust emission persists over at least three months during both active periods, where we find start dates for emission no later than 2003 July 24 ± 10 for the 2003 active period and 2014 July 28 ± 10 for the 2014 active period. From serendipitous observations by the Subaru Telescope in 2004 when the object was apparently inactive, we estimate that the nucleus has an absolute R-band magnitude of HR = 17.1 ± 0.3, corresponding to an effective nucleus radius of re ∼ 1.00 ± 0.15 km. The object’s faintness at that time means we cannot rule out the presence of activity, and so this computed radius should be considered an upper limit. We find that 313P’s orbit is intrinsically chaotic, having a Lyapunov time of Tl = 12,000 yr and being located near two three-body mean-motion resonances with Jupiter and Saturn, 11J-1S-5A and 10J+12S-7A, yet appears stable over >50 Myr in an apparent example of stable chaos. We furthermore find that 313P is the second main-belt comet, after P/2012 T1 (PANSTARRS), to belong to the ∼155 Myr old Lixiaohua asteroid family.
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SUBLIMATION-DRIVEN ACTIVITY IN MAIN-BELT COMET 313P/GIBBS
DOE Office of Scientific and Technical Information (OSTI.GOV)
Hsieh, Henry H.; Hainaut, Olivier; Novaković, Bojan
2015-02-10
We present an observational and dynamical study of newly discovered main-belt comet 313P/Gibbs. We find that the object is clearly active both in observations obtained in 2014 and in precovery observations obtained in 2003 by the Sloan Digital Sky Survey, strongly suggesting that its activity is sublimation-driven. This conclusion is supported by a photometric analysis showing an increase in the total brightness of the comet over the 2014 observing period, and dust modeling results showing that the dust emission persists over at least three months during both active periods, where we find start dates for emission no later than 2003more » July 24 ± 10 for the 2003 active period and 2014 July 28 ± 10 for the 2014 active period. From serendipitous observations by the Subaru Telescope in 2004 when the object was apparently inactive, we estimate that the nucleus has an absolute R-band magnitude of H{sub R} = 17.1 ± 0.3, corresponding to an effective nucleus radius of r{sub e} ∼ 1.00 ± 0.15 km. The object’s faintness at that time means we cannot rule out the presence of activity, and so this computed radius should be considered an upper limit. We find that 313P’s orbit is intrinsically chaotic, having a Lyapunov time of T{sub l} = 12,000 yr and being located near two three-body mean-motion resonances with Jupiter and Saturn, 11J-1S-5A and 10J+12S-7A, yet appears stable over >50 Myr in an apparent example of stable chaos. We furthermore find that 313P is the second main-belt comet, after P/2012 T1 (PANSTARRS), to belong to the ∼155 Myr old Lixiaohua asteroid family.« less
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Star formation around active galactic nuclei
NASA Technical Reports Server (NTRS)
Keel, William C.
1987-01-01
Active galactic nuclei (Seyfert nuclei and their relatives) and intense star formation can both deliver substantial amounts of energy to the vicinity of a galactic nucleus. Many luminous nuclei have energetics dominated by one of these mechanisms, but detailed observations show that some have a mixture. Seeing both phenomena at once raises several interesting questions: (1) Is this a general property of some kinds of nuclei? How many AGNs have surround starbursts, and vice versa? (2) As in 1, how many undiscovered AGNs or starbursts are hidden by a more luminous instance of the other? (3) Does one cause the other, and by what means, or do both reflect common influences such as potential well shape or level of gas flow? (4) Can surrounding star formation tell us anything about the central active nuclei, such as lifetimes, kinetic energy output, or mechanical disturbance of the ISM? These are important points in the understanding of activity and star formation in galactic nuclei. Unfortunately, the observational ways of addressing them are as yet not well formulated. Some preliminary studies are reported, aimed at clarifying the issues involved in study of the relationships between stellar and nonstellar excitement in galactic nuclei.
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Meteorites, Bolides and Comets: A Tale of Inconsistency
NASA Astrophysics Data System (ADS)
Jakes, P.; Padevet, V.
1992-07-01
Inhomogeneity of cometary nuclei has been established through the observed disruptions of comets [1] and through the determination of dust particle composition during the encounter of the Vega and Giotto satellites with comet Halley [2,3,4]. The raisin bread model of cometary nuclei [5,6] assumes the presence of solid (rock) and dust particle material set in the volatile rich, ice- cemented material. Rock material may contribute to the formation of dust particles. Gombosi and Houpis [5] argued that only the composition of dust particles derived from the icy, volatile component of the comet were analyzed and implied thus that the third cometary component present (raisins/rocks) has not been examined. The compositions of the cometary (Halley) dust and the interplanetary dust particles (IDPs) are "chondritic" (Blanford et al., 1988). It is difficult, therefore to estimate the proportion of cometary to asteroid-derived dust in near Earth space, e.g., among the IDPs [7] unless other criteria are available. Bolide multistation photographic tracking allows the determination of the orbital preencounter parameters of solid bodies (0.01-100,000 kg in mass) with the Earth, and allows us to classify them according to their ablation coefficient (tau), penetration depth into the atmosphere (PE), theoretical densities (sigma), and terminal velocities (V(sub)E). Four groups are recognized (Table 1). Three of the type I bolides were recovered as ordinary chondrites (Pribram, Lost City, and Innisfree). Ceplecha [8] has shown that 38% of bolides (fireballs) come from cometary orbits (11% from highly eccentric orbits typical of new comets), but most of the bolides (62%) originate at asteroidal orbits. Seven of the 14 known meteoric showers could be attributed to known comets: N,S Taurids to 1970 P/Encke, Lyrids to 1861 I Thatcher-Beaker, Perseids to 1862 III Swift-Tuttle- Simons, Orionids to 1835 III P/Halley, Draconids to 1946 V P/Giacobini-Zinner, Leonids to 1966 I Tempel-Tuttle, and Leo Minorids to 1739 Zanotti. Geminids were related to asteroid 3200 Phaeton, considered to be an "extinct comet." Spurny [9], using ablation coefficient and penetration depth criteria, found that Geminids (frequently) and Taurids (rarely) contain bolides of types I and II. This may indicate that meteoric showers from "comets" on AAA orbits contain some portion of "rocky" material comparable to chondrites. These observations revive Opik's (1963) idea that comets may be captured in the asteroid belt on AAA orbits and may contain (and supply) chondritic meteorites to the Earth [10]. If the relationship among large solid particles "native to the asteroid belt" and those from the outer solar system can be established, they can be scaled and applied to IDPs. We have studied the records of 292 bolides (Prairie and European networks) with measured terminal velocities. We attempt to use the terminal velocity, calculated density, estimated terminal mass, and mechanical strength to correlate features with the meteorite features. We compare the meteorite fall frequency [11] with the bolide features. Two extreme hypotheses (Table 1) are examined: (A) bolides of types IIIa and IIIb do not have equivalents among the meteorites and (B) all four bolide types have meteoritic equivalents, and only IDPs do not produce bolides (fireballs). If the entry parameters of meteoroids are similar, bodies with lower density should reach terminal velocity at higher altitudes than those with higher density. If it is assumed that fragmentation is the same for dense (I and II) and less dense bodies (IIIa and IIIb), the calculated terminal altitudes show that among the bolides exist materials with lower densities than those of recovered meteorites and that model A of the correlation between meteorite falls and bolide observations is likely [12]. If, however, the less dense bodies were more easily fragmented than denser bodies, the correlation is better for hypothesis B. Table 1, which in the hard copy appears here, shows fireball observations. Using the value of terminal velocities and the average value of ablation coefficients the terminal (residual) masses (m(sub)E) can be calculated. Among the bodies studied, 99 were heavier than 0.1 kg and 153 heavier than 0.01 kg. The parameter (m(sub)E) indicates the end of ablation in the atmosphere, but it cannot distinguish between meteoroids that were totally disintegrated and those genuinely decelerated. Similarly the calculated terminal altitudes and mechanical strength values do not provide a unequivocal interpretation. Correlation of bolide properties with meteorite falls could well be accommodated by the hypothesis B in which each bolide type has a meteorite equivalent. This has, however, some "outrageous" implications: comets may carry chondrites, icy dust balls do not produce fireballs; the extremely primitive carbon-rich particles represented by the IDPs do not form larger discrete bodies (fireballs) of "asteroidal" size; and the asteroid belt is a mixture of "native fractionated old bodies" together with the captured comets. Hypothesis B therefore contradicts the "established" scheme of the asteroid belt in which the non-differentiated meteorites (CI, CM, and CV) form the outer part of the asteroid belt, whereas the fractionated metamorphosed and igneous meteorites characterize the inner asteroids. References: [1] Whipple F. L., 1987, Phil. Trans. R. Soc. Lond., A 323, 339. [2] Dikov Yu. P. et al., 1991, Geochemistry International, 29, 33-38. [3] Kissel J., et al., 1986, Nature, 321, 326. [4] Solc M., et al., 1987, Publ. Astr. Inst. Czechosl., 67, 47. [5] Gombosi T. I. and Houpis H. L. F., 1986, Nature, 324, 43. [6] Delsemme A. H., 1977, Comets, asteroids, meteorites, Univ. of Toledo Press. [7] Gibson E. K., 1992, J. Geophys. Res., 97, E3 3865. [8] Ceplecha Z., 1988, Bull. Astr. Inst. Czech., 39, 221. [9] Spurny P., 1991, doc. diss., Astr. Inst. Czechosl. [10] Opik E. J., 1963, Adv. Astr. Astrophys., 2, 219. [11] Hutchinson R., et al., 1977, Appendix to Catalogue of Meteorites, British Museum, London. [12] Ceplecha Z. and McCrosky R. E., 1976, J. Geophys. Res., 81, 6257.
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Fabian, Andrew C.
1999-01-01
Active galactic nuclei are the most powerful, long-lived objects in the Universe. Recent data confirm the theoretical idea that the power source is accretion into a massive black hole. The common occurrence of obscuration and outflows probably means that the contribution of active galactic nuclei to the power density of the Universe has been generally underestimated. PMID:10220363
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NASA Technical Reports Server (NTRS)
Fletcher, L. A.; Allen, C. C.; Bastien, R.
2008-01-01
NASA's Johnson Space Center (JSC) and the Astromaterials Curator are charged by NPD 7100.10D with the curation of all of NASA s extraterrestrial samples, including those from future missions. This responsibility includes the development of new sample handling and preparation techniques; therefore, the Astromaterials Curator must begin developing procedures to preserve, prepare and ship samples at sub-freezing temperatures in order to enable future sample return missions. Such missions might include the return of future frozen samples from permanently-shadowed lunar craters, the nuclei of comets, the surface of Mars, etc. We are demonstrating the ability to curate samples under cold conditions by designing, installing and testing a cold curation glovebox. This glovebox will allow us to store, document, manipulate and subdivide frozen samples while quantifying and minimizing contamination throughout the curation process.
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The asteroids - Accretion, differentiation, fragmentation, and irradiation
NASA Technical Reports Server (NTRS)
Wilkening, L. L.
1979-01-01
Various types of meteorites have experienced processes of condensation, accretion, metamorphism, differentiation, brecciation, irradiation and fragmentation. A typical view of meteorite formation has been that the processes following accretion take place in a few asteroidal-sized (approximately 100 km) objects. Discovery of decay products of now extinct Al-26 and Pd-107 in meteorites, discovery of isotopic heterogeneity among meteorite types, re-analysis of meteorite cooling rates, and continuing study of meteoritic compositions have led some meteoriticists to conclude that meteorites obtained their chemical, isotopic, and some textural characteristics in objects initially less than 10 km in diameter. Such a scenario, which is described in this paper, raises the possibility that some of these small planetesimals may have been 'condensation nuclei' for the formation of comets as well as the precursors of asteroids.
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NASA Astrophysics Data System (ADS)
Shou, Y.; Combi, M.; Toth, G.; Tenishev, V.; Fougere, N.; Jia, X.; Rubin, M.; Huang, Z.; Hansen, K.; Gombosi, T.
2017-11-01
Improving our capability to interpret observations of cometary dust is necessary to deepen our understanding of the role of dust in the formation of comets and in altering the cometary environments. Models including dust grains are in demand to interpret observations and test hypotheses. Several existing models have taken into account the gas-dust interaction, varying sizes of dust grains and the cometary gravitational force. In this work, we develop a multi-fluid dust model based on the BATS-R-US code. This model not only incorporates key features of previous dust models, but also has the capability of simulating time-dependent phenomena. Since the model is run in the rotating comet reference frame, the centrifugal and Coriolis forces are included. The boundary conditions on the nucleus surface can be set according to the distribution of activity and the solar illumination. The Sun revolves around the comet in this frame. A newly developed numerical mesh is also used to resolve the real-shaped nucleus in the center and to facilitate prescription of the outer boundary conditions that accommodate the rotating frame. The inner part of the mesh is a box composed of Cartesian cells and the outer surface is a smooth sphere, with stretched cells filled in between the box and the sphere. Our model achieved comparable results to the Direct Simulation Monte Carlo method and the Rosetta/OSIRIS observations. It is also applied to study the effects of the rotating nucleus and the cometary activity and offers interpretations of some dust observations of comet 67P/Churyumov-Gerasimenko.
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The 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission.
Snodgrass, C; A'Hearn, M F; Aceituno, F; Afanasiev, V; Bagnulo, S; Bauer, J; Bergond, G; Besse, S; Biver, N; Bodewits, D; Boehnhardt, H; Bonev, B P; Borisov, G; Carry, B; Casanova, V; Cochran, A; Conn, B C; Davidsson, B; Davies, J K; de León, J; de Mooij, E; de Val-Borro, M; Delacruz, M; DiSanti, M A; Drew, J E; Duffard, R; Edberg, N J T; Faggi, S; Feaga, L; Fitzsimmons, A; Fujiwara, H; Gibb, E L; Gillon, M; Green, S F; Guijarro, A; Guilbert-Lepoutre, A; Gutiérrez, P J; Hadamcik, E; Hainaut, O; Haque, S; Hedrosa, R; Hines, D; Hopp, U; Hoyo, F; Hutsemékers, D; Hyland, M; Ivanova, O; Jehin, E; Jones, G H; Keane, J V; Kelley, M S P; Kiselev, N; Kleyna, J; Kluge, M; Knight, M M; Kokotanekova, R; Koschny, D; Kramer, E A; López-Moreno, J J; Lacerda, P; Lara, L M; Lasue, J; Lehto, H J; Levasseur-Regourd, A C; Licandro, J; Lin, Z Y; Lister, T; Lowry, S C; Mainzer, A; Manfroid, J; Marchant, J; McKay, A J; McNeill, A; Meech, K J; Micheli, M; Mohammed, I; Monguió, M; Moreno, F; Muñoz, O; Mumma, M J; Nikolov, P; Opitom, C; Ortiz, J L; Paganini, L; Pajuelo, M; Pozuelos, F J; Protopapa, S; Pursimo, T; Rajkumar, B; Ramanjooloo, Y; Ramos, E; Ries, C; Riffeser, A; Rosenbush, V; Rousselot, P; Ryan, E L; Santos-Sanz, P; Schleicher, D G; Schmidt, M; Schulz, R; Sen, A K; Somero, A; Sota, A; Stinson, A; Sunshine, J M; Thompson, A; Tozzi, G P; Tubiana, C; Villanueva, G L; Wang, X; Wooden, D H; Yagi, M; Yang, B; Zaprudin, B; Zegmott, T J
2017-07-13
We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively 'well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends-in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.This article is part of the themed issue 'Cometary science after Rosetta'. © 2017 The Author(s).
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Asteroid-comet continuum objects in the solar system.
Hsieh, Henry H
2017-07-13
In this review presented at the Royal Society meeting, 'Cometary science after Rosetta', I present an overview of studies of small solar system objects that exhibit properties of both asteroids and comets (with a focus on so-called active asteroids). Sometimes referred to as 'transition objects', these bodies are perhaps more appropriately described as 'continuum objects', to reflect the notion that rather than necessarily representing actual transitional evolutionary states between asteroids and comets, they simply belong to the general population of small solar system bodies that happen to exhibit a continuous range of observational, physical and dynamical properties. Continuum objects are intriguing because they possess many of the properties that make classical comets interesting to study (e.g. relatively primitive compositions, ejection of surface and subsurface material into space where it can be more easily studied, and orbital properties that allow us to sample material from distant parts of the solar system that would otherwise be inaccessible), while allowing us to study regions of the solar system that are not sampled by classical comets.This article is part of the themed issue 'Cometary science after Rosetta'. © 2017 The Author(s).
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The comet assay: ready for 30 more years.
Møller, Peter
2018-02-24
During the last 30 years, the comet assay has become widely used for the measurement of DNA damage and repair in cells and tissues. A landmark achievement was reached in 2016 when the Organization for Economic Co-operation and Development adopted a comet assay guideline for in vivo testing of DNA strand breaks in animals. However, the comet assay has much more to offer than being an assay for testing DNA strand breaks in animal organs. The use of repair enzymes increases the range of DNA lesions that can be detected with the assay. It can also be modified to measure DNA repair activity. Still, despite the long-term use of the assay, there is a need for studies that assess the impact of variation in specific steps of the procedure. This is particularly important for the on-going efforts to decrease the variation between experiments and laboratories. The articles in this Special Issue of Mutagenesis cover important technical issues of the comet assay procedure, nanogenotoxicity and ionising radiation sensitivity on plant cells. The included biomonitoring studies have assessed seasonal variation and certain predictors for the basal level of DNA damage in white blood cells. Lastly, the comet assay has been used in studies on genotoxicity of environmental and occupational exposures in human biomonitoring studies and animal models. Overall, the articles in this Special Issue demonstrate the versatility of the comet assay and they hold promise that the assay is ready for the next 30 years.
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Analyses of Cometary Silicate Crystals: DDA Spectral Modeling of Forsterite
NASA Technical Reports Server (NTRS)
Wooden, Diane
2012-01-01
Comets are the Solar System's deep freezers of gases, ices, and particulates that were present in the outer protoplanetary disk. Where comet nuclei accreted was so cold that CO ice (approximately 50K) and other supervolatile ices like ethane (C2H2) were preserved. However, comets also accreted high temperature minerals: silicate crystals that either condensed (greater than or equal to 1400 K) or that were annealed from amorphous (glassy) silicates (greater than 850-1000 K). By their rarity in the interstellar medium, cometary crystalline silicates are thought to be grains that formed in the inner disk and were then radially transported out to the cold and ice-rich regimes near Neptune. The questions that comets can potentially address are: How fast, how far, and over what duration were crystals that formed in the inner disk transported out to the comet-forming region(s)? In comets, the mass fractions of silicates that are crystalline, f_cryst, translate to benchmarks for protoplanetary disk radial transport models. The infamous comet Hale-Bopp has crystalline fractions of over 55%. The values for cometary crystalline mass fractions, however, are derived assuming that the mineralogy assessed for the submicron to micron-sized portion of the size distribution represents the compositional makeup of all larger grains in the coma. Models for fitting cometary SEDs make this assumption because models can only fit the observed features with submicron to micron-sized discrete crystals. On the other hand, larger (0.1-100 micrometer radii) porous grains composed of amorphous silicates and amorphous carbon can be easily computed with mixed medium theory wherein vacuum mixed into a spherical particle mimics a porous aggregate. If crystalline silicates are mixed in, the models completely fail to match the observations. Moreover, models for a size distribution of discrete crystalline forsterite grains commonly employs the CDE computational method for ellipsoidal platelets (c:a:b=8.14x8.14xl in shape with geometrical factors of x:y:z=1:1:10, Fabian et al. 2001; Harker et al. 2007). Alternatively, models for forsterite employ statistical methods like the Distribution of Hollow Spheres (Min et al. 2008; Oliveira et al. 2011) or Gaussian Random Spheres (GRS) or RGF (Gielen et al. 200S). Pancakes, hollow spheres, or GRS shapes similar to wheat sheaf crystal habit (e.g., Volten et al. 2001; Veihelmann et al. 2006), however, do not have the sharp edges, flat faces, and vertices seen in images of cometary crystals in interplanetary dust particles (IDPs) or in Stardust samples. Cometary forsterite crystals often have equant or tabular crystal habit (J. Bradley). To simulate cometary crystals, we have computed absorption efficiencies of forsterite using the Discrete Dipole Approximation (DDA) DDSCAT code on NAS supercomputers. We compute thermal models that employ a size distribution of discrete irregularly shaped forsterite crystals (nonspherical shapes with faces and vertices) to explore how crystal shape affects the shape and wavelength positions of the forsterite spectral features and to explore whether cometary crystal shapes support either condensation or annealing scenarios (Lindsay et al. 2012a, b). We find forsterite crystal shapes that best-fit comet Hale-Bopp are tetrahedron, bricks or brick platelets, essentially equant or tabular (Lindsay et al. 2012a,b), commensurate with high temperature condensation experiments (Kobatake et al. 2008). We also have computed porous aggregates with crystal monomers and find that the crystal resonances are amplified. i.e., the crystalline fraction is lower in the aggregate than is derived by fitting a linear mix of spectral features from discrete subcomponents, and the crystal resonances 'appear' to be from larger crystals (Wooden et al. 2012). These results may indicate that the crystalline mass fraction in comets with comae dominated by aggregates may be lower than deduced by popular methods that only emoy ensembles of discrete crystals.
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Cosmogenic nuclides in cometary materials: Implications for rate of mass loss and exposure history
NASA Astrophysics Data System (ADS)
Herzog, G. F.; Englert, P. A. J.; Reedy, R. C.
As planned, the Rosetta mission will return to earth with a 10-kg core and a 1-kg surface sample from a comet. The selection of a comet with low current activity will maximize the chance of obtaining material altered as little as possible. Current temperature and level of activity, however, may not reliably indicate previous values. Fortunately, from measurements of the cosmogenic nuclide contents of cometary material, one may estimate a rate of mass loss in the past and perhaps learn something about the exposure history of the comet. Perhaps the simplest way to estimate the rate of mass loss is to compare the total inventories of several long-lived cosmogenic radionuclides with the values expected on the basis of model calculations. Although model calculations have become steadily more reliable, application to bodies with the composition of comets will require some extension beyond the normal range of use. In particular, the influence of light elements on the secondary particle cascade will need study, in part through laboratory irradiations of volatile-rich materials. In the analysis of cometary data, it would be valuable to test calculations against measurements of short-lived isotopes.
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Dust density and mass distribution near comet Halley from Giotto observations
NASA Technical Reports Server (NTRS)
Mcdonnell, J. A. M.; Alexander, W. M.; Burton, W. M.; Bussoletti, E.; Clark, D. H.; Grard, J. L.; Gruen, E.; Hanner, M. S.; Sekanina, Z.; Hughes, D. W.
1986-01-01
The density and the mass spectrum of the dust near comet Halley have been measured by the Giotto space probe's dust impact detection system. The dust spectrum obtained at 291,000 km from the comet nucleus show depletion in small and intermediate masses; at about 600 km from the nucleus, however, the dust activity rises and the spectrum is dominated by larger masses. Most of the mass striking Giotto is noted to reside in the few large particles penetrating the dust shield. Momentum balances and energy considerations applied to an observed deceleration suggest that a large mass of the spacecraft was detached by an impact.
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Are Adonis and Hephaistos "Extinct" Comets?
NASA Astrophysics Data System (ADS)
Babadzhanov, P. B.
The investigation of the evolution of Earth-approaching asteroids with the aim of revealing their meteor streams is one of the ways to determine if these asteroids are extinct comets. The orbital evolution of asteroids 2101 Adonis and 2212 Hephaistos studied, respectively, by AlfanGoryachev and Everhart methods shows that these asteroids cross the Earth's orbit four times. Their possible meteoroid swarms may therefore produce four meteor showers each. In this work, the theoretically predicted orbital elements and radiants of these streams are compared to the available observational data. In the cases of both Adonis and Hephaistos, all four meteor showers are shown to be active. Most likely, these asteroids are extinct comets.
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ESA's Rosetta mission and the puzzles that Hale-Bopp left behind
NASA Astrophysics Data System (ADS)
1997-04-01
The scientific payload was confirmed by ESA's Science Programme Committee in February. Now the scientists must perfect the full range of ultra-sensitive yet spaceworthy instruments in good time for Rosetta's despatch by an Ariane 5 launcher in January 2003. And even as most of the world was admiring Comet Hale-Bopp at its brightest, dedicated astronomers were examining the comet that will be Rosetta's target. Although too faint to be seen with the naked eye, Comet Wirtanen made its closest approach to the Sun on 14 March and a fairly close approach to the Earth on 24 March. This comet comes back every 5.5 years. Rosetta will dance attendance on Comet Wirtanen, not at the next return in 2002, nor even in 2008, but in 2013. The project is an ambitious and patient effort to achieve the most thorough investigation of a comet ever attempted. As the successor to ESA's highly successful Giotto mission to Halley's Comet and Comet Grigg-Skjellerup (which took seven years) Rosetta will spend eight years positioning itself. It will manoeuvre around the planets until it is shadowing Comet Wirtanen far beyond Mars, on nearly the same path around the Sun. In 2011 it will rendezvous with the comet and fly near it. In April 2012 Rosetta will go into a near orbit around Comet Wirtanen, and escort it for 17 busy months, as it flies in to make its closest approach to the Sun in September 2013, at the climax of the mission. "The Giotto mission placed us at the forefront of cometary exploration," comments Roger Bonnet, ESA's director of science. "The motivation came from European scientists with a sharp sense of the special importance of comets for understanding the Solar System. The same enthusiasm drives us onward to Rosetta, which will ensure our continued leadership in this important branch of space science." Scientific tasks During its prolonged operations in very close company with the comet's nucleus, Rosetta will map and examine its entire surface from distances of 10 to 50 kilometres with a set of remote-sensing instruments. As the spacecraft moves around the nucleus at a very leisurely walking pace, other onboard instruments will analyse the dust and vapours, which will emanate from Comet Wirtanen with ever-increasing vigour as the Sun's rays warm it. Rosetta will drop a lander on to the comet's surface, for close inspection of its physical condition and chemical composition. The lander is a venture led by Germany, France and Italy, with participation from Austria, Finland, Hungary, Poland and the UK. As a box packed with scientific instruments and standing on three legs, the lander will be capable of anchoring itself to one spot and drilling into the surface. It may also be able to hop like a flea to visit another part of the nucleus. A combination of solar energy and electric batteries will enable operations to last for several months. "The combination of Rosetta in orbit around the comet and the lander on its surface is very powerful from a scientific point of view," says Gerhard Schwehm, ESA's project scientist for Rosetta. "We shall watch Comet Wirtanen brewing up like a volcano as it feels the heat of the Sun. In place of hazy impressions of the nucleus of a comet half hidden by its dust clouds, we shall see all the details with unprecedented clarity." Unanswered questions During and after the 1986 appearance of Halley's Comet, comet science made great progress. More recent comets have revealed important secrets to ESA's Infrared Space Observatory and to other space telescopes examining them at wavelengths unobservable from the Earth. Yet basic questions about comets remain unanswered. Just as the Rosetta Stone was the key that unlocked the meaning of Egyptian hieroglyphs, so the Rosetta spacecraft is intended to decipher the meaning of comets and their role in the origin and history of the Solar System. Here are a few of the main puzzles. * What does a comet weigh? Guesses about the density of cometary material vary widely, and only an orbiting spacecraft can give exact measurements of the comet's volume and mass. * Is a comet a dirty snowball or an icy dirtball? In other words, is it made of ices contaminated with mineral and tarry dust, or is it a consolidation of dust coated with ices? * Why is the nucleus of a comet so dark? Giotto established that Halley's nucleus is like brownish-black velvet, absorbing 96 per cent of the sunlight falling on it. Is the colour due to a surface deposit of tarry dust, or is the interior dark too? * Why are small regions of a comet highly active when most of its surface is not? Multiple jets of dust seen emanating from Halley's Comet, and spectacularly from Comet Hale-Bopp, imply that certain hot-spots differ physically or chemically from the rest of the comet's surface. * Is a comet made as single piece, or does it consist of loosely joined blocks, as suggested by the Giotto images? This relates to the questions of how comets are built, and why they break up into smaller fragments, as seen spectacularly with Comet Shoemaker-Levy 9 which hit Jupiter in 1994. * Does a dying comet evaporate and disappear, or does it simply exhaust the stocks of ice that drive the emissions of gas and dust from an active comet? If the latter answer is correct, dead comets persist long afterwards as dark, inactive masses of minerals and tar, and pose a lasting threat of collisions with the Earth. * What is a comet's exact composition? Many ingredients are known, and the approximate abundances of the main constituents. Details coming from Rosetta will pin down (1) how comets were fashioned from similar constituents of interstellar dust and (2) how comets contributed to building the planets, including the Earth, and stocking their atmospheres. * Is the tarry, carbon-rich material in comets a jumble of every kind of chemical that inorganic processes can make from carbon, nitrogen, oxygen and hydrogen, or does it contain special compounds? This is relevant to assessing the role of comets in the origin of life on the Earth. The comet specialist Uwe Keller of the Max-Planck Institut fur Aeronomie, Germany, is one of the Giotto veterans who has helped with the planning of Rosetta. He was in charge of Giotto's camera. "Rosetta is the mission we are all waiting for," Dr Keller comments. "After I spent six years analysing our images of the Halley nucleus, I say that basic scientific assumptions about the nature of comets are still contradictory. We shall settle the arguments only by the close, prolonged inspection that Rosetta will make possible." Engineering the Rosetta mission To build up the speed needed to adopt the same orbit around the Sun as Comet Wirtanen, Rosetta must steal energy of motion from the planets, in a swingby of Mars and two swingbys of the Earth. During its far-flung manoeuvres in pursuit of the comet, Rosetta will inspect the asteroids Mimistrobell and Rodari at close quarters. When Rosetta is far from the Earth, or on the wrong side of the Sun, communication will be difficult. The spacecraft will therefore have a high degree of robotic self-reliance. It will also be capable of hibernating for more than two years without attention -- a technique devised by ESA for the later stages of the Giotto mission. Rosetta will rely on solar power, even when more than five times further than the Earth from the Sun. Special low-intensity solar cells are under development for Rosetta. Conditions in this farthest phase of Rosetta's voyage will be very chilly, but ESA's engineers are satisfied that the temperatures inside the spacecraft can be kept within limits by black paint, multilayer insulation and electric heaters. Despite its originality and sophistication, Rosetta will be just a flying box with solar arrays like wings, looking rather like a telecommunications satellite. "Keep it simple," is the motto of John Credland, ESA's project manager for Rosetta. "Simplicity brings reliability," he explains, "and that is my overriding concern for the engineering of a spacecraft that has to survive and operate far from the Earth for nearly eleven years." To command Rosetta, and to receive its signals carrying new of the comet, ESA will use a new 32-metre deep-space tracking antenna at Perth in Australia, and a 15-metre antenna in Spain. The spacecraft operations, especially in the near-comet phase of the mission, will be a novel experience for the controllers at the European Space Operations Centre in Darmstadt, Germany. The gravity of the comet will be weak, and Rosetta's manoeuvres around it will be like a ballet in slow motion. At around 10 kilometres distance, the spacecraft will travel at only 1-2 kilometres per hour in relation to the comet and take about a week to circle once around the nucleus. Sometimes Rosetta will swoop even closer to the comet's surface, to inspect possible landing sights and to drop the lander. The spacecraft's thrusters will adjust the orbit. To keep manoeuvres to a minimum, and so conserve fuel and avoid polluting the comet's environment, computer simulations will help the spacecraft navigators to predict the consequences of any manoeuvre for weeks in advance. The target comet Present-day space propulsion systems allow a rendezvous only with a comet with a predictable and relatively small orbit around the Sun. All comets of this kind are "old", in the sense that they have visited the Sun's vicinity many times and are no longer vigorous in the dust and gas formation that makes their visible comas and tails. The second comet visited by Giotto, Comet Grigg-Skjellerup, was of this elderly kind. From among several short-period candidates, the mission team chose Comet Wirtanen as Rosetta's target comet because it offered the quickest timetable between the launch of the spacecraft and the completion of the mission. The comet was discovered by chance by Carl Wirtanen in 1948 on photographic plates at the Lick Observatory in California. In 1972 and 1984 encounters with the planet Jupiter reduced the size of Comet Wirtanen's orbit, and shortened the interval between its visits to the Sun from 6.65 to 5.5 years. Despite many observations no one really knows the comet's mass, size and shape. The uncertainties are reflected in the computer simulations of manoeuvres near the comet. These cover a wide range of possibilities from a lightweight comet to a massive one, and from a small comet 1 kilometre in diameter to a large one 20 kilometres wide. The best estimate may be 1.5 kilometres. But it is in the nature of a voyage of exploration like Rosetta's that you don't know what you will find!
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Autonomous Navigation Performance During The Hartley 2 Comet Flyby
NASA Technical Reports Server (NTRS)
Abrahamson, Matthew J; Kennedy, Brian A.; Bhaskaran, Shyam
2012-01-01
On November 4, 2010, the EPOXI spacecraft performed a 700-km flyby of the comet Hartley 2 as follow-on to the successful 2005 Deep Impact prime mission. EPOXI, an extended mission for the Deep Impact Flyby spacecraft, returned a wealth of visual and infrared data from Hartley 2, marking the fifth time that high-resolution images of a cometary nucleus have been captured by a spacecraft. The highest resolution science return, captured at closest approach to the comet nucleus, was enabled by use of an onboard autonomous navigation system called AutoNav. AutoNav estimates the comet-relative spacecraft trajectory using optical measurements from the Medium Resolution Imager (MRI) and provides this relative position information to the Attitude Determination and Control System (ADCS) for maintaining instrument pointing on the comet. For the EPOXI mission, AutoNav was tasked to enable continuous tracking of a smaller, more active Hartley 2, as compared to Tempel 1, through the full encounter while traveling at a higher velocity. To meet the mission goal of capturing the comet in all MRI science images, position knowledge accuracies of +/- 3.5 km (3-?) cross track and +/- 0.3 seconds (3-?) time of flight were required. A flight-code-in-the-loop Monte Carlo simulation assessed AutoNav's statistical performance under the Hartley 2 flyby dynamics and determined optimal configuration. The AutoNav performance at Hartley 2 was successful, capturing the comet in all of the MRI images. The maximum residual between observed and predicted comet locations was 20 MRI pixels, primarily influenced by the center of brightness offset from the center of mass in the observations and attitude knowledge errors. This paper discusses the Monte Carlo-based analysis that led to the final AutoNav configuration and a comparison of the predicted performance with the flyby performance.
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Distant Comets in the Early Solar System
NASA Technical Reports Server (NTRS)
Meech, Karen J.
2000-01-01
The main goal of this project is to physically characterize the small outer solar system bodies. An understanding of the dynamics and physical properties of the outer solar system small bodies is currently one of planetary science's highest priorities. The measurement of the size distributions of these bodies will help constrain the early mass of the outer solar system as well as lead to an understanding of the collisional and accretional processes. A study of the physical properties of the small outer solar system bodies in comparison with comets in the inner solar system and in the Kuiper Belt will give us information about the nebular volatile distribution and small body surface processing. We will increase the database of comet nucleus sizes making it statistically meaningful (for both Short-Period and Centaur comets) to compare with those of the Trans-Neptunian Objects. In addition, we are proposing to do active ground-based observations in preparation for several upcoming space missions.
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Dust emission from comets at large heliocentric distances. I - The case of comet Bowell /1980b/
NASA Technical Reports Server (NTRS)
Houpis, H. L. F.; Mendis, D. A.
1981-01-01
Alternative processes of dust emission from comets at large heliocentric distances are considered, in order to explain the dust coma observed in comet Bowell (1980b) at a heliocentric distance as large as 7.17 AU. It is shown that the electrostatic blow-off of dust from a charged, H2O-dominated nucleus having a layer of loose, fine dust may be the formation process of the dust coma, with the coma size expected from the process being comparable to the observed value and the dust grain size being equal to or less than 0.4 microns in size. The upper limit for the total mass in the coma is 3.9 x 10 to the 8th g, and the spatial extension less than 10,000 km. The observed activity may alternatively be due to dust entrainment by the sublimating gas from a CO2-dominated nucleus.
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Formation of methyl formate in comets by irradiation of methanol-bearing ices
NASA Astrophysics Data System (ADS)
Modica, P.; Palumbo, M. E.; Strazzulla, G.
2012-12-01
Methyl formate is a complex organic molecule considered potentially relevant as precursor of biologically active molecules. It has been observed in several astrophysical environments, such as hot cores, hot corinos, and comets. The processes that drive the formation of molecules in cometary ices are poorly understood. In particular it is not yet clear if molecules are directly accreted from the pre-solar nebula to form comets or are formed after accretion. The present work analyzes the possible role of cosmic ion irradiation and radioactive decay in methyl formate formation in methanol-bearing ices. The results indicate that cosmic ion irradiation can account for about 12% of the methyl formate observed in comet Hale-Bopp, while radioactive decay can account for about 6% of this amount. The need of new data coming from earth based and space observational projects as well as from laboratory experiments is outlined.
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Behavioral Characteristics and CO+CO2 Production Rates of Halley-type Comets Observed by NEOWISE
NASA Astrophysics Data System (ADS)
Rosser, J. D.; Bauer, J. M.; Mainzer, A. K.; Kramer, E.; Masiero, J. R.; Nugent, C. R.; Sonnett, S.; Fernández, Y. R.; Ruecker, K.; Krings, P.; Wright, E. L.; WISE, The; NEOWISE Teams
2018-04-01
From the entire data set of comets observed by NEOWISE, we have analyzed 11 different Halley-type Comets (HTCs) for dust production rates, CO+CO2 production rates, and nucleus sizes. Incorporating HTCs from previous studies and multiple comet visits, we have a total of 21 stacked visits, 13 of which are active and 8 for which we calculated upper limits of production. We determined the nucleus sizes of 27P, P/2006 HR30, P/2012 NJ, and C/2016 S1. Furthermore, we analyzed the relationships between dust production and heliocentric distance, and gas production and heliocentric distance. We concluded that for this population of HTCs, ranging in heliocentric distance from 1.21 to 2.66 au, there was no significant correlation between dust production and heliocentric distance, nor between gas production and heliocentric distance.
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To catch a comet: Technical overview of CAN DO G-324
NASA Technical Reports Server (NTRS)
Obrien, T. J. (Editor)
1986-01-01
The primary objective of the C. E. Williams Middle School Get Away Special CAN DO is the photographing of Comet Halley. The project will involve middle school students, grades 6 through 8, in the study and interpretation of astronomical photographs and techniques. G-324 is contained in a 5 cubic foot GAS Canister with an opening door and pyrex window for photography. It will be pressurized with one atmosphere of dry nitrogen. Three 35mm still cameras with 250 exposure film backs and different focal length lenses will be fired by a combination of automatic timer and an active comet detector. A lightweight 35mm movie camera will shoot single exposures at about 1/2 minute intervals to give an overlapping skymap of the mission. The fifth camera is a solid state television camera specially constructed for detection of the comet by microprocessor.
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Search for Activity in Comet-Asteroid Transition Object 107P/Wilson-Harrington
NASA Astrophysics Data System (ADS)
Khayat, Alain; Meech, K.; Pittichova, J.; Schorghofer, N.; Yang, B.; Sonnett, S.; Riesen, T.; Kleyna, J.; Kaluna, H.; Keane, J.
2010-10-01
Comet-asteroid transition object 107P/Wilson-Harrington was observed near its October 22, 2009 perihelion passage to search for activity. No activity was detected. Consequently, we place limits on possible dust production of 0.013 kg/s at 1.23 AU. Furthermore, the data was not sufficient to constrain a rotation period; however, it is clear that the rotation period is > 4hr. Our data is consistent with the observations of others (6.1 hr). Phase function fitting yielded a value of the phase coefficient beta= 0.0406 ± .0001 mag/deg, similar to C-type asteroids that have a linear phase curve at large phase angles. Thermal models for 107P/Wilson-Harrington show that the average loss rate of exposed crystalline ice at zero latitude is in the order of 0.3 meters/year. The derived high loss rate suggests that 107P/Wilson-Harrington is deprived of surface ice. Our observations and analysis confirm earlier findings that 107P/Wilson-Harrington is an example of the very few such objects discovered so far. Such study we made is a critical next step in understanding the life of dormant comets, and a window into the evolutionary end states of the lives of comets that become extinct. This work has been supported in part by AST-0807521 from the National Science Foundation.
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NASA Astrophysics Data System (ADS)
Lederer, S. M.; Osip, D. J.; Thomas-Osip, J. E.; DeBuizer, J. M.; Mondragon, L. A.; Schweiger, D. L.; Viehweg, J.; SB Collaboration
2005-08-01
An extensive observing campaign to monitor Comet 9P/Tempel 1 will be conducted from 20 June to 19 July, 2005 at Las Campanas Observatory, Chile. These observations will precede and follow the impact of the Deep Impact projectile, which is likely to create a crater on the nucleus that will act as a fresh active area on the surface of the comet. Discreet nucleus active areas, believed to be the source of coma gas and dust jets, will likely result in changing morphology in the coma. We present the initial results of the wide-field narrowband visible imaging of the comet. Data will be taken with the 2.5m DuPont telescope from 27 June - 9 July, following the comet from 4 rotations prior to impact, to 4 rotations after impact using the narrowband Hale-Bopp filters, including CN, C2, and two continuum filters. These data will allow an accurate determination of the rotation state of the embedded nucleus immediately preceding the impact event as well as a measure of any changes to the rotation state due to the impact. In addition, modeling of these data will provide the total dust and gas production rates from the unaltered nucleus compared to the enhanced dust and gas emission from the newly created active region and freely sublimating pieces of mantle material ejected into the coma by the impactor. We will monitor temporal changes (on hours and days time-scales) in the morphology of both the gas and refractory components. We will use coma morphology studies to estimate the dust and gas outflow velocities and infer the presence of discreet nucleus source regions (pre- and post-impact). Of particular interest is the study of the gas-to-dust ratio and the ratio of the minor carbon species emitted from the newly created active region relative to the pre-impact coma environment.
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Matrix metalloproteases inhibition and biocompatibility of gold and platinum nanoparticles.
Hashimoto, Masanori; Kawai, Koji; Kawakami, Hayato; Imazato, Satoshi
2016-01-01
Matrix metalloprotease (MMP) inhibitors improve the longevity of dental adhesives/tooth bonds; however, biocompatibility is required for their clinical use. This study evaluated the inhibition of MMPs and toxicity of two gold (AuNPs) and platinum nanoparticles (PtNPs) as possible compounds for use in dental adhesives. The MMP assay for studying the interaction of MMPs and nanoparticles (NPs) was evaluated by an MMP assay kit and gelatin zymography. Cultured L929 fibroblast cells or RAW264 macrophages were exposed to NPs. The cellular responses to NPs were examined using cytotoxic (cell viability) and genotoxic assays (comet assay), and transmission electron microscopic (TEM) analysis. The mechanical properties (elastic modulus) of the experimental resin loaded with NPs were examined using thermomechanical analysis. All NPs inhibited MMP activity at relatively low concentrations. The NPs inhibit MMPs by chelating with the Zn(2+) bound in the active sites of MMPs. No cytotoxic and genotoxic effects were found in AuNPs, whereas the PtNPs possessed both adverse effects. In TEM analysis, the NPs were localized mainly in lysosomes without penetration into nuclei. The mechanical properties of the resins increased when AuNPs were added in resins, but not by PtNPs. AuNPs are attractive candidates to inhibit MMPs and improve the mechanical properties of resins without cytotoxic/genotoxic effects to cells, and therefore should be suitable for applications in adhesive resin systems. © 2015 Wiley Periodicals, Inc.
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Comet Hyakutake to Approach the Earth in Late March 1996
NASA Astrophysics Data System (ADS)
1996-03-01
Astronomers Prepare for a Rare Event In the early morning of January 31, 1996, Japanese amateur astronomer Yuji Hyakutake made his second comet discovery within five weeks. He found the new comet near the border between the southern constellations of Hydra (The Water-Snake) and Libra (The Scales), amazingly just three degrees from the position where he detected another comet on December 26, 1995. After two weeks of hectic activity among amateur and professional astronomers all over the world, much interesting information has now been gathered about the new comet which has been designated C/1996 B2 (Hyakutake) . In particular, it has been found to move in a near-parabolic orbit that will bring it unusually close to the Earth next month. It is then expected to become bright enough to be seen with the unaided eye and to remain so during several weeks thereafter. Preparations are now made to observe the celestial visitor with a large number of telescopes, on the ground and in space. This event offers a rare opportunity to study the immediate surroundings of a cometary nucleus in detail and the specialists intend to make the most of it. Discovery and orbit Yuji Hyakutake, of profession photoengraver and a well-known amateur astronomer, announced his new discovery without delay, and within 24 hours, it had been sighted by several other observers in Japan and Australia. Experienced comet-watchers described its appearance as `diffuse with central condensation and of magnitude 11-12', i.e. a little more than 100 times fainter than what can be seen with the unaided eye. This brightness is not unusual for a comet discovered by an amateur, although it would probably have been missed, had it been just a little fainter. In the present case, the decisive factors for Hyakutake's success were undoubtedly his very powerful equipment (25 x 150 binoculars) and the advantageous combination of the comet's southern position in the sky and his location in Kagoshima, the southernmost prefecture of Japan. Within three days only, nearly 120 positional measurements of the comet were obtained, mostly by amateur observers in Australia, PR China, the Czech Republic, France, Japan, Spain and the U.S.A. This allowed Brian Marsden of the Central Bureau for Astronomical Telegrams of the International Astronomical Union (Cambridge, Mass., U.S.A.) to compute a preliminary orbit. It showed that the comet moves along a parabola - or at least an extremely elongated ellipse - and that it must therefore have come from far away and may never have been near the Sun before. At the time of discovery, the comet was about 280 million km from the Earth and outside the orbit of Mars. Moreover, the motion of the comet is such that it will continue to approach the Earth with a speed of about 58 km/sec during the next weeks and will pass within 15 million kilometres of our planet in late March. This corresponds to one tenth of the distance between the Earth and the Sun (0.1 AU) and, in cosmical terms, the passage is therefore a very close one. Information about some earlier comet encounters may be found in the Appendix at the end of this Press Release. Continued observations have confirmed this and have also allowed to fix the moment of closest passage as Monday, March 25, at about 7h UT. At that time, the comet will be moving northwards through the northern constellation of Draco (The Dragon) at the exceptional rate of 0.77 deg/hour. The event will be best observable from the northern hemisphere. Two days later, the comet passes within a few degrees of the northern celestial pole. The perihelion (the orbital point closest to the Sun) is reached on May 1, 1996, at a distance of 35 million kilometres from the Sun, far inside the orbit of the innermost planet, Mercury. From then on, the comet will rapidly move south, crossing the celestial equator in mid-May and reaching 70 degrees south in late July. Recent observations Comet Hyakutake obviously comes from far away, maybe even from the very distant `Oort Cloud' of comets that surrounds the solar system. In this sense it is different from the periodical comets which move in closed orbits around the Sun with revolution periods between a few years and some decades. Its `dirty snowball' nucleus of ices and dust has therefore not been heated by the Sun for a very long time, perhaps never, if this is its first visit to the inner regions of the solar system. Hence it is particularly difficult to predict its future performance. Nevertheless, the available observations seem to indicate that it is a quite `active' comet and that it may therefore become comparatively bright when it approaches the Earth and later at perihelion. But how bright ? Imaging as well as spectroscopic observations have been performed in order to better characterize Comet Hyakutake. On CCD-frames obtained of the comet in early February with telescopes at the ESO La Silla Observatory and elsewhere, an elongation is clearly visible (cf. ESO Press Photo 11/96 ) in the anti-sunward direction of the coma (the cloud of gas and dust that surrounds the cometary nucleus). A real tail has not yet developed, but this is expected to happen soon. The size of the coma was measured as at least 7 arcmin, corresponding to a projected diameter of nearly 500,000 kilometres. It is also of interest that until recently the coma otherwise appeared absolutely symmetrical - there was no indication of `jets', i.e. no large vents on the surface of the nucleus had yet become active. However, on images obtained with the ESO 3.6-metre telescope in the morning of February 13, a `jet'-like feature is seen which emerges south-east of the nucleus (i.e. from the sunlit side) and curls counter-clockwise towards the opposite side (the `tail'-direction). This is probably the first evidence of localized dust production on the surface of the nucleus. CCD observations were made on February 9 at the Lowell Observatory (Flagstaff, U.S.A.) through special optical filters which isolate the light from different components of the coma, e.g. the light emitted by the OH-, C2- and CN-molecules in gaseous form and also the reflected sunlight from the dust grains. They show that the gas production rates are almost as high as those measured at famous Comet Halley when it was at about the same distance from the Sun during its approach in late 1985. The dust production of Comet Hyakutake also seems to be quite impressive. The first spectra of the new comet were obtained at La Silla with the Boller and Chivens spectrograph at the ESO 1.52-metre telescope on February 8; they show comparatively strong emission of CN, C2 and C3 molecules, cf. ESO Press Photo 12/96. This is not unusual for a comet at the corresponding heliocentric distance. In conclusion, the recent observations show Comet Hyakutake to be an `active' comet. The evaporation of the ices on the surface of its nucleus, due to the heating of the Sun, is well underway and much dust is being ejected during this process. It is quite likely that this comet will put on a fine display, starting in mid-March and lasting until soon after the perihelion passage in early May. Nevertheless, there have been some cases [1] in recent times when the activity level of new comets did not develop as expected, so some caution is necessary. The encounter on March 25 By a straightforward extrapolation of the current brightness, it would appear that Comet Hyakutake will reach magnitude 1 on March 25, 1996, at the time of the closest approach to the Earth. This is almost as bright as the brightest stars in the sky. However, it is important to consider that this is the `integrated' brightness of the entire comet head which may fill an area of several degrees in diameter in the sky. Thus the comet will appear as a moderately bright, very diffuse object that is best visible in binoculars. There will be a central point of enhanced brightness, corresponding to the innermost part of the coma around the nucleus. The motion is sufficiently fast to be easily perceptible on the stellar background. We do not know the size of the nucleus yet, but assuming - optimistically, from the measured gas and dust production - that the diameter is 10 kilometres, i.e. about as large as that of Comet Halley, then the magnitude of the nucleus alone should be about 11 at the time of the closest encounter. It may therefore be well visible in even small telescopes, as a bright point near the centre of the diffuse coma. However, it will most probably not be possible to obtain resolved images of the nucleus with ground-based telescopes; even if the size turns out to be this large, the nucleus will only subtend an angle of about 0.15 arcsec and thus appear point-like. The comet's extremely rapid motion across the sky at the encounter will constitute a major technical-observational problem for most telescopes. Moreover, it cannot be excluded that the coma is so dense that the nucleus will be completely hidden from view. The only telescope which could possibly image the nucleus as an extended object is the Hubble Space Telescope, for which observations are now being planned. Still, there is no doubt that the upcoming event offers very bright prospects for the investigation of the near-nucleus environment of a comet. Another technique which will most likely be attempted is that of radar soundings; the return time for a signal will only be 100 seconds. In the past, only a handful of comets have been investigated in this way and none in great detail. However, in view of the recent, great technological advances in this field, it should in principle be possible to `image' the nucleus of Comet Hyakutake with some of the largest radio telescopes. Predictions for the appearance of the tail(s) at the encounter are still very uncertain, since their development has not yet started. In the best case, the dust tail may become quite impressive and reach a length of many degrees, and the expected ion tail could also be quite long. The perihel passage The brightness at perihel on May 1 will probably exceed that at the Earth encounter and Comet Hyakutake could then become a very spectacular object. How bright it will actually be is much dependent on the amount of dust released from the nucleus as it approaches the Sun. Unfortunately, the viewing conditions will not be very good and the full moon on May 3 will also adversely influence the sight. Appendix: Comet encounters with the Earth There is no doubt that the close encounter with C/1996 B2 (Hyakutake) is a relatively rare event. According to Brian Marsden (Central Bureau for Astronomical Telegrams of the International Astronomical Union, Cambridge, Mass., U.S.A.): The approach of C/1996 B2 to the Earth on March 25 (0.10 AU) [2] is the closest for any comet since 1983 (when there were two comets coming to 0.06 AU and 0.03 AU within a month of each other), and it is the fifth closest approach of any comet during the past century. What is unique about this comet is that no other comet is known then to have gone on to pass anything like as close to the Sun as this one does (0.23 AU on May 1). One of the 1983 comets had about twice this comet's perihelion distance, but the approach to the Earth was well after perihelion. There was possibly a comet with a perihelion distance comparable to this one that came closer to the Earth after perihelion in the year 400, but that is very uncertain. The time interval between passage near the Earth and subsequent passage near the Sun is longer for C/1996 B2 (37 days) than for any closer Earth approach since that of the famous Lexell comet in 1770 (43 days), that comet holding the record confirmed approach to the Earth (0.015 AU or 2.2 million kilometres). C/1996 B2 is intrinsically the brightest Earth-approacher since the early eighteenth century, and the 55 days between discovery and Earth approach is a record for a pre-perihelic Earth approach. More information about other close encounters and collisions of comets with the Earth may be found in an article by Zdenek Sekanina and Don Yeomans (Jet Propulsion Laboratory, CALTECH, Pasadena, U.S.A.) which appeared in 1984 in the American journal The Astronomical Journal , Volume 89, page 154. Notes: [1] Prominent examples are Comet Kohoutek in 1973 and Comet Austin in 1990. [2] 1 Astronomical Unit (AU) = 149.6 million kilometres (the mean distance between the Earth and the Sun). Note also that ESO has set up a special Home Page for the Comet Hyakutake event ( http://www.eso.org/educnpubrelns/comet-hyakutake.html) where new information from ESO will be brought.
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Organic Nano-Grains in Comet 103P/Hartley 2: The Organic Glue of Porous Aggregate Grains?
NASA Technical Reports Server (NTRS)
Wooden, D. H.; Russo, N.Dello; Li, A.; Woodward, C. E.; Kelley, M. S.; Harker, D. E.; Cook, J. C.; Vervack, R. J.; Geballe, T. R.
2013-01-01
The GNIRS instrument on the Gemini 8--m telescope observed comet 103P/Hartley on 2010-- Dec--04UT, a month after the EPOXI Mission encounter, and detected the 3.3 and 3.4 um bands in emission. The 3.3/3.4 ratio and the broad band widths are consistent with experiments of heated (approximately 600 K) aliphatic carbon (-CH3, -CH2) thin films. For the 3.4 micron band to be in emission, the aliphatic bonds must be attached to a carrier possessing the strongly UV--absorbing C=C aromatic rings, and these rings have to be less than 50--100 carbon atoms (4-6 Angstrom) for attached -CH bonds to also generate a 3.3 micron-band in emission. Slightly larger (=10Å) Very Small Grains (VSGs) can absorb single UV photons comparable to or exceeding their heat capacity, thermally fluctuate and release IR photon(s). The 3.3 micron and 3.4 micron bands observed by GNIRS suggest that organic macromolecules/ nano--grains with both aliphatic and aromatic bonds are fluorescing/thermally fluctuating in the coma. Aliphatic and aromatic materials have been seen in Stardust samples and the primitive carbonaceous chondrite 'Tagish Lake'. The larger the ratio of the -CH2/-CH3 components of the aliphatic 3.4 micron band, the more 'primitive' the organic material. In a Stardust organic globule, some aliphatic bonds were transformed into aromatic bonds during the low dosage of Transmission Electron Microscope imaging. Conversely, lab experiments show irradiation of ices containing small PAHs generates aliphatic organics. Photo--processing of ices also likely forms the ubiquitous aliphatic coatings that appear on the surfaces of all silicate subgrains constituting nine cometary interplanetary dust particles. The aliphatic coatings, dominated by -CH2, likely were important in sticking the aggregates together, and existed prior to incorporation of dust aggregates into comet nuclei. These comet aliphatics may be some of the sought--after precursors to the more robust and complex organics studied as Insoluble Organic Matter in carbonaceous chondrites. Aliphatic coatings on submicron grains, however, will not be observable in absorption because they are fairly transparent, nor do the aliphatic carbonaceous coatings produce the 3.4 micron emission band because the particles they are attached to are too large (too many vibration modes). We must probe the nano--sized organic carriers that undergo substantive thermal fluctuations in cometary comae and emit at 3.3 3.4 micron. Observations of the 3.3 and 3.4 micron emission features contribute to characterizing the evolution of organics prior to their incorporation into cometary nuclei as well as their rapid evolution in cometary comae, which in turn contributes to deepening our understanding of the evolution of organics on the surfaces of asteroids and outer icy bodies in our solar system. Studying organics in comets contributes to understanding the formation and evolution pathways of ISM organics through to the formation of the robust insoluble organic matter in meteorites. A'Hearn, M.F., et al. 2011, Science, 332, 1396; Bockelee--Morvan, D. et al. 1995, Icarus, 116, 18; De Gregorio, B.T., et al. 2010, GCA, 74, 4454; Dello Russo, N., et al. 2011, ApJ, 734, L8; Dischler et al. 1983, Solid State Communications, 48, 105; Flynn, G., et al. 2010a, LPSC, 41, #1079; Flynn, G., et al. 2010b, COSPAR, 38, F31--0012--10; Flynn, G., Wirick, S. 2011, LPSC, 42, #1856; Fomenkova, et al. 1994, GCA 58, 4503; Matrajt, G., et al. 2013, ApJ, 765, 145; Schutte, et al. 1993, ApJ, 415, 397; Wooden, D.H. et al. 2011, EPSC--DPS, 1557; Wooden, D.H. et al. 2013, submitted.
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Structures of twilight patrol in the "Churyumov's Unified network" to ensure continuous monitoring
NASA Astrophysics Data System (ADS)
Churyumov, K. I.; Steklov, A. F.; Vidmachenko, A. P.; Dashkiev, G. N.; Steklov, E. A.; Slipchenko, A. S.; Romaniuk, Ya. O.; Nevodovskyi, P. V.
2016-10-01
1. Three types of astronomical observations, and three classes of astronomical observatories. Over 70% of the observer's time in astronomical observatories accounted for the night of observation after the end of astronomical twilight. Prior to 15.02.2013, from the famous invasion of the Chelyabinsk large meteoroid in morning twilight, astronomers practically no carried out the twilight observations. But it is such morning and evening twilight observation, became the main "highlight" of the authors in the past four years [3, 5, 7]. Results were unexpected, and they allowed us to state that in our time the astronomical observatory (AO) should be divided into AO for nighttime astronomical observations (NAO), daily astronomical observations (DAO) and AO for twilight astronomical observations (SAO). 2. The real problem of AO DAO and SAO. We affirm, that in the interest of health and safety the inhabitants of our cities, astronomers are obliged significantly expand a circle and list of observations; need to include in it astrophysical observations and registration of facts and traces of all kinds of hazardous aerospace invasions into the sky over our cities. Society and the state allocate their money on the development of astronomical observatories, and therefore are entitled to demand recoil in the form of constant monitoring to ensure nocturnal, daytime and twilight control, for their safety the realities of modern complex time. And it is, in the conditions of aggravation of ecological problems, at climate evolution and of the increasing amount of harmful technogenic pollutants emissions in conditions of constant asteroid and comet hazard [10, 11], and especially within the present conditions of hybrid wars [8, 9]. That is why it is necessary give off sufficient observational time for the monitoring control on the facts and trail of all sorts of dangerous invasions. All astronomical observatories could create their own sectors, which would provide ground and space calibrating control of facts and traces of all kinds of dangerous invasions. 3. Twilight patrol of "Churyumov Unified Network" and the study of invasions of fragments of cometary nuclei in the Earth's atmosphere. The costs of the study of the comet Churyumov-Gerasimenko 67P and its nuclei, on all mission of Rosetta-Philae, amounted to about EUR 2 billion [6]. Its results have significantly improved our understanding of the physics of cometary phenomena have further exacerbated problems of asteroid and comet hazard. In 2016, astronomers a lot of effort and time allocated for study of the disintegration of cometary nucleus of Ikeya - Murakami (P / 2010 V1) at least 17 of fragments. The authors have created a twilight patrol of "United Network Churyumov" to implement of daytime and twilight observations
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NASA Astrophysics Data System (ADS)
Eicher, David J.; Levy, David H.
2013-11-01
Foreword David H. Levy; Preface; Acknowledgments; 1. Strange lights in the sky; 2. Great comets of the past; 3. What are comets?; 4. Comets of the modern era; 5. Comets in human culture; 6. Where comets live; 7. The expanding science of comets; 8. Observing comets; 9. Imaging comets; Glossary; Bibliography; Index.
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Short-wavelength infrared (1.3-2.6 μm) observations of the nucleus of Comet 19P/Borrelly
Soderblom, L.A.; Britt, D.T.; Brown, R.H.; Buratti, B.J.; Kirk, R.L.; Owen, T.C.; Yelle, R.V.
2004-01-01
During the last two minutes before closest approach of Deep Space 1 to Comet 19P/Borrelly, a long exposure was made with the short-wavelength infrared (SWIR) imaging spectrometer. The observation yielded 46 spectra covering 1.3–2.6 μm; the footprint of each spectrum was ∼160 m × width of the nucleus. Borrelly's highly variegated and extremely dark 8-km-long nucleus exhibits a strong red slope in its short-wavelength infrared reflection spectrum. This slope is equivalent to J–K and H–K colors of ∼0.82 and ∼0.43, respectively. Between 2.3–2.6 μm thermal emission is clearly detectable in most of the spectra. These data show the nucleus surface to be hot and dry; no trace of H2O ice was detected. The surface temperature ranged continuously across the nucleus from ⩽300 K near the terminator to a maximum of ∼340 K, the expected sub-solar equilibrium temperature for a slowly rotating body. A single absorption band at ∼2.39 μm is quite evident in all of the spectra and resembles features seen in nitrogen-bearing organic molecules that are reasonable candidates for compositional components of cometary nuclei. However as of yet the source of this band is unknown.
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Are Comets 42P/Neujmin 3 and 53P/Van Biesbroeck Parts of one Comet?
NASA Astrophysics Data System (ADS)
Pittichova, J.; Meech, K. J.; Valsecchi, G. B.; Pittich, E. M.
2003-05-01
We want to present preliminary results of the observations of the physical parameters of comets 42P/Neujmin 3 and 53P/Van Biesbroeck: brightness, nucleus activity, rotation period, light-curve and color changes from our first three optical observing runs (March, and May 2003) at Mauna Kea, using UH 2.2m telescope and Tek2048 CCD camera. Comets 42P/Neujmin 3 and 53P/Van Biesbroeck have very well determined orbits, and their orbital histories are very interesting. Their current orbits are not very similar to each other; however, numerical integrations have shown that both comets had a rather close approach to Jupiter in January 1850, and that, before 1850, the two orbits were nearly identical. Given the extremely low probability of a chance coincidence of the six orbital elements at a given time, the natural conclusion is that the two objects are fragments of a single comet that split sometime in the late 1849 or early 1850. Among the known cases of split periodic comets, this one is peculiar for a number of reasons: 1. the splitting was probably not due to tidal stresses, since the 1850 encounter with Jupiter took place well outside the Roche lobe; 2. it is the only case discovered through a dynamical study; 3. in the only other case of splitting of a Jupiter family comet, that of 3D/Biela, the fragments did not survive for more than a couple of revolutions, whereas in the present case both fragments have passed perihelion more than ten times since the splitting. If these two comets are fragments of a single parent body, then they should show a certain degree of physical and chemical similarity, which we would like to obtain from spectroscopic observation in 2004, when both comets are close to their perihelion. Acknowledgments: Support for this work was provided by NASA Grant No. NAG5-12236 and Scientific Grant Agency VEGA of the Slovak Academy of Sciences, grant No. 2/1005/21.
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Analysis of Polarimetric, Photometric, and Spectroscopic Observations of Comet C/1996 Q1 (Tabur)
NASA Astrophysics Data System (ADS)
Kiselev, N. N.; Jockers, K.; Rosenbush, V. K.; Korsun, P. P.
2001-11-01
We present the imaging polarimetry and photometry of Comet C/1996 Q1 (Tabur) obtained on October 10, 1996, with a two-channel focal reducer attached to the 2-m Pik Terskol Observatory telescope through blue (λ4430/44 Å) and red (λ6420/26 Å) continuum filters and through a λ6620/59 Å filter that isolated the NH_2(0.7.0) band. We analyze the λ3600-9300 Å long-slit spectrograms of the comet taken on October 5-6, 1996, with the 2.6-m Crimean Astrophysical Observatory telescope. The NH_2(0.8.0) λ6408 Å emission and an unidentified λ6428 Å emission were found to fall within the pass band of the red filter. The blue filter transmits weak unidentified emissions at λ4424-4444 Å and partially C_2(λ4360 Å). Correction for the depolarizing effect of molecular emissions resulted in an increase of the dust polarization by 2-4% in the near-nucleus region and by almost a factor of 2 in the outer coma regions. However, the polarization and color differences between different coma regions remained even after correction for the contribution of emissions. We found no dust polarization difference between the gas comet Tabur and the dust comet C/1988 A1 (Liller), which are believed to be fragments of a common parent comet. The NH_2coma was found to be elongated perpendicular to the comet radius vector. The causes of the spatial asymmetry in the NH_2molecular distribution are yet to be established. We study the evolution of activity and the spatial distribution of dust brightness, polarization, and color in the comet. We consider a taxonomic classification of gas and dust comets according to dust polarization properties. The polarization differences between dust and gas comets at large phase angles are most likely related both to the actual differences in dust and to the effect of molecular emissions, nuclear gas- and dust-production rates and to the evolution of grain properties with distance from the nucleus.
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Sulfur activation at the Little Boy-Comet Critical Assembly: a replica of the Hiroshima bomb
DOE Office of Scientific and Technical Information (OSTI.GOV)
Kerr, G.D.; Emery, J.F.; Pace, J.V. III
1985-04-01
Studies have been completed on the activation of sulfur by fast neutrons from the Little Boy-Comet Critical Assembly which replicates the general features of the Hiroshima bomb. The complex effects of the bomb's design and construction on leakage of sulfur-activation neutrons were investigated both experimentally and theoretically. Our sulfur activation studies were performed as part of a larger program to provide benchmark data for testing of methods used in recent source-term calculations for the Hiroshima bomb. Source neutrons capable of activating sulfur play an important role in determining neutron doses in Hiroshima at a kilometer or more from the pointmore » of explosion. 37 refs., 5 figs., 6 tabs.« less
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Deaton, J D; Guerrero, T; Howard, T H
1992-01-01
In vitro Ca++ activates gelsolin to sever F-actin and form a gelsolin-actin (GA) complex at the+end of F-actin that is not dissociated by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) but is separated by EGTA+PIP/PIP2. The gelsolin blocks the+end on the actin filament, but the-end of the filament can still initiate actin polymerization. In thrombin activated platelets, evidence suggests that severing of F-actin by gelsolin increases GA complex, creates one-end actin nucleus and one cryptic+end actin nucleus per cut, and then dissociates to yield free+ends to nucleate rapid actin assembly. We examined the role of F-actin severing in creation and regulation of nuclei and polymerization in polymorphonuclear neutrophils (PMNs). At 2-s intervals after formyl peptide (FMLP) activation of endotoxin free (ETF) PMNs, change in GA complex was correlated with change in+end actin nuclei,-end actin nuclei, and F-actin content. GA complex was quantitated by electrophoretograms of proteins absorbed by antigelsolin from cells lysed in 10 mM EGTA,+end actin nuclei as cytochalasin (CD) sensitive and-end actin nuclei as CD insensitive increases in G-pyrenyl actin polymerization rates induced by the same PMNs, and F-actin content by NBDphallacidin binding to fixed cells. Thirty three percent of gelsolin was in GA complex in basal ETF PMNs; from 2-6 s, GA complexes dissociate (low = 15% at 10 s) and sequentially+end nuclei and F-actin content and then-end nuclei increase to a maximum at 10 s. At > s GA complex increase toward basal and + end nuclei and F-actin content returned toward basal. These kinetic data show gelsolin regulates availability of + end nuclei and actin polymerization in FMLP. However, absence of an initial increase in GA complex or - end nucleating activity shows FMLP activation does not cause gelsolin to sever F- or to bind G-actin to create cryptic + end nuclei in PMNs; the results suggest the + nucleus formation is gelsolin independent. PMID:1337290
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Deaton, J D; Guerrero, T; Howard, T H
1992-12-01
In vitro Ca++ activates gelsolin to sever F-actin and form a gelsolin-actin (GA) complex at the+end of F-actin that is not dissociated by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) but is separated by EGTA+PIP/PIP2. The gelsolin blocks the+end on the actin filament, but the-end of the filament can still initiate actin polymerization. In thrombin activated platelets, evidence suggests that severing of F-actin by gelsolin increases GA complex, creates one-end actin nucleus and one cryptic+end actin nucleus per cut, and then dissociates to yield free+ends to nucleate rapid actin assembly. We examined the role of F-actin severing in creation and regulation of nuclei and polymerization in polymorphonuclear neutrophils (PMNs). At 2-s intervals after formyl peptide (FMLP) activation of endotoxin free (ETF) PMNs, change in GA complex was correlated with change in+end actin nuclei,-end actin nuclei, and F-actin content. GA complex was quantitated by electrophoretograms of proteins absorbed by antigelsolin from cells lysed in 10 mM EGTA,+end actin nuclei as cytochalasin (CD) sensitive and-end actin nuclei as CD insensitive increases in G-pyrenyl actin polymerization rates induced by the same PMNs, and F-actin content by NBDphallacidin binding to fixed cells. Thirty three percent of gelsolin was in GA complex in basal ETF PMNs; from 2-6 s, GA complexes dissociate (low = 15% at 10 s) and sequentially+end nuclei and F-actin content and then-end nuclei increase to a maximum at 10 s. At > s GA complex increase toward basal and + end nuclei and F-actin content returned toward basal. These kinetic data show gelsolin regulates availability of + end nuclei and actin polymerization in FMLP. However, absence of an initial increase in GA complex or - end nucleating activity shows FMLP activation does not cause gelsolin to sever F- or to bind G-actin to create cryptic + end nuclei in PMNs; the results suggest the + nucleus formation is gelsolin independent.
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Outer planets and icy satellites
NASA Technical Reports Server (NTRS)
Drobyshevski, E. M.
1991-01-01
The resources offered by the outer bodies in the Solar System, starting with the main belt asteroids and Jovian System, are not only larger and more diverse but may even be easier to reach than, say, those of Mars. The use of their material, including water and organic matter, depends exclusively on the general strategy of exploration of the Solar System. Of major interest in this respect are the large ice satellites - Titan, Ganymede, and Callisto. Motion through the planetary magnetospheres excites in their ice envelopes megampere currents which, in the presence of rocky, etc., inclusions with electronic conduction should lead to the bulk electrolysis of ice and accumulation in it of 2H2 + O2 in the form of a solid solution. With the concentration of 2H2 + O2 reaching about 15 wt. percent, the solution becomes capable of detonation by a strong meteoritic impact. An explosion of Ganymede's ice envelope about 0.5 By ago could account for the formation of the Trojans and irregular satellites, all known differences between Ganymede and Callisto, and many other things. The explosion of a small icy planet with M approx less than 0.5 Moon created the asteroid belt. Two to three explosions occurred on Io, and two on Europa. The specific features of the longperiod comets close to Saturn's orbit permit dating Titan's envelope explosion as 10,000 yr ago, which produced its thick atmosphere, young Saturn's rings, as well as a reservoir of ice fragments saturated by 2H2 + O2, i.e., cometary nuclei between the orbits of Jupiter and Saturn. Thus these nuclei should contain, besides organic matter, also 2H2 + O2, which could be used for their transportation as well as for fuel for spaceships. Ices of such composition can reside deep inside Deimos, the Trojans, C-asteroids, etc. The danger of a future explosion of Callisto's electrolyzed ices, which would result in a catastrophic bombardment of the Earth by comets, may be high enough to warrant a revision of the priorities and strategy of space exploration.
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Outer planets and icy satellites
NASA Astrophysics Data System (ADS)
Drobyshevski, E. M.
The resources offered by the outer bodies in the Solar System, starting with the main belt asteroids and Jovian System, are not only larger and more diverse but may even be easier to reach than, say, those of Mars. The use of their material, including water and organic matter, depends exclusively on the general strategy of exploration of the Solar System. Of major interest in this respect are the large ice satellites - Titan, Ganymede, and Callisto. Motion through the planetary magnetospheres excites in their ice envelopes megampere currents which, in the presence of rocky, etc., inclusions with electronic conduction should lead to the bulk electrolysis of ice and accumulation in it of 2H2 + O2 in the form of a solid solution. With the concentration of 2H2 + O2 reaching about 15 wt. percent, the solution becomes capable of detonation by a strong meteoritic impact. An explosion of Ganymede's ice envelope about 0.5 By ago could account for the formation of the Trojans and irregular satellites, all known differences between Ganymede and Callisto, and many other things. The explosion of a small icy planet with M approx less than 0.5 Moon created the asteroid belt. Two to three explosions occurred on Io, and two on Europa. The specific features of the longperiod comets close to Saturn's orbit permit dating Titan's envelope explosion as 10,000 yr ago, which produced its thick atmosphere, young Saturn's rings, as well as a reservoir of ice fragments saturated by 2H2 + O2, i.e., cometary nuclei between the orbits of Jupiter and Saturn. Thus these nuclei should contain, besides organic matter, also 2H2 + O2, which could be used for their transportation as well as for fuel for spaceships. Ices of such composition can reside deep inside Deimos, the Trojans, C-asteroids, etc. The danger of a future explosion of Callisto's electrolyzed ices, which would result in a catastrophic bombardment of the Earth by comets, may be high enough to warrant a revision of the priorities and strategy of space exploration.
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Transformative Small Body Science Enabled with Pan-STARSS Survey Data
NASA Astrophysics Data System (ADS)
Meech, Karen J.; Kleyna, Jan T.; Keane, Jacqueline V.; Hainaut, Olivier R.; MIcheli, Marco
2018-01-01
In the first 5 Myr of Solar System formation, gas imprinted a local chemical signature on the planetesimals which were subsequently redistributed during planet formation. Decades-long ground- and space-based studies have tried to map our solar system’s protoplanetary disk chemistry using volatiles in comets. We now know that comet volatiles (H2O, CO, CO2 and organics) have distinct chemical classes. This data contradicts traditional ideas that all volatile-rich bodies formed in the outer disk. In-situ space comet missions have suggested, however, that comets preserve their pristine volatile inventory, and perhaps even their heritage of ices prior to the protoplanetary disk. Recently, a profusion of dynamical models has been developed that can reproduce some of the key characteristics of today’s solar system. Some models require significant giant planet migration, while others do not. The UH-led Pan-STARRS1 survey (PS1) can offer transformative insight into small bodies and the early solar system, providing a preview of LSST. In 2013 PS1 discovered an asteroidal object on a long-period comet orbit, the first of a class of tailless objects informally called Manxes. The second Manx discovered had a surface composition similar to inner solar system rocky S-type material, suggesting the intriguing possibility that we are looking at fresh inner solar system Earth-forming material, preserved for billions of years in the Oort cloud. Currently 10-15 of these objects are discovered each year, with PS1 dominating the discoveries. The number of rocky inner solar system Manx objects can be used to constrain solar system formation models. PS1 is also very good at discovering faint active objects at large distances, including the remarkable discovery of a comet active beyond 16 au from the sun. By searching the PS1 database once these discoveries are made, it is possible to extend the orbit arc backwards in time, allowing us to model the activity, and understand the chemistry and physics of ices and activity in the outer solar system. These discoveries will help us tie together chemistry and dynamics in our solar system with new resolved ALMA observations of protoplanetary disks. Support from NSF grants AST-1617015, 1413736.
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Global Intracellular Slow-Wave Dynamics of the Thalamocortical System
Sheroziya, Maxim
2014-01-01
It is widely accepted that corticothalamic neurons recruit the thalamus in slow oscillation, but global slow-wave thalamocortical dynamics have never been experimentally shown. We analyzed intracellular activities of neurons either from different cortical areas or from a variety of specific and nonspecific thalamic nuclei in relation to the phase of global EEG signal in ketamine-xylazine anesthetized mice. We found that, on average, slow-wave active states started off within frontal cortical areas as well as higher-order and intralaminar thalamus (posterior and parafascicular nuclei) simultaneously. Then, the leading edge of active states propagated in the anteroposterior/lateral direction over the cortex at ∼40 mm/s. The latest structure we recorded within the slow-wave cycle was the anterior thalamus, which followed active states of the retrosplenial cortex. Active states from different cortical areas tended to terminate simultaneously. Sensory thalamic ventral posterior medial and lateral geniculate nuclei followed cortical active states with major inhibitory and weak tonic-like “modulator” EPSPs. In these nuclei, sharp-rising, large-amplitude EPSPs (“drivers”) were not modulated by cortical slow waves, suggesting their origin in ascending pathways. The thalamic active states in other investigated nuclei were composed of depolarization: some revealing “driver”- and “modulator”-like EPSPs, others showing “modulator”-like EPSPs only. We conclude that sensory thalamic nuclei follow the propagating cortical waves, whereas neurons from higher-order thalamic nuclei display “hub dynamics” and thus may contribute to the generation of cortical slow waves. PMID:24966387
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VLBI Monitoring of the Bright Gamma-Ray Blazar PKS 0537-441
2010-06-01
active state by Fermi. It is one of the brightest ,),-ray blazars detected in the southern sky so far. The TANAMI (Tracking Active Galactic Nuclei...Active Galactic Nuclei with Austral Milliarcsecond Interferometry (TAN AMI) program (Ojha et a1. (2010» has been monitoring south- ern sky blazars such...Telescope. Studying Active Galactic Nuclei (AGN) at different wavelengths is crucial in order to understand AGN-jets and differentiate between
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DOE Office of Scientific and Technical Information (OSTI.GOV)
McClain, D.E.; Kalinich, J.F.; Poplack, J.K.
1989-02-01
Beta-glucuronidase, a lysosomal marker enzyme, associates with purified nuclei from HeLa and MOLT-4 cell lines in a radiation dose-dependent manner, up to 300 cGy in MOLT-4 cells, and 1000 cGy in HeLa cells. In MOLT-4 cells (200-cGy exposure), there is a significant increase in beta-glucuronidase activity detected in the nuclear fraction 24 h postirradiation with a maximum association occurring at 72 h. In HeLa cells (1000-cGy exposure), a significant association is first detected 24 h postirradiation with a maximum association at 48 h. The association is not the result of nonspecific contamination occurring during nuclei purification since nuclei from irradiatedmore » cells show no greater levels of plasma membrane marker and mitochondrial marker than controls. The nature of the association remains unclear, but activity is not removed by detergents used in the nuclei isolation procedure, and incubation of the nuclei with EDTA reverses the association only modestly. Exposure of nuclei from irradiated cells to anisotonic buffers also results in only a small decrease in beta-glucuronidase activity associated with the nuclei. These observations suggest that lysosomal hydrolases become intimately associated with the nuclei of irradiated cells.« less
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Reynoso, M S; Alvarez, C M; De la Cruz, L; Escoto, M D; Sánchez, J J G
2015-12-11
Corn is a major crop and various herbicides are used to maximize its production, which include a dicamba-atrazine mixture. This has great advantages, but can also induce DNA damage. Genotoxic activity was assessed by comet assay following application of two concentrations of dicamba-atrazine: 1000-2000 and 2000-4000 ppm. Apical meristem leaf nuclei from 119 varieties of sweetcorn plants from Mexico and South America, and from five commercial sweetcorn hybrids were used. Each accession comprised two individuals per concentration and two controls. Significant genotoxic activity (P < 0.001) was observed following treatment with 1000-2000 and 2000-4000 ppm compared to the negative control. There was no difference in the genotoxic activity induced by both 1000-2000 and 2000-4000 ppm concentrations in plants from Mexico and South America (P > 0.05) except (P < 0.05) in the 2000-4000 ppm treated plants from Mexico and the 1000-2000 ppm treated plants from South America. Sweetcorn hybrids showed significant genetic damage (P < 0.01) at all concentrations compared to the negative controls. Thus, the dicamba-atrazine mixture caused genetic damage to corn plants, and it suggested that Mexican sweetcorn is more sensitive to dicamba-atrazine than the maize varieties from South America. Neither hybrid status nor the origin avoids DNA damage caused by Marvel. Thus, maize can be useful as a biomonitor of genetic damage induced by chemicals and to identify possible phenotypes based upon the amount of genetic damage induced by herbicides and selection of resistant genotypes.
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Gamboa, Rodríguez T.; Gamboa, Aldeco R.; Bravo, Alvarez H.; Ostrosky, Wegman P.
2008-01-01
The economy of the state of Tabasco is based on oil extraction. However, this imposes major effects to the environment and communities. Examples are the Polycyclic Aromatic Hydrocarbons (PAHs) that may be found in the soil, water and sediment of the region. Their volatility makes them available to living beings and results in genotoxic activity. The purpose of this study was to quantify the levels of PAHs in the air at several points in the state, and to analyze their relationship with possible damage to DNA on local inhabitants. Single Cell Gel Electrophoresis Assay (Comet Assay) was applied to peripheral blood lymphocytes of five groups of children between six and 15 years of age. PAH samples were analyzed following US/EPA TO-13-A method. Results indicated the presence in the air of most of the 16 PAHs considered as high priority by EPA, some of which have been reported with carcinogenic activity. Differences (p<0.05) were found between PAHs concentration in the gaseous component and in the particulate component of air samples, with the greatest values for the gaseous component. Greatest PAH concentrations were detected in areas with high oil extraction activities. Children groups from high oil activity areas presented genotoxic damage labeled from moderate to high according to DNA migration from nuclei (Tail Length: 14.2 – 42.14 μm and Tail/Head: 0.97 – 2.83 μm) compared with control group (12.25 and 0.63 μm, respectively). The group with greatest cell damage was located in the area with the greatest oil activity. We conclude that the presence of PAHs in the air may represent a health risk to populations that are chronically exposed to them at high oil activity regions. PMID:19151429
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Slight hypercalcemia is not associated with positive responses in the Comet Assay in male rat liver.
Thiel, Anette; Hamel, Annie; Schaefer, Katrien; Cardoso, Renato; Beilstein, Paul
2017-08-01
Maintenance of physiological levels of intracellular and extracellular calcium is essential for life. Increased intracellular calcium levels are involved in cell death (apoptosis and necrosis) and are associated with positive responses in the Comet assay in vitro. In addition, high calcium and vitamin D intakes were reported to induce apoptosis in adipose tissue in obese mice and to increase DNA-migration in the Comet assay. To investigate increased serum concentration of calcium as a potential confounding factor in the regulatory Comet assay in vivo, we induced mild hypercalcemia in male Wistar rats by 3-day continuous intravenous infusion of calcium gluconate and performed the Comet assay in the liver in line with regulatory guidelines. The results of the study showed that mild increases in serum calcium concentration (up to 1.4 times above the concurrent control) and increased urinary calcium concentration (up to 27.8 times above the concurrent control) results in clinical signs like mild tremor, faster respiration rate and decreased activity in a few animals. However, under the conditions of the study, no increase in the %Tail DNA in the Comet assay and no indication of liver damage as determined by histopathological means were observed. Thus, mild increases in plasma calcium did not lead to positive results in a genotoxicity assessment by the Comet assay in the rat liver. This result is important as it confirms the reliability of this assay for regulatory evaluation of safety. Copyright © 2017 DSM Nutritional Products AG. Published by Elsevier B.V. All rights reserved.
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ACE-SWICS In Situ Plasma Composition of Fragmented Comet 73P/Schwassmann-Wachmann 3
NASA Astrophysics Data System (ADS)
Gilbert, J. A.; Lepri, S. T.; Rubin, M.; Zurbuchen, T.
2013-12-01
The interiors of comets contain some of the most pristine material in the solar system. Comet 73P/Schwassmann-Wachmann 3, discovered in 1930 with a double nucleus, is a Jupiter-family comet with a 5.34-year period. This comet split into 5 fragments in 1995 and disintegrated into nearly 70 pieces in 2006. In May and June of 2006, recently ionized cometary particles originating from some of these fragments were collected with the ACE-SWICS sensor. Due to a combination of the close proximity of the fragments passing between ACE-SWICS and the Sun, and the instrument characteristics, unique measurements regarding the charge state composition and the elemental abundances of both cometary and heliospheric plasma were made during this time. The cometary material released from some of these fragments can be identified by the concentrations of water-group pick-up ions having a mass-per-charge of 16-18 amu/e. With a focus on Helium, Carbon, and water-group ions, we present an analysis of the cometary plasma. Charge state ratios of C+/O+ fall below 0.1 during detection of comet fragment plasma, and there is a clear increase in He+ during fragment crossings. The C/O ratio and He charge states are used to provide constraints on the activity of the cometary fragments and also the spatial distribution of the extended and ionized cometary tail.
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The Implications of the Excited Rotation of Comet 252P/2000 G1 (LINEAR)
NASA Astrophysics Data System (ADS)
Li, Jian-Yang; Samarasinha, Nalin H.; Kelley, Michael S. P.; Farnocchia, Davide; Mutchler, Max J.; Ren, Yanqiong; Lu, Xiaoping; Tholen, David J.; Lister, Tim; Micheli, Marco
2018-01-01
Jupiter Family comet (JFC) 252P/LINEAR had a close encounter to Earth on 2016 March 21. We imaged the comet with the Hubble Space Telescope Wide Field Camera 3 UVIS channel through the V- and r’-band filters spanning ~8 hours on 2016 April 4. The pixel scale of 2.7 km/pixel allowed us to study the structure of the cometary coma at scales of a few kilometers to a few hundred kilometers from the nucleus, a characteristic that is unique to our data. The dust coma of 252P showed a strong, well defined, narrow and nearly linear feature in the sunward direction, and its projected position angle moved about the nucleus for ~60 deg in 8 hours, consistent with an apparent periodicity of ~7.24 hours. On the other hand, the lightcurve measured in both V- and r’-band images from a 13 km radius aperture, after corrected for color term, showed a variability of >0.14 mag that is consistent with an apparent periodicity of ~5.4 hours or its multiples. We suggest that the two different periodicities derived from coma morphology and the lightcurve is a strong indication that the nucleus of 252P is in a non-principal axis (NPA) rotation, joining two other confirmed NPA rotators (1P/Halley and 103P/Hartley 2) and comets that are potentially in NPA rotational states (e.g., 2P/Encke). However, this apparition has been unusual for 252P. In the past three perihelion passages since discovery, the comet was very weakly active compared to other JFCs. Meteor evidence also exists that it probably has been very weakly active for a few hundred years. But in our data, we saw a very active comet in this 2016 apparition with an active fraction of 40% to >100%, representing an increase of 100x with respect to its recent past. Based on our observations, 252P has a small nucleus with a radius of ~0.3 km, which suggests that its rotational state could be relatively easily changed by torques caused by outgassing. Since the very weak outgassing in the past is not likely to change the rotational state of 252P, the origin of its excited rotational state is interesting. Exploring the possible scenarios to excite the rotation of 252P may place constraints on its activity history. We will discuss results from our investigations.
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NASA Astrophysics Data System (ADS)
Lara, L. M.; Lowry, S.; Vincent, J.-B.; Gutiérrez, P. J.; Rożek, A.; La Forgia, F.; Oklay, N.; Sierks, H.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; Agarwal, J.; Auger, A.-T.; A'Hearn, M. F.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Besse, S.; Bodewits, D.; Cremonese, G.; Davidsson, B.; Da Deppo, V.; Debei, S.; De Cecco, M.; El-Maarry, M. R.; Ferri, F.; Fornasier, S.; Fulle, M.; Groussin, O.; Gutiérrez-Marques, P.; Güttler, C.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Knollenberg, J.; Kovacs, G.; Kramm, J.-R.; Kührt, E.; Küppers, M.; Lazzarin, M.; Lin, Z.-Y.; López-Moreno, J. J.; Magrin, S.; Marzari, F.; Michalik, H.; Moissl-Fraund, R.; Moreno, F.; Mottola, S.; Naletto, G.; Pajola, M.; Pommerol, A.; Thomas, N.; Sabau, M. D.; Tubiana, C.
2015-11-01
Context. During the most recent perihelion passage in 2009 of comet 67P/Churyumov-Gerasimenko (67P), ground-based observations showed an anisotropic dust coma where jet-like features were detected at ~ 1.3 AU from the Sun. The current perihelion passage is exceptional as the Rosetta spacecraft is monitoring the nucleus activity since March 2014, when a clear dust coma was already surrounding the nucleus at 4.3 AU from the Sun. Subsequently, the OSIRIS camera also witnessed an outburst in activity between April 27 and 30, and since mid-July, the dust coma at rh ~ 3.7-3.6 AU preperihelion is clearly non-isotropic, pointing to the existence of dust jet-like features. Aims: We aim to ascertain on the nucleus surface the origin of the dust jet-like features detected as early as in mid-July 2014. This will help to establish how the localized comet nucleus activity compares with that seen in previous apparitions and will also help following its evolution as the comet approaches its perihelion, at which phase most of the jets were detected from ground-based observations. Determining these areas also allows locating them in regions on the nucleus with spectroscopic or geomorphological distinct characteristics. Methods: Three series of dust images of comet 67P obtained with the Wide Angle Camera (WAC) of the OSIRIS instrument onboard the Rosetta spacecraft were processed with different enhancement techniques. This was made to clearly show the existence of jet-like features in the dust coma, whose appearance toward the observer changed as a result of the rotation of the comet nucleus and of the changing observing geometry from the spacecraft. The position angles of these features in the coma together with information on the observing geometry, nucleus shape, and rotation, allowed us to determine the most likely locations on the nucleus surface where the jets originate from. Results: Geometrical tracing of jet sources indicates that the activity of the nucleus of 67P gave rise during July and August 2014 to large-scale jet-like features from the Hapi, Hathor, Anuket, and Aten regions, confirming that active regions may be present on the nucleus localized at 60° northern latitude as deduced from previous comet apparitions. There are also hints that large-scale jets observed from the ground are possibly composed, at their place of origin on the nucleus surface, of numerous small-scale features.
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NASA Technical Reports Server (NTRS)
Donn, B. (Editor); Mumma, M. J. (Editor); Jackson, W. M. (Editor); Ahearn, M. (Editor); Harrington, R. (Editor)
1976-01-01
Papers are presented dealing with observations of comets. Topic discussed include: photometry, polarimetry, and astrometry of comets; detection of water and molecular transitions in comets; ion motions in comet tails; determination of comet brightness and luminosity; and evolution of cometary orbits. Emphasis is placed on analysis of observations of comet Kohoutek.
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Biological Ice Nuclei: They are Everywhere, What are Their Roles? (Invited)
NASA Astrophysics Data System (ADS)
Schnell, R. C.
2009-12-01
Biological ice nuclei active at temperatures warmer than -2C were first observed in the late 1960s associated with decaying grass and tree leaves; discovered more by accident than in a planned experiment. The active component of the decaying leaves was subsequently found to be produced by a few living bacteria, the two most ubiquitous being strains of P. syringae and E. herbicola. The active bacterial ice nuclei are easily deactivated by anaerobic, chemical and heat stresses. The same grass and tree leaves, when well decayed, generally contain less active ice nuclei (threshold temperatures of -5C to - 6C) in the 0.1 micron diameter range compared to the larger (1 micron) bacteria associated ice nuclei. The well decayed leaf litter ice nuclei are stable over a wide range of stresses and time; some samples of leaf derived nuclei stored at room temperature have exhibited the same ice nucleus concentration for over 30 years. Fungi also have active ice nuclei that are stable over many decades. Active ice nuclei are found in marine waters associated with plankton, and are produced by at least one marine dinoflagellate (Heterocapsa niei) that expresses ice nucleus activity almost as warm as terrestrial bacteria ice nuclei. Living ice nucleus bacteria have been found in marine fogs far at sea, in precipitation in Antarctica as well as over many continental areas, in air in the high Arctic, on vegetation around the world, on remote ice bound islands, and growing on and inside water storing vegetation on isolated tropical mountain peaks. But why? What is the evolutionary advantage for the ice nucleus gene to be expressed in such a wide range of environments, by greatly different species? There is an energy cost for bacteria and fungi to support the ice gene, so it probably is not a genetic anomaly. Possibly the ice nuclei play many roles? These could include damaging plants to acquire a food source, an aid in survival and dispersal in clouds, initiation of precipitation to help plant growth, initiating ice formation and subsequent scavenging of water vapor in cold climates (e.g. Arctic and high elevation lichen), living in symbiosis with high elevation vegetation that freezes nightly, and probably a range of others we have not observed or yet hypothesized. Bacterial ice nucleation is truly an intriguing and fantastic phenomenon for which we have just begun to understand.
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Pro-Am Collaboration for Support of NASA Comet ISON Observing Campaign (CIOC)
NASA Astrophysics Data System (ADS)
Yanamandra-Fisher, P. A.; Warner, E.
2013-09-01
From the initial discovery of C/2012 S1 (ISON) by Russian amateur astronomers in September 2012 [1] to the present day, amateur astronomers provide valuable resources of global coverage, data, and legacy knowledge to the professional community. The NASA Comet ISON Observing Campaign (CIOC) has leveraged professional-amateur collaborations via web and social media as part of its mission to facilitate a multi-spectral and multi-facility observation campaign that includes an armada of NASA's ground-based facilities, orbital observatories, and spacecraft. One of the most important goals of these pro-am collaborations is the monitoring of the morphological, photometric, and activity-related evolution of the comet.
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ESA innovation rescues Ultraviolet Observatory
NASA Astrophysics Data System (ADS)
1995-10-01
Astrophysicist Freeman J. Dyson from the Institute for Advanced Studies in Princeton characterizes IUE as "A little half-meter mirror sitting in the sky, unnoticed by the public, pouring out results". By use of the IUE satellite, astronomers obtain access to the ultraviolet radiation of celestial bodies in unique ways not available by any other means, neither from the ground nor by any other spacecraft currently in orbit. IUE serves a wide community of astronomers all over Europe, the United States and many other parts of the world. It allows the acquisition of critical data for fundamental studies of comets and their evaporation when they approach the Sun, of the mechanisms driving the stellar winds which make many stars lose a significant fraction of their mass (before they die slowly as White Dwarfs or in sudden Supernova explosions), as well as in the search to understand the ways in which black holes possibly power the violent nuclei of Active galaxies. One year ago the project was threatened with termination and serious concern was expressed by astronomers about the potential loss of IUE's capabilities, as a result of NASA not continuing to operate the spacecraft. Under the leadership of ESA, the three Agencies involved in the operations of IUE (ESA, NASA and the United Kingdom's Particle Physics and Astronomy Research Council, PPARC), reviewed the operations agreements of the Project. A minor investment allowing the implementation of modern management and engineering techniques as well as a complete revision of the communication infrastructure of the project and continuous improvements in efficiency in the ESA management, also taking advantage of today's technologies, both in computing and communications, have made it possible to continue IUE operations within the financial means available, with ESA taking up most of NASA's share in the operations. According to Dr. Willem Wamsteker, ESA's Dutch IUE Project Scientist, "it was a extremely interesting experience to have the opportunity to do an in-depth review of operational procedures established in 1978 and be given the chance to streamline these through the application of the tools available to engineers and scientists in 1995." The innovative arrangements were designed and developed at the ESA IUE Observatory, which is located in Spain at ESA's Villafranca Satellite Tracking Station in Villanueva de la Canada near Madrid. As a result, ESA is now performing all of WE's science observations (16 hours per day) from the Villafranca station. All the processing of the observations transmitted by the satellite and the subsequent rapid data distribution to the research scientists world-wide is now done from Villafranca. NASA does maintain its role in the programme in the area of operational spacecraft maintenance support, satellite communications and data re-processing for IUE's Final Archive. Thus the IUE Project could be extended and the final IUE observing program can now be implemented. In particular, this will involve critical studies on comets (e,g. on Comet Hale-Bopp), on stellar wind structures, on the enigmatic mini-quasars (which are thought to power the nuclei of Active Galaxies), as well as performing pre- studies which will optimize the utilization of the Hubble Space Telescope. Prof. R.M. Bonnet, Director of the ESA Science Programme comments "I am quite pleased that we have been able to secure the extension of our support for the scientists in Europe and the world to this highly effective mission. Also the scientists can be proud of the utilization of IUE, with more than 3000 learned publications and 200 Doctoral dissertations based on data from IUE. Through this they demonstrate in turn to be very appreciative of our efforts in the Science Programme".
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Correlation Between Cometary Gas/Dust Ratios and Heliocentric Distance
NASA Astrophysics Data System (ADS)
Harrington, Olga; Womack, Maria; Lastra, Nathan
2017-10-01
We compiled CO-based gas/dust ratios for several comets out to heliocentric distances, rh, of 8 au to probe whether there is a noticeable change in comet behavior over the range that water-ice sublimation starts. Previously, gas/dust ratios were calculated for an ensemble of comets using Q(CO2)/efp values derived from infrared measurements, which showed that the gas/dust ratio follows a rh-2 within 4 AU, but is flat at greater distances (Bauer et al. 2015). Our project focuses on gas/dust ratios for which CO is assumed to be the dominant gas, in order to test whether similar breaks in slope occur for CO. The gas/dust ratios were calculated from measurements of CO production rates (mostly from millimeter-wavelength spectroscopy) and reflected sunlight of comets (mostly via reported visual magnitudes of dusty comets). We present our new CO-based gas/dust ratios at different heliocentric distances, compare them to existing CO2-based gas/dust ratios, and discuss implications for CO-driven and CO2-driven activity. We discuss O.H. acknowledges support from the Hartmann Student Travel Grant program. M.W. acknowledges support from NSF grant AST-1615917.
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In Situ Plasma Measurements of Fragmented Comet 73P Schwassmann-Wachmann 3
NASA Astrophysics Data System (ADS)
Gilbert, J. A.; Lepri, S. T.; Rubin, M.; Combi, M.; Zurbuchen, T. H.
2015-12-01
The interiors of comets contain some of the most pristine material in the solar system. Comet 73P/Schwassmann-Wachmann 3, discovered in 1930, is a Jupiter-family comet with a 5.34-year period. This comet split into 5 fragments in 1995 and disintegrated into nearly 70 major pieces in 2006. In 2006 May and June, recently ionized cometary particles originating from fragments including and surrounding some of these major objects were collected with the ACE/SWICS and Wind/STICS sensors. Due to a combination of the instrument characteristics and the close proximity of the fragments passing between those spacecraft and the Sun, unique measurements regarding the charge state composition and the elemental abundances of both cometary and heliospheric plasma were made during that time. The cometary material released from some of these fragments can be identified by the concentrations of water-group pickup ions having a mass-per-charge ratio of 16-18 amu e-1, indicating that while these fragments are small, they are still actively sublimating. We present an analysis of cometary composition, spatial distribution, and heliospheric interactions, with a focus on helium, C+/O+, and water-group ions.
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IN SITU PLASMA MEASUREMENTS OF FRAGMENTED COMET 73P SCHWASSMANN–WACHMANN 3
DOE Office of Scientific and Technical Information (OSTI.GOV)
Gilbert, J. A.; Lepri, S. T.; Combi, M.
2015-12-10
The interiors of comets contain some of the most pristine material in the solar system. Comet 73P/Schwassmann–Wachmann 3, discovered in 1930, is a Jupiter-family comet with a 5.34-year period. This comet split into 5 fragments in 1995 and disintegrated into nearly 70 major pieces in 2006. In 2006 May and June, recently ionized cometary particles originating from fragments including and surrounding some of these major objects were collected with the ACE/SWICS and Wind/STICS sensors. Due to a combination of the instrument characteristics and the close proximity of the fragments passing between those spacecraft and the Sun, unique measurements regarding themore » charge state composition and the elemental abundances of both cometary and heliospheric plasma were made during that time. The cometary material released from some of these fragments can be identified by the concentrations of water-group pickup ions having a mass-per-charge ratio of 16–18 amu e{sup −1}, indicating that while these fragments are small, they are still actively sublimating. We present an analysis of cometary composition, spatial distribution, and heliospheric interactions, with a focus on helium, C{sup +}/O{sup +}, and water-group ions.« less
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Determination of the coma dust back-scattering of 67P for phase angles from 1.2° to 75°
NASA Astrophysics Data System (ADS)
Fink, Uwe; Doose, Lyn
2018-07-01
A phase curve is derived for the dust coma of comet 67P/Churyumov-Gerasimenko (67P) from 1.2° to 74° using images from the OSIRIS camera system on board the Rosetta mission during the period 2014 July 25 to 2015 February 23 as the spacecraft approached the comet. We analyzed 123 images of the continuum filter at 612.6 nm and 60 images of the 375 nm UV continuum filter of the Wide Angle Camera. Our method of extracting a phase curve, close to the nucleus, taking into account illumination conditions, activity of the comet, strong radial radiance intensity decrease and varying phase angles across the image, is described in detail. Our derived backscattering phase curve is considerably steeper than earlier published data. The radiance of the scattering dust in the 612.6 nm filter increases by about a factor of 12 going from a phase angle of 75° to a phase angle of 2.0°. The phase curve for the 375 nm filter is similar but there is reasonable evidence that the I/F color ratio between the two filters changes from a roughly neutral color ratio of 1.2 to a more typical red color of ∼ 2.0 as the activity of the comet increases. No substantial change in the shape of the phase curve could be discerned between 2014 August and 2015 February 19-23 when the comet increased considerably in activity. The phase curve behavior on the illuminated side of the comet and the dark side is in general similar. A comparison of our phase curve with a recent phase curve for 67P by Bertini et al. for the phase angle range ∼15°-80°, where our two reductions overlap, shows good agreement (as does our color ratio between the 612.6 nm and the 375 nm filters) despite the fact that the two phase curve determinations observed the comet at different dust activity levels, at different distances from the nucleus and used completely different observing and data reduction methodologies. Trial scattering calculations demonstrate that the observed strong backscattering most likely arises from particles in the size range 1-20 μm. Our observed backscattering phase curve gives no constraints on the real index of refraction, the particle size distribution or the minimum and maximum particle size cut-offs. However, an upper limit to the imaginary index of refraction of ∼0.01 was required, making these particles quite transparent. Simple spherical scattering calculations including particle size distributions can fit the general characteristics of the phase curve but cannot produce a satisfactory detailed fit.
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Tegos, G; Vargas, C; Perysinakis, A; Koukkou, A I; Christogianni, A; Nieto, J J; Ventosa, A; Drainas, C
2000-11-01
Release of ice nuclei in the growth medium of recombinant Halomonas elongata cells expressing the inaZ gene of Pseudomonas syringae was studied in an attempt to produce cell-free active ice nuclei for biotechnological applications. Cell-free ice nuclei were not retained by cellulose acetate filters of 0.2 microm pore size. Highest activity of cell-free ice nuclei was obtained when cells were grown in low salinity (0.5-5% NaCl, w/v). Freezing temperature threshold, estimated to be below -7 degrees C indicating class C nuclei, was not affected by medium salinity. Their density, as estimated by Percoll density centrifugation, was 1.018 +/- 0.002 gml(-1) and they were found to be free of lipids. Ice nuclei are released in the growth medium of recombinant H. elongata cells probably because of inefficient anchoring of the ice-nucleation protein aggregates in the outer membrane. The ice+ recombinant H. elongata cells could be useful for future use as a source of active cell-free ice nucleation protein.
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Methane clathrates in the solar system.
Mousis, Olivier; Chassefière, Eric; Holm, Nils G; Bouquet, Alexis; Waite, Jack Hunter; Geppert, Wolf Dietrich; Picaud, Sylvain; Aikawa, Yuri; Ali-Dib, Mohamad; Charlou, Jean-Luc; Rousselot, Philippe
2015-04-01
We review the reservoirs of methane clathrates that may exist in the different bodies of the Solar System. Methane was formed in the interstellar medium prior to having been embedded in the protosolar nebula gas phase. This molecule was subsequently trapped in clathrates that formed from crystalline water ice during the cooling of the disk and incorporated in this form into the building blocks of comets, icy bodies, and giant planets. Methane clathrates may play an important role in the evolution of planetary atmospheres. On Earth, the production of methane in clathrates is essentially biological, and these compounds are mostly found in permafrost regions or in the sediments of continental shelves. On Mars, methane would more likely derive from hydrothermal reactions with olivine-rich material. If they do exist, martian methane clathrates would be stable only at depth in the cryosphere and sporadically release some methane into the atmosphere via mechanisms that remain to be determined. In the case of Titan, most of its methane probably originates from the protosolar nebula, where it would have been trapped in the clathrates agglomerated by the satellite's building blocks. Methane clathrates are still believed to play an important role in the present state of Titan. Their presence is invoked in the satellite's subsurface as a means of replenishing its atmosphere with methane via outgassing episodes. The internal oceans of Enceladus and Europa also provide appropriate thermodynamic conditions that allow formation of methane clathrates. In turn, these clathrates might influence the composition of these liquid reservoirs. Finally, comets and Kuiper Belt Objects might have formed from the agglomeration of clathrates and pure ices in the nebula. The methane observed in comets would then result from the destabilization of clathrate layers in the nuclei concurrent with their approach to perihelion. Thermodynamic equilibrium calculations show that methane-rich clathrate layers may exist on Pluto as well. Key Words: Methane clathrate-Protosolar nebula-Terrestrial planets-Outer Solar System. Astrobiology 15, 308-326.
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NASA Technical Reports Server (NTRS)
Nishino, H.
1977-01-01
Unit activity of lateral hypothalamic area (LHA) and Ventromedian nuclei (VMN) was recorded in urethane anesthetized male rats. A 5 to 10 sec. a 3-5 min and a circadian rhythmicity were observed. In about 15% of all neurons, spontaneous activity of LHA and VMN showed reciprocal relationships. Subthreshold stimuli applied at a slow rate in the septum and the suprachiasmatic nuclei (SCN) suppressed the rhythms without changing firing rates. On the other hand, stimulation of the optic nerve at a rate of 5 to 10/sec increased firing rates in 1/3 of neurons of SCN. Iontophoretically applied acetylcholine increased 80% of tested neurons of SCN, whereas norepinephrine, dopamine and 5 HT inhibited 64, 60 and 75% of SCN neurons respectively. These inhibitions were much stronger in neurons, the activity of which was increased by optic nerve stimulation. Stimulation of the SCN inhibited the tonic activity in cervical sympathetic nerves.
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Spectroscopy of asteroids in unusual orbits
NASA Technical Reports Server (NTRS)
Cochran, W. D.; Cochran, A. L.; Barker, E. S.
1986-01-01
Medium-resolution spectroscopy of a collection of nonmain-belt asteroids has been obtained in order to search for possible cometlike spectral features. The asteroids include nine earth approachers, two Trojans, and the unusual object 2060 Chiron. All spectra were obtained and reduced in the same manner as comet data in the McDonald Observatory Faint Comet Survey. No indication of cometary activity was found in any of the asteroids observed.
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The definition of ESA's scientific programme for the 1980's.
NASA Astrophysics Data System (ADS)
Russo, A.
1997-09-01
The following topics were dealt with: discussing a long-term strategy for ESA's scientific activities; the SAC's (Science Advisory Committee) vision of European space science in the 1980s; the role of Spacelab (and Ariane); more money for science?; studying future scientific projects (the comets and the Moon); the selection of ESA's next scientific mission (the comet and the stars, the SPC decision, Giotto and Hipparcos adopted).
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Photometric Modeling of a Cometary Nucleus: Taking Hapke Modeling to the Limit
NASA Technical Reports Server (NTRS)
Buratti, B. J.; Hicks, M. D.; Soderblom, L.; Hillier, J.; Britt, D.
2002-01-01
In the past two decades, photometric models developed by Bruce Hapke have been fit to a wide range of bodies in the Solar System: The Moon, Mercury, several asteroids, and many icy and rocky satellites. These models have enabled comparative descriptions of the physical attributes of planetary surfaces, including macroscopic roughness, particle size and size-distribution, the single scattering albedo, and the compaction state of the optically active portion of the regolith. One challenging type of body to observe and model, a cometary nucleus, awaited the first space based mission to obtain images unobscured by coma. The NASA-JPL Deep Space 1 Mission (DS1) encountered the short-period Jupiter-family comet 19/P Borrelly on September 22, 2001, about 8 days after perihelion. Prior to its closest approach of 2171 km, the remote-sensing package on the spacecraft obtained 25 CCD images of the comet, representing the first closeup, unobscured view of a comet's nucleus. At closest approach, corresponding to a resolution of 47 meters per pixel, the intensity of the coma was less than 1% of that of the nucleus. An unprecedented range of high solar phase angles (52-89 degrees), viewing geometries that are in general attainable only when a comet is active, enabled the first quantitative and disk-resolved modeling of surface photometric physical parameters.
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Time travel and chemical evolution - A look at the outer solar system
NASA Astrophysics Data System (ADS)
Owen, T.
1987-12-01
It has been hypothesized that the chemical conditions today on the planets and moons of the outer solar system are similar to conditions on earth soon after it formed. If this is so, much can be learned about the chemistry that led to life on earth. While Jupiter is a poor terrestrial analog, its satellite Europa has a smooth icy surface that may cover a layer of liquid water tens of kilometers deep. It is possible that sunlight could filter through cracks in the ice, providing energy to drive chemical reactions in the water below the ice. It is noted that the surface of Titan may include lakes or oceans of ethane and that Triton may also have liquids on its surface. Studies of cometary nuclei will be undertaken during the Comet Rendezvous-Asteroid Flyby mission.