Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

1993-07-01

Concerning comets: 1955 III Mrkos, 1955 IV Bakharev-Macfarlane-Krienke, 1955 V Honda, 1956 III Mrkos, 1956 IV P/Olbers, 1957 V Mrkos, 1961 II Candy, 1961 V Wilson-Hubbard, 1962 III Seki-Lines, 1962 V P/Tuttle-Giacobini-Kresák, 1963 I Ikeya, 1963 III Alcock, 1964 VI Tomita-Gerber-Honda, 1964 IX Everhart, 1965 VIII Ikeya-Seki, 1966 II Barbon, 1966 V Kilston, 1967 III Wild, 1967 IV Seki, 1967 V P/Tuttle, 1967 X P/Tempel 2, 1970 I Daido-Fujikawa, 1975 IX Kobayashi-Berger-Milon, 1979 X Bradfield, 1986 III P/Halley, 1989 X P/Brorsen-Metcalf, 1989 XIX Okazaki-Levy-Rudenko, 1990 III Cernis-Kiuchi-Nakamura, 1990 V Austin, 1990 XIV P/Honda-Mrkos-Pajdušáková, 1990 XVII Tsuchiya-Kiuchi, 1990 XX Levy, 1990 XXI P/Encke, 1990 XXVIII P/Wild 2, 1991 XI P/Levy, 1991 XV P/Hartley 2, 1991a1 Shoemaker-Levy, 1992h Spacewatch, 1992l P/Giclas, 1992n P/Schuster, 1992ο P/Daniel, 1992s P/Ciffréo, 1992t P/Swift-Tuttle, 1992u P/Väisälä 1, 1992x P/Schaumasse, 1992y Shoemaker, 1992a1 Ohshita, 1993a Mueller, 1993e P/Shoemaker-Levy 9, P/Smirnova-Chernykh, P/Schwassmann-Wachmann 1.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

1993-10-01

Concerning comets: 1955 III Mrkos, 1955 IV Bakharev-Macfarlane-Krienke, 1955 V Honda, 1956 III Mrkos, 1956 IV P/Olbers, 1957 III Arend-Roland, 1957 V Mrkos, 1958 III Burnham, 1959 VIII P/Giacobini-Zinner, 1960 II Burnham, 1973 XII Kohoutek, 1974 III Bradfield, 1975 IX Kobayashi-Berger-Milon, 1975 X Suzuki-Saigusa-Mori, 1975 XI Bradfield, 1975 XII Mori-Sato-Fujikawa, 1976 IV Bradfield, 1976 VI West, 1979 VII Bradfield, 1980 X P/Stephan-Oerma, 1980 XII Meier, 1980 XIII P/Tuttle, 1981 II Panther, 1981 IV P/Borrelly, 1981 XIX P/Swift-Gehrels, 1982 I Bowell, 1982 IV P/Grigg-Skjellerup, 1982 VI Austin, 1982 VII P/d'Arrest, 1982 VIII P/Churyumov-Gerasimenko, 1983 V Sugano-Saigusa-Fujikawa, 1983 VII IRAS-Araki-Alcock, 1983 X P/Tempel 2, 1983 XI P/Tempel 1, 1983 XIII P/Kopff, 1983 XIV P/IRAS, 1983 XV Shoemaker, 1984 III P/Hartley-IRAS, 1984 IV P/Crommelin, 1984 XI P/Faye, 1984 XIII Austin, 1984 XIV P/Wild 2, 1984 XVI P/Shoemaker 1, 1984 XXIII Levy-Rudenko, 1985 I P/Tsuchinshan 1, 1985 XIII P/Giacobini-Zinner, 1985 XV P/Giclas, 1985 XVI P/Ciffréo, 1985 XVII Hartley-Good, 1985 XVIII P/Shoemaker 3, 1985 XIX Thiele, 1986 I P/Boethin, 1986 III P/Halley, 1986 VIII P/Machholz, 1986 XVII Levy, 1986 XVIII Terasako, 1987 II Sorrells, 1987 VII Wilson, 1987 XIX P/Schwassmann-Wachmann 2, 1987 XXI Levy, 1987 XXIII Rudenko, 1987 XXIV P/Brooks 2, 1987 XXVII P/Kohoutek, 1987 XXIX Bradfield, 1988 IV Furuyama, 1988 XIV P/Tempel 2, 1989 III Shoemaker, 1989 XV P/Schwassmann-Wachmann 1, 1989 XIX Okazaki-Levy-Rudenko, 1990 V Austin, 1990 XVII Tsuchiya-Kiuchi, 1990 XX Levy, 1990 XXI P/Encke, 1990 XXVI Arai, 1991 I P/Metcalf-Brewington, 1991 XV P/Hartley 2, 1991 XVII P/Arend-Rigaux, 1991a1 Shoemaker-Levy, 1991g1 Zanotta-Brewington, 1992c P/Howell, 1992d Tanaka-Machholz, 1992e P/Singer Brewster, 1992f P/Shoemaker-Levy 8, 1992h Spacewatch, 1992j P/Ashbrook-Jackson, 1992t P/Swift-Tuttle, 1992u P/Väisälä 1, 1992w P/Slaughter-Burnham, 1992x P/Schaumasse, 1992y Shoemaker, 1993a Mueller, 1993d Mueller, 1993e P/Shoemaker-Levy 9, 1993f P/Forbes, 1993i P/Holmes, 1993j P/Neujmin 3, 1993k P/Shajn-Schaldach, 1993l P/Helin-Lawrence, 1993m P/Hartley 3, 1993n P/Whipple, 1993ο P/West-Kohoutek-Ikemura, 1993p Mueller, P/Smirnova-Chernykh.

The Disruption and Demise of Periodic Comet Shoemaker-Levy 9

NASA Technical Reports Server (NTRS)

Asphaug, Erik; Benz, Willy; Cuzzi, Jeffrey (Technical Monitor)

1994-01-01

The impact of the fragmented comet Shoemaker-Levy 9 (SL9) into Jupiter this July promises to change our understanding of the outer solar system. More than twenty mountain-sized conglomerates of ice and rock will hit the atmosphere at approx. 50 km/s over the course of a week beginning July 16, releasing approx. 10(exp 4) to 10(exp8) megatons of energy per burst, and providing unique and perhaps pivotal clues to the properties of comets and the physics of massive atmospheres. Because the fragments will strike the far side of Jupiter, data acquisition, analysis and interpretation will be quite sensitive to the actual size and energy of the fragments. We therefore examine an event which took place two summers ago, unnoticed and unobserved: the disruption of SL9 into a "string of pearls' as it passed within the Roche limit at perijove. We first demonstrate, on the basis of timescales of tidal interaction, that the comet could not have broken into 20+ fragments through a hierarchy of brittle fracture events. Next, noting that the tidal stress was too weak to have even fragmented an uncompressed mass of freshly fallen snow, we run models for a strengthless comet held together only by self-gravity. We explore the initial size, density, and rotation. We conclude that a 4 km diameter comet (smaller if a prograde rotator) of density approx. 0.5 g/cu cm disrupts and disperses into a chain of fragments similar to Shoemaker-Levy 9, whether we begin with 21, 85, 169, 700 or 2000 sub-grains. Gravitational reaccumulation is evidently the answer, and there is no need to invoke the presence of 21 "cometesimals" as the subscale of the comet. To explain how a comet can be weaker than uncompacted snow, we show that the ring-plane crossing prior to perijove could have caused total damage. Finally, we compute the tidal stress on impactors as they approach Jupiter this July. Objects of various density are moderately distorted but not disrupted by the time they strike the planet.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

1993-01-01

Concerning comets: 1973 XII Kohoutek, 1975 IX Kobayashi-Berger-Milon, 1976 VI West, 1976 XI P/d'Arrest, 1977 XIV Kohler, 1979 X Bradfield, 1980 X P/Stephan-Oterma, 1980 XV Bradfield, 1981 II Panther, 1982 VI Austin, 1983 V Sugano-Saigusa-Fujikawa, 1983 VII IRAS-Araki-Alcock, 1983 XIII P/Kopff, 1984 XIII Austin, 1984 XXIII Levy-Rudenko, 1985 XIII P/Giacobini-Zinner, 1985 XVII Hartley-Good, 1985 XIX Thiele, 1986 I P/Boethin, 1986 III P/Halley, 1986 XVIII Terasako, 1987 II Sorrells, 1987 III Nishikawa-Takamizawa-Tago, 1987 X P/Grigg-Skjellerup, 1987 XXIII Rudenko, 1987 XXIX Bradfield, 1987 XXXII McNaught, 1987 XXXIII P/Borrelly, 1988 IV Furuyama, 1988 V Liller, 1988 XIV P/Tempel 2, 1988 XV Machholz, 1988 XX Yanaka, 1988 XXIV Yanaka, 1989 X P/Brorsen-Metcalf, 1989 XV P/Schwassmann-Wachmann 1, 1989 XIX Okazaki-Levy-Rudenko, 1989 XXI Helin-Roman-Alu, 1989 XXII Aarseth-Brewington, 1990 III Černis-Kiuchi-Nakamura, 1990 VI Skorichenko-George, 1990 VIII P/Schwassmann-Wachmann 3, 1990 IX P/Peters-Hartley, 1990 X P/Wild 4, 1990 XIV P/Honda Mrkos-Pajdušáková, 1990 XVII Tsuchiya-Kiuchi, 1990 XXI P/Encke, 1990 XXVI Arai, 1991 XI P/Levy, 1991 XV P/Hartley 2, 1991 XVI P/Wirtanen, 1991 XVII P/Arend-Rigaux, 1991 XXI P/Faye, 1991 XXIII P/Shoemaker 1, 1991 XXIV Shoemaker-Levy, 1991l Helin-Lawrence, 1991ο P/Chernykh, 1991r Helin-Alu, 1991a1 Shoemaker-Levy, 1991g1 Zanotta-Brewington, 1991h1 Mueller, 1912d Tanaka-Machholz, 1992f P/Shoemaker-Levy 8, 1992k Machholz, 1992l P/Giclas, 1992p P/Brewington, 1992q Helin-Lawrence, 1992s P/Ciffréo, 1992t P/Swift-Tuttle, 1992u P/Väisälä, 1992x P/Schaumasse, 1992y Shoemaker, 1992a1 Ohshita, 1993a Mueller, P/Smirnova-Chernykh.

Evolution of the P/Shoemaker-Levy 9 Gang

NASA Image and Video Library

1998-05-02

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. http://photojournal.jpl.nasa.gov/catalog/PIA01264

Hubble Space Telescope observations of comet P/Shoemaker-Levy 9 (1993e)

USGS Publications Warehouse

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.

Radiative signals from impact of Shoemaker-Levy on Jupiter

NASA Technical Reports Server (NTRS)

Ahrens, Thomas J.; Orton, Glenn S.; Takata, Toshiko; Okeefe, John D.

1994-01-01

The temperature and internal energy fields calculated by Takata et al. in the plume are used to calculate the greybody thermal radiation emitted versus wavelength to predict what might be observed by several spectral sensors operating from different platforms when fragments of Comet Shoemaker-Levy 9 (SL-9) impact Jupiter in July 1994. A SPH code was used by Takata et al. to calculate the full three dimensional flow and thermodynamic fields in the comet fragment and the atmosphere of Jupiter. We determined the fragment penetration depth, energy partitioning between the atmosphere and the impactor, and energy density deposited per unit length over the trajectory. Once the impactor had disintegrated and stopped, and the strong atmospheric shock decayed, the flow is driven by buoyancy effects. We then used our SPH code to calculate the flow and thermodynamic fields: pressure, article velocity, temperature, and internal energy distributions in the plume. The calculations for 2 and 10 km cometary fragments yield maximum deposition depths of approximately 175 and 525 km, respectively (1 bar = 0 km depth). We also calculated that 0.7 and 0.6 of the initial kinetic energy of the 10 and 2 km bolides, respectively, are deposited as internal energy in Jupiter's atmosphere.

Tidal disruption and the appearance of periodic comet Shoemaker-Levy 9

NASA Technical Reports Server (NTRS)

Sekanina, Z.; Chodas, P. W.; Yeomans, D. K.

1994-01-01

A unified model is formulated to interpret quantitatively the observed characteristics of the nuclear train, the two dust trails, and the tail region of P/Shoemaker-Levy 9 in terms of a collisionally modified rotation velocity distribution of the comet's debris. Since there is no evidence for the comet's out-gassing, the model does not assume activity. The discruption of the parent comet was due primarily to tidal stesses during its extremely close approach to Juptier in July 1992. The original nucleus is found to have been most probably approximately 5 km in radius or, equivalently, approximately 10(exp 17) g in mass. The dynamical separation of the debris occurred apparently approximately 2.2 hr after the perijove passage, even though the actual fragmentation of the original mass is likely to have begun before closest approach. Physical breakp was accompanied by ubiquitous low-velocity collisions among the particulates, resulting in a rearrangement of the initial rotaional velocities into a rapidly 'thermalized' distribution, characterized by a long tail of relatively high velocities for the debris that populates the dust trails far from the nuclear train. Compelling evidence is presented for secondary fragmentation events, indicative of the comet's continuing disintegration. Secondary fragmentation may be caused by rotational bursting of the massive fragments that had been cracked but unbroken during the tidal disruption. Impact conditions and possible interactions of the comet's debris with the jovian system during the encounter in July 1994 are described.

MONTH-LONG EVOLUTION OF THE D/G JUPITER IMPACT SITES FROM COMET P/SHOEMAKER-LEVY 9

NASA Technical Reports Server (NTRS)

2002-01-01

This series of snapshots, taken with NASA's Hubble Space Telescope, shows evolution of the comet P/Shoemaker-Levy 9 impact region called the D/G complex. This feature was produced by two nuclei of comet P/Shoemaker-Levy 9 that collided with Jupiter on 17 and 18 July 1994, respectively, and was later modified again by the impact of the S fragment on 21 July 1994. Upper Left: This first image was taken about 90 minutes after the G impact on 18 July 1994. Nearly all of the structure in this image was created by the impact of fragment G, although a small dark spot to the left was the remainder of small fragment D that collided one day earlier. The explosion of the nucleus in Jupiter's atmosphere created the unique ring structure, which may be analogous to a 'sonic boom' on earth. Though this structure is best seen for the G impact, it is not unique. Hubble reveals similar rings around several other fresh impact sites. They are all clear evidence for coherent outward motion of this wave phenomena. Upper right: This second image, obtained on 23 July, shows that the Jovian winds have swept the material into a striking 'curly-cue' structure. Lower left, right: The structure seen in earlier views has disappeared rapidly in the images taken on 30 July and 24 August, respectively. Almost all of the changes between the images are due to Jupiter's east-west winds that play a key role in the dispersing of the dark material. Hubble Space Telescope's high resolution will allow astronomers to continue to trace the impact debris as it is transported by the Jovian winds. This information promises to advance current understanding of the physics of Jupiter's atmosphere. These black and white images were taken in near-ultraviolet light with the Wide Field Planetary Camera 2. They have been processed to correct for the curvature of Jupiter, so that the impact region appears flat, as if the viewer were hovering directly overhead. Each image is centered on -46 degrees latitude and 28 degrees. The north-south extent in the image spans from -26 to -66 deg. latitude and the east-west extent of the region spans +/- 30 degrees on either side of 28 degrees longitude. credit: H. Hammel, MIT and NASA

Modeling of the Plume Development Phase of the Shoemaker-Levy 9 Comet Impact

NASA Astrophysics Data System (ADS)

Palotai, Csaba J.; Korycansky, D.; Deming, D.; Harrington, J.

2008-09-01

We present a progress report on our numerical simulations of the plume blowout and flight/splash phases of the Shoemaker-Levy 9 (SL9) comet impact into Jupiter's atmosphere. For this project we have modified the ZEUS-MP/2 three-dimensional hydrodynamic model (Hayes et al. ApJ.SS. 165. 174-183, 2006) to be suitable for Jovian atmospheric simulations. To initialize our model we map the final state of high-resolution SL9 impact simulations of Korycansky et al. (ApJ 646. 642-652, 2006) onto our larger, stationary grid. In the current phase of the research we investigate how the dynamical chaos in the impact model affects simulations of the subsequent phases. We adapt the atmospheric radiation model from the 2D splash calculation of Deming and Harrington (ApJ 561. 455-467, 2001) to calculate realistic wavelength-dependent lightcurves and low-resolution spectra. Our goal is to compare synthetic images created from model output to the data taken by the Hubble Space Telescope of plumes on the limb of Jupiter during the impacts of various SL9 fragments (Hammel et al. Science 267. 1288-1296, 1995). Details of the model, validation of the code, and results of our latest simulations will be presented. This material is based on work supported by National Science Foundation Grant No. 0307638 and National Aeronautics and Space Administration Grant No. NNG 04GQ35G .

Ups and downs in planetary science

USGS Publications Warehouse

Shoemaker, Carolyn S.

1999-01-01

The field of planetary science as it developed during the lifetimes of Gene and Carolyn Shoemaker has sustained a period of exciting growth. Surveying the skies for planet-crossing asteroids and comets and studying the results of their impact upon the planets, especially the Earth, was for Gene and Carolyn an intense and satisfying quest for knowledge. It all started when Gene envisioned man going to the Moon, especially himself. After that, one thing led to another: the study of nuclear craters and a comparison with Meteor Crater, Arizona; the Apollo project and a succession of unmanned space missions to the inner and outer planets; an awareness of cratering throughout our solar system; the search for near-Earth asteroids and comets; a study of ancient craters in Australia; and the impact of Shoemaker-Levy 9 on Jupiter. The new paradigm of impact cratering as a cause for mass extinction and the opening of space for the development of new life forms have been causes to champion.

Mid-IR Spectroscopy of the Jovian Stratosphere perturbed by comet P/Shoemaker-Levy 9 Impact

NASA Technical Reports Server (NTRS)

Hunten, Don M.; Sprague, A. L.; Bjoraker, G. L.; Witteborn, F. C.; Kozlowski, R. W. H.; Wooden, D. H.

1996-01-01

The objective was to obtain spectra from 5 to 14 micron before, during, and after the impacts. We were awarded 2 flights of the KAO which was based in Melbourne, Australia for the events. Impacts R and W were covered, and the observations were completely successful. A paper reporting the observation of water vapor is in press, and other work is in progress as limited funding permits. The text of this report is adapted from that of the Icarus paper.

The Encounter of P/Shoemaker-Levy 9 with the Jovian Plasma and Extended Sodium Cloud

NASA Technical Reports Server (NTRS)

Niciejewski, R. J.

1997-01-01

The encounter of comet P/Shoemaker-Levy 9 with Jupiter during July, 1994, provided an unprecedented opportunity to observe any potential perturbations in the Jovian plasma torus and extended sodium cloud as the comet entered the planet's atmosphere. Though the most obvious affect of the encounter was the distinctive response of the visible disk to the impact of the cometary fragments, the potential disruptions to the extended Jovian atmosphere and the restoration of the system to equilibrium also provided a test for the current interpretation of the Jovian plasma torus and sodium magneto-nebula. The observations that were performed for this grant were made by a complementary group of researchers and could not have been made if the individuals worked singly. In a sense, the exciting opportunity provided by this astronomical event also provided a mechanism to test the potential of pooling limited resources from several sources to construct a state-of-the-art spectrally resolving instrument, to acquire the necessary time and resources from institutions that maintain world-class optical telescopes, to perform the observations with the assistance of students, and to analyze the data sets.

Numerical Simulations Of The Impact Of Comet Shoemaker-Levy 9: Plume Development

NASA Astrophysics Data System (ADS)

Palotai, Csaba J.; Korycansky, D.; Deming, D.; Harrington, J.; Reese, C.

2007-10-01

We present results of our three-dimensional, hydrodynamic simulations of the impact of comet Shoemaker-Levy 9 (SL9) into the atmosphere of Jupiter. In the current phase of the research we focus on the plume blowout and splashback phases of the SL9 event. We have modified the Zeus-MP/2 model (Hayes et al. 2006) to be suitable for our investigation, adding a Jovian atmospheric profile, Tillotson equation of state for the impactor, and the Coriolis terms. As an initial condition of our high-resolution simulations we use the energy deposition profile taken from the SL9 impact modeling of Korycansky et al. (2006). The effects of the Coriolis force during the shockwave propagation are tested through sensitivity tests. The viscosity in the splash model is adjusted until the outer part of the plume re-entry shock matches the expanding infrared rings (McGregor et al. 1996). The molecular viscosity being well-known, this will place a strong constraint on the Jovian eddy viscosity. We add radiative terms from previous 2D splash calculation of Deming and Harrington (2001) to allow us to calculate realistic wavelength-dependent lightcurves and low-resolution spectra for direct comparison to data. This work is supported by National Science Foundation Grant No. 0307638 and National Aeronautics and Space Administration Grant No. NNG 04GQ35G.

Month-long Evolution of the D/G Jupiter Impact Sites from Comet P/Shoemaker-Levy 9

NASA Technical Reports Server (NTRS)

1994-01-01

This series of snapshots, taken with NASA's Hubble Space Telescope, shows evolution of the comet P/Shoemaker-Levy 9 impact region called the D/G complex. This feature was produced by two nuclei of comet P/Shoemaker-Levy 9 that collided with Jupiter on 17 and 18 July 1994, respectively, and was later modified again by the impact of the S fragment on 21 July 1994.

Upper Left: This first image was taken about 90 minutes after the G impact on 18 July 1994. Nearly all of the structure in this image was created by the impact of fragment G, although a small dark spot to the left was the remainder of small fragment D that collided one day earlier. The explosion of the nucleus in Jupiter's atmosphere created the unique ring structure, which may be analogous to a 'sonic boom' on Earth. Though this structure is best seen for the G impact, it is not unique. Hubble reveals similar rings around several other fresh impact sites. They are all clear evidence for coherent outward motion of this wave phenomena.

Upper right: This second image, obtained on 23 July, shows that the Jovian winds have swept the material into a striking 'curly-cue' structure.

Lower left, right: The structure seen in earlier views has disappeared rapidly in the images taken on 30 July and 24 August, respectively. Almost all of the changes between the images are due to Jupiter's east-west winds that play a key role in the dispersing of the dark material.

Hubble Space Telescope's high resolution will allow astronomers to continue to trace the impact debris as it is transported by the Jovian winds. This information promises to advance current understanding of the physics of Jupiter's atmosphere.

These black and white images were taken in near-ultraviolet light with the Wide Field Planetary Camera 2. They have been processed to correct for the curvature of Jupiter, so that the impact region appears flat, as if the viewer were hovering directly overhead. Each image is centered on -46 degrees latitude and 28 degrees. The north-south extent in the image spans from -26 to -66 deg. latitude and the east-west extent of the region spans +/- 30 degrees on either side of 28 degrees longitude.

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/

Plasma effects on the interaction of a comet with Jupiter

NASA Technical Reports Server (NTRS)

Kellogg, Paul J.

1994-01-01

I consider some plasma effects to be expected when the fragments of Comet Shoemaker-Levy 9 crash into Jupiter. Emphasis is put on pre-impact effects, and on the possibility of significant radio emission. It is shown than an ionizing shock will develop at altitudes below about 600 km, and that significant ionization will exist above that altitude. The incoming comet and its surroundings will then represent a rapidly moving conductor in a strong magnetic field and will induce large currents in Jupiter's magnetosphere, similar both qualitatively and quantitatively to a way in which Io interacts with Jupiter's magnetic field and with the plasma of the torus. This process is thought to be involved in the generation of decametric radiation, so that the impact of the comet may also produce such radiation. The power involved in this interaction is estimated to be at least 1/15th of the power due to Io, and its duration to be for 10-20 s before the comet's impact with the surface of Jupiter.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

Concerning comets: 1962 VIII Humason, 1971 V Toba, 1975 XI Bradfield, 1979 X Bradfield, 1980 X P/Stephan-Oterma, 1980 XI P/Encke, 1980 XIII P/Tuttle, 1981 II Panther, 1982 VI Austin, 1982 VIII P/Churyumov-Gerasimenko, 1983 V Sugano-Saigusa-Fujikawa, 1983 VII IRAS-Araki-Alcock, 1983 XIII P/Kopff, 1984 III P/Hartley-IRAS, 1985 XIII P/Giacobini-Zinner, 1985 XVII Hartley-Good, 1985 XIX Thiele, 1986 III P/Halley, 1986h P/Schwassmann-Wachmann 2, 1986j P/Comas Solá, 1986k P/Kohoutek, 1986l Wilson, 1986m P/Grigg-Skjellerup, 1986n Sorrells, 1987h P/Howell, 1987l P/Reinmuth 2, 1987m P/Brooks 2, 1987n P/Harrington, 1987p P/Borrelly, 1987r P/Reinmuth 1, 1987s Bradfield, 1987u Rudenko, 1987y Levy, 1987z P/Shoemaker-Holt, 1987b1 McNaught, 1987d1 Ichimura, 1987f1 Furuyama, 1988a Liller, 1988b Shoemaker, 1988c Maury-Phinney, 1988e Levy, P/Schwassmann-Wachmann 1.

Comet Shoemaker-Levy-9 impact with Jupiter: Aeronomical predictions

NASA Technical Reports Server (NTRS)

Cravens, T. E.

1994-01-01

The fragments of comet Shoemaker-Levy-9 will enter the atmosphere of Jupiter during July 20-26, 1994. Significant amounts of water vapor will be injected into the upper atmosphere of Jupiter either from the comet itself or from the lower atmosphere of Jupiter. The photochemistry of both the neutral gas and the ionosphere will be greatly altered by the influx of this water vapor or the atomic oxygen generated by the dissociation of the water. Enhanced abundances of H2O (or other species such as NH3) in the atmosphere above the homopause should persist for at least a year and should be globally distributed. The odd oxygen (i.e., O or H2O or OH) associated with the cometary water influx alters the ion chemistry by removing H(+) ions, which also has the effect of reducing the ionospheric electron density because H(+) is ordinarily the main ion species in the Jovian ionosphere. The density of H3(+), both in the auroral and non-auroral ionosphere, will also be reduced due to presence of water. This ion species has been detected spectroscopically at Jupiter, and a drop in its abundance should be detectable. The major ion species will become H3O(+) which could reach a peak density as high as 10(exp 4)/cu cm in the non-auroral ionosphere and 10(exp 5)/cu cm in the auroral ionosphere. It should be possible to detect this ion species spectroscopically from Earth-based observatories.

ARC-1994-AC94-0353-2B

NASA Image and Video Library

1994-07-01

Photo Artwork composite by JPL This depiction of comet Shoemaker-Levy 9 impacting Jupiter is shown from several perspectives. IMAGE B shows the perspective from Galileo spacecraft which can observe the impact point directly. For visual appeal, most of the large cometary fragments are shown close to one another in this image. At the time of Jupiter impact, the fragments will be separated from one another by serveral times the distances shown. This image was created by D.A. Seal of JPL's Mission Design Section using orbital computations provIded by P.W. Chodas and D.K. Yeomans of JPL's Navigation Section.

Tidal Forces as Drivers of Collisional Evolution

NASA Technical Reports Server (NTRS)

Asphaug, E.; Agnor, C.; Williams, Q.

2005-01-01

Planetary collisions are usually understood as shock-related phenomena, analogous to impact cratering. But at large scales, where the impact timescale is comparable to the gravitational timescale, collisions can be dominated by gravitational torques and disruptive tides. Shock physics fares poorly, in many respects, in explaining asteroid and meteorite genesis. Melts, melt residues, welded agglomerates and hydrous and gasrich phases among meteorites lead to an array of diverse puzzles whose solution might be explained, in part, by the thermomechanics of tidal unloading. Comet Shoemaker-Levy 9 disrupted in a process that is common in the present and ancestral solar system, so here we consider specific effects tidal disruption had on the evolution of asteroids, comets and meteorites the unaccreted residues of planet formation.

SPH Calculations of Comet Shoemaker-Levy-9/Jupiter Impact

NASA Astrophysics Data System (ADS)

Wingate, C. A.; Hoffman, N. M.; Stellingwerf, R. F.

1994-05-01

The impact of Comet Shoemaker-Levy 9 has been simulated in 2D axisymmetric geometry and full 3D using the Los Alamos Smooth Particle Hydrodynamics code (SPHINX). The objective of this study is to calculate energy deposition profiles and fireball evolution histories for a range of comet parameters. We hope to use these results to infer comet properties from observations. The modeling proceeds in two phases. In Phase I, the collision of the incoming fragment, or bolide, is calculated, and its kinetic energy profile is differentiated to give an energy deposition profile. The deposition profile is used as input to Phase II (see companion paper by Stellingwerf et al.) in which the fireball evolution is calculated. Two different bolide densities were simulated, 0.2 g/cm(3) and 0.92 g/cm(3) . The incoming bolide velocity was 60 km/sec and the impact angle was taken to be 45 degrees. Since the calculation is 2D, this means simply that the bolide's depth in the atmosphere is equal to its distance traveled times the cosine of 45 degrees. The baseline calculation assumed a spherical bolide with a diameter of 1 km. Various physical models were used for the bolide including perfect gas equations of state (eos), more realistic eos's and strength of materials. The model for the Jupiter atmosphere was a fit to the Orton atmosphere. The eos for the atmosphere for most of the calculations was taken to be a perfect gas with a gamma of 1.2. A sesame tabular eos was also used. Rather than modeling the entire atmosphere, small sections were modeled using blocks of particles with blocks being shuffled in and out as the calculation progressed. Calculations were done with different size sections to test the sensitivity of the results to this procedure. The results indicate energy deposition for the 0.2 density, 1 km diameter case occurring between 50-200 km. The penetration is seen to increase somewhat as the bolide resolution is improved.

Generation Mechanisms UV and X-ray Emissions During SL9 Impact

NASA Technical Reports Server (NTRS)

Waite, J. Hunter, Jr.

1997-01-01

The purpose of this grant was to study the ultraviolet and X-ray emissions associated with the impact of comet Shoemaker-Levy 9 with Jupiter. The University of Michigan task was primarily focused on theoretical calculations. The NAGW-4788 subtask was to be largely devoted to determining the constraints placed by the X-ray observations on the physical mechanisms responsible for the generation of the X-rays. Author summarized below the ROSAT observations and suggest a physical mechanism that can plausibly account for the observed emissions. It is hoped that the full set of activities can be completed at a later date. Further analysis of the ROSAT data acquired at the time of the impact was necessary to define the observational constraints on the magnetospheric-ionospheric processes involved in the excitation of the X-ray emissions associated with the fragment impacts. This analysis centered around improvements in the pointing accuracy and improvements in the timing information. Additional pointing information was made possible by the identification of the optical counterparts to the X-ray sources in the ROSAT field-of-view. Due to the large number of worldwide observers of the impacts, a serendipitous visible plate image from an observer in Venezuela provided a very accurate location of the present position of the X-ray source, virtually eliminating pointing errors in the data. Once refined, the pointing indicated that the two observed X-ray brightenings that were highly correlated in time with the K and P2 events were brightenings of the X-ray aurora (as identified in images prior to the impact).Appendix A "ROSAT observations of X-ray emissions from Jupiter during the impact of comet Shoemaker-Levy 9' also included.

Time-resolved photometry of Io and Europa in the course of impacts of A and Q secondary nuclei of D/comet Shoemaker-Levy 9.

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.

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.

ARC-1994-AC94-0353-2A

NASA Image and Video Library

1994-07-01

Photo Artwork composite by JPL This depiction of comet Shoemaker-Levy 9 impacting Jupiter is shown from several perspectives. IMAGE A is shown from the perspective of Earth based observers. For visual appeal, most of the large cometary fragments are shown close to one another in this image. At the time of Jupiter impact, the fragments will be separated from one another by serveral times the distances shown. This image was created by D.A. Seal of JPL's Mission Design Section using orbital computations provIded by P.W. Chodas and D.K. Yeomans of JPL's Navigation Section.

ARC-1994-AC94-0353-2D

NASA Image and Video Library

1994-07-01

Photo Artwork composite by JPL This depiction of comet Shoemaker-Levy 9 impacting Jupiter is shown from several perspectives. IMAGE D depicts a generic view from Jupiter's south pole. For visual appeal, most of the large cometary fragments are shown close to one another in this image. At the time of Jupiter impact, the fragments will be separated from one another by serveral times the distances shown. This image was created by D.A. Seal of JPL's Mission Design Section using orbital computations provIded by P.W. Chodas and D.K. Yeomans of JPL's Navigation Section.

Rocket FUV Observations of the Io Plasma Torus During the Shoemaker-Levy/9 Impacts

NASA Technical Reports Server (NTRS)

Stern, S. A.; Slater, D.; Cash, W.; Wilkinson, E.; Green, J.; Gladstone, R.

1995-01-01

We observed the Io torus from 820-1140 A on universal time (UT) 20.25 July 1994 from a sounding rocket telescope/spectrograph. These observations serve as only the fourth published spectrum of the torus in this wavelength range, and the only far ultraviolet (FUV) data documenting the state of the torus during the Shoemaker Levy 9 Impacts.

Tidal disruption of Periodic Comet Shoemaker-Levy 9 and a constraint on its mean density

NASA Technical Reports Server (NTRS)

Boss, Alan P.

1994-01-01

The apparent tidal disruption of Periodic Comet Shoemaker-Levy 9 (1993e) during a close encounter within approximately 1.62 planetary radii of Jupiter can be used along with theoretical models of tidal disruption to place an upper bound on the density of the predisruption body. Depending on the theoretical model used, these upper bounds range from rho(sub c) less than 0.702 +/- 0.080 g/cu cm for a simple analytical model calibrated by numerical smoothed particle hydrodynamics (SPH) simulations to rho(sub c) less than 1.50 +/- 0.17 g/cu cm for a detailed semianalytical model. The quoted uncertainties stem from an assumed uncertainty in the perijove radius. However, the uncertainty introduced by the different theoretical models is the major source of error; this uncertainty could be eliminated by future SPH simulations specialized to cometary disruptions, including the effects of initially prolate, spinning comets. If the SPH-based upper bound turns out to be most appropriate, it would be consistent with the predisruption body being a comet with a relatively low density and porous structure, as has been asserted previously based on observations of cometary outgassing. Regardless of which upper bound is preferable, the models all agree that the predisruption body could not have been a relatively high-density body, such as an asteroid with rho approximately = 2 g/cu cm.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

1999-07-01

Concerning comets: C/1995 O1 (Hale-Bopp), C/1996 J1 (Evans-Drinkwater), C/1997 BA6 (Spacewatch), C/1997 D1 (Mueller), C/1997 H2 (SOHO), C/1997 J1 (Mueller), C/1997 J2 (Meunier-Dupouy), C/1997 N1 (Tabur), C/1997 O1 (Tilbrook), C/1997 T1 (Utsunomiya), C/1998 H1 (Stonehouse), C/1998 J1 (SOHO), C/1998 K1 (Mueller), C/1998 K2 (LINEAR), C/1998 K5 (LINEAR), C/1998 M1 (LINEAR), C/1998 M2 (LINEAR), C/1998 M3 (Larsen), C/1998 M4 (LINEAR), C/1998 M5 (LINEAR), C/1998 P1 (Williams), C/1998 T1 (LINEAR), C/1998 U5 (LINEAR), C/1999 F1 (Catalina), C/1999 F2 (Dalcanton), C/1999 H1 (Lee), C/1999 H3 (LINEAR), C/1999 J2 (Skiff), C/1999 J3 (LINEAR), C/1999 J4 (LINEAR), C/1999 K2 (Ferris), C/1999 K3 (LINEAR), C/1999 K5 (LINEAR), C/1999 K6 (LINEAR), C/1999 K7 (LINEAR), C/1999 K8 (LINEAR), C/1999 L2 (LINEAR), C/1999 N2 (Lynn), 2P/Encke, 9P/Tempel 1, 10P/Tempel 2, 21P/Giacobini-Zinner, 29P/Schwassmann-Wachmann 1, 37P/Forbes, 43P/Wolf-Harrington, 46P/Wirtanen, 48P/Johnson, 49P/Arend-Rigaux, 52P/Harrington-Abell, 55P/Tempel-Tuttle, 62P/Tsuchinshan 1, 65P/Gunn, 69P/Taylor, 78P/Gehrels 2, 81P/Wild 2, 88P/Howell, 92P/Lovas 1, 94P/Russell 4, 95P/Chiron, 100P/Hartley 1, 103P/Hartley 2, 104P/Kowal 2, 105P/Singer Brewster, 118P/Shoemaker-Levy 4, 121P/Shoemaker-Holt 2, 128P/Shoemaker-Holt 1, 132P/Helin-Roman-Alu 2, 134P/Kowal-Vávrová, 135P/Shoemaker-Levy 8, 137P/Shoemaker-Levy 2, 140P/Bowell-Skiff, P/1998 U3 (Jäger), P/1998 W1 (Spahr), P/1999 DN3 (Korlević-Jurić), P/1999 E1 (Li), P/1999 G1 (LINEAR), P/1999 J5 (LINEAR).

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.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

1985-04-01

Concerning comets: 1961 VIII Seki, 1962 III Seki-Lines, 1963 I Ikeya, 1963 III Alcock, 1964 VIII Ikeya, 1965 VIII Ikeya-Seki, 1966 V Kilston, 1967 II Rudnicki, 1968 I Ikeya-Seki, 1968 VI Honda, 1969 IX Tago-Sato-Kosaka, 1970 II Bennett, 1971 V Toba, 1973 XII Kohoutek, 1974 II P/Schwassmann-Wachmann 1, 1974 III Bradfield, 1975 IX Kobayashi-Berger-Milon, 1975 X Suzuki-Saigusa-Mori, 1975 XII Mori-Sato-Fujikawa, 1976 VI West, 1976 XI P/d'Arrest, 1979 X Bradfield, 1980 XI P/Encke, 1980 XIII P/Tuttle, 1980 XV Bradfield, 1981 II Panther, 1982i P/Halley, 1983 XIII P/Kopff, 1983n P/Crommelin, 1983v P/Hartley-IRAS, 1983w P/Clark, 1984c P/Neujmin, 1984f Shoemaker, 1984g P/Wolf-Harrington, 1984h P/Faye, 1984i Austin, 1984j P/Takamizawa, 1984k P/Arend-Rigaux, 1984m P/Schaumasse, 1984p Tsuchinshan 1, 1984q P/Shoemaker 1, 1984s Shoemaker, 1984t Levy-Rudenko.

Long-range consequences of interplanetary collisions

NASA Technical Reports Server (NTRS)

Sagan, Carl; Ostro, Steven J.

1994-01-01

As Comet Shoemaker-Levy 9 races toward its mid-July collision with the planet Jupiter, considerable public attention is focused on catastrophic impacts with the Earth -- in the past and in the future. In recent years calls have been made to develop technologies that could deflect any asteroid or comet on a collision course. Careful consideration must be given to the nature and time scale of the risk and to the cost-effectiveness and possible problems in the suggested solutions. Risk assessment, threat removal, and resources misuse are examined. The greatest concern is to have a poorly informed public -- exerting pressure for means to mitigate even non-existent threats. The only foreseeable solution is a combination of accurate orbit estimation, realistic threat assessment, and effective public education.

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.

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

Prospects for Jovian seismological observations following the impact of comet Shoemaker-Levy 9

NASA Technical Reports Server (NTRS)

Deming, Drake

1994-01-01

The impact of each fragment of comet SL-9 will produce a downward-propagating pressure wave which will travel at the sound speed through the jovian interior. Since the sound speed increases with depth, most of the energy in the pressure pulse will be strongly refracted and return to the surface, as recently computed by Marley (1994). This wave may in principle be observable as it propagates into the stratosphere, using sufficiently sensitive thermal infrared imaging. If so, it will provide a unique opportunity to constrain models of the jovian interior. This paper extends Marley's calculations to include the effect of the limited spatial resolution which will be characteristic of real observations. The wave pattern on the disk will consist of closely spaced regions of alternating temperature increases and decreases. Spatial averaging will significantly reduce the observed amplitude for resolutions attainable using earth-based telescopes, but the waves should remain above the detection limit.

Atlas of Great Comets

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.

ARC-1994-AC94-0353-2C

NASA Image and Video Library

1994-07-01

Photo Artwork composite by JPL This depiction of comet Shoemaker-Levy 9 impacting Jupiter is shown from several perspectives. IMAGE C is shown from the Voyager 2 spacecraft, which may observe the event from its unique position at the outer reaches of the solar system. For visual appeal, most of the large cometary fragments are shown close to one another in this image. At the time of Jupiter impact, the fragments will be separated from one another by serveral times the distances shown. This image was created by D.A. Seal of JPL's Mission Design Section using orbital computations provIded by P.W. Chodas and D.K. Yeomans of JPL's Navigation Section.

Comet Shoemaker-Levy 9: Impact on Jupiter and plume evolution

NASA Technical Reports Server (NTRS)

Takata, Toshiko; O'Keefe, John D.; Ahrens, Thomas J.; Orton, Glenn S.

1994-01-01

The impact of fragments of Comet Shoemaker-Levy 9 on Jupiter and the resulting vapor plume expansion are investigated by conducting three-dimensional numerical simulations using the smoothed particle hydrodynamics (SPH) method. An icy body, representing the cometary fragments, with a velocity of 60 km/sec and a diameter of 2 km can penetrate to 350 km below the 1-bar pressure level in the atmosphere. Most of the initial kinetic energy of the fragment is transferred to the atmosphere between 50 km and 300 km below the 1-bar pressure level. The shock-heated atmospheric gas in the wake is totally dissociated and partially ionized. Scaling our SPH results to other sizes indicates that fragments larger than approximately 100 m in diameter can penetrate to below the visible cloud decks. The energy deposited in the atmosphere is explosively released in the upward expansion of the resulting plume. The plume preferentially expands upward rather than horizontally due to the density gradient of the ambient atmosphere. It rises greater than or equal to 10(exp 2) km in approximately 10(exp 2) sec. Eventually the total atmospheric mass ejected to above 1 bar is greater than or equal to 40 times the initial mass of the impactor. The plume temperature at a radius approximately 10(exp 3) km is greater than 10(exp 3) K for 10(exp 3) sec for a 2-km fragment. We predict that impact-induced plumes will be observable with the remote sensing instruments of the Galileo spacecraft. As the impact site rotates into the view of Earth some 20 min after the impact, the plume expansion will be observable using the Hubble Space Telescope (HST) and from visible and infrared instruments on groundbased telescopes. The rising plume reaches approximately 3000 km altitude in approximately 10 min and will be visible from Earth.

Jupiter's atmospheric composition from the Cassini thermal infrared spectroscopy experiment

NASA Technical Reports Server (NTRS)

Kunde, V. G.; Flasar, F. M.; Jennings, D. E.; Bezard, B.; Strobel, D. F.; Conrath, B. J.; Nixon, C. A.; Bjoraker, G. L.; Romani, P. N.; Achterberg, R. K.;

Our cometary environment

NASA Astrophysics Data System (ADS)

Napier, W. M.; Clube, S. V. M.

1997-03-01

The encounter of a small armada of spacecraft with Halley's Comet in 1986, the disintegration and multiple impact of Comet Shoemaker - Levy 9 on Jupiter in 1994, and the application of new technologies to the detection of distant solar system bodies, have led to great revisions in the understanding of comets. Further, rapid improvements in computing power and numerical techniques have permitted the dynamical evolution of comets and asteroids to be followed far into the future and past, and the relationships between families of small interplanetary bodies to be explored. The small body environment is now generally recognized as strongly interacting with the terrestrial one, and may be hazardous on timescales of human as well as geological interest. We review our current understanding of the cometary environment, with particular regard to the hazard it presents. It appears that many comets are handed down from the Oort - Öpik cloud, which is dynamically sensitive to the galactic environment, through the planetary system into Earth-crossing orbits. Thus, the terrestrial environment is subject to stresses which vary cyclically on a number of timescales from planetary to galactic.

Explosion of comet Shoemaker-Levy 9 on entry into the Jovian atmosphere

NASA Technical Reports Server (NTRS)

Mac Low, Mordecai-Mark; Zahnle, Kevin

1994-01-01

We use the astrophysical hydrocode ZEUS to compute high-resolution models of the disruption and deceleration of cometary fragments striking Jupiter. We find that simple analytic and semianalytic models work well for kilometer-size impactors. We show that previous numerical models that placed the explosion much deeper in the atmosphere failed to fully resolve important gasdynamical instabilities. These instabilities tear the comet apart, greatly increase its effective cross section, and bring it to an abrupt halt. A 1 km diameter fragment loses over 90% of its kinetic energy within a single scale height at an atmospheric pressure of order 10 bars. For all practical purposes, it explodes.

The origin of external oxygen in Jupiter and Saturn's environments

NASA Astrophysics Data System (ADS)

Cavalié, T.; Lellouch, E.; Hartogh, P.; Moreno, R.; Billebaud, F.; Bockelée-Morvan, D.; Biver, N.; Cassidy, T.; Courtin, R.; Crovisier, J.; Dobrijevic, M.; Feuchtgruber, H.; González, A.; Greathouse, T.; Jarchow, C.; Kidger, M.; Lara, L. M.; Rengel, M.; Orton, G.; Sagawa, H.; de Val-Borro, M.

2014-12-01

This paper reviews the recent findings of the Herschel Solar System Observations Key Program (Hartogh et al. 2009), as well as ground-based supporting observations, regarding the origin of external oxygen in the environments of Jupiter and Saturn. Herschel-HIFI and PACS observations have been used to shown that the Shoemaker-Levy 9 comet is the source of Jupiter's stratospheric water, and that Enceladus (and its geysers) are most probably the source of water for Saturn and Titan.

ARC-1994-AC94-0353-2

NASA Image and Video Library

1994-07-01

Photo Artwork composite by JPL This depiction of comet Shoemaker-Levy 9 impacting Jupiter is shown from several perspectives. IMAGE A is shown from the perspective of Earth based observers. IMAGE B shows the perspective from Galileo spacecraft which can observe the impact point directly. IMAGE C is shown from the Voyager 2 spacecraft, which may observe the event from its unique position at the outer reaches of the solar system. IMAGE D depicts a generic view from Jupiter's south pole. For visual appeal, most of the large cometary fragments are shown close to one another in this image. At the time of Jupiter impact, the fragments will be separated from one another by serveral times the distances shown. This image was created by D.A. Seal of JPL's Mission Design Section using orbital computations provIded by P.W. Chodas and D.K. Yeomans of JPL's Navigation Section.

Jupiter After the 2009 Impact: Hubble Space Telescope Imaging of the Impact-Generated Debris and Its Temporal Evolution

NASA Technical Reports Server (NTRS)

Hammel, H. B.; Wong, M. H.; Clarke, J. T.; de Pater, I.; Fletcher, L. N.; Hueso, R.; Noll, K.; Orton, G. S.; Perez-Hoyos, S.; Sanchez-Lavega, A.;

The Hummingbird GC-IMS: In Situ Analysis of a Cometary Nucleus

NASA Technical Reports Server (NTRS)

Kojiro, Daniel R.; Carle, Glenn C.; Cohen, Martin J.; Wernlund, Roger F.; Stimac, Robert M.; Takeuchi, Norishige; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

Comets are of enormous scientific interest for many reasons. They are primitive bodies that date back to the earliest stages of solar system formation and, because of their small size and because they have been stored in the outer reaches of the solar system, their pristine nature has been preserved better than for any other class of body. They are extremely rich in highly volatile elements, many in the form of ices, and are richer in organic matter than any other known solar system body. It is strongly suspected that in addition to their content of primordial solar nebular material, they also incorporate unprocessed matter from the interstellar medium. Impacts by comets occur onto all the planets and satellites, often with major consequences (e.g., the dinosaur extinction event at the KIT boundary), or sometimes just providing a spectacular cosmic event (e.g., the collision of comet Shoemaker-Levy 9 with Jupiter). A mission to analyze a cometary nucleus must be capable of detecting and identifying over 30 molecular species among several different chemical groups. The Hummingbird Mission will rendezvous with, orbit, characterize, and make multiple descents to the nucleus of a comet. Hummingbird will employ a Gas Chromatograph - Ion Mobility Spectrometer (GC-IMS) as part-of a suite of sophisticated instruments for a comprehensive in situ elemental, molecular, and isotopic analysis of the comet.

Detection of CS in Neptune's atmosphere from ALMA observations

NASA Astrophysics Data System (ADS)

Moreno, R.; Lellouch, E.; Cavalié, T.; Moullet, A.

2017-12-01

Context. The large and vertically non-uniform abundance of CO in Neptune's atmosphere has been interpreted as the result of past cometary impact(s), either single or distributed in size and time, which could also be at the origin of Neptune's HCN. Aims: We aim to provide observational support for this scenario by searching for other comet-induced species, in particular carbon sulfide (CS) which has been observed continuously in Jupiter since the 1994 Shoemaker-Levy 9 impacts. Methods: In April 2016 we used the ALMA interferometer to search for CS(7-6) at 342.883 GHz in Neptune. Results: We report on the detection of CS in Neptune's atmosphere, the first unambiguous observation of a sulfur-bearing species in a giant planet beyond Jupiter. Carbon sulfide appears to be present only at submillibar levels, with a column density of (2.0-3.1) × 1012 cm-2, and a typical mixing ratio of (2-20) × 10-11 that depends on its precise vertical location. The favoured origin of CS is deposition by a putative large comet impact several centuries ago, and the strong depletion of CS with respect to CO - compared to the Jupiter case - is likely due to the CS sticking to aerosols or clustering to form polymers in Neptune's lower stratosphere. Conclusions: The CS detection, along with recent analyses of the CO profile, reinforces the presumption of a large comet impact into Neptune 1000 yr ago, that delivered CO, CS, and HCN at the same time.

(abstract) Cometary Particles as a Tracer of Jupiter's Stratospheric Circulation

NASA Technical Reports Server (NTRS)

West, R. A.; Friedson, A. J.

1993-01-01

The impact of fragments of comet Shoemaker-Levy 9 on Jupiter's atmosphere in July 1994 may provide an unprecedented opportunity to study Jupiter's stratospheric circulation. Recent calculations by Z. Sekanina predict that much of the comet material will be deposited in Jupiter's stratosphere. If so, and if the material is deposited in a confined region (10 000 km or less, horizontally) we can expect a situation analogous to an El Chichon or Pinatubo event for the terrestrial stratosphere. Initially the volatile material will be vaporized and will rapidly recondense. The large ice crystals and dust particles will rain out and be lost to the troposphere. The cloud of small particles which remain may have settling times of more than a year. These submicron to micron particles would probably be easily seen in methane filter images in the near-IR, and possibly in the ultraviolet. An observational program to monitor the dispersal of this cloud or clouds would reveal much about the nature of the circulation. Some predictions about the meridional evolution of the clouds can be made already, based on the meridional circulation model of West et al. unless the impact itself significantly disrupts the annual average circulation well after the initial transients die away.

A Simple Model for the Light Curve Generated by a Shoemaker-Levy 9 Impact

NASA Technical Reports Server (NTRS)

Zahnle, Kevin; Mordecai-Mark, Mac Low

1995-01-01

The impact of a typical Shoemaker-Levy 9 fragment produced three light peaks as seen from Earth. The first peak is related to the entry of the fragment into the Jovian atmosphere. The second peak occurs when the exploding fireball rises above Jupiter's limb into direct view from Earth. The third peak, much the brightest, occurs when the ejecta plume falls back on the atmosphere. By contrast, Galileo, which had a direct view of the impacts, saw two peaks, one at entry, and one at plumefall. Here we present a simple, highly idealized model of a ballistic plume, which we then use to fit the observed light curve of the R impact as recorded at Mauna Kea and Mount Palomar. From the light curve we find that the nominal R fragment had diameter 450-500 m and mass approx. 2-3 x 10(exp 13) g. The uncertainty in the mass is probably about a factor of 3, with a smaller event more likely than a larger one.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

1995-07-01

Concerning comets: C/1958 D1 (Burnham), C/1959 Q1 (Alcock), C/1959 Q2 (Alcock), C/1959 Y1 (Burnham), C/1960 Y1 (Candy), C/1961 O1 (Wilson-Hubbard), C/1961 R1 (Humason), C/1961 T1 (Seki), C/1962 H1 (Honda), C/1963 A1 (Ikeya), C/1963 F1 (Alcock), C/1963 R1 (Pereyra), C/1964 N1 (Ikeya), C/1964 P1 (Everhart), C/1966 P1 (Kilston), C/1966 P2 (Barbon), C/1966 R1 (Ikeya-Everhart), C/1966 T1 (Rudnicki), C/1967 Y1 (Ikeya-Seki), C/1968 H1 (Tago-Honda-Yamamoto), C/1968 L1 (Whitaker-Thomas), C/1968 N1 (Honda), C/1968 Q1 (Bally-Clayton), C/1968 Q2 (Honda), C/1968 U1 (Wild), C/1968 Y1 (Thomas), C/1969 O1 (Kohoutek), C/1969 P1 (Fujikawa), C/1969 Y1 (Bennett), C/1970 B1 (Daido-Fujikawa), C/1970 N1 (Abe), C/1970 U1 (Suzuki-Sato-Seki), C/1971 E1 (Toba), C/1972 E1 (Bradfield), C/1972 L1 (Sandage), C/1972 U1 (Kojima), C/1973 A1 (Heck-Sause), C/1973 E1 (Kohoutek), C/1975 T1 (Mori-Sato-Fujikawa), C/1975 T2 (Suzuki-Saigusa-Mori), C/1975 V1 (West), C/1975 V2 (Bradfield), C/1975 X1 (Sato), C/1976 D1 (Bradfield), C/1977 V1 (Tsuchinshan), C/1984 N1 (Austin), C/1987 P1 (Bradfield), C/1988 A1 (Liller), C/1989 Q1 (Okazaki-Levy-Rudenko), C/1989 X1 (Austin), C/1990 E1 (Černis-Kiuchi-Nakamura), C/1990 K1 (Levy), C/1990 N1 (Tsuchiya-Kiuchi), C/1991 A2 (Arai), C/1991 F2 (Helin-Lawrence), C/1991 T2 (Shoemaker-Levy), C/1991 X2 (Mueller), C/1991 Y1 (Zanotta-Brewington), C/1992 F1 (Tanaka-Machholz), C/1992 U1 (Shoemaker), C/1992 W1 (Ohshita), C/1994 J2 (Takamizawa), C/1994 N1 (Nakamura-Nishimura-Machholz), C/1994 T1 (Machholz), 1P/Halley, 2P/Encke, 4P/Faye, 6P/d'Arrest, 8P/Tuttle, 9P/Tempel 1, 10P/Tempel 2, 15P/Finlay, 16P/Brooks 2, 19P/Borrelly, 23P/Brorsen-Metcalf, 24P/Schaumasse, 29P/Schwassmann-Wachmann 1, 31P/Schwassmann-Wachmann 2, 40P/Väisälä 1, 41P/Tuttle-Giacobini-Kresák, 45P/Honda-Mrkos-Pajdušáková, 51P/Harrington, 59P/Kearns-Kwee, 64P/Swift-Gehrels, 65P/Gunn, 71P/Clark, 73P/Schwassmann-Wachmann 3, 75P/Kohoutek, 76P/West-Kohoutek-Ikemura, 77P/Longmore, 78P/Gehrels 2, 85P/Boethin, 95P/Chiron, 97P/Metcalf-Brewington, 103P/Hartley 2, 104P/Kowal 2, 108P/Ciffréo, 109P/Swift-Tuttle, 110P/Hartley 3, 116P/Wild 4, P/1991 L3 (Levy), P/1991 V1 (Shoemaker-Levy 6), P/1992 Q1 (Brewington), P/1993 W1 (Mueller 5), P/1994 P1 (Machholz 2).

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.

From Tunguska to Chelyabinsk via Jupiter

NASA Astrophysics Data System (ADS)

Artemieva, Natalia A.; Shuvalov, Valery V.

2016-06-01

The Tunguska event remained enigmatic for almost 100 years until the collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 helped to resolve this enigma and allowed us to adequately interpret the more recent Chelyabinsk event. Airbursts typically occur if a meteoroid entering Earth's atmosphere is 10-100 m in diameter, i.e., its energy ranges from 0.5 (Chelyabinsk) to 20 (Tunguska) Mt TNT. All this energy is released in the atmosphere with strong shock waves generated during the entry reaching the surface and causing substantial damage. Atmospheric plumes are capable of dispersing extraterrestrial materials worldwide. Modern civilization is extremely vulnerable to those relatively small disturbances that recur on a decadal timescale and are still difficult to predict.

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/

Lessons Learned from Providing Internet Support for the Shoemaker-Levy 9 Observing Campaign

NASA Astrophysics Data System (ADS)

Raugh, A. C.

1994-12-01

In January of 1994, the comet/asteroid team of the University of Maryland Astronomy Department (including staff of the Small Bodies Node of the Planetary Data System) accepted the task of providing a central communications link for observers of the SL9 impact. To that end we established an email exploder, a log-in type bulletin board account, World Wide Web pages and an anonymous FTP server on an existing department node. It was obvious from the comments received from observers, however, that the nature of the impacts made reliable communication on the timescale of minutes to hours absolutely essential to extracting the best possible data from the concerted observations. To provide as stable a link as possible, we took several specific actions: we focused our efforts on providing well-defined services to the smaller community of observers, rather than attempting to provide complete service to the general public; we kept the solutions simple, both to implement and to maintain; and we developed contingency plans to be implemented immediately in the event of hardware failure, network failure or CPU overload.

New Observations at the Slate Islands Impact Structure, Lake Superior

NASA Technical Reports Server (NTRS)

Dressler, B. O.; Sharpton, V. L.; Schnieders, B.; Scott, J.

1995-01-01

Slate Islands, a group of 2 large and several small islands, is located in northern Lake Superior, approximately 10 km south of Terrace Bay. Shatter cones, breccias and shock metamorphic features provide evidence that the Slate Islands Structure was formed as a result of asteroid or comet impact. Most of the island group is believed to represent the central uplift of a complex impact crater. The structure possibly has a diameter of about 32 km. For Sage (1978, 1991) shock metamorphic features, shatter cones and pervasive rock brecciation are the results of diatreme activity. The present investigations represent the second year of a co-operative study of the Lunar and Planetary Institute, Houston, Texas and the Field Services Section (Northwest) of the Ontario Geological Survey. The objective of this investigation is to come to a better understanding of the formation of mid-size impact structures on Earth and the planets of the solar system. Impact processes played a fundamental role in the formation of the planets and the evolution of life on Earth. Meteorite and comet impacts are not a phenomenon of the past. Last year, more than 20 pieces of the Shoemaker-Levy 9 impacted on Jupiter and the Tunguska comet impacted in Siberia in the early years of this century. The study of impact processes is a relatively young part of geoscience and much is still to be learnt by detailed field and laboratory investigations. The State Islands Structure has been selected for the present detailed investigations because of the excellent shoreline outcrops of rock units related to the impact. The structure is a complex impact crater that has been eroded so that important lithological and structural elements are exposed. We know of no other mid-size terrestrial impact structure with equal or better exposures. In this publication we present preliminary results of our 1994 and 1995 field and laboratory investigations. We have tentatively identified a few impact melt and a considerable number of suevite occurrences.

Professor Thomas J. Ahrens and Shock Wave Physics in Russia

NASA Astrophysics Data System (ADS)

Fortov, Vladimir E.; Kanel, Gennady I.

2011-06-01

Since his earlier works on the equations of state and dynamic mechanical properties of rocks and other materials Prof. T.J. Ahrens furnished large influence on development of the shock wave physics in Russia. He always demonstrates a choice of excellent problems and a level of productivity in the field of shock compression science which is unparalleled. In recognition of his great contribution into science and international scientific collaboration Prof. Ahrens has been elected in Russian Academy of Sciences as its foreign member. In the presentation, emphasis will be done on the Comet Shoemaker-Levy project in which we had fruitful informal collaboration, on the problem of wide-range equations of state, and on stress relaxation at shock compression of solids.

The Impact of a Large Object with Jupiter in July 2009

NASA Astrophysics Data System (ADS)

Sanchez-Lavega, Agustin; Wesley, A.; Orton, G.; Chodas, P.; Hueso, R.; Perez-Hoyos, S.; Fletcher, L.; Yanamandra-Fisher, P.; Legarreta, J.; Gomez-Forrellad, J. M.

2010-05-01

The only major impact ever observed directly in the Solar System was that of a large fragmented comet with Jupiter in July (1994) (Comet Shoemaker-Levy 9; SL9). We report here the observation of a second, single, large impact on Jupiter that occurred on 19 July 2009 at a latitude of -55° with an orthogonal entry trajectory and a lower incidence angle compared to those of SL9. The size of the initial aerosol cloud debris was 4,800 km East-West and 2,500 km North-South. Comparison its properties with those produced by the SL9 fragments, coupled with dynamical calculations of possible pre-impact orbits, indicates that the impactor was most probably an icy body with a size of 0.5-1 km. We calculate that the rate of collisions of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in the near-infrared methane absorption bands at 890 nm and in the 2.12 to 2.3 μm K methane-hydrogen absorption band, where the high-altitude aerosols detach by their brightness relative to Jupiter's primary clouds. We present measurements of the debris dispersion by Jovian winds from a long-term imaging campaign with ground-based telescopes. Ackowledgements: Work was supported by the Spanish MICIIN AYA2009-10701 with FEDER and Grupos Gobierno Vasco IT-464-07, by NASA funds to JPL, Caltech, by the NASA Postdoctoral Program at JPL, and by the Glasstone Fellowship program at Oxford.

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.

Waves, Plumes and Bubbles from Jupiter Comet Impacts

NASA Astrophysics Data System (ADS)

Palotai, Csaba J.; Sankar, Ramanakumar; McCabe, Tyler; Korycansky, Donald

2017-10-01

We present results from our numerical simulations of jovian comet impacts that investigate various phases of the Shoemaker-Levy 9 (SL9) and the 2009 impacts into Jupiter's atmosphere. Our work includes a linked series of observationally constrained, three-dimensional radiative-hydrodynamic simulations to model the impact, plume blowout, plume flight/splash, and wave-propagation phases of those impact events. Studying these stages using a single model is challenging because the spatial and temporal scales and the temperature range of those phases may differ by orders of magnitudes (Harrington et al. 2004). In our simulations we model subsequent phases starting with the interpolation of the results of previous simulations onto a new, larger grid that is optimized for capturing all key physics of the relevant phenomena while maintaining computational efficiency. This enables us to carry out end-to-end simulations that require no ad-hoc initial conditions. In this work, we focus on the waves generated by various phenomena during the impact event and study the temporal evolution of their position and speed. In particular, we investigate the shocks generated by the impactor during atmospheric entry, the expansion of the ejected plume and the ascent of the hot bubble of material from terminal depth. These results are compared to the observed characteristics of the expanding SL9 rings (Hammel et al. 1995). Additionally, we present results from our sensitivity tests that focus on studying the differences in the ejecta plume generation using various impactor parameters (e.g., impact angle, impactor size, material, etc.). These simulations are used to explain various phenomena related to the SL9 event and to constrain the characteristics of the unknown 2009 impactor body. This research was supported by National Science Foundation Grant AST-1627409.

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.

Comet Shoemaker-Levy 9, Jupiter, and Impact Shock Chemistry

NASA Technical Reports Server (NTRS)

Zahnle, Kevin; Cuzzi, Jeffrey (Technical Monitor)

1996-01-01

Four years ago this month, a hitherto unknown comet in loose orbit around Jupiter passed so near the giant planet that it was torn apart into 20 fragments by tides. One orbit later, two years ago this month, the fragments of doomed comet P/Shoemaker Levy (SL9) fell into Jupiter. The enormous energies of these impacts (the largest fragments were nearly 1 km across and, hitting at 60 km/s, released some 2-4 x 10(exp 27) ergs) produced enormous explosions. Several of the ejecta plumes were imaged towering 3000 km above Jupiter's limb. The heat released when the plumes fell was considerable and easily observed on Earth. The impacts produced strong shocks, both promptly at the impact site and again, later, and over thousands of kilometers, when the ejecta plume reentered the atmosphere. The focus of this talk will be to discuss what the SL9 impacts taught us about impact shock chemistry - the processes, the ingredients, the results - and what inferences we may draw for impacts on early Earth. Shock chemistry generates a suite of molecules not usually seen on Jupiter. The most surprising report was of a huge amount of diatomic sulfur S2 at the site of the G impact. Other unusual products include CS, CS2, OCS, H2S, SO2, HCN, CO, and H2O; although H2S and H2O are doubtless abundant below the visible clouds. Hot or enhanced CH4 and NH3 were also detected. A general rule of shock chemistry is that CO forms until either C or O is exhausted. If O greater than C, the other products are oxidized, and excess O goes to H2O. If C greater than O, the other products are reduced, and excess C goes to HCN, C2H2, and a wide variety of more complicated organics. Ultimately, given time, the carbon would react all the way to graphite, but in practice the reactions are incomplete. The dark ejecta debris were probably composed in part of carbonaceous particles generated by the shocks. In a sense, the SL9 impacts performed the famous Miller-Urey experiment on a grand scale, with one result being the production of a lot of complex brown organic solids (called "tholins"). We use, a straightforward chemical kinetics model for the H, N, C, O, S system to follow the nonequilibrium chemistry behind the shocks. The model traces the evolving chemical composition of a parcel of gas by directly integrating the web of chemical reactions. Pressure and temperature histories of the parcels are patterned after those calculated by numerical hydrodynamic simulations of the ejecta plume. A given plume parcel is generally shocked twice; t.e a parcel shocked near the impact site is ejected at high velocity and is shocked again when it reenters the atmosphere. The final state of the gas depends mostly on the second shock, provided that the latter is hot enough. The chemical evidence is ambiguous, but most indications are that C greater than O in the shocked, reacting gas. Telltale signatures of abundant oxygen - SO2, SO, CO2, O2 - were not seen, while signatures of abundant carbon - CS, CS2, and HCN - were. On the other hand, abundant H2O would appear to require O greater than C, and two other observed sulfur species, S2 and OCS, appear to form more easily in a somewhat oxidized gas, presumable vaporized from the comet itself. Since on general principles one expects the -comet to have had a more-or-less cosmic composition, i.e. O greater than C, the production of CS, CS2, and HCN probably requires C greater than O in the shocked jovian air. This in turn implies that even the largest fragments released the bulk of their energy above the jovian water table, in all likelihood above 5 bars . There is no evidence in favor of the proposition that a significant amount of wet jovian air was shocked strongly enough to coax water to react; i.e. wet jovian air saw only temperatures significantly below 2000 K.

Search for the 22 GHz water maser emission in selected comets

NASA Astrophysics Data System (ADS)

Cosmovici, C. B.; Pluchino, S.; Montebugnoli, S.; Pogrebenko, S.

2014-06-01

Following the first evidence of planetary water maser emission induced by the collision of comet Shoemaker/Levy with Jupiter and the puzzling detection of the 22 GHz water emission line in Comet Hyakutake we started in the period 2002-2008 systematic observations of selected comets at 22 GHz (1.35 cm) with the aim of clarifying the unusual behavior of the maser line in the cometary “scenario”. Using a fast multichannel spectrometer coupled to the 32 m dish of the Medicina (Bologna, Italy) Radio Telescope we investigated 6 bright or sungrazing comets down to a heliocentric distance of 0.11 AU: 96P/Machholz, 153P/ Ikeya-Zhang, C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2002 T7 (Linear), and 73P/Schwassmann-Wachmann 3. All of them, similarly to Comet Hyakutake, demonstrate spectral features that, if real and due to the 1.35 cm water vapor transition, are strongly (up to tens of km/s) shifted relative to the radial velocity of the nucleus and, at least sometimes, seem to be present as two separate peaks. If our interpretation of these spectral peaks is correct, there must be some mechanism of acceleration of neutral water molecules up to the velocities of ions. We discuss here the results achieved and the possible explanation of the chemo-physical constraints. First possible detection of the water maser emission line at 22 GHz in sun-grazing comets Observed puzzling acceleration of neutral water molecules at ion velocities and split of the line in two components. Evidence of plasma-grain interaction in sun-grazing comets. Possible new detections in six peculiar comets.

Temporal Behavior of Ammonia and Temperature in the Jovian Stratosphere following the SL9 Impacts

NASA Technical Reports Server (NTRS)

Kostiuk, Ttheodor; Fast, K.; Livengood, T.; Buhl, D.; Espenak, F.; Romani, P.; Betz, A.; Boreiko, R.

1999-01-01

We will present new results in the study of temporal changes in ammonia (NH3) abundance, altitude distribution, and temperature in the stratosphere of Jupiter after the Comet Shoemaker-Levy 9 impact in 1994. Data obtained by Betz et al. (1994) using infrared heterodyne spectroscopy were analyzed using a newly developed beam integration radiative transfer code. The spectra are from six different impact regions and were acquired from hours to three weeks following the impact. The data consist of single NH3 stratospheric emission line profiles near 10 microns measured at a resolving power of approximately 10(exp 7). The true line profiles and the new radiative transfer program permitted the simultaneous retrieval of information on both the NH3 abundance and thermal structure as well as to set constraints on the altitude distribution of stratospheric ammonia. Retrieved column densities varied from approximately 10(exp 18) to 10(exp 16) over the three week period. Over the same time period the altitude of the emitting region varied from levels above the few mbar pressure region to below the 50 mbar pressure regions. Stratospheric temperatures hours after impact were approximately 220 K and about 8 days after impact returned to the quiescent levels (approximately 170-180 K). Results from this self-consistent set of measurements will be presented, compared to those from other measurements, and compared to theoretical retrievals from photochemical models for NH3 in the Jovian stratosphere.

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.

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.

The variability of meteoroid falling

NASA Astrophysics Data System (ADS)

Velasco Herrera, V. M.; Cordero, G.

2016-10-01

We analysed a historical catalogue of meteoroid falling during the last 400 years. We report here for the first time the synchronization between observed meteors and solar barycentric parameters in 19.6 and 13.2 years periodicities using a new multiple cross wavelet. The group of moderated number of meteors is distributed around the positive phase of the solar barycentric periodicity of 13.2 years. While the group of severe number of meteors are distributed on the positive phase of the solar barycentric periodicity of 19.6 years. These periodicities could be associated with Jupiter periodicities. So understanding the modulation of meteoroid falling is important for determining the falling patterns of these objects and for knowing when it is more likely to expect the entry of one of these objects into the Earth's atmosphere, because bodies falling onto the Earth can cause damage from minor impacts to mass-extinctions events. One of the most extreme events was the formation of the Chicxulub impact crater 65,000,000 years ago that caused one of the five major mass extinctions in the last 500,000,000 years. During the 20th and 21st centuries, a series of events demonstrated the importance of collisions between planets and small bodies (comets and asteroids), which included our own planet. In the case of the Earth, we can cite three examples: Tunguska, Curuça and Chelyabinsk. These events invite us to think that perhaps the occurrence of this phenomenon might be more common than we realize, but the lack of communication or people in the area where they happened prevents us from having a complete record. Modern man has not witnessed the impact of large asteroids or comets on our planet, but it has been observed on other planetary bodies. The most spectacular of these events was the collision of fragments of the comet Shoemaker-Levy 9 with Jupiter in 1994. The total energy of the 21 impacts on Jupiter's atmosphere was estimated as the equivalent of tens of millions of megatons of TNT.

ARC-1994-AC94-0353-1

NASA Image and Video Library

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)

Secondary Fragmentation of Comet Shoemaker-Levy 9 and the Ramifications for the Progenitor's Breakup in July 1992

NASA Technical Reports Server (NTRS)

Sekanina, Z.; Chodas, P. W.; Yeomans, D. K.

1998-01-01

Comprehensive analysis of discrete events of secondary fragmentation leads to a conceptually new understanding of the process of disintegration of comet Shoemaker-Levy 9. We submit that the jovian tidal forces inflicted extensive cracks throughout the interior of the original nucleus but did not split it apart. The initial disruption was apparently accomplished by stresses exerted on the cracked object by its fast rotation during the early post-perijove period of time. We argue that this disruption was in fact a rapid sequence of episodes during July 1992 that gave birth to the 12 on-train, or primary, fragments: A, C, D, E, G, H, K, L, Q (later Q(sub 1)), R, S, and W. The discrete events of secondary fragmentation, which gave birth to the off-train fragments, are understood in this scenario as stochastic manifestations of the continuing process of progressive disintegration. Of the 13 off-train fragments considered, nine were secondary--B, F, G(sub 2), M, N, P (later P(sub 2) or P(sub 2a)), Q(sub 2), U, and V--and four tertiary (J, P(sub 1), P(sub 2b), and T). The separation parameters of 11 off-train fragments were determined. The vectorial distribution of separation velocities of these fragments shows a strong concentration toward a great circle, unquestionably an effect of the approximately conserved angular momentum of the progenitor comet since the time of its initial disruption. Also apparent is their clumping (except for P(sub 1)) to a segment along the great circle, implying that the fragments were consistently released from one side of their parents, thus explaining for the first time why the off-train fragments preferentially appeared on one side of the nuclear train. In order to obtain a consistent solution, our model requires that the points of separation be on the antisolar side of the parent fragments, where thermal stresses are likely to enhance the effect of rotation. The episodes of secondary fragmentation are found to have nine months after the close encounter with Jupiter in early July 1992, and the separation velocities ranged between 0.36 and 1.7 m/s. The spin-axis position is determined to have been nearly in the jovicentric orbit plane, which rules out the Asphaug-Benz-Solem strengthless aggregate model as a plausible breakup hypothesis. Since the separation velocities are rotational in nature, they cannot substantially exceed the critical limit for centrifugal breakup and offer an estimate for the original nuclear dimensions. The comet's nucleus is found to have been approximately 10 km in diameter and spinning rapidly. With the exception of P(sub 1) and apparently also P(sub 2) and F, no nongravitational deceleration was detected in the motions of the off-train fragments. Serious doubts are cast on continuing appreciable activity of any of these fragments. Indeed, when it was necessary to introduce a deceleration into the equations of motion, the effect appears to have been due to the action of solar radiation pressure on the centroid of centimeter-sized particulates in the disintegrating condensations.

Observations of comet Levy 1990c in the (OI) 6300-A line with an imaging Fabry-Perot

NASA Technical Reports Server (NTRS)

Prasad, C. Debi; Jockers, Klaus; Rauer, H.; Geyer, E. H.

1992-01-01

We have observed the comet Levy 1990c during 16-25 August 1990 using the MPAE focal reducer system based Fabry-Perot etalon coupled with the 1 meter telescope of the Observatory of Hoher List. The free spectral range and resolution limit of the interferometer was approximately 2.18 A and approximately 0.171 A respectively. Classical Fabry-Perot fringes were recorded on a CCD in the cometary (OI) 6300 A line. They are well resolved from telluric air glow and cometary NH2 emission. Our observations indicate that the (OI) is distributed asymmetrically with respect to the center of the comet. In this paper we report the spatial distribution of (OI) emission and its line width in the coma of comet Levy.

COMETS!

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.

Progress of Cometary Science in the Past 100 Years

NASA Technical Reports Server (NTRS)

Sekanina, Zdenek

1999-01-01

Enormous strides made by cometary science during the 20th century defy any meaningful comparison of its state 100 years ago and now. The great majority of the subfields enjoying much attention nowadays did not exist in the year 1900. Dramatic developments, especially in the past 30-50 years, have equally affected observational and theoretical studies of comets. The profound diversification of observing techniques has been documented by the ever widening limits on the electromagnetic spectrum covered. While the time around 1900 marked an early period of slow and painful experimentation with photographic methods in cometary studies, observations of comets from the x-ray region to the radio waves have by now become routine. Many of the new techniques, and all those involved with the wavelengths shorter than about 300 nm, were made possible by another major breakthrough of this century - observing from space. Experiments on dedicated Earth-orbiting satellites as well as several deep-space probes have provided fascinating new information on the nature and makeup of comets. In broader terms, much of the progress has been achieved thanks to fundamental discoveries and major advances in electronics, whose applications resulted in qualitatively new instruments (e.g. radiotelescopes) and sensors or detectors (e.g. CCD arrays). The most universal effect on the entire cometary science, from observing to data handling to quantitative interpretations, has been, as in any other branch of science, due to the introduction of electronic computers, with their processing capabilities not only unheard of, but literally unimaginable, in the age of classical desk calculators. As if all this should not be enough, the today's generations of comet scientists have, in addition, been blessed with nature's highly appreciated cooperation. Indeed, in the span of a dozen years, between 1985 and 1997, we were privileged to witness four remarkable cometary events: (i) a return of Halley's celebrated comet; (ii) the impact of an extensively fragmented comet Shoemaker-Levy 9 into Jupiter - a once-in-a-millenium episode; (iii) a closeup, appearance of a small but very active Earth-approaching comet Hyakutake; and (iv) an unforgettable celestial show of comet Hale-Bopp, one of the brightest and the most massive comets ever observed. We have been - and for many years to come will be - harvesting scientifically lucrative findings based on the flood of data accumulated during observational campaigns organized for these and other recent objects. Our understanding of cometary phenomena will continue to grow as observing techniques are further being improved and as more sophisticated theories are being developed. Recent accomplishments achieved in the rapidly expanding field of comets are certain to stimulate the members of this astronomical community in their quest for new discoveries in the 21st century!

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

Impacts and evolution: future prospects.

PubMed

Morrison, David

2003-01-01

The discipline of astrobiology includes the dynamics of biological evolution. One of the major ways that the cosmos influences life is through the catastrophic environmental disruptions caused when comets and asteroids collide with a planet. We now recognize that such impacts have caused mass extinctions and played a major role in determining the evolution of life on Earth. The time-averaged impact flux as a function of projectile energy can be derived from lunar cratering statistics as well as the current population of near Earth asteroids (NEAs). Effects of impacts of various energies can be modeled, using data from historic impacts [such as the Cretaceous-Tertiary (KT) impactor 65 million years ago] and the observed 1994 bombardment of Jupiter by fragments of Comet Shoemaker-Levy 9. It is of particular interest to find from such models that the terrestrial environment is highly vulnerable to perturbation from impacts, so that even such a small event as the KT impact (by a projectile 10-15 km in diameter) can lead to a mass extinction. Similar considerations allow us to model the effects of still smaller (and much more likely) impacts, down to the size of the asteroid that exploded over Tunguska in 1908 (energy approximately 10 megatons). Combining the impact flux with estimates of environmental and ecological effects reveals that the greatest contemporary hazard is associated with impactors near 1 million megatons in energy (approximately 2 km in diameter for an asteroid). The current impact hazard is significant relative to other natural hazards, and arguments can be developed to illuminate a variety of public policy issues. The first priority in any plan for defense against impactors is to survey the population of Earth-crossing NEAs and project their orbits forward in time. This is the purpose of the Spaceguard Survey, which has already found more than half of the NEAs >1 km in diameter. If there is an NEA on a collision course with Earth, it can be discovered and the impact predicted with decades or more of warning. It is then possible to consider how to deflect or disrupt the NEA. Unlike other natural hazards, the impact risk can be largely eliminated, given sufficient advanced knowledge to take action against the threatening projectile.

Impacts and evolution: future prospects

NASA Technical Reports Server (NTRS)

Morrison, David

2003-01-01

The discipline of astrobiology includes the dynamics of biological evolution. One of the major ways that the cosmos influences life is through the catastrophic environmental disruptions caused when comets and asteroids collide with a planet. We now recognize that such impacts have caused mass extinctions and played a major role in determining the evolution of life on Earth. The time-averaged impact flux as a function of projectile energy can be derived from lunar cratering statistics as well as the current population of near Earth asteroids (NEAs). Effects of impacts of various energies can be modeled, using data from historic impacts [such as the Cretaceous-Tertiary (KT) impactor 65 million years ago] and the observed 1994 bombardment of Jupiter by fragments of Comet Shoemaker-Levy 9. It is of particular interest to find from such models that the terrestrial environment is highly vulnerable to perturbation from impacts, so that even such a small event as the KT impact (by a projectile 10-15 km in diameter) can lead to a mass extinction. Similar considerations allow us to model the effects of still smaller (and much more likely) impacts, down to the size of the asteroid that exploded over Tunguska in 1908 (energy approximately 10 megatons). Combining the impact flux with estimates of environmental and ecological effects reveals that the greatest contemporary hazard is associated with impactors near 1 million megatons in energy (approximately 2 km in diameter for an asteroid). The current impact hazard is significant relative to other natural hazards, and arguments can be developed to illuminate a variety of public policy issues. The first priority in any plan for defense against impactors is to survey the population of Earth-crossing NEAs and project their orbits forward in time. This is the purpose of the Spaceguard Survey, which has already found more than half of the NEAs >1 km in diameter. If there is an NEA on a collision course with Earth, it can be discovered and the impact predicted with decades or more of warning. It is then possible to consider how to deflect or disrupt the NEA. Unlike other natural hazards, the impact risk can be largely eliminated, given sufficient advanced knowledge to take action against the threatening projectile.

Problems with the Younger Dryas Boundary (YDB) Impact Hypothesis

NASA Astrophysics Data System (ADS)

Boslough, M.

2009-12-01

One breakthrough of 20th-century Earth science was the recognition of impacts as an important geologic process. The most obvious result is a crater. There are more than 170 confirmed terrestrial impact structures with a non-uniform spatial distribution suggesting more to be found. Many have been erased by tectonics and erosion. Deep water impacts do not form craters, and craters in ice sheets disappear when the ice melts. There is growing speculation that such hidden impacts have caused frequent major environmental events of the Holocene, but this is inconsistent with the astronomically-constrained population of Earth-crossing asteroids. Impacts can have consequences much more significant than excavation of a crater. The K/T boundary mass extinction is attributed to the environmental effects of a major impact, and some researchers argue that other extinctions, abrupt climate changes, and even civilization collapses have resulted from impacts. Nuclear winter models suggest that 2-km diameter asteroids exceed a "global catastrophe threshold" by injecting sufficient dust into the stratosphere to cause short-term climate changes, but would not necessarily collapse most natural ecosystems or cause mass extinctions. Globally-catastrophic impacts recur on timescales of about one million years. The 1994 collision of Comet Shoemaker-Levy 9 with Jupiter led us recognize the significance of terrestrial airbursts caused by objects exploding violently in Earth’s atmosphere. We have invoked airbursts to explain rare forms of non-volcanic glasses and melts by using high-resolution computational models to improve our understanding of atmospheric explosions, and have suggested that multiple airbursts from fragmented impactors could be responsible for regional effects. Our models have been cited in support of the widely-publicized YDB impact hypothesis. Proponents claim that a broken comet exploded over North America, with some fragments cratering the Laurentide Ice Sheet. They suggest an abrupt climate change caused by impact-triggered meltwater forcing, along with massive wildfires, resulted in megafaunal extinctions and collapse of the Clovis culture. We argue that the physics of fragmentation, dispersion, and airburst is not consistent with the hypothesis; that observations are no more compatible with impact than with other causes; and that the probability of the scenario is effectively nil. Moreover, millennial-scale climate events are far more frequent than catastrophic impacts, and pose a much greater threat to humanity. Sandia is a multiprogram laboratory operated by Sandia Corp, a Lockheed Martin Company, for the US DOE under Contract DE-AC04-94AL85000. Probability density for largest asteroid impact since Last Glacial Maximum based on power-law size distribution. Comets are orders of magnitude less likely. Grazing trajectory or recent fragmentation further reduces probability.

Accurate Determination of Comet and Asteroid Orbits Leading to Collision With Earth

NASA Technical Reports Server (NTRS)

Roithmayr, Carlos M.; Kay-Bunnell, Linda; Mazanek, Daniel D.; Kumar, Renjith R.; Seywald, Hans; Hausman, Matthew A.

2005-01-01

Movements of the celestial bodies in our solar system inspired Isaac Newton to work out his profound laws of gravitation and motion; with one or two notable exceptions, all of those objects move as Newton said they would. But normally harmonious orbital motion is accompanied by the risk of collision, which can be cataclysmic. The Earth s moon is thought to have been produced by such an event, and we recently witnessed magnificent bombardments of Jupiter by several pieces of what was once Comet Shoemaker-Levy 9. Other comets or asteroids may have met the Earth with such violence that dinosaurs and other forms of life became extinct; it is this possibility that causes us to ask how the human species might avoid a similar catastrophe, and the answer requires a thorough understanding of orbital motion. The two red square flags with black square centers displayed are internationally recognized as a warning of an impending hurricane. Mariners and coastal residents who know the meaning of this symbol and the signs evident in the sky and ocean can act in advance to try to protect lives and property; someone who is unfamiliar with the warning signs or chooses to ignore them is in much greater jeopardy. Although collisions between Earth and large comets or asteroids occur much less frequently than landfall of a hurricane, it is imperative that we learn to identify the harbingers of such collisions by careful examination of an object s path. An accurate determination of the orbit of a comet or asteroid is necessary in order to know if, when, and where on the Earth s surface a collision will occur. Generally speaking, the longer the warning time, the better the chance of being able to plan and execute action to prevent a collision. The more accurate the determination of an orbit, the less likely such action will be wasted effort or, what is worse, an effort that increases rather than decreases the probability of a collision. Conditions necessary for a collision to occur are discussed, and warning times for long-period comets and near-Earth asteroids are presented.

The big comet crash of 1994. Intensive observational campaign at ESO

NASA Astrophysics Data System (ADS)

1994-01-01

Astronomers all over the world are preparing themselves for observations of a most unique event: during a period of six days in July 1994, at least 21 fragments of comet Shoemaker-Levy 9 will collide with giant planet Jupiter. At the European Southern Observatory, an intensive observational campaign with most of the major telescopes at La Silla is being organized with the participation of a dozen international teams of astronomers. This is the first time ever that it has been possible to predict such a collision. Although it is difficult to make accurate estimates, it is likely that there will be important, observable effects in the Jovian atmosphere. WHAT IS KNOWN ABOUT THE COMET ? Comet Shoemaker-Levy 9 is the ninth short-period comet discovered by Gene and Carolyn Shoemaker and David Levy. It was first seen on a photographic plate obtained on 18 March 1993 with the 18-inch Schmidt telescope at the Mount Palomar Observatory, California. It was close in the sky to Jupiter and orbital calculations soon showed that it moves in a very unusual orbit. While other comets revolve around the Sun, this one moves in an elongated orbit around Jupiter. It is obvious that it must have been ``captured'' rather recently by the gravitational field of the planet. It was also found that Shoemaker-Levy 9 consists of several individual bodies which move like ``pearls on a string'' in a majestic procession. It was later determined that this is because the comet suffered a dramatic break-up due to the strong attraction of Jupiter at the time of an earlier close passage to this planet in July 1992. High-resolution Hubble Space Telescope images have shown the existence of up to 21 individual fragments (termed ``nuclei''), whose diameters probably range between a few kilometres and a few hundred meters. There is also much cometary dust visible around the nuclei; it is probably a mixture of grains of different sizes, from sub-millimetre sand up to metre-sized boulders. No outgassing has so far been observed from Shoemaker-Levy 9, but this is not unusual for a comet at this large distance from the Sun, about 750 million kilometres. The most recent observations obtained with telescopes at Hawaii in mid-January 1994 have shown changes in the relative brightness of the individual nuclei, and many of them have now developed individual comet ``tails''. Where and when will the collision take place ? Accurate determinations of the positions of the individual nuclei have permitted to calculate quite precise orbits and it can now be said with 99 percent certainty that all of them will indeed collide with Jupiter. The points of impact are in the Jovian southern hemisphere, at -43 +- 0.6 deg latitude. Unfortunately, these impacts will happen just behind Jupiter's limb, i.e., out of sight from the Earth. However, due to the rapid rotation of the planet, the impact sites will come into view only about 10 minutes later at the very limb where they will be seen ``from the side''. It is also fortunate that the American spacecraft Galileo, now approaching Jupiter, will then be ``only'' about 200 million km away and will have a good view of the impact sites. On the basis of the recent observations, the impact times can now be predicted to about +-40 minutes. The first, rather small nucleus (``A'') will hit the upper layers of Jupiter's atmosphere on July 16, 1994 at about 18:45 Universal Time (UT); the apparently biggest nucleus (``Q'') on July 20, also at 18:45 UT, and the last one in the train (``W''), on July 22 at 07:00 UT. WHAT IS LIKELY TO HAPPEN AT JUPITER ? The comet nuclei will hit Jupiter at a high velocity, about 60 km/sec. The correspondingly large motion energy (the ``kinetic energy'') will all be deposited in the Jovian atmosphere. For a 1 km fragment, this is about equal to 10^28 erg, or no less than about 250,000 Megatons. When one of the cometary nuclei enters the upper layers of the Jovian atmosphere, it will be heated by the friction, exactly as a meteoroid in the Earth's atmosphere, and its speed will decrease very rapidly. Depending of the size of the fragment, it may evaporate completely within a few seconds, while it is still above the dense cloud layer that forms the visible ``surface'' of Jupiter, or it may plunge right through these clouds (and therefore out of sight) into increasingly denser, lower layers, where it ultimately comes to a complete stop and disintegrates in a giant explosion. All of the kinetic energy is released during this process. One part will heat the surrounding atmosphere to very high temperatures; this will result in a flash of light that lasts a few seconds. Within the next minutes, a plume of hot gas will begin to rise over the impact site. It may reach an altitude of several hundred kilometres above the cloud layers and will quickly spread out in all horizontal directions. Another part of the energy will be transformed into shock waves that will propagate into the interior of Jupiter, much as seismic waves from an earthquake do inside the Earth. When these waves again reach the upper layers of the atmosphere, they may be seen as slight increases in the local temperature along expanding circles with the impact sites at their centres (like waves on a water surface). The shock waves may also start oscillations of the entire planet, like those of a ringing bell. During the past months, atmospheric scientists have attempted to calculate the details of these impacts, but the uncertainties are still rather large. Moreover, the magnitudes of the overall effects are entirely dependent on the energies involved, i.e., on the still not well determined sizes (masses) of the cometary nuclei. It is also expected that there will be some kind of interaction between the cometary dust and Jupiter's strong magnetic field. The fast-moving dust grains may become electrically charged. This will possibly have a significant influence on Jupiter's radio emission and therefore be directly observable with Earth-based radio telescopes, as well as from several spacecraft, including Ulysses, now en route towards its first pass below the Sun. There may also be changes in the plasma torus that girdles Jupiter near the orbit of the volcanic moon Io, and some cometary dust particles may collect in Jupiter's faint ring. All in all, this spectacular event offers a unique opportunity to study Jupiter and its atmosphere. It may also provide a first ``look'' into its hitherto unobservable inner regions. Nobody knows for sure, how dramatic the effects of the impacts will actually be, but unless we are prepared to observe them, we may lose a great chance that is unlikely to come back in many years, if ever. WHICH PREPARATIONS HAVE BEEN MADE AT ESO ? In November of last year, a group of 25 cometary and planetary specialists from Europe and the U.S.A. met at ESO to discuss possible observations from the ESO La Silla observatory in connection with the cometary impacts at Jupiter. In a resulting report, they emphazised that ESO is in a particularly advantageous situation in this respect, because the excellent site of this observatory is located in the south and Jupiter will be 12 degrees south of the celestial equator at the time of the event and therefore well observable from here; the time available from observatories in the northern hemisphere will be much more restricted. Moreover, many different observing techniques are available at La Silla; this provides optimal conditions for effective coordination of the various programmes, in particular what concerns imaging and spectral observations in the infrared and submillimetre wavebands. A joint request for a coordinated observing programme was submitted by the group to the ESO Observing Programmes Committee. During its meeting at the end of November 1993, this committee reacted very positively and a substantial number of observing nights at the major telescopes at La Silla was granted at the time of the impacts in July 1994. The total amount of observing time to this programme is just over 40 full nights, a quantity never allocated for any single astronomical event at ESO. This clearly illustrates the importance attached to this very special programme. At this moment, the more than 30 astronomers involved are in the middle of the complex and detailed preparations for this unique event, less than six months from now. Together with observational programmes at other observatories, they will provide efficient coverage of the collisions and the associated effects. WHICH OBSERVATIONS WILL BE CARRIED OUT AT ESO ? Some of the earliest observations at ESO will be carried out with the Danish 1.54 m telescope by a small team of ESO astronomers led by Olivier Hainaut. Beginning in late April 1994, images will be obtained of comet Shoemaker-Levy 9 which will allow to further improve the accuracy of the orbit and thereby to increase the precision with which the times of the individual impacts can be predicted. It is expected that such observations, when made carefully up to the last days before the first impacts, will result in a final timing accuracy of a few minutes; this will of course be of importance for all other observations, both from the ground, and especially for those being carried out from the spacecraft. A team from the Munich Observatory (Germany) under the leadership of Heinz Barwig will perform rapid brightness mesurements of Jupiter's moons at the predicted times of the impacts with their special high-speed photometer attached to the ESO 1 metre telescope. The flashes from the impacts will be reflected from the surfaces of those Jupiter moons which are in view of the impact sites. If this happens when a moon is in full sunlight, the relative increase of intensity will probably only be of the order of 1. However, if one of the moons is located in the shadow of Jupiter and is at the same time visible from the Earth, then the relative brightening may be very conspicuous. Whether this will be the case will of course depend on the exact moments of the impacts. Also at the time of the impacts, a group of French astronomers, headed by Bruno Sicardy of the Observatoire de Paris, will mount a special CCD camera at the Danish telescope, which will be used for different types of observations. They also hope to be able to detect some of the expected light flashes from the Jupiter moons. In addition, this programme will monitor changes in the cloud structure around the impact sites. It may also be possible to obtain low-resolution spectra which will show the temperature of the flashes, but in view of their very short duration, a few seconds at most, this will not be easy. The same instrument will also be used by Nick Thomas of the Max-Planck-Institut fur Aeronomie (Lindau, Germany) to image the Jupiter plasma torus in order to detect possible changes after the impacts. Spectral observations of the comet will be made with the ESO 1.5 m telescope in April by Heike Rauer, also from the Max-Planck-Institut fur Aeronomie. They are expected to lead to a better knowledge about the physical and chemical state of the impacting bodies. For instance, are they really so ``dusty'', as present observations seem to indicate, or do they contain large amounts of gas ? If so, what kind of molecules are present ? This will help to refine the predictions of the impact effects. Imaging and spectral observations of the comet for the same general purposes will also be obtained in early July with the EMMI instrument at the 3.5 m New Technology Telescope by an international team headed by Rita Schulz, formerly at the University of Maryland and now at the Max-Planck-Institut fur Aeronomie. No less than 46 observing hours have been allocated at the Swedish-ESO Submillimetre Telescope (SEST) to an international group headed by Daniel Gautier, Observatoire de Paris-Meudon. During the impacts, the cometary molecules will be mixed with those in the Jovian atmosphere, some of which may come from very deep layers. Together they will be carried upwards in the plume, described above. This may provide a rare opportunity, not only to register the submillimetre emissions from those molecules which are already known to be present in the comet and on Jupiter, but also to detect new and unknown molecules otherwise not accessible for direct observations, either from the interior of the cometary nuclei or from deep down in Jupiter's enormous atmosphere. Infrared observations will play a very important role during the ESO campaign. A new ESO-developed instrument, TIMMI (Thermal Infrared Multi-Mode Instrument) will be mounted at the ESO 3.6 m telescope and will provide detailed infrared images of the impact areas when they become visible at the limb. Two teams will be active here; one is led by Timothy A. Livengood from NASA Goddard Space Flight Center (U.S.A.) and includes several ESO staff astronomers. Thanks to the excellent imaging capabilities of TIMMI in the far-infrared spectral region, this group will be able to look far down into the atmosphere and to measure minute temperature variations. This should make it possible to register the effects of the shockwaves that arise when the cometary energy is deposited in the atmosphere. The second group at the 3.6 m telescope, led by Benoit Mosser from Institut d'Astrophysique, Paris, will be looking for short- and long-term oscillations of the entire planet during the days and nights following the impacts. It is agreed that such observations will not be easy, but they offer the best hope we presently have of learning about the internal structure of Jupiter. It may be deduced from the observed frequencies and modes of oscillation. A particularly interesting problem is whether Jupiter really possesses a core of metallic hydrogen, as postulated by some scientists. Infrared images will also be made by Klaus Jockers from the Max-Planck-Institut fur Aeronomie with the ESO infrared IRAC camera at the MPI/ESO 2.2 m telescope. Since they will be obtained at shorter wavelengths than those at TIMMI, they will show higher layers of the atmosphere and the possible changes (streaming motions, new whirls and eddies ?) which may result from the impacts. These programmes will therefore complement eachother. A total of no less than 13 half-nights have been allocated at the 3.5 m New Technology Telescope. They will be shared between two groups which will both use the IRSPEC instrument to obtain detailed infrared spectra of the impact sites. One team is headed by Rita Schulz, the other by Therese Encrenaz from Observatoire de Paris. Among many others, they hope to observe some of the molecules which may be present in the deeper layers of the Jovian atmosphere, e.g., water, ammonium and phosphine (PH3). HOW WILL THE MEDIA LEARN ABOUT THE RESULTS FROM ESO ? Together, these programmes add up to a very significant observational effort at ESO in connection with this astronomical event. Although it is difficult to predict at this moment whether all of the above mentioned phenomena will actually be observed, there is an obvious and great interest in these programmes from all sides. To support the public information about the outcome, it is the intention of the ESO Information Service to provide the media with regular and rapid updates about the observational progress at the La Silla telescopes. For this, a special ESO news service will be activated some days before the series of impacts begin - it will be accessible for all interested parties during the critical period. More details about this service will be announced in a later Press Release.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

2000-01-01

Concerning comets: C/1995 O1 (Hale-Bopp), C/1997 BA6 (Spacewatch), C/1998 K2 (LINEAR), C/1998 M1 (LINEAR), C/1998 M5 (LINEAR), C/1998 P1 (Williams), C/1998 T1 (LINEAR), C/1998 W3 (LINEAR), C/1999 E1 (Li), C/1999 F2 (Dalcanton), C/1999 H1 (Lee), C/1999 H3 (LINEAR), C/1999 J2 (Skiff), C/1999 J3 (LINEAR), C/1999 K2 (Ferris), C/1999 K5 (LINEAR), C/1999 K6 (LINEAR), C/1999 K8 (LINEAR), C/1999 L2 (LINEAR), C/1999 L3 (LINEAR), C/1999 N2 (Lynn), C/1999 S3 (LINEAR), C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/1999 T2 (LINEAR), C/1999 T3 (LINEAR), C/1999 U1 (Ferris), C/1999 U4 (Catalina-Skiff), C/1999 Y1 (LINEAR), 4P/Faye, 10P/Tempel 2, 29P/Schwassmann-Wachmann 1, 37P/Forbes, 50P/Arend, 59P/Kearns-Kwee, 63P/Wild 1, 65P/Gunn, 74P/Smirnova-Chernykh, 84P/Giclas, 106P/Schuster, 108P/Ciffréo, 114P/Wisemann-Skiff, 117P/Helin-Roman-Alu 1, 136P/Mueller 3, 137P/Shoemaker-Levy 2, 141P/Machholz 2, P/1998 U4 (Spahr), P/1999 RO28 (LEONOS), P/1999 U3 (LINEAR), P/1999 V1 (Catalina), P/1999 X1 (Hug-Bell).

Instrument performance enhancement and modification through an extended instrument paradigm

NASA Astrophysics Data System (ADS)

Mahan, Stephen Lee

An extended instrument paradigm is proposed, developed and shown in various applications. The CBM (Chin, Blass, Mahan) method is an extension to the linear systems model of observing systems. In the most obvious and practical application of image enhancement of an instrument characterized by a time-invariant instrumental response function, CBM can be used to enhance images or spectra through a simple convolution application of the CBM filter for a resolution improvement of as much as a factor of two. The CBM method can be used in many applications. We discuss several within this work including imaging through turbulent atmospheres, or what we've called Adaptive Imaging. Adaptive Imaging provides an alternative approach for the investigator desiring results similar to those obtainable with adaptive optics, however on a minimal budget. The CBM method is also used in a backprojected filtered image reconstruction method for Positron Emission Tomography. In addition, we can use information theoretic methods to aid in the determination of model instrumental response function parameters for images having an unknown origin. Another application presented herein involves the use of the CBM method for the determination of the continuum level of a Fourier transform spectrometer observation of ethylene, which provides a means for obtaining reliable intensity measurements in an automated manner. We also present the application of CBM to hyperspectral image data of the comet Shoemaker-Levy 9 impact with Jupiter taken with an acousto-optical tunable filter equipped CCD camera to an adaptive optics telescope.

Kuiper Airborne Observatory's Telescope Stabilization System: Disturbance Sensitivity Reduction Via Velocity Loop Feedback

NASA Technical Reports Server (NTRS)

Lawrence, David P.; Tsui, K. C.; Tucker, John; Mancini, Ronald E. (Technical Monitor)

1995-01-01

In July of 1994 the Kuiper Airborne Observatory's (KAO) Telescope Stabilization System (TSS) was upgraded to meet performance goals necessary to view the Shoemaker-Levy 9 comet collision with Jupiter. The KAO is a modified C-141 Aircraft supporting a 36 inch Infrared telescope used to gather and analyze astronomical data. Before the upgrade, the TSS exhibited approximately a 10 arc-second resolution pointing accuracy. The majority of the inaccuracy was attributable to aircraft vibration and wind buffeting entering through the aircraft's telescope door opening; in other words, the TSS was overly sensitive to external disturbances. Because of power limitations and noise requirements, improving the pointing accuracy of the telescope required more sophistication than simply raising the bandwidth as some classical control strategies might suggest. Instead, relationships were developed between the disturbance sensitivity and closed loop transfer functions. These relationships suggested that employing velocity feedback along with an increase in current loop gain would dramatically improve the pointing resolution of the TSS by decreasing the control system's sensitivity to external disturbances. With the implementation of some classical control techniques and the above philosophy, the KAO's TSS's resolution was improved to approximately 2-3 arc-seconds.

Unraveling the formation of HCPH(X2A') molecules in extraterrestrial environments: crossed molecular beam study of the reaction of carbon atoms, C(3Pj), with phosphine, PH3(X1A1).

PubMed

Guo, Y; Gu, X; Zhang, F; Sun, B J; Tsai, M F; Chang, A H H; Kaiser, R I

2007-05-03

The reaction between ground state carbon atoms, C(3P(j)), and phosphine, PH3(X(1)A1), was investigated at two collision energies of 21.1 and 42.5 kJ mol(-1) using the crossed molecular beam technique. The chemical dynamics extracted from the time-of-flight spectra and laboratory angular distributions combined with ab initio calculations propose that the reaction proceeds on the triplet surface via an addition of atomic carbon to the phosphorus atom. This leads to a triplet CPH3 complex. A successive hydrogen shift forms an HCPH2 intermediate. The latter was found to decompose through atomic hydrogen emission leading to the cis/trans-HCPH(X(2)A') reaction products. The identification of cis/trans-HCPH(X(2)A') molecules under single collision conditions presents a potential pathway to form the very first carbon-phosphorus bond in extraterrestrial environments like molecular clouds and circumstellar envelopes, and even in the postplume chemistry of the collision of comet Shoemaker-Levy 9 with Jupiter.

Ultraviolet and visible variability of the coma of Comet Levy (1990c)

NASA Technical Reports Server (NTRS)

Feldman, P. D.; Budzien, S. A.; Festou, M. C.; A'Hearn, M. F.; Tozzi, G. P.

1992-01-01

A visible lightcurve of Comet Levy obtained with the IUE Fine Error Sensor has revealed short-term coma variability. A production-rate source function is derivable from these data which implies a nucleus exhibiting hemispherically asymmetric activity. The ratio of gas-to-dust-production rates is also noted to exhibit asymmetry. The low dust-outflow velocity derived from observations, at about 200 m/sec, indicates a distribution that is rich in large, 3-10 micron particles.

Tabulation of comet observations.

NASA Astrophysics Data System (ADS)

1999-10-01

Concerning comets: C/1995 O1 (Hale-Bopp), C/1997 BA6 (Spacewatch), C/1997 J2 (Meunier-Dupouy), C/1998 K5 (LINEAR), C/1998 M2 (LINEAR), C/1998 M5 (LINEAR), C/1998 P1 (Williams), C/1998 Q1 (LINEAR), C/1998 T1 (LINEAR), C/1998 U5 (LINEAR), C/1999 F2 (Dalcanton), C/1999 H1 (Lee), C/1999 H3 (LINEAR), C/1999 J2 (Skiff), C/1999 J3 (LINEAR), C/1999 K2 (Ferris), C/1999 K3 (LINEAR), C/1999 K5 (LINEAR), C/1999 K6 (LINEAR), C/1999 K8 (LINEAR), C/1999 L2 (LINEAR), C/1999 N2 (Lynn), C/1999 N4 (LINEAR), C/1999 S3 (LINEAR), C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/1999 T2 (LINEAR), C/1999 T3 (LINEAR), C/1999 U1 (Ferris), 2P/Encke, 4P/Faye, 10P/Tempel 2, 21P/Giacobini-Zinner, 29P/Schwassmann-Wachmann 1, 37P/Forbes, 46P/Wirtanen, 50P/Arend, 52P/Harrington-Abell, 59P/Kearns-Kwee, 74P/Smirnova-Chernykh, 84P/Giclas, 88P/Howell, 93P/Lovas 1, 106P/Schuster, 114P/Wiseman-Skiff, 136P/Mueller 3, 137P/Shoemaker-Levy 2, 141P/Machholz 2, 142P/Ge-Wang, P/1998 G1 (LINEAR), P/1998 QP54 (LONEOS-Tucker), P/1998 S1 (LINEAR-Mueller), P/1998 U2 (Mueller), P/1998 U3 (Jäger), P/1998 W1 (Spahr), P/1998 Y1 (LINEAR), P/1999 RO2 (LONEOS).

Comparison of the plasma tails of four comets: P/Halley, Okazaki-Levy-Rudenko, Austin, and Levy

NASA Technical Reports Server (NTRS)

Farnham, Tony L.; Meech, Karen J.

1994-01-01

Photographic and charge coupled device (CCD) plasma tail observations are compared for four comets: P/Halley (22 nights in 1985/1986), Okazaki-Levy-Rudenko 1989 XIX (1989 December 2), Austin 1990 V (nine nights in 1990), and Levy 1990 XX (two nights in 1991). We present a discussion of several image-processing techniques used to enhance the visibility of the plasma tail features in order to measure velocities, accelerations, and position angles. The data are used to assess the validity of various physical mechanisms proposed to explain plasma tail phenomena. Seven disconnection events were observed in the comet P/Halley data, two in the Austin data, and none for the other comets. Analysis of these data suggests that while the crossing of the solar neutral sheet (the sector boundary) is a prominent factor in the production of a disconnection event, it is likely that several mechanisms are at work. A sector boundary crossing has been ruled out as the cause of either the 1986 April 26 P/Halley disconnection or the 1990 May 5/6 Austin disconnection. The motions of the disconnection events, knots, and condensations in the tails were seen to increase from 30-60 km/s near the nucleus (within 10(exp 6) km) to 80-100 km/s at 10(exp 7) km, consistent with either bulk motion or Alfven waves. Distinguishing between the two cases is not possible with these data. It was found that although the tail ray rotation rate slows as the ray approaches the tail axis, it is not a good indicator of the solar wind speed. Historical plasma tail data are also used to look for clues as to why some comets form well-developed plasma tails and others do not.

Dealing with the Asteroid Impact Hazard

NASA Technical Reports Server (NTRS)

Morrison, David

2001-01-01

The small fraction of the asteroids with Earth-crossing or Earth-approaching orbits is of special interest to us because many will eventually impact our planet. The time-averaged impact flux as a function of projectile energy can be derived from lunar cratering statistics, although we have little information on the possible variability of this flux over time. The effects of impacts of various energies can be modeled, using data from historic impacts (such as the KT impactor 65 million years ago), nuclear explosive testing, and the observed 1994 bombardment of Jupiter by fragments of comet Shoemaker-Levy 9. It is of particular interest to find from such models that the terrestrial environment is highly vulnerable to perturbation from impacts, so that even such a small event as the KT impact (by a projectile roughly 15 km in diameter) can lead to a mass extinction. Combining the impact flux with estimates of environmental and ecological effects reveals that the greatest contemporary hazard is associated with impactors near one million megatons energy. The current impact hazard is significant relative to other natural hazards, and arguments can be developed to illuminate a variety of public policy issues. These include the relative risk of different impact scenarios and the associated costs and probability of success of countermeasures. It is generally agreed that the first step is to survey and catalogue the thousand-or-so Near Earth Asteroids (NEAs), and we review the status of the Spaceguard NEA Survey. We compare the efficiency of various ground and space-based approaches and consider the challenges of international coordination and the problems and opportunities associated with communicating the results with the press and the public. It is also important to reflect on how the impact hazard might be dealt with by both national governments and international decision-making bodies, and to anticipate ways of mitigating the danger if a NEA were located on an apparent Earth-impact trajectory. As the most extreme known example of a natural hazard with low probability but severe global consequences. the NEA impact hazard calls for the most careful consideration and planning.

K/T boundary stratigraphy: Evidence for multiple impacts and a possible comet stream

NASA Technical Reports Server (NTRS)

Shoemaker, E. M.; Izett, G. A.

1992-01-01

A critical set of observations bearing on the K/T boundary events were obtained from several dozen sites in western North America. Thin strata at and adjacent to the K/T boundary are locally preserved in association with coal beds at these sites. The strata were laid down in local shallow basins that were either intermittently flooded or occupied by very shallow ponds. Detailed examination of the stratigraphy at numerous sites led to the recognition of two distinct strata at the boundary. From the time that the two strata were first recognized, E.M. Shoemaker has maintained that they record two impact events. We report some of the evidence that supports this conclusion.

The Impact of a Large Object on Jupiter in 2009 July

NASA Technical Reports Server (NTRS)

Sanchez-Lavega, A.; Wesley, A.; Orton, G.; Hueso, R.; Perez-Hoyos, S.; Fletcher, L. N.; Yanamandra-Fisher, P.; Legarreta, J.; de Pater, I.; Hammel, H.;

Comet 'Bites the Dust' Around Dead Star

NASA Technical Reports Server (NTRS)

2006-01-01

[figure removed for brevity, see original site] Infrared Spectrometer Graph

This artist's concept illustrates a comet being torn to shreds around a dead star, or white dwarf, called G29-38. NASA's Spitzer Space Telescope observed a cloud of dust around this white dwarf that may have been generated from this type of comet disruption. The findings suggest that a host of other comet survivors may still orbit in this long-dead solar system.

The white dwarf G29-38 began life as a star that was about three times as massive as our sun. Its death involved the same steps that the sun will ultimately undergo billions of years from now. According to theory, the G29-38 star became brighter and brighter as it aged, until it bloated up into a dying star called a red giant. This red giant was large enough to engulf and evaporate any terrestrial planets like Earth that happened to be in its way. Later, the red giant shed its outer atmosphere, leaving behind a shrunken skeleton of star, called a white dwarf. If the star did host a planetary system, outer planets akin to Jupiter and Neptune and a remote ring of icy comets would remain.

The Spitzer observations provide observational evidence for this orbiting outpost of comet survivors. Astronomers speculate that one such comet was knocked into the inner regions of G29-38, possibly by an outer planet. As the comet approached very close to the white dwarf, it may have been torn apart by the star's tidal forces. Eventually, all that would be left of the comet is a disk of dust.

This illustration shows a comet in the process of being pulverized: part of it still exists as a chain of small clumps, while the rest has already spread out into a dusty disk. Comet Shoemaker-Levy 9 broke apart in a similar fashion when it plunged into Jupiter in 1994. Evidence for Comets Found in Dead Star's Dust The graph of data, or spectrum, from NASA's Spitzer Space Telescope indicates that a dead star, or white dwarf, called G29-38, is shrouded by a cloud of dust. The data also demonstrate that this dust contains some of the same types of minerals found in comet Hale-Bopp.

The findings tell a possible tale of solar system survival. Though the dust seen by Spitzer is likely from a comet that recently perished, its presence suggests that an icy distant ring of comets may still orbit the dead star.

These data were collected by Spitzer's infrared spectrometer, an instrument that cracks light open like a geode, revealing its coveted components. In this spectrum, light from the white dwarf is on the left, at ultraviolet and visible wavelengths. The spectrum on the right, at infrared wavelengths longer than about 2 microns, shows much more light than can be explained by a white dwarf alone. The bump seen around a wavelength of 10 microns offers a clue to the source of this excess infrared light. It signifies the presence of silicate minerals, which are found in our own solar system on Earth, in sandy beaches, and in comets and asteroids. These silicate grains appear to be very small like those in comets, so astronomers favor the theory that a comet recently broke apart around the dead star.

A Study of Short-Term Variations in Jupiter's Synchrotron Emission

NASA Technical Reports Server (NTRS)

Klein, M.J.; Gulkis, S.; Bolton, S. J.; Levin, S. M.

1999-01-01

Earth-based observations of the flux density and polarization of Jupiter's microwave emission provide useful data to test and constrain computational models of synchrotron radio emission from the inner regions of the Jovian magnetosphere. Stimulated by the sudden brightening of the synchrotron emission caused by the impacts of comet Shoemaker-Levy 9 in 1994, the observational techniques of the NASA-JPL Jupiter Patrol were modified to search for other short-term variations unrelated to the SL-9 event. The characteristics of the improved data base are described and the results of the search for variability on timescales of 5 to 100 days are reported. The first results of Jupiter observations from the Goldstone-Apple Valley Radio Telescope (GAVRT) project are reported and included in the data base. GAVRT is a new project in science education that engages middle- and high school students in science research. The paper also includes new observations of Jupiter's rotational beamed emission, commonly known as the "beaming curve", that describes the observed flux density as a function of System III longitude. The shape of the "beaming curve" is known to change with the parameter D(sub E), the declination of the earth relative to Jupiter's rotational equator. While the history of Jupiter's beaming curve exhibits remarkable stability and repeatability as a function of D(sub E), there may be evidence for short term departures from the nominal curves. Data supporting this tentative conclusion are presented. Preliminary results of a study comparing the observations and computer simulations of the synchrotron beaming curve will also be presented and discussed (see companion paper, "Modeling Jupiter's Synchrotron Emission", by Bolton et. al.). The research reported in this paper was performed by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

"Word of Discovery": A Planetary Example from Volume I of the Astronomical Journal

NASA Astrophysics Data System (ADS)

Hockey, T.

1998-09-01

In 1850, William Lassell (1799-1880) discovered a series of bright white spots, in the south temperate latitudes of Jupiter, unlike any that that been seen before. Lassell's note on these STZ features is a useful example of how astronomical discoveries of the day were communicated among astronomers. Word of Lassell's Spots spread quickly by nineteenth-century standards. This was due, in part, to the recent appearance of journals devoted exclusively to astronomy. The transition from letters as a means of conveying scientific information to journals is reflected in the propagation of Lassell's announcement: a report of Lassell's description of the white spots to the Royal Astronomical Society appeared in the Monthly Notices of the Royal Astronomical Society along with a woodblock print of one of his drawings. This report reappeared shortly thereafter in German translation. It was part of a letter to the editor of the Astronomische Nachrichten, Heinrich Schumacher (1780-1850), from an English correspondent of his, the Reverend Richard Sheepshanks (1974-1855). (Sheepshanks was himself editor of the Monthly Notices of the Royal Astronomical Society.) It then made its way across the Atlantic as a letter from Schumacher to Benjamin Gould (1824-1896), who published it in the first volume of his upstart Astronomical Journal. There it appears in English, again, as Schumacher quoting Sheepshanks quoting Lassell! The observations by Lassell and William Dawes (1799-1868) of this phenomenon also were the first major planetary discovery made using a silvered-glass reflecting telescope. Lassell's Spots have remained in the "astronomical news" of the last 150 years: Most recently, they appeared worldwide in images showing the Comet Shoemaker-Levy 9 impact sites.

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.

Tracking Jupiter at microwave frequencies after the 2009 impact

NASA Astrophysics Data System (ADS)

Horiuchi, Shinji; García-Miró, Cristina; Rizzo, Ricardo; Forster, James; Hofstadter, Mark; Dorcey, Ryan; Jauncey, David; de Pater, Imke; Baines, Graham; Sotuela, Ioanna

2010-05-01

On 19 July 2009, amateur astronomer Anthony Wesley located near Canberra, Australia, discovered an anomalous dark feature near Jupiter's south pole. It was soon confirmed with additional observations that the new feature was an impact site created by an unknown object. The only other observed collision with Jupiter occurred 15 years earlier with the catastrophic impact of the Shoemaker-Levy 9 Comet (SL9). Unlike the well-predicted SL9 event, the biggest question to answer this time is whether the impact body was a comet or an asteroid. We started a campaign to track Jupiter at microwave frequencies with NASA's Deep Space Network (DSN), in Canberra, Goldstone (California), and Madrid, and the Allen Telescope Array (ATA) in California. A 34m DSN radio telescope at Goldstone was operated by students through GAVRT program. Our primary goal was first to detect molecular radio emissions possibly originating from cometary core components, such as OH, H2O, and NH3, and second to detect radio burst in non-thermal continuum emissions, as observed after the SL-9 impact 15 years ago. We used a 70m radio telescope in Canberra and another 70m in Madrid to search for molecular emissions at 1.6 GHz for OH, 22 GHz for water vapors, 23 GHz for ammonia. Several radio spectroscopy observing sessions have been successfully conducted from 23 July to 1 August. We also started continuum emission monitoring, mainly at 2.3 GHz and 8.4 GHz using 34m and 70m DSN telescopes and the ATA. At early stage of this still on-going monitoring, joint observations were conducted with two 34m telescopes in Canberra and the ATA on 30 July and 9 August in order to have long continuous time coverage and to check flux density scales using a common calibrator source. To highlight this campaign, on 22 November we undertook the Jupiter: Project 24 for the International Year of Astronomy. This campaign was over 24 hours of continuous observation of Jupiter using all three DSN complexes around the world. A couple of DSN 34m telescopes were operated by students organized by two educational programs: GAVRT in California and PARTNeR in Madrid. The Jupiter: Project 24 observations were broadcasted to the world in real time via the Internet. In this talk, we will present a summary of results from the molecular emission search and the continuum flux density monitoring. The evolution of the non-thermal Jupiter radio emission after the July 2009 impact will be discussed, along with a comparison to the increase in the synchrotron radiation caused by the SL9 impact in 1994.

Temporal Evolution of SL-9 Impact Sites on Jupiter and Global Maps of Jupiter from Multi-Observatory Visible and Infrared Images

NASA Technical Reports Server (NTRS)

Limaye, Sanjay S.

1996-01-01

The objective of this research was to investigate the temporal behavior of the impact features on Jupiter created by the fragments of the Shoemaker Levy-9 comet that collided with the planet in July 1994. The primary observations used in the study were ground based images of Jupiter acquired from the Swedish Solar Vacuum Tube on the island of La Palma in the Canary Islands. The measurement of position of the impact features in images acquired immediately after the impact over a period of a few days revealed that the apparent drift rates were too high and that a repetitive pattern could be seen in the longitude position on successive rotations. This could be explained only by the fact that the measured longitudes of the impact sites were being affected by parallax due to a significant elevation of the impact debris above the nominal cloud top altitude value used for image navigation. Once the apparent positions are analyzed as a function of the meridian angle, the parallax equation can be used to infer the height of the impact features above the cloud deck, once the true impact position (longitude) for the feature is known. Due to their inherent high spatial resolution, the HST measurements of the impact site locations have been accepted widely. However, these suffer from the parallax themselves since few of them were obtained at central meridian. Ground based imaging have the potential to improve this knowledge as they do observe most of the impact sites on either side of the central meridian, except for the degraded resolution. Measurements over a large number of images enables us to minimize the position error through regression and thus estimate both the actual impact site location devoid of parallax bias, and also of the altitude level of the impact debris above the cloud deck. With rapid imaging there is the potential to examine the time evolution of the altitude level. Several hundred ground based images were processed, navigated and subjected to the impact site location measurements. HST images were also acquired and used to calibrate the results and to improve the sample. The resources available enabled an in-depth study only of impact site A, however, many more images have since become available through the global network observations through Lowell Observatory.

The Detection of a Striking Increase in the Microwave Emission from Jupiter's Radiation Belts in June and July 2003.

NASA Astrophysics Data System (ADS)

Klein, M. J.; Bolton, S. J.; Levin, S. M.; Mac Laren, D.

2004-12-01

Synchrotron emission from energetic electrons in Jupiter's radiation belts has been routinely measured by ground-based radio telescopes for three decades. The NASA-JPL Jupiter Patrol, using NASA's Deep Space Network (DSN) antennas at Goldstone, CA., has reported significant (5 %-to-30 %) variations in Jupiter's flux density near 13-cm wavelength with timescales from a few days to several months. In this paper we report observations of an unusually sudden increase in flux density from 3.8 to 4.3 Jy that occurred between 20 June and 15 July 2003. The rate of increase (approximately 0.6 percent per day) is the steepest increase that we have detected with the exception of the increase in 1994 following the impacts of fragments from comet Shoemaker-Levy 9. More than half of the reported observations were conducted by middle- and high school students from classrooms across the nation. The students and their teachers are participants in the Goldstone-Apple Valley Radio Telescope (GAVRT) science education project, which is a partnership involving NASA, the Jet Propulsion Laboratory and the Lewis Center for Educational Research (LCER) in Apple Valley, CA. Working with the Lewis Center over the Internet, GAVRT students conduct remotely controlled radio astronomy observations using 34-m antennas at Goldstone. We also report preliminary results from a special GAVRT observing campaign conducted in the fall of 2003 before, during and after the controlled impact of the Galileo spacecraft into the Jovian atmosphere. Simultaneous observations were made at 3.5 and 13 cm wavelengths three-to-four days per week. These data are being incorporated into synchrotron emission studies of the state of the radiation belts during the last weeks of the Galileo mission. The JPL contribution to this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

HUT observations of carbon monoxide in the coma of Comet Levy (1990c)

NASA Technical Reports Server (NTRS)

Feldman, P. D.; Davidsen, A. F.; Blair, W. P.; Bowers, C. W.; Dixon, W. V.; Durrance, S. T.; Henry, R. C.; Kriss, G. A.; Kruk, J.; Moos, H. W.

1991-01-01

Observations of comet Levy (1990c) were made with the Hopkins Ultraviolet Telescope during the Astro-1 Space Shuttle mission on 10 Dec. 1990. The spectrum, covering the wavelength range 415 to 1850 A at a spectral emission of 3 A (in first order), shows the presence of carbon monoxide and atomic hydrogen, carbon, and sulfur in the coma. Aside from H I Lyman-beta, no cometary features are detected below 1200 A, although cometary O I and O II would be masked by the same emissions present in the day airglow spectrum. The 9.4 x 116 arcsec aperture corresponds to 12,000 x 148,000 km at the comet. The derived production rate of CO relative to water, 0.13 + or - 0.02, compared with the same ratio derived from IUE observations (made in Sep. 1990) which sample a much smaller region of the coma, 0.04 + or - 0.01, suggests the presence of an extended source of CO, as was found in comet Halley. Upper limits on Ne and Ar abundance are within an order of magnitude or solar abundances.

Observations of Comet Levy (1990c) with the Hopkins Ultraviolet Telescope

NASA Technical Reports Server (NTRS)

Feldman, P. D.; Davidsen, A. F.; Blair, W. P.; Bowers, C. W.; Dixon, W. V.; Durrance, S. T.; Henry, R. C.; Ferguson, H. C.; Kimble, R. A.; Gull, Theodore R.

1991-01-01

Observations of Comet Levy (1990c) were made with the Hopkins Ultraviolet Telescope during the Astro-1 Space Shuttle mission on December 10, 1990. The spectrum, covering the wavelength range 415-1850 A at a spectral resolution of 3 A, shows the presence of carbon monoxide and atomic hydrogen, carbon, and sulfur in the coma. Aside from H I Lyman-beta, no cometary features are detected below 1200 A, although cometary O I and O II would be masked by the same emissions present in the day airglow spectrum. The 9.4 x 116 arcsecond aperture corresponds to 12,000 x 148,000 km at the comet. The derived production rate of CO relative to water is 0.11 + or - 0.02, compared with 0.04 + or - 0.01 derived from IUE observations (made in September 1990) which sample a much smaller region of the coma. This suggests the presence of an extended source of CO, as was found in comet Halley. Upper limits on Ne and Ar abundance are within one order of magnitude of solar abundances.

To Boldly Go: America's Next Era in Space. Probing the Primordial Constituents of Our Solar System

NASA Technical Reports Server (NTRS)

1995-01-01

Dr. France Cordova, NASA's Chief Scientist, chaired this, another seminar in the Administrator's Seminar Series. She introduced NASA Administrator, Daniel S. Goldin, who greeted the attendees, and noted that, from the day people first looked into the sky, they've wondered what was up there, who or what created it, is Earth unique, what shaped the solar system, what is the Kuiper Belt and why is it there, and what are the solar system's building blocks. NASA's missions may discover some of the answers. Dr. Cordova then introduced Dr. Anita Cochran, research scientist at the University of Texas. Dr. Cochran has been searching for some of this information. She is especially interested in finding out when various planets and asteroids were discovered, what their orbits are, when the solar system was formed, and more about the comets in the Kuiper Belt. Are they icy planetisimals that helped form our solar system? Dr. Toby Owen of the University of Hawaii faculty spoke next. He believes that life on Earth exists because comets brought water and a variety of light elements to Earth from the outer parts of the solar system. Without them, we couldn't exist. He noted that noble gases don't mix with other gases. Gases come to Earth via rocks and by bombardment. Ice can trap argon and carbon, but not neon. Dr. Owens concluded with comments that we need 'better numbers for the Martian atmosphere', and it would be good to get samples of material from a comet. The third speaker was Dr. Eugene Shoemaker of the Lowell Observatory and the U.S. Geological Survey. He is credited with discovering more than 800 asteroids and learning about the Oort Cloud, which is believed to be a cloud of rocks and dust that may surround our solar system and be where comets originate. Comet storms reoccur about every 30 million years. Dr. Shoemaker suggested that since we are presently in a period of comet showers, it would be good to get a comet sample. It might provide insight regarding the origin of life. Additional information is included in the original extended abstract.

Nitrogen and Oxygen Photochemistry following SL9

NASA Technical Reports Server (NTRS)

Moses, Julianne I.; Allen, Mark; Gladstone, G. Randall

1995-01-01

The collision of Shoemaker Levy 9 (SL9) with Jupiter caused many new molecular species to be deposited in the Jovian stratosphere. We use a photochemical model to follow the evolution of the impact derived species. Our results regarding the nitrogen and oxygen compounds are presented here. NH3 photolysis initiates the nitrogen photochemistry. Much of the nitrogen ends up in N2, nitrogen-sulfur compounds, and HCN, but NH3 and nitriles such as C2H3CN may also exist in observable quantities for a year or so after the impacts. Oxygen species survive for a long time in the Jovian stratosphere. The only major oxygen containing compounds that exhibit dramatic changes in the lower stratosphere in the first year following the impacts are SO, SO2, and OCS - H2O, CO2, and CO are comparatively stable. We discuss the important photochemical processes operating on the nitrogen and oxygen species in the Jovian stratosphere, make prediction concerning the temporal variation of the major species, and identify molecules that might act as good tracers for atmospheric dynamics.

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.

Earth Observation

NASA Image and Video Library

2011-07-06

ISS028-E-014782 (6 July 2011) --- The Shoemaker (formerly Teague) Impact Structure, located in Western Australia in a drainage basin south of the Waldburg Range, presents an other-worldly appearance in this detailed photograph recorded from onboard the International Space Station on July 6. The Shoemaker impact site is approximately 30 kilometers in diameter, and is clearly defined by concentric ring structures formed in sedimentary rocks (brown to dark brown, image center) that were deformed by the impact event approximately 1630 million years ago, according to the Earth Impact Database. Several saline and ephemeral lakes?Nabberu, Teague, Shoemaker, and numerous smaller ponds?occupy the land surface between the concentric ring structures. Differences in color result from both water depth and suspended sediments, with some bright salt crusts visible around the edges of smaller ponds (image center The Teague Impact Structure was renamed Shoemaker in honor of the late Dr. Eugene M. Shoemaker, a pioneer in the field of impact crater studies and planetary geology, and founder of the Astrogeology Branch of the United States Geological Survey. The image was recorded with a digital still camera using a 200 mm lens, and is provided by the ISS Crew Earth Observations experiment and Image Science & Analysis Laboratory, Johnson Space Center.

The 8-13 micron spectra of comets and the composition of silicate grains

NASA Technical Reports Server (NTRS)

Hanner, Martha S.; Lynch, David K.; Russell, Ray W.

1994-01-01

We have analyzed the existing spectra of seven comets which show an emission feature at 7.8-13 micrometers. Most have been converted to a common calibration, taking into account the SiO feature in late-type standard stars. The spectra are compared with spectra of the Trapezium, interplanetary dust particles (IDPs), laboratory mineral samples, and small particle emission models. The emission spectra show a variety of shapes; there is no unique 'cometary silicate'. A peak at 11.20-11.25 micrometers, indicative of small crystalline olivine particles, is seen in only three comets of this sample, P/Halley, Bradfield 1987 XXIX, and Levy 1990 XX. The widths of the emission features range from 2.6 to 4.1 micrometers (FWHM). To explain the differing widths and the broad 9.8 micrometers maximum, glassy silicate particles, including both pyroxene and olivine compositions, are the most plausible candidates. Calculations of emission models confirm that small grains of glassy silicate well mixed with carbonaceous material are plausible cometary constituents. No single class of chondritic aggregate IDPs exhibits spectra closely matching the comet spectra. A mixture of IDP spectra, particularly the glass-rich aggregates, approximately matches the spectra of comets P/Halley, Levy, and Bradfield 1987 XXIX. Yet, if comets are simply a mix of IDP types, it is puzzling that the classes of IDPs are so distinct. None of the comet spectra match the spectrum of the Trapezium. Thus, the mineralogy of the cometary silicates is not the same as that of the interstellar medium. The presence of a component of crystalline silicates in comets may be evidence of mixing between high- and low-temperature regions in the solar nebula.

The Nature of Punctuational Crises and the Spenglerian Model of Civilization

NASA Astrophysics Data System (ADS)

Clube, S. V. M.

Mankind's essentially untroubled state of mind in the presence of comets during the last two centuries has been fortified by the overall relative brevity of cometary apparitions and the calculated infrequency of cometary encounters with planets. During the course of the Space Age, however, the fact of cometary splitting has also become increasingly secure and there is growing appreciation of the fact that mankind's state of mind can never be altogether relaxed. Indeed a watershed in the modern perception of cometary facts has evidently been reached with the most recent and devastating example of cometary splitting, that of the fragmentation of Comet P/Shoemaker-Levy 9 and its subsequent bombardment of planet Jupiter. Thus there is a recognized tendency now amongst comets, especially those in short-period orbits, due to the occasionally excessive effects of solar irradiation, planetary tides and small body impacts, which gives rise to individual swarms of cometary debris, and it is the resulting repeated penetration of such dispersed swarms by our planet which apparently increases the danger to mankind from time to time. The danger comprises global coolings, atmospheric pollution and super-Tunguska events, the cometary debris being responsible for both high-level dust insertions and low-level multimegaton explosions in the Earth's atmosphere along with a generally enhanced fireball flux. Historically, the presence of such danger was drawn to mankind's attention by the observed bombardments over several decades due to "blazing stars threatening the world with famine, plague and war; to princes death; to kingdoms many curses; to all estates many losses; to herdsmen rot; to ploughmen hapless seasons; to sailors storms; to cities civil treasons." The sense of cosmic destiny aroused by these bombardments evidently involved degrees of fatalism and public anxiety which were deplored by both ecclesiastical authorities and secular administrations with the result that acknowledged dispensers of prognosis and mitigation who endorsed the adverse implications of 'blazing stars' (astrologers, soothsayers etc.) were commonly impugned and censured. Nowadays, of course, we are able to recognise that the Earth's environment is not only one of essentially uniformitarian calm, as formerly assumed, but one that is also interrupted by 'punctuational crises', each crisis being the sequence of events which arises due to the fragmentation of an individual comet whose orbit intersects the Earth's. That even modest crises can arouse apprehension is known through the circumstances of the nineteenth century break-up of Comet Biela. Indeed it seems that these crises are rather frequently characterized by relatively violent (paradigm shifting) transmutations of human society such as were originally proposed by Spengler and Toynbee more than sixty years ago on the basis of historical analysis alone. It would appear, then, that the historical fear of comets which has been with us since the foundation of civilization, far from being the reflection of an astrological perception of the cosmos which was deranged and therefore abandoned, has a perfectly rational basis in occasional cometary fragmentation events. Such events recur and evidently have quite serious implications for society and government today. Thus when cosmic danger returns and there is growing awareness of the fact, we find that society is capable of becoming uncontrollably convulsed as 'enlightenment' spreads. A revival of millenarian expectations under these circumstances, for example, is not so much an underlying consequence but a deviant manifestation of the violent turmoil into which society falls, often to revolutionary effect.

Cratering on Small Bodies: Lessons from Eros

NASA Astrophysics Data System (ADS)

Chapman, C. R.

2003-01-01

Cratering and regolith processes on small bodies happen continuously as interplanetary debris rains down on asteroids, comets, and planetary satellites. Butthey are very poorly observed and not well understood. On the one hand, we have laboratory experimentation at small scales and we have examination of large impact craters (e.g. Meteor Crater on Earth and imaging of abundant craters on terrestrial planets and outer planet moons). Understanding cratering on bodies of intermediate scales, tens of meters to hundreds of km in size, involves either extrapolation from our understanding of cratering phenomena at very different scales or reliance on very preliminary, incomplete examination of the observational data we now have for a few small bodies. I review the latter information here. It has been generally understood that the role of gravity is greatly diminished for smaller bodies, so a lot of cratering phenomena studied for larger bodies is less applicable. But it would be a mistake to imagine that laboratory experiments on gravitationless rocks (usually at 1 g) are directly applicable, except perhaps to those monolithic Near Earth Asteroids (NEAs) some tens of meters in size that spin very rapidly and can be assumed to be "large bare rocks" with "negative gravity". Whereas it had once been assumed that asteroids smaller than some tens of km diameter would retain little regolith, it is increasingly apparent that regolith and megoregolith processes extend down to bodies only hundreds of meters in size, perhaps smaller. Yet these processes are very different from those that pertain to the Moon, which is our chief prototype of regolith processes. The NEAR Shoemaker spacecraft's studies of Eros provide the best evidence to date about small-body cratering processes, as well as a warning that our theoretical understanding requires anchoring by direct observations. Eros: "Ponds", Paucity of Small Craters, and Other Mysteries. Although Eros is currently largely detached from interactions with main-belt asteroids in its Earth-approaching orbit, almost all of its cratering history must have occurred in the main belt, where it almost certainly lived for a long time and where the impact rate is orders-of-magnitude greater than in its present environment. Thus NEAR Shoemaker's year-long orbital studies of Eros should be representative of asteroidal cratering processes for medium-small (tens of km) asteroids generally - with the caveat that small bodies are made of many different materials, ranging from metal to whatever comets are made of, and we already have indications from NEAR Shoemaker's flyby of Mathilde that responses to impacts on such bodies may be very different from what is observed on rocky Eros. As viewed from a distance, the saturated crater fields on Eros look similar to those on Ida and, indeed, on the Moon itself. It is at smaller scales, never before studied for asteroids, where Eros# appearance diverted dramatically from expectations based on modest extrapolations from our lunar experience. Flat, level "ponds" are common on Eros and were certainly not expected. Most striking, however, is the virtual absence of small-scale (cm to meters) craters and the dominance of rocks and boulders on the surface. Apparently many of the larger boulders were distributed about Eros by the comparatively recent impact that produced the Shoemaker crater, providing insight to ejecta processes on small bodies. But, assuming that Shoemaker didn't form practically "yesterday", the dearth of small craters is extremely puzzling. Some researchers have attempted to explain the shortage by traditional geological processes; I will explain why these fail and we are being forced to turn to explanations involving shortages of small projectiles in the asteroid belt (e.g. due to the Yarkovsky Effect). Even if projectile shortages help to explain the data, other non-lunar processes must be at work, as well. Mass-wasting processes are evident on large crater walls and the ponds reflect a still-not-understood deposition or sedimentation process. The boulder-strewn surface itself also serves to "armour" the surface against impacts. The role of seismic shaking on small bodies also must play a major role, relatively unfamiliar for larger bodies. I will summarize the observations of Eros that shed light on these various processes. Even Smaller Bodies. An interest in sub-km scale bodies has developed in the context of imagining how a potentially dangerous NEA might be diverted. Meanwhile, observational evidence concerning their general geophysical configurations has grown rapidly. A significant proportion of these bodies (approx. 20%) appear to have satellites or be binary in nature, and most of the remainder exhibit properties consistent with being "rubble piles" of one form or another. Eros, with less than a millionth the mass of the Moon, turned out to be extremely non-lunar-like in its small-scale responses to impact cratering. NEAs of the size being analyzed as prototypes for deflection are a millionth the mass of Eros. We should not expect our insights from Eros, therefore, to be directly applicable to them. And as we learn more about small asteroids and comets, we must expect to be surprised.

Survey and Risk Assessment of Near Earth Asteroids

NASA Astrophysics Data System (ADS)

Zhao, H. B.

2010-07-01

In 1994, 21 fragments of comet Shoemaker-Levy 9 impacted Jupiter with a velocity of about 60 km/s, which is the first grand collision between celestial bodies observed by human beings. The impact makes us informed definitely that the earth is faced with the small but serious threat of Near Earth Objects (NEOs). Chinese scientists of Purple Mountain Observatory proposed a plan of Chinese Near Earth Object Survey (CNEOS) in the conference on NEOs held in the building of the World Headquarters of United Nations, New York in 1995. This project started in 1998. During the past 7 years, CNEOS proceeded in selecting observational site, manufacturing telescope and CCD detector, carrying out observation, reducing mass data, and assessing impact risk from NEOs. Will those so-called potential hazardous asteroids be the terminator of mankind? In 2007, NASA proposed the Spaceguard goal to detect, track, catalogue and characterize 90% of the potentially hazardous objects with diameters greater than 140 m. This dissertation reviews the current situation of research on asteroids and NEOs, which will greatly enhance our understanding of the planetary sciences. The project of CNEOS, including selecting observational site, manufacturing telescope and CCD detector, had been put in practice since 1998. The telescope of CNEOS is a 1.04/1.20/1.80 m Schmidt telescope, equipped with a 4096 by 4096 CCD detector which has drift-scanning function. In this dissertation, the advantage and disadvantage of drift-scanning and corresponding observational method are discussed. This dissertation discusses residential district of asteroids and distribution of visual magnitudes of asteroids. As a result, we draw three principles of observational plan. This dissertation also develops algorithms of pretreatment of astronomical image, extracting objects, and cross-identification, then discusses the methods of identifying and classifying of move objects, establishes software to realize the reduction of the mass data. Until November 2007, CNEOS had found 332 new asteroids including an Apollo type NEO and a Jupiter-family periodic comet. The observation quantity of CNEOS ranked the eighth among all 378 asteroid observation plans, and the accuracy of positional reduction was also quite well. The dissertation carries out the research of dynamics of asteroids. A software on orbit determination, differential correction, dynamical evolution and asteroid ephemeris is reconstructed. This dissertation reviews the history of impact prediction theory, and covers the linear techniques for analyzing encounters, consisting of precise orbit determination and propagation followed by target plane analysis. The impact probabilities and risks between three NEOs and the earth in 200 years are calculated. In this dissertation, a set of numerical algorithms are built to discuss the observational prediction of Northern Taurids under the effect of the lunar gravitational assembling in 2011. In addition, the earth satellite measurement, the lunar orbiter measurement and lunar laser ranging measurement are used to constrain the intermediate-range gravity from λ = 1.2×107 ˜ 3.8 × 108 m.

Research in Celestial Mechanics and Differential Equations.

DTIC Science & Technology

Contents: A geopotential representation with sampling functions; Sampling functions as an alternative to spherical harmonics; The Levi - Civita ...restricted problem of three bodies ; Secular perturbations of periodic comets; Resonance in the restricted problem of three bodies ; Two centers of

Can Plume-Forming Asteroid Airbursts Generate Meteotsunami in Deep Water?

NASA Astrophysics Data System (ADS)

Boslough, M.

2015-12-01

Hydrocode simulations suggest that the 1908 Tunguska explosion was a plume-forming airburst analogous to those caused by Comet Shoemaker-Levy 9 (SL9) collisions with Jupiter in 1994. A noctilucent cloud that appeared over Europe following the Tunguska event is similar to post-impact features on Jupiter, consistent with a collapsed plume containing condensation from the vaporized asteroid. Previous workers treated Tunguska as a point explosion and used seismic records, barograms, and extent of fallen trees to determine explosive yield. Estimates were based on scaling laws derived from nuclear weapons data, neglecting directionality, mass, and momentum of the asteroid. This point-source assumption, with other simplifications, led to a significant overestimate. Tunguska seismic data were consistent with ground motion from a vertical point impulse of 7×1018dyn sec caused by the downward blast wave of a 12.5-megaton nuclear explosion at an altitude of 8.5 km for an effective momentum multiplication factor (β) of ~80. However, simulations of a 3-megaton collisional airburst reveal that the upward-directed momentum contained in a ballistic plume can reach this level within the first minute after the explosion (β≈300). The reaction impulse from such an airburst is therefore similar to a much larger non-plume-forming nuclear explosion. Momentum is coupled through the atmosphere to the surface, generating disproportionately large seismic signatures. This result suggests that coupling from an over-water plume-forming airburst could be a more efficient tsunami source mechanism than a collapsing impact cavity or direct air blast because the characteristic time of the plume is closer to that of a long-period wave in deep water. As the plume accelerates upward, it creates a slowly-rising and sustained overpressure with a ramp wave that propagates outward at the speed of sound, generating a tsunami in deep ocean by the same mechanism that yields slower meteotsunami in shallow basins. This hypothesis is consistent with the observation of prominent internal waves observed propagating radially outward from several SL9 impacts, even though the waves were not in Proudman resonance. Because of slow compression, the SL9 waves grew with a Froude number of ~1.6, the same as that of the sound speed in air over ~4.6-km-deep water.

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.

TASS - The Amateur Sky Survey

NASA Astrophysics Data System (ADS)

Droege, T. F.; Albertson, C.; Gombert, G.; Gutzwiller, M.; Molhant, N. W.; Johnson, H.; Skvarc, J.; Wickersham, R. J.; Richmond, M. W.; Rybski, P.; Henden, A.; Beser, N.; Pittinger, M.; Kluga, B.

1997-05-01

As a non-astronomer watching Shoemaker/Levy 9 crash into Jupiter through postings on sci.astro, it occurred to me that it might be fun to build a comet finding machine. After wild speculations on how such a device might be built - I considered a 26" x 40" fresnel lens and a string of pin diodes -- postings to sci.astro brought me down to earth. I quickly made contact with both professionals and amateurs and found that there was interesting science to be done with an all sky survey. After several prototype drift scan cameras were built using various CCDs, I determined the real problem was software. How does one get the software written for an all sky survey? Willie Sutton could tell you, "Go where the programmers are." Our strategy has been to build a bunch of drift scan cameras and just give them away (without software) to programmers found on the Internet. This author reports more success by this technique than when he had a business and hired and paid programmers at a cost of a million or so a year. To date, 22 drift scan cameras have been constructed. Most of these are operated as triplets spaced 15 degrees apart in Right Ascension and with I, V, I filters. The cameras use 135mm fl, f.2.8 camera lenses for a plate scale of 14 arc seconds per pixel and reach magnitude 13. With 512 pixels across the drift scan direction and running through the night, a triplet will collect 200 Mb of data on three overlapping areas of 3 x 120 degrees each. To date four of the triplets and one single have taken data. Production has started on 25 second generation cameras using 2k x 2k devices and a barn door mount.

Visible and Near-IR Imaging of Giant Planets: Outer Manifestations of Deeper Secrets

NASA Astrophysics Data System (ADS)

Hammel, Heidi B.

1996-09-01

Visible and near-infrared imaging of the giant planets -- Jupiter, Saturn, Uranus, and Neptune -- probes the outermost layers of clouds in these gaseous atmospheres. Not only are the images beautiful and striking in their color and diversity of detail, they also provide quantitative clues to the dynamical and chemical processes taking place both at the cloud tops and deeper in the interior: zonal wind profiles can be extracted; wavelength-dependent center-to-limb brightness variations yield valuable data for modeling vertical aerosol structure; the presence of planetary-scale atmospheric waves can sometimes be deduced; variations of cloud color and brightness with latitude provide insight into the underlying mechanisms driving circulation; development and evolution of discrete atmospheric features trace both exogenic and endogenic events. During the 1980's, our understanding of the giant planets was revolutionized by detailed visible-wavelength images taken by the Voyager spacecraft of these planets' atmospheres. However, those images were static: brief snapshots in time of four complex and dynamic atmospheric systems. In short, those images no longer represent the current appearance of these planets. Recently, our knowledge of the atmospheres of the gas giant planets has undergone major new advances, due in part to the excellent imaging capability and longer-term temporal sampling of the Hubble Space Telescope (HST) and the Galileo Mission to Jupiter. In this talk, I provide an update on our current understanding of the gas giants based on recent visible and near-infrared imaging, highlighting results from the collision of Comet Shoemaker-Levy 9 with Jupiter, Saturn's White Spots, intriguing changes in the atmosphere of Uranus, and Neptune's peripatetic clouds.

This Month in Astronomical History: Preliminary Survey Results

NASA Astrophysics Data System (ADS)

Wilson, Teresa

2017-01-01

This Month in Astronomical History is a short (~500 word) column on the AAS website that revisits significant astronomical events or the lives of people who have made a large impact on the field. The monthly column began in July 2016 at the request of the Historical Astronomical Division. Examples of topics that have been covered include Comet Shoemaker-Levy’s collision with Jupiter, the discovery of the moons of Mars, the life of Edwin Hubble, Maria Mitchell’s comet discovery, and the launch of Sputnik II. A survey concerning the column is in progress to ensure the column addresses the interests and needs of a broad readership, including historians, educators, research astronomers, and the general public. Eleven questions focus on the style and content of the column, while eight collect simple demographics. The survey has been available on the AAS website since and was mentioned in several AAS newsletters; however, non-members of AAS were also recruited to include respondents from a variety of backgrounds. Preliminary results of the survey are presented and will be used to hone the style and content of the column to serve the widest possible audience. Responses continue to be collected at: https://goo.gl/forms/Lhwl2aWJl2Vkoo7v1

Tidal Distortion and Disruption of Earth-Crossing Asteroids

NASA Astrophysics Data System (ADS)

Richardson, D. C.; Bottke, W. F.

1996-09-01

There is mounting evidence that most km-sized objects in the solar system are ``rubble-piles'', fragile objects composed of loose collections of smaller components all held together by self-gravity rather than tensile strength. The evidence includes: (a) the paucity of fast rotating km-sized asteroids (Harris, 1996, LPSC 27, 977); (b) the tidal disruption of Comet Shoemaker-Levy 9 (SL9) and observations of crater chains on the Moon and Galilean satellites (Schenk et al., 1996, Icarus 121, 149); (c) observations of extremely large craters on Phobos, Gaspra, and Ida; and (d) hydrocode models that realistically treat asteroid impacts (Love and Ahrens, 1996, Icarus, in press). Accordingly, we predict that Earth's tidal forces play a major role in the evolution of rubble-pile Earth-crossing objects (ECOs). By modeling close encounters between the Earth and our rubble-piles (for details, see Bottke et al., this issue), we found that Earth's tidal forces can make the progenitors undergo: (a) ``SL9-type'' disruption (formation of clumps of roughly equal size along the fragment train; this outcome may explain specific crater chains seen on the Moon); (b) mass shedding (over half of the primary remains intact; in many cases, the shed fragments go into orbit around the progenitor, producing binary asteroids, which could explain the population of doublet craters seen on the terrestrial planets (Bottke and Melosh, 1996, Nature 381, 51)); (c) reshaping accompanied by spin-up or spin-down (this mechanism could explain the large aspect ratio (2.76), unusual shape, and short rotation period (5.2 hours) of 1620 Geographos as well as the short rotation periods of many other ECOs). Mass shedding events for ECOs occur more frequently at low velocities relative to Earth than at high velocities, corresponding to low (e, i) values. Thus, Earth's tidal forces should be most effective at disrupting large ECOs (and producing small bodies) in this region. This localized disruption mechanism may explain observations by Rabinowitz et al. (1993, Nature 363, 704), who claim to see an ``excess'' number of small ECOs (D < 50 m) at low (e, i) relative to their expectation based on the number of large ECOs seen elsewhere.

Polarimetric Study of Jupiter's Atmosphere

NASA Astrophysics Data System (ADS)

Yanamandra-Fisher, P. A.; McLean, W.; Wesley, A.; Miles, P.; Masding, P.

2017-12-01

Jupiter's atmosphere displays polarization, attributed to changes in the clouds/thermal filed that can be brought about by endogenic dynamical processes such merger of vortices; global, planetary scale upheavals, and external factors such as celestial collisions (such as D/Shoemaker-Levy 9 impact with Jupiter in 1994, etc.). Although the range of phase angles available from Earth for Jupiter is restricted to a narrow range, limb polarization measurements provide constraints on the polarimetric properties. Jupiter is known to exhibit a strong polar limb polarization and a low equatorial limb polarization due to the presence of haze particles and Rayleigh scattering at the poles. In contrast, at the equator, the concentration of particulates in the high atmosphere might change, changing the polarimetric signature and aurorae at both poles. The polarimetric maps, in conjunction with thermal maps and albedo maps, can provide constraints on modeling efforts to understand the nature of the aerosols/hazes in Jovian atmosphere. With Jupiter experiencing morphological changes at many latitudes, we have initiated a polarimetric observing campaign of Jupiter, in conjunction with The PACA Project and preliminary results will be discussed. Some of our observations are acquired by a team of professional/amateur planetary imagers astronomers.

Simple models of SL-9 impact plumes in flight

NASA Astrophysics Data System (ADS)

Harrington, J.; Deming, D.

1998-09-01

We have extended our ballistic Monte-Carlo model of the Shoemaker-Levy 9 impact plumes (J. Harrington and D. Deming 1996. Simple models of SL9 impact plumes, Bull. Am. Astron. Soc. 28 1150--1151) to calculate the appearance of the plumes in flight. We compare these synthetic images to the data taken by the Hubble Space Telescope of plumes on the limb of Jupiter during impacts A, E, G, and W. The model uses a parameterized version of the final power-law velocity distribution from the impact models of Zahnle and Mac Low. The observed plume heights, lightcurve features, and debris patterns fix the values of model parameters. The parameters that best reproduce the debris patterns dictate an approximately conic plume geometry, with the apex of the cone initially near the impact site, the cone's axis pointed in the direction from which the impactor came, and an opening angle >45sp ° from the axis. Since material of a given velocity is, at any given time, a certain distance from the cone apex, the geometry spreads high-velocity material much thinner than low-velocity material. The power law exponent of -1.55 combines with this effect to make mass density fall off as the -3.55 power of the velocity (or distance from the plume base). However, the outer shell of highest-velocity material, corresponding to the atmospheric shock wave, carries considerably elevated mass density. We are currently studying the range of reasonable optical properties to determine whether the visible plume tops corresponded to the physical top of this shell, or to a lower density contour.

Workshop on Observations of Recent Comets (1990)

NASA Technical Reports Server (NTRS)

Huebner, Walter F. (Editor); Wehinger, Peter A. (Editor); Rahe, Jurgen (Editor); Konno, Ichishiro (Editor)

1990-01-01

Potential interpretations are presented for observations of four comets: Brorsen-Metcalf (1989o), Okazaki-Levy-Rudenko (1989r), Aarseth-Brewington (1989a1), and Austin (1989o1). The relationship of minor species with each other and possible parents as well as with dust are being pursued in a number of investigations. Of particular interest are the abundance ratios of CH4 to CO and NH3 to N2. The need for closer collaboration betwen observing teams and modelers is examined. The need for dust size distribution as a function of cometocentric distance to be analyzed in closer collaboration between observers and modelers is discussed.

High-Resolution Spectroscopy of Stratospheric Ethane Following the Jupiter Impact of 2009

NASA Technical Reports Server (NTRS)

Fast, Kelly; Kostiuk, Theodor; Livengood, Timothy A.; Hewagama, Tilak; Amen, John

2010-01-01

We report on high-resolution infrared spectroscopy of ethane (C2H6) performed at the latitude of an impact site on Jupiter discovered on 19 July 2009 by A. Wesley from a location in Murrumbateman, Australia. The observations used the NASA Goddard Space Flight Center's Heterodyne Instrument for Planetary Wind and Composition (HIPWAC) at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. HIPWAC is a mid-infrared (9-12 microns) heterodyne spectrometer operating at the highest limit of spectral resolving power (lambda\\Delta\\lambda > l06), providing information on atmospheric constituent abundance and temperature through fully resolved tine shapes. Ethane is a stable trace product of methane photochemistry that is nearly uniformly mixed in Jupiter's stratosphere, providing an effective probe of that altitude region. Ethane emission line profiles near 11,74 microns in the Ug band were measured in Jupiter's stratosphere at 25 MHz (11.00083/cm) resolution. A sequence of spectra of ethane acquired over a range of longitude at the impact latitude (56S planetocentric) probes constituent abundance and temperature profile, both on and off the impact region. Near the site of the impact, ethane emission increased above levels measured well outside the impact region. Radiative transfer analysis indicates increased ethane mole fraction (30% greater). Variation in the measured continuum level and line intensities within 75deg of the impact longitude indicate the presence of an opacity source (haze) at altitudes near and above the tropopause and as high as the 10-mbar level near the impact site. The indication of possible haze opacity up to the 10-mbar level in the atmosphere is consistent with measurements made by HIPWAC's predecessor as part of the IRTF Shoemaker Levy-9 campaign in 1994.

Impact Cratering Calculations

NASA Technical Reports Server (NTRS)

Ahrens, Thomas J.

1997-01-01

Understanding the physical processes of impact cratering on planetary surfaces and atmospheres as well as collisions of finite-size self-gravitating objects is vitally important to planetary science. The observation has often been made that craters are the most ubiquitous landform on the solid planets and the satellites. The density of craters is used to date surfaces on planets and satellites. For large ringed basin craters (e.g. Chicxulub), the issue of identification of exactly what 'diameter' transient crater is associated with this structure is exemplified by the arguments of Sharpton et al. (1993) versus those of Hildebrand et al. (1995). The size of a transient crater, such as the K/T extinction crater at Yucatan, Mexico, which is thought to be the source of SO,-induced sulfuric acid aerosol that globally acidified surface waters as the result of massive vaporization of CASO, in the target rock, is addressed by our present project. The impact process excavates samples of planetary interiors. The degree to which this occurs (e.g. how deeply does excavation occur for a given crater diameter) has been of interest, both with regard to exposing mantle rocks in crater floors, as well as launching samples into space which become part of the terrestrial meteorite collection (e.g. lunar meteorites, SNC's from Mars). Only in the case of the Earth can we test calculations in the laboratory and field. Previous calculations predict, independent of diameter, that the depth of excavation, normalized by crater diameter, is d(sub ex)/D = 0.085 (O'Keefe and Ahrens, 1993). For Comet Shoemaker-Levy 9 (SL9) fragments impacting Jupiter, predicted excavation depths of different gas-rich layers in the atmosphere, were much larger. The trajectory and fate of highly shocked material from a large impact on the Earth, such as the K/T bolide is of interest. Melosh et al. (1990) proposed that the condensed material from the impact upon reentering the Earth's atmosphere induced. radiative heating, and producing global firestorms. The observed reentry splash of the SL-9 impact-induced plumes that reimpact Jupiter (Boslough et al., 1994) supported Melosh's K/T model. The fate of early primitive planetary atmospheres during the latter stages of planetary accretion, resulting from impactors in the 100 to 103 km diameter require modeling, e.g. Newman et al. (1997). Ahrens (1990; 1993) and Chen and Ahrens (1997) found that upon delivery of most of the impact energy to the solid planet, very large ground motions arise, which couple sufficient kinetic energy to the atmosphere to cause substantial atmospheric escape. The trade-off of this model with that of Cameron (1997) who suggests that atmospheric blow-off occurs as a result of the massive impact-induced heating of the atmosphere and Pepin (1997) who uses this heating event to model differential hydrodynamic loss of lighter atmospheric gases, requires further research.

Serendipitous images of methanol in Comet Levy (1900 XX)

NASA Technical Reports Server (NTRS)

Hoban, Susan

1993-01-01

Reuter's (1992) model of the IR fluorescence of methanol is used to retrieve a methanol production rate of 3 +/- 1 x 10 exp 26/s and an abundance relative to water of about 0.1 percent. It is argued that calibration is of paramount importance and that a near-simultaneous spectrum is necessary for achieving a reliable estimate of the continuum underlying the emission feature.

Observations of cometary parent molecules with the IRAM radio telescope

NASA Technical Reports Server (NTRS)

Colom, P.; Despois, D.; Paubert, G.; Bockelee-Morvan, D.; Crovisier, Jacques

1992-01-01

Several rotational transitions of HCN, H2S, H2CO, and CH3OH were detected in comets P/Brorsen-Metcalf 1989 X, Austin (1989c1) and Levy (1990c) with the Institute for Millimeter Radioastronomy (IRAM) 30-m radio telescope. This allows us to determine the production rates of these molecules and to probe the physical conditions of the coma.

ISO's analysis of Comet Hale-Bopp

NASA Astrophysics Data System (ADS)

1997-03-01

The European Space Agency's Infrared Space Observatory ISO inspected Comet Hall-Bopp during the spring and autumn of 1996. The need to keep ISO's telescope extremely cold restricts the spacecraft's pointing in relation to the Sun and the Earth and it ruled out observations at other times. The analyses of the 1996 observations are not yet complete, but already they give new insight into the nature of comets. Comet Hale-Bopp is believed to be a large comet with a nucleus up to 40 kilometres wide. It was discovered in July 1995 by two American astronomers working independently, Alan Hale and Thomas Bopp. At that time, the comet was a billion kilometres away from the Sun, but 200 times brighter than Halley's Comet was, when at a comparable distance. Comet Hale-Bopp will make its closest approach to the Earth on 22 March, and its closest approach to the Sun (perihelion) on 1 April 1997. Some scientific results from ISO The discovery of Comet Hale-Bopp occurred before ISO's launch in November 1995. When first observed by ISO in March and April 1996, the comet was still 700 million kilometres from the Sun, and almost as far from the Earth and ISO. With its privileged view of infrared wavebands inaccessible from the Earth's surface, ISO's photometer ISOPHOT discovered that carbon dioxide was an important constituent of the comet's emissions of vapour.ISOPHOT measured the temperature of the dust cloud around Comet Hale-Bopp. In March 1996, when the comet was still more than 700 million kilometres from the Sun, the dust cloud was at minus 120 degrees C. When ISOPHOT made similar observations in October 1996, the comet was 420 million kilometres from the Sun, and the dust cloud had warmed to about minus 50 degrees C. Intensive observations of Comet Hale-Bopp were also made by ISO's Short-Wave Spectrometer SWS, the Long-Wave Spectrometer LWS, and the ISOPHOT spectrometer PHOT-S. Results are due for publication at the end of March. They will give details about the composition of the comet's dust and vapour, and also rates of escape of vapour, which will help in assessing the loss of material from Comet Hale-Bopp during this visit to the Sun's vicinity. "Watch out for some fascinating news," says Thijs de Graauw of Groningen University, who is in charge of the SWS instrument used in this study. "What excites me is the opportunity we shall have to compare dusty Comet Hale-Bopp, seen in the Solar System, with dusty objects far away among the stars which seem to be made of similar materials. Infrared astronomy has a special ability to unify cosmic chemistry at all scales from little dust grains in the Earth's vicinity to vast and distant galaxies." The dust itself interests the infrared astronomers, not least because their view of the Universe at large is spoiled to some extent by dust left behind by comets. Together with fine debris from asteroids, the comet dust makes a bright infrared band around the sky, which corresponds with the zodiacal light sometimes seen by eye, slanting above the horizon at twilight. ISO's predecessor, the US-Dutch-UK infrared astronomical satellite IRAS, found trails of comet dust much longer and more persistent than the familiar comet tails. ISO has seen a trail from Comet Kopff. By detecting dust grains that are typically much larger than those seen by visible light, ISO scientists hope to learn more about the dust's long-term behaviour in the Solar System. A series of images of Comet Hale-Bopp, obtained by the camera ISOCAM in October 1996, is the subject of continuing analysis. Leading this work in progress is Philippe Lamy of Marseille, France. "We hope to unveil the nucleus of the comet," Professor Lamy explains. "In principle, the Hubble Space Telescope can see finer details by visible light, but the contrast of the nucleus against the bright surrounding coma is superior at infrared wavelengths. This is because the thermal emission from the nucleus is very large and can be detected thanks to the high spatial resolution of ISO. We have a long time coverage of the comet, so we hope to determine the light-curve of the nucleus -- which, in turn, will reveal its gross shape and an estimate of its rotation period." A commanding role in comet research As comets are relics from the construction of the Solar System, and played a major role in the formation of the planets, they are a link between the Earth and the wider Universe of stars. The carbon compounds contained in comets probably contributed raw materials for the origin of life on the Earth, and according to one theory the Earth's oceans were made from comet ice. Growing knowledge of the composition and behaviour of comets is therefore crucial for a fuller understanding of our cosmic origins. ESA has a commanding role in space research on comets. Its Giotto spacecraft was the most daring of the international fleet of spacecraft that visited Halley's Comet in March 1986. Giotto obtained exceptional pictures and other data as it passed within 600 kilometres of the nucleus. Dust from the comet badly damaged the spacecraft, but in a navigational tour de force Giotto made an even closer approach to Comet Grigg-Skjellerup in July 1992. Now ESA is planning the Rosetta mission that will rendezvous with Comet Wirtanen and fly in company with it, making observations far more detailed than the fast flybys of Halley's Comet and Comet Grigg-Skjellerup could achieve. As for space astronomy, the International Ultraviolet Explorer, in which ESA was a partner, made unrivalled observations of Halley's Comet by ultraviolet light. ESA is also a partner in the Hubble Space Telescope, which saw the historic impacts of Comet Shoemaker-Levy 9 on Jupiter in July 1994, and has recently observed Comet Hyakutake as well as Hale-Bopp. The SOHO spacecraft, built by ESA for a joint ESA-NASA project to examine the Sun, has a distinctive view of comets. It has observed the hydrogen coronas of comets with its SWAN instrument. SOHO's coronagraph LASCO observed Comet Hyakutake rounding the Sun (when it was invisible to ground-based observers) and has discovered seven new comets very close to the Sun. Only ISO provides astronomers with information from comets across a very wide range of infrared wavelengths unobservable from the ground. Besides Comet Hale-Bopp, ISO has examined Comets Schwassmann-Wachmann 1, Chiron, Kopff, IRAS 1 and Wirtanen. The last of these, Comet Wirtanen, is the target of the Rosetta mission and is now making one of its six-yearly visits to the Sun's vicinity. Dietrich Lemke of Heidelberg, Germany, who is in charge of the ISOPHOT instrument in ISO, summarizes ISO's unique contribution. "By measuring the extremely weak heat rays from these frosty objects at different distances," Professor Lemke says, "we have a thermometer to gauge a comet's growing fever when it nears the Sun. As the temperature rises, first one kind of ice evaporates, and then another, producing various chemical signatures in the infrared spectrum. We can also characterize the mineral dust coming out of the comet. So ISO offers a vivid impression of comets in action which no other instrument can match." Photos are available on the ESA home page on Internet : http://www.estec.esa.nl/spdwww/iso/html/hale-bopp.htm

Public Sector Training: A "Blind" Spot in the 1999 South African National Levy-Grant Policy

ERIC Educational Resources Information Center

Paterson, Andrew

2005-01-01

In 2000, South Africa implemented a levy-grant policy (Skills Development Levies Act, 1999) to give an incentive for workplace training across private and public sector workplaces alike, but the impact of the levy-grant scheme in the public sector was restricted by financial and management processes unique to that environment. This article shows…

Simple Models of SL-9 Impact Plumes

NASA Astrophysics Data System (ADS)

Harrington, J.; Deming, L. D.

1996-09-01

The impacts of the larger fragments of Comet Shomaker-Levy 9 on Jupiter left debris patterns of consistent appearance, likely caused by the landing of the observed impact plumes. Realistic fluid simulations of impact plume evolution may take months to years for even single computer runs. To provide guidance for these models and to elucidate the most basic aspects of the plumes, debris patterns, and their ultimate effect on the atmosphere, we have developed simple models that reproduce many of the key features. These Monte-Carlo models divide the plume into discrete mass elements, assign to them a velocity distribution based on numerical impact models, and follow their ballistic trajectories until they hit the planet. If particles go no higher than the observed ~ 3,000 km plume heights, they cannot reach the observed crescent pattern located ~ 10,000 km from the impact sites unless they slide horizontally after ballistic flight. By introducing parameterized sliding or higher trajectories, we can reproduce most of the observed impact features, including the central streak, the crescent, and the ephemeral ring located ~ 30,000 km from the impact sites. We also keep track of the amounts of energy and momentum delivered to the atmosphere as a function of time and location, for use in atmospheric models (D. Deming and J. Harrington, this meeting).

Role of stereoscopic imaging in the astronomical study of nearby stars and planetary systems

NASA Astrophysics Data System (ADS)

Mark, David S.; Waste, Corby

1997-05-01

The development of stereoscopic imaging as a 3D spatial mapping tool for planetary science is now beginning to find greater usefulness in the study of stellar atmospheres and planetary systems in general. For the first time, telescopes and accompanying spectrometers have demonstrated the capacity to depict the gyrating motion of nearby stars so precisely as to derive the existence of closely orbiting Jovian-type planets, which are gravitationally influencing the motion of the parent star. Also for the first time, remote space borne telescopes, unhindered by atmospheric effects, are recording and tracking the rotational characteristics of our nearby star, the sun, so accurately as to reveal and identify in great detail the heightened turbulence of the sun's corona. In order to perform new forms of stereo imaging and 3D reconstruction with such large scale objects as stars and planets, within solar systems, a set of geometrical parameters must be observed, and are illustrated here. The behavior of nearby stars can be studied over time using an astrometric approach, making use of the earth's orbital path as a semi- yearly stereo base for the viewing telescope. As is often the case in this method, the resulting stereo angle becomes too narrow to afford a beneficial stereo view, given the star's distance and the general level of detected noise in the signal. With the advent, though, of new earth based and space borne interferometers, operating within various wavelengths including IR, the capability of detecting and assembling the full 3-dimensional axes of motion of nearby gyrating stars can be achieved. In addition, the coupling of large interferometers with combined data sets can provide large stereo bases and low signal noise to produce converging 3- dimensional stereo views of nearby planetary systems. Several groups of new astronomical stereo imaging data sets are presented, including 3D views of the sun taken by the Solar and Heliospheric Observatory, coincident stereo views of the planet Jupiter during impact of comet Shoemaker-Levy 9, taken by the Galileo spacecraft and the Hubble Space Telescope, as well as views of nearby stars. Spatial ambiguities arising in singular 2-dimensional viewpoints are shown to be resolvable in twin perspective, 3-dimensional stereo views. Stereo imaging of this nature, therefore, occupies a complementary role in astronomical observing, provided the proper fields of view correspond with the path of the orbital geometry of the observing telescope.

Meteorites for K-12 Classrooms: NASA Meteorite Educational Materials

NASA Astrophysics Data System (ADS)

Lindstrom, M.; Allen, J.

1995-09-01

The fall of a new meteorite is an event that catches the interest of the public in matters of science. The threat of a huge impact like last year's comet Shoemaker-Levy 9 gives us all reason to evaluate such potential risks. NASA's meteorite educational materials use our natural interest in rocks from space to present classroom activities on planetary science. The meteorite educational package includes a meteorite sample disk, a teachers's guide and a slide set. The sample disk is a lucite disk containing chips of six different kinds of meteorites (3 chondrites, achondrite, iron, stony-iron). EXPLORING METEORITE MYSTERIES is a teacher's guide with background information and 19 hands-on or heads-on activities for grades 4-12. It was prepared in a partnership of planetary scientists and teachers. The slide set consists of 48 slides with captions to be used with the activities. The materials will be available in Fall 1995. Teachers may obtain a loan of the whole package from NASA Teacher Resource Centers; researchers may borrow them from the JSC meteorite curator. The booklet is available separately from the same sources, and the slide set will be available from NASA CORE. EXPLORING METEORITE MYSTERIES is an interdisciplinary planetary science unit which teaches basic science concepts and techniques together with math, reading, writing and social studies The activities are done in a variety of different teaching styles which emphasize observation, experimentation and critical thinking. The activities are ideal for middle schools where teaming makes interdisciplinary units desireable, but most of the activities can be easily modified for grade levels from upper elementary through high school. Meteorites are a natural subject for interdisciplinary teaching because their study involves all fields of science and offers fascinating historical accounts and possibilities for creative expression. Topics covered in EXPLORING METEORITE MYSTERES are centered around basic questions: Where did they come from? What are they? How did they form? How do they affect people? The unit begins with the story of two boys who observed the fall of the Noblesville meteorite in 1991 and concludes with activities on using space resources, careers, and tabloid science. The NASA meteorite educational materials provide teachers with information, activities and slides to use meteorites to teach the interdisciplinary science of the solar system. It also provides planetary scientists with activities to take to local schools and ideas for sharing their knowledge with their communities.

100 and counting : SOHO's score as the world's top comet finder

NASA Astrophysics Data System (ADS)

2000-02-01

Like nearly all of SOHO's discoveries, the 100th comet showed up in images from the LASCO instrument. This is a set of coronagraphs that view the space around the Sun out to 20 million kilometres, while blotting out the bright solar disk with masks. Developed for SOHO by a multinational team led by the US Naval Research Laboratory, LASCO watches for mass ejections from the Sun that threaten to disturb the Earth's space environment. The comet discoveries are a big bonus. SOHO's experts spot many of the comets as soon as the images come in. But still pictures and movies from LASCO are freely available on the Internet to astronomers around the world, who can discover less obvious comets without leaving their desks. This was the case when Kazimieras Cernis of the Institute of Theoretical Physics and Astronomy in Vilnius, Lithuania, found SOHO-100. "On 4 February I saw the comet as a small speck of light in the previous day's LASCO images," Cernis explained. "It had no visible tail, but it was too fuzzy to be an asteroid. By the time I had seen the object moving steadily across the sky in six successive images, I was convinced it was a comet and I sent the details to the SOHO scientists for verification." The competition to find SOHO's 100th comet was keen. An amateur astronomer, Maik Meyer of Frauenstein, Germany, discovered SOHO-98 and 99. On 5 February, less than 24 hours after Cernis reported the candidate SOHO-100, Meyer found the candidate SOHO-101. On the same day and in the same LASCO images Douglas Biesecker, a member of the SOHO science team, spotted the candidate SOHO-102 travelling ahead of 101. Computations have now validated the orbits for all three candidates, and shown them to be bona fide comet discoveries. Other amateur astronomers have used the LASCO images to find comets. In the summer of 1999 Terry Lovejoy in Australia found five, and since September 1999 an amateur in England, Jonathan Shanklin, has spotted three more. "SOHO is a special chance for comet hunters," said Shanklin, who is director of the British Astronomical Association's comet section. "It allows amateurs to discover some of the smallest comets ever seen. Yet they link us to sightings of great comets going back more than 2000 years." Nine of the comets found with LASCO, including SOHO-100, 101 and 102, passed the Sun at a safe distance. SOHO-49, which showed up in LASCO images in May 1998 and was designated as Comet 1998 J1, became visible to the naked eye in the southern hemisphere. But the great majority of SOHO's comets failed to survive very close encounters with the Sun. Snowballs in hell Of the first 100 SOHO comets, 92 vaporized in the solar atmosphere. Isaac Newton suggested 300 years ago that infalling comets might supply the Sun with fuel, but no one has ever tracked a comet that definitely hit the bright surface. Near misses are well known, and 100 years ago Heinrich Kreutz in Kiel, Germany, realized that several comets seen buzzing the Sun seemed to have a common origin, because they came from the same direction among the stars. These comets are now called the Kreutz sungrazers, and the 92 vanishing SOHO comets belong to that class. They were not unexpected. Between 1979 and 1989 the P78-1 and SMM solar satellites spotted 16 comets closing with the Sun. Life is perilous for a sungrazer. The mixture of ice and dust that makes up a comet's nucleus is heated like the proverbial snowball in hell, and can survive its visit to the Sun only if it is quite large. What's more, the very strong tidal effect of the Sun's gravity can tear the loosely glued nucleus apart. The disruption that created the many SOHO sungrazers was similar to the fate of Comet Shoemaker-Levy 9, which went too close to Jupiter and broke up into many pieces that eventually fell into the massive planet in 1994. "SOHO is seeing fragments from the gradual break-up of a great comet, perhaps the one that the Greek astronomer Ephorus saw in 372 BC," commented Brian Marsden of the Center for Astrophysics in Cambridge, Massachusetts. "Ephorus reported that the comet split in two. This fits with my calculation that two comets on similar orbits revisited the Sun around AD 1100. They split again and again, producing the sungrazer family, all still coming from the same direction." The sungrazing comets slant in from the south, at 35 degrees to the plane where the Earth and the other planets orbit. As SOHO moves around the Sun, in step with the Earth, it sees the comets approaching the Sun from the east (left) in February and from the west (right) in August. In June and November the sungrazers seem to head straight up towards the Sun. "The rate at which we've discovered comets with LASCO is beyond anything we ever expected," said Douglas Biesecker, the SOHO scientist personally responsible for the greatest number of discoveries, 45. "We've increased the number of known sungrazing comets by a factor of four. This implies that there could be as many as 20,000 fragments." Their ancestor must have been enormous by cometary standards. Although SOHO's sungrazers are all too small to survive, other members of the family are still large enough to reappear, depleted but intact, after their close encounters with the Sun. Among them were the Great September Comet (1882) and Comet Ikeya-Seki (1965). The history of splitting gives clues to the strength of comets, which will be of practical importance if ever a comet seems likely to hit the Earth. And the fragments seen as SOHO comets reveal the internal composition of comets, freshly exposed, in contrast to the much-altered surfaces of objects like Halley's Comet that have visited the Sun many times. LASCO reveals how much visible dust each comet releases. Gas produced by evaporating ice is detected by another instrument on SOHO, the Ultraviolet Coronagraph Spectrometer or UVCS, and enables scientists to measure the speed of the solar wind as it emerges from the Sun. A comet spotted by its gas cloud The count of SOHO's comet discoveries would be one fewer without a recent bonus from SWAN. This instrument's name unpacks into Solar Wind Anisotropies, and it was provided by the French Service d'Aéronomie and the Finnish Meteorological Institute. SWAN looks away from the Sun to survey atomic hydrogen in the Solar System, which glows with ultraviolet light and is altered by the solar wind. The instrument also sees large clouds of hydrogen surrounding comets, produced by the break-up of water molecules evaporating from the comets' ice. In December 1999 the International Astronomical Union retrospectively credited SWAN and SOHO with finding Comet 1997 K2 in SWAN full-sky images from May to July 1997. It made number 93 on the SOHO scorecard. This comet remained outside the orbit of the Earth even at its closest approach to the Sun. Although it was presumably a small, faint comet, the gas cloud grew to a width of more than 4 million kilometres. "The discovery was a surprise," said Teemu Mäkinen, a Finnish member of the SWAN group. "Our normal procedure is to observe hydrogen clouds of comets detected by other people. In that respect, SWAN on SOHO is the most important instrument now available for routinely measuring the release of water vapour from comets." When Comet Wirtanen, the target for ESA's Rosetta mission (2003), made its most recent periodic visit to the Sun, it pumped out water vapour at a rate of 20,000 tons a day, according to the SWAN data. For the great Comet Hale-Bopp the rate reached 20 million tons a day and SWAN watched its hydrogen cloud grow to 70 million kilometres -- by far the largest object ever seen in the Solar System.

The Shoemaker's Knife

ERIC Educational Resources Information Center

Thomson, Ian

2010-01-01

Archimedes, the famous Greek mathematician, lived from 287 BCE until approximately 212 BCE. He thought that the figure of two semi-circles on a straight line enclosed by a larger semi-circle resembled a shoemaker's knife. Archimedes called this figure an "arbelos" since arbelos is the Greek word for a shoemaker's knife. The author describes the…

Terminal Ballistics. A Preliminary Report

DTIC Science & Technology

1941-01-01

In all of the above, it has been tacitly assumed that the projectile suffers no deformation on impact or during pen- etration. T, Levi - Civita ...dimensionless; 6. kr velocity coefficient in Levi - Civita A»; sec/ft; 16. k........material coefficient in de Giorgi formula; di- mensionless; 17. k...sectional area of projectile; in ; 6. A*.» effective area on Levi - Civita hypothesis; in2 ; 16. A(x).....area cross-section at distance x from nose

Mars Exploration Rover APXS Results from Matijevic Hill

NASA Technical Reports Server (NTRS)

Cohen, B. A.; Clark, B. C.; Gellert, R.; Klingelhoefer, G.; Ming, D. W.; Mittlefehldt, D. W.; Morris, R. V.; Schrader, C. M.; Schroeder, C.; Yen, A. S.;

Dynamic Fracture Toughness Evaluation by Measurement of CTOD (Crack Tip Opening Displacement).

DTIC Science & Technology

1988-03-15

fracture toughness of structural steels were reported by Shoemaker and Rolfe [1]; these and similar results are also presented in the text by Rolfe and...8217 MPaV/-m/s. Following the dynamic tests of Shoemaker and Rolfe , extensions of the familiar ASTM E-399 static fracture toughness tests were examined. This...s.V.: **.4* .4 5, -~ 5 5 - 𔃿 .4.4 References [1] Shoemaker, A.K. and Rolfe , S.T., "The Static and Dynamic Low-Temperature Crack-Toughness

Degradation of Endeavour Crater, Mars

NASA Technical Reports Server (NTRS)

Grant, J. A.; Crumpler, L. S.; Parker, T. J.; Golombek, M. P.; Wilson, S. A.; Mittlefehldt, D. W.

2015-01-01

The Opportunity rover has traversed portions of two western rim segments of Endeavour, a 22 km-diameter crater in Meridiani Planum, for the past three years. The resultant data enables the evaluation of the geologic expression and degradation state of the crater. Endeavour is Noa-chian-aged, complex in morphology, and originally may have appeared broadly similar to the more pristine 20.5 km-diameter Santa Fe complex crater in Lunae Palus (19.5degN, 312.0degE). By contrast, Endeavour is considerably subdued and largely buried by younger sulfate-rich plains. Exposed rim segments dubbed Cape York (CY) and Solander Point/Murray Ridge/Pillinger Point (MR) located approximately1500 m to the south reveal breccias interpreted as remnants of the ejecta deposit, dubbed the Shoemaker Formation. At CY, the Shoemaker Formation overlies the pre-impact rocks, dubbed the Matijevic Formation.

Deep Impact Spots Quarry

NASA Technical Reports Server (NTRS)

2005-01-01

Sixty-nine days before it gets up-close-and-personal with a comet, NASA's Deep Impact spacecraft successfully photographed its quarry, comet Tempel 1, at a distance of 39.7 million miles. The image, taken on April 25, 2005, is the first of many comet portraits Deep Impact will take leading up to its historic comet encounter on July 4.

Myth and Reality: Employer Sponsored Training in Australia

ERIC Educational Resources Information Center

Smith, Andy; Billett, Stephen

2005-01-01

In 1990, Australia implemented an employer training levy, the Training Guarantee Scheme. The Training Guarantee was abolished by the incoming Coalition federal government in 1996 after much negative publicity about its impact, particularly on small business. Recently, there have been calls to revive the notion of an employer training levy as a…

Meet EPA Scientist Jody Shoemaker, Ph.D.

EPA Pesticide Factsheets

EPA research chemist Jody Shoemaker, Ph.D., works to support Agency efforts to protect drinking water. She helps develop methods for analyzing organic chemicals on the Drinking Water Contaminant Candidate List (CCL).

Education Funding Crisis in the Suburbs: The Impact of the 2007-09 Recession Recovery Policies and the New York State Tax Levy Cap on School District Financial Planning Practices

ERIC Educational Resources Information Center

Galligan, John J.; Annunziato, Anthony

2017-01-01

This article examines the impact of the fiscal recovery policies stemming from the 2007-09 economic recession and the implementation of the 2011 New York State Property Tax Levy Cap on the budgets of school districts located within a Long Island, New York suburban township. The research basis of this paper is based on two studies conducted by the…

Landing and Population Hazard Analysis for Stardust Entry in Operations and Entry Planning

NASA Technical Reports Server (NTRS)

Tooley, Jeffrey; Desai, Prasun N.; Lynos, Daniel T.; Hirst, Edward A.; Wahl, Tom E.; Wawrzyniak, Georffery G.

2006-01-01

Stardust is a comet sample return mission that successfully returned to Earth on January 15, 2006. Stardust's targeted landing area was the Utah Test and Training Range in the Northwest corner of Utah. Requirements for the risks associated with landing were levied on Stardust by the Utah Test and Training Range and NASA. This paper describes the analysis to verify that these requirements were met and and includes calculation of debris survivability, generation of landing site selection plots, and identification of keep-out zones, as well as appropriate selection of the landing site. Operationally the risk requirements were all met for both of the GOMO-GO polls, so entry was authorized.

Training Guarantee: A Levy To Improve the Quality of Australian Workforce.

ERIC Educational Resources Information Center

Navaratnam, K. K.

The Training Guarantee Act (TGA) passed by the Federal Parliament of Australia in 1990 establishes a training guarantee scheme. It requires employers to invest in high quality, employment-related training that will most benefit their businesses. The levy is having an impact on many facets of human resource development in Australia. In seeking to…

Recent Results From the Opportunity Rover's Exploration of Endeavour Crater, Mars

NASA Technical Reports Server (NTRS)

Arvidson, R. E.; Squyres, S. W.; Gellert, R.; Mittlefehldt, D. W.

2014-01-01

The Mars Exploration Rover Opportunity is beginning its 11th year of exploration and as of sol 3535 (1/3/14 UTC) has traversed 38,729 m (based on wheel turns) across the plains of Meridiani and the rim of the approx. 22 km wide Noachian Endeavour Crater. Opportunity has investigated ancient sulfate-rich sand-stones (Burns formation) that dominate the plains and formed in ancient playa and dune environments, characterized impact breccias (Shoemaker formation) and their aqueous alteration on Endeavour's Cape York rim segment, and investigated extensive aqueous alteration of rocks on Cape York's Matijevic Hill that stratigraphically underlie Shoemaker formation and predate the Endeavour-forming event. In this abstract results from Opportunity's recent exploration of Endeavour's rim are covered, focusing on comparing what was found on Matijevic Hill with observations acquired on Murray Ridge, where Opportunity will spend its sixth winter at Cook Haven.

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!

Comet Impacts as a Source of Methane on Titan

NASA Astrophysics Data System (ADS)

Howard, Michael; Goldman, N.; Vitello, P. A.

2006-12-01

We model comet impacts on Titan as a possible source of atmospheric methane. That is, we study the formation of methane in comet impacts using chemical equilibrium calculations coupled with arbitrary Lagrange-Eulerian (ALE) hydrodynamics. That is, we study the chemical transformation of comet material under high pressure and temperature conditions as it impacts Titan. We assume that the comet is composed of ice, graphite, nitrogen and some hydrocarbons. For certain pressure and temperature regimes, in chemical equilibrium, a significant amount of ice and graphite can be transformed into methane. As a result, we find that a significant amount of methane can be formed in comet collisions on Titan. The methane is formed in the post-impact vapor clouds that form as the comet material expands and cools. We use molecular dynamics to construct an equation of state for the ice surface structures and the comet material. We also study kinetic processes for methane formation during the expansion and cooling phase. We discuss the implication of our results for comets as a possible source of abiotic methane on Titan and its implications on the origin of life. We also discuss the various uncertainties in our model. * This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

Electron impact excitation of carbon monoxide in comet Hale-Bopp

NASA Astrophysics Data System (ADS)

Campbell, L.; Brunger, M. J.

2009-02-01

The fourth positive emissions of carbon monoxide in the coma of comet Hale-Bopp have been assumed to be due mainly to fluorescence induced by sunlight. Based on this assumption they were used to deduce the abundance of carbon monoxide in the comet, giving a value higher than in other comets. Emissions produced by electron impact excitation of CO were not considered. Recent measurements and theoretical calculations of integral cross sections for electron impact excitation of CO allow the contribution of electron impact to be calculated, giving about 40% of the total. This implies that the abundance of CO in the outer coma of comet Hale-Bopp was only 60% of that previously deduced. However, as the high proportion of CO in comet Hale-Bopp was also seen in some other measurements, alternative explanations are considered. The method of calculation is tested by successfully predicting the O I emission at 1356 Å, supporting the belief that this line is due to electron impact excitation.

Understanding the Effects of Collisional Evolution and Spacecraft Impact Experiments on Comets and Asteroids

NASA Technical Reports Server (NTRS)

Lederer, S.M.; Jensen, E.A.; Fane, M.; Smith, D.C.; Holmes, J.; Keller, L.P.; Lindsay, S.S.; Wooden, D.H.; Whizin, A.; Cintala, M.J.;

INTRODUCTION: Award of the 2003 Hannes Alfvén Prize of the European Physical Society to Professor Vladimir Evgenievitch Fortov

NASA Astrophysics Data System (ADS)

Wagner, F.

2003-12-01

The Hannes Alfvén Prize of the European Physical Society for Outstanding Contributions to Plasma Physics (2003) has been awarded to Vladimir Evgenievitch Fortov `for his seminal contributions in the area of non-ideal plasmas and strongly coupled Coulomb systems, and for his pioneering work on the generation and investigation of plasmas under extreme conditions'. Vladimir Evgenievitch Fortov was born on 23 January 1946 in Noginsk, Russia. He studied physics at the Moscow Institute of Physics and Technology (PhD in 1976). In 1978 he was made a Professor and in 1991 he was awarded the Chair of the Moscow Institute of Physics and Technology. In the same year he became a Member of the Russian Academy of Sciences and was its vice-chairman from 1996 to 2001. From 1996 to 1998, Professor Fortov went into politics where he was just as successful, becoming Deputy Prime Minister of the Government of the Russian Federation and Minister of Science and Technology of the Russian Federation. Professor Fortov has made outstanding experimental and theoretical contributions to low temperature plasma physics. His pioneering work investigating non-ideal plasmas produced by intense shock waves initiated a new research field---the physical properties of highly compressed plasmas with strong inter-particle interactions. Under the leadership of Professor Fortov, experimental methods for generating and diagnosing these plasmas under extreme conditions were developed. To generate intense shock waves, a broad spectrum of drivers was used---chemical explosives, hypervelocity impact, lasers, relativistic electrons, heavy-ion and soft x-ray beams. Measurements of the equation of state, transport and optical properties of strongly coupled plasmas were carried out, including the interesting region lying between condensed matter and rarefied plasmas where specific plasma phase transitions and insulator--metal transitions were expected and explored. In another area of strongly coupled plasmas, Professor Fortov led theoretical and experimental studies on `dusty plasmas', carried out over a wide range of plasma parameters, using a broad spectrum of experimental techniques and devices. These studies embraced thermal combustion, glow and rf discharges and plasmas induced by cosmic ultraviolet and nuclear radiation. Under many of these conditions, ordered structures of dust in plasma liquids and plasma crystals were observed for the first time. Investigations of dusty plasmas induced by solar radiation and dust structures in DC glow discharges were first carried out on the Mir space station under micro-gravity conditions. The Russian--German experiment on dusty plasma crystals in space was successfully started on the International Space Station (ISS) in March 2001. This experiment was the first physics experiment on board the ISS. On the basis of his experimental results, Professor Fortov developed a general method of constructing semi-empirical equations of state of highly compressed materials. He put forward theoretical models of thermodynamical, transport and optical properties of strongly non-ideal plasmas. On the basis of these models Professor Fortov developed two-dimensional and three-dimensional computer codes for computer simulations of the processes in advanced energetic, space, nuclear and aviation systems based on high energy density plasmas. Professor Fortov has not only contributed to plasma theory but also to more applied topics. His laboratory participated in international space projects like the VEGA project (plasma dust impact phenomena), as well as the Halley Comet exploration, and studied plasma and shock wave phenomena stimulated by the impact of the Shoemaker-Levy 9 comet with Jupiter. Professor Fortov is an internationally well known scientist. He collaborates actively with many plasma laboratories and institutions. He has received many national and international awards, including several USSR and Russian State Awards, the A P Karpinskii-Toepfer Scientific Award for Physics and Chemistry (1997), the P Bridgman Award for High Pressure Plasma Investigations and Achievements in High Pressure Physics and Chemistry (1999), the A Einstein Medal of UNESCO (2000) and the Max Planck Award for Physics (2002). It is therefore with great pleasure and honour that the Plasma Physics Division of the European Physical Society has awarded the Hannes Alfvén prize this year to Professor Vladimir Evgenievitch Fortov. This article first appeared on the Europhyisics News website.

The Age of Lunar South Circumpolar Craters Haworth, Shoemaker, Faustini, and Shackleton: Implications for Regional Geology, Surface Processes, and Volatile Sequestration

NASA Technical Reports Server (NTRS)

Tye, A. R.; Fassett, C. I.; Head, J. W.; Mazarico, E.; Basilevsky, A. T.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

2015-01-01

The interiors of the lunar south circumpolar craters Haworth, Shoemaker, Faustini, and Shackleton contain permanently shadowed regions (PSRs) and have been interpreted to contain sequestered volatiles including water ice. Altimetry data from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter provide a new means of examining the permanently shadowed interiors of these craters in unprecedented detail. In this study, we used extremely high-resolution gridded LOLA data of Haworth, Shoemaker, Faustini, and Shackleton to determine the size-frequency distributions and the spatial density of craters superposing their rims, inner slopes, and floors. Based on their population of superposed D greater than or equal to 2 km craters, Haworth, Shoemaker, and Faustini have pre-Nectarian formation ages. Shackleton is interpreted as having a Late Imbrian age on the basis of craters with diameter D greater than or equal to 0.5 km superposed on its rim. The local density of craters with sub-km diameters across our study area is strongly dependent on slope; because of its steep interior slopes, the lifetime of craters on the interior of Shackleton is limited. The slope-dependence of the small crater population implies that the population in this size range is controlled primarily by the rate at which craters are destroyed. This is consistent with the hypothesis that crater removal and resurfacing is a result of slopedependent processes such as diffusive mass wasting and seismic shaking, linked to micrometeorite and meteorite bombardment. Epithermal neutron flux data and UV albedo data show that these circumpolar PSRs, particularly Shoemaker, may have approximately 1-2% water ice by mass in their highly porous surface regolith, and that Shoemaker may have approximately 5% or more water ice by mass in the near subsurface. The ancient formation ages of Shoemaker, Faustini and Haworth, and the Late Imbrian (approximately 3.5 Ga) crater retention ages of their floors suggests that any water ice that might have been deposited in their permanently shadowed areas was insufficient to modify the superposed crater population since that time.

Dust Impact Monitor (SESAME-DIM) on-board Rosetta/Philae: Aerogel as comet analog material

NASA Astrophysics Data System (ADS)

Flandes, Alberto; Albin, Thomas; Arnold, Walter; Fischer, Hans-Herbert; Hirn, Attila; Loose, Alexander; Mewes, Cornelia; Podolak, Morris; Seidensticker, Klaus J.; Volkert, Cynthia; Krüger, Harald

2018-03-01

On 12 November 2014, during the descent of the Rosetta lander Philae to the surface of comet 67P/Churyumov-Gerasimenko the Dust Impact Monitor (DIM) on board Philae recorded an impact of a cometary dust impact of a cometary dust particle at 2.4 km from the comet surface (5 km from the nucleus' barycentre). In this work, we report further experiments that support the identification of this particle. We use aerogel as a comet analog material to characterise the properties of this particle. Our experiments show that this particle has a radius of 0.9 mm, a low density of 0.25 g/cm3 and a high porosity close to 90%. The particle likely moved at near 4 m/s with respect to the comet.

The Shoemaker's Knife--An Approach of the Polya Type.

ERIC Educational Resources Information Center

Libeskind, Shlomo; Lott, Johnny W.

1984-01-01

Archimedes' shoemaker's knife problem is interesting in its own right and also allows the demonstration of heuristic teaching ideas and a different method of doing a routine construction. The focus in the article is on the thought processes involved and questions asked when attempting proofs with the problem. (MNS)

Comet Tempel 1 Six Years Later

NASA Image and Video Library

2011-02-18

This image shows the surface of comet Tempel 1 before and after NASA Deep Impact mission sent a probe into the comet in 2005. The region was imaged by Deep Impact before the collision left, then six years later on by NASA Stardust-NExT mission.

Simulation of Comet Impact and Survivability of Organic Compounds

NASA Astrophysics Data System (ADS)

Liu, Benjamin; Lomov, Ilya; Blank, Jennifer; Antoun, Tarabay

2007-06-01

Comets have been proposed as a mechanism for the transport of complex organic compounds to Earth. For this to occur, a significant fraction of organic compounds must survive the shock loading, in particular the high temperatures, due to impact. 2D and 3D numerical simulations were performed to study the thermodynamic states due to a comet impact. The comet was modeled as a 1-km diameter icy sphere traveling at the Earth's escape velocity (11 km/s) impacting a half-space of basalt. Simulations were performed with GEODYN, a parallel, multi-material, Godunov-based Eulerian code employing adaptive mesh refinement. A constitutive model calibrated for hard rock was used for basalt. Tabular equations of state were used to account for the extreme conditions present upon shock loading. A major focus of the study was tracking the thermodynamic state of the comet material. Both the maximum temperature experienced and the phase were tracked for each point in the comet Temperature histories in the comet were also recorded. These quantities were used to estimate viability of organic compounds upon impact. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

Hubble Tracks Jupiter Storms

NASA Technical Reports Server (NTRS)

1995-01-01

NASA's Hubble Space Telescope is following dramatic and rapid changes in Jupiter's turbulent atmosphere that will be critical for targeting observations made by the Galileo space probe when it arrives at the giant planet later this year.

This Hubble image provides a detailed look at a unique cluster of three white oval-shaped storms that lie southwest (below and to the left) of Jupiter's Great Red Spot. The appearance of the clouds, as imaged on February 13, 1995 is considerably different from their appearance only seven months earlier. Hubble shows these features moving closer together as the Great Red Spot is carried westward by the prevailing winds while the white ovals are swept eastward. (This change in appearance is not an effect of last July's comet Shoemaker-Levy 9 collisions with Jupiter.)

The outer two of the white storms formed in the late 1930s. In the centers of these cloud systems the air is rising, carrying fresh ammonia gas upward. New, white ice crystals form when the upwelling gas freezes as it reaches the chilly cloud top level where temperatures are -200 degrees Fahrenheit (- 130 degrees Centigrade).

The intervening white storm center, the ropy structure to the left of the ovals, and the small brown spot have formed in low pressure cells. The white clouds sit above locations where gas is descending to lower, warmer regions. The extent of melting of the white ice exposes varied amounts of Jupiter's ubiquitous brown haze. The stronger the down flow, the less ice, and the browner the region.

A scheduled series of Hubble observations will help target regions of interest for detailed scrutiny by the Galileo spacecraft, which will arrive at Jupiter in early December 1995. Hubble will provide a global view of Jupiter while Galileo will obtain close-up images of structure of the clouds that make up the large storm systems such as the Great Red Spot and white ovals that are seen in this picture.

This color picture is assembled from a series of images taken by the Wide Field Planetary Camera 2, in planetary camera mode, when Jupiter was at a distance of 519 million miles (961 million kilometers) from Earth. These images are part of a set of data obtained by a Hubble Space Telescope (HST) team headed by Reta Beebe of New Mexico State University.

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/

Education and Outreach for Volunteer Planetary Defense

NASA Astrophysics Data System (ADS)

Burke, J. D.

2016-12-01

When a large meteor exploded over Chelyabinsk in 2013, people saw the bright flash and rushed to windows. Then the blast wave hit and many were injured by flying glass fragments. Education about airbursts might have reduced the casualties. Education and Public Outreach (EPO) can also be important in broadening public involvement in preparations for dealing with cosmic hazards. Amateur astronomers have an important role in discovering potentially hazardous asteroids and comets, and also in making follow-up observations after discovery. This is especially important for Southern Hemisphere observing sites where professional observers are relatively few. The Planetary Society makes small Shoemaker grants to aid amateur astronomers in this work. Much more could be done if educators, students and the general public were aware of the opportunity and the need. Beyond this, public engagement is essential to raise and maintain support for active agencies, including the UN-sponsored International Asteroid Warning Network (IAWN) and Space Mission Planning Advisory Group (SMPAG). This paper will describe and advocate EPO efforts in support of these and other Volunteer Planetary Defense activities.

Effect of fire on a seed bank pathogen and on seeds of its host Bromus tectorum

Treesearch

J. Beckstead; S.E. Meyer; L.E. Street; P.S. Allen

2010-01-01

The generalist pathogen Pyrenophora semeniperda (Brittlebank and Adam) Shoemaker occurs primarily in cheatgrass (Bromus tectorum L.) seed banks, where it causes high seed mortality (Beckstead et al. 2007; Meyer et al. 2007). How does fire impact survival of a fungal seed pathogen, P. semeniperda, versus survival of the seeds of its cheatgrass host, the invasive Bromus...

Proposal to conserve the name Helminthosporium maydis Y. Nisik. & C. Miyake (Bipolaris maydis) against H. maydis Brond. and Ophiobolus heterostrophus (Ascomycota: Pleosporales: Pleosporaceae)

USDA-ARS?s Scientific Manuscript database

The name Bipolaris maydis (Y. Nisik. & C. Miyake) Shoemaker is the type of the genus Bipolaris Shoemaker, while Cochliobolus heterostrophus (Drechsler) Drechsler is the type of the genus Cochliobolus Drechsler. Initially described as Helminthosporium maydis Y. Nisik. & C. Miyake, Bipolaris maydis is...

Can comet clouds around neutron stars explain gamma-ray bursts?

NASA Technical Reports Server (NTRS)

Tremaine, S.; Zytkow, A. N.

1986-01-01

The proposal of Harwit and Salpeter (1973) that gamma-ray bursts are due to impacts of comets onto neutron stars is examined further. It is assumed that most stars are formed with comet clouds similar to the Oort comet cloud which surrounds the sun, and it is suggested that there are at least four mechanisms by wich neutron stars may be formed while retaining their comet clouds: a spherically symmetric supernova explosion in an isolated star, accretion-induced collapse of a white dwarf in a cataclysmic variable with a very low mass secondary, accretion-induced collapse of a white dwarf in a wide binary with a low-mass giant companion, and coalescence of a close binary composed of two white dwarfs. Estimates are given of the cometary impact rates for such systems. It is suggested that if the wide binary scenario is correct, optical bursts may arise from the impact of comets onto the white dwarf remnant of the giant companion.

Robert Shoemaker, PhD | Division of Cancer Prevention

Cancer.gov

Dr. Robert Shoemaker obtained his PhD in human genetics from the Graduate School of Public Health of the University of Pittsburgh in 1975. Following postdoctoral experience at the Armed Forces Institute of Pathology he moved to the Children's Hospital Medical Center of Akron. His research on pediatric tumors led to an interest in the genetics of drug resistance and new drug

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.

Placing the Deep Impact Mission into context: Two decades of observations of 9P/Tempel 1 from McDonald Observatory

NASA Astrophysics Data System (ADS)

Cochran, A. L.; Barker, E. S.; Caballero, M. D.; Györgey-Ries, J.

2009-01-01

We report on low-spectral resolution observations of Comet 9P/Tempel 1 from 1983, 1989, 1994 and 2005 using the 2.7 m Harlan J. Smith telescope of McDonald Observatory. This comet was the target of NASA's Deep Impact mission and our observations allowed us to characterize the comet prior to the impact. We found that the comet showed a decrease in gas production from 1983 to 2005, with the decrease being different factors for different species. OH decreased by a factor 2.7, NH by 1.7, CN by 1.6, C 3 by 1.8, CH by 1.4 and C 2 by 1.3. Despite the decrease in overall gas production and these slightly different decrease factors, we find that the gas production rates of OH, NH, C 3, CH and C 2 ratioed to that of CN were constant over all of the apparitions. We saw no change in the production rate ratios after the impact. We found that the peak gas production occurred about two months prior to perihelion. Comet Tempel 1 is a "normal" comet.

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.

Comet impacts and chemical evolution on the bombarded earth

NASA Technical Reports Server (NTRS)

Oberbeck, Verne R.; Aggarwal, Hans

1992-01-01

Amino acids yields for previously published shock tube experiments are used with minimum Cretaceous-Tertiary (K/T) impactor mass and comet composition to predict AIB amino acid K/T boundary sediment column density. The inferred initial concentration of all amino acids in the K/T sea and in similar primordial seas just after 10 km comet impacts would have been at least 10 exp -7 M. However, sinks for amino acids must also be considered in calculating amino acid concentrations after comet impacts and in assessing the contribution of comets to the origin of life. The changing concentration of cometary amino acids due to ultraviolet light is compared with the equilibrium concentration of amino acids produced in the sea from corona discharge in the atmosphere, deposition in water, and degradation by ultraviolet light. Comets could have been more important than endogenous agents for initial evolution of amino acids. Sites favorable for chemical evolution of amino acids are examined, and it is concluded that chemical evolution could have occurred at or above the surface even during periods of intense bombardment of earth before 3.8 billion years ago.

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.

Spacecraft Images Comet Target Jets

NASA Image and Video Library

2010-11-04

NASA Deep Impact spacecraft High- and Medium-Resolution Imagers HRI and MRI captured multiple jets emanating from comet Hartley 2 turning on and off while the spacecraft is 8 million kilometers 5 million miles away from the comet.

Deep Impact Spots Quarry

NASA Image and Video Library

2005-04-27

Taken on April 25, 2005, sixty-nine days before it gets up-close-and-personal with a comet, NASA Deep Impact spacecraft successfully photographed its quarry, comet Tempel 1, at a distance of 39.7 million miles.

Unveiling Clues from Spacecraft Missions to Comets and Asteroids through Impact Experiments

NASA Technical Reports Server (NTRS)

Lederer, Susan M.; Jensen, Elizabeth; Fane, Michael; Smith, Douglas; Holmes, Jacob; Keller, Lindasy P.; Lindsay, Sean S.; Wooden, Diane H.; Whizin, Akbar; Cintala, Mark J.;

Fundamental Automated Scheduling System (FASS): A Second Look.

DTIC Science & Technology

1986-12-01

Mr. J.H. Shoemaker and Mr. Ron Flatley of Norfolk Naval Shipyard; Mr. Bob Brunner of Long Beach Naval Shipyard; Mr. Barry Brinson of Charleston...Management, McGraw-Hill, 1978. Pressman , Roger S.. Software Engineering: A Practitioner’s Approach, McGraw-Hill, 1982. Project Systems Consultants Inc...J.H. Shoemaker Code 377 Norfolk Naval Shipyard Portsmouth. Vireinih 23709-5000 13. Mr. Barry Brinson-I Code 377 Charleston Naval Shipyard Charleston

Comets, Charisma, and Celebrity: Reflections on Their Deep Impact

NASA Astrophysics Data System (ADS)

Olson, R. J. M.; Pasachoff, J. M.

In celebration of the Deep Impact Mission, this essay explores the influence of comets on the arts and sciences since the beginning of recorded time. Through images, ranging from the sublime to the humorous, it probes the reasons why comets are among the most charismatic visual spectacles in the universe and why, even as scientific missions unmask their mysteries, they remain iconic symbols and harbingers of change.

Cosmic impact: What are the odds?

NASA Astrophysics Data System (ADS)

Harris, A. W.

2009-12-01

Firestone et al. (PNAS 104, 16016-16021, 2007) propose that the impact of a ~4 km diameter comet (or multiple bodies making up a similar mass) led to the Younger Dryas cooling and extinction of megafauna in North America, 12,900 years ago. Even more provocatively, Firestone et al. (Cycle of Cosmic Catastrophes, Bear & Co. Books, 2006, 392pp), suggest that a nearby supernova may have produced a comet shower leading to the impact event, either by disturbing the Oort Cloud or by direct injection of 4-km comet-like bodies to the solar neighborhood. Here we show: (a) A supernova shockwave or mass ejection is not capable of triggering a shower of comets from the Oort Cloud. (b) An Oort Cloud shower from whatever cause would take 100,000 years or more for the perturbed comets to arrive in the inner solar system, and the peak flux would persist for some hundreds of thousands more years. (c) Even if all 20 solar masses or so of ejected matter from a SN were in the form of 4-km diameter balls, the probability of even one such ball hitting the Earth from an event 100 light years away would be about 3e-5. (d) A 4-km diameter ball traveling fast enough to get here from 100 LY away in some tens of thousands of years would deliver the energy of a 50 km diameter impactor traveling at typical Earth-impact velocity (~20 km/sec). We review the current impact flux on the Earth from asteroids and comets, and show that the probability of an impact of a 4-km diameter asteroid in an interval of 13,000 years is about one in a thousand, and the probability of a comet impact of that size is a few in a million. An "impact shower" caused by the injection or breakup of comets or asteroids in the inner solar system by whatever means would take tens to hundreds of thousands of years to clear out, thus the population of NEOs we see now with our telescopic surveys is what we’ve had for the last few tens of thousands of years, at least. Faced with such low odds, the evidence that such a large cosmic impact is the cause of the Younger Dryas boundary and cooling, and that there is no other possible cause, needs to be extraordinary indeed.

Using nudges to reduce waste? The case of Toronto's plastic bag levy.

PubMed

Rivers, Nicholas; Shenstone-Harris, Sarah; Young, Nathan

2017-03-01

The overuse of disposable plastic bags is a major environmental problem across the globe. In recent years, numerous jurisdictions have sought to curb disposable bag use by implementing a levy or fee at the point of purchase. These levies are typically small and symbolic (around $0.05 per bag), but serve as a highly-visible and continuous reminder to consumers. As such, they are consistent with nudging policies that seek to encourage broad changes in behaviour through small, non-coercive measures that influence people's thinking about an issue. While existing empirical evidence suggests that nudges are highly effective in reducing disposable bag use, we argue that many of these studies are flawed because they lack adequate temporal and geographic controls. We use longitudinal data from four waves of a major Canadian survey to analyze the effect of a disposable bag levy in the City of Toronto. Controlling for demographics and changes in social norms over time, we find that the levy increased the use of reusable shopping bags by 3.4 percentage points. Moreover, we find that the impact of the policy was highly variable across behavioural and demographic groups. The levy was highly effective in encouraging people who already used reusable bags to use them more frequently, while having no effect on infrequent users. We also find that the effects are limited to households with high socio-economic status (as measured by income, educational attainment, and housing situation). This suggests important limitations for nudging policy more generally, as people with lower socio-economic status appear to have been unaffected by this behavioural prompt. Copyright © 2016 Elsevier Ltd. All rights reserved.

Periodic Comet Showers, Mass Extinctions, and the Galaxy

NASA Technical Reports Server (NTRS)

Rampino, M. R.; Stothers, R. B.

2000-01-01

Geologic data on mass extinctions of life and evidence of large impacts on the Earth are thus far consistent with a quasi-periodic modulation of the flux of Oort cloud comets. Impacts of large comets and asteroids are capable of causing mass extinction of species, and the records of large impact craters and mass show a correlation. Impacts and extinctions display periods in the range of approximately 31 +/- 5 m.y., depending on dating methods, published time scales, length of record, and number of events analyzed. Statistical studies show that observed differences in the formal periodicity of extinctions and craters are to be expected, taking into consideration problems in dating and the likelihood that both records would be mixtures of periodic and random events. These results could be explained by quasi-periodic showers of Oort Cloud comets with a similar cycle. The best candidate for a pacemaker for comet showers is the Sun's vertical oscillation through the plane of the Galaxy, with a half-period over the last 250 million years in the same range. We originally suggested that the probability of encounters with molecular clouds that could perturb the Oort comet cloud and cause comet showers is modulated by the Sun's vertical motion through the galactic disk. Tidal forces produced by the overall gravitational field of the Galaxy can also cause perturbations of cometary orbits. Since these forces vary with the changing position of the solar system in the Galaxy, they provide a mechanism for the periodic variation in the flux of Oort cloud comets into the inner solar system. The cycle time and degree of modulation depend critically on the mass distribution in the galactic disk. Additional information is contained in the original extended abstract.

A STUDY OF DUST AND GAS AT MARS FROM COMET C/2013 A1 (SIDING SPRING)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kelley, Michael S. P.; Farnham, Tony L.; Bodewits, Dennis

Although the nucleus of comet C/2013 A1 (Siding Spring) will safely pass Mars in 2014 October, the dust in the coma and tail will more closely approach the planet. Using a dynamical model of comet dust, we estimate the impact fluence. Based on our nominal model no impacts are expected at Mars. Relaxing our nominal model's parameters, the fluence is no greater than ∼10{sup –7} grains m{sup –2} for grain radii larger than 10 μm. Mars-orbiting spacecraft are unlikely to be impacted by large dust grains, but Mars may receive as many as ∼10{sup 7} grains, or ∼100 kg of total dust.more » We also estimate the flux of impacting gas molecules commonly observed in comet comae.« less

Observation of freakish-asteroid-discovered-resembles support my idea that many dark comets were arrested and lurked in the solar system after every impaction

NASA Astrophysics Data System (ADS)

Cao, Dayong

2014-03-01

New observations show that some asteroids are looked like comets. http://www.astrowatch.net/2013/11/freakish-asteroid-discovered-resembles.html, http://www.astrowatch.net/2013/11/astronomers-puzzle-over-newfound.html. It supports my idea that ``many dark comets with very special tilted orbits were arrested and lurked in the solar system'' - ``Sun's companion-dark hole seasonal took its dark comets belt and much dark matter to impact near our earth. And some of them probability hit on our earth. So this model kept and triggered periodic mass extinctions on our earth every 25 to 27 million years. After every impaction, many dark comets with very special tilted orbits were arrested and lurked in the solar system. Because some of them picked up many solar matter, so it looked like the asteroids. When the dark hole-Tyche goes near the solar system again, they will impact near planets.'' The idea maybe explains why do the asteroid looks like the comet? Where are the asteroids come from? What relationship do they have with the impactions and extinctions? http://meetings.aps.org/link/BAPS.2011.CAL.C1.7, http://meetings.aps.org/Meeting/CAL12/Event/181168, http://meetings.aps.org/link/BAPS.2013.MAR.H1.267. During 2009 to 2010, I had presented there are many dark comets like dark Asteroids near the orbit of Jupiter in ASP Meetings. In 2010, NASA's WISE found them. http://meetings.aps.org/link/BAPS.2011.APR.K1.17, http://www.nasa.gov/mission_pages/WISE/news/wise20100122.html Avoid Earth Extinction Associ.

Limb of Copernicus Impact Crater

NASA Technical Reports Server (NTRS)

1991-01-01

Copernicus is 93 km wide and is located within the Mare Imbrium Basin, northern nearside of the Moon (10 degrees N., 20 degrees W.). Image shows crater floor, floor mounds, rim, and rayed ejecta. Rays from the ejecta are superposed on all other surrounding terrains which places the crater in its namesake age group: the Copernican system, established as the youngest assemblage of rocks on the Moon (Shoemaker and Hackman, 1962, The Moon: London, Academic Press, p.289- 300).

Comet Dead Ahead

NASA Technical Reports Server (NTRS)

2005-01-01

This image shows comet Tempel 1 as seen through the clear filter of the medium resolution imager camera on Deep Impact. It was taken on June 26, 2005, when the spacecraft was 7,118,499.4 kilometers (4,423,435 miles) away from the comet. Eight images were combined to create this picture, and a logarithmic stretch was applied to enhance the coma of the comet.

27 CFR 70.162 - Levy and distraint on salary and wages.

Code of Federal Regulations, 2010 CFR

2010-04-01

... salary and wages. 70.162 Section 70.162 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX... § 70.162 Levy and distraint on salary and wages. (a) Notice of intent to levy. Levy may be made for any... salary or wages. A levy on salary or wages is continuous from the time of the levy until the liability...

Seasonal variations as predictive factors of the comet assay parameters: a retrospective study.

PubMed

Geric, Marko; Gajski, Goran; Orešcanin, Višnja; Garaj-Vrhovac, Vera

2018-02-24

Since there are several predicting factors associated with the comet assay parameters, we have decided to assess the impact of seasonal variations on the comet assay results. A total of 162 volunteers were retrospectively studied, based on the date when blood donations were made. The groups (winter, spring, summer and autumn) were matched in terms of age, gender, smoking status, body mass index and medical diagnostic exposure in order to minimise the impact of other possible predictors. Means and medians of the comet assay parameters were higher when blood was sampled in the warmer period of the year, the values of parameters being the highest during summer. Correlation of meteorological data (air temperature, sun radiation and sun insolation) was observed when data were presented as the median per person. Using multivariate analysis, sampling season and exposure to medical radiation were proved to be the most influential predictors for the comet assay parameters. Taken together, seasonal variation is another variable that needs to be accounted for when conducting a cohort study. Further studies are needed in order to improve the statistical power of the results related to the impact of sun radiation, air temperature and sun insolation on the comet assay parameters.

Deep Impact: 19 gigajoules can make quite an impression

NASA Technical Reports Server (NTRS)

Kubitschek, D.; Bank, T.; Frazier, W.; Blume, W.; Null, G.; Mastrodemos, N.; Synnott, S.

2001-01-01

Deep Impact will impact the comet Tempel-1 on July 4, 2005. The impact event will be clearly visible from small telescopes on Earth, especially in the IR bands. When combined with observations taken from the Flyby spacecraft, this science data set will provide unique insight into the materials and structure within the comet, and the strength of the surface.

Hydrodynamic Modeling of the Deep Impact Mission into Comet Tempel 1

NASA Astrophysics Data System (ADS)

Sorli, Kya; Remington, Tané; Bruck Syal, Megan

2018-01-01

Kinetic impact is one of the primary strategies to deflect hazardous objects off of an Earth-impacting trajectory. The only test of a small-body impact is the 2005 Deep Impact mission into comet Tempel 1, where a 366-kg mass impactor collided at ~10 km/s into the comet, liberating an enormous amount of vapor and ejecta. Code comparisons with observations of the event represent an important source of new information about the initial conditions of small bodies and an extraordinary opportunity to test our simulation capabilities on a rare, full-scale experiment. Using the Adaptive Smoothed Particle Hydrodynamics (ASPH) code, Spheral, we explore how variations in target material properties such as strength, composition, porosity, and layering affect impact results, in order to best match the observed crater size and ejecta evolution. Benchmarking against this unique small-body experiment provides an enhanced understanding of our ability to simulate asteroid or comet response to future deflection missions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-739336-DRAFT.

Disruption of giant comets in the solar system and around other stars

NASA Technical Reports Server (NTRS)

Whitmire, D. P.; Matese, J. J.

1988-01-01

In a standard cometary mass distribution (dN/dM) alpha M(-a), a = 1.5 to 2.0) most of the mass resides in the largest comets. The maximum mass M sub max for which this distribution holds uncertain but there are theoretical and observational indications that M sub max is at least approx. 10(23)g. Chiron, although formally classified as an asteroid, is most likely a giant comet in this mass range. Its present orbit is unstable and it is expected to evolve into a more typical short period comet orbit on a timescale of approx. 10(6) to 10(7)yr. The breakup of a chiron-like comet of mass approx. 10(23)g could in principle produce approx. 10(5) Halley-size comets, or a distribution with an even larger number. If a giant comet was in a typical short period comet orbit, such a breakup could result in a relatively brief comet shower (duration approx. less than 10(6)yr) with some associated terrestrial impacts. However, the most significant climatic effects may not in general be due to the impacts themselves but to the greatly enhanced zodiacal dust cloud in the inner Solar System. (Although this is probably not the case for the unique K-T impact). Researchers used a least Chi square program with error analysis to confirm that the 2 to 5 micrometer excess spectrum of Giclas 29 to 38 can be adequately fitted with either a disk of small inefficient (or efficient) grains or a single temperature black body. Further monitoring of this star may allow discrimination between these two models.

On Course for a Comet

NASA Technical Reports Server (NTRS)

2005-01-01

This image shows comet Tempel 1 as seen through the clear filter of the medium resolution imager camera on Deep Impact. It was taken on June 27, 2005, when the spacecraft was 6,229,030.3 kilometers (3,870,719 miles) away from the comet. Three images were combined to create this picture, and a logarithmic stretch was applied to enhance the coma of the comet.

Interstellar Object ’Oumuamua as an Extinct Fragment of an Ejected Cometary Planetesimal

NASA Astrophysics Data System (ADS)

Raymond, Sean N.; Armitage, Philip J.; Veras, Dimitri

2018-03-01

’Oumuamua was discovered passing through our solar system on a hyperbolic orbit. It presents an apparent contradiction, with colors similar to those of volatile-rich solar system bodies but with no visible outgassing or activity during its close approach to the Sun. Here, we show that this contradiction can be explained by the dynamics of planetesimal ejection by giant planets. We propose that ’Oumuamua is an extinct fragment of a comet-like planetesimal born a planet-forming disk that also formed Neptune- to Jupiter-mass giant planets. On its pathway to ejection ’Oumuamua’s parent body underwent a close encounter with a giant planet and was tidally disrupted into small pieces, similar to comet Shoemaker–Levy 9’s disruption after passing close to Jupiter. We use dynamical simulations to show that 0.1%–1% of cometary planetesimals undergo disruptive encounters prior to ejection. Rocky asteroidal planetesimals are unlikely to disrupt due to their higher densities. After disruption, the bulk of fragments undergo enough close passages to their host stars to lose their surface volatiles and become extinct. Planetesimal fragments such as ’Oumuamua contain little of the mass in the population of interstellar objects but dominate by number. Our model makes predictions that will be tested in the coming decade by the Large Synoptic Survey Telescope.

On the relationship between gas and dust in 15 comets: an application to Comet 103P/Hartley 2 target of the NASA EPOXI mission of opportunity

NASA Astrophysics Data System (ADS)

Sanzovo, G. C.; Sanzovo, D. Trevisan; de Almeida, A. A.

After the success of Deep Impact mission to hit the nucleus of Comet 9P/Tempel 1 with an impactor, the concerns are turned now to the possible reutilization of this dormant flyby spacecraft in the study of another comet, for only about 10% of the cost of the original mission. Comet 103P/Hartley 2 on UT 2010 October 11 is the most attractive target in terms of available fuel at rendezvous and arrival time at the comet. In addition, the comet has a low inclination so that major orbital plane changes in the spacecraft trajectory are unnecessary. In an effort to provide information concerning the planning of this new NASA EPOXI space mission of opportunity, we use in this work, visual magnitudes measurements available from International Comet Quarterly (ICQ) to obtain, applying the Semi-Empirical Method of Visual Magnitudes - SEMVM (de Almeida, Singh, & Huebner 1997), the water production rates (in molecules/s) related to its perihelion passage of 1997. When associated to the water vaporization theory of Delsemme (1982), these rates allowed the acquisition of the minimum dimension for the effective nuclear radius of the comet. The water production rates were then converted into gas production rates (in g/s) so that, with the help of the strong correlation between gas and dust found for 12 periodic comets and 3 non-period comets (Trevisan Sanzovo 2006), we obtained the dust loss rates (in g/s), its behavior with the heliocentric distance and the dust-to-gas ratios in this physically attractive rendezvous target-comet to Deep Impact spacecraft at a closest approach of 700 km.

Sunny Side of a Comet

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Figure 1: Temperature Map

This image composite shows comet Tempel 1 in visible (left) and infrared (right) light (figure 1). The infrared picture highlights the warm, or sunlit, side of the comet, where NASA's Deep Impact probe later hit. These data were acquired about six minutes before impact. The visible image was taken by the medium-resolution camera on the mission's flyby spacecraft, and the infrared data were acquired by the flyby craft's infrared spectrometer.

Collisional Histories of Comets and Trojan Asteroids: Insights from Forsterite and Enstatite Impact Studies

NASA Technical Reports Server (NTRS)

Lederer. S. M.; Jensen, E. A.; Wooden, D. H.; Lindsay, S. S.; Smith, D. C.; Cintala, M. J.; Nakamura-Messenger, K.; Keller, L. P.

2012-01-01

Impacts into forsterite and orthoenstatite at speeds typically encountered by comets demonstrate that shock imparted by collisions is detectable in the infrared signatures of their dust. The spectral signatures can be traced to physical alterations in their crystalline structures, as observed in TEM imaging and modeled using a dipole approximation. These results yield tantalizing insights into the collisional history of our solar system, as well as the history of individual comets and Trojan asteroids.

Wild Duck Cluster

NASA Technical Reports Server (NTRS)

2005-01-01

On April 7, 2005, the Deep Impact spacecraft's Impactor Target Sensor camera recorded this image of M11, the Wild Duck cluster, a galactic open cluster located 6 thousand light years away. The camera is located on the impactor spacecraft, which will image comet Tempel 1 beginning 22 hours before impact until about 2 seconds before impact. Impact with comet Tempel 1 is planned for July 4, 2005.

Halley's Comet Makes a Comeback.

ERIC Educational Resources Information Center

Glenn, William H.

1984-01-01

Presents information on Halley's Comet including its discovery, impact on history, planned investigations related to its 1986 return, where and when to make observations, and predicted calendar of events. Gives general information on comets such as physical structure, theoretical origin, and paths and provides an annotated reference list. (JM)

Comet/Asteroid Protection System (CAPS): A Space-Based System Concept for Revolutionizing Earth Protection and Utilization of Near-Earth Objects

NASA Technical Reports Server (NTRS)

Mazanek, Daniel D.; Roithmayr, Carlos M.; Antol, Jeffrey; Kay-Bunnell, Linda; Werner, Martin R.; Park, Sang-Young; Kumar, Renjith R.

2002-01-01

There exists an infrequent, but significant hazard to life and property due to impacting asteroids and comets. There is currently no specific search for long-period comets, smaller near-Earth asteroids, or smaller short-period comets. These objects represent a threat with potentially little or no warning time using conventional ground-based telescopes. These planetary bodies also represent a significant resource for commercial exploitation, long-term sustained space exploration, and scientific research. The Comet/Asteroid Protection System (CAPS) would expand the current detection effort to include long-period comets, as well as small asteroids and short-period comets capable of regional destruction. A space-based detection system, despite being more costly and complex than Earth-based initiatives, is the most promising way of expanding the range of detectable objects, and surveying the entire celestial sky on a regular basis. CAPS is a future spacebased system concept that provides permanent, continuous asteroid and comet monitoring, and rapid, controlled modification of the orbital trajectories of selected bodies. CAPS would provide an orbit modification system capable of diverting kilometer class objects, and modifying the orbits of smaller asteroids for impact defense and resource utilization. This paper provides a summary of CAPS and discusses several key areas and technologies that are being investigated.

Deep Impact Spacecraft Collides With Comet Tempel 1 (Video)

NASA Technical Reports Server (NTRS)

2005-01-01

After 172 days and 268 million miles of deep space travel, the NASA Deep Impact spacecraft successfully reached out and touched comet Tempel 1. The collision between the coffee table-sized space probe and city-sized comet occurred July 4, 2005 at 12:52 a.m. CDT. Comprised of images taken by the targeting sensor aboard the impactor probe, this movie shows the spacecraft approaching the comet up to just seconds before impact. Mission scientists expect Deep Impact to provide answers to basic questions about the formation of the solar system. Principal investigator for Deep Impact, Dr. Michael A'Hearn of the University of Maryland in College Park, is responsible for the mission, and project management is handled by the Jet Propulsion Laboratory in Pasadena, California. The program office at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama assisted the Science Mission Directorate at NASA Headquarters in Washington with program management, technology planning, systems assessment, flight assurance and public outreach. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation of Boulder, Colorado. (NASA/JPL-Caltech/UMD)

Impact-Facilitated Hydrothermal Alteration in the Rim of Endeavour Crater, Mars

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Schroeder, C.; Farrand, W. H.; Crumpler, L. S.; Yen, A. S.

2017-01-01

Endeavour crater, a Noachian-aged, 22 km diameter impact structure on Meridiani Planum, Mars, has been investigated by the Mars Exploration Rover Opportunuity for over 2000 sols (Mars days). The rocks of the western rim region (oldest to youngest) are: (i) the pre-impact Matijevic fm.; (ii) rim-forming Shoemaker fm. polymict impact breccias; (iii) Grasberg fm., fine-grained sediments draping the lower slopes; and (iv) Burns fm., sulfate-rich sandstones that onlap the Grasberg fm. The rim is segmented and transected by radial fracture zones. Evidence for fluid-mediated alteration includes m-scale detections of phyllosilicates from orbit, and cm-scale variations in rock/soil composition/mineralogy documented by the Opportunity instrument suite. The m-scale phyllosilicate detections include Fe(3+)-Mg and aluminous smectites that occur in patches in the Matijevic and Shoemaker fms. Rock compositions do not reveal substantial differences for smectite-bearing compared to smectite-free rocks. Interpretation: large-scale hydrothermal alteration powered by impact-deposited heat acting on limited water supplies engendered mineralogic transfomations under low water/rock, near-isochemical conditions. The cm-scale alterations, localized in fracture zones, occurred at higher water/rock as evidenced by enhanced Si and Al contents through leaching of more soluble elements, and deposition of Mg, Ni and Mn sulphates and halogen salts in soils. Visible/near infrared reflectance of narrow curvilinear red zones indicate higher nanophase ferric oxide contents and possibly hydration compared to surrounding outcrops. Broad fracture zones on the rim have reflectance features consistent with development of ferric oxide minerals. Interpretation: water fluxing through the fractures in a hydrothermal system resulting from the impact engendered alteration and leaching under high water/rock conditions. Late, localized alteration is documented by Ca-sulfate-rich veins that are not confined to fracture zones; some cross-cut the Grasberg fm. Interpretation: late fluid mobilization of soluble elements, likely in a later alteration event.

Glycolaldehyde and Ethylene Glycol on Nearly Isotropic Comets

NASA Astrophysics Data System (ADS)

Butler, Jayden; Zellner, Nicolle; McCaffrey, Vanessa

2017-01-01

The delivery of glycolaldehyde (GLA) and ethylene glycol (EG) could be could be important for understanding the origin of life. GLA, the simplest sugar, is a building block for ribose, the backbone of RNA; EG is a reduced alcohol variant of GLA, found to be created by the impact of GLA under simulated cometary impact conditions (McCaffrey et al. 2014). GLA and EG have been found in regions of the interstellar medium and recently on nearly isotropic comets (NICs), which originate in the Oort Cloud. NICs are long period comets (P > 200 years) and have orbits that are nearly randomly inclined to the ecliptic plane (Mumma & Charnley et al. 2011). Based on impact experiments that assess survivability of these molecules (McCaffrey et al. 2014), we aim to determine the mass of GLA and EG that could have been delivered on comets since the formation of the Solar System. The focus of the current study is to determine the abundances of GLA and EG on C/1995 O1 (Hale-Bopp), C/2012 F6 (Lemmon), C/2013 R1 (Lovejoy 2013), and C/2014 Q2 (Lovejoy 2014), all of which have been found to possess at least one of these molecules. Using published values of observed production rates of water, GLA, and EG (e.g., Biver et al. 2015), we have estimated a range of masses of these molecules of interest on their host comets. Even with a high degree of uncertainty in comet diameters and volumes, we estimate that 109 to 1017 kg of these molecules could be delivered by a single comet, and that 108 to 1017 kg could have survived the impact.

Deep Impact: excavating comet Tempel 1.

PubMed

A'Hearn, M F; Belton, M J S; Delamere, W A; Kissel, J; Klaasen, K P; McFadden, L A; Meech, K J; Melosh, H J; Schultz, P H; Sunshine, J M; Thomas, P C; Veverka, J; Yeomans, D K; Baca, M W; Busko, I; Crockett, C J; Collins, S M; Desnoyer, M; Eberhardy, C A; Ernst, C M; Farnham, T L; Feaga, L; Groussin, O; Hampton, D; Ipatov, S I; Li, J-Y; Lindler, D; Lisse, C M; Mastrodemos, N; Owen, W M; Richardson, J E; Wellnitz, D D; White, R L

2005-10-14

Deep Impact collided with comet Tempel 1, excavating a crater controlled by gravity. The comet's outer layer is composed of 1- to 100-micrometer fine particles with negligible strength (<65 pascals). Local gravitational field and average nucleus density (600 kilograms per cubic meter) are estimated from ejecta fallback. Initial ejecta were hot (>1000 kelvins). A large increase in organic material occurred during and after the event, with smaller changes in carbon dioxide relative to water. On approach, the spacecraft observed frequent natural outbursts, a mean radius of 3.0 +/- 0.1 kilometers, smooth and rough terrain, scarps, and impact craters. A thermal map indicates a surface in equilibrium with sunlight.

The effects on population health status of using dedicated property taxes to fund local public health agencies

PubMed Central

2011-01-01

Background In the United States, a dedicated property tax describes the legal authority given to a local jurisdiction to levy and collect a tax for a specific purpose. We investigated for an association of locally dedicated property taxes to fund local public health agencies and improved health status in the eight states designated as the Mississippi Delta Region. Methods We analyzed the difference in health outcomes of counties with and without a dedicated public health tax after adjusting for a set of control variables using regression models for county level data from 720 counties of the Mississippi Delta Region. Results Levying a dedicated public health tax for counties with per capita income above $28,000 is associated with improved health outcomes of those counties when compared to counties without a dedicated property tax for public health. Alternatively, levying a dedicated property tax in counties with lower per capita income is associated with poor health outcomes. Conclusions There are both positive and negative consequences of using dedicated property taxes to fund public health. Policymakers should carefully examine both the positive association of improved health outcomes and negative impact of taxation on poor populations before authorizing the use of dedicated local property tax levies to fund public health agencies. PMID:21672231

The effects on population health status of using dedicated property taxes to fund local public health agencies.

PubMed

Honoré, Peggy A; Fos, Peter J; Wang, Xueyuan; Moonesinghe, Ramal

2011-06-14

In the United States, a dedicated property tax describes the legal authority given to a local jurisdiction to levy and collect a tax for a specific purpose. We investigated for an association of locally dedicated property taxes to fund local public health agencies and improved health status in the eight states designated as the Mississippi Delta Region. We analyzed the difference in health outcomes of counties with and without a dedicated public health tax after adjusting for a set of control variables using regression models for county level data from 720 counties of the Mississippi Delta Region. Levying a dedicated public health tax for counties with per capita income above $28,000 is associated with improved health outcomes of those counties when compared to counties without a dedicated property tax for public health. Alternatively, levying a dedicated property tax in counties with lower per capita income is associated with poor health outcomes. There are both positive and negative consequences of using dedicated property taxes to fund public health. Policymakers should carefully examine both the positive association of improved health outcomes and negative impact of taxation on poor populations before authorizing the use of dedicated local property tax levies to fund public health agencies.

Survival of Glycolaldehyde and Production of Sugar Compounds via Comet Impact Delivery

NASA Astrophysics Data System (ADS)

Zellner, N.; McCaffrey, V.; Crake, C.; Butler, J.; Robbins, J.; Fodor, A.

2017-12-01

Impact experiments using glycolaldehyde (GLA), a two-carbon sugar precursor that has been detected in regions of the interstellar medium and on comets, have been conducted at the Experimental Impact Laboratory at NASA's Johnson Space Center. Samples of GLA and GLA mixed with montmorillonite clays were subjected to the pressure conditions that are found during impact delivery of biomolecules by comets, asteroids, or meteors; pressures ranged from 4.5 GPa to 25 GPa. Results show that large amounts of GLA survived the impacts and moderate amounts of threose, erythrose, and glycolic acid were produced in these impacts. Total amounts are dependent on impact pressure. Ethylene glycol, a reduced variant of GLA that has also been detected in the interstellar medium and on comets, was also produced. The results of these experimental impacts provide evidence that large amounts of GLA, EG, and other biomolecules were available on habitable moons or planets, especially during the era of late heavy bombardment ( 4.2 to 3.7 billion years ago) when life may have been developing on Earth. The presence and availability of these biomolecules, under appropriate conditions, may be important for understanding the origin of life as we know it. Glycolaldehyde in particular, may be an important molecule in the production of ribose, the five-carbon sugar in RNA.

Hyperactivity and Dust Composition of Comet 103P/Hartley 2 During the EPOXI Encounter

NASA Astrophysics Data System (ADS)

Harker, David E.; Woodward, Charles E.; Kelley, Michael S. P.; Wooden, Diane H.

2018-05-01

Short-period comet 103P/Hartley 2 (103P) was the flyby target of the Deep Impact eXtended Investigation on 2010 November 4 UT. This comet has a small hyperactive nucleus, i.e., it has a high water production rate for its surface area. The underlying cause of the hyperactivity is unknown; the relative abundances of volatiles in the coma of 103P are not unusual. However, the dust properties of this comet have not been fully explored. We present four epochs of mid-infrared spectra and images of comet 103P observed from Gemini-South +T-ReCS on 2010 November 5, 7, 21 and December 13 UT, near and after the spacecraft encounter. Comet 103P exhibited a weak 10 μm emission feature ≃1.14 ± 0.01 above the underlying local 10 μm continuum. Thermal dust grain modeling of the spectra shows the grain composition (mineralogy) was dominated by amorphous carbon and amorphous pyroxene with evidence for Mg-rich crystalline olivine. The grain size has a peak grain radius range of a peak ∼ 0.5–0.9 μm. On average, the crystalline silicate mass fraction is ≃0.24, fairly typical of other short-period comets. In contrast, the silicate-to-carbon ratio of ≃0.48–0.64 is lower compared to other short-period comets, which indicates that the flux measured in the 10 μm region of 103P was dominated by amorphous carbon grains. We conclude that the hyperactivity in comet 103P is not revealing dust properties similar to the small grains seen with the Deep Impact experiment on comet 9P/Tempel 1 or from comet C/1995 O1 (Hale–Bopp).

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.

Parent volatiles in comet 9P/Tempel 1: before and after impact

NASA Technical Reports Server (NTRS)

Mumma, Michael J.; DiSanti, Michael A.; Magee-Sauer, Karen; Bonev, Boncho P.; Villanueva, Geronimo L.; Kawakita, Hideyo; Dello Russo, Neil; Gibb, Erika L.; Blake, Geoffrey A.; Lyke, James E.;

Funding services from the bottom up: an overview of Senior Services Levy Programs in Ohio.

PubMed

Payne, Michael; Applebaum, Robert; Molea, Marcus; Ross, Doris E

2007-08-01

Since the 1980s, Ohio counties have pursued a somewhat unique strategy for funding services for the 60-and-older population. Using local property-tax levies, Ohio counties bring in more than $100 million yearly to support a range of services for older people. In this article we report on information from the 2005 Ohio Senior Service Levy Survey, including information for states or counties that may be interested in implementing senior-service levies of their own. A survey was completed by 56 of 59 Ohio counties that operated senior-service levies in 2004. We pilot tested the survey instrument with input from three counties (urban, rural, and a mix of both). Overall, the survey responses provided information on a range of components, including size of levy, types of services provided, number of older citizens served, quality and evaluation efforts, and advice on initiating successful levy campaigns. Ohio is one of only five states raising money for senior services through countywide, property-tax levies. Although there is some debate about the appropriateness of property-tax levies as a means of funding senior services, these levies are being met very favorably at the polls in Ohio. Because funding from the Older Americans Act has not kept pace with inflation or with the increasing number of older people, other states may look at Ohio's experience with senior-service levies with increasing interest.

Simulation of Comet Impact and Survivability of Organic Compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, B T; Lomov, I N; Blank, J G

Comets have long been proposed as a potential means for the transport of complex organic compounds to early Earth. For this to be a viable mechanism, a significant fraction of organic compounds must survive the high temperatures due to impact. We have undertaken three-dimensional numerical simulations to track the thermodynamic state of a comet during oblique impacts. The comet was modeled as a 1-km water-ice sphere impacting a basalt plane at 11.2 km/s; impact angles of 15{sup o} (from horizontal), 30{sup o}, 45{sup o}, 65{sup o}, and 90{sup o} (normal impact) were examined. The survival of organic cometary material, modeledmore » as water ice for simplicity, was calculated using three criteria: (1) peak temperatures, (2) the thermodynamic phase of H{sub 2}O, and (3) final temperature upon isentropic unloading. For impact angles greater than or equal to 30{sup o}, no organic material is expected to survive the impact. For the 15{sup o} impact, most of the material survives the initial impact and significant fractions (55%, 25%, and 44%, respectively) satisfy each survival criterion at 1 second. Heating due to deceleration, in addition to shock heating, plays a role in the heating of the cometary material for nonnormal impacts. This effect is more noticeable for more oblique impacts, resulting in significant deviations from estimates using scaling of normal impacts. The deceleration heating of the material at late times requires further modeling of breakup and mixing.« less

Solar wind interaction with comet 67P: Impacts of corotating interaction regions

NASA Astrophysics Data System (ADS)

Edberg, N. J. T.; Eriksson, A. I.; Odelstad, E.; Vigren, E.; Andrews, D. J.; Johansson, F.; Burch, J. L.; Carr, C. M.; Cupido, E.; Glassmeier, K.-H.; Goldstein, R.; Halekas, J. S.; Henri, P.; Koenders, C.; Mandt, K.; Mokashi, P.; Nemeth, Z.; Nilsson, H.; Ramstad, R.; Richter, I.; Wieser, G. Stenberg

2016-02-01

We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1-2.7 AU from the Sun and the neutral outgassing rate ˜1025-1026 s-1, the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30 km. The ionospheric low-energy (˜5 eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below -20 V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (˜10-100 eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.

Comet/Asteroid Protection System (CAPS): Preliminary Space-Based Concept and Study Results

NASA Technical Reports Server (NTRS)

Mazanek, Daniel D.; Roithmayr, Carlos M.; Antol, Jeffrey; Park, Sang-Young; Koons, Robert H.; Bremer, James C.; Murphy, Douglas G.; Hoffman, James A.; Kumar, Renjith R.; Seywald, Hans

2005-01-01

There exists an infrequent, but significant hazard to life and property due to impacting asteroids and comets. There is currently no specific search for long-period comets, smaller near-Earth asteroids, or smaller short-period comets. These objects represent a threat with potentially little or no warning time using conventional ground-based telescopes. These planetary bodies also represent a significant resource for commercial exploitation, long-term sustained space exploration, and scientific research. The Comet/Asteroid Protection System (CAPS) is a future space-based system concept that provides permanent, continuous asteroid and comet monitoring, and rapid, controlled modification of the orbital trajectories of selected bodies. CAPS would expand the current detection effort to include long-period comets, as well as small asteroids and short-period comets capable of regional destruction. A space-based detection system, despite being more costly and complex than Earth-based initiatives, is the most promising way of expanding the range of detectable objects, and surveying the entire celestial sky on a regular basis. CAPS would provide an orbit modification system capable of diverting kilometer class objects, and modifying the orbits of smaller asteroids for impact defense and resource utilization. This Technical Memorandum provides a compilation of key related topics and analyses performed during the CAPS study, which was performed under the Revolutionary Aerospace Systems Concepts (RASC) program, and discusses technologies that could enable the implementation of this future system.

Implications of theories of asteroid and comet impact for policy options for management of spent nuclear fuel and high-level radioactive wastes

USGS Publications Warehouse

Trask, Newell J.

1994-01-01

Concern with the threat posed by terrestrial asteroid and comet impacts has heightened as the catastrophic consequences of such events have become better appreciated. Although the probabilities of such impacts are very small, a reasonable question for debate is whether such phenomena should be taken into account in deciding policy for the management of spent fuel and high-level radioactive waste. The rate at which asteroid or comet impacts would affect areas of surface storage of radioactive waste is about the same as the estimated rate at which volcanic activity would affect the Yucca Mountain area. The Underground Retrievable Storage (URS) concept could satisfactorily reduce the risk from cosmic impact with its associated uncertainties in addition to providing other benefits described by previous authors.

Tying Extinction Events to Comet Impacts Large Enough to Cause an Extinction in Themselves.

NASA Astrophysics Data System (ADS)

Burgener, J. A.

2017-12-01

Comets over 35 km in size impacting Earth will create vast fireballs, and will boil large parts of the oceans, causing extinction events in themselves. They will likely provide enough energy to shatter the crust and eject large masses of molten rock from the mantle, forming traps. Traps are clearly associated with extinction events, but are not expected to cause extinctions. While Chicxulub is recognized to have occurred at the time of the K/Pg boundary layer, it is recognized as being too small in itself to cause an extinction. Are large comet impacts likely? The Kuiper belt has more than 100,000 objects over 100 km in diameter and millions over 10 km. Typically their orbits are less stable than asteroid orbits due to large bodies such as Pluto moving through the belt. The asteroid belt has only 10,000 objects over 10 km diameter. Comet impacts should be more common than asteroid impacts, yet none of the recognized craters are expected to be due to comets. There are many features on Earth that are poorly explained by Plate Tectonics that would be well explained if they were considered to be comet impact craters. A consideration of the Black Sea and the Tarim Basin will show that impact interpretations are a better fit than the present Plate Tectonics' explanations. Both basins are in the midst of mountain building from plate collisions, but are themselves not being disturbed by the plate collisions. Both are ellipses angled at 23.4 degrees to the equator, matching the angle expected for a low angle impact from a comet traveling in the ecliptic. Both are too deep at 15 km depths to be standard oceans (typically 5 km deep). Both are filled with horizontal layers of sediments, undisturbed by the mountain building occurring at the edges. Both have thin crusts and high Moho boundaries. Both have thin lithosphere. Yet both show GPS movement of the land around them moving away from them, as though they were much thicker and stronger than the surrounding land. The Tarim Basin is 1000 km X 380 km, and the Black Sea is in two sections each 600 km X 350 km. They would require impactors in the range of 35 - 40 km diameter, hitting at impact angles of 20 - 30 degrees. The fireballs from such impacts would cover nearly half the planet, which would be large enough in themselves to cause extinctions.

The small-comet hypothesis: An upper limit to the current impact rate on the moon

NASA Astrophysics Data System (ADS)

Grier, Jennifer A.; McEwen, Alfred S.

Frank et al. [1986b] and Frank and Sigwarth [1993] hypothesized the intense bombardment of the terrestrial atmosphere by small comets. Their model requires that the Moon is impacted by small comets (107-108 g) at a rate of almost one per minute. We calculate that an object of this mass, even with an exceedingly low density and relatively low velocity, will nevertheless produce a crater at least 50 m in diameter. These craters will excavate immature lunar soil and produce a very bright spot with a diameter of at least 150 m. If low-density comets exist that might not create deep craters [O'Keefe and Ahrens, 1982], they will nevertheless disturb the regolith sufficiently to create detectable bright spots. If the small-comet hypothesis is correct then the near-global lunar imaging returned by Clementine in 1994 should reveal ∼107 bright spots in locations where craters are not present in images acquired in the 1960's and early 1970's. We find no new bright spots in a carefully-studied area of 5.2×104 km², so an upper limit to the current cratering rate by small comets is 33/yr, ∼104 below that expected if the small-comet hypothesis were valid.

78 FR 50051 - Notice of Availability of the Final Environmental Impact Statement for the Tarmac King Road...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-16

... DEPARTMENT OF DEFENSE Department of the Army, Corps of Engineers Notice of Availability of the Final Environmental Impact Statement for the Tarmac King Road Limestone Mine Proposed in Levy County... from limestone extraction, material stockpiling, roads, and other infrastructure over a period of...

78 FR 60284 - Submission for OMB Review; Comment Request

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-01

... OMB Review; Comment Request Title: Federally Assisted State Transmitted (FAST) Levy. OMB No.: New... proposing a new information collection using the Federally Assisted State Transmitted Levy (FAST Levy) application. FAST Levy is a centralized, secure and automated method of collecting and disseminating...

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.

Electron impact ionization in the vicinity of comets

NASA Astrophysics Data System (ADS)

Cravens, T. E.; Kozyra, J. U.; Nagy, A. F.; Gombosi, T. I.; Kurtz, M.

1987-07-01

The solar wind interacts very strongly with the extensive cometary coma, and the various interaction processes are initiated by the ionization of cometary neutrals. The main ionization mechanism far outside the cometary bow shock is photoionization by solar extreme ultraviolet radiation.Electron distributions measured in the vicinity of comets Halley and Giacobini-Zinner by instruments on the VEGA and ICE spacecraft, respectively, are used to calculate electron impact ionization frequencies. Ionization by electrons is of comparable importance to photoionization in the magnetosheaths of Comets Halley and Giacobini-Zinner. The ionization frequency in the inner part of the cometary plasma region of comet Halley is several times greater than the photoionization value. Tables of ionization frequencies as functions of electron temperature are presented for H2O, CO2, CO, O, N2, and H.

Peptide synthesis triggered by comet impacts: A possible method for peptide delivery to the early Earth and icy satellites

NASA Astrophysics Data System (ADS)

Sugahara, Haruna; Mimura, Koichi

2015-09-01

We performed shock experiments simulating natural comet impacts in an attempt to examine the role that comet impacts play in peptide synthesis. In the present study, we selected a mixture of alanine (DL-alanine), water ice, and silicate (forsterite) to make a starting material for the experiments. The shock experiments were conducted under cryogenic conditions (77 K), and the shock pressure range achieved in the experiments was 4.8-25.8 GPa. The results show that alanine is oligomerized into peptides up to tripeptides due to the impact shock. The synthesized peptides were racemic, indicating that there was no enantioselective synthesis of peptides from racemic amino acids due to the impact shock. We also found that the yield of linear peptides was a magnitude higher than those of cyclic diketopiperazine. Furthermore, we estimated the amount of cometary-derived peptides to the early Earth based on two models (the Lunar Crating model and the Nice model) during the Late Heavy Bombardment (LHB) using our experimental data. The estimation based on the Lunar Crating model gave 3 × 109 mol of dialanine, 4 × 107 mol of trialanine, and 3 × 108 mol of alanine-diketopiperazine. Those based on the Nice model, in which the main impactor of LHB is comets, gave 6 × 1010 mol of dialanine, 1 × 109 mol of trialanine, and 8 × 109 mol of alanine-diketopiperazine. The estimated amounts were comparable to those originating from terrestrial sources (Cleaves, H.J., Aubrey, A.D., Bada, J.L. [2009]. Orig. Life Evol. Biosph. 39, 109-126). Our results indicate that comet impacts played an important role in chemical evolution as a supplier of linear peptides, which are important for further chemical evolution on the early Earth. Our study also highlights the importance of icy satellites, which were formed by comet accumulation, as prime targets for missions searching for extraterrestrial life.

KSC-05PD-0128

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. On Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., the Boeing Delta II rocket carrying the Deep Impact spacecraft stands out against an early dawn sky. Scheduled for liftoff at 1:47 p.m. EST today, Deep Impact will head for space and a rendezvous with Comet Tempel 1 when the comet is 83 million miles from Earth. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-05PD-0124

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. On Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., the Boeing Delta II rocket carrying the Deep Impact spacecraft is bathed in light waiting for tower rollback before launch. Scheduled for liftoff at 1:47 p.m. EST today, Deep Impact will head for space and a rendezvous with Comet Tempel 1 when the comet is 83 million miles from Earth. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

Lessons Learned in the Decommissioning of the Stardust Spacecraft

NASA Technical Reports Server (NTRS)

Larson, Timothy W.

2012-01-01

The Stardust spacecraft completed its prime mission in 2006, returning samples from the coma of comet Wild 2 to earth in the sample return capsule. Still healthy, and in a heliocentric orbit, the Stardust spacecraft was repurposed for a new mission - Stardust NExT. This new mission would take the veteran spacecraft to a 2011 encounter with comet Tempel 1, providing a new look at the comet visited in 2005 by the Deep Impact mission. This extended mission for Stardust would push it to the limits of its fuel reserves, prompting several studies aimed at determining the actual remaining fuel on board. The results were used to plan mission events within the constraints of this dwindling resource. The team tracked fuel consumption and adjusted the mission plans to stay within the fuel budget. This effort intensified toward the end of the mission, when a final assessment showed even less remaining fuel than previously predicted, triggering a delay in the start of comet imaging during the approach phase. The flyby of comet Tempel 1 produced spectacular up close views of this comet, imaging previously seen areas as well as new territory, and providing clear views of the location of the 2005 impact. The spacecraft was decommissioned about a month after the flyby, revealing that the fuel tank was now empty after having flown successfully for 12 years, returned comet dust samples to earth, and flown by an asteroid and two comets.

Looking Back at a Job Well Done

NASA Technical Reports Server (NTRS)

2005-01-01

This image shows the view from Deep Impact's flyby spacecraft as it turned back to look at comet Tempel 1. Fifty minutes earlier, the spacecraft's probe was run over by the comet. That collision kicked up plumes of ejected material, seen here streaming away from the back side of the comet. This image was taken by the flyby craft's high-resolution camera.

The worldwide impact of Donati's comet on art and society in the mid-19th century

NASA Astrophysics Data System (ADS)

Gasperini, Antonella; Galli, Daniele; Nenzi, Laura

2011-06-01

Donati's comet was one of the most spectacular astronomical events of the nineteenth century. Its extended sword-like tail was a spectacular sight that inspired several literary and artistic representations. Traces of Donati's comet are found in popular magazines, children's books, collection cards, and household objects through the beginning of the twentieth century.

Capturing the Coma

NASA Technical Reports Server (NTRS)

2005-01-01

This image shows comet Tempel 1, as seen by the Deep Impact spacecraft on June 21, 2005. It was taken using the clear filter of the spacecraft's medium resolution imager camera. The spacecraft was 11,564,081.7 kilometers (7,185,920 miles) away from the comet. Twelve images were combined together, and a logarithmic stretch was applied to enhance the coma of the comet.

Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Hartley 2

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.

Attitude Determination and Control Subsystem (ADCS) Preparations for the EPOXI Flyby of Comet Haley 2

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).

Space missions to comets

NASA Technical Reports Server (NTRS)

Neugebauer, M. (Editor); Yeomans, D. K. (Editor); Brandt, J. C. (Editor); Hobbs, R. W. (Editor)

1979-01-01

The broad impact of a cometary mission is assessed with particular emphasis on scientific interest in a fly-by mission to Halley's comet and a rendezvous with Tempel 2. Scientific results, speculations, and future plans are discussed.

Blinded by the Jets

NASA Image and Video Library

2005-07-04

This image shows the view from NASA Deep Impact probe 30 minutes before it was pummeled by comet Tempel 1. The picture brightness has been enhanced to show the jets of dust streaming away from the comet.

The LCO/Gemini-South campaign for Deep Impact target Comet 9P/Tempel 1: Temporally resolved wide-field narrowband imaging results

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.

Micro-ion Traps for Detection of (Pre)-Biotic Organic Compounds on Comets

NASA Technical Reports Server (NTRS)

vanAmerom, Friso H. W.; Chaudhary, A.; Short, R. T.; Brinkerhoff, William; Glavin, Daniel; Mahaffy, Paul R.; Roman, Patrick A.

2013-01-01

Comets are currently believed to be a mixture of interstellar and nebular material. Many of the volatiles in comets are attributed to interstellar chemistry, because the same species of carbonaceous compounds are also observed in ices in interstellar molecular (ISM) clouds. Comets are thus likely to be a relatively pristine reservoir of primitive material and carbonaceous compounds in our solar system. They could be a major contributor to the delivery of prebiotic organic compounds, from which life emerged through impacts on early Earth. Mass spectrometers are very powerful tools to identify unknown chemicals, and much progress bas been made in miniaturizing mas spectrometers for space applications. Most miniatu rized mass spectrometers developed to date, however, are still relatively large, power hungry, complicated to assemble, and would have significant impact on space flight vehicle total payload and resource allocations.

Campaign Expenditures in School Levy Referenda and Their Relationship to Voter Approval: Evidence from Ohio, 2007-2010

ERIC Educational Resources Information Center

Ingle, William Kyle; Johnson, Paul Andrew; Givens, Matt Ryan; Rampelt, Jerry

2013-01-01

Using logistic regression, this study sought to understand the relationship between district characteristics, district finances, levy characteristics, and campaign expenditures with new operating levy outcomes. We found that employee benefits as a percentage of the district's budget were negatively associated with levy outcomes, while salaries…

27 CFR 70.161 - Levy and distraint.

Code of Federal Regulations, 2010 CFR

2010-04-01

... OF THE TREASURY (CONTINUED) PROCEDURES AND PRACTICES PROCEDURE AND ADMINISTRATION Collection of... the 10th day of the month would reach the amount due on the sale, although the buyer need not satisfy.... Similarly, a levy only reaches property in the possession of the person levied upon at the time the levy is...

Try, Try, Again: A Two-Step Strategy for Passing School Levies

ERIC Educational Resources Information Center

Johnson, Paul A.

2008-01-01

Passing property tax issues is an increasing challenge for many school districts. This article examines 21 school levy strategies identified through a literature review associated with successful school levy campaigns. These strategies were then used as a framework to evaluate one district's attempts to pass a school bond levy. Whereas the study…

Evaluating the hazard from Siding Spring dust: Models and predictions

NASA Astrophysics Data System (ADS)

Christou, A.

2014-12-01

Long-period comet C/2013 A1 (Siding Spring) will pass at a distance of ~140 thousand km (9e-4 AU) - about a third of a lunar distance - from the centre of Mars, closer to this planet than any known comet has come to the Earth since records began. Closest approach is expected to occur at 18:30 UT on the 19th October. This provides an opportunity for a ``free'' flyby of a different type of comet than those investigated by spacecraft so far, including comet 67P/Churyumov-Gerasimenko currently under scrutiny by the Rosetta spacecraft. At the same time, the passage of the comet through Martian space will create the opportunity to study the reaction of the planet's upper atmosphere to a known natural perturbation. The flip-side of the coin is the risk to Mars-orbiting assets, both existing (NASA's Mars Odyssey & Mars Reconnaissance Orbiter and ESA's Mars Express) and in transit (NASA's MAVEN and ISRO's Mangalyaan) by high-speed cometary dust potentially impacting spacecraft surfaces. Much work has already gone into assessing this hazard and devising mitigating measures in the precious little warning time given to characterise this object until Mars encounter. In this presentation, we will provide an overview of how the meteoroid stream and comet coma dust impact models evolved since the comet's discovery and discuss lessons learned should similar circumstances arise in the future.

Odin space telescope monitoring of water vapor in the stratosphere of Jupiter

NASA Astrophysics Data System (ADS)

Cavalié, T.; Biver, N.; Hartogh, P.; Dobrijevic, M.; Billebaud, F.; Lellouch, E.; Sandqvist, Aa.; Brillet, J.; Lecacheux, A.; Hjalmarson, Å.; Frisk, U.; Olberg, M.; Odin Team

2012-02-01

The Odin space telescope has monitored the H2O (110-101) line in Jupiter's stratosphere over the 2003-2009 period. When comparing these data with previous spectra obtained with SWAS and Odin over the 1999-2002 period, we see no significant variations in the line-to-continuum ratio of the H2O line over the whole period. We have however tentatively identified a decrease by ∼15% of the line-to-continuum ratio between 2002 and 2007-2009, indicating that there was less H2O in the stratosphere of Jupiter in 2007-2009 than anticipated. We have tested the IDP (interplanetary dust particles) and SL9 (Shoemaker-Levy 9) 1D time-dependent models presented in Cavalié et al. [2008, Observation of water vapor in the stratosphere 613 of Jupiter with the Odin space telescope. Planetary and Space Science 56, 1573-1584]. We present a series of scenarios that lead to satisfactory fits of the whole data set (1999-2002 and 2003-2009 periods) based on IDP and SL9 models. The evolution of Jupiter's stratospheric H2O that we have tentatively observed has however to be confirmed by Herschel/HIFI observations. If the decrease of the line-to-continuum ratio is confirmed by future observations, it would be a direct evidence that Jupiter's H2O comes from SL9. In addition, this study shows that new constraints on Jupiter's eddy diffusion coefficient profile could be obtained (in the pressure ranges that are probed) from the monitoring of SL9 species in its stratosphere.

New Mission Old Spacecraft: EPOXI's Approach to the Comet Hartley-2

NASA Technical Reports Server (NTRS)

Rieber, Richard R.; LaBorde, Gregory R.

2012-01-01

NASA's Deep Impact mission ended successfully in 2005 after an impact and close flyby of the comet 9P/Tempel-1. The Flyby spacecraft was placed in hibernation and was left to orbit the sun. In 2007, engineers at the Jet Propulsion Laboratory brought the spacecraft out of hibernation and successfully performed two additional missions. These missions were EPOCh, Extra-solar Planetary Observation and Characterization, a photometric investigation of transiting exo-planets, and DIXI, Deep Impact eXtended Investigation, which maneuvered the Flyby spacecraft towards a close encounter with the comet 103P/Hartley- 2 on 4 November 2010. The names of these two scientific investigations combine to form the overarching mission's name, EPOXI. The encounter with 103P/Hartley-2 was vastly different from the prime mission's encounter with 9P/Tempel-1. The geometry of encounter was nearly 180 ? different and 103P/Hartley-2 was approximately one-quarter the size of 9P/Tempel-1. Mission operations for the comet flyby were broken into three phases: a) Approach, b) Encounter, and c) Departure. This paper will focus on the approach phase of the comet encounter. It will discuss the strategies used to decrease both cost and risk while maximizing science return and some of the challenges experienced during operations.

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.

Polarization of Hazes and Aurorae on Jupiter

NASA Astrophysics Data System (ADS)

Yanamandra-Fisher, Padma A.; McLean, Will; PACA_Jupiter

2017-10-01

Our solar system planets show a large variety of atmospheric polarization properties, from the thick, highly polarizing haze on Titan and the poles of Jupiter, Rayleigh scattering by molecules on Uranus and Neptune, to clouds in the equatorial region of Jupiter or on Venus. Changes in the clouds/thermal filed can be brought about by endogenic dynamical processes such merger of vortices; global, planetary scale upheavals, and external factors such as celestial collisions (such as D/Shoemaker-Levy 9 impact with Jupiter in 1994, etc.). Although the range of phase angles available from Earth for outer planets is restricted to a narrow range, limb polarization measurements provide constraints on the polarimetric properties. For example, at the equator, much of the observed reflected radiation is due to the presence of clouds and therefore, low polarization. Polar asymmetry exists between the two poles, while the planetary disk is unpolarized. Jupiter is known to exhibit a strong polar limb polarization and a low equatorial limb polarization due to the presence of haze particles and Rayleigh scattering at the poles. In contrast, at the equator, the concentration of particulates in the high atmosphere might change, changing the polarimetric signature and aurorae at both poles. The polarimetric maps, in conjunction with thermal maps and albedo maps, can provide constraints on modeling efforts to understand the nature of the aerosols/hazes in Jovian atmosphere. With Jupiter experiencing morphological changes at many latitudes, we have initiated a polarimetric observing campaign of Jupiter, in conjunction with The PACA Project. With NASA/Juno mission in a 53-day orbit around Jupiter, and recent outbreaks in the atmosphere, changes in the polarimetric signature will provide insight to the changes occurring in the atmosphere. Some of our observations are acquired by a team of professional/amateur planetary imagers astronomers based in the U.K., Australia and Europe. France. Details/results of these studies will be presented to optimize the observing strategy of planetary atmospheres and their role in the atmospheric retrievals and the next stage of polarimetric exploration of Jupiter.

48 CFR 252.225-7033 - Waiver of United Kingdom levies.

Code of Federal Regulations, 2010 CFR

2010-10-01

... waiver of levies included in the price of this contract, the U.S. Government reserves the right to reduce the contract price by the amount of the levy waived plus associated indirect costs and profit or fee... attempt to obtain a waiver of any commercial exploitation levies included in the price of this contract...

A Million Comet Pieces

NASA Technical Reports Server (NTRS)

2006-01-01

[figure removed for brevity, see original site] A Million Comet Pieces (poster version)

This infrared image from NASA's Spitzer Space Telescope shows the broken Comet 73P/Schwassman-Wachmann 3 skimming along a trail of debris left during its multiple trips around the sun. The flame-like objects are the comet's fragments and their tails, while the dusty comet trail is the line bridging the fragments.

Comet 73P /Schwassman-Wachmann 3 began to splinter apart in 1995 during one of its voyages around the sweltering sun. Since then, the comet has continued to disintegrate into dozens of fragments, at least 36 of which can be seen here. Astronomers believe the icy comet cracked due the thermal stress from the sun.

The Spitzer image provides the best look yet at the trail of debris left in the comet's wake after its 1995 breakup. The observatory's infrared eyes were able to see the dusty comet bits and pieces, which are warmed by sunlight and glow at infrared wavelengths. This comet debris ranges in size from pebbles to large boulders. When Earth passes near this rocky trail every year, the comet rubble burns up in our atmosphere, lighting up the sky in meteor showers. In 2022, Earth is expected to cross close to the comet's trail, producing a noticeable meteor shower.

Astronomers are studying the Spitzer image for clues to the comet's composition and how it fell apart. Like NASA's Deep Impact experiment, in which a probe smashed into comet Tempel 1, the cracked Comet 73P/Schwassman-Wachmann 3 provides a perfect laboratory for studying the pristine interior of a comet.

This image was taken from May 4 to May 6 by Spitzer's multi-band imaging photometer, using its 24-micron wavelength channel.

CO2 Orbital Trends in Comets

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.

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.

Tempel Alive with Light

NASA Technical Reports Server (NTRS)

2005-01-01

This spectacular image of comet Tempel 1 was taken 67 seconds after it obliterated Deep Impact's impactor spacecraft. The image was taken by the high-resolution camera on the mission's flyby craft. Scattered light from the collision saturated the camera's detector, creating the bright splash seen here. Linear spokes of light radiate away from the impact site, while reflected sunlight illuminates most of the comet surface. The image reveals topographic features, including ridges, scalloped edges and possibly impact craters formed long ago.

Deep Impact comet encounter: design, development, and operations of the Big Event at Tempel 1

NASA Technical Reports Server (NTRS)

Wissler, Steven

2005-01-01

Deep Impact is NASA's eighth Discovery mission. This low-cost, focused planetary science investigation gathered the data necessary to help scientists unlock early secrets of our solar system. The comet encounter with Tempel 1 was a complex event - requiring extremely accurate timing, robutstness to an unknown environment, and flight team adaptability. The mission operations and flight systems performance were spectacular for approach, impact, and lookback imaging on July 4, 2005.

Deep Impact comet encounter: design, development, and operations of the big event at Tempel 1

NASA Technical Reports Server (NTRS)

Wissler, Steven; Rocca, Jennifer; Kubitschek, Daniel

2005-01-01

Deep Impact is NASA's eighth Discovery mission. This low-cost, focused planetary science investigation gathered the data necessary to help scientists unlock early secrets of our solar system. The comet encounter with Tempel 1 was a complex event - requiring extremely accurate timing, robustness to an unknown environment, and flight team adaptibility. The mission operations and flight systems performance were spectacular for approach, impact, and lookback imaging on July 4, 2005.

KSC-04PD-2460

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. On Launch Pad 17-B at Cape Canaveral Air Force Station, the second stage of the Boeing Delta II rocket arrives at the top of the mobile service tower. The element will be mated to the Delta II, which will launch NASAs Deep Impact spacecraft. A NASA Discovery mission, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing an impactor on a course to hit the comets sunlit side, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measure the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determine the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

26 CFR 301.6343-2 - Return of wrongfully levied upon property.

Code of Federal Regulations, 2011 CFR

2011-04-01

... IRS may return— (i) The specific property levied upon; (ii) An amount of money equal to the amount of money levied upon; or (iii) An amount of money equal to the amount of money received by the United... property, the property may be returned at any time. An amount equal to the amount of money levied upon or...

26 CFR 301.6343-2 - Return of wrongfully levied upon property.

Code of Federal Regulations, 2010 CFR

2010-04-01

... IRS may return— (i) The specific property levied upon; (ii) An amount of money equal to the amount of money levied upon; or (iii) An amount of money equal to the amount of money received by the United... property, the property may be returned at any time. An amount equal to the amount of money levied upon or...

26 CFR 301.6343-1 - Requirement to release levy and notice of release.

Code of Federal Regulations, 2011 CFR

2011-04-01

... person upon whom the levy was made of such a release, if the director determines that any of the... levy was made is satisfied or the period of limitations provided in section 6502 (and any period during which the period of limitations is suspended as provided by law) has lapsed. A levy is considered made...

Physical Mechanism of Comet (and Asteroid) Outbursts: The Movie

NASA Astrophysics Data System (ADS)

Hartmann, W. K.

2015-07-01

A film made during impact experiments at NASA Ames illustrates a mechanism in which regolith can become gas charged and then erupt to create outbursts as observed on comets (and "asteroids" such as 2060 Chiron).

Close encounters and collisions of comets with the earth

NASA Technical Reports Server (NTRS)

Sekanina, Z.; Yeomans, D. K.

1984-01-01

A computer search for earth-approaching comets among those listed in Marsden's (1983) updated orbit catalog has identified 36 cases at which minimum separation distance was less than 2500 earth radii. A strong representation of short period comets in the sample is noted, and the constant rate of the close approaching comets in the last 300 years is interpreted to suggest the lack of long-period comets intrinsically fainter than an absolute magnitude of about 11. A comet-earth collision rate derived from the statistics of these close encounters implies an average period of 33-64 million years between any two events. This rate is comparable with the frequency of geologically recent global catastrophes which appear to be associated with extraterrestrial object impacts, such as the Cretaceous-Tertiary extinction 65 million years ago and the late Eocene event 34 million years ago.

Comet nongravitational forces and meteoritic impacts

NASA Technical Reports Server (NTRS)

Matese, John J.; Whitman, Patrick G.; Whitmire, Daniel P.

1992-01-01

We have considered those comets whose original orbits have been determined to be hyperbolic when only planetary perturbations are accounted for. It is found that formally unbound incident trajectories correlate most confidently with orbits that have small perihelion distances and move in a retrograde sense relative to planetary motion. Arguments are presented that these results are not due to measurement error or to selection effects. We conclude that the phenomenon is attributable to enhanced volatility leading to abnormally large nongravitational forces. Since the effect is absent in the prograde small-perihelia population, increased insolation is not the sole explanation. It is suggested that the significance of the retrograde correlation is connected with a larger energy of relative motion between retrograde comets and a population of prograde ecliptic meteoroids which impact the comet mantle exposing the underlying volatiles. The subsequent enhanced outgassing is the cause of the larger nongravitational forces.

Assessing Atmospheric Water Injection from Oceanic Impacts

NASA Technical Reports Server (NTRS)

Pierazzo, E.

2005-01-01

Collisions of asteroids and comets with the Earth s surface are rare events that punctuate the geologic record. Due to the vastness of Earth s oceans, oceanic impacts of asteroids or comets are expected to be about 4 times more frequent than land impacts. The resulting injections of oceanic water into the upper atmosphere can have important repercussions on Earth s climate and atmospheric circulation. However, the duration and overall effect of these large injections are still unconstrained. This work addresses atmospheric injections of large amounts of water in oceanic impacts.

Dust impact effects recorded by the APV-N experiment during Comet Halley encounters

NASA Astrophysics Data System (ADS)

Oberc, P.; Orlowski, D.; Klimov, S.

1986-12-01

During the Vega 1 and 2 comet Halley encounters plasma wave instrument APV-N entered a region of impulsive noise 220,000 km from nucleus. The noise is attributed to dust grain impacts onto spacecraft body. Regression analysis of impact induced effects recorded during flyby shows that from 100,000 km from closest approach most plasma wave spectra measured by APV-N onboard Vega 1 and 2 are significantly influenced by dust impact effects. Signals associated with large dust impacts are directly recorded on the E2 0.1 to 25 Hz electric field waveform channel.

KSC-05PD-0126

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. On Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., shadows paint the Boeing Delta II rocket carrying the Deep Impact spacecraft as the mobile service tower at left is rolled back before launch.Scheduled for liftoff at 1:47 p.m. EST today, Deep Impact will head for space and a rendezvous with Comet Tempel 1 when the comet is 83 million miles from Earth. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-05PD-0125

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. On Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., the Boeing Delta II rocket carrying the Deep Impact spacecraft looms into the night sky as the mobile service tower at right is rolled back before launch. Scheduled for liftoff at 1:47 p.m. EST today, Deep Impact will head for space and a rendezvous with Comet Tempel 1 when the comet is 83 million miles from Earth. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-05PD-0127

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. On Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., the Boeing Delta II carrying the Deep Impact spacecraft rocket shines under spotlights in the early dawn hours as it waits for launch. Scheduled for liftoff at 1:47 p.m. EST today, Deep Impact will head for space and a rendezvous with Comet Tempel 1 when the comet is 83 million miles from Earth. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-05PD-0129

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. The sun rises behind Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., where the Boeing Delta II rocket carrying the Deep Impact spacecraft waits for launch. Gray clouds above the horizon belie the favorable weather forecast for the afternoon launch. Scheduled for liftoff at 1:47 p.m. EST today, Deep Impact will head for space and a rendezvous with Comet Tempel 1 when the comet is 83 million miles from Earth. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

The Impact Imperative: Laser Ablation for Deflecting Asteroids, Meteoroids, and Comets From Impacting the Earth

NASA Technical Reports Server (NTRS)

Campbell, Jonathan W.; Phipps, Claude; Smalley, Larry; Reilly, Jim; Boccis, Dona; Howell, Joe T., Jr. (Technical Monitor)

2002-01-01

Impacting at hypervelocity, an asteroid struck the Earth approximately 65 million years ago in the Yucatan Peninsula area. This triggered the extinction of almost 70% of the species of life on Earth including the dinosaurs. Other impacts prior to this one have caused even greater extinctions. Preventing collisions with the Earth by hypervelocity asteroids, meteoroids, and comets is the most important immediate space challenge facing human civilization. This is the Impact Imperative. We now believe that while there are about 2000 earth orbit crossing rocks greater than 1 kilometer in diameter, there may be as many as 200,000 or more objects in the 100 m size range, Can anything be done about this fundamental existence question facing our civilization? The answer is a resounding yes! By using an intelligent combination of Earth and space based sensors coupled with an infra-structure of high-energy laser stations and other secondary mitigation options, we can deflect inbound asteroids, meteoroids, and comets and prevent them from striking the Earth.

The Direct Economic Impact of Texas' Expenditure on Public Baccalaureate and Post Baccalaureate Education. ASHE Annual Meeting Paper.

ERIC Educational Resources Information Center

Creech, Sandra K.; And Others

This study sought to quantify economic impacts associated with Texas state expenditures on higher education by (1) quantifying the reduction in Texas' economic activity associated with reduced spending by the private sector due to taxes levied for higher education; and (2) quantifying the increase in Texas' economic activity associated with the…

Ground-Based Observations of 9P/Tempel 1 - The Deep Impact Mission

NASA Astrophysics Data System (ADS)

Meech, K. J.; Bauer, J. M.; A'Hearn, M. F.

1999-09-01

The Deep Impact mission, one of the two recently approved Discovery missions, will deliver a 500 kg copper projectile to the comet 9P/Tempel 1 on July 4, 2005, to excavate a crater. The goal will be to watch the cratering event, measure the change in activity level caused by the impact, and will be the first experiment to sample deeply below the surface of a comet. In preparation for a successful mission, we will begin a vigorous ground-based observing campaign to characterize the nucleus of 9P/Tempel 1. The ground-based observations will characterize the pre-impact activity levels for comparison after the impact, characterize the nucleus in terms of a rotational light curve and pole position, get an estimate of the nucleus size and albedo, model the dust production rates, and search for the appearance of gaseous species as the comet approaches perihelion. The observing campaign as already begun with some intensive observations of the comet during the following observing runs: UT Date & Nts & Telescope & r[AU] & No. & Exp 12/97 & 1 &Keck II & 4.48 & 2 & 240 1/98 & 1 &UH 2.2m & 4.44 & 7 & 4200 2/98 & 1 &CTIO1.5m & 4.36 & 3 & 1800 4/98 & 2 &UH 2.2m & 4.26 & 8 & 4800 1/99 & 6 &UH 2.2m & 3.14 &133 &17220 3/99 & 4 &UH 2.2m & 2.88 &181 &54000 5/99 & 2 &UH 2.2m & 2.47 & 9 & 810 7 /99 & 2 &UH 2.2m & 2.19 & 9 & 1620 The 1999 January and March observations were made to search for the rotation period of the comet, as well as to obtain deep images to model the coma. The results of the rotational light curve observations will be presented, as well as a compilation of the heliocentric light curve from the data from earlier epochs. In addition, a detailed, comprehensive multi-wavelength ground-based observing plan will be presented to characterize the nucleus before the 2005 July 4 Deep Impact encounter with the comet. This project has been funded through the NASA Planetary Astronomy Program to date, NAG 4494.

EPOXI Trip to Meet Comet Hartley 2

NASA Image and Video Library

2010-10-26

This frame from a movie begins with the launch of NASA Deep Impact on Jan. 12, 2005, from Cape Canaveral, Fla. On July 4, 2005, the mission released a probe into Comet Tempel 1, revealing its pristine, inner material.

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.

Smectite deposits in Marathon Valley, Endeavour Crater, Mars, identified using CRISM hyperspectral reflectance data

NASA Astrophysics Data System (ADS)

Fox, V. K.; Arvidson, R. E.; Guinness, E. A.; McLennan, S. M.; Catalano, J. G.; Murchie, S. L.; Powell, K. E.

2016-05-01

The ~100 m wide Marathon Valley crosscuts the Cape Tribulation rim segment of the 22 km diameter, Noachian-age Endeavour impact crater on Mars. Single-scattering albedo spectra retrieved from three Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) Full-Resolution Targeted (FRT, regularized to 18 m/pixel) and two Along Track Oversampled (ATO, regularized to 12 m/pixel) observations indicate the presence of Fe3+-Mg2+ smectite exposures located in Marathon Valley with combination vibration metal-OH absorption strength comparable to smectite spectral signatures in Mawrth Vallis. The Opportunity rover was directed to the exposures and documented the presence of Shoemaker formation impact breccias that have been isochemically altered, likely by fracture-controlled aqueous fluids.

A simulation model to predict the fiscal and public health impact of a change in cigarette excise taxes.

PubMed

van Walbeek, Corné

2010-02-01

(1) To present a model that predicts changes in cigarette consumption and excise revenue in response to excise tax changes, and (2) to demonstrate that, if the industry has market power, increases in specific taxes have better tobacco control consequences than increases in ad valorem taxes. All model parameters are user-determined. The model calculates likely changes in cigarette consumption, smoking prevalence and excise tax revenues due to an excise tax change. The model is applicable to countries that levy excise tax as specific or ad valorem taxes. For a representative low-income or middle-income country a 20% excise tax increase decreases cigarette consumption and industry revenue by 5% and increases excise tax revenues by 14%, if there is no change in the net-of-tax price. If the excise tax is levied as a specific tax, the industry has an incentive to raise the net-of-tax price, enhancing the consumption-reducing impact of the tax increase. If the excise tax is levied as an ad valorem tax, the industry has no such incentive. The industry has an incentive to reduce the net-of-tax price in response to an ad valorem excise tax increase, undermining the public health and fiscal benefits of the tax increase. This paper presents a simple web-based tool that allows policy makers and tobacco control advocates to estimate the likely consumption, fiscal and mortality impacts of a change in the cigarette excise tax. If a country wishes to reduce cigarette consumption by increasing the excise tax, a specific tax structure is better than an ad valorem tax structure.

A Cyber-Astronaut's Final Moves

NASA Technical Reports Server (NTRS)

2005-01-01

This image shows how Deep Impact's impactor targeted comet Tempel 1 as the spacecraft made its final approach in the early morning hours of July 4, Eastern time. The autonomous navigation system on the probe was designed to make as many as three impactor targeting maneuvers, identified as ITMs in this picture, to correct its course to the comet.

The upper left dot indicates where the probe would have passed the comet's nucleus if no maneuvers were performed. The dot below the nucleus shows where the probe would have flown past the comet if only the first maneuver was made. The leftmost dot on the nucleus marks the spot where the probe would have crunched the comet if only the first two maneuvers had been performed. The lower dot on the nucleus indicates the vicinity where, once the third maneuver was performed, the probe met its final reward and collided with the comet.

The Road to Tempel (Artist's Concept)

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Quick Time Movie for PIA02106 The Road to Tempel

This animation chronicles the travels of NASA's Deep Impact spacecraft, from its launch in January of 2005 to its dramatic impact 172 days later with comet Tempel 1. The times listed below were updated on July 2, 2005, and differ from those referred to in the animation.

The final phase of the mission, called the encounter phase, includes two targeting maneuvers, the last of which occurs at 5:07 p.m. Pacific time (8:07 p.m. Eastern time), July 2. Six hours later, the spacecraft releases an impactor into the path of the charging comet. Twelve minutes later, the remaining craft, called the flyby, steers itself away from the comet's path. The free impactor then autonomously fine-tunes its trajectory, with the goal of hitting the sunlit side of Tempel 1. Impact is scheduled to occur at 10:52 p.m. Pacific time, July 3 (1:52 a.m. Eastern time, July 4).

The flyby spacecraft will watch the collision from the sidelines, snapping pictures up to 13 minutes after impact. At that point, the craft stops taking images and enters a protective mode, in which its shields block dust from the comet's inner coma. Fifty-nine minutes after impact, the flyby turns around for one last photo opportunity.

Rosetta Images of Comet 67P/CHURYUMOV-GERASIMENKO: Inferences from its Terrain and Structure

NASA Astrophysics Data System (ADS)

Wallis, Max; Wickramasinghe, N. Chandra

The Rosetta mission has given us remarkable images of comet 67P/C-G both from the orbiter, and recently from the Philae lander during its brief days before running out of power. Though its crust is very black, there are several indicators of an underlying icy morphology. Comet 67P displays smooth, planar `seas' (the largest 600 m × 800 m) and flat-bottomed craters, both features seen also on Comet Tempel-1. Comet 67P's surface is peppered with mega-boulders (10-70 km) like Comet Hartley-2, while parallel furrowed terrain appears as a new ice feature. The largest sea (`Cheops' Sea, 600 m × 800 m) curves around one lobe of the 4 km diameter comet, and the crater lakes extending to ~150 m across are re-frozen bodies of water overlain with organic-rich debris (sublimation lag) of order 10 cm. The parallel furrows relate to flexing of the asymmetric and spinning two-lobe body, which generates fractures in an underlying body of ice. The mega-boulders are hypothesised to arise from bolide impacts into ice. In the very low gravity, boulders ejected at a fraction of 1 m/s would readily reach ~100 m from the impact crater and could land perched on elevated surfaces. Where they stand proud, they indicate stronger refrozen terrain or show that the surface they land on (and crush) sublimates more quickly. Outgassing due to ice-sublimation was already evident in September at 3.3 AU, with surface temperature peaks of 220-230 K, which implies impure ice mixtures with less strongly-bound H2O. Increasing rates of sublimation as Rosetta follows comet 67P around its 1.3 AU perihelion will further reveal the nature and prevalence of near-surface ices.

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.

Impact Induced Climate Change on Venus: The Role of Large Comets

NASA Astrophysics Data System (ADS)

Grinspoon, D. H.; Bullock, M. A.

2000-10-01

The surface temperature of Venus is a sensitive function of the abundances of greenhouse gases and also of cloud structure. In previous work we have studied the climate impact of past and continued outgassing of greenhouse and cloud-forming gases (1) and tectonic signatures that may have resulted from volcanically induced climate change (2). These studies showed that in outgassing events where large amounts of both H2O and SO2 are released, the increased albedo that arises from thickening of the clouds can, to some extent, ameliorate the greenhouse warming expected from increased abundances of these IR absorbing gases. The largest warming typically arises several hundred million years after an outgassing event when most of the excess SO2 has been removed by reaction with surface minerals, but much of the atmospheric H2O remains (because it is removed by exospheric escape on longer time scales). This combination - enhanced H2O abundance with SO2 returned to 'normal' - leads to maximum warming because the cloud thickness, and thus the albedo, is limited by the availability of SO2, whereas IR absorption in CO2 windows by enhanced H2O can cause warming on the order of 100 K. It seems likely that large comet impacts should also produce such a situation. The atmosphere of Venus currently contains 7 x 1018 grams of water, about as much as in a 25 km diameter comet. Comets may have been an important contributor to the current water inventory on Venus. Much of this may have been supplied by a few large comet impacts in the last several hundred million years (3). We will report on new runs of our Venus Evolutionary Climate Model which simulate the volatile input from large comet impacts and investigate the climate effects of these events. Calculation will be done with cometary delivery alone, and in conjunction with various outgassing scenarios. This allows us to examine how the vulnerability of the Venusian climate system to impact induced climate change is affected by the relative timing of large magmatic and impact events. (1) Bullock, M.A., and D.H. Grinspoon, J. Geophys. Res. 101, 7521-7529, 1996. (2) Solomon, S.C., M. A. Bullock, and D. H. Grinspoon, Science, 286: 87-90, 1999. (3) Grinspoon, D.H. and J.S. Lewis, Icarus, 74, 21-35, 1988.

Physical Mechanism of Comet Outbursts: The Movie

NASA Astrophysics Data System (ADS)

Hartmann, William K.

2014-11-01

During experiments conducted in 1976 at the NASA Ames Research Center’s Vertical Gun Facility (VGF), the author studied low velocity impacts into simulated regolith powders and gravels, in order to examine physics of low-velocity collisions during early solar system planetesimal formation. In one “accidental” experiment, the bucket of powder remained gas-charged during evacuation of the VGF vacuum chamber. The impactor, moving at 5.5 m/s, disturbed the surface, initiating eruptions of dust-charged gas, shooting in jets from multiple vents at speeds up to about 3 m/s, with sporadic venting until 17 seconds after the impact. This experiment was described in [1], which concluded that it simulated comet eruption phenomena. In this hypothesis, a comet nucleus develops a lag deposit of regolith in at least some regions. At a certain distance from the sun, the thermal wave penetrates to an ice-rich depth, causing sublimation. Gas rises into the regolith, collects in pore spaces, and creates a gas-charged powder, as in our experiment. Any surface disturbance, such as a meteoroid, may initiate a temporary eruption, or eventually the gas pressure becomes sufficient to blow off the overburden. Our observed ejection speed would be sufficient to launch dust off of a kilometer-scale comet nucleus.Film (100 frames/s) of the event was obtained, but was partially torn up in a projector. It has recently been reconstituted (Centric Photo Labs, Tucson) and dramatically illustrates various cometary phenomena. Parabolic curtains of erupted material resemble curtains of material photographed from earth in real comet comas, “falling back” under solar wind forces. In retrospect, the mechanism photographed here helps explain:*sporadic eruptions in Comet P/Schwassmann-Wachmann 1 (near-circular orbit at ~6 A.U., where repeated recharge may occur).*sporadic eruptions on “asteroid” 2060 Chiron (which stays beyond 8.5 A.U.). *the thicker dust curtain (and longer eruption?) than predicted for the Deep Impact experiment in Comet Tempel 1.The film is posted on the Planetary Science Institute website, www.psi.edu/hartmann. [1] Hartmann, W. K. 1993 Physical Mechanism of Comet Outbursts: An Experimental Result. Icarus 104, 226-233.

Planetary Defense: Are we currently looking for our keys under the lamp post?

NASA Astrophysics Data System (ADS)

Nuth, J. A., III; Barbee, B.; Leung, R. Y.

2016-12-01

Planetary Defense is a serious and important endeavor and the approach taken to date is a sensible beginning. Finding and cataloging all potentially hazardous asteroids and supporting research into relevant topics required to divert such a threat to our home planet is a necessary, but far from sufficient set of activities required to ensure the survival of our species. Concentrating our efforts on the asteroid threat is relatively easy. Most asteroids move in near-circular orbits, are relatively close to the ecliptic plane and are likely to be detected as hazards many decades in advance of a potential impact. The single most likely problem that will be encountered in deflecting such a threat will be developing the political will to fund the project while there is still ample time for multiple deflection techniques to be applied successfully. While asteroid threats can be mitigated, comets are the invisible danger lurking in the vast, dark parking lot that is the outer solar system. Very few comets falling into the inner solar system will be detected more than two years before their arrival: refinement of a new comet's trajectory requires months of observation before its hazard potential can be realistically assessed and knowledge of the composition, mass and shape of the body cannot be refined sufficiently to design a deflection campaign without much more observational effort. To make matters worse, because of the highly elliptical orbits of most new comets, some of which can be far out of the ecliptic plane while a few can even be in retrograde orbits, the impact velocity of a typical comet will be significantly higher than that of an asteroid. If this increase is only a factor of two, then a typical comet carries four times the impact energy of an asteroid of similar size, though much higher multipliers are possible. The distribution of meteor stream velocities can be examined to place bounds on this threat. Finally, the time required to assemble and launch an asteroid deflection mission starting from scratch and with a high probability of success could exceed three years from mission approval. Based on the recent passage of Comet Siding Spring one must therefore conclude that a successful comet deflection mission must begin well before a hazardous comet is even detected, much less characterized as a significant threat.

Description and Analysis of Core Samples: The Lunar Experience

NASA Technical Reports Server (NTRS)

McKay, David S.; Allton, Judith H.

1997-01-01

Although no samples yet have been returned from a comet, extensive experience from sampling another solar system body, the Moon, does exist. While, in overall structure, composition, and physical properties the Moon bears little resemblance to what is expected for a comet, sampling the Moon has provided some basic lessons in how to do things which may be equally applicable to cometary samples. In particular, an extensive series of core samples has been taken on the Moon, and coring is the best way to sample a comet in three dimensions. Data from cores taken at 24 Apollo collection stations and 3 Luna sites have been used to provide insight into the evolution of the lunar regolith. It is now well understood that this regolith is very complex and reflects gardening (stirring of grains by micrometeorites), erosion (from impacts and solar wind sputtering), maturation (exposure on the bare lunar surface to solar winds ions and micrometeorite impacts) and comminution of coarse grains into finer grains, blanket deposition of coarse-grained layers, and other processes. All of these processes have been documented in cores. While a cometary regolith should not be expected to parallel in detail the lunar regolith, it is possible that the upper part of a cometary regolith may include textural, mineralogical, and chemical features which reflect the original accretion of the comet, including a form of gardening. Differences in relative velocities and gravitational attraction no doubt made this accretionary gardening qualitatively much different than the lunar version. Furthermore, at least some comets, depending on their orbits, have been subjected to impacts of the uppermost surface by small projectiles at some time in their history. Consequently, a more recent post-accretional gardening may have occurred. Finally, for comets which approach the sun, large scale erosion may have occurred driven by gas loss. The uppermost material of these comets may reflect some of the features of this erosional process, such as crust formation, and variations with depth might be expected. Overall, the upper few meters of a comet may be as complex in their own way as the upper few meters of the lunar regolith have proven to be, and by analogy, detailed studies of core samples containing this depth information will be needed to understand these processes and the details of the accretional history and the subsequent alteration history of comets.

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.

Scientific rationale and strategies for a first comet mission: Report of the Comet Halley science working group

NASA Technical Reports Server (NTRS)

1977-01-01

The science objectives of a first comet mission are reviewed and related to what is known or can be expected to be learned in the near future from ground-based and near earth observations. A set of instruments and their science objectives are defined for a mission to Comet Halley during its 1985/86 apparition. The benefits from a fast flyby, a slow flyby, or a rendezvous mission and the relative impact of each on the instrument payload were assessed. The relative scientific value of encounters with the comet at distances from the sun ranging from 1 AU to 2.5 AU, including possible tradeoffs between flyby velocity and distance was considered. Pre- and post-perihelion encounters were likewise evaluated.

Simulation of Prebiotic Processing by Comet and Meteoroid Impact: Implications for Life on Early Earth and Other Planets

NASA Technical Reports Server (NTRS)

Dateo, Christopher E.

2003-01-01

We develop a reacting flow model to simulate the shock induced chemistry of comets and meteoroids entering planetary atmospheres. Various atmospheric compositions comprising of simpler molecules (i.e., CH4, CO2, H2O, etc.) are investigated to determine the production efficiency of more complex prebiotic molecules as a function of composition, pressure, and entry velocity. The possible role of comets and meteoroids in creating the inventory of prebiotic material necessary for life on Early Earth is considered. Comets and meteoroids can also introduce new materials from the Interstellar Medium (ISM) to planetary atmospheres. The ablation of water from comets, introducing the element oxygen into Titan's atmosphere will also be considered and its implications for the formation of organic and prebiotic material.

Dynamical and collisional evolution of Halley-type comets

NASA Astrophysics Data System (ADS)

van der Helm, E.; Jeffers, S. V.

2012-03-01

The number of observed Halley-type comets is hundreds of times less than predicted by models (Levison, H.F., Dones, L., Duncan, M.J. [2001]. Astron. J. 121, 2253-2267). In this paper we investigate the impact of collisions with planetesimals on the evolution of Halley-type comets. First we compute the dynamical evolution of a sub-set of 21 comets using the MERCURY integrator package over 100 Myr. The dynamical lifetime is determined to be of the order of 105-106 years in agreement with previous work. The collisional probability of Halley-type comets colliding with known asteroids, a simulated population of Kuiper-belt objects, and planets, is calculated using a modified, Öpik-based collision code. Our results show that the catastrophic disruption of the cometary nucleus has a very low probability of occurring, and disruption through cumulative minor impacts is concluded to be negligible. The dust mantle formed from ejected material falling back to the comet’s surface is calculated to be less than a few centimeters thick, which is insignificant compared to the mantle formed by volatile depletion, while planetary encounters were found to be a negligible disruption mechanism.

Wild 2 Close Look

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site] Figure 1

This image shows the comet Wild 2, which NASA's Stardust spacecraft flew by on Jan. 2, 2004. This image is the closest short exposure of the comet, taken at an11.4-degree phase angle, the angle between the camera, comet and the Sun. The listed names on the diagram (see Figure 1) are those used by the Stardust team to identify features. 'Basin' does not imply an impact origin.

KSC-04PD-2413

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. On Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., a crane begins lifting the third in a set of three Solid Rocket Boosters (SRBs). The SRBs will be hoisted up the mobile service tower and join three others already mated to the Boeing Delta II rocket that will launch the Deep Impact spacecraft. A NASA Discovery mission, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing an impactor on a course to hit the comets sunlit side, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measure the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determine the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

Deep Impact's EPO Program: Final Report

NASA Astrophysics Data System (ADS)

McFadden, Lucy-Ann A.; Warner, E. M.; McLaughlin, S.; Behne, J.; Ristvey, J.; Rountree-Brown, M.

2006-09-01

NASA's Deep Impact mission sent an impactor spacecraft into the path of periodic comet 9P/Tempel 1 on July 4, 2005. The Education and Public Outreach goals of the mission were to effectively communicate the mission to target audiences, particularly educators and students with an emphasis on critical thinking using science, math and engineering concepts. A second goal was to invite audiences to participate throughout the mission using products and interactive programs. In the six-years of the mission, we built a community of scientists, educators, students, and both amateur and technically proficient astronomers, who brought the excitement of the mission to their own community. The web site was the focus of the program (http://deepimpact.umd.edu or deepimpact.jpl.nasa.gov). A monthly electronic newsletter sent to an ever- growing distribution list kept subscribers up to date on mission activities. A program to send your name to the comet engaged the public. Curriculum enhancements covering the physics of crater formation, nature of comets and a case study in optimized decision-making designed for students are available (http://deepimpact.umd.edu/educ/index.html). Mathematical (http://deepimpact.umd.edu/disczone/challenge.html) and conceptual questions of a technical nature (http://deepimpact.umd.edu/disczone/braintwist.html) are posed and solved in Mission Challenges and Brain Twisters. Materials provided for students and amateur astronomers to acquire comet observing skills are available (http://deepimpact.umd.edu/amateur/index.shtml).The Small Telescope Science Program was a successful pro-amateur collaboration providing information on brightness variations of the comet both before and after impact (http://deepimpact.umd.edu/stsp/). The night, of impact, events were held at public venues around the world where the excitement of a successful mission exploring the inside of a comet was felt. Results are at http://deepimpact.umd.edu/results/index.html. The mission is over but the web site has been archived and continues to hold material useful to educators and the interested public. This work was supported by NASA NASW00004 Deep Impact mission.

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

Mcdonald Observatory 9P/TEMPEL 1 Data V1.0

NASA Astrophysics Data System (ADS)

Cochran, A. L.; Barker, E. S.; Caballero, M. D.; Gyorgey-Ries, J.

2010-01-01

We report on low-spectral resolution observations of comet 9P/Tempel 1 from 1983, 1989, 1994 and 2005 using the 2.7m Harlan J. Smith telescope of McDonald Observatory. This comet was the target of NASA's Deep Impact mission and our observations allowed us to characterize the comet prior to the impact. In the published paper, we showed that the comet decreased in gas production from 1983 to 2005, with the decrease being different factors for different species. OH decreased by a factor 2.7, NH by 1.7, CN by 1.6, C3 by 1.8, CH by 1.4 and C2 by 1.3. Despite the decrease in overall gas production and these slightly different decrease factors, we found that the ratios of the gas production rates of OH, NH, C3, CH and C2 that of CN were constant over all of the apparitions. We saw no change in the production rate ratios after the impact. We found that the peak gas production occurred about two months prior to perihelion. This data set represents the integrated fluxes and column densities, mentioned in the published paper, which were used to derive the production rates in the paper.

Tax levy financing for local public health: fiscal allocation, effort, and capacity.

PubMed

Riley, William J; Gearin, Kimberly J; Parrotta, Carmen D; Briggs, Jill; Gyllstrom, M Elizabeth

2013-12-01

Local health departments (LHDs) rely on a wide variety of funding sources, and the level of financing is associated with both LHD performance in essential public health services and population health outcomes. Although it has been shown that funding sources vary across LHDs, there is no evidence regarding the relationship between fiscal allocation (local tax levy); fiscal effort (tax capacity); and fiscal capacity (community wealth). The purpose of this study is to analyze local tax levy support for LHD funding. Three research questions are addressed: (1) What are tax levy trends in LHD fiscal allocation? (2) What is the role of tax levy in overall LHD financing? and (3) How do local community fiscal capacity and fiscal effort relate to LHD tax levy fiscal allocation? This study focuses on 74 LHDs eligible for local tax levy funding in Minnesota. Funding and expenditure data for 5 years (2006 to 2010) were compiled from four governmental databases, including the Minnesota Department of Health, the State Auditor, the State Demographer, and the Metropolitan Council. Trends in various funding sources and expenditures are described for the time frame of interest. Data were analyzed in 2012. During the 2006-2010 time period, total average LHD per capita expenditures increased 13%, from $50.98 to $57.63. Although the overall tax levy increase in Minnesota was 25%, the local tax levy for public health increased 5.6% during the same period. There is a direct relationship between fiscal effort and LHD expenditures. Local funding reflects LHD community priorities and the relative importance in comparison to funding other local programs with tax dollars. In Minnesota, local tax levy support for local public health services is not keeping pace with local tax support for other local government services. These results raise important questions about the relationship between tax levy resource effort, resource allocation, and fiscal capacity as they relate to public health spending in local communities. © 2013 Published by American Journal of Preventive Medicine on behalf of American Journal of Preventive Medicine.

Geological implications of impacts of large asteroids and comets on the earth

NASA Technical Reports Server (NTRS)

Silver, L. T. (Editor); Schultz, P. H. (Editor)

1982-01-01

The present conference discusses such topics as large object fluxes in near-earth space and the probabilities of terrestrial impacts, the geological record of impacts, dynamics modeling for large body impacts on continents and oceans, physical, chemical, and biological models of large impacts' atmospheric effects, dispersed impact ejecta and their signatures, general considerations concerning mass biological extinctions, the Cretaceous/Tertiary boundary event, geochemical signatures in the stratigraphic record, and other phanerozoic events. Attention is given to terrestrial impact rates for long- and short-period comets, estimates of crater size for large body impact, a first-order estimate of shock heating and vaporization in oceanic impacts, atmospheric effects in the first few minutes after an impact, a feasibility test for biogeographic extinction, and the planktonic and dinosaur extinctions.

Dynamic Acquisition and Retrieval Tool (DART) for Comet Sample Return : Session: 2.06.Robotic Mobility and Sample Acquisition Systems

NASA Technical Reports Server (NTRS)

Badescu, Mircea; Bonitz, Robert; Kulczycki, Erick; Aisen, Norman; Dandino, Charles M.; Cantrell, Brett S.; Gallagher, William; Shevin, Jesse; Ganino, Anthony; Haddad, Nicolas;

Impact as a general cause of extinction: A feasibility test

NASA Technical Reports Server (NTRS)

Raup, David M.

1988-01-01

Large body impact has been implicated as the possible cause of several extinction events. This is entirely plausible if one accepts two propositions: (1) that impacts of large comets and asteroids produce environmental effects severe enough to cause significant species extinctions and (2) that the estimates of comet and asteroid flux for the Phanerozoic are approximately correct. A resonable next step is to investigate the possibility that impact could be a significant factor in the broader Phanerozoic extinction record, not limited merely to a few events of mass extinction. Monte Carlo simulation experiments based on existing flux estimates and reasonable predictions of the relationship between bolide diameter and extinction are discussed. The simulation results raise the serious possibility that large body impact may be a more pervasive factor in extinction than has been assumed heretofore. At the very least, the experiments show that the comet and asteroid flux estimates combined with a reasonable kill curve produces a reasonable extinction record, complete with occasional mass extinctions and the irregular, lower intensity extinctions commonly called background extinction.

Reservoirs for Comets: Compositional Differences Based on Infrared Observations

NASA Astrophysics Data System (ADS)

Disanti, Michael A.; Mumma, Michael J.

Tracing measured compositions of comets to their origins continues to be of keen interest to cometary scientists and to dynamical modelers of Solar System formation and evolution. This requires building a taxonomy of comets from both present-day dynamical reservoirs: the Kuiper Belt (hereafter KB), sampled through observation of ecliptic comets (primarily Jupiter Family comets, or JFCs), and the Oort cloud (OC), represented observationally by the long-period comets and by Halley Family comets (HFCs). Because of their short orbital periods, JFCs are subjected to more frequent exposure to solar radiation compared with OC comets. The recent apparitions of the JFCs 9P/Tempel 1 and 73P/Schwassmann-Wachmann 3 permitted detailed observations of material issuing from below their surfaces—these comets added significantly to the compositional database on this dynamical class, which is under-represented in studies of cometary parent volatiles. This chapter reviews the latest techniques developed for analysis of high-resolution spectral observations from ˜2-5 μm, and compares measured abundances of native ices among comets. While no clear compositional delineation can be drawn along dynamical lines, interesting comparisons can be made. The sub-surface composition of comet 9P, as revealed by the Deep Impact ejecta, was similar to the majority of OC comets studied. Meanwhile, 73P was depleted in all native ices except HCN, similar to the disintegrated OC comet C/1999 S4 (LINEAR). These results suggest that 73P may have formed in the inner giant planets' region while 9P formed farther out or, alternatively, that both JFCs formed farther from the Sun but with 73P forming later in time.

Reservoirs for Comets: Compositional Differences Based on Infrared Observations

NASA Astrophysics Data System (ADS)

Disanti, Michael A.; Mumma, Michael J.

2008-07-01

Tracing measured compositions of comets to their origins continues to be of keen interest to cometary scientists and to dynamical modelers of Solar System formation and evolution. This requires building a taxonomy of comets from both present-day dynamical reservoirs: the Kuiper Belt (hereafter KB), sampled through observation of ecliptic comets (primarily Jupiter Family comets, or JFCs), and the Oort cloud (OC), represented observationally by the long-period comets and by Halley Family comets (HFCs). Because of their short orbital periods, JFCs are subjected to more frequent exposure to solar radiation compared with OC comets. The recent apparitions of the JFCs 9P/Tempel 1 and 73P/Schwassmann-Wachmann 3 permitted detailed observations of material issuing from below their surfaces—these comets added significantly to the compositional database on this dynamical class, which is under-represented in studies of cometary parent volatiles. This chapter reviews the latest techniques developed for analysis of high-resolution spectral observations from ˜2 5 μm, and compares measured abundances of native ices among comets. While no clear compositional delineation can be drawn along dynamical lines, interesting comparisons can be made. The sub-surface composition of comet 9P, as revealed by the Deep Impact ejecta, was similar to the majority of OC comets studied. Meanwhile, 73P was depleted in all native ices except HCN, similar to the disintegrated OC comet C/1999 S4 (LINEAR). These results suggest that 73P may have formed in the inner giant planets’ region while 9P formed farther out or, alternatively, that both JFCs formed farther from the Sun but with 73P forming later in time.

Review of Theoretical Approaches to Nonlinear Supercavitating Flows

DTIC Science & Technology

2001-02-01

hodograph) method to flow past a body with a curved topography was considered iy Levi - Civita [15] and Villat [24]. 2.3. Mixed boundary value problem...streamline flow around a body with a curved boundary 5.1. Levi - Civita approach Levi - Civita [15] was the first to propose an approach to solution of the plane...enotes a real parameter to 1)e determfineid. The second step is formulation of a imiixed bounidary value problem for Levi - Civita [15] function dw v WLC

The Influence of the Number of Different Stocks on the Levy-Levy-Solomon Model

NASA Astrophysics Data System (ADS)

Kohl, R.

The stock market model of Levy, Levy, Solomon is simulated for more than one stock to analyze the behavior for a large number of investors. Small markets can lead to realistic looking prices for one and more stocks. A large number of investors leads to a semi-regular fashion simulating one stock. For many stocks, three of the stocks are semi-regular and dominant, the rest is chaotic. Aside from that we changed the utility function and checked the results.

Deep Impact Spacecraft Collides With Comet Tempel 1-Video

NASA Technical Reports Server (NTRS)

2005-01-01

After 172 days and 268 million miles of deep space travel, the NASA Deep Impact spacecraft successfully reached out and touched comet Tempel 1. The collision between the coffee table-sized space probe and city-sized comet occurred July 4, 2005 at 12:52 a.m. CDT. The objects met at 23,000 miles per hour. The heat produced by the impact was at least several thousand degrees Kelvin and at that extreme temperature, just about any material begins to glow. This movie, made up of images taken by the medium resolution camera aboard the spacecraft, from May 1 to July 2, shows the Deep Impact approach to comet Tempel 1. The spacecraft detected 3 outbursts during this time period, on June 14th, June 22nd, and July 2nd. The movie ends during the final outburst. Mission scientists expect Deep Impact to provide answers to basic questions about the formation of the solar system. Principal investigator, Dr. Michael A'Hearn of the University of Maryland in College Park, is responsible for the mission, and project management is handled by the Jet Propulsion Laboratory in Pasadena, California. The program office at Marshall Space Flight Center MSFC) in Huntsville, Alabama, assisted the Science Mission Directorate at NASA Headquarters in Washington with program management, technology planning, systems assessment, flight assurance and public outreach. The spacecraft was built for NASA by Ball Aerospace & Technologies Corporation of Boulder, Colorado. (NASA/JPL-Caltech/UMD)

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.

Noachian Impact Ejecta on Murray Ridge and Pre-impact Rocks on Wdowiak Ridge, Endeavour Crater, Mars: Opportunity Observations

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.; Gellert, R.; Ming, D. W.; Morris, R. V.; Schroeder, C.; Yen, A. S.; Farrand, W. H.; Arvidson, R. E.; Franklin, B. J.; Grant, J. A.;

A model for wind-extension of the Copernicus ejecta blanket

NASA Technical Reports Server (NTRS)

Rehfuss, D. E.; Michael, D.; Anselmo, J. C.; Kincheloe, N. K.

1977-01-01

The interaction between crater ejecta and the transient wind from impact-shock vaporization is discussed. Based partly on Shoemaker's (1962) ballistic model of the Copernicus ejecta and partly on Rehfuss' (1972) treatment of lunar winds, a simple model is developed which indicates that if Copernicus were formed by a basaltic meteorite impacting at 20 km/s, then 3% of the ejecta mass would be sent beyond the maximum range expected from purely ballistic trajectories. That 3% mass would, however, shift the position of the outer edge of the ejecta blanket more than 400% beyond the edge of the ballistic blanket. For planetary bodies lacking an intrinsic atmosphere, the present model indicates that this form of hyperballistic transport can be very significant for small (no more than about 1 kg) ejecta fragments.

De la boule de neige sale au canard en caoutchouc noir, 67P/ Churyumov Gerasimenko, From the dirty snowball to the rubber black duck, 67P/ Churyumov Gerasimenko

NASA Astrophysics Data System (ADS)

Borg, Janet

2016-12-01

Rosetta has ended its mission on 30 September 2016 with a controlled impact in the Ma'at region on the small lobe of comet 67P/ Churyumov Gerasimenko. Since its arrival in the vicinity of the comet in august 2014, Rosetta has spent more than two years living with the comet, investigating its nucleus and its environment. It has witnessed how a comet changes as it approached perihelia and after, returned to the outer solar system. This paper is a summary of the main results obtained from the returned data that give a completely new image of what is a comet. In the future, information obtained from the analysis of more data will of course lead to more progress in a better understanding of comets, and more generally of the formation of the solar system and even of the emergence of live on Earth.

KSC-05PD-0113

NASA Technical Reports Server (NTRS)

2005-01-01

JET PROPULSION LABORATORY, CALIF. At Ball Aerospace in Boulder, Colo., the infrared (IR) spectrometer for the Deep Impact flyby spacecraft is inspected in the instrument assembly area in the Fisher Assembly building clean room. Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. The spectrometer is part of the High Resolution Instrument in the spacecraft. This imager will be aimed at the ejected matter as the crater forms, and an infrared 'fingerprint' of the material from inside of the comet's nucleus will be taken. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission. Launch of Deep Impact is scheduled for Jan. 12 from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla.

26 CFR 301.6331-1 - Levy and distraint.

Code of Federal Regulations, 2010 CFR

2010-04-01

... ADMINISTRATION PROCEDURE AND ADMINISTRATION Seizure of Property for Collection of Taxes § 301.6331-1 Levy and... property, belonging to such Indian. (b) Continuing levies and successive seizures—(1) Continuing effect of... any exempt amount pursuant to section 6334). (2) Successive seizures. Whenever any property or rights...

Delivery of organics to Mars through asteroid and comet impacts

NASA Astrophysics Data System (ADS)

Frantseva, K.; Mueller, M.; van der Tak, F. F. S.; ten Kate, I. L.; Greenstreet, S.

2017-09-01

Preliminary results show that the asteroid-borne organic flux on Mars is comparable to the IPD rate; asteroids certainly cannot be neglected. Comets, on the other hand, contribute only 0.01% of the IDP-borne rate and can be neglected in the process of organic delivery to Mars.

Oort spike comets with large perihelion distances

NASA Astrophysics Data System (ADS)

Królikowska, Małgorzata; Dybczyński, Piotr A.

2017-12-01

The complete sample of large-perihelion nearly-parabolic comets discovered during the period 1901-2010 is studied, starting with their orbit determination. Next, an orbital evolution that includes three perihelion passages (previous-observed-next) is investigated in which a full model of Galactic perturbations and perturbations from passing stars is incorporated. We show that the distribution of planetary perturbations suffered by actual large-perihelion comets during their passage through the Solar system has a deep, unexpected minimum around zero, which indicates a lack of 'almost unperturbed' comets. Using a series of simulations we show that this deep well is moderately resistant to some diffusion of the orbital elements of the analysed comets. It seems reasonable to assert that the observed stream of these large-perihelion comets experienced a series of specific planetary configurations when passing through the planetary zone. An analysis of the past dynamics of these comets clearly shows that dynamically new comets can appear only when their original semimajor axes are greater than 20 000 au. On the other hand, dynamically old comets are completely absent for semimajor axes longer than 40 000 au. We demonstrate that the observed 1/aori-distribution exhibits a local minimum separating dynamically new from dynamically old comets. Long-term dynamical studies reveal a wide variety of orbital behaviour. Several interesting examples of the action of passing stars are also described, in particular the impact of Gliese 710, which will pass close to the Sun in the future. However, none of the obtained stellar perturbations is sufficient to change the dynamical status of the analysed comets.

7 CFR 1207.510 - Levy of assessments.

Code of Federal Regulations, 2010 CFR

2010-01-01

... AGREEMENTS AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE POTATO RESEARCH AND PROMOTION... assessment rate of 3 cents per hundredweight shall be levied on all potatoes produced within the 50 states of the United States. (2) No assessment shall be levied on potatoes grown in the 50 States of the United...

7 CFR 1207.510 - Levy of assessments.

Code of Federal Regulations, 2013 CFR

2013-01-01

... AGREEMENTS AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE POTATO RESEARCH AND PROMOTION... assessment rate of 3 cents per hundredweight shall be levied on all potatoes produced within the 50 states of the United States. (2) No assessment shall be levied on potatoes grown in the 50 States of the United...

7 CFR 1207.510 - Levy of assessments.

Code of Federal Regulations, 2011 CFR

2011-01-01

... AGREEMENTS AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE POTATO RESEARCH AND PROMOTION... assessment rate of 3 cents per hundredweight shall be levied on all potatoes produced within the 50 states of the United States. (2) No assessment shall be levied on potatoes grown in the 50 States of the United...

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.

The Spaceguard Survey: Report of the NASA International Near-Earth-Object Detection Workshop

NASA Technical Reports Server (NTRS)

Morrison, David (Editor)

1992-01-01

Impacts by Earth-approaching asteroids and comets pose a significant hazard to life and property. Although the annual probability of the Earth being struck by a large asteroid or comet is extremely small, the consequences of such a collision are so catastrophic that it is prudent to assess the nature of the threat and to prepare to deal with it. The first step in any program for the prevention or mitigation of impact catastrophes must involve a comprehensive search for Earth-crossing asteroids and comets and a detailed analysis of their orbits. At the request of the U.S. Congress, NASA has carried out a preliminary study to define a program for dramatically increasing the detection rate of Earth-crossing objects, as documented in this workshop report.

Dynamical Modeling of Comet Dust: The STARDUST and ROSETTA Mission Targets

NASA Astrophysics Data System (ADS)

Kelley, M. S.; Reach, W. T.

2003-12-01

Comets 81P/Wild 2 and 67P/Churyumov-Gerasimenko are the respective targets for the NASA STARDUST and ESA ROSETTA missions. As such, the dust environment of each comet is of particular importance, simultaneously being a key to mission success (e.g. dust collection) and a possible spacecraft hazard (impacts with large particles). We present dynamical modeling of the comae and dust trails of comets 81P/Wild 2 and 67P/Churyumov-Gerasimenko and compare these models to ground-based observations. At the heart of our code is the 15th order integrator described by Everhart (1985, IAU Colloq. 83, 185-202). We integrate the radiation and gravitational forces acting on a dust particle due to the Sun and planets to determine a released particle's position relative to the parent comet at the time of an observation (either by telescope or spacecraft). Comparing zero ejection velocity syndyne curves to observations we obtain a first order estimate of the dust trail particle sizes, which typically range near the millimeter sizes or larger. If we input best guesses for ejection velocities, sizes, and emission histories into a Monte-Carlo integration we can simulate a coma and provide a particle size distribution estimate for various spacecraft impact parameters on large scales.

Re-evaluating the 38th Parallel Serial Impact Hypothesis

NASA Astrophysics Data System (ADS)

Evans, K. R.; Davis, G. H.; Miao, X.; Mickus, K. L.; Miller, J. F.; Morrow, J. R.

2008-12-01

The idea that the 38th-parallel structures across Kansas, Missouri, and Illinois are serial impacts has been controversial. In addition to the original eight, two other structures are proximal to the 38th parallel, Dent Branch and Silver City Dome. Only Weaubleau, Decaturville, and Crooked Creek contain quartz grains with multiple directions of planar deformational features (PDFs). Shatter cones have been found at Decaturville and Crooked Creek. Key macroscopic observations of these impacts include: (1) circular outlines and notable central uplifts, (2) remarkably intense levels of structural deformation (folding, faulting, fracturing, and brecciation), (3) deformation dying out with depth and laterally away from the central uplift, and (4) associated igneous rocks only as clasts. From field and core studies and published reports, we consider other structures along the 38th parallel to be dubious (Hazelgreen), intrusive, (Hick's Dome), or volcanic in origin (Silver City Dome, Rose Dome, Furnace Creek, Dent Branch, and Avon). The age of the Weaubleau structure is constrained biostratigraphically as middle Mississippian (latest Osagean or early Meramecian). Crooked Creek and Decaturville are deeply eroded; their ages are poorly constrained. Crooked Creek contains isolated blocks of sandstone of late Osagean age, but the stratigraphic context of the blocks is poorly known. Other investigators contend the age of Decaturville is Pennsylvanian or Permian, based on CRM paleomagnetism and occurrence of an isolated sulfide breccia body in the central uplift. The Ozark plateau experienced Missouri Valley Type (MVT) sulfide mineralization during the Ouachita orogeny, but our examination of a sample from the sulfide breccia shows it is shattered pyrite and differs from typical MVT deposits. If the breccia is not associated with the regional mineralization, a middle Mississippian age cannot be excluded. Weaubleau, Decaturville, and Crooked Creek are aligned across 199 km. A line connecting the centers of the central uplifts of Weaubleau and Crooked Creek passes 1.5 km north of the center of Decaturville. Monte Carlo simulation was used to examine the probability that three temporally unrelated impacts could be aligned (±2° angular discordance) randomly over relatively short distances in an area that approximates the continental land surface. Modeling variables included number of impacts (N=200, N=300...N=1,000) and search radii (100-600 km). Twenty repetitions of 10,000 runs provided for analysis of standard deviation. For N=200 and radius of 100 km, an average of 6.6±2.5 aligned sets were found. For N=300, the results were 25.9±3.7, yielding a probability of P=0.003. Larger sample sizes and wider search radii produced more probable results, but given the number of known impacts (~175), it is highly improbable that Weaubleau, Decaturville, and Crooked Creek structures could be aligned but not temporally related. If Weaubleau, Decaturville, and Crooked Creek were products of a serial impact, they were not analogous with the Shoemaker-Levy 9 impacts on Jupiter, where planetary rotation affected the distribution, so the impacts would have occurred within seconds. In Mississippian paleogeographic reconstructions, the direction of impact would have been WSW-ENE, arguably along the ecliptic and near the equator. The distribution of deformation at Weaubleau suggests an oblique impact from present-day WSW-ENE, an argument against the serial impact hypothesis.

Comets and the origins and evolution of life; Proceedings of the Conference, Univ. of Wisconsin, Eau Claire, Sept. 30-Oct. 2, 1991

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).

Inter-laboratory comparison of the in vivo comet assay including three image analysis systems.

PubMed

Plappert-Helbig, Ulla; Guérard, Melanie

2015-12-01

To compare the extent of potential inter-laboratory variability and the influence of different comet image analysis systems, in vivo comet experiments were conducted using the genotoxicants ethyl methanesulfonate and methyl methanesulfonate. Tissue samples from the same animals were processed and analyzed-including independent slide evaluation by image analysis-in two laboratories with extensive experience in performing the comet assay. The analysis revealed low inter-laboratory experimental variability. Neither the use of different image analysis systems, nor the staining procedure of DNA (propidium iodide vs. SYBR® Gold), considerably impacted the results or sensitivity of the assay. In addition, relatively high stability of the staining intensity of propidium iodide-stained slides was found in slides that were refrigerated for over 3 months. In conclusion, following a thoroughly defined protocol and standardized routine procedures ensures that the comet assay is robust and generates comparable results between different laboratories. © 2015 Wiley Periodicals, Inc.

Numerical Modelling of the Deep Impact Mission Experiment

NASA Technical Reports Server (NTRS)

Wuennemann, K.; Collins, G. S.; Melosh, H. J.

2005-01-01

NASA s Deep Impact Mission (launched January 2005) will provide, for the first time ever, insights into the interior of a comet (Tempel 1) by shooting a approx.370 kg projectile onto the surface of a comets nucleus. Although it is usually assumed that comets consist of a very porous mixture of water ice and rock, little is known about the internal structure and in particular the constitutive material properties of a comet. It is therefore difficult to predict the dimensions of the excavated crater. Estimates of the crater size are based on laboratory experiments of impacts into various target compositions of different densities and porosities using appropriate scaling laws; they range between 10 s of meters up to 250 m in diameter [1]. The size of the crater depends mainly on the physical process(es) that govern formation: Smaller sizes are expected if (1) strength, rather than gravity, limits crater growth; and, perhaps even more crucially, if (2) internal energy losses by pore-space collapse reduce the coupling efficiency (compaction craters). To investigate the effect of pore space collapse and strength of the target we conducted a suite of numerical experiments and implemented a novel approach for modeling porosity and the compaction of pores in hydrocode calculations.

Mass Spectum Imaging of Organics Injected into Stardust Aerogel by Cometary Impacts

NASA Technical Reports Server (NTRS)

Clemett, S. J.; Nakamura-Messenger, K.; Messenger, S.

2014-01-01

Comets have largely escaped the hydrothermal processing that has affected the chemistry and mineralogy of even the most primitive meteorites. Consequently, they are expected to better preserve nebular and interstellar organic materials. Organic matter constitutes roughly 20-30% by weight of vol-atile and refractory cometary materials [1,2]. Yet organic matter identified in Stardust aerogel samples is only a minor component [3-5]. The dearth of intact organic matter, fine-grained and pre-solar materials led to suggestions that comet 81P/Wild-2 is com-posed largely of altered materials, and is more similar to meteorites than the primitive view of comets [6]. However, fine-grained materials are particularly susceptible to alteration and destruction during the hypervelocity impact. While hypervelocity capture can cause thermal pyrolysis of organic phases, some of the impacting organic component appears to have been explosively dispersed into surrounding aerogel [7]. We used a two-step laser mass spectrometer to map the distribution of organic matter within and sur-rounding a bulbous Stardust track to constrain the dispersion of organic matter during the impact.

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.

CoMET: Cost and Mass Evaluation Tool for Spacecraft and Mission Design

NASA Technical Reports Server (NTRS)

Bieber, Ben S.

2005-01-01

New technology in space exploration is often developed without a complete knowledge of its impact. While the immediate benefits of a new technology are obvious, it is harder to understand its indirect consequences, which ripple through the entire system. COMET is a technology evaluation tool designed to illuminate how specific technology choices affect a mission at each system level. COMET uses simplified models for mass, power, and cost to analyze performance parameters of technologies of interest. The sensitivity analysis that CoMET provides shows whether developing a certain technology will greatly benefit the project or not. CoMET is an ongoing project approaching a web-based implementation phase. This year, development focused on the models for planetary daughter craft, such as atmospheric probes, blimps and balloons, and landers. These models are developed through research into historical data, well established rules of thumb, and engineering judgment of experts at JPL. The model is validated by corroboration with JpL advanced mission studies. Other enhancements to COMET include adding launch vehicle analysis and integrating an updated cost model. When completed, COMET will allow technological development to be focused on areas that will most drastically improve spacecraft performance.

27 CFR 70.241 - Property exempt from levy.

Code of Federal Regulations, 2010 CFR

2010-04-01

... taxpayer's salary, wages, or other income as is necessary to comply with such order or decree. The taxpayer... released from levy will actually be applied in satisfaction of the support obligation. The appropriate TTB... salary, wage, or other income for each pay period which shall be exempt from levy. Any request for such...

27 CFR 70.188 - Expense of levy and sale.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 27 Alcohol, Tobacco Products and Firearms 2 2014-04-01 2014-04-01 false Expense of levy and sale. 70.188 Section 70.188 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU... Excise and Special (Occupational) Tax Disposition of Property § 70.188 Expense of levy and sale. The...

27 CFR 70.188 - Expense of levy and sale.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 27 Alcohol, Tobacco Products and Firearms 2 2010-04-01 2010-04-01 false Expense of levy and sale. 70.188 Section 70.188 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU... Excise and Special (Occupational) Tax Disposition of Property § 70.188 Expense of levy and sale. The...

27 CFR 70.188 - Expense of levy and sale.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 27 Alcohol, Tobacco Products and Firearms 2 2012-04-01 2011-04-01 true Expense of levy and sale. 70.188 Section 70.188 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU... Excise and Special (Occupational) Tax Disposition of Property § 70.188 Expense of levy and sale. The...

27 CFR 70.188 - Expense of levy and sale.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 27 Alcohol, Tobacco Products and Firearms 2 2013-04-01 2013-04-01 false Expense of levy and sale. 70.188 Section 70.188 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU... Excise and Special (Occupational) Tax Disposition of Property § 70.188 Expense of levy and sale. The...

27 CFR 70.188 - Expense of levy and sale.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 27 Alcohol, Tobacco Products and Firearms 2 2011-04-01 2011-04-01 false Expense of levy and sale. 70.188 Section 70.188 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU... Excise and Special (Occupational) Tax Disposition of Property § 70.188 Expense of levy and sale. The...

Meteoroids and impact craters

USGS Publications Warehouse

Spall, H.

1986-01-01

Many meteoroids are associted with comets; as a comet travels around the sun it leaves a trail of debris behind it and it is this debris which produces meteor showers. Other meteoroids come from the asteroid belt, a zone between Mars and Jupiter filled with thousands of dwarf worlds that failed to coalesce into planets. 

Piaget and Levy-Bruhl.

PubMed

Jahoda, G

2000-08-01

Levy-Bruhl exerted a powerful influence, seldom considered, on Piaget. The Levy-Bruhlian thesis of a "pre-logical mentality" characterized by "mystical participation" is outlined, together with its initial reception. The first evidence of Piaget's interest in it dates from 1920, and when he began his studies of children's thinking he compared it with that of 'primitives," also adopting Levy-Bruhl's concept of "participation." By 1928 Piaget had elaborated a theory of the social foundations of different types of thought, which he regarded as also explaining the alleged similarity between the thinking of primitives and children. Both are subject to constraint, primitives by elders and children by parents and teachers. Logical as opposed to pre-logical thought was said to depend on cooperation in free social interaction. Piaget continued to maintain essentially the same views long after Levy-Bruhl himself had renounced the notion of pre-logicality.

Shock Effects on Cometary-Dust Simulants

NASA Technical Reports Server (NTRS)

Lederer, Susan M.; Jensen, Elizabeth; Wooden, Diane H.; Lindsay, Sean S.; Smith, Douglas H.; Nakamura-Messenger, Keiko; Keller, Lindsay P.; Cardenas, Francisco; Cintala, Mark J.; Montes, Roland

2014-01-01

While comets are perhaps best known for their ability to put on spectacular celestial light shows, they are much more than that. Composed of an assortment of frozen gases mixed with a collection of dust and minerals, comets are considered to be very primitive bodies and, as such, they are thought to hold key information about the earliest chapters in the history of the solar system. (The dust and mineral grains are usually called the "refractory" component, indicating that they can survive much higher temperatures than the ices.) It has long been thought, and spacecraft photography has confirmed, that comets suffer the effects of impacts along with every other solar system body. Comets spend most of their lifetimes in the Kuiper Belt, a region of the solar system between 30 and 50 times the average distance of the Earth from the Sun, or the Oort Cloud, which extends to approximately 1 light year from the Sun. Those distances are so far from the Sun that water ice is the equivalent of rock, melting or vaporizing only through the action of strong, impact-generated shock waves.

Global environmental effects of impact-generated aerosols: Results from a general circulation model

NASA Technical Reports Server (NTRS)

Covey, Curt; Ghan, Steven J.; Walton, John J.; Weissman, Paul R.

1989-01-01

Interception of sunlight by the high altitude worldwide dust cloud generated by impact of a large asteroid or comet would lead to substantial land surface cooling, according to the three-dimensional atmospheric general circulation model (GCM). This result is qualitatively similar to conclusions drawn from an earlier study that employed a one-dimensional atmospheric model, but in the GCM simulation the heat capacity of the oceans, not included in the one-dimensional model, substantially mitigates land surface cooling. On the other hand, the low heat capacity of the GCM's land surface allows temperatures to drop more rapidly in the initial stages of cooling than in the one-dimensional model study. GCM-simulated climatic changes in the scenario of asteroid/comet winter are more severe than in nuclear winter because the assumed aerosol amount is large enough to intercept all sunlight falling on earth. Impacts of smaller objects could also lead to dramatic, though of course less severe, climatic changes, according to the GCM. An asteroid or comet impact would not lead to anything approaching complete global freezing, but quite reasonable to assume that impacts would dramatically alter the climate in at least a patchy sense.

Evidence of Collisional Histories of Asteroids, Comets and Meteorites: Comparisons with Shocked Minerals

NASA Technical Reports Server (NTRS)

Lederer, Susan M.; Jensen, Elizabeth; Smith, Douglas; Fane, Michael; Whizin, Akbar; Landsman, Zoe A.; Wooden, Diane H.; Lindsay, Sean S.; Cintala, Mark; Keller, Lindsay P.;

Environmental Perturbations Caused by the Impacts of Asteroids and Comets

NASA Technical Reports Server (NTRS)

Toon, Owen B.; Zahnle, Kevin; Morrison, David; Turco, Richard; Covey, Curt

1997-01-01

We review the major mechanisms proposed to cause extinctions at the Cretaceous-Tertiary geological boundary following an asteroid impact. We then discuss how the proposed extinction may relate to the impact of asteroids or comets in general. We discuss the limitations of these mechanisms in terms of the spatial scale that may be affected, and the time scale over which the effects may last. Our goal is to provide relatively simple prescriptions for evaluating the importance of colliding objects having a range of energies and compositions. We also identify the many uncertainties concerning the environmental effects of impacts. We conclude that, for impact energies below about 10(exp 4) Mts (megatons of TNT equivalent) - i.e., impact frequencies less than in 6 x 10(exp 4) yr, corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m, respectively - blast damage, earthquakes, and fires should be important on a scale of 10(exp 4) or 10(exp 5) km (exp 2), which corresponds to the area damaged in many natural disasters of recent history. However, tsunami could be more damaging, flooding a kilometer of coastal plane over entire ocean basins. In the energy range of 10(exp 4) to 10 (exp 5) Mts (intervals up to 3 x 10(exp 5) yr; comets and asteroids with sizes up to 800 m and 1.5 km, respectively) water vapor injections and ozone loss become significant on the global scale. In the submicrometer dust injection fraction from the pulverized target material is much higher than is presently thought to be most likely, then dust injection could be important in this energy range.

Prevention before profits: a levy on food and alcohol advertising.

PubMed

Harper, Todd A; Mooney, Gavin

2010-04-05

The recent interest in health promotion and disease prevention has drawn attention to the role of the alcohol and junk-food industries. Companies supplying, producing, advertising or selling alcohol or junk food (ie, foods with a high content of fat, sugar or salt) do so to generate profits. Even companies marketing "low-carbohydrate" beers, "mild" cigarettes, or "high-fibre" sugary cereals are not primarily concerned about population health, more so increased sales and profits. In a competitive market, it is assumed that consumers make fully informed choices about costs and benefits before purchasing. However, consumers are not being fully informed of the implications of their junk-food and alcohol choices, as advertising of these products carries little information on the health consequences of consumption. We propose that there should be a levy on advertising expenditure for junk food and alcoholic beverages to provide an incentive for industry to promote healthier products. Proceeds of the levy could be used to provide consumers with more complete and balanced information on the healthy and harmful impacts of food and alcohol choices. Our proposal addresses two of the greatest challenges facing Australia's preventable disease epidemic - the imbalance between the promotion of healthier and unhealthy products, and securing funds to empower consumer choice.

Asteroids and Comets Outreach Compilation

NASA Technical Reports Server (NTRS)

1999-01-01

Contents include various different animations in the area of Asteroids and Comets. Titles of the short animated clips are: STARDUST Mission; Asteroid Castallia Impact Simulation; Castallia, Toutatis and the Earth; Simulation Asteroid Encounter with Earth; Nanorover Technology Task; Near Earth Asteroid Tracking; Champollian Anchor Tests; Early Views of Comets; Exploration of Small Bodies; Ulysses Resource Material from ESA; Ulysses Cometary Plasma Tail Animation; and various discussions on the Hale-Bopp Comet. Animation of the following are seen: the Stardust aerogel collector grid collecting cometary dust particles, comet and interstellar dust analyzer, Wiper-shield and dust flux monitor, a navigation camera, and the return of the sample to Earth; a comparison of the rotation of the Earth to the Castallia and Tautatis Asteroids; an animated land on Tautatis and the view of the motion of the sky from its surface; an Asteroid collision with the Earth; the USAF Station in Hawaii; close-up views of asteroids; automatic drilling of the Moon; exploding Cosmic Particles; and the dropping off of the plasma tail of a comet as it travels near the sun.

The STARDUST Discovery Mission: Data from the Encounter with Comet Wild 2 and the Expected Sample Return

NASA Technical Reports Server (NTRS)

Sandford, Scott A.

2004-01-01

On January 2,2004, the STARDUST spacecraft made the closest ever flyby (236 km) of the nucleus of a comet - Comet Wild 2. During the fly by the spacecraft collected samples of dust from the coma of the comet. These samples will be returned to Earth on January 15,2006. After a brief preliminary examination to establish the nature of the returned samples, they will be made available to the general scientific community for study. In addition to its aerogel dust collector, the STARDUST spacecraft was also equipped with instruments that made in situ measurements of the comet during the flyby. These included several dust impact monitors, a mass spectrometer, and a camera. The spacecraft's communication system was also used to place dynamical constraints on the mass of the nucleus and the number of impacts the spacecraft had with large particles. The data taken by these instruments indicate that the spacecraft successfully captured coma samples. These instruments, particularly the camera, also demonstrated that Wild 2 is unlike any other object in the Solar System previously visited by a spacecraft. During my talk I will discuss the scientific goals of the STARDUST mission and provide an overview of its design and flight to date. I will then end with a description of the exciting data returned by the spacecraft during the recent encounter with Wild 2 and discuss what these data tell us about the nature of comets. It will probably come as no surprise that the encounter data raise as many (or more) new questions as they answer old ones.

Can voter-approved tax levies provide fiscal advantages and stability for local public health agencies?

PubMed

Schmalzried, Hans D; Fallon, L Fleming

2013-01-01

Major funding cuts have occurred throughout the United States public health system during the past several years. Funding for local public health agency (LPHA) services and programs is obtained through a patchwork of sources that vary both within and among states. Even though local city and county sources provide a significant proportion of funding for LPHAs, information available in the literature about these revenues is sparse and is not clearly described. This study focused on a single specific revenue stream included in the local sources (local city and county) category: funds voted on directly by the public. The primary purpose of this study was to examine whether this type of funding source provided fiscal advantages for LPHAs. Specifically, we wanted to see how sensitive levy votes were to changing general economic conditions. A questionnaire to collect LPHA levy data was developed, approved, and mailed to county boards of elections in Ohio (n = 88). Elections officials were asked to provide voting results for all LPHA levy ballot attempts since 1994 regardless of outcome. In the study period (1994 through 2011), 250 LPHA property tax levies were placed on election ballots in Ohio. LPHAs were successful in 155 (62.0%) and unsuccessful in 95 (38.0%) attempts. Over the 18-year period, the most noteworthy outcome was a 94.6% pass rate for renewal levies. Our study demonstrated that voter-approved tax levies provide some fiscal advantages for LPHAs: higher per capita revenues than those who have to rely on other sources of income and predictable revenue streams. This translates into more funds being available for public health programs and services. Property tax levies allow citizens to make direct investments in their local health departments.

[An illustrious unknown. Giuseppe Levi among science, anti-fascism and Nobel Prizes].

PubMed

Grignolio, Andrea; De Sio, Fabio

2009-01-01

The anatomist Giuseppe Levi (1872-1965) is unanimously considered one of the major figures of Italian biomedical sciences in the 20th century. His fame, however, is mainly derived from having nurtured three Nobel Prize winners, namely Salvador E. Luria, Rita Levi Montalcini and Renato Dulbecco. In reappraising Levi's role in the development of Italian science and culture in general, this article aims at questioning both the narrowness of earlier accounts and a certain kind of genealogical approach to the history of scientific disciplines and academic schools. We will here consider Giuseppe Levi as an instance of two major cultural phenomena: the development of experimental biology in Italy and continental Europe and the anti-fascist socialist culture expressed by a part of the Italian intellectuals. In so doing, we will reassess the historical specificity of the scientific maturation of Levi's three famous students, on the one hand, while on the other we will consider in some depth the cultural and moral environment in which Levi thrived and his role as a moral example for his students. Such revision, we will argue, have a direct bearing on more general historiographical issues, namely, the need for a stronger contextualization of the birth and consolidation of research traditions, implying a rejection of simplistic genealogical reconstructions, and the role of academic schools and institutional settings in the definition of novel, multidisciplinary scientific approaches. Finally, the following will highlight the importance of a more careful outlook on the master-pupil relationship in academic context, addressing issues of both continuity and rupture. The article is subdivided in two main sections, the first devoted to Levi as a scientist, the second to his Anti-fascism.

High Concentrations of Hydrogen-bearing Volatiles at the Base of Poleward-facing slopes in the Moon's Large Southern Permanently Shadowed Regions.

NASA Astrophysics Data System (ADS)

McClanahan, T. P.; Mitrofanov, I. G.; Boynton, W. V.; Chin, G.; Livengood, T. A.; Litvak, M. L.; Sanin, A. B.; Starr, R. D.

2016-12-01

In this paper we review evidence that indicates that high concentrations of hydrogen-bearing volatiles are biased towards the base of poleward-facing slopes (PFS) in the Moon's large southern permanently shadowed regions (PSR). Results are derived from a correlated study of Lunar Reconnaissance Orbiter instrument maps of: epithermal neutron leakage flux observed by the Lunar Exploration Neutron Detector (LEND), topography derived from the Lunar Observing Laser Altimeter (LOLA) and surface thermal maps derived from the Diviner radiometer. Maximum concentrations of hydrogen-volatiles, likely as water ice, are observed in the Cabeus crater's PSR, 0.62 wght% water-equivalent-hydrogen. Detailed studies show that the occurrence of hydrogen-volatiles at the base of the (PFS) are correlated with the locations of low PSR temperatures of Cabeus, Haworth, Shoemaker and Faustini. LEND observations show no consistent correlation to smaller impact craters and the lowest temperatures within the PSR's. It is not presently known if the high volatile concentrations are due to downslope migration or thermal stability in the PFS breaks in slope. 15-km Full-width at Half-Maximum (FWHM) is shown to be an upper-bounds condition for the LEND collimated sensor's spatial resolution, derived from a cross-sectional profile, through the permanently shadowed region at Cabeus'. LEND's high-resolution spatial response is further illustrated in a 220-km long profile cut through the co-aligned permanently shadowed regions and partially-illuminated ridges of Haworth, Shoemaker, Faustini and Amundsen craters.

Comet and meteorite traditions of Aboriginal Australians

NASA Astrophysics Data System (ADS)

Hamacher, Duane W.

2014-06-01

This research contributes to the disciplines of cultural astronomy (the academic study of how past and present cultures understand and utilise celestial objects and phenomena) and geomythology (the study of geological events and the formation of geological features described in oral traditions). Of the hundreds of distinct Aboriginal cultures of Australia, many have oral traditions rich in descriptions and explanations of comets, meteors, meteorites, airbursts, impact events, and impact craters. These views generally attribute these phenomena to spirits, death, and bad omens. There are also many traditions that describe the formation of meteorite craters as well as impact events that are not known to Western science.

Imaging the interiors of near-earth objects with radio reflection tomography

NASA Technical Reports Server (NTRS)

Safaeinili, A.; Ostro, S. J.

2002-01-01

Scenarios for mitigation of asteroid comet collisions include the use of explosives to deflect or destroythe projectile. However, as demonstrated by Asphaug et al.( 1998), the outcome of explosive energy transfer to an asteroid or comet (via a bomb or a hypervelocity impact) is extremely sensitive to the pre-existing configuration of fractures and voids.

Assessment of Mechanisms for Jovian Synchrotron Variability Associated with Comet SL-9

NASA Technical Reports Server (NTRS)

Bolton, S. J.; Thorne, R. M.

1995-01-01

The impact comet SL-9 with Jupiter induced a number of variations in Jupiter's synchrotron radiation, including an increase in emission intensity, spectral changes, and a possible broadening in the latitudinal distribution of the emission. Considered are three potential mechanisms for inducing such effects (electron acceleration, radial diffusion, and pitch-angle scattering), and their consequences.

27 CFR 70.164 - Surrender of property subject to levy in the case of life insurance and endowment contracts.

Code of Federal Regulations, 2010 CFR

2010-04-01

... the case of life insurance and endowment contracts. (a) In general. This section provides special rules relating to the surrender of property subject to levy in the case of life insurance and endowment... subject to levy in the case of life insurance and endowment contracts. 70.164 Section 70.164 Alcohol...

Shape, Density, and Geology of the Nucleus of Comet 103P/Hartley 2

NASA Technical Reports Server (NTRS)

Thomas, P.C.; A'hearn, Michael F.; Veverka, Joseph; Belton, Michael J. S.; Kissel, Jochen; Belton, Michael J. S.; Klaasen, Kenneth P.; McFadden, Lucy A.; Melosh, H. Jay; Schultz, Peter H.;

KSC-04PD-2671B

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. A worker at Astrotech Space Operations in Titusville, Fla., begins fueling the Deep Impact spacecraft. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-04PD-2669

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Workers at Astrotech Space Operations in Titusville, Fla., suit up before fueling the Deep Impact spacecraft. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-04PD-2668

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Workers at Astrotech Space Operations in Titusville, Fla., suit up before fueling the Deep Impact spacecraft. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-04PD-2671A

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. A worker at Astrotech Space Operations in Titusville, Fla., begins fueling the Deep Impact spacecraft. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

2D-photochemical modeling of Saturn’s stratosphere: hydrocarbon and water distributions

NASA Astrophysics Data System (ADS)

Hue, Vincent; Cavalié, Thibault; Hersant, Franck; Dobrijevic, Michel; Greathouse, Thomas; Lellouch, Emmanuel; Hartogh, Paul; Cassidy, Timothy; Spiga, Aymeric; Guerlet, Sandrine; Sylvestre, Melody

2014-11-01

Saturn’s axial tilt of 27° produces seasons in a similar way as on Earth. The seasonal forcing over Saturn’s 30 years period influences the production/loss of the major atmospheric absorbers and coolants through photochemistry, and influences therefore Saturn’s stratospheric temperatures. We have developed a 2D time-dependent photochemical model of Saturn’s atmosphere [Hue et al., in prep.], coupled to a radiative-climate model [Greathouse et al., 2008] to study seasonal effects on its atmospheric composition. Cassini spacecraft has revealed that the distribution of hydrocarbons in Saturn’s stratosphere [Guerlet et al., 2009] differs from pure photochemical predictions, i.e. without meridional transport [Moses et al., 2005]. Differences between the observed distribution of hydrocarbons and 2D-photochemical predictions are likely to be an indicator of dynamical forcing.Disentangling the origin of water in the stratosphere of this planet has been a long-term issue. Due to Saturn’s cold tropopause trap, which acts as a transport barrier, the water vapor observed by the Infrared Space Observatory (ISO) [Feuchtgruber et al., 1997] has an external origin. Three external sources have been identified: (i) permanent flux from interplanetary dust particles, (ii) local sources form planetary environments (rings, satellites), (iii) large cometary impacts, similar to Shoemaker-Levy 9 on Jupiter. Previous observations of Saturn with Herschel’s Hsso program [Hartogh et al., 2009] led to the detection of a water torus around Saturn [Hartogh et al., 2011], fed by Enceladus’ geysers. A substantial fraction of this torus is predicted to be a local source of water for Saturn’s and its satellites, as it will spread in this system [Cassidy et al., 2010]. Using the new 2D-photochemical model, we test here the validity of Enceladus’ torus as the source of Saturn’s stratospheric water.References : Hue et al., in prep. Greathouse et al., 2008. AGU Fall Meeting(Abstract P21B06). Guerlet et al., 2009. Icarus, 203, 214-232. Moses et al., 2005. JGR 110. Feuchtgruber et al., 1997. 389, 159-162. Hartogh et al., 2009. PSS 57, 1596-1606 Hartogh et al., 2011. A&A, 532, L2. Cassidy et al., 2010. Icarus, 209, 696-703

Ultraviolet Observations of Coronal Mass Ejection Impact on Comet 67P/Churyumov–Gerasimenko by Rosetta Alice

NASA Astrophysics Data System (ADS)

Noonan, John W.; Stern, S. Alan; Feldman, Paul D.; Broiles, Thomas; Wedlund, Cyril Simon; Edberg, Niklas J. T.; Schindhelm, Eric; Parker, Joel Wm.; Keeney, Brian A.; Vervack, Ronald J., Jr.; Steffl, Andrew J.; Knight, Matthew M.; Weaver, Harold A.; Feaga, Lori M.; A’Hearn, Michael; Bertaux, Jean-Loup

2018-07-01

The Alice ultraviolet spectrograph on the European Space Agency Rosetta spacecraft observed comet 67P/Churyumov–Gerasimenko in its orbit around the Sun for just over two years. Alice observations taken in 2015 October, two months after perihelion, show large increases in the comet’s Lyβ, O I 1304, O I 1356, and C I 1657 Å atomic emission that initially appeared to indicate gaseous outbursts. However, the Rosetta Plasma Consortium instruments showed a coronal mass ejection (CME) impact at the comet coincident with the emission increases, suggesting that the CME impact may have been the cause of the increased emission. The presence of the semi-forbidden O I 1356 Å emission multiplet is indicative of a substantial increase in dissociative electron impact emission from the coma, suggesting a change in the electron population during the CME impact. The increase in dissociative electron impact could be a result of the interaction between the CME and the coma of 67P or an outburst coincident with the arrival of the CME. The observed dissociative electron impact emission during this period is used to characterize the O2 content of the coma at two peaks during the CME arrival. The mechanism that could cause the relationship between the CME and UV emission brightness is not well constrained, but we present several hypotheses to explain the correlation.

Development of Sample Handling and Analytical Expertise For the Stardust Comet Sample Return

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bradley, J; Bajt, S; Brennan, S

NASA's Stardust mission returned to Earth in January 2006 with ''fresh'' cometary particles from a young Jupiter family comet. The cometary particles were sampled during the spacecraft flyby of comet 81P/Wild-2 in January 2004, when they impacted low-density silica aerogel tiles and aluminum foils on the sample tray assembly at approximately 6.1 km/s. This LDRD project has developed extraction and sample recovery methodologies to maximize the scientific information that can be obtained from the analysis of natural and man-made nano-materials of relevance to the LLNL programs.

The impactor flux in the Pluto-Charon system

NASA Technical Reports Server (NTRS)

Weissman, Paul R.; Stern, S. Alan

1994-01-01

Current impact rates of comets on Pluto and Charon are estimated. It is shown that the dominant sources of impactors are comets from the Kuiper belt and the inner Oort cloud, each of whose perihelion distribution extends across Pluto's orbit. In contrast, long-period comets from the outer Oort cloud are a negligible source of impactors. The total predicted number of craters is not sufficient to saturate the surface areas of either Pluto of Charon over the age of the Solar System. However, heavy cratering may have occurred early in the Solar System's history during clearing of planetesimals from the outer planets' zone.

Eros in Stereo

NASA Image and Video Library

2000-05-07

Stereo imaging, an important tool on NASA NEAR Shoemaker for geologic analysis of Eros, provides three-dimensional information on the asteroid landforms and structures. 3D glasses are necessary to view this image.

Attitudes of Educational Decision Makers toward AVTI Governance and the Local Tax Levy. An Independent Paper.

ERIC Educational Resources Information Center

LiaBraaten, James Clayton

A study investigated the attitudes of vocational education decision makers toward the governance of Minnesota's Area Vocational Technical Institutes (AVTIs) and the impact removal of a local tax to support the AVTIs might have on governance. Five categories of individuals, all considered vocational education decision makers, were surveyed: AVTI…

77 FR 26316 - Progress Energy Florida; Final Environmental Impact Statement for Combined Licenses for Levy...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-03

..., Rockville, Maryland, 20852 or from NRC's Agencywide Documents Access and Management System (ADAMS). ADAMS is accessible from the NRC's Web site at www.nrc.gov/reading-rm/adams.html . The ADAMS accession numbers for the... . In addition, the following four public libraries have agreed to make the final EIS available to the...

Observing team from the University of Wyoming

NASA Technical Reports Server (NTRS)

2002-01-01

July 19, 1994An observing team from the University of Wyoming , the University of Rochester, and the University of Minnesota is obtaining infrared images of the recent comet impacts on Jupiter. The observations are being made with the Wyoming Infrared Observatory 2.3-meter telescope near Laramie, using an infrared camera developed at Rochester. The accompanying image of Jupiter, obtained on the evening of Sunday July 17, shows three bright spots near the lower left. These are the impact sites of (from left to right) fragments C, A, and E. The other features visible are the bright polar and equatorial regions, and also the Great Red Spot, located below the equator and somewhat to the right.At this relatively short infrared wavelength (2.2 micrometers) the planet it mostly dark because the methane in the Jupiter atmosphere absorbs any sunlight which passes through a significant depth of that atmosphere. Bright regions usually correspond to high altitude clouds which reflect the sunlight before it can penetrate the deeper atmosphere and be absorbed. The bright nature of the impact spots therefore indicates the presence of high altitude haze or clouds -- material carried up from the lower atmosphere by the fireball and plume from the comet impact. More detailed measurements at a variety of wavelengths should reveal the chemical composition of the haze material. The observing team will be continuing their work throughout the comet impact period and expect to obtain images of the plumes from the other comet fragments which will be striking Jupiter later this week.Co ntact: Robert R. Howell Department of Physics and Astronomy University of Wyoming Laramie, WY 82070 307-766-6150

Evidence of Collisional Histories of Asteroids, Comets and Meteorites: Comparisons with Shocked Minerals

NASA Astrophysics Data System (ADS)

Lederer, Susan M.; Jensen, Elizabeth; Smith, Douglas; Fane, Michael; Whizin, Akbar; Landsman, Zoe A.; Wooden, Diane H.; Lindsay, Sean S.; Cintala, Mark; Keller, Lindsay P.; Zolensky, Michael

2017-10-01

Evidence of the collisional history of comets and asteroids has been emerging from analyses of cometary forsterite and enstatite returned from Comet Wild 2 by the Stardust mission (Keller et al.Geochim. Cosmochim. Acta 72, 2008; Tomeoka et al. MAPS 43, 2008; Jacobs et al. MAPS 44, 2009). Likewise, shock metamorphism is observed in many meteoritic forsterites and enstatites (McCausland et al. AGU, 2010), suggesting similar collisional histories for asteroids. Further exploration of the effects of collisions is slated for the upcoming Asteroid Impact Mission/Double Asteroid Redirection Test (AIM/DART) mission, expected for launch in 2020. DART will impact Didymoon, the companion of the larger 65803 Didymos (1996 G2) asteroid, and AIM will use its instrumentation to characterize the impact.A suite of relevant impact experiments have been carried out in the Experimental Impact Laboratory at the NASA Johnson Space Center at velocities ranging from ~2.0 - 2.8 km s-1 and temperatures from 25°C to -100°C. Targets include a suite of minerals typically found in cometary dust and in asteroids and meteorites: Mg-rich forsterite (olivine), enstatite (orthopyroxene), diopside (clinopyroxene), magnesite (Mg-rich carbonate), and serpentine (phyllosilicate). Transmission Electron Microscope (TEM) imaging indicates evidence of shock similar to that seen in forsterite and enstatite from Comet Wild 2. Fourier Transform Infrared (FTIR) Spectroscopy will also be used for comparisons with meteorite spectra. A quantitative analysis of the shock pressures required to induce planar dislocations and spectral effects with respect to wavelength will also be presented.Funding provided by the NASA PG&G grant 09-PGG09-0115, NSF grant AST-1010012. Special thanks to NASA EIL staff, F. Cardenas and R. Montes.

Information Fusion and Control in Hierarchical Systems

DTIC Science & Technology

2013-05-01

structures of statistical manifolds are elucidated by computing the canonical Levi - Civita affine con- nection as well as Riemannian and scalar curvatures...with a Riemannian metric and a family of affine connections, including, but not exclusively, the canonical Levi - Civita affine connection [45]. By...canonical Levi - Civita affine connection as well as Riemannian and scalar curvatures. The relationship between the Ricci curvature tensor field and the

26 CFR 404.6334(d)-1 - Minimum exemption from levy for wages, salary, or other income.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 26 Internal Revenue 18 2010-04-01 2010-04-01 false Minimum exemption from levy for wages, salary... ADMINISTRATION UNDER THE TAX REFORM ACT OF 1976 § 404.6334(d)-1 Minimum exemption from levy for wages, salary, or... period. Paragraph (c) of this section contains rules relating to the minimum amount of wages, salary, or...

26 CFR 404.6334(d)-1 - Minimum exemption from levy for wages, salary, or other income.

Code of Federal Regulations, 2012 CFR

2012-04-01

... ADMINISTRATION UNDER THE TAX REFORM ACT OF 1976 § 404.6334(d)-1 Minimum exemption from levy for wages, salary, or other income. (a) In general. Under section 6331(a), if an individual liable for any tax neglects or... person is not a minor child of the individual with respect to whom amounts are exempt from levy under...

26 CFR 404.6334(d)-1 - Minimum exemption from levy for wages, salary, or other income.

Code of Federal Regulations, 2013 CFR

2013-04-01

... ADMINISTRATION UNDER THE TAX REFORM ACT OF 1976 § 404.6334(d)-1 Minimum exemption from levy for wages, salary, or other income. (a) In general. Under section 6331(a), if an individual liable for any tax neglects or... person is not a minor child of the individual with respect to whom amounts are exempt from levy under...

26 CFR 404.6334(d)-1 - Minimum exemption from levy for wages, salary, or other income.

Code of Federal Regulations, 2014 CFR

2014-04-01

... ADMINISTRATION UNDER THE TAX REFORM ACT OF 1976 § 404.6334(d)-1 Minimum exemption from levy for wages, salary, or other income. (a) In general. Under section 6331(a), if an individual liable for any tax neglects or... person is not a minor child of the individual with respect to whom amounts are exempt from levy under...

26 CFR 404.6334(d)-1 - Minimum exemption from levy for wages, salary, or other income.

Code of Federal Regulations, 2011 CFR

2011-04-01

... ADMINISTRATION UNDER THE TAX REFORM ACT OF 1976 § 404.6334(d)-1 Minimum exemption from levy for wages, salary, or other income. (a) In general. Under section 6331(a), if an individual liable for any tax neglects or... person is not a minor child of the individual with respect to whom amounts are exempt from levy under...

Environmental Perturbations Caused by the Impacts of Comets and Asteroids on Earth

NASA Technical Reports Server (NTRS)

Toon, Owen B.; Lawless, James G. (Technical Monitor)

1994-01-01

The extinction mechanisms proposed at the Cretaceous-Tertiary geological boundary are reviewed and related to the impact of asteroids or comets in general. For impact energies below 10(exp 4) Megatons (less than 6 x 10(exp 4) years; asteroid diameter less than 650 m), blast, earthquake, and fire may destroy local areas up to 10(exp 5) square m. Tidal waves could flood a kilometer inland over entire ocean basins. The energy range from 105 to 106 Megatons (less than 2 x 10(exp 6) years; asteroid diameter less than 3 km) is transitional. Dust lifted, sulfur released from within impacting asteroids, and soot from fires started by comets can produce climatologically significant optical depths of 10. At energies beyond 10(exp 7) Megatons, blast and earthquake damage is regional (10(exp 6) square cm). Tsunami cresting to 100 m and flooding 20 km inland will sweep the coastal zones of the world's oceans. Fires will be set globally. Light levels may drop so low from the smoke, dust and sulfate that vision is not possible. At energies approaching 10(exp 9) Megatons the ocean surface waters may be acidified by sulfur. The combination of these effects would be devastating.

France tries to save its ailing national health insurance system.

PubMed

Sorum, Paul Clay

2005-07-01

France has provided universal health care through employment-based health insurance funds. As its governments have increasingly used tax revenues to supplement payroll levies, they have assumed a larger role. Faced with widening deficits in the funds' accounts, the National Assembly adopted in August 2004 legislation designed to decrease health expenses, increase revenues to the funds, and improve quality of care. The apparent impacts of the so-called Douste-Blazy law are to reaffirm social solidarity and equality of access; to reinforce central control rather than relying more on decentralized and market forces; to give the now-unified funds a stronger director, shielded not only from labor and business but also, possibly, from the central government; to allow French private physicians to retain their unrivaled freedom of prescription; and to continue France's reliance on taxes as well as payroll levies to finance its health care.

Comet Hunters: A Citizen Science Project to Search for Comets in the Main Asteroid Belt

NASA Astrophysics Data System (ADS)

Hsieh, Henry H.; Schwamb, Megan Elizabeth; Zhang, Zhi-Wei; Chen, Ying-Tung; Wang, Shiang-Yu; Lintott, Chris

2016-10-01

Fully automated detection of comets in wide-field surveys remains a challenge, as even highly successful comet-finding surveys like Pan-STARRS rely on a combination of both automated flagging algorithms and vetting by human eyes. To take advantage of the long-noted superiority of the human eye over computer algorithms in certain types of pattern recognition, particularly when dealing with a range of target morphologies of interest, we have created a citizen science website with the aim of allowing the general public to aid in the search for active asteroids, which are objects that occupy dynamically asteroidal orbits yet exhibit comet-like dust emission due to sublimation, impact disruption, rotational destabilization, or other effects. Located at comethunters.org, the Comet Hunters website was built using the Zooniverse Project Builder (https://www.zooniverse.org/lab), and displays images of known asteroids obtained either from archival data obtained between 1999 and 2014 by the Suprime-Cam wide-field imager mounted on the 8-m Subaru telescope on Mauna Kea in Hawaii, or more contemporary data obtained by the Hyper Suprime-Cam (HSC) wide-field imager also on the Subaru Telescope as part of the ongoing HSC Subaru Strategic Program (SSP) survey. By using observations from such a large-aperture telescope, most of which have never been searched for solar system objects, much less cometary ones, we expect that volunteers should be able to make genuinely scientifically significant discoveries, and also provide valuable insights into the potential and challenges of searching for comets in the LSST era. To date, over 13,000 registered volunteers have contributed 350,000 classifications. We will discuss the design and construction of the Comet Hunters website, and also discuss early results from the project.This work uses data generated via the Zooniverse.org platform, development of which was supported by a Global Impact Award from Google, and by the Alfred P. Sloan Foundation.The HSC SSP collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. Instrumentation and software for HSC were developed by NAOJ, Kavli IPMU, the University of Tokyo, KEK, ASIAA, and Princeton University.

The physical mechanism of comet outbursts: An experiment

NASA Technical Reports Server (NTRS)

Hartmann, William K.

1993-01-01

During a series of impact experiments into regolith-like powders at the NASA Ames Research Center Vertical Gun Facility in 1976, I observed and filmed a unique anomalous event that may illuminate outburst mechanisms in comets. During one test, a new batch of basalt powder (half the mass in particles less than 800 microns in diameter) retained some air pressure while the vacuum chamber was being evacuated. As a result, the projectile impacted into gas-charged regolith. Instead of ejecting the normal, relatively negligible amount of debris, the disturbance triggered a major eruption that lasted at least 18 seconds. The experimental results have been recently re-analyzed with reference to cometary phenomena. A series of frames from this eruption experiment are shown. The ejecta velocities of 150 to 300 cm/s would have been sufficient to drive debris into the coma of a comet nucleus smaller than a few kilometers diameter. The event suggests a mechanism for comet outbursts, discussed briefly by Hartmann et al.: the pore space in a layer of regolith, possibly with weak effective tensile strength, becomes gas charged as ice slowly sublimates. Once the effective tensile strength is exceeded by the gas pressure, the surface fails locally, triggering an eruption such as photographed here. This model is consistent with the emerging view of regolith materials on comets and is closest to the recent model of Rickman et al. The earlier models generally picture a more uniform flow of debris off the comet, not outbursts. Rickman et al. allow gas pressure to build until it matches the overburden pressure, followed by 'instantaneous blow-off'. They note that as soon as the mantle is found to be unstable, we consider it to be instantaneously swept away by the gas pressure. The main new points made here are that the experiment gives a more realistic view of the blow-off process after surface failure occurs, and the present model gives a recharge mechanism that can explain recurrent outbursts on comets such as P/Schwassmann-Wachmann 1 and 2060 Chiron. In fact, the resulting jets resemble distinct jet structures in high-resolution comet comae.

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

The Meteoroid Fluence at Mars Due to Comet C/2013 A1 (Siding Spring)

NASA Technical Reports Server (NTRS)

Moorhead, A.; Wiegert, P.; Blaauw, R.; McCarty, C.; Kingery, A.; Cooke, W.

2014-01-01

Long-period comet C/2013 A1 (Siding Spring) will experience a close encounter with Mars on 2014 Oct 19. A collision between the comet and the planet has been ruled out, but the comet's coma may envelop Mars and its man-made satellites. By the time of the close encounter, five operational spacecraft will be present near Mars. Characterizing the coma is crucial for assessing the risk posed to these satellites by meteoroid impacts. We present an analytic model of cometary comae that describes the spatial and size distributions of cometary dust and meteoroids. This model correctly reproduces, to within an order of magnitude, the number of impacts recorded by Giotto near 1P/Halley [1] and by Stardust near comet 81P/Wild 2 [2]. Applied to Siding Spring, our model predicts a total particle fluence near Mars of 0.02 particles per square meter. In order to determine the degree to which Siding Spring's coma deviates from a sphere, we perform numerical simulations which take into account both gravitational effects and radiative forces. We take the entire dust component of the coma and tail continuum into account by simulating the ejection and evolution of dust particles from comet Siding Spring. The total number of particles simulated is essentially a free parameter and does not provide a check on the total fluence. Instead, these simulations illustrate the degree to which the coma of Siding Spring deviates from the perfect sphere described by our analytic model (see Figure). We conclude that our analytic model sacrifices less than an order of magnitude in accuracy by neglecting particle dynamics and radiation pressure and is thus adequate for order-of-magnitude fluence estimates. Comet properties may change unpredictably and therefore an analytic coma model that enables quick recalculation of the meteoroid fluence is highly desirable. NASA's Meteoroid Environment Office is monitoring comet Siding Spring and taking measurements of cometary brightness and dust production. We will discuss our coma model and nominal fluence taking the latest observations into account.

Atmospheric Impacts of a Close Cometary Encounter

NASA Astrophysics Data System (ADS)

Aylett, Tasha; Chipperfield, Martyn; Diego Carrillo Sánchez, Juan; Feng, Wuhu; Forster, Piers; Plane, John

2017-04-01

Although a close encounter with a comet is extremely unlikely, a significant perturbation to the flux of Earth-bound dust from a comet's close passage could have huge implications for both the chemistry of the atmosphere and climate. For example, following the close passage of Comet Halley to Earth in A.D. 536, dark skies, reduced day lengths and a protracted global cooling were reported [1], for which an extraterrestrial disturbance is likely to be at least partly responsible. Indeed, the recent encounter of Comet Siding Spring with Mars provided evidence that the risks posed by such an event are significant [2]. We have run sensitivity simulations using the Whole Atmosphere Community Climate Model (WACCM) with an elevated Meteoric Input Function (MIF) to investigate such an encounter - specifically, Comet Halley in A.D. 536. The simple analytical model developed by Moorhead et al. [3] has been incorporated into an atmospheric chemical ablation model to provide the MIF of several meteoric species (Na, Fe, Si, Mg and S) in the mesosphere and lower thermosphere (70-120 km) for input into WACCM. Key effects of this additional input on the chemistry of the upper atmosphere and the metal layers have been explored in the simulations and effects on mesospheric and stratospheric ozone chemistry have been assessed. In addition to any effects on atmospheric chemistry, WACCM will also be used to provide insight into the impacts of a high dust flux on the Earth's climate. References [1] Stothers, R. B. (1984), Mystery Cloud of Ad-536, Nature, 307(5949), 344-345. [2] Schneider, N. M., et al. (2015), MAVEN IUVS observations of the aftermath of the Comet Siding Spring meteor shower on Mars, Geophys Res Lett, 42(12), 4755-4761. [3] Moorhead, A. V., P. A. Wiegert, and W. J. Cooke (2014), The meteoroid fluence at Mars due to Comet C/2013 A1 (Siding Spring), Icarus, 231, 13-21.

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.

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.

One-Way Trip to Tempel

NASA Technical Reports Server (NTRS)

2005-01-01

[figure removed for brevity, see original site] Quick Time Movie for PIA02135 Impactor Targeting Sensor Approach

This movie shows Deep Impact's impactor probe approaching comet Tempel 1. It is made up of images taken by the probe's impactor targeting sensor. The probe collided with the comet at 10:52 p.m. Pacific time, July 3 (1:52 a.m. Eastern time, July 4).

EPOXI and Stardust NExT: The Management Challenges of Two Comet Flybys in Three Months

NASA Technical Reports Server (NTRS)

Larson, Timothy W.

2012-01-01

The EPOXI and Stardust NExT missions were missions of opportunity utilizing the Deep Impact and Stardust spacecraft, respectively. These new missions took advantage of the cost savings of utilizing spacecraft that were already flying for new science investigations. Both were retargeted to fly by an additional comet. EPOXI visited Hartley 2, significantly smaller than the other Jupiter family comets visited previously. Stardust NExT flew by Tempel 1, providing a second look at the comet previously studied by Deep Impact in 2005. Both projects were part of NASA's Discovery Program. In order to further save costs, the projects were combined into a single project office at JPL. This provided some efficiencies due to the similarity of the missions, but having the flybys space only three months apart posed challenges for the project management team to ensure each project was ready for its critical event and ensuring each received the proper support from the management team. The project office relied on an integrated calendar for tracking and scheduling meetings, reviews, and other key events. The project management team also coordinated their availability for both projects to maintain involvement with each team to ensure effective risk identification and management.

Getting Closer

NASA Image and Video Library

2005-06-20

One of the two pictures of Tempel 1 (see also PIA02101) taken by Deep Impact's medium-resolution camera is shown next to data of the comet taken by the spacecraft's infrared spectrometer. This instrument breaks apart light like a prism to reveal the "fingerprints," or signatures, of chemicals. Even though the spacecraft was over 10 days away from the comet when these data were acquired, it detected some of the molecules making up the comet's gas and dust envelope, or coma. The signatures of these molecules -- including water, hydrocarbons, carbon dioxide and carbon monoxide -- can be seen in the graph, or spectrum. Deep Impact's impactor spacecraft is scheduled to collide with Tempel 1 at 10:52 p.m. Pacific time on July 3 (1:52 a.m. Eastern time, July 4). The mission's flyby spacecraft will use its infrared spectrometer to sample the ejected material, providing the first look at the chemical composition of a comet's nucleus. These data were acquired from June 20 to 21, 2005. The picture of Tempel 1 was taken by the flyby spacecraft's medium-resolution instrument camera. The infrared spectrometer uses the same telescope as the high-resolution instrument camera. http://photojournal.jpl.nasa.gov/catalog/PIA02100

A Comparison of the Size Frequency Distributions of the Quasi-circular Flat-floor Depression Structures on Comet 67P/Churyumov-Gerasimenko and Comet Wild 2

NASA Astrophysics Data System (ADS)

Ip, Wing-Huen; Li, Yuan; Lin, Zhong-Yi; Lee, Jui-chi; Besse, Sebastien; Vincent, Jean-Baptiste; Pajola, Maurizio; Gabriele, Cremonese; Alice, Lucchetti

2015-04-01

The close-up views of comet 67P/Churyumov-Gerasimenko by the OSIRIS camera system on board Rosetta have shown that the nucleus structure can be broadly divided into three parts: head, body and neck (Sierks et al., 2015; Thomas et al., 2015). The surfaces of the head and body are covered by near-circular flat-floor depression structures (or pits). The relatively large diameter-to-depth ratios do not follow the pattern of impact craters. Some of these structures are embedded with sinkholes characterized by active outgassing in the form of dust jets (Vincent et al., 2015). The largest structure with a diameter of about one km - if of the same physical nature - is located at the tip of the head in Hamehit. Such steep-walled and flat-floored depressions have also been found on comet 81P/Wild 2 by Stardust in the 2004 encounter (Brownlee et al., 2004). The size frequency distributions of these surface structures are similar even though they have different power-law behaviors. This comparative study suggests the interesting possibility that the flat-floored depressions on both comets could have similar origin and evolutionary history. From a comparison of the size frequency distributions of the impact craters on the Martian moons, Phobos and Deimos, and the Saturnian icy moon, Phoebe, with that of comet Wild 2, Cheng et al. (2013) proposed that erosion/subsidence process of impact craters due to active outgassing could be at play in the modification of the original diameter-depth relation to the present flat-floored structure. Floor collapse of a deep-seated cavity filled with volatile ice is another alternative mechanism (Vincent et al., 2015). Because the bulk density of comet 67P is only 470+/-45 kg/m3, its interior must be highly porous. It remains to be investigated how would such porous structure be related to the quasi-circular depression features (Marchi et al., 2015). References: Brownlee, D. et al., (2004), Science,304, 1764-1769. Cheng, A.F. et al. (2013) Icarus, 222, 808-817. Machi, S. et al. (2015) LPSC abstract, in press. Sierks, H. et al. (2015) Science, in press. Thomas, N. et al. (2015) Science, in press. Vincent, J.-B. et al. (2015) Science, submitted.

Can the comet assay be used reliably to detect nanoparticle-induced genotoxicity?

PubMed

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.

Charged particle dynamics in the presence of non-Gaussian Lévy electrostatic fluctuations

DOE PAGES

Del-Castillo-Negrete, Diego B.; Moradi, Sara; Anderson, Johan

2016-09-01

Full orbit dynamics of charged particles in a 3-dimensional helical magnetic field in the presence of -stable Levy electrostatic fluctuations and linear friction modeling collisional Coulomb drag is studied via Monte Carlo numerical simulations. The Levy fluctuations are introduced to model the effect of non-local transport due to fractional diffusion in velocity space resulting from intermittent electrostatic turbulence. The probability distribution functions of energy, particle displacements, and Larmor radii are computed and showed to exhibit a transition from exponential decay, in the case of Gaussian fluctuations, to power law decay in the case of Levy fluctuations. The absolute value ofmore » the power law decay exponents are linearly proportional to the Levy index. Furthermore, the observed anomalous non-Gaussian statistics of the particles' Larmor radii (resulting from outlier transport events) indicate that, when electrostatic turbulent fluctuations exhibit non-Gaussian Levy statistics, gyro-averaging and guiding centre approximations might face limitations and full particle orbit effects should be taken into account.« less

The EUV Emission in Comet-Solar Corona Interactions

NASA Technical Reports Server (NTRS)

Bryans, Paul; Pesnell, William Dean; Schrijver, Carolus J.; Brown, John C.; Battams, Karl; Saint-Hilaire, Pasal; Liu, Wei; Hudson, Hugh S.

2011-01-01

The Atmospheric Imaging Assembly (AlA) on the Solar Dynamics Observatory (SDO) viewed a comet as it passed through the solar corona on 2011 July 5. This was the first sighting of a comet by a EUV telescope. For 20 minutes, enhanced emission in several of the AlA wavelength bands marked the path of the comet. We explain this EUV emission by considering the evolution of the cometary atmosphere as it interacts with the ambient solar atmosphere. Water ice in the comet rapidly sublimates as it approaches the Sun. This water vapor is then photodissociated, primarily by Ly-alpha, by the solar radiation field to create atomic Hand O. Other molecules present in the comet also evaporate and dissociate to give atomic Fe and other metals. Subsequent ionization of these atoms can be achieved by a number of means, including photoionization, electron impact, and charge exchange with coronal protons and other highly-charged species. Finally, particles from the cometary atmosphere are thermalized to the background temperature of the corona. Each step could cause emission in the AlA bandpasses. We will report here on their relative contribution to the emission seen in the AlA telescopes.

High energy density soft X-ray momentum coupling to comet analogs for NEO mitigation

DOE PAGES

Remo, J. L.; Lawrence, R. J.; Jacobsen, S. B.; ...

2016-09-27

Here, we applied MBBAY high fluence pulsed radiation intensity driven momentum transfer analysis to calculate X-ray momentum coupling coefficients C M=(Pa s)/(J/m 2) for two simplified comet analog materials: i) water ice, and ii) 70% water ice and 30% distributed olivine grains. The momentum coupling coefficients (C M) max of 50×10 –5 s/m, are about an order of magnitude greater than experimentally determined and computed MBBAY values for meteoritic materials that are analogs for asteroids. From the values for comet analog materials we infer applied energies (via momentum transfer) required to deflect an Earth crossing comet from impacting Earth bymore » a sufficient amount (~1 cm/s) to avert collision ~a year in advance. Comet model calculations indicate for C M = 5 × 10 –4 s/m the deflection of a 2 km comet with a density 600 kg/m 3 by 1 cm/s requires an applied energy on the target surface of 5 × 10 13 J, the equivalent of 12 kT of TNT. Depending on the geometrical configuration of the interaction the explosive yield required could be an order of magnitude higher.« less

Reconciling the Dawn-Dusk Asymmetry in Mercury’s Exosphere with the Micrometeoroid Impact Directionality

NASA Astrophysics Data System (ADS)

Pokorný, Petr; Sarantos, Menelaos; Janches, Diego

2017-06-01

Combining dynamical models of dust from Jupiter-family comets and Halley-type comets, we demonstrate that the seasonal variation of the dust/meteoroid environment at Mercury is responsible for producing the dawn-dusk asymmetry in Mercury’s exosphere observed by the MESSENGER spacecraft. Our latest models, calibrated recently from ground-based and space-borne measurements, provide unprecedented statistics that enable us to study the longitudinal and latitudinal distribution of meteoroids impacting Mercury’s surface. We predict that the micrometeoroid impact vaporization source is expected to undergo significant motion on Mercury’s surface toward the nightside during Mercury’s approach to aphelion and toward the dayside when the planet is approaching the Sun.

KSC-04PD-2533

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Ball Aerospace technicians at Astrotech in Titusville, Fla., begin lifting the high-gain communications antenna to attach it to an overhead crane. The antenna will be installed on the Deep Impact spacecraft. A NASA Discovery mission, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. During the encounter phase, the high-gain antenna transmits near-real- time images of the impact back to Earth. The spacecraft is scheduled to launch Jan. 8 aboard a Boeing Delta II rocket from Launch Complex 17-B at Cape Canaveral Air Force Station, Fla.

Reconciling the Dawn-Dusk Asymmetry in Mercury's Exosphere with the Micrometeoroid Impact Directionality

NASA Technical Reports Server (NTRS)

Pokorny, Petr; Sarantos, Menelaos; Janches, Diego

2017-01-01

Combining dynamical models of dust from Jupiter-family comets and Halley-type comets, we demonstrate that the seasonal variation of the dust/meteoroid environment at Mercury is responsible for producing the dawn-dusk asymmetry in Mercury's exosphere observed by the MESSENGER spacecraft. Our latest models, calibrated recently from ground-based and space-borne measurements, provide unprecedented statistics that enable us to study the longitudinal and latitudinal distribution of meteoroids impacting Mercury's surface. We predict that the micrometeoroid impact vaporization source is expected to undergo significant motion on Mercury's surface toward the nightside during Mercury's approach to aphelion and toward the dayside when the planet is approaching the Sun.

Major achievements of the Rosetta mission in connection with the origin of the solar system

NASA Astrophysics Data System (ADS)

Barucci, M. A.; Fulchignoni, M.

2017-10-01

Comets have been studied from a long time and are believed to preserve pristine materials, so they are fundamental to understand the origin of the solar system and life. Starting in the early 1990s, ESA decided to have a more risky and fantastic mission to a comet. As Planetary Cornerstone mission of the ESA Horizon 2000 program, the Rosetta mission was selected with the aim of realizing two asteroid fly-bys, a rendezvous with a comet to deliver a surface science package and to hover around the comet from 4 AU inbound up to perihelion and outbound back to 3.7 AU. The mission was successfully launched on March 2, 2004 with Ariane V that started its 10-year journey toward comet 67P/Churyumov-Gerasimenko. After several planetary gravity assists, Rosetta flew by two asteroids—on September 5, 2008 (Steins) and on July 10, 2010 (Lutetia), respectively, and performed the comet orbit insertion maneuver on August 6, 2014. The onboard instruments characterized the nucleus orbiting the comet at altitudes down to few kilometers. On November 12, 2014, the lander Philae was delivered realizing the first landing ever on a comet surface. Although the exploration of the comet was planned up to the end of 2015, the mission duration was extended for nine more months than the nominal one, to follow the comet on its outbound orbit. To terminate the mission, following a series of very low orbits, a controlled impact of Rosetta spacecraft with the comet was realized on September 30, 2016. The scientific objectives of the mission have been largely achieved. The challenging mission provided the science community with an enormous quantity of data of extraordinary scientific value. In this paper, a detailed description of the mission and the highlights of the obtained scientific results on the exploration of an extraordinary world are presented. The paper also includes lessons learned and directions for the future.

18 CFR 35.29 - Treatment of special assessments levied under the Atomic Energy Act of 1954, as amended by Title...

Code of Federal Regulations, 2011 CFR

2011-04-01

... assessments levied under the Atomic Energy Act of 1954, as amended by Title XI of the Energy Policy Act of... Other Filing Requirements § 35.29 Treatment of special assessments levied under the Atomic Energy Act of... relating to special assessments under the Atomic Energy Act of 1954, as amended by the Energy Policy Act of...

18 CFR 35.29 - Treatment of special assessments levied under the Atomic Energy Act of 1954, as amended by Title...

Code of Federal Regulations, 2012 CFR

2012-04-01

... assessments levied under the Atomic Energy Act of 1954, as amended by Title XI of the Energy Policy Act of... Other Filing Requirements § 35.29 Treatment of special assessments levied under the Atomic Energy Act of... relating to special assessments under the Atomic Energy Act of 1954, as amended by the Energy Policy Act of...

18 CFR 35.29 - Treatment of special assessments levied under the Atomic Energy Act of 1954, as amended by Title...

Code of Federal Regulations, 2010 CFR

2010-04-01

... assessments levied under the Atomic Energy Act of 1954, as amended by Title XI of the Energy Policy Act of... Other Filing Requirements § 35.29 Treatment of special assessments levied under the Atomic Energy Act of... relating to special assessments under the Atomic Energy Act of 1954, as amended by the Energy Policy Act of...

18 CFR 35.29 - Treatment of special assessments levied under the Atomic Energy Act of 1954, as amended by Title...

Code of Federal Regulations, 2013 CFR

2013-04-01

... assessments levied under the Atomic Energy Act of 1954, as amended by Title XI of the Energy Policy Act of... Other Filing Requirements § 35.29 Treatment of special assessments levied under the Atomic Energy Act of... relating to special assessments under the Atomic Energy Act of 1954, as amended by the Energy Policy Act of...

18 CFR 35.29 - Treatment of special assessments levied under the Atomic Energy Act of 1954, as amended by Title...

Code of Federal Regulations, 2014 CFR

2014-04-01

... assessments levied under the Atomic Energy Act of 1954, as amended by Title XI of the Energy Policy Act of... Other Filing Requirements § 35.29 Treatment of special assessments levied under the Atomic Energy Act of... relating to special assessments under the Atomic Energy Act of 1954, as amended by the Energy Policy Act of...

Notes of the Design of Two Supercavitating Hydrofoils

DTIC Science & Technology

1975-07-01

Foil Section Characteristics Definition Tulin Two -Term Levi - Civita Larock and Street Two -Term three pararreter Prcgram and Inputs linearized two ...36 NOMENCLATURE Symbol Description Dimensions AIA 2 Angle distribution multipliers in Levi - radians Civita Program AR Aspect ratio CL Lift coefficient...angle of attack radian B Constant angle in Levi - Civita program radian 6 Linearized angle of attack superposed degrees C Wu’s 1955 program parameter

A Chemical Model of the Coma of Comet C/2009 P1 (Garradd)

NASA Astrophysics Data System (ADS)

Boice, Daniel C.; Kawakita, H.; Kobayashi, H.; Naka, C.; Phelps, L.

2012-10-01

Modeling is essential to understand the important physical and chemical processes that occur in cometary comae. Photochemistry is a major source of ions and electrons that further initiate key gas-phase reactions, leading to the plethora of molecules and atoms observed in comets. The effects of photoelectrons that react via impacts are important to the overall ionization. We identify the relevant processes within a global modeling framework to understand simultaneous observations in the visible and near-IR of Comet C/2009 (Garradd) and to provide valuable insights into the intrinsic properties of its nucleus. Details of these processes are presented in the collision-dominated, inner coma of the comet to evaluate the relative chemical pathways and the relationship between parent and sibling molecules. Acknowledgements: We appreciate support from the NSF Planetary Astronomy Program.

Apollo Field Geology: 45 Years of Digesting Rocks, Field Data, and Future Objectives

NASA Astrophysics Data System (ADS)

Schmitt, H. H.

2012-12-01

Twelve Apollo astronauts participated in the Lunar Field Geological Experiment, overseen by Gene Shoemaker, Gordon Swann, and Bill Muehlberger and their Co-Investigators. In conjunction with geologists and engineers of the Geological Survey and NASA, this team planned, trained and executed the first extraterrestrial field geological investigation. As a result, astronaut sample selection, observations, photo-documentation and experiment deployment underpin 45 years of laboratory analyses and interpretation by thousands of lunar and planetary scientists. --Current hypotheses related to the origin, evolution and nature of the Moon would be far different had Apollo geological explorations not occurred, even assuming that all robotic missions flown before and since Apollo were flown. *Would we have recognized lunar meteorites without the broad suite of Apollo samples to guide us? If we eventually had properly identified such meteorites, would their chemistry and age data give us the same detailed insights about the origin and evolution of the Moon without the highly specific field documentation of samples collected by the astronauts? *Would we recognize that the early history of the Earth and Mars up to 3.8 billion years ago, including the development of life's precursors, was a period of the prolonged violence due to impacts of asteroids and comets? Would we have realized that clay minerals, produced by the alteration of impact-generated glass and debris, would have been dominant components and potential templates for complex organic molecules in the terrestrial and Martian environments? *Would we fully understand the surface environments of asteroids and young terrestrial planets without the detailed dissection and analysis of Apollo's lunar regolith samples? *Would the Moon's near-surface environment, and its mantle and core structure, be as well defined as they are without the ground-truth provided by Apollo samples and the equipment carefully emplaced there by the Apollo astronauts? *Would we finally be having an observation-based debate about testable hypotheses related to the origin of the Moon without the pristine samples of volatile-rich, orange and green pyroclastic glass? *Would we know of the three potential sources of lunar water-ice in permanent shadow, namely, comets, solar wind, and primordial water, without Apollo's samples of the regolith and pristine pyroclastic glasses? *Would we know the extent of the distributed resources of the Moon, including solar Helium-3, without regolith samples from six sites on the Moon? *Without the broad spectrum of Apollo samples, many other questions about the Moon would still be open or unasked. --Future lunar and planetary geological exploration should focus both on expanding science related to the history of the Earth and other planets and on preparations for permanent human settlement. In optimizing that exploration, an enhanced partnership between field activities undertaken by humans and robots should be developed. Robotic precursor and post-cursor support of planning, equipment deployment, and systematic data-gathering can add significantly to the normal returns provided by the insights of trained and experienced field geologists. They should do what humans do best, that is, react instantaneously and with perspicacity to new situations, discoveries and challenges.

Society of Critical Care Medicine

MedlinePlus

... Liberation Sepsis ICU Management Coding and Billing ICU Design Workforce ICU REPORT Disaster ICU Benchmarking Tools International ... Family Award for Ethics Honorary Life Membership ICU Design Citation ICU Heroes Lifetime Achievement Norma J. Shoemaker ...

Botswana alcohol policy and the presidential levy controversy.

PubMed

Pitso, Joseph M N; Obot, Isidore S

2011-05-01

To assess the state of alcohol policy in Botswana in the context of a substantial levy imposed on alcohol sales by the President. DESIGN, MEASUREMENTS: Analysis of policy documents and media reports to describe the drivers of policy formation. Botswana. Legislation aimed at addressing the problem of excessive consumption of alcohol in the country has been proposed and enacted since independence in 1966 and a draft national alcohol policy is currently being debated. The policy recognizes the need to protect the rights of adult citizens of Botswana to purchase and consume alcohol in a safe and well-regulated manner and the role of government in ensuring that vulnerable members of the community are protected against the impact of harmful use of alcohol. In 2008, controversy erupted over the proposal by the President of the country to impose a 70% levy on alcohol products, later reduced to 30%. The industry responded by threatening to go to court and has since focused their response on what they claim to be serious economic losses due to reduced consumption of their products. The ongoing controversy in Botswana calls attention to the role of the industry in influencing the debate on alcohol and the need to keep in mind overall public health interest in efforts to develop and implement a national alcohol policy. © 2011 The Authors, Addiction © 2011 Society for the Study of Addiction.

New Research by CCD Scanning for Comets and Asteroids

NASA Technical Reports Server (NTRS)

Gehrels, Tom; McMillan, Robert S.

1997-01-01

The purpose of Spacewatch is to explore the various populations of small objects within the solar system. Spacewatch provides data for studies of comets and asteroids, finds potential targets for space missions, and provides information on the environmental problem of possible impacts. Moving objects are discovered by scanning the sky with charge-coupled devices (CCDs) on the 0.9-meter Spacewatch Telescope of the University of Arizona on Kitt Peak. Each Spacewatch scan consists of three drift scan passes over an area of sky using a CCD filtered to a bandpass of 0.5-1.0 microns (approximately V+R+I with peak sensitivity at 0.7 micron). The effective exposure time for each pass is 143 seconds multiplied by the secant of the declination. We have been finding some 30,000 new asteroids per year and applying their statistics to the study of the collisional history of the solar system. As of the end of the observing run of Nov. 1997, Spacewatch had found a total of 153 Near-Earth Asteroids (NEAs) and 8 new comets since the project began in the 1980s, and had recovered one lost comet. The total number of NEAs found by Spacewatch big enough to be hazardous if they were to impact the Earth is 36. Spacewatch is also efficient in recovery of known comets and has detected and reported positions for more than 137,000 asteroids, mostly new ones in the main belt, including more than 16,000 asteroids designated by the Minor Planet Center (MPC).

Jupiter - Friend or Foe?

NASA Astrophysics Data System (ADS)

Horner, J.; Jones, B. W.

2008-09-01

It has long been believed that the planet Jupiter has played a beneficial role in the development of life on the Earth, acting as a shield from objects which would otherwise go on to significantly raise the impact flux experienced by our planet. Without Jupiter, the story goes, the Earth would have experienced a far greater number of impacts, making it far less hospitable to burgeoning life. In an on-going series of separate studies[1,2], we have examined the effects of varying the mass of Jupiter on the impact flux that the Earth would experience from Near-Earth Objects sourced from the Asteroid belt, short-period comets sourced from the Edgeworth-Kuiper belt, and long-period comets sourced from the Oort cloud. The results are remarkable - it seems that, far from being a shield, Jupiter actually acts to increase the impact flux experienced by the Earth over that which would be expected without the planet. Still more surprising, in the cases of the asteroids and Edgeworth-Kuiper belt objects, it seems that a Jupiter around 0.2 times the mass of "our Jupiter" would be even more threatening, sending a still greater number of objects our way. In order to simulate such disparate populations, different approaches to population construction were needed. The asteroidal and short-period comet populations each contained 100,000 test particles, moving on orbits typical of their class. The asteroids were initially distributed between 2 and 4 AU, with orbits of varying eccentricity and inclination, with number density varying as a function of semi-major axis. The short-period cometary flux was obtained through simulation of a population based on the subset of known Centaurs and Scattered Disk Objects which are Neptune-crossing, and have perihelia beyond the orbit of Uranus. These objects are the parents of the short-period comets, and were chosen since they are a population beyond the current influence of the planet Jupiter. Since our goal was to study the effect of Jupiter's mass on the impact flux at the Earth from the two populations, we followed our 100,000 particle populations for 10 million years, under the influence of the giant planets. Each particle was followed until it either hit something, or was ejected from the system. In this manner, we were able to follow the flux of objects onto the Earth as a function of time. The simulations were repeated over a wide range of Jupiter masses, with all other variables being held constant, allowing us to observe the variations in impact flux as a function of Jovian mass. In the cases of the asteroids and the short-period comets, Jupiter was observed to significantly modify the impact flux which would be experienced by the planet Earth. It was immediately obvious, however, that the old idea that Jupiter shields us from impacts no longer holds. For both of these populations, the lowest impact rates were experienced when the Jupiter-like planet in the system had the lowest mass, rose rapidly to a peak flux at around 0.2 Jupiter masses, before falling away more slowly. Therefore, for the asteroids and short-period comets, it seems that our Jupiter does offer some shielding, when compared to the case where the planet has a mass of around 0.2 MJ, but, compared to the scenario where no Jupiter is present at all (or the Jupiter in question has very low mass), Jupiter actually acts to increase the Earth-bound flux. Simulations are currently underway with the goal of analysing the effects of Jupiter's mass on the impact flux from the long-period comets (deflected inward towards the Earth from the Oort cloud). Further into the future, we intend to study the effects of Jovian position of the impact flux, with the goal of answering, once and for all, the question - "Jupiter - Friend or Foe?".

The Shape, Internal Structure and Dynamics of 433 Eros from the NEAR Laser Ranging Investigation

NASA Astrophysics Data System (ADS)

Zuber, M. T.; Smith, D. E.; Cheng, A. F.; Garvin, J. B.; NLR Science Team

2000-10-01

The NEAR Laser Rangefinder, an instrument on the NEAR-Shoemaker spacecraft, has been mapping the detailed shape of asteroid 433 Eros since February 29, 2000. The instrument has a range resolution of 31 cm and a surface spot size that varies between 8 to 45 m (depending on orbital altitude), yielding along-track profiles that are often contiguous or overlapping. The NLR has so far provided over 7 million valid measurements of the range from the NEAR-Shoemaker spacecraft to the surface of 433 Eros, which are converted to mass-centered radii through solutions for the spacecraft orbit from Doppler tracking. The current spherical harmonic model, produced in a joint solution between altimetry and Doppler, is to degree and order 48 and is characterized by a spatial resolution of 470 m and a vertical accuracy of a few tens of meters. The shape model has an RMS misfit of 1000 +/- 126 m to an ellipsoid, which represents a poor fit compared to other measured asteroids. Eros' complex shape was dominated by collisions but the asteroid shows no evidence of dumbbell-like structure suggestive of a contact binary bound loosely by self-gravitation. Clustered regions of high slopes on the walls of the two largest depressions represent evidence for structural competence. The offset between the asteroid's center of mass and center of figure can be explained by a density gradient of only 4.3 kg m-3 km-1. This minor deviation of internal structure from homogeneity is likely due to variations in mechanical competence (regolith distribution and variations in internal porosity) rather than composition. Regolith thicknesses of a few tens of meters are inferred from depths of topographic benches in craters. Impact crater morphology shows evidence of influence from both gravity and structural control. Small-scale topography reveals ridges and grooves likely generated by impact-related fracturing.

General Rotorcraft Aeromechanical Stability Program (GRASP) - Theory Manual

DTIC Science & Technology

1990-10-01

the A basis. Two symbols frequently encountered in vector operations that use index notation are the Kronecker delta eij and the Levi - Civita epsilon...Blade root cutout fijk Levi - Civita epsilon permutation symbol 0 pretwist angle 0’ pretwist per unit length (d;) Oi Tait-Bryan angles K~i moment strains...the components of the identity tensor in a Cartesian coordinate system, while the Levi Civita epsilon consists of components of the permutation

Kernel-Correlated Levy Field Driven Forward Rate and Application to Derivative Pricing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bo Lijun; Wang Yongjin; Yang Xuewei, E-mail: xwyangnk@yahoo.com.cn

2013-08-01

We propose a term structure of forward rates driven by a kernel-correlated Levy random field under the HJM framework. The kernel-correlated Levy random field is composed of a kernel-correlated Gaussian random field and a centered Poisson random measure. We shall give a criterion to preclude arbitrage under the risk-neutral pricing measure. As applications, an interest rate derivative with general payoff functional is priced under this pricing measure.

D'Alembert's paradox, 1900-1914: Levi-Civita and his Italian and French followers

NASA Astrophysics Data System (ADS)

Tazzioli, Rossana

2017-07-01

Before the First World War, Tullio Levi-Civita (1873-1941) was already a well-known mathematician in Italy and abroad, in particular in France. Professor at the University of Padua since 1898, he had published important contributions to tensor calculus, theory of relativity, differential geometry, hydrodynamics, and the three-body problem. In 1918, when he moved to the University of Rome, he created an international school of mathematics. In this paper, we focus on d'Alembert's paradox to which Levi-Civita and some of his Italian and French followers contributed remarkable solutions. This case-study is used to illustrate Levi-Civita's approach to hydrodynamics and its influence in Italy and France, especially in the period 1910-1914.

C/2013 A1 (Siding Spring vs. Mars)

NASA Technical Reports Server (NTRS)

Moorhead, Althea; Cooke, William

2013-01-01

Comet C/2013 A1 (Siding Spring): recently discovered long period comet. Will have close encounter with Mars on October 19, 2014. Collision is extremely unlikely. Passing through the coma and/or tail is likely. Increases risk to Martian spacecraft. Meteoroids (100 microns or larger): approx. or <20% chance of impact per square meter due to coma and tail. Gas may also a ect Martian atmosphere.

Lunar Gene Bank for Endangered Species

NASA Astrophysics Data System (ADS)

Swain, R. K.; Behera, D.; Sahoo, P. K.; Swain, S. K.; Sasmal, A.

2012-03-01

In the face of failure of conservation programs, a Gene Bank in the lunar PSR, preferably the Shoemaker crater incorporating natural cryopreservation will provide permanent preservation of germplasms to protect endangered species from extinction.

Near-Earth Object (NEO) Hazard Background

NASA Technical Reports Server (NTRS)

Mazanek, Daniel D.

2005-01-01

The fundamental problem regarding NEO hazards is that the Earth and other planets, as well as their moons, share the solar system with a vast number of small planetary bodies and orbiting debris. Objects of substantial size are typically classified as either comets or asteroids. Although the solar system is quite expansive, the planets and moons (as well as the Sun) are occasionally impacted by these objects. We live in a cosmic shooting gallery where collisions with Earth occur on a regular basis. Because the number of smaller comets and asteroids is believed to be much greater than larger objects, the frequency of impacts is significantly higher. Fortunately, the smaller objects, which are much more numerous, are usually neutralized by the Earth's protective atmosphere. It is estimated that between 1000 and 10,000 tons of debris fall to Earth each year, most of it in the form of dust particles and extremely small meteorites. With no atmosphere, the Moon's surface is continuously impacted with dust and small debris. On November 17 and 18, 1999, during the annual Leonid meteor shower, several lunar surface impacts were observed by amateur astronomers in North America. The Leonids result from the Earth's passage each year through the debris ejected from Comet Tempel-Tuttle. These annual showers provide a periodic reminder of the possibility of a much more consequential cosmic collision, and the heavily cratered lunar surface acts a constant testimony to the impact threat. The impact problem and those planetary bodies that are a threat have been discussed in great depth in a wide range of publications and books, such as The Spaceguard Survey , Hazards Due to Comets and Asteroids, and Cosmic Catastrophes. This paper gives a brief overview on the background of this problem and address some limitations of ground-based surveys for detection of small and/or faint near-Earth objects.

Impact of energy taxation on economy, environmental and public health quality.

PubMed

Wang, Baoqing; Liu, Bowei; Niu, Honghong; Liu, Jianfeng; Yao, Shu

2018-01-15

This paper argues computable general equilibrium model and assess impact of energy taxation on economy, environmental and public health quality in Tianjin. In order to investigate different energy taxation based on medical cost and labor loss, the computable general equilibrium model integrating with input-output table and social accounting matrix (SAM) was constructed. The medical expense caused by air pollution of Tianjin in 2007 is 396 million yuan and death for 18104 people, which accounted for the total GDP and population 0.754‰ and 1.6‰, respectively. The results show that the enery taxes levy can improve the GDP, but it is only slightly. The energy taxes have adverse impact on energy sector because that the energy cost is increased. The scale of production is reduced, and the capital and labor resources are transferred to low energy consumption low emissions sector. The energy tax levy can reduce air pollutants concentration and improve air environmental quality. The PM 10 , SO 2 and NO 2 concentration in the energy taxes 5%-30% was reduced by 0.24%-0.24%, 0.09-0.52% and 0.29%-0.52% respectively. The medical expense has little impact on GDP, but labor loss has a certain effect on GDP. For higher energy taxes rate, the health effects on GDP can reach 0.06%-0.16%. This simultaneous economic and environmental improvement and health effect would thus have positive implications regarding energy taxes of the country. Copyright © 2017 Elsevier Ltd. All rights reserved.

A Unified Theory of Impact Crises and Mass Extinctions: Quantitative Tests

NASA Technical Reports Server (NTRS)

Rampino, Michael R.; Haggerty, Bruce M.; Pagano, Thomas C.

1997-01-01

Several quantitative tests of a general hypothesis linking impacts of large asteroids and comets with mass extinctions of life are possible based on astronomical data, impact dynamics, and geological information. The waiting of large-body impacts on the Earth derive from the flux of Earth-crossing asteroids and comets, and the estimated size of impacts capable of causing large-scale environmental disasters, predict that impacts of objects greater than or equal to 5 km in diameter (greater than or equal to 10 (exp 7) Mt TNT equivalent) could be sufficient to explain the record of approximately 25 extinction pulses in the last 540 Myr, with the 5 recorded major mass extinctions related to impacts of the largest objects of greater than or equal to 10 km in diameter (greater than or equal to 10(exp 8) Mt Events). Smaller impacts (approximately 10 (exp 6) Mt), with significant regional environmental effects, could be responsible for the lesser boundaries in the geologic record.

The Role of Eigensolutions in Nonlinear Inverse Cavity-Flow-Theory. Revision.

DTIC Science & Technology

1985-06-10

The method of Levi Civita is applied to an isolated fully cavitating body at zero cavitation number and adapted to the solution of the inverse...Eigensolutions in Nonlinear Inverse Cavity-Flow Theory [Revised] Abstract: The method of Levi Civita is applied to an isolated fully cavitating body at...problem is not thought * to present much of a challenge at zero cavitation number. In this case, - the classical method of Levi Civita [7] can be

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.

The 1990 MB: The first Mars Trojan

NASA Technical Reports Server (NTRS)

Innanen, Kimmo A.; Mikkola, Seppo; Bowell, Edward; Muinonen, Karri; Shoemaker, Eugene M.

1991-01-01

Asteroid 1990 MB was discovered by D. H. Levy and H. E. Holt during the course of the Mars and Earth Crossing Asteroid and Comet Survey. An orbit based on a 9 day arc and the asteroid's location near Mars' L5 (trailing Lagrangean) longitude led E. Boswell to speculate that it might be in 1:1 resonance with Mars, analogous to the Trojan asteroids of Jupiter. Subsequent observations strengthened the possibility, and later calculations confirmed it. Thus 1990 MB is the first known asteroid in 1:1 resonance with a planet other than Jupiter. The existence of 1990 MB (a small body most likely between 2 and 4 km in diameter) provides remarkable confirmation of computer simulations. These self consistent n-body simulations demonstrated this sort of stability for Trojans of all the terrestrial planets over at least a 2 million year time base. The discovery of 1990 MB suggests that others of similar or smaller diameter may be found. Using hypothetical populations of Mars Trojans, their possible sky plane distributions were modeled as a first step in undertaking a systematic observational search of Mars' L4 and L5 libration regions.

Will Deep Impact Make a Splash?

NASA Technical Reports Server (NTRS)

Sheldon, Robert B.; Hoover, Richard B.

2005-01-01

Recent cometary observations from spacecraft flybys support the hypothesis that short-period comets have been substantially modified by the presence of liquid water. Such a model can resolve many outstanding questions of cometary dynamics, as well as the differences between the flyby observations and the dirty snowball paradigm. The model also predicts that the Deep Impact mission, slated for a July 4, 2005 collision with Comet Temple-1, will encounter a layered, heterogenous nucleus with subsurface liquid water capped by dense crust. Collision ejecta will include not only vaporized material, but liquid water and large pieces of crust. Since the water will immediately boil, we predict that the water vapor signature of Deep Impact may be an order of magnitude larger than that expected from collisional vaporization alone.

Global environmental effects of impact-generated aerosols: Results from a general circulation model, revision 1

NASA Technical Reports Server (NTRS)

Covey, Curt; Ghan, Steven J.; Walton, John J.; Weissman, Paul R.

1989-01-01

Interception of sunlight by the high altitude worldwide dust cloud generated by impact of a large asteroid or comet would lead to substantial land surface cooling, according to our three-dimensional atmospheric general circulation model (GCM). This result is qualitatively similar to conclusions drawn from an earlier study that employed a one-dimensional atmospheric model, but in the GCM simulation the heat capacity of the oceans substantially mitigates land surface cooling, an effect that one-dimensional models cannot quantify. On the other hand, the low heat capacity of the GCM's land surface allows temperatures to drop more rapidly in the initial stage of cooling than in the one-dimensional model study. These two differences between three-dimensional and one-dimensional model simulations were noted previously in studies of nuclear winter; GCM-simulated climatic changes in the Alvarez-inspired scenario of asteroid/comet winter, however, are more severe than in nuclear winter because the assumed aerosol amount is large enough to intercept all sunlight falling on earth. Impacts of smaller objects could also lead to dramatic, though less severe, climatic changes, according to our GCM. Our conclusion is that it is difficult to imagine an asteroid or comet impact leading to anything approaching complete global freezing, but quite reasonable to assume that impacts at the Alvarez level, or even smaller, dramatically alter the climate in at least a patchy sense.

Gone in a Flash

NASA Image and Video Library

2005-07-04

This image shows the initial ejecta that resulted when NASA Deep Impact probe collided with comet Tempel 1 on July 3, 2005. It was taken by the spacecraft high-resolution camera 13 seconds after impact.

Is 50 cent the price of the optimal copayment? - a qualitative study of patient opinions and attitudes in response to a 50 cent charge on prescription drugs in a publicly funded health system in Ireland

PubMed Central

2013-01-01

Background A 50 cent prescription levy was introduced in 2010 on the General Medical Services (GMS) scheme (Irish public health insurance). This study sought to examine patient attitudes and opinions surrounding the 50 cent copayment. Given the small momentary value of the prescription fee, these results are of interest to policymakers internationally who wish to reduce copayments rather than abolish them. Methods A qualitative research design was used; semi structured interviews were carried out. Twenty four GMS eligible participants were interviewed in 23 interviews. Fifteen females and 9 males took part. Ages varied from 31- >70 years. Patients were invited to be interviewed in both independent and chain community pharmacies in three types of setting; 1) a socially deprived urban area, 2) a suburban affluent area and 3) a rural area. The Framework method was used for data management and analysis using QSR International’s NVivo 9.2 qualitative data analysis software. The “Francis method” was used to test for data saturation. Results Results are of interest to the Irish context and also at a broader international level. Patients were mostly accepting of the prescription levy with some reservations concerning an increased price and the way in which generated revenue would be used by government. Participants identified waste of prescription drugs at the hand of patients (moral hazard), but there was discordant opinion on whether the 50 cent copayment would halt this moral hazard. Interviewees felt the levy was affordable, albeit some may suffer a financial impact more than others. Conclusions This qualitative study gives important insights into the experiences of GMS patients with regard to the prescription levy. Information regarding the appropriateness of a 50 cent copayment as a symbolic copayment needs to be confirmed by quantitative analysis. Further insight is required from a younger population. PMID:23305316

Triggering the Activation of Main-belt Comets: The Effect of Porosity

NASA Astrophysics Data System (ADS)

Haghighipour, N.; Maindl, T. I.; Schäfer, C. M.; Wandel, O. J.

2018-03-01

It has been suggested that the comet-like activity of Main-belt comets (MBCs) is due to the sublimation of sub-surface water-ice that is exposed when these objects are impacted by meter-sized bodies. We recently examined this scenario and showed that such impacts can, in fact, excavate ice and present a plausible mechanism for triggering the activation of MBCs. However, because the purpose of that study was to prove the concept and identify the most viable ice-longevity model, the porosity of the object and the loss of ice due to the heat of impact were ignored. In this paper, we extend our impact simulations to porous materials and account for the loss of ice due to an impact. We show that for a porous MBC, impact craters are deeper, reaching to ∼15 m, implying that if the activation of MBCs is due to the sublimation of sub-surface ice, this ice has to be within the top 15 m of the object. Results also indicate that the loss of ice due to the heat of impact is negligible, and the re-accretion of ejected ice is small. The latter suggests that the activities of current MBCs are most probably from multiple impact sites. Our study also indicates that for sublimation from multiple sites to account for the observed activity of the currently known MBCs, the water content of MBCs (and their parent asteroids) needs to be larger than the values traditionally considered in models of terrestrial planet formation.

KSC-04PD-2670

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Workers at Astrotech Space Operations in Titusville, Fla., get ready to begin fueling the Deep Impact spacecraft, seen wrapped in a protective cover in the background. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-04PD-2673

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Workers at Astrotech Space Operations in Titusville, Fla., begin fueling operations of the Deep Impact spacecraft, seen wrapped in a protective cover in the background. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-04PD-2674

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Workers at Astrotech Space Operations in Titusville, Fla., begin fueling operations of the Deep Impact spacecraft, seen wrapped in a protective cover in the background. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-04PD-2671

NASA Technical Reports Server (NTRS)

2004-01-01

KENNEDY SPACE CENTER, FLA. Workers at Astrotech Space Operations in Titusville, Fla., get ready to begin fueling the Deep Impact spacecraft, seen wrapped in a protective cover in the background. Scheduled for liftoff Jan. 12, Deep Impact will probe beneath the surface of Comet Tempel 1 on July 4, 2005, when the comet is 83 million miles from Earth, and reveal the secrets of its interior. After releasing a 3- by 3-foot projectile to crash onto the surface, Deep Impacts flyby spacecraft will collect pictures and data of how the crater forms, measuring the craters depth and diameter, as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network. Deep Impact is a NASA Discovery mission.

KSC-05PD-0133

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. From the nearby Press Site at Cape Canaveral Air Force Station, Fla., photographers capture the exciting launch of the Deep Impact spacecraft at 1:47 p.m. EST. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

KSC-05PD-0134

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. Erupting from the flames and smoke beneath it, NASAs Deep Impact spacecraft lifts off at 1:47 p.m. EST today from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

KSC-05PD-0131

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. Erupting from the flames and smoke beneath it, NASAs Deep Impact spacecraft lifts off at 1:47 p.m. EST today from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

KSC-05PD-0135

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. Erupting from the flames and smoke beneath it, NASAs Deep Impact spacecraft lifts off at 1:47 p.m. EST today from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

KSC-05PD-0136

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. Engulfed by flames and smoke, NASAs Deep Impact spacecraft lifts off at 1:47 p.m. EST today from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

KSC-05PD-0130

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. With a burst of flames, NASAs Deep Impact spacecraft lifts off at 1:47 p.m. EST today from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

A Geometric Framework for the Kinematics of Crystals With Defects

DTIC Science & Technology

2006-02-01

which parallel transport preserves dot products of vectors, i.e. r G G ¼ 0. It is called the Levi - Civita connection [57] or the Riemannian connection...yielding a null covariant derivative of the metric tensor is called a metric connection. The Levi – Civita connection of (8) is metric. Note that in...tensor formed by inserting the Levi – Civita con- nection (8) into (10). A geometric space B0 with metric G having R G ¼ 0 is called flat. One may show

Analysis of Curved Target-Type Thrust Reversers

DTIC Science & Technology

1974-06-07

methods f-or two -dimensional cases, the Levi - Civita method provides a \\ariet> t>l bucket shapes and enables one to round off the sharp corners of...surface In the present work three methods arc employed to investigate the deflection of mviscid. incompressible curved surfaces: Levi - Civitas ...shapes are shown in Fig. V A special case for (T, =0 31416 and fr2= 0.47124, and A = 0. ,*46, (/< = 6X ), is shown in Fig 4. Fvidently, Levi - Civita "s

The Role of Eigensolutions in Nonlinear Inverse Cavity-Flow-Theory.

DTIC Science & Technology

1983-01-25

ere, side if necessary and id.ntify hv hlock number) " The method of Levi Civita is applied to an isolated fully cavitating body at zero cavitation... Levi Civita is applied to an isolated fully cavitating body at zero cavitation number and adapted to the solution of the inverse problem in which one...case, the classical method of Levi Civita [71 can be applied to an isolated •Numbers in square brackets indicate citations in the references listed below

On Anholonomic Deformation, Geometry, and Differentiation

DTIC Science & Technology

2013-02-01

αβχ are not necessarily Levi - Civita connection coefficients). The vector cross product × obeys, for two vectors V and W and two covectors α and β , V...three-dimensional space. 2.2.5. Euclidean space. Let GAB(X ) = GA · GB be the metric tensor of the space. The Levi - Civita connection coefficients of GAB...curvature tensor of the Levi - Civita connection vanishes identically: G R A BCD = 2 ( ∂[B G A C]D + G A[B|E|G EC]D ) = 0. (43) In n

Modulating terrestrial impacts from Oort cloud comets by the adiabatically changing galactic tides

NASA Astrophysics Data System (ADS)

Matese, J. J.; Whitman, P. G.; Innanen, K. A.; Valtonen, M. J.

Time modulation of the flux of new Jupiter-dominated Oort cloud comets is the subject of interest here. The major perturbation of these comets during the present epoch is due to the tidal field of the relatively smooth distribution of matter in the galactic disk. A secondary source of the near-parabolic comet flux are stars penetrating the inner Oort cloud and providing impulses that create brief comet showers. Substantial stellar-induced showers occur approximately every 100 m.y. Less frequent (but stronger) impulses due to giant molecular clouds can also perturb comets from the inner cloud. These occur on timescales of approximately equal to 500 m.y. In contrast to these infrequent stochastic shower phenomena is the continuously varying tidal-induced flux due to the galaxy. As the Sun orbits the galactic center it undergoes quasiharmonic motion about the galactic midplane, which is superimposed on the small eccentricity, near-Keplerian motion in the plane having epicycle period approximately equal to 150 m.y. In the process the galactic tidal field on the Sun/cloud system will vary causing a modulation of the observable Oort cloud flux. We have created a model of the galactic matter distribution as it affects the solar motion over a time interval ranging from 300 m.y. in the past to 100 m.y. into the future. As constraints on the disk's compact dark matter component we require consistency with the following: (1) the observed galactic rotation curve, (2) today's flux distribution of new comets, (3) the studies of K-giant distributions, and (4) the periodicity found in the terrestrial cratering record. The adiabatically varying galactic tidal torque is then determined and used to predict the time dependence of the flux. We find that a model in which approximately half the disk matter is compact is consistent with these constraints. Under such circumstances the peak-to-trough flux variation will be approx. equal to 5:1 with a full width of 9 m.y. This variability will manifest in the terrestrial cratering record and is consistent with the observed cratering periodicity, if over half of the impacts on Earth are caused by comets or asteroids that originate in the outer Oort cloud.

Modeling H2O and CO2 in Optically Thick Comets Using Asymmetric Spherical Coupled Escape Probability and Application to Comet C/2009 P1 Garradd Observations of CO, H2O, and CO2

NASA Astrophysics Data System (ADS)

Gersch, Alan M.; Feaga, Lori M.; A’Hearn, Michael F.

2018-02-01

We have adapted Coupled Escape Probability, a new exact method of solving radiative transfer problems, for use in asymmetrical spherical situations for use in modeling optically thick cometary comae. Here we present the extension of our model and corresponding results for two additional primary volatile species of interest, H2O and CO2, in purely theoretical comets. We also present detailed modeling and results for the specific examples of CO, H2O, and CO2 observations of C/2009 P1 Garradd by the Deep Impact flyby spacecraft.

Lunar and Planetary Science XXXV: Asteroids, Meteors, Comets

NASA Technical Reports Server (NTRS)

2004-01-01

Reports included:Long Term Stability of Mars Trojans; Horseshoe Asteroids and Quasi-satellites in Earth-like Orbits; Effect of Roughness on Visible Reflectance Spectra of Planetary Surface; SUBARU Spectroscopy of Asteroid (832) Karin; Determining Time Scale of Space Weathering; Change of Asteroid Reflectance Spectra by Space Weathering: Pulse Laser Irradiation on Meteorite Samples; Reflectance Spectra of CM2 Chondrite Mighei Irradiated with Pulsed Laser and Implications for Low-Albedo Asteroids and Martian Moons; Meteorite Porosities and Densities: A Review of Trends in the Data; Small Craters in the Inner Solar System: Primaries or Secondaries or Both?; Generation of an Ordinary-Chondrite Regolith by Repetitive Impact; Asteroid Modal Mineralogy Using Hapke Mixing Models: Validation with HED Meteorites; Particle Size Effect in X-Ray Fluorescence at a Large Phase Angle: Importance on Elemental Analysis of Asteroid Eros (433); An Investigation into Solar Wind Depletion of Sulfur in Troilite; Photometric Behaviour Dependent on Solar Phase Angle and Physical Characteristics of Binary Near-Earth-Asteroid (65803) 1996 GT; Spectroscopic Observations of Asteroid 4 Vesta from 1.9 to 3.5 micron: Evidence of Hydrated and/or Hydroxylated Minerals; Multi-Wavelength Observations of Asteroid 2100 Ra-Shalom: Visible, Infrared, and Thermal Spectroscopy Results; New Peculiarities of Cometary Outburst Activity; Preliminary Shape Modeling for the Asteroid (25143) Itokawa, AMICA of Hayabusa Mission; Scientific Capability of MINERVA Rover in Hayabusa Asteroid Mission; Characteristics and Current Status of Near Infrared Spectrometer for Hayabusa Mission; Sampling Strategy and Curation Plan of Hayabusa Asteroid Sample Return Mission; Visible/Near-Infrared Spectral Properties of MUSES C Target Asteroid 25143 Itokawa; Calibration of the NEAR XRS Solar Monitor; Modeling Mosaic Degradation of X-Ray Measurements of 433 Eros by NEAR-Shoemaker; Scattered Light Remediation and Recalibration of near Sheomaker s NIS Global Dataaset at 433 Eros; Evaluation of Preparation and Measuring Techniques for Interplanetary Dust Particles for the MIDAS Experiment on Rosetta; Chiron: a Proposed Remote Sensing Prompt Gamma Ray Activation Analysis Instrument for a Nuclear Powered Prometheus Mission;From Present Surveying to Future Prospecting of the Asteroid Belt; Asteroid Physical Properties Probe Microgravity Testing of a Surface Sampling System for Sample Return from Small Solar System Bodies;and Penetrator Coring Apparatus for Cometary Surfaces.

The impact of lymphocyte isolation on induced DNA damage in human blood samples measured by the comet assay.

PubMed

Bausinger, Julia; Speit, Günter

2016-09-01

The comet assay is frequently used in human biomonitoring for the detection of exposure to genotoxic agents. Peripheral blood samples are most frequently used and tested either as whole blood or after isolation of lymphocytes (i.e. peripheral blood mononuclear cells, PBMC). To investigate a potential impact of lymphocyte isolation on induced DNA damage in human blood samples, we exposed blood ex vivo to mutagens with different modes of genotoxic action. The comet assay was performed either directly with whole blood at the end of the exposure period or with lymphocytes isolated directly after exposure. In addition to the recommended standard protocol for lymphocyte isolation, a shortened protocol was established to optimise the isolation procedure. The results indicate that the effects of induced DNA strand breaks and alkali-labile sites induced by ionising radiation and alkylants, respectively, are significantly reduced in isolated lymphocytes. In contrast, oxidative DNA base damage (induced by potassium bromate) and stable bulky adducts (induced by benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide; BPDE) seem to be less affected. Our findings suggest that in vivo-induced DNA damage might also be reduced in isolated lymphocytes in comparison with the whole blood depending of the types of DNA damage induced. Because only small genotoxic effects can generally be expected in human biomonitoring studies with the comet assay after occupational and environmental exposure to genotoxic agents, any loss might be relevant and should be avoided. The possibility of such effects and their potential impact on variability of comet assay results in human biomonitoring should be considered when performing or evaluating such kind of studies. © The Author 2016. 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.

The effect of different methods and image analyzers on the results of the in vivo comet assay.

PubMed

Kyoya, Takahiro; Iwamoto, Rika; Shimanura, Yuko; Terada, Megumi; Masuda, Shuichi

2018-01-01

The in vivo comet assay is a widely used genotoxicity test that can detect DNA damage in a range of organs. It is included in the Organisation for Economic Co-operation and Development Guidelines for the Testing of Chemicals. However, various protocols are still used for this assay, and several different image analyzers are used routinely to evaluate the results. Here, we verified a protocol that largely contributes to the equivalence of results, and we assessed the effect on the results when slides made from the same sample were analyzed using two different image analyzers (Comet Assay IV vs Comet Analyzer). Standardizing the agarose concentrations and DNA unwinding and electrophoresis times had a large impact on the equivalence of the results between the different methods used for the in vivo comet assay. In addition, there was some variation in the sensitivity of the two different image analyzers tested; however this variation was considered to be minor and became negligible when the test conditions were standardized between the two different methods. By standardizing the concentrations of low melting agarose and DNA unwinding and electrophoresis times between both methods used in the current study, the sensitivity to detect the genotoxicity of a positive control substance in the in vivo comet assay became generally comparable, independently of the image analyzer used. However, there may still be the possibility that other conditions, except for the three described here, could affect the reproducibility of the in vivo comet assay.

The comet assay: ready for 30 more years.

PubMed

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.

Aerosol particle and organic vapor concentrations at industrial work sites in Malaysia.

PubMed

Armstrong, R W; Rood, M J; Sani, S; Mohamed, M; Rashid, M; Jab, A T; Landsberger, S

2001-01-01

The objective of this study was to establish baseline data about air pollutants potentially related to nasopharyngeal carcinoma (NPC) in the Federal Territory and Selangor, Malaysia. During 1991-1993, ambient air quality was monitored at 42 work sites representing ten industrial sectors: adhesive manufacturing, foundries, latex processing, metalworking, plywood/veneer milling, ricemilling, rubber tire manufacturing, sawmilling, shoemaking, and textile related industries. At each work site, aerosol particle size distributions and concentrations of formaldehyde, benzene, toluene, isopropyl alcohol, and furfural were measured. Mean aerosol particle concentrations ranged from 61 micrograms/m3 in foundries to 5,578 micrograms/m3 in ricemills, with five industries (adhesives, metalworking, ricemilling, sawmilling, and shoemaking) exceeding the US EPA 24-hr ambient air standard for PM-10. Formaldehyde concentrations exceeded the threshold limit value (TLV) in adhesives factories. Other vapours and elements measured were well below TLVs.

On the HCN and CO 2 abundance and distribution in Jupiter's stratosphere

NASA Astrophysics Data System (ADS)

Lellouch, E.; Bézard, B.; Strobel, D. F.; Bjoraker, G. L.; Flasar, F. M.; Romani, P. N.

2006-10-01

Observations of Jupiter by Cassini/CIRS, acquired during the December 2000 flyby, provide the latitudinal distribution of HCN and CO 2 in Jupiter's stratosphere with unprecedented spatial resolution and coverage. Following up on a preliminary study by Kunde et al. [Kunde, V.G., and 41 colleagues, 2004. Science 305, 1582-1587], the analysis of these observations leads to two unexpected results (i) the total HCN mass in Jupiter's stratosphere in 2000 was (6.0±1.5)×10 g, i.e., at least three times larger than measured immediately after the Shoemaker-Levy 9 (SL9) impacts in July 1994 and (ii) the latitudinal distributions of HCN and CO 2 are strikingly different: while HCN exhibits a maximum at 45° S and a sharp decrease towards high Southern latitudes, the CO 2 column densities peak over the South Pole. The total CO 2 mass is (2.9±1.2)×10 g. A possible cause for the HCN mass increase is its production from the photolysis of NH 3, although a problem remains because, while millimeter-wave observations clearly indicate that HCN is currently restricted to submillibar ( ˜0.3 mbar) levels, immediate post-impact infrared observations have suggested that most of the ammonia was present in the lower stratosphere near 20 mbar. HCN appears to be a good atmospheric tracer, with negligible chemical losses. Based on 1-dimensional (latitude) transport models, the HCN distribution is best interpreted as resulting from the combination of a sharp decrease (over an order of magnitude in K) of wave-induced eddy mixing poleward of 40° and an equatorward transport with ˜7 cms velocity. The CO 2 distribution was investigated by coupling the transport model with an elementary chemical model, in which CO 2 is produced from the conversion of water originating either from SL9 or from auroral input. The auroral source does not appear adequate to reproduce the CO 2 peak over the South Pole, as required fluxes are unrealistically high and the shape of the CO 2 bulge is not properly matched. In contrast, the CO 2 distribution can be fit by invoking poleward transport with a ˜30 cms velocity and vigorous eddy mixing ( K=2×10 cms). While the vertical distribution of CO 2 is not measured, the combined HCN and CO 2 results imply that the two species reside at different stratospheric levels. Comparing with the circulation regimes predicted by earlier radiative-dynamical models of Jupiter's stratosphere, and with inferences from the ethane and acetylene stratospheric latitudinal distribution, we suggest that CO 2 lies in the middle stratosphere near or below the 5-mbar level.

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.

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.

TRIGGERING SUBLIMATION-DRIVEN ACTIVITY OF MAIN BELT COMETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haghighipour, N.; Maindl, T. I.; Dvorak, R.

2016-10-10

It has been suggested that the comet-like activity of main belt comets (MBCs) is due to the sublimation of sub-surface water–ice that has been exposed as a result of their surfaces being impacted by meter-sized bodies. We have examined the viability of this scenario by simulating impacts between meter-sized and kilometer-sized objects using a smooth particle hydrodynamics approach. Simulations have been carried out for different values of the impact velocity and impact angle, as well as different target material and water-mass fractions. Results indicate that for the range of impact velocities corresponding to those in the asteroid belt, the depthmore » of an impact crater is slightly larger than 10 m, suggesting that if the activation of MBCs is due to the sublimation of sub-surface water–ice, this ice has to exist no deeper than a few meters from the surface. Results also show that ice exposure occurs in the bottom and on the interior surface of impact craters, as well as on the surface of the target where some of the ejected icy inclusions are re-accreted. While our results demonstrate that the impact scenario is indeed a viable mechanism to expose ice and trigger the activity of MBCs, they also indicate that the activity of the current MBCs is likely due to ice sublimation from multiple impact sites and/or the water contents of these objects (and other asteroids in the outer asteroid belt) is larger than the 5% that is traditionally considered in models of terrestrial planet formation, providing more ice for sublimation. We present the details of our simulations and discuss their results and implications.« less

Levi Kilcher | NREL

Science.gov Websites

Levi is an expert in ocean turbulence, tidal processes, and surface waves. He has more than 10 years of the state identify renewable energy and energy efficiency opportunities that fit the climate and met

Impact on Comets and Asteroids

NASA Technical Reports Server (NTRS)

OKeefe, John D.; Stewart, Sarah T.; Ahrens, Thomas J.

2001-01-01

We characterized the impact physics in collisions on porous bodies by various density projectiles and defined different penetration modes (compression, spreading, or breakup) based on transitions between instability regimes. Additional information is contained in the original extended abstract.

Comet Ejecta in Aerogel

NASA Image and Video Library

2006-02-21

This image from NASA shows a particle impact on the aluminum frame that holds the aerogel tiles. The debris from the impact shot into the adjacent aerogel tile producing the explosion pattern of ejecta framents captured in the material.

Lowell 72-IN Images and Photom. Of 9P/TEMPEL 1 V1.0

NASA Astrophysics Data System (ADS)

Buie, M. W.; Pate, J.; McLaughlin, S. A.

2010-01-01

This data set contains broadband R images and derived photometry of comet 9P/Tempel 1, the target of the Deep Impact mission. Data were acquired by M. Buie at the Perkins 72-inch telescope of the Lowell Observatory during 11 nights of observing from 28 September 2000 through 14 January 2001, about 8.5 to 12.5 months after the comet passed through perihelion on 2 January 2000.

MEST-Tyche will take its dark comets to impact our solar system in 20 years

NASA Astrophysics Data System (ADS)

Cao, Dayong

2012-03-01

Tyche has many dark comets like Oort cloud. It went near our solar system every 25-27 million years. It could take its dark comets to impact our earth. Tyche and its dark comet absorb light like a dark light which is a negative black-body radiation. (1) Eddν=-c1dνd^3dνe^c2dνd/Td-1. Among it, Ed: the dark energy, νd: the dark frequence, Td: the dark temperature, c1d,c2d: the constant. So when they go near us, their wave has a against Doppler redshift as 0.000165. And they will inbreak solar system at the rate of 99AU/y, from the distance of 1,500AU and in 20 years. It can cause the broken ozonosphere, the lithosphere to crack, many big activity volcanic and the continental drift. And it can darked the light and colded the climate to the Great Ice Age. Not only it will break our environment by a special ``nuclear explosion'' under low temperature, but also the dark life will change the Genetic code of our life. So it will kill many lives and will produce new life. So it could trigger the Mass Extinction. We can bulid up a new pair of nuclear reactor (include dark nuclear energy) to drive a universal craft and can change the orbit of our earth for evading the impaction. We need a new life-information technology to develop our life and consciousness.

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).

Space shuttle launch era spacecraft injection errors and DSN initial acquisition

NASA Technical Reports Server (NTRS)

Khatib, A. R.; Berman, A. L.; Wackley, J. A.

1981-01-01

The initial acquisition of a spacecraft by the Deep Space Network (DSN) is a critical mission event. This results from the importance of rapidly evaluating the health and trajectory of a spacecraft in the event that immediate corrective action might be required. Further, the DSN initial acquisition is always complicated by the most extreme tracking rates of the mission. The DSN initial acquisition characteristics will change considerably in the upcoming space shuttle launch era. How given injection errors at spacecraft separation from the upper stage launch vehicle (carried into orbit by the space shuttle) impact the DSN initial acquisition, and how this information can be factored into injection accuracy requirements to be levied on the Space Transportation System (STS) is addressed. The approach developed begins with the DSN initial acquisition parameters, generates a covariance matrix, and maps this covariance matrix backward to the spacecraft injection, thereby greatly simplifying the task of levying accuracy requirements on the STS, by providing such requirements in a format both familiar and convenient to STS.

The ESA mission to Comet Halley

NASA Technical Reports Server (NTRS)

Reinhard, R.

1981-01-01

The Europeon Space Agency's approximately Giotto mission plans for a launch in July 1985 with a Halley encounter in mid-March 1986 4 weeks after the comet's perihelion passage. Giotto carries 10 scientific experiments, a camera, neutral, ion and dust mass spectrometers, a dust impact detector system, various plasma analyzers, a magnetometer and an optical probe. The instruments are described, the principles on which they are based are described, and the experiment key performance data are summarized. The launch constraints the helicentric transfer trajectory, and the encounter scenario are analyzed. The Giotto spacecraft major design criteria, spacecraft subsystem and the ground system are described. The problem of hypervelocity dust particle impacts in the innermost part of the coma, the problem of spacecraft survival, and the adverse effects of impact-generated plasma aroung the spacecraft are considered.

Flying over decades

NASA Astrophysics Data System (ADS)

Hoeller, Judith; Issler, Mena; Imamoglu, Atac

Levy flights haven been extensively used in the past three decades to describe non-Brownian motion of particles. In this presentation I give an overview on how Levy flights have been used across several disciplines, ranging from biology to finance to physics. In our publication we describe how a single electron spin 'flies' when captured in quantum dot using the central spin model. At last I motivate the use of Levy flights for the description of anomalous diffusion in modern experiments, concretely to describe the lifetimes of quasi-particles in Josephson junctions. Finished PhD at ETH in Spring 2015.

Testability of VLSI (Very Large Scale Integration) Leakage Faults in CMOS (Complementary Metal Oxide Semiconductor).

DTIC Science & Technology

1983-09-01

has been reviewed and is approved for publication. Im Ŕ APPROVED: . L,.. &- MARK W. LEVI Project Engineer APPROVED: W.S. TUTHILL, Colonel, USAF Chief...ebetract entered In Block 20, if different from Report) Same IS. SUPPLEMENTARY NOTES RADC Project Engineer: Mark W. Levi (RBRP) This effort was funded...masking the presence of another fault which was a functional or reliability hazard. ’." • ’ ",, ,~ MARK W. LEVI A ec . ston For 1\\ T’ ir I .] / r "- T A

Space Radar of Image Aorounga Impact Crater, Chad

NASA Image and Video Library

1999-04-15

The impact of an asteroid or comet several hundred million years ago left scars in the landscape that are still visible in this spaceborne radar image of an area in the Sahara Desert of northern Chad.

Space Radar Image of Possible String of Impact Creaters

NASA Image and Video Library

1999-04-15

The impact of an asteroid or comet several hundred million years ago left scars in the landscape that are still visible in this spaceborne radar image of an area in the Sahara Desert of northern Chad.

Comets as Messengers from the Early Solar System - Emerging Insights on Delivery of Water, Nitriles, and Organics to Earth

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.

KSC-05PP-0138

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. Emerging through the smoke and steam, the Boeing Delta II rocket carrying NASAs Deep Impact spacecraft lifts off at 1:47 p.m. EST from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

KSC-05PD-0137

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. After a perfect liftoff at 1:47 p.m. EST today from Launch Pad 17-B, Cape Canaveral Air Force Station, Fla., the Boeing Delta II rocket with Deep Impact spacecraft aboard soars through the clear blue sky. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

KSC-05PD-0132

NASA Technical Reports Server (NTRS)

2005-01-01

KENNEDY SPACE CENTER, FLA. Guests of NASA gather near the launch site at Cape Canaveral Air Force Station, Fla., to watch the Deep Impact spacecraft as it speeds through the air after a perfect launch at 1:47 p.m. EST. A NASA Discovery mission, Deep Impact is heading for space and a rendezvous 83 million miles from Earth with Comet Tempel 1. After releasing a 3- by 3-foot projectile (impactor) to crash onto the surface July 4, 2005, Deep Impacts flyby spacecraft will reveal the secrets of the comets interior by collecting pictures and data of how the crater forms, measuring the craters depth and diameter as well as the composition of the interior of the crater and any material thrown out, and determining the changes in natural outgassing produced by the impact. It will send the data back to Earth through the antennas of the Deep Space Network.

Collisional Histories of Comets and Trojan Asteroids: Diopside, Magnesite, and Fayalite Impact Studies

NASA Technical Reports Server (NTRS)

Lederer, S. M.; Jensen, E. A.; Wooden, D. H.; Lindsay, S. S.; Nakamura-Messenger, K.; Smith, D. C.; Keller, L. P.; Cintala, M. J.; Zolensky, M. E.

2012-01-01

Comets and asteroids have weathered dynamic histories, as evidenced by their rough surfaces. The Nice model describes a violent reshuffling of small bodies during the Late Heavy Bombardment, with collisions acting to grind these planetesimals away. This creates an additional source of impact material that can re-work the surfaces of the larger bodies over the lifetime of the solar system. Here, we investigate the possibility that signatures due to impacts (e.g. from micrometeoroids or meteoroids) could be detected in their spectra, and how that can be explained by the physical manifestation of shock in the crystalline structure of minerals. All impact experiments were conducted in the Johnson Space Center Experimental Impact Laboratory using the vertical gun. Impact speeds ranged from approx.2.0 km/s to approx.2.8 km/s. All experiments were conducted at room temperature. Minerals found in comets and asteroids were chosen as targets, including diopside (MgCaSi2O6, monoclinic pyroxene), magnesite (MgCO3, carbonate), and fayalite (FeSiO4, olivine). Impacted samples were analyzed using a Fourier Transform Infrared Spectrometer (FTIR) and a Transmission Electron Microscope (TEM). Absorbance features in the 8-13 m spectral region demonstrate relative amplitude changes as well as wavelength shifts. Corresponding TEM images exhibit planar shock dislocations in the crystalline structure, attributed to deformation at high strain and low temperatures. Elongating or shortening the axes of the crystalline structure of forsterite (Mg2SiO4, olivine) using a discrete dipole approximation model (Lindsay et al., submitted) yields changes in spectral features similar to those observed in our impacted laboratory minerals.

Planetary Defense Architecture for Mitigating Short-Term Warning Cosmic Threats: READI Project

NASA Technical Reports Server (NTRS)

Nambiar, Shrrirup; Hussein, Alaa; Silva-Martinez, Jackelynne; Reinert, Jessica; Gonzalez, Fernando

2016-01-01

Earth is being constantly bombarded by a large variety of celestial bodies and has been since its formation 4.5 billion years ago. Among those bodies, mainly asteroids and comets, there are those that have the potential to create large scale destruction upon impact. The only extinction-level impact recorded to date was 65 million years ago, during the era of dinosaurs. The probability of another extinction-level, or even city-killer, impact may be negligible, but the consequences can be severe for the biosphere and for our species. Therefore it is highly imperative for us to be prepared for such a devastating impact in the near future, especially since humanity is at the threshold of wielding technologies that allow us to do so. Majority of scientists, engineers, and policymakers have focused on long-term strategies and warning periods for Earth orbit crossing Near-Earth Objects (NEOs), and have suggested methods and policies to tackle such problems. However, less attention has been paid to short warning period NEO threats. Such NEOs test current technological and international cooperation capabilities in protecting ourselves, and can create unpredictable devastation ranging from local to global scale. The most recent example is the Chelyabinsk incident in Russia. This event has provided a wakeup call for space agencies and governments around the world towards establishing a Planetary Defense Program. The Roadmap for EArth Defense Initiative (READI) is a project by a team of international, intercultural, and interdisciplinary participants of the International Space University's Space Studies Program 2015 hosted by Ohio University, Athens, OH proposing a roadmap for space agencies, governments, and the general public to tackle NEOs with a short warning before impact. Taking READI as a baseline, this paper presents a technical description of methodologies proposed for detection and impact mitigation of a medium-sized comet (up to 800m across) with a short-warning period of two years on a collision course with Earth. The hypothetical comet is on a highly-inclined orbit having a high probability for Earth impact after its perihelion. For detection, we propose a space-based infrared detection system consisting of two satellites located at the Earth-Moon Lagrange points L1 and L2 coupled with space observatories, like the James Webb telescope and the Centennial telescope. These telescopes are supported by ground-based telescopes, like the Arecibo and Green Bank telescope, in the search for NEOs. Upon detection, the comet is tracked constantly using space- and ground-based telescopes. The deflection system is two-pronged, firstly involving the use of a high energy Directed Energy Laser Terminals (DELT) placed at Sun-Earth Lagrange points L4 and L5 so as to initiate and increase the ablation rate of the comet and deviate it from its collision trajectory, and secondly by the Hypervelocity Comet Intercept Vehicle (HCIV), a space-borne system combining a kinetic impactor with a thermonuclear device. The policy and international collaboration aspects to implement these methods are also outlined in the paper. The techniques mentioned could also be applied to mitigate medium-to-large sized asteroids (up to 2km across).

Architecture for Mitigating Short-Term Warning Cosmic Threats: READI Project

NASA Technical Reports Server (NTRS)

Nambiar, Shrrirup P.; Hussein, Alaa; Silva-Martinez, Jackelynne; Reinert, Jessica; Gonzalez, Fernando

2016-01-01

Earth is being constantly bombarded by a large variety of celestial bodies and has been since its formation 4.5 billion years ago. Among those bodies, mainly asteroids and comets, there are those that have the potential to create large scale destruction upon impact. The only extinction-level impact recorded to date was 65 million years ago, during the era of dinosaurs. The probability of another extinction-level, or even city-killer, impact may be negligible, but the consequences can be severe for the biosphere and for our species. Therefore it is highly imperative for us to be prepared for such a devastating impact in the near future, especially since humanity is at the threshold of wielding technologies that allow us to do so. Majority of scientists, engineers, and policymakers have focused on long-term strategies and warning periods for Earth orbit crossing Near-Earth Objects (NEOs), and have suggested methods and policies to tackle such problems. However, less attention has been paid to short warning period NEO threats. Such NEOs test current technological and international cooperation capabilities in protecting ourselves, and can create unpredictable devastation ranging from local to global scale. The most recent example is the Chelyabinsk incident in Russia. This event has provided a wakeup call for space agencies and governments around the world towards establishing a Planetary Defense Program. The Roadmap for EArth Defense Initiative (READI) is a project by a team of international, intercultural, and interdisciplinary participants of the International Space University's Space Studies Program 2015 hosted by Ohio University, Athens, OH proposing a roadmap for space agencies, governments, and the general public to tackle NEOs with a short warning before impact. Taking READI as a baseline, this paper presents a technical description of methodologies proposed for detection and impact mitigation of a medium-sized comet (up to 800m across) with a short-warning period of two years on a collision course with Earth. The hypothetical comet is on a highly-inclined orbit having a high probability for Earth impact after its perihelion. For detection, we propose a space-based infrared detection system consisting of two satellites located at the Earth-Moon Lagrange points L1 and L2 coupled with space observatories, like the James Webb telescope and the Centennial telescope. These telescopes are supported by ground-based telescopes, like the Arecibo and Green Bank telescope, in the search for NEOs. Upon detection, the comet is tracked constantly using space- and ground-based telescopes. The deflection system is two-pronged, firstly involving the use of a high energy Directed Energy Laser Terminals (DELT) placed at Sun-Earth Lagrange points L4 and L5 so as to initiate and increase the ablation rate of the comet and deviate it from its collision trajectory, and secondly by the Hypervelocity Comet Intercept Vehicle (HCIV), a space-borne system combining a kinetic impactor with a thermonuclear device. The policy and international collaboration aspects to implement these methods are also outlined in the paper. The techniques mentioned could also be applied to mitigate medium-to-large sized asteroids (up to 2km across).

Formation of bi-lobed 67P/C-G-like shapes by sub-catastrophic collisions

NASA Astrophysics Data System (ADS)

Jutzi, Martin; Benz, Willy

2016-10-01

Small bodies with a bi-lobe shape such as comet 67P/C-G have been argued to form as the result of low velocity (v ≈ vesc) collisional mergers of similar-sized bodies very early on in the history of the solar system [1]. However, the recent analysis of the subsequent collisional survival of the global structure and shape of comet 67P/C-G strongly suggests that such a structure will not survive until today [2]. Hence, the comet must have acquired its present characteristics as a result of a collision occurring at later time when the relative velocities between small bodies are much higher (v >> vesc).One possible scenario would be that 67P/C-G-like bi-lobe structures form as the result of collisional disruptions of larger parent bodies [3]. Whether the internal properties of such larger parent bodies, the timing of such a collision, and the subsequent survival of the shape produced is compatible with observations will remain to be seen.Here, we propose a scenario in which the final bi-lobe shapes result from low-energy, sub-catastrophic impacts. We start with bodies of about the same mass as comet 67P/C-G, which are rotating and are slightly elongated (i.e., with properties which are consistent with the outcome of the disruptions of larger bodies). We use a SPH shock physics code to model the impacts, the subsequent re-accumulation of material and the reconfiguration into a stable final shape. Our modelling results suggest that these kind of collisions result in "splitting" events which frequently lead to formation of bi-lobe 67P/C-G-like shapes.The frequency of such small-scale impact events is consistent with a young (less than 1 Gy) age of the shape of comet 67P/C-G [2]. Equally important, the probability for such a shape-forming event to take place without a subsequent shape-destroying event occurring until today is reasonably high.Although the collisions considered in this work can alter the global shape, their respective energy is small enough not to lead to any substantial global-scale heating or compaction, consistent with the observed primordial characteristics of comets.[1] Jutzi&Asphaug, 2015, Science 348. [2] Jutzi et al., submitted. [3] Schwartz et al., in prep.

How primordial is the structure of comet 67P/C-G (and of comets in general)?

NASA Astrophysics Data System (ADS)

Morbidelli, Alessandro; Jutzi, Martin; Benz, Willy; Toliou, Anastasia; Rickman, Hans; Bottke, William; Brasser, Ramon

2016-10-01

Several properties of the comet 67P-CG suggest that it is a primordial planetesimal. On the other hand, the size-frequency distribution (SFD) of the craters detected by the New Horizons missions at the surface of Pluto and Charon reveal that the SFD of trans-Neptunian objects smaller than 100km in diameter is very similar to that of the asteroid belt. Because the asteroid belt SFD is at collisional equilibrium, this observation suggests that the SFD of the trans-Neptunian population is at collisional equilibrium as well, implying that comet-size bodies should be the product of collisional fragmentation and not primordial objects. To test whether comet 67P-CG could be a (possibly lucky) survivor of the original population, we conducted a series of numerical impact experiments, where an object with the shape and the density of 67P-CG, and material strength varying from 10 to 1,000 Pa, is hit on the "head" by a 100m projectile at different speeds. From these experiments we derive the impact energy required to disrupt the body catastrophically, or destroy its bi-lobed shape, as a function of impact speed. Next, we consider a dynamical model where the original trans-Neptunian disk is dispersed during a phase of temporary dynamical instability of the giant planets, which successfully reproduces the scattered disk and Oort cloud populations inferred from the current fluxes of Jupiter-family and long period comets. We find that, if the dynamical dispersal of the disk occurs late, as in the Late Heavy Bombardment hypothesis, a 67P-CG-like body has a negligible probability to avoid all catastrophic collisions. During this phase, however, the collisional equilibrium SFD measured by the New Horizons mission can be established. Instead, if the dispersal of the disk occurred as soon as gas was removed, a 67P-CG-like body has about a 20% chance to avoid catastrophic collisions. Nevertheless it would still undergo 10s of reshaping collisions. We estimate that, statistically, the last reshaping collision should have happened 250My-1Gy ago, implying that the actual morphology of 67P-CG should be younger than this age.

Does Comet WILD-2 contain Gems?

NASA Technical Reports Server (NTRS)

Chi, M.; Ishii, H.; Dai, Z. R.; Toppani, A.; Joswiak, D. J.; Leroux, H.; Zolensky, M.; Keller, L. P.; Browning, N. D.

2007-01-01

It is expected that Comet Wild-2 dust should resemble anhydrous carbon-rich, chondritic porous (CP) interplanetary dust particles (IDPs) collected in the stratosphere because some CP IDPs are suspected to be from comets. The rarity of carbonaceous grains and presolar silicates, as well as the presence of high-temperature inner solar nebula minerals in the Wild-2 sample (e.g. osbornite and melilite), appear incompatible with most CP IDPs. However, it is premature to draw firm conclusions about the mineralogy of comet Wild-2 because only approx. 1% of the sample has been examined. The most abundant silicates in CP IDPs are GEMS (glass with embedded metal and sulfides). Nonsolar O isotopic compositions confirm that at least some GEMS in IDPs are presolar amorphous silicates. The presence or absence of GEMS in the Wild-2 sample is important because it addresses, (a) the relationship between CP IDPs and comets, and (b) the hypothesis that other GEMS in IDPs formed in the solar nebula. Here we show that most of the GEMSlike materials so far identified in Stardust aerogel were likely impact generated during collection. At the nanometer scale, they are compositionally and crystallographically distinct from GEMS in IDPs.

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.

The use of comet assay in plant toxicology: recent advances

PubMed Central

Santos, Conceição L. V.; Pourrut, Bertrand; Ferreira de Oliveira, José M. P.

2015-01-01

The systematic study of genotoxicity in plants induced by contaminants and other stress agents has been hindered to date by the lack of reliable and robust biomarkers. The comet assay is a versatile and sensitive method for the evaluation of DNA damages and DNA repair capacity at single-cell level. Due to its simplicity and sensitivity, and the small number of cells required to obtain robust results, the use of plant comet assay has drastically increased in the last decade. For years its use was restricted to a few model species, e.g., Allium cepa, Nicotiana tabacum, Vicia faba, or Arabidopsis thaliana but this number largely increased in the last years. Plant comet assay has been used to study the genotoxic impact of radiation, chemicals including pesticides, phytocompounds, heavy metals, nanoparticles or contaminated complex matrices. Here we will review the most recent data on the use of this technique as a standard approach for studying the genotoxic effects of different stress conditions on plants. Also, we will discuss the integration of information provided by the comet assay with other DNA-damage indicators, and with cellular responses including oxidative stress, cell division or cell death. Finally, we will focus on putative relations between transcripts related with DNA damage pathways, DNA replication and repair, oxidative stress and cell cycle progression that have been identified in plant cells with comet assays demonstrating DNA damage. PMID:26175750

10 CFR Appendix K to Part 50 - ECCS Evaluation Models

Code of Federal Regulations, 2012 CFR

2012-01-01

... stated circumstances shall be justified by comparative analyses or by experimental data. 4. Critical Heat..., ASME, New York, 1969. (3) Hench-Levy. J. M. Healzer, J. E. Hench, E. Janssen, S. Levy, “Design Basis...

10 CFR Appendix K to Part 50 - ECCS Evaluation Models

Code of Federal Regulations, 2013 CFR

2013-01-01

... stated circumstances shall be justified by comparative analyses or by experimental data. 4. Critical Heat..., ASME, New York, 1969. (3) Hench-Levy. J. M. Healzer, J. E. Hench, E. Janssen, S. Levy, “Design Basis...

10 CFR Appendix K to Part 50 - ECCS Evaluation Models

Code of Federal Regulations, 2014 CFR

2014-01-01

... stated circumstances shall be justified by comparative analyses or by experimental data. 4. Critical Heat..., ASME, New York, 1969. (3) Hench-Levy. J. M. Healzer, J. E. Hench, E. Janssen, S. Levy, “Design Basis...

Magnetism of Minor Bodies in the Solar System: From 433 Eros, passing Braille, Steins, and Lutetia towards Churyumov-Gerasimenko and 1999 JU3.

NASA Astrophysics Data System (ADS)

Hercik, David; Auster, Hans-Ulrich; Heinisch, Philip; Richter, Ingo; Glassmeier, Karl-Heinz

2015-04-01

Minor bodies in the solar system, such as asteroids and comets, are important sources of information for our knowledge of the solar system formation. Besides other aspects, estimation of a magnetization state of such bodies might prove important in understanding the early aggregation phases of the protoplanetary disk, showing the level of importance of the magnetic forces in the processes involved. Meteorites' magnetization measurements suggest that primitive bodies consist of magnetized material. However, space observations from various flybys give to date diverse results for a global magnetization estimation. The flybys at Braille and Gaspra indicate possible higher magnetization (~ 10-3 Am2/kg), while flybys at Steins and Lutetia show no significant values in the global field change illustrating low global magnetization. Furthermore, the interpretation of remote (during flybys) measurements is very difficult. For correct estimates on the local magnetization one needs (in the best case) multi-point surface measurements. Single point observation has been done by NEAR-Shoemaker on 433 Eros asteroid, revealing no signature in magnetic field that could have origin in asteroid magnetization. Similar results, no magnetization observed, have been provided by evaluation of recent data from ROMAP (Philae lander) and RPC-MAG (Rosetta orbiter) instruments from comet 67P/Churyumov-Gerasimenko. The ROMAP instrument provided measurements from multiple points of the cometary surface as well as data along ballistic path between multiple touchdowns, which support the conclusion of no global magnetization. However, even in case of the in-situ on surface observations the magnetization estimate has a limiting spatial resolution that is dependent on the distance from the surface (~ 50 cm in case of ROMAP). To get information about possible smaller magnetized grains distribution and magnetization strength, the sensor shall be placed as close as possible to the surface. For such observations the next ideal candidate mission is Hayabusa-II with its Mascot lander equipped with fluxgate magnetometer. The small-sized lander shall deliver the magnetometer within centimeters from the surface, providing measurements on multiple points thanks to a hopping ability. The mission has been recently launched (December 2014) and is aiming to a C-type asteroid 1999 JU3 to reach it in 2018. The results will hopefully add some piece of information to the still unclear question of minor solar system bodies magnetization.

Satellite orbits in Levi-Civita space

NASA Astrophysics Data System (ADS)

Humi, Mayer

2018-03-01

In this paper we consider satellite orbits in central force field with quadratic drag using two formalisms. The first using polar coordinates in which the satellite angular momentum plays a dominant role. The second is in Levi-Civita coordinates in which the energy plays a central role. We then merge these two formalisms by introducing polar coordinates in Levi-Civita space and derive a new equation for satellite orbits which unifies these two paradigms. In this equation energy and angular momentum appear on equal footing and thus characterize the orbit by its two invariants. Using this formalism we show that equatorial orbits around oblate spheroids can be expressed analytically in terms of Elliptic functions. In the second part of the paper we derive in Levi-Civita coordinates a linearized equation for the relative motion of two spacecrafts whose trajectories are in the same plane. We carry out also a numerical verification of these equations.

The UK sugar tax - a healthy start?

PubMed

Jones, C M

2016-07-22

The unexpected announcement by the UK Chancellor of the Exchequer of a levy on sugar sweetened beverages (SSBs) on the 16 March 2016, should be welcomed by all health professionals. This population based, structural intervention sends a strong message that there is no place for carbonated drinks, neither sugared nor sugar-free, in a healthy diet and the proposed levy has the potential to contribute to both general and dental health. The sugar content of drinks exempt from the proposed sugar levy will still cause tooth decay. Improving the proposed tax could involve a change to a scaled volumetric tax of added sugar with a lower exemption threshold. External influences such as the Common Agricultural Policy and the Transatlantic Trade and Investment Partnership may negate the benefits of the sugar levy unless it is improved. However, the proposed UK sugar tax should be considered as a start in improving the nation's diet.

A Multi-Verse Optimizer with Levy Flights for Numerical Optimization and Its Application in Test Scheduling for Network-on-Chip.

PubMed

Hu, Cong; Li, Zhi; Zhou, Tian; Zhu, Aijun; Xu, Chuanpei

2016-01-01

We propose a new meta-heuristic algorithm named Levy flights multi-verse optimizer (LFMVO), which incorporates Levy flights into multi-verse optimizer (MVO) algorithm to solve numerical and engineering optimization problems. The Original MVO easily falls into stagnation when wormholes stochastically re-span a number of universes (solutions) around the best universe achieved over the course of iterations. Since Levy flights are superior in exploring unknown, large-scale search space, they are integrated into the previous best universe to force MVO out of stagnation. We test this method on three sets of 23 well-known benchmark test functions and an NP complete problem of test scheduling for Network-on-Chip (NoC). Experimental results prove that the proposed LFMVO is more competitive than its peers in both the quality of the resulting solutions and convergence speed.

A Multi-Verse Optimizer with Levy Flights for Numerical Optimization and Its Application in Test Scheduling for Network-on-Chip

PubMed Central

Hu, Cong; Li, Zhi; Zhou, Tian; Zhu, Aijun; Xu, Chuanpei

2016-01-01

We propose a new meta-heuristic algorithm named Levy flights multi-verse optimizer (LFMVO), which incorporates Levy flights into multi-verse optimizer (MVO) algorithm to solve numerical and engineering optimization problems. The Original MVO easily falls into stagnation when wormholes stochastically re-span a number of universes (solutions) around the best universe achieved over the course of iterations. Since Levy flights are superior in exploring unknown, large-scale search space, they are integrated into the previous best universe to force MVO out of stagnation. We test this method on three sets of 23 well-known benchmark test functions and an NP complete problem of test scheduling for Network-on-Chip (NoC). Experimental results prove that the proposed LFMVO is more competitive than its peers in both the quality of the resulting solutions and convergence speed. PMID:27926946

[From psychotherapy to psychoanalysis: Max Levy-Suhl (1876-1947)].

PubMed

Hermanns, Ludger M; Schröter, Michael; Stroeken, Harry

2014-01-01

From psychotherapy to psychoanalysis: Max Levy-Suhl (1876-1947). Levy-Suhl can be considered one of the great practising psychotherapists in early 20th century Berlin. He was active in various fields, including ophthalmology, forensic adolescent psychiatry and hypnosis. Prominent among his publications were two handbooks of psychotherapeutic methods. His attitude towards psychoanalysis shifted from initial criticism to acceptance. Ca. 1930 he experienced some kind of conversion, resulting in his training at the Berlin Institute and becoming a member of the German Psychoanalytic Society. As a Jew being forced to emigrate in 1933, Levy-Suhl turned to the Netherlands where he had a psychoanalytic children's home in Amersfoort, followed by an analyst's practice in Amsterdam. He survived the German occupation, but apparently as a broken man. After the war he committed suicide.--The paper is complemented by an appendix, containing documents and an extensive bibliography.

Iron, magnesium, and silicon in dust from Comet Halley

NASA Technical Reports Server (NTRS)

Lawler, Mark E.; Brownlee, Donald E.; Temple, Scott; Wheelock, Maya M.

1989-01-01

The highest-quality impact mass spectrometer data from the Vega-1 and Giotto spacecraft are presently used to study the Mg, Si, and Fe composition of dust grains in Comet Halley. The results thus obtained are in general agreement with previously reported data, but differ with respect to ion ratio dispersions. A lack of sharp clustering in the data indicates that none of the detected particles can be characterized as single mineral grains; an abundant glass content in the solids may be indicated. The best match of the distribution of Fe/(Fe+Mg) is with interplanetary particles containing high temperature, Mg-rich silicates dominated by anhydrous minerals, so that Comet Halley may be a mixture of ice and high-temperature anhydrous minerals.

How Tiny Collisions Shape Mercury

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

If space rocks are unpleasant to encounter, space dust isnt much better. Mercurys cratered surface tells of billions of years of meteoroid impacts but its thin atmosphere is what reveals its collisional history with smaller impactors. Now new research is providing a better understanding of what were seeing.Micrometeoroids Ho!The inner solar system is bombarded by micrometeoroids, tiny particles of dust (on the scale of a tenth of a millimeter) emitted by asteroids and comets as they make their closest approach to the Sun. This dust doesnt penetrateEarths layers of atmosphere, but the innermost planet of our solar system, Mercury, doesnt have this convenient cushioning.Just as Mercury is affected by the impacts of large meteoroids, its also shaped by the many smaller-scale impacts it experiences. These tiny collisions are thought to vaporize atoms and molecules from the planets surface, which quickly dissociate. This process adds metals to Mercurys exosphere, the planets extremely tenuous atmosphere.Modeling PopulationsDistribution of the directions from which meteoroids originate before impacting Mercurys surface, as averaged over its entire orbit. Local time of 12 hr corresponds to the Sun-facing side. A significant asymmetry is seen between the dawn (6 hrs) and dusk (18 hrs) rates. [Pokorn et al. 2017]The metal distribution in the exosphere provides a way for us to measure the effect of micrometeoroid impacts on Mercury but this only works if we have accurate models of the process. A team of scientists led by Petr Pokorn (The Catholic University of America and NASA Goddard SFC) has now worked to improve our picture of micrometeoroid impact vaporization on Mercury.Pokorn and collaborators argue that two meteoroid populations Jupiter-family comets (short-period) and Halley-type comets (long-period) contribute the dust for the majority of micrometeoroid impacts on Mercury. The authors model the dynamics and evolution of these two populations, reproducing the distribution of directions from which micrometeoroids strike Mercury during its yearly orbit.Schematic of Mercury in its orbit around the Sun. The dawn side leads the orbital motion, while the dusk side trails it.Geometry of an OrbitMercurys orbit is unique in our solar system: it circles the Sun twice for every three rotations on its own axis so if you were on Mercury, youd see a single day pass over the span of two years. As with all prograde planets, the edge leading the Mercurys orbit marks the dawn terminator, while the edge trailing the planets orbital motion marks the dusk terminator.Pokorn and collaborators find a significant asymmetry in the impact vaporization that occurs on Mercurys dawn side versus its dusk side. This is due to impact geometry (since the dusk side is shielded from impacts in the direction of motion) and seasonal variation of the dust/meteoroid environment around the planet. The authors show that the source of impact vaporization shifts toward the nightside as Mercury approaches aphelion, and toward the dayside when the planet approaches the Sun.Importance of Long-Period CometsSeasonal variations of the relative vaporization rate from the authors model (black line) compared to measurements of Mercurys exospheric abundance of Ca. The contribution of long-period comets is shown by the blue line. [Pokorn et al. 2017]The dawn/dusk asymmetry and the seasonal variations predicted by the model are all nicely consistent NASAs MESSENGER spacecraft observations of the metal distribution in Mercurys exosphere.What makes Pokorn and collaborators model work so well? Their inclusion of the long-period, Halley-type comets is key: the high impact velocity of the micrometeoroids produced by this family play a significant role in shaping the impact vaporization rate of Mercurys surface.This work successfully demonstrates that we can use measurements of Mercurys exosphere as a unique tool to constrain the dust population in the inner solar system.CitationPetr Pokorn et al 2017 ApJL 842 L17. doi:10.3847/2041-8213/aa775d

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

Carbon-rich particles in Comet Halley

NASA Technical Reports Server (NTRS)

Clark, Benton C.

1990-01-01

The majority of particles detected in the coma of Comet Halley contain carbon atoms; many of these grains appear to consist preponderately or only of light elements. These light-element particles may be composed of organic compounds. Of the possible combinations of the elements hydrogen, carbon, nitrogen, and oxygen, numerous examples are found of particles containing the combinations (H,C,O,N), (H,C,N), (H,C,O), and (H,C). These results may bear on the recent detection of polyoxymethylene fragments, the observation of cyanojets (CN patterns consistent with release from solid particles), the possible presence of cyanopolyacetylenes or HCN polymer and the make-up of the CHON particles. If cometary matter could reach the surface of the earth without complete disruption, these diverse organic and mixed particles could create unique microenvironments, possibly with significant or even pivotal prebiotic chemical activity. Here a speculative insight into possible relationships between carbon in comets and carbon in life is given, as well as a brief overview of on-going analysis of data from the highly successful Particle Impact Analyzer (PIA) experiment flown on the Giotto spacecraft for the flyby of Comet Halley (development and implementation of PIA was under the direction of J. Kissel of the Max Planck Institute for Kernphysik, Heidelberg). PIA is a time-of-flight analyzer which obtains mass spectra of ions from individual particles impacting on a Pt-Ag foil target within the instrument.

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.

Recent researches into solid bodies and magnetic fields in the solar system; Proceedings of the Topical Meeting and Symposium, Ottawa, Canada, May 16-June 2, 1982

NASA Technical Reports Server (NTRS)

Vette, J. I. (Editor); Runcorn, S. K. (Editor); Gruen, E. (Editor); Mcdonnell, J. A. M.

1982-01-01

Topics discussed include the magnetic history of the early solar system, impact processes in solid bodies (e.g., meteoroids and asteroids), and topics related to cometary missions. The section devoted to cometary missions lays particular stress on missions to Comet Halley; attention is given to such aspects of these missions as the investigation of hypervelocity impact on the Giotto Halley mission dust shield, the detection of energetic cometary and solar particles by the EPONA instrument on the Giotto mission, the dust hazard near Comet Halley in regard to the Vega project, and cometary ephemerides for spacecraft flyby missions.

Geochemical evidence for a comet shower in the late Eocene

USGS Publications Warehouse

Farley, K.A.; Montanari, A.; Shoemaker, E.M.; Shoemaker, C.S.

1998-01-01

Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ~1 My before and ended ~1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ~36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.

The dust distribution within the inner coma of comet P/Halley 1982i - Encounter by Giotto's impact detectors

NASA Technical Reports Server (NTRS)

Mcdonnell, J. A. M.; Evans, G. C.; Evans, S. T.; Alexander, W. M.; Burton, W. M.; Firth, J. G.; Bussoletti, E.; Grard, R. J. L.; Hanner, M. S.; Sekanina, Z.

1987-01-01

Analyses are presented of Giotto's Dust Impact Detection System experiment measurements of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on March 13 and 14, 1986. Ground-based CCD imagery of the inner coma dust continuum at the time of the encounter are used to derive the area of grains intercepted by Giotto. Data obtained at large masses show clear evidence of a decrease in the mass distribution index at these masses within the coma; it is shown that such a value of the mass index can furnish sufficient mass for consistency with an observed deceleration.

Deep Impact on Its Way

NASA Technical Reports Server (NTRS)

2005-01-01

This Jan. 13 photograph was taken by Mt Palomar's 200-inch telescope as the Deep Impact spacecraft was at a distance of about 260,000 kilometers (163,000 miles) from Earth and moving at a speed of about 16,000 kilometers per hour (10,000 miles per hour). The high speed of the spacecraft causes it to appear as a long streak across the sky in the constellation Virgo during the 10-minute exposure time of the image.

The spacecraft will travel to comet Tempel 1 and release an impactor, creating a crater on the surface of the comet. Scientists believe the exposed materials may give clues to the formation of our solar system.

Before the Deep Impact Collision

NASA Image and Video Library

2011-02-18

This series of images shows the area where NASA Deep Impact probe collided with the surface of comet Tempel 1 in 2005. The view zooms in as the images progress from top left to right, and then bottom left to right.

48 CFR 252.232-7010 - Levies on Contract Payments.

Code of Federal Regulations, 2010 CFR

2010-10-01

... amount of tax debt. (b) When a levy is imposed on a payment under this contract and the Contractor... notify the IRS to attempt to resolve the tax situation. (d) Any DoD determination under this clause is...

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.

Observation of asteroid 2013 TV135 supports my idea that a new impaction will come in 20 years

NASA Astrophysics Data System (ADS)

Cao, Dayong

2014-03-01

Asteroid 2013 TV135 who will impact in 2023 was newly discovered by Ukrainian astronomers in 2013. It supports my idea that a new impaction will come in 20 years. http://www.nasa.gov/mission_pages/asteroids/news/asteroid20131017.html, http://meetings.aps.org/link/BAPS.2011.DFD.LA.24, http://meetings.aps.org/link/BAPS.2012.APR.K1.78, http://meetings.aps.org/link/BAPS.2013.APR.S2.14. The Sun's companion-dark hole, which is made of dark matter seasonal took its dark comets belt, dark matter, dark lives, and the pressed asteroids belt to impact near our earth. These impactions and dark matter's killers caused seasonal extinctions and produced new species. By many dark comets and asteroids impacting, the dark impaction model is a high probability impaction model; the impaction would not change the orbit of the invisible dark hole, so that it could keep accurate periodicity impactions. With the space-time center, the dark hole system is a negative Einstein's model by ``mass-energy coordinate.'' Sun and Dark hole build up the balance system. Through studying the model, the rule of the impaction can be calculated. Avoid Earth Extinction Association.

Modeling the Deep Impact Near-nucleus Observations of H2O and CO2 in Comet 9P/Tempel 1 Using Asymmetric Spherical Coupled Escape Probability

NASA Astrophysics Data System (ADS)

Gersch, Alan M.; A’Hearn, Michael F.; Feaga, Lori M.

2018-04-01

We have applied our asymmetric spherical adaptation of Coupled Escape Probability to the modeling of optically thick cometary comae. Expanding on our previously published work, here we present models including asymmetric comae. Near-nucleus observations from the Deep Impact mission have been modeled, including observed coma morphology features. We present results for two primary volatile species of interest, H2O and CO2, for comet 9P/Tempel 1. Production rates calculated using our best-fit models are notably greater than those derived from the Deep Impact data based on the assumption of optically thin conditions, both for H2O and CO2 but more so for CO2, and fall between the Deep Impact values and the global pre-impact production rates measured at other observatories and published by Schleicher et al. (2006), Mumma et al. (2005), and Mäkinen et al. (2007).

Cometary delivery of organic molecules to the early earth

NASA Technical Reports Server (NTRS)

Chyba, Christopher F.; Thomas, Paul J.; Sagan, Carl; Brookshaw, Leigh

1990-01-01

It has long been speculated that earth accreted prebiotic organic molecules important for the origins of life from impacts of carbonaceous asteroids and comets during the period of heavy bombardment 4.5 x 10 to the 9th to 3.8 x 10 to the 9th years ago. A comprehensive treatment of comet-asteroid interaction with the atmosphere, surface impact, and resulting organic pyrolysis demonstrates that organics will not survive impacts at velocities greater than about 10 kilometers per second and that even comets and asteroids as small as 100 meters in radius cannot be aerobraked to below this velocity in 1-bar atmospheres. However, for plausible dense (10-bar carbon dioxide) early atmospheres, it is found that 4.5 x 10 to the 9th years ago earth was accreting intact cometary organics at a rate of at least about 10 to the 6th to 10 to the 7th kilograms per year, a flux that thereafter declined with a half-life of about 10 to the 8th years. These results may be put in context by comparison with terrestrial oceanic and total biomasses, about 3 x 10 to the 12th kilograms and about 6 x 10 to the 14th kilograms, respectively.

Special Spotlight: Levi A. Garraway, M.D., Ph.D.

Cancer.gov

Dr. Levi A. Garraway, a former CRCHD CURE trainee, received the prestigious Jane Cooke Wright Lectureship Award at the 2014 meeting of the American Association for Cancer Research and presented "The Cancer Genome in Biology, Therapy, and Drug Resistance.”

Impact cratering through geologic time

USGS Publications Warehouse

Shoemaker, E.M.; Shoemaker, C.S.

1998-01-01

New data on lunar craters and recent discoveries about craters on Earth permit a reassessment of the bombardment history of Earth over the last 3.2 billion years. The combined lunar and terrestrial crater records suggest that the long-term average rate of production of craters larger than 20 km in diameter has increased, perhaps by as much as 60%, in the last 100 to 200 million years. Production of craters larger than 70 km in diameter may have increased, in the same time interval, by a factor of five or more over the average for the preceding three billion years. A large increase in the flux of long-period comets appears to be the most likely explanation for such a long-term increase in the cratering rate. Two large craters, in particular, appear to be associated with a comet shower that occurred about 35.5 million years ago. The infall of cosmic dust, as traced by 3He in deep sea sediments, and the ages of large craters, impact glass horizons, and other stratigraphic markers of large impacts seem to be approximately correlated with the estimated times of passage of the Sun through the galactic plane, at least for the last 65 million years. Those are predicted times for an increased near-Earth flux of comets from the Oort Cloud induced by the combined effects of galactic tidal perturbations and encounters of the Sun with passing stars. Long-term changes in the average comet flux may be related to changes in the amplitude of the z-motion of the Sun perpendicular to the galactic plane or to stripping of the outer Oort cloud by encounters with large passing stars, followed by restoration from the inner Oort cloud reservoir.

Proposal to conserve the name Bipolaris against Cochliobolus (Ascomycota: Pleosporales: Pleosporaceae)

USDA-ARS?s Scientific Manuscript database

The fungal genera Bipolaris Shoemaker and Cochliobolus Drechsler have been applied to economically important plant pathogens causing diseases of cereal crops worldwide, especially southern corn leaf blight. There are major accounts of these genera including those incorporating molecular phylogenetic...

Hartley 2 in 3-D

NASA Image and Video Library

2010-11-18

This 3-D image shows the region where NASA Deep Impact mission sent a probe into the surface of comet Tempel 1 in 2005. This picture was taken six years after the Deep Impact collision. 3D glasses are necessary to view this image.

HT-COMET: a novel automated approach for high throughput assessment of human sperm chromatin quality.

PubMed

Albert, Océane; Reintsch, Wolfgang E; Chan, Peter; Robaire, Bernard

2016-05-01

Can we make the comet assay (single-cell gel electrophoresis) for human sperm a more accurate and informative high throughput assay? We developed a standardized automated high throughput comet (HT-COMET) assay for human sperm that improves its accuracy and efficiency, and could be of prognostic value to patients in the fertility clinic. The comet assay involves the collection of data on sperm DNA damage at the level of the single cell, allowing the use of samples from severe oligozoospermic patients. However, this makes comet scoring a low throughput procedure that renders large cohort analyses tedious. Furthermore, the comet assay comes with an inherent vulnerability to variability. Our objective is to develop an automated high throughput comet assay for human sperm that will increase both its accuracy and efficiency. The study comprised two distinct components: a HT-COMET technical optimization section based on control versus DNAse treatment analyses ( ITALIC! n = 3-5), and a cross-sectional study on 123 men presenting to a reproductive center with sperm concentrations categorized as severe oligozoospermia, oligozoospermia or normozoospermia. Sperm chromatin quality was measured using the comet assay: on classic 2-well slides for software comparison; on 96-well slides for HT-COMET optimization; after exposure to various concentrations of a damage-inducing agent, DNAse, using HT-COMET; on 123 subjects with different sperm concentrations using HT-COMET. Data from the 123 subjects were correlated to classic semen quality parameters and plotted as single-cell data in individual DNA damage profiles. We have developed a standard automated HT-COMET procedure for human sperm. It includes automated scoring of comets by a fully integrated high content screening setup that compares well with the most commonly used semi-manual analysis software. Using this method, a cross-sectional study on 123 men showed no significant correlation between sperm concentration and sperm DNA damage, confirming the existence of hidden chromatin damage in men with apparently normal semen characteristics, and a significant correlation between percentage DNA in the tail and percentage of progressively motile spermatozoa. Finally, the use of DNA damage profiles helped to distinguish subjects between and within sperm concentration categories, and allowed a determination of the proportion of highly damaged cells. The main limitations of the HT-COMET are the high, yet indispensable, investment in an automated liquid handling system and heating block to ensure accuracy, and the availability of an automated plate reading microscope and analysis software. This standardized HT-COMET assay offers many advantages, including higher accuracy and evenness due to automation of sensitive steps, a 14.4-fold increase in sample analysis capacity, and an imaging and scoring time of 1 min/well. Overall, HT-COMET offers a decrease in total experimental time of more than 90%. Hence, this assay constitutes a more efficient option to assess sperm chromatin quality, paves the way to using this assay to screen large cohorts, and holds prognostic value for infertile patients. Funded by the CIHR Institute of Human Development, Child and Youth Health (IHDCYH; RHF 100625). O.A. is a fellow supported by the Fonds de la Recherche du Québec - Santé (FRQS) and the CIHR Training Program in Reproduction, Early Development, and the Impact on Health (REDIH). B.R. is a James McGill Professor. The authors declare no conflicts of interest. © The Author 2016. 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.

78 FR 32258 - Proposed Information Collection Activity; Comment Request

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-29

... DEPARTMENT OF HEALTH AND HUMAN SERVICES Administration for Children and Families Proposed... Levy (FAST Levy). OMB No.: New Collection. Description: State IV-D child support enforcement agencies... institutions. To assist states in fulfilling this statutory requirement the federal Office of Child Support...

Three component plasma electron distribution in the intermediate ionized coma of Comet Giacobini-Zinner

NASA Astrophysics Data System (ADS)

Zwickl, R. D.; Baker, D. N.; Bame, S. J.; Feldman, W. C.; Fuselier, S. A.; Huebner, W. F.; McComas, D. J.; Young, D. T.

1986-04-01

The observation of three distinct components of the electron distribution function measured in the intermediate ionized coma (IIC) and plasma tail of Comet Giacobini-Zinner is reported. It is believed that the cold component represents electrons produced close to the comet nucleus by ionization of cometary matter and subsequent cooling by Coulomb collisions. The second component also appears to be composed of electrons produced by photoionization of cometary neutrals, but sufficiently far from the nucleus that the distributions are largely unaffected by Coulomb interactions. The hot component is probably a population of electrons originating in the solar wind. Throughout the IIC, the electrostatic potential of the spacecraft was very low (less than 0.8 eV), implying that ICE generated very little impact-produced plasma during its passage.

The Degradational History of Endeavour Crater, Mars

NASA Technical Reports Server (NTRS)

Grant, J. A.; Parker, T. J.; Crumpler, L. S.; Wilson, S. A.; Golombek, M. P.; Mittlefehldt, D. W.

2015-01-01

Endeavour crater (2.28 deg S, 354.77 deg E) is a Noachian-aged 22 km-diameter impact structure of complex morphology in Meridiani Planum. The degradation state of the crater has been studied using Mars Reconnaissance Orbiter and Opportunity rover data. Exposed rim segments rise approximately 10 m to approximately 100 m above the level of the embaying Burns Formation and the crater is 200-500 m deep with the southern interior wall exposing over approximately 300 m relief. Both pre-impact rocks (Matijevic Formation) and Endeavour impact ejecta (Shoemaker Formation) are present at Cape York, but only the Shoemaker crops out (up to approximately 140 m) along the rim segment from Murray Ridge to Cape Tribulation. Study of pristine complex craters Bopolu and Tooting, and morphometry of other martian complex craters, enables us to approximate Endeavour's pristine form. The original rim likely averaged 410 m (+/-)200 m in elevation and a 250-275 m section of ejecta ((+/-)50-60 m) would have composed a significant fraction of the rim height. The original crater depth was likely between 1.5 km and 2.2 km. Comparison between the predicted original and current form of Endeavour suggests approximately 100-200 m rim lowering that removed most ejecta in some locales (e.g., Cape York) while thick sections remain elsewhere (e.g., Cape Tribulation). Almost complete removal of ejecta at Cape York and minimal observable offset across fractures indicates current differences in rim relief are not solely due to original rim relief. Rim segments are embayed by approximately 100-200 m thickness of plains rocks outside the crater, but thicker deposits lie inside the crater. Ventifact textures confirm ongoing eolian erosion with the overall extent difficult to estimate. Analogy with degraded Noachian-aged craters south of Endeavour, however, suggests fluvial erosion dominated rim degradation in the Noachian and was likely followed by approximately 10s of meters modification by alternate processes. Such degradation is consistent with 1) the interpretation of a pediment on the rim flanks of Endeavour, 2) the formation of features such as Marathon Valley, 3) the nearly complete removal of ejecta at Cape York, 4) preservation of a thicker section of ejecta at Cape Tribulation and perhaps, 5) the origin of some gaps in the rim around the crater. A paucity of debris shed from the rim indicates most degradation occurred prior to embayment by the plains rocks.

Zimbabwe's national AIDS levy: A case study.

PubMed

Bhat, Nisha; Kilmarx, Peter H; Dube, Freeman; Manenji, Albert; Dube, Medelina; Magure, Tapuwa

2016-01-01

We conducted a case study of the Zimbabwe National AIDS Trust Fund ('AIDS Levy') as an approach to domestic government financing of the response to HIV and AIDS. Data came from three sources: a literature review, including a search for grey literature, review of government documents from the Zimbabwe National AIDS Council (NAC), and key informant interviews with representatives of the Zimbabwean government, civil society and international organizations. The literature search yielded 139 sources, and 20 key informants were interviewed. Established by legislation in 1999, the AIDS Levy entails a 3% income tax for individuals and 3% tax on profits of employers and trusts (which excluded the mining industry until 2015). It is managed by the parastatal NAC through a decentralized structure of AIDS Action Committees. Revenues increased from inception to 2006 through 2008, a period of economic instability and hyperinflation. Following dollarization in 2009, annual revenues continued to increase, reaching US$38.6 million in 2014. By policy, at least 50% of funds are used for purchase of antiretroviral medications. Other spending includes administration and capital costs, HIV prevention, and monitoring and evaluation. Several financial controls and auditing systems are in place. Key informants perceived the AIDS Levy as a 'homegrown' solution that provided country ownership and reduced dependence on donor funding, but called for further increased transparency, accountability, and reduced administrative costs, as well as recommended changes to increase revenue. The Zimbabwe AIDS Levy has generated substantial resources, recently over US$35 million per year, and signals an important commitment by Zimbabweans, which may have helped attract other donor resources. Many key informants considered the Zimbabwe AIDS Levy to be a best practice for other countries to follow.

Impact of Xist RNA on chromatin modifications and transcriptional silencing maintenance at different stages of imprinted X chromosome inactivation in vole Microtus levis.

PubMed

Shevchenko, Alexander I; Grigor'eva, Elena V; Medvedev, Sergey P; Zakharova, Irina S; Dementyeva, Elena V; Elisaphenko, Eugeny A; Malakhova, Anastasia A; Pavlova, Sophia V; Zakian, Suren M

2018-03-01

In vole Microtus levis, cells of preimplantation embryo and extraembryonic tissues undergo imprinted X chromosome inactivation (iXCI) which is triggered by a long non-coding nuclear RNA, Xist. At early stages of iXCI, chromatin of vole inactive X chromosome is enriched with the HP1 heterochromatin-specific protein, trimethylated H3K9 and H4K20 attributable to constitutive heterochromatin. In the study, using vole trophoblast stem (TS) cells as a model of iXCI, we further investigated chromatin of the inactive X chromosome of M. levis and tried to find out the role of Xist RNA. We demonstrated that chromatin of the inactive X chromosome in vole TS cells also contained the SETDB1 histone methyltransferase and KAP1 protein. In addition, we observed that Xist RNA did not contribute significantly to maintenance of X chromosome inactive state during iXCI in vole TS cells. Xist repression affected neither transcriptional silencing caused by iXCI nor maintenance of trimethylated H3K9 and H4K20 as well as HP1, KAP1, and SETDB1 on the inactive X chromosome. Moreover, the unique repertoire of chromatin modifications on the inactive X chromosome in vole TS cells could be disrupted by a chemical compound, DZNep, and then restored even in the absence of Xist RNA. However, Xist transcript was necessary for recruitment of an additional repressive histone modification, trimethylated H3K27, to the inactive X chromosome during vole TS cell differentiation.

The final year of the Rosetta mission

NASA Astrophysics Data System (ADS)

Accomazzo, Andrea; Ferri, Paolo; Lodiot, Sylvain; Pellon-Bailon, Jose-Luis; Hubault, Armelle; Urbanek, Jakub; Kay, Ritchie; Eiblmaier, Matthias; Francisco, Tiago

2017-07-01

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. 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. Originally foreseen till the end of 2015, the mission was extended for another nine months to follow the comet on its outbound arc of the orbit. In view of the acquired experience and of the approaching end of mission the spacecraft was flown at much closer distances from the nucleus so that the scientific instruments had the chance to perform unique measurements. Following this phase of very close orbits, on the 30th of September 2016 Rosetta was set on a collision course trajectory with the comet to terminate the mission with a controlled impact. This paper describes the details of the extended mission phase and the issues encountered during these months. It also includes the changes implemented on the spacecraft and in the operations concept to optimise the remaining mission time. The paper also includes the lessons learned from this unique and complex mission phase.

An Optimal Mitigation Strategy Against the Asteroid Impact Threat with Short Warning Time

NASA Technical Reports Server (NTRS)

Wie, Bong; Barbee, Brent; Pitz, Alan; Kaplinger, Brian; Hawkins, Matt; Winkler, Tim; Premaratne, Pavithra; Vardaxis, George; Lyzhoft, Joshua; Zimmerman, Ben

2015-01-01

To develop an innovative yet practically implementable mitigation technique for the most probable impact threat of an asteroid or comet with short warning time (i.e., when we don't have sufficient warning times for a deflection mission).

The effects of urbanization on Lepomis macrochirus using the comet assay

EPA Science Inventory

Urbanization has been linked to increased concentrations of polycyclic aromatic hydrocarbons in natural waterways. This study was designed to examine the impact of urbanization and a wastewater treatment plant by investigating the impact on field-collected bluegill (Lepomis macr...

The Johnson Space Center Experimental Impact Lab: Contributions Toward Understanding the Evolution of the Solar System

NASA Technical Reports Server (NTRS)

See, T. H.; Montes, R.

2012-01-01

Impact is the most common and only weathering phenomenon affecting all the planetary bodies (e.g., planets, satellites, asteroids, comets, etc.) in the solar system. NASA Johnson Space Center s Experimental Impact Laboratory (EIL) includes three accelerators that are used in support of research into the effects of impact on the formation and evolution of the solar system. They permit researchers to study a wide variety of phenomena associated with high-velocity impacts into a wide range of geologic targets and materials relevant to astrobiological studies. By studying these processes, researchers can investigate the histories and evolution of planetary bodies and the solar system as a whole. While the majority of research conducted in the EIL addresses questions involving planetary impacts, work involving spacecraft components has been performed on occasion. An example of this is the aerogel collector material flown on the Stardust spacecraft that traveled to Comet Wild-2. This capture medium was tested and flight qualified using the 5 mm Light-Gas Gun located in the EIL.

A Novel Porosity Model for Use in Hydrocode Simulations

NASA Technical Reports Server (NTRS)

Wuennemann, K.; Collins, G. S.; Melosh, H. J.

2005-01-01

Introduction: Numerical modeling of impact cratering has reached a high degree of sophistication; however, the treatment of porous materials still poses a large problem in hydrocode calculations. Porosity plays only a minor role in the formation of large craters on most planetary objects, but impacts on comets are believed to be highly affected by the presence of porosity, which may be as much as 80%. The upcoming Deep Impact Mission (launched January 2005) will provide more detailed data about the composition of a comet (Tempel 1) by shooting a approx.370 kg projectile onto the surface of its nucleus. The numerical simulations of such impact events requires an appropriate model for how pore space in the comet is crushed out during the violent initial stage of the impact event. Most hydro-codes compute the pressure explicitly using an "equation of state" (EOS) for each material, which relates changes in density and internal energy to changes in pressure. The added complication introduced by porosity is that changes in a material s density are due to both the closing of pore space (compaction) and compression of the matrix. The amount of resistance to volume change and the amount of irreversible work done during these two processes is very different; it is far easier to compact a porous material sample than to compress a non-porous sample of the same material. As an alternative to existing porosity models, like the Pdot(alpha) model [1], we present a novel approach for dealing with the compaction of porosity in hydrocode calculations.

Research Outcomes and Their Applications.

ERIC Educational Resources Information Center

Gagne, Robert M.

1984-01-01

Reviews articles by Shoemaker, Morell, and Smith that appear in this issue and summarizes their suggestions for translating research into practice. Other, more aggressive approaches--the "survival gambit," the "cost-effectiveness ploy," the "younger-generation-is-going-to-hell argument," and the "infiltration route"--are suggested. (MBR)

The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros

USGS Publications Warehouse

Veverka, J.; Farquhar, B.; Robinson, M.; Thomas, P.; Murchie, S.; Harch, A.; Antreasian, P.G.; Chesley, S.R.; Miller, J.K.; Owen, W.M.; Williams, B.G.; Yeomans, D.; Dunham, D.; Heyler, G.; Holdridge, M.; Nelson, R.L.; Whittenburg, K.E.; Ray, J.C.; Carcich, B.; Cheng, A.; Chapman, C.; Bell, J.F.; Bell, M.; Bussey, B.; Clark, B.; Domingue, D.; Gaffey, M.J.; Hawkins, E.; Izenberg, N.; Joseph, J.; Kirk, R.; Lucey, P.; Malin, M.; McFadden, L.; Merline, W.J.; Peterson, C.; Prockter, L.; Warren, J.; Wellnitz, D.

2001-01-01

The NEAR-Shoemaker spacecraft was designed to provide a comprehensive characterization of the S-type asteroid 433 Eros (refs 1-3), an irregularly shaped body with approximate dimensions of 34 ?? 13 ?? 13 km. Following the completion of its year-long investigation, the mission was terminated with a controlled descent to its surface, in order to provide extremely high resolution images. Here we report the results of the descent on 12 February 2001, during which 70 images were obtained. The landing area is marked by a paucity of small craters and an abundance of 'ejecta blocks'. The properties and distribution of ejecta blocks are discussed in a companion paper. The last sequence of images reveals a transition from the blocky surface to a smooth area, which we interpret as a 'pond'. Properties of the 'ponds' are discussed in a second companion paper. The closest image, from an altitude of 129 m, shows the interior of a 100-m-diameter crater at 1-cm resolution.

China's "market economics in command": footwear workers' health in jeopardy.

PubMed

Chen, M S; Chan, A

1999-01-01

This study of occupational safety and health (OSH) problems in the footwear industry in China, the world's largest shoemaker, is based on four years of research in China supplemented by research in Taiwan, Australia, and the United States. With the advent of the economic reforms of the early 1980s, the Chinese state is being driven by an economic imperative under which the profit motive overrides other concerns, causing a deterioration in OSH conditions. Footwear workers are being exposed to high levels of benzene, toluene, and other toxic solvents contained in the adhesives used in the shoe-making process. Many workers have been afflicted with aplastic anemia, leukemia, and other health problems. Most of China's current permissible exposure limits to toxins are either outdated or underenforced. As a result, the Chinese state's protection of footwear workers' health is inadequate. The article aims to draw the attention of the international OSH community to the importance of setting specific exposure standards for the footwear industry worldwide.