A Post-Stardust Mission View of Jupiter Family Comets

NASA Technical Reports Server (NTRS)

Zolensky, M.

2011-01-01

Before the Stardust Mission, many persons (including the mission team) believed that comet nuclei would be geologically boring objects. Most believed that comet nucleus mineralogy would be close or identical to the chondritic interplanetary dust particles (IDPs), or perhaps contain mainly amorphous nebular condensates or that comets might even be composed mainly of preserved presolar material [1]. Amazingly, the results for Comet Wild 2 (a Jupiter class comet) were entirely different. Whether this particular comet will ultimately be shown to be typical or atypical will not be known for a rather long time, so we describe our new view of comets from the rather limited perspective of this single mission.

OpenComet: An automated tool for comet assay image analysis

PubMed Central

Gyori, Benjamin M.; Venkatachalam, Gireedhar; Thiagarajan, P.S.; Hsu, David; Clement, Marie-Veronique

2014-01-01

Reactive species such as free radicals are constantly generated in vivo and DNA is the most important target of oxidative stress. Oxidative DNA damage is used as a predictive biomarker to monitor the risk of development of many diseases. The comet assay is widely used for measuring oxidative DNA damage at a single cell level. The analysis of comet assay output images, however, poses considerable challenges. Commercial software is costly and restrictive, while free software generally requires laborious manual tagging of cells. This paper presents OpenComet, an open-source software tool providing automated analysis of comet assay images. It uses a novel and robust method for finding comets based on geometric shape attributes and segmenting the comet heads through image intensity profile analysis. Due to automation, OpenComet is more accurate, less prone to human bias, and faster than manual analysis. A live analysis functionality also allows users to analyze images captured directly from a microscope. We have validated OpenComet on both alkaline and neutral comet assay images as well as sample images from existing software packages. Our results show that OpenComet achieves high accuracy with significantly reduced analysis time. PMID:24624335

OpenComet: an automated tool for comet assay image analysis.

PubMed

Gyori, Benjamin M; Venkatachalam, Gireedhar; Thiagarajan, P S; Hsu, David; Clement, Marie-Veronique

2014-01-01

Reactive species such as free radicals are constantly generated in vivo and DNA is the most important target of oxidative stress. Oxidative DNA damage is used as a predictive biomarker to monitor the risk of development of many diseases. The comet assay is widely used for measuring oxidative DNA damage at a single cell level. The analysis of comet assay output images, however, poses considerable challenges. Commercial software is costly and restrictive, while free software generally requires laborious manual tagging of cells. This paper presents OpenComet, an open-source software tool providing automated analysis of comet assay images. It uses a novel and robust method for finding comets based on geometric shape attributes and segmenting the comet heads through image intensity profile analysis. Due to automation, OpenComet is more accurate, less prone to human bias, and faster than manual analysis. A live analysis functionality also allows users to analyze images captured directly from a microscope. We have validated OpenComet on both alkaline and neutral comet assay images as well as sample images from existing software packages. Our results show that OpenComet achieves high accuracy with significantly reduced analysis time.

The Archive of the Amateur Observation Network of the International Halley Watch. Volume 1; Comet Giacobini-Zinner

NASA Technical Reports Server (NTRS)

Edberg, Stephen J. (Editor)

1996-01-01

The International Halley Watch (IHW) was organized for the purpose of gathering and archiving the most complete record of the apparition of a comet, Comet Halley (1982i = 1986 III = 1P/Halley), ever compiled. The redirection of the International Cometary Explorer (ICE), toward Comet Giacobini-Zinner (1984e = 1985 XIII = 21P/Giacobini-Zinner) prompted the initiation of a formal watch on that comet. All the data collected on P/Giacobini-Zinner and P/Halley have been published on CD-ROM in the Comet Halley Archive. This document contains a printed version of the archive data, collected by amateur astronomers, on these two comets. Volume 1 contains the Comet Giacobini-Zinner data archive and Volume 2 contains the Comet Halley archive. Both volumes include information on how to read the data in both archives, as well as a history of both comet watches (including the organizing of the network of astronomers and lessons learned from that experience).

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

Comets and the Stardust Mission

ScienceCinema

LLNL - University of California Television

2017-12-09

The occasional appearance of comets has awed humans throughout history. But how much do we really know about comets? Did a comet kill the dinosaurs? And, what can comets tell us about our own ancient history? With comet dust from NASA's Stardust mission, scientists like Hope Ishii, a Research Scientist at Lawrence Livermore National Laboratory, are beginning to answer these questions. She and high school teacher Tom Shefler look at how comets formed, their role in the Earth's history and the clues about what happened over 4 billion years ago. Series: Science on Saturday [5/2008] [Science] [Show ID: 14492

Comets and the Stardust Mission

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

LLNL - University of California Television

2008-05-16

The occasional appearance of comets has awed humans throughout history. But how much do we really know about comets? Did a comet kill the dinosaurs? And, what can comets tell us about our own ancient history? With comet dust from NASA's Stardust mission, scientists like Hope Ishii, a Research Scientist at Lawrence Livermore National Laboratory, are beginning to answer these questions. She and high school teacher Tom Shefler look at how comets formed, their role in the Earth's history and the clues about what happened over 4 billion years ago. Series: Science on Saturday [5/2008] [Science] [Show ID: 14492

Development and characteristics of Mechanical Porous Ambient Comet Simulants as comet surface analogs

NASA Astrophysics Data System (ADS)

Carey, Elizabeth M.; Peters, Gregory H.; Choukroun, Mathieu; Chu, Lauren; Carpenter, Emma; Cohen, Brooklin; Panossian, Lara; Zhou, Yu Meng; Sarkissian, Ani; Moreland, Scott; Shiraishi, Lori R.; Backes, Paul; Zacny, Kris; Green, Jacklyn R.; Raymond, Carol

2017-11-01

Comets are icy remnants of the Solar System formation, and as such contain some of the most primitive volatiles and organic materials. Sampling the surface of a comet is a high priority for the New Frontiers program. Planetary simulants are crucial to the development of adequate in situ instruments and sample acquisition systems. A high-fidelity comet surface simulant has been developed to support hardware design and development for one Comet Surface Sample Return tool, the BiBlade Comet Sampler. Mechanical Porous Ambient Comet Simulants (MPACS) can be manufactured to cover a wide range of desired physical properties, such as density and cone penetration resistance, and exhibit a brittle fracture mode. The structure of the MPACS materials is an aggregated composite structure of weakly-bonded grains of very small size (diameter ≤ 40 μm) that are most relevant to the structure of the surface of a comet nucleus.

The effect of multiple encounters on short period comet orbits

NASA Technical Reports Server (NTRS)

Lowrey, B. E.

1972-01-01

The observed orbital elements of short period comets are found to be consistent with the hypothesis of derivation from long period comets as long as two assumptions are made. First, the distribution of short period comets has been randomized by multiple encounters with Jupiter and second, the short period comets have lower velocities of encounter with Jupiter than is generally expected. Some 16% of the observed short period comets have lower encounter velocities than is allowed mathematically using Laplace's method. This may be due to double encounter processes with Jupiter and Saturn, or as a result of prolonged encounters. The distribution of unobservable short period comets can be inferred in part from the observed comets. Many have orbits between Jupiter and Saturn with somewhat higher inclinations than those with perihelions near the earth. Debris from those comets may form the major component of the zodiacal dust.

ACTIVITY OF 50 LONG-PERIOD COMETS BEYOND 5.2 au

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

Sárneczky, K.; Szabó, Gy. M.; Csák, B.

2016-12-01

Remote investigations of ancient matter in the solar system have traditionally been carried out through observations of long-period (LP) comets, which are less affected by solar irradiation than their short-period counterparts orbiting much closer to the Sun. Here we summarize the results of our decade-long survey of the distant activity of LP comets. We found that the most important separation in the data set is based on the dynamical nature of the objects. Dynamically new comets are characterized by a higher level of activity on average: the most active new comets in our sample can be characterized by Afρ valuesmore » >3–4, higher than those for our most active returning comets. New comets develop more symmetric comae, suggesting a generally isotropic outflow. In contrast to this, the comae of recurrent comets can be less symmetrical, ocassionally exhibiting negative slope parameters, which suggest sudden variations in matter production. The morphological appearance of the observed comets is rather diverse. A surprisingly large fraction of the comets have long, tenuous tails, but the presence of impressive tails does not show a clear correlation with the brightness of the comets.« less

Suicide Comet HD Video

NASA Image and Video Library

2010-03-16

Captured March 12, 2010 The SOHO spacecraft captured a very bright, sungrazing comet as it rocketed towards the Sun (Mar. 12, 2010) and was vaporized. This comet is arguably the brightest comet that SOHO has observed since Comet McNaught in early 2007. The comet is believed to belong to the Kreutz family of comets that broke up from a much larger comet many hundreds of years ago. They are known to orbit close to the Sun. A coronal mass ejection (CME) burst away from the Sun during the bright comet’s approach. Interestingly, a much smaller comet that preceded this one can be seen about half a day earlier on just about the identical route. And another pair of small comets followed the same track into the Sun after the bright one. Such a string of comets has never been witnessed before by SOHO. SOHO's C3 coronagraph instrument blocks out the Sun with an occulting disk; the white circle represents the size of the Sun. The planet Mercury can also be seen moving from left to right just beneath the Sun. To learn more and to download the video and still images go here: sohowww.nascom.nasa.gov/pickoftheweek/old/15mar2010/ Credit: NASA/GSFC/SOHO

The Comet Halley Handbook: An Observer's Guide. Second Edition.

ERIC Educational Resources Information Center

Yeomans, Donald K.

This handbook contains information on: (1) the orbit of comet Halley; (2) the expected physical behavior of comet Halley in 1985-1986, considering brightness estimates, coma diameters, and tail lengths; (3) observing conditions for comet Halley in 1985-1986; and (4) observing conditions for the dust tail of comet Halley in 1985-1986. Additional…

Observations of faint comets with the IUE

NASA Astrophysics Data System (ADS)

Festou, M.

1982-06-01

Spectral observations of eight comets, including seven periodic comets, made in the range 1150-3400 A with the IUE satellite are presented. Comet Bradfield, the sole nonperiodic comet observed, is found to exhibit strong OH and atomic hydrogen emissions from the decomposition of water, along with oxygen, carbon, sulfur, carbon disulfide, C2 and CO2(plus) emissions and a faint continuum due to dust at longer wavelengths. Comets Encke, Tuttle and Stefan-Oterma appear to have identical spectra in the UV, showing evidence of much gas, little dust and few ions (only CO2(plus) detected), and differing from comet Bradfield only in the lack of C2 emission. All eight comets observed by IUE, including Seargent, Meier, Borrelly and Panther, had the same chemical composition, consisting mainly of water with a few per mil or per cent CN, C2, C3 and CS. The water production rates of the periodic comets range from levels 6 times less to 11 times more than that of Comet Bradfield, which may be related to nuclear size or cometary age.

The Archive of the Amateur Observation Network of the International Halley Watch. Volume 2; Comet Halley

NASA Technical Reports Server (NTRS)

Edberg, Stephen J. (Editor)

1996-01-01

The International Halley Watch (IHW) was organized for the purpose of gathering and archiving the most complete record of the apparition of a comet, Halley's Comet (1982i = 1986 III = 1P/Halley), ever compiled. The redirection of the International Sun-Earth Explorer 3 (ISEE-3) spacecraft, subsequently renamed the International Cometary Explorer (ICE), toward Comet Giacobini- Zinner (1984e = 1985 XIII = 21P/Giacobini-Zinner) prompted the initiation of a formal watch on that comet. All the data collected on P/Giacobini-Zinner and P/Halley have been published on CD-ROM in the Comet Halley Archive. This document contains a printed version of the archive data, collected by amateur astronomers, on these two comets. Volume 1 contains the Comet Giacobini-Zinner data archive and Volume 2 contains the Comet Halley archive. Both volumes include information on how to read the data in both archives, as well as a history of both comet watches (including the organizing of the network of astronomers and lessons learned from that experience).

The Archive of the Amateur Observation Network of the International Halley Watch. Volume 1; Comet Giacobini-Zinner

NASA Technical Reports Server (NTRS)

Edberg, Stephen J. (Editor)

1966-01-01

The International Halley Watch (IHW) was organized for the purpose of gathering and archiving the most complete record of the apparition of a comet, Halley's Comet (1982i = 1986 III = 1P/Halley), ever compiled. The redirection of the International Sun-Earth Explorer 3 (ISEE-3) spacecraft, subsequently renamed the International Cometary Explorer (ICE), toward Comet Giacobini-Zinner (1984e = 1985 XIII = 21P/Giacobini-Zinner) prompted the initiation of a formal watch on that comet. All the data collected on P/Giacobini-Zinner and P/Halley have been published on CD-ROM in the Comet Halley Archive. This document contains a printed version of the archive data, collected by amateur astronomers, on these two comets. Volume 1 contains the Comet Giacobini-Zinner data archive and Volume 2 contains the Comet Halley archive. Both volumes include information on how to read the data in both archives, as well as a history of both comet watches (including the organizing of the network of astronomers and lessons learned from that experience).

Disappearance and disintegration of comets

NASA Technical Reports Server (NTRS)

Sekanina, Z.

1984-01-01

The present investigation has the objective to provide a summary of the existing evidence on the disappearance of comets and to draw conclusions regarding the physical processes involved in the disappearance. Information concerning the classification of evidence and the causes of apparent disappearance of comets is presented in a table. Attention is given to the dissipating comets, the headless sungrazing comet 1887 I, and the physical behavior of the dissipating comets and the related phenomena. It is found that all comets confined to the planetary region of the solar system decay on astronomically short time scales. However, only some of them appear to perish catastrophically. Some of the observed phenomena could be successfully interpreted. But little insight has been obtained into the character of the processes which the dissipating comets experience.

An Introduction to Comets and Their Origin.

ERIC Educational Resources Information Center

Chapman, Robert D.; Brandt, John C.

1985-01-01

Presents excerpts from "The Comet Book," a nontechnical primer on comets. Various topics discusses in these excerpts include such basic information about comets as their components, paths, and origins. (DH)

Competitive Memory Training (COMET) for OCD: a self-treatment approach to obsessions.

PubMed

Schneider, Brooke C; Wittekind, Charlotte E; Talhof, Alina; Korrelboom, Kees; Moritz, Steffen

2015-01-01

Competitive Memory Training (COMET) is a cognitive intervention that aims to change the maladaptive cognitive-emotional networks underlying obsessive-compulsive disorder (OCD). COMET has not been previously tried as a self-help intervention. The present study tested the preliminary feasibility, acceptability, and effectiveness of COMET for OCD implemented as a self-help intervention. Sixty-five participants with OCD recruited through online OCD self-help fora completed an online baseline assessment including measures of OCD symptoms, self-esteem, and depression. Participants were randomly assigned to either COMET or a wait-list control group. All participants were approached 4 weeks later to complete an online post-assessment. There was no evidence for a greater decline of OCD symptoms or depression under COMET. When analyses were limited to only those participants who reported reading the entire manual at least once, self-esteem was higher at post-assessment in the COMET group. Although 78.1% of patients in the COMET group rated it as appropriate for self-administration, only 56.5% performed COMET exercises regularly and 26.4% read the entire manual at least once. The feasibility and effectiveness of COMET as a self-help internet intervention for OCD was not supported in this study. Further work is needed to better understand if modifications to our implementation of COMET may yield improved outcomes.

Current ideas on the nature of comets

NASA Technical Reports Server (NTRS)

Rahe, J.

1984-01-01

The chemical composition, emission and line spectra, and structure of comet nuclei, cometary atmospheres, and comet tails are discussed. The role of ultraviolet and infrared astronomy in defining comets is examined.

Comet Halley Returns. A Teacher's Guide, 1985-1986.

ERIC Educational Resources Information Center

Chapman, Robert D.; Bondurant, R. Lynn, Jr.

This booklet was designed as an aid for elementary and secondary school teachers. It is divided into two distinct parts. Part I is a brief tutorial which introduces some of the most important concepts about comets. Areas addressed include: the historical importance of Comet Halley; how comets are found and names; cometary orbits; what Comet Halley…

Comet rendezvous mission study

NASA Technical Reports Server (NTRS)

Friedlander, A. L.; Wells, W. C.

1971-01-01

Four periodic comets with perihelia between 1980 and 1986 (Encke, d'Arrest, Kipff, and Halley) are used as candidates for the comet rendezvous mission study. All these comet apparitions are especially favorable for rendezvous missions, because of early earth-based comet recovery, good opportunities to view their activity from earth, and reasonable launch vehicle and trajectory requirements for nominal payloads.

Comet nucleus sample return mission

NASA Technical Reports Server (NTRS)

1983-01-01

A comet nucleus sample return mission in terms of its relevant science objectives, candidate mission concepts, key design/technology requirements, and programmatic issues is discussed. The primary objective was to collect a sample of undisturbed comet material from beneath the surface of an active comet and to preserve its chemical and, if possible, its physical integrity and return it to Earth in a minimally altered state. The secondary objectives are to: (1) characterize the comet to a level consistent with a rendezvous mission; (2) monitor the comet dynamics through perihelion and aphelion with a long lived lander; and (3) determine the subsurface properties of the nucleus in an area local to the sampled core. A set of candidate comets is discussed. The hazards which the spacecraft would encounter in the vicinity of the comet are also discussed. The encounter strategy, the sampling hardware, the thermal control of the pristine comet material during the return to Earth, and the flight performance of various spacecraft systems and the cost estimates of such a mission are presented.

Special Report: Chemistry of Comets.

ERIC Educational Resources Information Center

A'Hearn, Michael F.

1984-01-01

Discusses the chemistry of comets. How comets provide clues to the birth of the solar system, photolytic reactions on comets involving water, chemical modeling, nuclear chemistry, and research findings are among the areas considered. (JN)

Fab Five

NASA Image and Video Library

2010-11-04

This montage from NASA EPOXI mission shows the only five comets imaged up close with spacecraft. The comets vary in shape and size. Comet Hartley 2 is by far the smallest and the most active of small comets.

COMET-AR User's Manual: COmputational MEchanics Testbed with Adaptive Refinement

NASA Technical Reports Server (NTRS)

Moas, E. (Editor)

1997-01-01

The COMET-AR User's Manual provides a reference manual for the Computational Structural Mechanics Testbed with Adaptive Refinement (COMET-AR), a software system developed jointly by Lockheed Palo Alto Research Laboratory and NASA Langley Research Center under contract NAS1-18444. The COMET-AR system is an extended version of an earlier finite element based structural analysis system called COMET, also developed by Lockheed and NASA. The primary extensions are the adaptive mesh refinement capabilities and a new "object-like" database interface that makes COMET-AR easier to extend further. This User's Manual provides a detailed description of the user interface to COMET-AR from the viewpoint of a structural analyst.

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 gas production rate of periodic comet d'Arrest

NASA Technical Reports Server (NTRS)

Festou, Michel C.; Feldman, Paul D.; Ahearn, Michael F.

1992-01-01

Comet P/d'Arrest is a potential target for a rendezvous mission to a short period comet. Its light curve is rather peculiar, the comet being active only after perihelion passage. One apparition out of two is easy to observe from the ground. The 1995 apparition of the comet will offer a unique opportunity to characterize the outgassing properties of its nucleus.

Using the EUV to Weigh a Sun-Grazing Comet as it Disappears in the Solar Corona

NASA Technical Reports Server (NTRS)

Pesnell, William Dean; Schrijiver, Carolus J.; Brown, John C.; Battams, Karl; Saint-Hilaire, Pascal; Hudson Hugh S.; Lui, Wei

2012-01-01

On July 6,2011, the Atmospheric Imaging Assembly (AlA) on the Solar Dynamics Observatory (SDO) observed a comet in most of its EUY passbands. The comet disappeared while moving through the solar corona. The comet penetrated to 0.146 solar radii ($\\simapprox.100,000 km) above the photosphere before its EUY faded. Before then, the comet's coma and a tail were observed in absorption and emission, respectively. The material in the variable tail quickly fell behind the nucleus. An estimate of the comet's mass based on this effect, one derived from insolation, and one using the tail's EUY brightness, all yield $\\sim 50$ giga-grams some 10 minutes prior to the end of its visibility. These unique first observations herald a new era in the study of Sun-grazing comets close to their perihelia and of the conditions in the solar corona and solar wind. We will discuss the observations and interpretation of the comet by SDO as well as the coronagraph observations from SOHO and STEREO. A search of the SOHO comet archive for other comets that could be observed in the SDO; AlA EUY channels will be described

Disappearance of 19P/Borrelly's Silicate Feature in 2001 Apparition Is Attributed to Increase in Grain Size

NASA Technical Reports Server (NTRS)

Wooden, D. H.; Woodward, C. E.; Harker, D. E.

2002-01-01

We report on observations and analysis of HIFOGS 10 microns spectrophotometry of short period comet 19P/Borrelly on 2003 October 13, 15 UT at the NASA IRTF. 19P/Borrelly is one of two short period comets, comet 4PIFaye being the other, to have a silicate feature detected. During Borrelly s perihelion passage in 1994 December, a silicate feature was present with a flux-to-continuum ratio of 0.25. Two apparitions later in 2003 October, the silicate feature is absent. Thermal emission modeling using amorphous olivine and amorphous carbon shows that a slight increase in grain size accounts for the disappearance of the silicate feature. Analysis of 19P/Borrelly suggests grain size, and not the absence of olivine minerals, may be responsible for the absence of silicate features in most short period comets. 19P/Borrelly is one of the more active short period comets. However, short period comets as a family are less active than long period comets. Short period comets probably originated in the Kuiper Belt and suffered collisions while in residence in the outer solar system. Upon evolution into orbits that take them through the inner solar system, the surfaces of short period comets are exposed to sunlight through their many perihelion passages. This is in contrast to long period comets which probably originated near Jupiter and were expelled to the Oort cloud where they have existed and been exposed to cosmic ray processing. By studying the grain properties in short period comets and comparing to long period comets, we compare the effects on the grain populations of different parent body evolution histories. Upcoming opportunities to study short and long period comets will be advertised.

The discovery rate of new comets in the age of large surveys. Trends, statistics, and an updated evaluation of the comet flux

NASA Astrophysics Data System (ADS)

Fernández, Julio A.

We analyze a sample of 58 Oort cloud comets (OCCs) (original orbital energies x in the range 0 < x < 100, in units of 10-6 AU-1), plus 45 long-period comets with negative orbital energies or poorly determined or undetermined x, discovered during the period 1999-2007. To analyze the degree of completeness of the sample, we use Everhart's (1967 Astr. J 72, 716) concept of “excess magnitude” (in magnitudes × days), defined as the integrated magnitude excess that a given comet presents over the time above a threshold magnitude for detection. This quantity is a measure of the likelihood that the comet will be finally detected. We define two sub-samples of OCCs: 1) new comets (orbital energies 0 < x < 30) as those whose perihelia can shift from outside to the inner planetary region in a single revolution; and 2) inner cloud comets (orbital energies 30 ≤ x < 100), that come from the inner region of the Oort cloud, and for which external perturbers (essentially galactic tidal forces and passing stars) are not strong enough to allow them to overshoot the Jupiter-Saturn barrier. From the observed comet flux and making allowance for missed discoveries, we find a flux of OCCs brighter than absolute total magnitude 9 of ≃0.65 ± 0.18 per year within Earth's orbit. From this flux, about two-thirds corresponds to new comets and the rest to inner cloud comets. We find striking differences in the q-distribution of these two samples: while new comets appear to follow an uniform q-distribution, inner cloud comets show an increase in the rate of perihelion passages with q.

Comet 67P Seen by Kepler

NASA Image and Video Library

2016-10-07

The European Space Agency's Rosetta mission concluded its study of comet 67P/Churyumov-Gerasimenko on Sept. 30, 2016. NASA's planet-hunting Kepler spacecraft observed the comet during the final month of the Rosetta mission, while the comet was not visible from Earth. This animation is composed of images from Kepler of the comet. From Sept. 7 through Sept. 20, the Kepler spacecraft, operating in its K2 mission, fixed its gaze on comet 67P. From the distant vantage point of Kepler, the comet's nucleus and tail could be observed. The long-range view from Kepler complements the closeup view of the Rosetta spacecraft, providing context for the high-resolution investigation Rosetta performed as it descended closer and closer to the comet. During the two-week period of study, Kepler took a picture of the comet every 30 minutes. The animation shows a period of 29.5 hours of observation from Sept. 17 thru Sept. 18. The comet is seen passing through Kepler's field of view from top right to bottom left, as outlined by the diagonal strip. The white dots represent stars and other regions in space studied during K2's tenth observing campaign. As a comet travels through space it sheds a tail of gas and dust. The more material that is shed, the more surface area there is to reflect sunlight. A comet's activity level can be obtained by measuring the reflected sunlight. Analyzing the Kepler data, scientists will be able to determine the amount of mass lost each day as comet 67P travels through the solar system. An animation is available at http://photojournal.jpl.nasa.gov/catalog/PIA21072

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.

15 years of comet photometry: A comparative analysis of 80 comets

NASA Technical Reports Server (NTRS)

Osip, David J.; Schleicher, David G.; Millis, Robert L.; Hearn, M. F. A.; Birch, P. V.

1992-01-01

In 1976 we began a program of narrowband photometry of comets that has encompassed well over 400 nights of observations. To date, the program has provided detailed information on 80 comets, 11 of which have been observed on multiple apparitions. In this paper we present the observed range of compositions (molecular production rate ratios) and dustiness (gas production compared with AF-rho) for a well sampled group of comets. Based on these results we present preliminary analysis of taxonomic groupings as well as the abundance ratios we associate with a 'typical' comet.

THE NEOWISE-DISCOVERED COMET POPULATION AND THE CO + CO{sub 2} PRODUCTION RATES

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

Bauer, James M.; Stevenson, Rachel; Kramer, Emily

2015-12-01

The 163 comets observed during the WISE/NEOWISE prime mission represent the largest infrared survey to date of comets, providing constraints on dust, nucleus size, and CO + CO{sub 2} production. We present detailed analyses of the WISE/NEOWISE comet discoveries, and discuss observations of the active comets showing 4.6 μm band excess. We find a possible relation between dust and CO + CO{sub 2} production, as well as possible differences in the sizes of long and short period comet nuclei.

How do the surfaces of comets evolve with time?: Insights from Rosetta's two-year journey with 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Elmaarry, M. R.; Groussin, O.; Thomas, N.; Pajola, M.; Auger, A. T.; Davidsson, B. J. R.; Hu, X.; Hviid, S. F.; Joerg, K.; Güttler, C.; Tubiana, C.; Bodewits, D.; Fornasier, S.; Vincent, J. B.; Sierks, H.

2017-12-01

Prior to the Rosetta mission at comet 67P/Churyumov-Gerasimenko (hereinafter referred to as 67P), we had limited snapshots of comets from flyby missions: the only comet other than 67P that showed evidence of long-term or seasonal changes was comet Tempel 1 because it was visited by spacecrafts on two separate occasions. With Rosetta, it was possible to monitor the surface of a comet continuously for approximately two years with high spatial resolution, which led to the discovery of a wide variety of changes that occur on comets, and made it possible to constrain the timing and rates of these changes. Comet 67P showed a variety of changes that affected its consolidated materials such as collapsing cliffs, moving boulders, and propagating fractures, which indicate ongoing weathering and erosion on the surface. Similarly, the comet's smooth and unconsolidated materials also displayed changes. However, these changes were mainly transient or short-lived involving the development of circular features that vary in size with time, textural changes in the "dusty" mantles, and retreating scarps similar in scale to what has been previously observed at Tempel 1. The changes in the smooth terrains are more difficult to explain but appear related to insolation since most of the changes to the surface of the comet occurred at, or close to, perihelion, mainly when the comet was around 2 AU away from the Sun. While many (100s) of changes have been detected so far on the surface, they are nonetheless small-scale, and minimally affecting the overall shape or landscape of the comet. This would suggest that higher activity is likely at the earlier stages of a comet's introduction into the inner solar system when comets possibly possess a higher inventory of volatiles (particularly CO and CO2), and/or amorphous ice.

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.

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!

Infrared Observations of Cometary Dust and Nuclei

NASA Technical Reports Server (NTRS)

Lisse, Carey

2004-01-01

This bibliography lists citations for publications published under the grant. Subjects of the publications include cometary dust, instellar and interplanetary dust, comet nuclei and comae, Comet Hale-Bopp, infrared observations of comets, mass loss, and comet break-up.

Study of a comet rendezvous mission. Volume 2: Appendices

NASA Technical Reports Server (NTRS)

1972-01-01

Appendices to the comet Encke rendezvous mission consider relative positions of comet, earth and sun; viewing condition for Encke; detection of Taurid meteor streams; ephemeris of comet Encke; microwave and optical techniques in rendezvous mission; approach instruments; electrostatic equilibrium of ion engine spacecraft; comet flyby data for rendezvous spacecraft assembly; observations of P/Encke extracted from a compilation; and summary of technical innovations.

Anatomy of a Busted Comet

NASA Technical Reports Server (NTRS)

2008-01-01

[figure removed for brevity, see original site] Poster Version (Figure 1)

NASA's Spitzer Space Telescope captured the picture on the left of comet Holmes in March 2008, five months after the comet suddenly erupted and brightened a millionfold overnight. The contrast of the picture has been enhanced on the right to show the anatomy of the comet.

Every six years, comet 17P/Holmes speeds away from Jupiter and heads inward toward the sun, traveling the same route typically without incident. However, twice in the last 116 years, in November 1892 and October 2007, comet Holmes mysteriously exploded as it approached the asteroid belt. Astronomers still do not know the cause of these eruptions.

Spitzer's infrared picture at left hand side of figure 1, reveals fine dust particles that make up the outer shell, or coma, of the comet. The nucleus of the comet is within the bright whitish spot in the center, while the yellow area shows solid particles that were blown from the comet in the explosion. The comet is headed away from the sun, which lies beyond the right-hand side of figure 1.

The contrast-enhanced picture on the right shows the comet's outer shell, and strange filaments, or streamers, of dust. The streamers and shell are a yet another mystery surrounding comet Holmes. Scientists had initially suspected that the streamers were small dust particles ejected from fragments of the nucleus, or from hyerpactive jets on the nucleus, during the October 2007 explosion. If so, both the streamers and the shell should have shifted their orientation as the comet followed its orbit around the sun. Radiation pressure from the sun should have swept the material back and away from it. But pictures of comet Holmes taken by Spitzer over time show the streamers and shell in the same configuration, and not pointing away from the sun. The observations have left astronomers stumped.

The horizontal line seen in the contrast-enhanced picture is a trail of debris that travels along with the comet in its orbit.

The Spitzer picture was taken with the spacecraft's multiband imaging photometer at an infrared wavelength of 24 microns.

Organic Volatiles in Comet 73P-B/Schwassmann-Wachmann 3 Observed during Its Outburst: A Clue to the Formation Region of the Jupiter-Family Comets

NASA Astrophysics Data System (ADS)

Kobayashi, Hitomi; Kawakita, Hideyo; Mumma, Michael J.; Bonev, Boncho P.; Watanabe, Jun-ichi; Fuse, Tetsuharu

2007-10-01

We report the chemical composition of organic molecules in fragment B of comet 73P/Schwassmann-Wachmann 3 (SW3). Comet SW3 is a Jupiter-family comet that split into three fragments during its 1995 apparition and later into additional components. It was expected that fresh ices from deep within the presplit nucleus were exposed on the surface of each fragment. We observed SW3 with the Subaru telescope in 2006 early May when component B was disintegrating rapidly. If this exposed fresh ices from deeper layers of the original nucleus, mixing ratios obtained from our observations may reflect the pristine nature of the comet. Based on our results, comet SW3-B was depleted in C2H6 and C2H 2 with respect to most comets from the Oort Cloud reservoir, suggesting its formation region might have differed from that of the dominant Oort Cloud comets. Furthermore, the chemical composition of SW3-B was similar to that of SW3-C, suggesting that the presplit nucleus was almost homogeneous in volatile composition. The combined results demonstrate that depleted-organics comets from a common formation zone entered both reservoirs, of Jupiter-family comets and and Oort Cloud comets, but likely in different fractions. This Letter is based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This work was financially supported by the Ministry of Education, Science, and Culture, Grant-in-Aid for Young Scientists 19740107 (H. K.).

Determination of orbits of comets: P/Kearns-Kwee, P/Gunn, including nongravitational effects in the comets' motion

NASA Technical Reports Server (NTRS)

Todorovic-Juchniewicz, Bozenna; Sitarski, Grzegorz

1992-01-01

To improve the orbits, all the positional observations of the comets were collected. The observations were selected and weighted according to objective mathematical criteria and the mean residuals a priori were calculated for both comets. We took into account nongravitational effects in the comets' motion using Marsden's method applied in two ways: either determining the three constant parameters, A(sub 1), A(sub 2), A(sub 3) or the four parameters A, eta, I, phi connected with the rotating nucleus of the comet. To link successfully all the observations, we had to assume for both comets that A(t) = A(sub O)exp(-B x t) where B was an additional nongravitational parameter.

Trajectories for spacecraft encounters with Comet Honda-Mrkos-Pajdusakova in 1996

NASA Technical Reports Server (NTRS)

Dunham, David W.; Jen, Shao-Chiang; Farquhar, Robert W.

1989-01-01

Early in 1996, the relatively bright short-period Comet Honda-Mrkos-Pajdusakova (HMP) will pass only 0.17 astronomical unit from the earth, providing both an unusually favorable apparition for ground-based observers and an opportunity for a spacecraft to reach Comet HMP on relatively low-energy trajectories. The Japanense Institute of Space and Astronautical Sciences Sakigake spacecraft is expected to fly by Comet HMP on February 3, 1996, after utilizing four earth swingbys to modify its orbit. If the camera on the ESA Giotto spacecraft is inoperable, Giotto may also be sent to Comet HMP. In addition, 1-year earth-return trajectories to Comet HMP are described, along with some that can be extended to encounter Comet Giacobini-Zinner in 1998.

Discovering the Nature of Comets.

ERIC Educational Resources Information Center

Whipple, Fred L.

1986-01-01

"The Mystery of Comets" by Dr. Fred Whipple provides an introduction to the modern picture of comets and his personal reminiscences of how his model of comets came to be. An adaptation of several sections of the book is presented. (JN)

Ultraviolet Spectra of Comets Observed with the International Ultraviolet Explorer Satellite Observatory.

NASA Astrophysics Data System (ADS)

Weaver, Harold Anthony, Jr.

Ultraviolet spectra of seven comets observed with the International Ultraviolet Explorer (IUE) satellite are presented. Observations of comet Bradfield (1979 X) made in early 1980 allow a comprehensive study of the production of water by this comet. By comparing the observations to the predictions of two water models of the coma (Haser and vectorial), it is determined that these measurements support the idea of a comet composed principally of water ice. The vaporization of the water has a rather unexpected heliocentric variation, decreasing as r('-3.7) over the entire range of observations. Atomic carbon is relatively abundant in the coma of comet Bradfield; the production rate of carbon is roughly 5-10% of the water production rate. Analysis of the spatial brightness profiles of the strongest atomic carbon emission does not reveal the identity of the source of the observed carbon, but the data are apparently inconsistent with a photodissociation source that is either CO or CO(,2). A comparison of the ultraviolet spectrum of periodic comet Encke, recorded by the IUE between 1980 October 24 and November 5, with similar spectra of short and long period comets shows the gaseous composition of P/Encke to be virtually identical to that of the other comets. If P/Encke is indeed the remains of a once giant comet, this similarity implies a homogeneous structure for the cometary ice nucleus. The OH(0,0) band brightness distribution shows a spatial variation similar to the visible fan-shaped image of the comet. Comets P/Tuttle (1980h), P/Stephan-Oterma (1980g), and Meier (1980q) were observed during November-December 1980 with IUE, while comets P/Borrelly (1980i) and Panther (1980u) were observed with IUE on 6 March 1981. The spectra of these comets are compared with those of comets Bradfield (1979 X) and P/Encke, as well as with each other. In order to simplify the interpretation of the data and to minimize the dependence upon a specific model, the spectra are compared at approximately the same value of heliocentric distance whenever possible. Effects due to helicentric velocity, geocentric distance, and optical depth are also discussed. All of the cometary spectra are remarkably similar, which suggests that these comets may have a common composition and origin.

Episodic Aging and End States of Comets

NASA Technical Reports Server (NTRS)

Sekanina, Zdenek

2008-01-01

It is known that comets are aging very rapidly on cosmic scales, because they rapidly shed mass. The processes involved are (i) normal activity - sublimation of ices and expulsion of dust from discrete emission sources on and/or below the surface of a comet's nucleus, and (ii) nuclear fragmentation. Both modes are episodic in nature, the latter includes major steps in the comet's life cycle. The role and history of dynamical techniques used are described and results on mass losses due to sublimation and dust expulsion are reviewed. Studies of split comets, Holmes-like exploding comets, and cataclysmically fragmenting comets show that masses of 10 to 100 million tons are involved in the fragmentation process. This and other information is used to investigate the nature of comets' episodic aging. Based on recent advances in understanding the surface morphology of cometary nuclei by close-up imaging, a possible mechanism for large-scale fragmentation events is proposed and shown to be consistent with evidence available from observations. Strongly flattened pancake-like shapes appear to be required for comet fragments by conceptual constraints. Possible end states are briefly examined.

Random, double- and single-strand DNA breaks can be differentiated in the method of Comet assay by the shape of the comet image.

PubMed

Georgieva, Milena; Zagorchev, Plamen; Miloshev, George

2015-10-01

Comet assay is an invaluable tool in DNA research. It is widely used to detect DNA damage as an indicator of exposure to genotoxic stress. A canonical set of parameters and specialized software programs exist for Comet assay data quantification and analysis. None of them so far has proven its potential to employ a computer-based algorithm for assessment of the shape of the comet as an indicator of the exact mechanism by which the studied genotoxins cut in the molecule of DNA. Here, we present 14 unique measurements of the comet image based on the comet morphology. Their mathematical derivation and statistical analysis allowed precise description of the shape of the comet image which in turn discriminated the cause of genotoxic stress. This algorithm led to the development of the "CometShape" software which allowed easy discrimination among different genotoxins depending on the type of DNA damage they induce. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The study of the physics of cometary nuclei

NASA Technical Reports Server (NTRS)

Whipple, F. L.; Marsden, B. G.; Sekanina, Z.

1975-01-01

Research in the area of split and hyperbolic comets, orbital calculations, and interstellar comets is discussed. Other topics discussed include the role of comets in galactic chemistry, gamma ray bursts, and predicted favorable visibility conditions for anomalous tails of comets.

Comet flyby sample return

NASA Technical Reports Server (NTRS)

Tsou, P.; Albee, A.

1985-01-01

The results of a joint JPL/CSFC feasability study of a low-cost comet sample return flyby mission are presented. It is shown that the mission could be undertaken using current earth orbiter spacecraft technology in conjunction with pathfinder or beacon spacrcraft. Detailed scenarios of missions to the comets Honda-Mrkos-Pajdusakova (HMP), comet Kopff, and comet Giacobini-Zinner (GZ) are given, and some crossectional diagrams of the spacecraft designs are provided.

Halley’s comet; a benevolent visitor to Earth

USGS Publications Warehouse

Spall, H.

1986-01-01

In 1705 Edmund Halley, Professor of Geometry at Oxford University, collected and organized a mass of information on comets observed in 1531, 1607, and 1682, a task for which he had an uncommon genius. He was able to show that the comets had very similar orbits, and correctly drew the conclusion that they were the same object and more importantly that comets could therefore be periodic. He predicted that this comet would again be visible from the Earth in 1759. Since then it has been known as Halley's comet and it has played a significant role in the development of astronomy. 

A New Orbit for Comet C/1865 B1 (Great Southern Comet of 1865)

NASA Astrophysics Data System (ADS)

Branham, Richard L., Jr.

2018-04-01

Comet C/1865 B1 (Great southern comet of 1865), observed only in the southern hemisphere, is one of a large number of comets with parabolic orbits. Given that there are 202 observations in right ascension and 165 in declination it proves possible to calculate a better orbit than that Körber published in 1887, the orbit used in various catalogs and data bases. C/1865 B1's orbit is hyperbolic and statistically distinguishable from a parabola. This object, therefore, cannot be considered an NEO. The comet has a small perihelion distance of 0.026 AU.

Cometary ephemerides - needs and concerns

NASA Technical Reports Server (NTRS)

Yeomans, D. K.

1981-01-01

With the use of narrow field-of-view instrumentation on faint comets, the accuracy requirements upon computed ephemerides are increasing. It is not uncommon for instruments with a one arc minute field-of-view to be tracking a faint comet that is not visible without a substantial integration time. As with all ephemerides of solar syste objects, the computed motion and reduction of these observations, the computed motion of a comet is further depenent upon effects related to the comet's activity. Thus, the ephemeris of an active comet is corrupted by both observational errors and errors due to the comet's activity.

From the Vega mission to comet Halley to the Rosetta mission to comet 67/P Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Zelenyi, L. M.; Ksanfomality, L. V.

2016-12-01

The data acquired by the Vega and Giotto spacecraft, while investigating comet 1P/Halley in 1986, are compared to the results of the first phase of exploration of the nucleus of comet 67P/Churyumov-Gerasimenko performed with the Rosetta and Philae modules. The course of the Rosetta mission activity and the status of the modules after the Philae probe landing on the comet's nucleus are overviewed. Since some elements of the touchdown equipment failed, a number of in-situ experiments on the comet's nucleus were not carried out.

A new activity index for comets

NASA Technical Reports Server (NTRS)

Whipple, Fred L.

1992-01-01

An activity index, AI, is derived from observational data to measure the increase of activity in magnitudes for comets when brightest near perihelion as compared to their inactive reflective brightness at great solar distances. Because the observational data are still instrumentally limited in the latter case and because many comets carry particulate clouds about them at great solar distances, the application of the activity index is still limited. A tentative application is made for the comets observed by Max Beyer over a period of nearly 40 years, providing a uniform magnitude system for the near-perihelion observations. In all, 32 determinations are made for long-period (L-P) comets and 15 for short-period (S-P). Although the correlations are scarcely definitive, the data suggest that the faintest comets are just as active as the brightest and that the S-P comets are almost as active as those with periods (P) exceeding 10(exp 4) years or those with orbital inclinations of i less than 120 deg. Comets in the range 10(exp 2) less than P less than 10(exp 4) yr. or with i greater than 120 deg appear to be somewhat more active than the others. There is no evidence to suggest aging among the L-P comets or to suggest other than a common nature for comets generally.

The long-term dynamical behavior of short-period comets

NASA Technical Reports Server (NTRS)

Levison, Harold F.; Duncan, Martin J.

1993-01-01

The orbits of the known short-period comets under the influence of the Sun and all the planets except Mercury and Pluto are numerically integrated. The calculation was undertaken in order to determine the dynamical lifetimes for these objects as well as explaining the current orbital element distribution. It is found that a comet can move between Jupiter-family and Halley-family comets several times in its dynamical lifetime. The median lifetime of the known short-period comets from the time they are first injected into a short-period comet orbit to ultimate ejection is approximately 50,000 years. The very flat inclination distribution of Jupiter-family comets is observed to become more distended as it ages. The only possible explanation for the observed flat distribution is that the comets become extinct before their inclination distribution can change significantly. It is shown that the anomalous concentration of the argument of perihelion of Jupiter-family comets near 0 and 180 deg is a direct result of their aphelion distance being close to 5.2AU and the comet being recently perturbed onto a Jupiter-family orbit. Also the concentration of their aphelion near Jupiter's orbit is a result of the conservation of the Tisserand invariant during the capture process.

The population, magnitudes, and sizes of Jupiter family comets

NASA Astrophysics Data System (ADS)

Fernández, J. A.; Tancredi, G.; Rickman, H.; Licandro, J.

1999-12-01

We analyze the sample of measured nuclear magnitudes of the observed Jupiter family (JF) comets (taken as those with orbital periods P < 20 years and Tisserand parameters T > 2). We find a tendency of the measured nuclear magnitudes to be fainter as JF comets are observed with CCD detectors attached to medium- and large-size telescopes (e.g. Spacewatch Telescope). However, a few JF comets observed very far from the Sun (4-7 AU) show a wide dispersion of their derived absolute nuclear magnitudes which suggests that either these JF comets keep active all along the orbit, so the reported unusually bright distant magnitudes were strongly contaminated by a coma, or some of the measured ``nuclear magnitudes'' were grossly overestimated (i.e. their brightness underestimated). The cumulative mass distribution of JF comets is found to follow a power-law of index s = - 0.88 +/- 0.08, suggesting a distribution significantly steeper than that for both small main-belt asteroids and near-Earth asteroids. The cumulative mass distribution of JF comets with q < 2 AU tends to flatten for absolute (visual) nuclear magnitudes H_N > 16, which is probably due to incompleteness of discovery of fainter comets and/or a real scarcity of small comets due, perhaps, to much shorter physical lifetimes. In particular, no JF comets fainter than H_N ~ 19.5 are found in the sample, suggesting that the critical size for a comet to be still active may be of about 0.4 km radius for an assumed geometric albedo of 0.04. Possibly, smaller comet nuclei disintegrate very quickly into meteor streams. Most absolute nuclear magnitudes are found in the range 15-18, corresponding to nuclear radii in the range 0.8-3.3 km (for the same geometric albedo). We find that a large majority of JF comets with perihelion distances q > 2.5 AU are brighter than absolute nuclear magnitude H_N = 16, suggesting that only a very small fraction (a few percent) of the population of the JF comets with large q has so far been detected. A similar trend is noted for the corresponding absolute total magnitudes H_T taken from Kresák & Kresáková's (1994) catalog. By analyzing the H_N and H_T data, and trends in the discovery rate of JF comets as a function of their perihelion distances, the overall population of JF comets within Jupiter's region (q < 5.2 AU) up to an absolute nuclear magnitude H_N = 18.5 is estimated to be from several thousand to about 104 members. The q-distribution of JF comets shows a steep increase with q, which is consistent with JF comets coming from a flat intermediate source in the Jupiter-Saturn region.

Using a medium-throughput comet assay to evaluate the global DNA methylation status of single cells

PubMed Central

Lewies, Angélique; Van Dyk, Etresia; Wentzel, Johannes F.; Pretorius, Pieter J.

2014-01-01

The comet assay is a simple and cost effective technique, commonly used to analyze and quantify DNA damage in individual cells. The versatility of the comet assay allows introduction of various modifications to the basic technique. The difference in the methylation sensitivity of the isoschizomeric restriction enzymes HpaII and MspI are used to demonstrate the ability of the comet assay to measure the global DNA methylation level of individual cells when using cell cultures. In the experiments described here, a medium-throughput comet assay and methylation sensitive comet assay are combined to produce a methylation sensitive medium-throughput comet assay to measure changes in the global DNA methylation pattern in individual cells under various growth conditions. PMID:25071840

The McDonald Observatory Faint Comet Survey - Gas production in 17 comets

NASA Technical Reports Server (NTRS)

Cochran, Anita L.; Barker, Edwin S.; Ramseyer, Tod F.; Storrs, Alex D.

1992-01-01

The complete Intensified Dissector Scanner data set on 17 comets is presented, and production rates are derived and analyzed. It is shown that there is a strong degree of homogenization in the production rate ratios of many comets. It also appears that the ratio of the production rates of the various species has no heliocentric distance dependence, except for the case of NH2. When speaking of the gas in the coma of a comet, it appears that comets must have been formed under remarkably uniform conditions, and that they must have evolved and formed their comae in a similar manner. The data presented here constitute strong evidence that the minor species must be bound up in a lattice and that the interior of a comet must be reasonably uniform.

Perspectives on Comets, Comet-like Asteroids, and Their Predisposition to Provide an Environment That Is Friendly to Life

NASA Astrophysics Data System (ADS)

Bosiek, Katharina; Hausmann, Michael; Hildenbrand, Georg

2016-04-01

In recent years, studies have shown that there are many similarities between comets and asteroids. In some cases, it cannot even be determined to which of these groups an object belongs. This is especially true for objects found beyond the main asteroid belt. Because of the lack of comet fragments, more progress has been made concerning the chemical composition of asteroids. In particular, the SMASSII classification establishes a link between the reflecting spectra and chemical composition of asteroids and meteorites. To find clues for the chemical structure of comets, the parameters of all known asteroids of the SMASSII classification were compared to those of comet groups like the Encke-type comets, the Jupiter-family comets, and the Halley-type comets, as well as comet-like objects like the damocloids and the centaurs. Fifty-six SMASSII objects similar to comets were found and are categorized as comet-like asteroids in this work. Aside from the chemistry, it is assumed that the available energy on these celestial bodies plays an important role concerning habitability. For the determination of the available energy, the effective temperature was calculated. Additionally, the size of these objects was considered in order to evaluate the possibility of a liquid water core, which provides an environment that is more likely to support processes necessary to create the building blocks of life. Further study of such objects could be notable for the period of the Late Heavy Bombardment and could therefore provide important implications for our understanding of the inner workings of the prebiotic evolution within the Solar System since the beginning.

Perspectives on Comets, Comet-like Asteroids, and Their Predisposition to Provide an Environment That Is Friendly to Life.

PubMed

Bosiek, Katharina; Hausmann, Michael; Hildenbrand, Georg

2016-04-01

In recent years, studies have shown that there are many similarities between comets and asteroids. In some cases, it cannot even be determined to which of these groups an object belongs. This is especially true for objects found beyond the main asteroid belt. Because of the lack of comet fragments, more progress has been made concerning the chemical composition of asteroids. In particular, the SMASSII classification establishes a link between the reflecting spectra and chemical composition of asteroids and meteorites. To find clues for the chemical structure of comets, the parameters of all known asteroids of the SMASSII classification were compared to those of comet groups like the Encke-type comets, the Jupiter-family comets, and the Halley-type comets, as well as comet-like objects like the damocloids and the centaurs. Fifty-six SMASSII objects similar to comets were found and are categorized as comet-like asteroids in this work. Aside from the chemistry, it is assumed that the available energy on these celestial bodies plays an important role concerning habitability. For the determination of the available energy, the effective temperature was calculated. Additionally, the size of these objects was considered in order to evaluate the possibility of a liquid water core, which provides an environment that is more likely to support processes necessary to create the building blocks of life. Further study of such objects could be notable for the period of the Late Heavy Bombardment and could therefore provide important implications for our understanding of the inner workings of the prebiotic evolution within the Solar System since the beginning.

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.

Physical observations of comets: Their composition, origin and evolution

NASA Technical Reports Server (NTRS)

Cochran, Anita L.; Barker, Edwin S.; Cochran, William D.

1991-01-01

The composition, origins, and evolution of comets were studied. The composition was studied using spectroscopic observations of primarily brighter comets at moderate and high resolution for the distribution of certain gases in the coma. The origins was addressed through an imaging search for the Kuiper belt of comets. The evolution was addressed by searching for a link between comets and asteroids using an imaging approach to search for an OH coma.

Disappearance of 19P/Borrelly's Silicate Feature in 2001 Apparition Is Attributed to Increase in Grain Size

NASA Astrophysics Data System (ADS)

Wooden, D. H.; Woodward, C. E.; Harker, D. E.

2003-05-01

We report on observations and analysis of HIFOGS 10 \\micron \\ spectrophotometry of short period comet 19P/Borrelly on 2003 October 13, 15 UT at the NASA IRTF. 19P/Borrelly is one of two short period comets, comet 4P/Faye being the other, to have a silicate feature detected (Hanner et al. 1996, Icarus, 124, 344). During Borrelly.s perihelion passage in 1994 December, a silicate feature was present with a flux-to-continuum ratio of 0.25. Two apparitions later in 2003 October, the silicate feature is absent. Thermal emission modeling (cf. Harker et al. 2002, ApJ, 580, 579) using amorphous olivine and amorphous carbon shows that a slight increase in grain size accounts for the disappearance of the silicate feature. Analysis of 19P/Borrelly suggests grain size, and not the absence of olivine minerals, may be responsible for the absence of silicate features in most short period comets. 19P/Borrelly is one of the more active short period comets. However, short period comets as a family are less active than long period comets. Short period comets probably originated in the Kuiper Belt and suffered collisions while in residence in the outer solar system. Upon evolution into orbits that take them through the inner solar system, the surfaces of short period comets are exposed to sunlight through their many perihelion passages. This is in contrast to long period comets which probably originated near Jupiter and were expelled to the Oort cloud where they have existed and been exposed to cosmic ray processing. By studying the grain properties in short period comets and comparing to long period comets, we compare the effects on the grain populations of different parent body evolution histories. Upcoming opportunities to study short and long period comets will be advertised. This research is supported in part by an NSF Grant to the University of Minnesota.

Comet Odyssey: Comet Surface Sample Return

NASA Astrophysics Data System (ADS)

Weissman, Paul R.; Bradley, J.; Smythe, W. D.; Brophy, J. R.; Lisano, M. E.; Syvertson, M. L.; Cangahuala, L. A.; Liu, J.; Carlisle, G. L.

2010-10-01

Comet Odyssey is a proposed New Frontiers mission that would return the first samples from the surface of a cometary nucleus. Stardust demonstrated the tremendous power of analysis of returned samples in terrestrial laboratories versus what can be accomplished in situ with robotic missions. But Stardust collected only 1 milligram of coma dust, and the 6.1 km/s flyby speed heated samples up to 2000 K. Comet Odyssey would collect two independent 800 cc samples directly from the surface in a far more benign manner, preserving the primitive composition. Given a minimum surface density of 0.2 g/cm3, this would return two 160 g surface samples to Earth. Comet Odyssey employs solar-electric propulsion to rendezvous with the target comet. After 180 days of reconnaissance and site selection, the spacecraft performs a "touch-and-go” maneuver with surface contact lasting 3 seconds. A brush-wheel sampler on a remote arm collects up to 800 cc of sample. A duplicate second arm and sampler collects the second sample. The samples are placed in a return capsule and maintained at colder than -70 C during the return flight and at colder than -30 C during re-entry and for up to six hours after landing. The entire capsule is then refrigerated and transported to the Astromaterials Curatorial Facility at NASA/JSC for initial inspection and sample analysis by the Comet Odyssey team. Comet Odyssey's planned target was comet 9P/Tempel 1, with launch in December 2017 and comet arrival in June 2022. After a stay of 300 days at the comet, the spacecraft departs and arrives at Earth in May 2027. Comet Odyssey is a forerunner to a flagship Cryogenic Comet Sample Return mission that would return samples from deep below the nucleus surface, including volatile ices. This work was supported by internal funds from the Jet Propulsion Laboratory.

Comet Hartley 2 Gets a Visitor Artist Concept

NASA Image and Video Library

2010-10-26

This artist concept shows a view of NASA EPOXI mission spacecraft during its Nov. 4, 2010 flyby of comet Hartley 2. The fluffy shell around the comet, called a coma, is made up of gas and dust that blew off the comet core, or nucleus.

Comet Hartley 2 Looms Large in the Sky

NASA Image and Video Library

2010-11-03

NASA EPOXI mission took this image of comet Hartley 2 on Nov. 2, 2010. The spacecraft will fly by the comet on Nov. 4, 2010. The white blob and the halo around it are the comet outer cloud of gas and dust, called a coma.

Astronomical Resources: A Selected Halley's Comet Reading List.

ERIC Educational Resources Information Center

Fraknoi, Andrew

1985-01-01

Presents annotated lists of: (1) general introductory books about comets and Comet Halley; (2) books about comet history and lore; (3) introductory books for younger children; and (4) books for the serious amateur astronomer. A list of magazine and journal articles is included. (JN)

Realm of the comets

NASA Technical Reports Server (NTRS)

Weissman, Paul R.

1987-01-01

Studies of Jovian perturbations of the orbits of long-period comets led to the concept of the Oort cloud of 180 billion comets at 50,000-150,000 AU from the sun. Several comets are induced to move toward the sun every million years by the passage of a star at a distance of a few light years. The location of the cloud has since been revised to 20,000-100,000 AU, and comets are now accepted as remnant material fron the proto-solar system epoch. The galactic disk and random, close-passing stars may also cause rare, large perturbations in the orbits of the cloud comets, sending large numbers of comets through the inner solar system. The resulting cometary storm is a candidate cause for the wholesale extinction of dinosaurs in the Cretaceous-Terniary transition due to large number of planetesimals, or one large comet, striking the earth, in a short period of time. The IRAS instruments have detected similar clouds of material around other stars.

Realm of the comets

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

Weissman, P.R.

1987-03-01

Studies of Jovian perturbations of the orbits of long-period comets led to the concept of the Oort cloud of 180 billion comets at 50,000-150,000 AU from the sun. Several comets are induced to move toward the sun every million years by the passage of a star at a distance of a few light years. The location of the cloud has since been revised to 20,000-100,000 AU, and comets are now accepted as remnant material fron the proto-solar system epoch. The galactic disk and random, close-passing stars may also cause rare, large perturbations in the orbits of the cloud comets, sendingmore » large numbers of comets through the inner solar system. The resulting cometary storm is a candidate cause for the wholesale extinction of dinosaurs in the Cretaceous-Terniary transition due to large number of planetesimals, or one large comet, striking the earth, in a short period of time. The IRAS instruments have detected similar clouds of material around other stars.« less

A Comet Engulfs Mars: MAVEN Observations of Comet Siding Spring's Influence on the Martian Magnetosphere

NASA Technical Reports Server (NTRS)

Espley, Jared R.; Dibraccio, Gina A.; Connerney, John E. P.; Brain, David; Gruesbeck, Jacob; Soobiah, Yasir; Halekas, Jasper S.; Combi, Michael; Luhmann, Janet; Ma, Yingjuan

2015-01-01

The nucleus of comet C/2013 A1 (Siding Spring) passed within 141,000?km of Mars on 19 October 2014. Thus, the cometary coma and the plasma it produces washed over Mars for several hours producing significant effects in the Martian magnetosphere and upper atmosphere. We present observations from Mars Atmosphere and Volatile EvolutioN's (MAVEN's) particles and field's instruments that show the Martian magnetosphere was severely distorted during the comet's passage. We note four specific major effects: (1) a variable induced magnetospheric boundary, (2) a strong rotation of the magnetic field as the comet approached, (3) severely distorted and disordered ionospheric magnetic fields during the comet's closest approach, and (4) unusually strong magnetosheath turbulence lasting hours after the comet left. We argue that the comet produced effects comparable to that of a large solar storm (in terms of incident energy) and that our results are therefore important for future studies of atmospheric escape, MAVEN's primary science objective.

Autonomous Onboard Science Data Analysis for Comet Missions

NASA Technical Reports Server (NTRS)

Thompson, David R.; Tran, Daniel Q.; McLaren, David; Chien, Steve A.; Bergman, Larry; Castano, Rebecca; Doyle, Richard; Estlin, Tara; Lenda, Matthew

2012-01-01

Coming years will bring several comet rendezvous missions. The Rosetta spacecraft arrives at Comet 67P/Churyumov-Gerasimenko in 2014. Subsequent rendezvous might include a mission such as the proposed Comet Hopper with multiple surface landings, as well as Comet Nucleus Sample Return (CNSR) and Coma Rendezvous and Sample Return (CRSR). These encounters will begin to shed light on a population that, despite several previous flybys, remains mysterious and poorly understood. Scientists still have little direct knowledge of interactions between the nucleus and coma, their variation across different comets or their evolution over time. Activity may change on short timescales so it is challenging to characterize with scripted data acquisition. Here we investigate automatic onboard image analysis that could act faster than round-trip light time to capture unexpected outbursts and plume activity. We describe one edge-based method for detect comet nuclei and plumes, and test the approach on an existing catalog of comet images. Finally, we quantify benefits to specific measurement objectives by simulating a basic plume monitoring campaign.

Spectrophotometry of 25 comets - Post-Halley updates for 17 comets plus new observations for eight additional comets

NASA Technical Reports Server (NTRS)

Newburn, Ray L., Jr.; Spinrad, Hyron

1989-01-01

The best possible production figures within the current post-Halley framework and available observations are given for H2O, O(1D), CN, C3, C2 and dust in 25 comets. Of these, the three objects with the smallest mixing ratios of all minor species have moderate to little or no dust and appear 'old'. Comets with large amounts of CN are very dusty, and there is a clear correlation of CN with dust, although comets with little or no dust still have some CN. Thus, CN appears to have at least two sources, dust and one or more parent gases. Also, the C2/CN production ratio changes continuously with heliocentric distance in every comet considered, suggesting that C2 production may be a function of coma density as well as parental abundance. Dust production ranges from essentially zero in Comet Sugano-Saigusa-Fujikawa up to 67,000 kg/s for Halley on March 14, 1986.

Observations of faint comets at McDonald Observatory: 1978-1980

NASA Technical Reports Server (NTRS)

Barker, E. S.; Cochran, A. L.; Rybski, P. M.

1981-01-01

Modern observational techniques, developed for spectroscopy and photometry of faint galaxies and quasars, successfully applied to faint comets on the 2.7 m telescope. The periodic comets Van Biesbrock, Ashbrook-Jackson, Schwassmann-Wachmann 1, Tempel 2, Encke, Forbes, Brooks 2, Stephan-Oterma and the new comets Bradfield (19791), Bowell (1980b), Chernis-Petrauskas (1980k) were observed. The comets ranged in magnitude from 10th to 20th magnitude. For comets fainter than 19th magnitude, reflectance spectra at 100A resolution and area photometry were obtained. On comets of 17th or 18th magnitude, spectrometric scans (6A resolution) of the nucleus or inner coma region. On those comets which are brighter than 16th magnitude spatial spectrophotometric (6A resolution) studies of the inner and extended comae were done. An extensive spatial study of the comae of P/Encke and P/Stephen-Oterma, correlated with heliocentric distance is taking place. The observing process used is described and examples of the results obtained to date are discussed.

The 3.4 micron emission in comets

NASA Technical Reports Server (NTRS)

Brooke, Tim Y.; Knacke, Roger F.; Owen, T. C.; Tokunaga, Alan T.

1989-01-01

Emission features near 3.4 microns were detected in comet Bradfield (1987s) on 17 Nov. 1987 UT, and, marginally, on two earlier dates, with the Cooled Grating Array Spectrometer at the NASA Infrared Radio Telescope Facility (IRTF) (Brooke et al., 1988b). The central wavelength (3.36 microns) and width (approx. 0.15 microns) of the strongest feature coincide with those observed in comet Halley. A weaker emission feature at 3.52 microns and a strong feature extending shortward of 2.9 microns were also detected. This brings the number of comets in which these three features have been seen to three, two new (Bradfield, Wilson) and one old (Halley). It seems almost certain that the 3.4 micron features are emissions by C-H groups in complex molecules. Based on the similarity of the 3.4 micron features in comets Halley and Wilson, the authors suggest that a particular set of organic compounds may be common to all comets (Brooke et al. 1988a). The absence of the feature in some comets could then be due to photodestruction or evaporation of the organics when the comet approaches the sun, in combination with a predominance of thermal emission from non C-H emitting grains. Detection of the 3.4 micron emission feature in comet Bradfield at 4 = 0.9 AU provides support for this argument. Complex organics in comets could have been formed by particle irradiation of parent ices in the nucleus or been incorporated as grains at the time the comets formed. Since the most heavily irradiated layers of Halley would have been lost in its hundreds of perihelion passages, the authors believe the more likely explanation is that the 3.4 micron emitting material was incorporated in comet nuclei at the time of formation. The 3.4 micron comet feature resembles, but is not identical to, the interstellar 3.29 micron (and longer wavelength) emission features and the broad 3.4 micron feature seen in absorption toward the Galactic center. Detailed comparisons of cometary and interstellar organics will require comet spectra with signal-to-noise and spectral resolution comparable to that available in spectra of the interstellar medium. Such observations are currently being planned.

A volatility index for comets

NASA Technical Reports Server (NTRS)

Whipple, Fred L.

1992-01-01

The variations in total brightness of a comet when it is most active, near perihelion, are presently used as the bases of a volatility index (VI) for short-period (SP) and long-period (LP) comets. Volatility does not correlate with period among the LP comets, and thereby shows no 'aging' effect; similarly, the VI measurements are the same for SP and for LP comets and exhibit no correlation with (1) absolute magnitude near perihelion, (2) orbital inclination, or (3) activity index measuring the intrinsic brightness change from great solar distances to the maximum near perihelion. Active comets are shown to be basically alike irrespective of their orbits or 'ages'.

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.

Report of the Comet Science Working Group

NASA Technical Reports Server (NTRS)

1979-01-01

General scientific questions and measurement objectives that can be addressed on a first comet mission relate to: (1) the chemical nature and the physical structure of comet nuclei as well as the changes that occur as functions of time and orbital position; (2) the chemical and physical nature of the atmospheres and ionospheres of comets, the processes which occur in them, and the development of these atmospheres and ionospheres as functions of time and orbital position; and (3) the nature of comet tails, the processes by which they are formed, and the interaction of comets with the solar wind. Capabilities of the various instruments required are discussed.

Disintegration of comet nuclei

NASA Astrophysics Data System (ADS)

Ksanfomality, Leonid V.

2012-02-01

The breaking up of comets into separate pieces, each with its own tail, was seen many times by astronomers of the past. The phenomenon was in sharp contrast to the idea of the eternal and unchangeable celestial firmament and was commonly believed to be an omen of impending disaster, especially for comets with tails stretching across half the sky. It is only now that we have efficient enough space exploration tools to see comet nuclei and even - in the particular case of small comet Hartley-2 in 2010 - to watch their disintegration stage. There are also other suspected candidates for disintegration in the vast family of comet nuclei and other Solar System bodies.

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.

VLA observations of the OH emission from Comet Wilson (1986) - The value of high resolution in both spatial and velocity coordinates

NASA Technical Reports Server (NTRS)

Palmer, Patrick; De Pater, Imke; Snyder, Lewis E.

1989-01-01

In comparison with Comet Halley, the radio OH emission from Comet Wilson behaved very erratically, changing rapidly in position as well as in velocity, while the emission and brightness distribution from Comet Halley displayed apparent stability. A few months later, nearer perihelion, just the opposite behavior was observed at UV wavelengths. Another difference between the two comets is that the OH emission from Comet Halley seemed confined to a region a few times 100.000 km in size, while the emission from Comet Wilson showed up in sporadic blobs, with variable intensities and velocities, at distances as far as 10 to the 6th km from the nucleus. This behavior in Comet Wilson may be associated with the disintegration of the outer frosting associated with new comets and possibly with the fragmentation and ejection of cometesimals from the nucleus. As part of the data analysis, it is demonstrated that lengthening the integration time and lowering the velocity resolution affects the symmetry of the OH images and spectral-line profiles. As a consequence, asymmetric cometary OH line profiles may be more common than previously thought.

Term Projects on Interstellar Comets

ERIC Educational Resources Information Center

Mack, John E.

1975-01-01

Presents two calculations of the probability of detection of an interstellar comet, under the hypothesis that such comets would escape from comet clouds similar to that believed to surround the sun. Proposes three problems, each of which would be a reasonable term project for a motivated undergraduate. (Author/MLH)

Development and Testing of Harpoon-Based Approaches for Collecting Comet Samples

NASA Technical Reports Server (NTRS)

Purves, Lloyd (Compiler); Nuth, Joseph (Compiler); Amatucci, Edward (Compiler); Wegel, Donald; Smith, Walter; Church, Joseph; Leary, James; Kee, Lake; Hill, Stuart; Grebenstein, Markus;

The Rotation Temperature of Methanol in Comet 103P/Hartley 2

NASA Technical Reports Server (NTRS)

Chuang, Yo-Ling; Kuan, Yi-Jehng; Milam, Stefanie; Charnley, Steven B.; Coulson, Iain M.

2012-01-01

Considered to be relics from Solar System formation, comets may provide the vital information connecting Solar Nebula and its parent molecular cloud. Study of chemical and physical properties of comets is thus important for our better understanding of the formation of Solar System. In addition, observing organic molecules in comets may provide clues fundamental to our knowledge on the formation of prebiotically important organic molecules in interstellar space, hence, may shed light on the origin of life on the early Earth. Comet 103PIHartley 2 was fIrst discovered in 1986 and had gone through apparitions in 1991, 1997, and 2004 with an orbital period of about 6 years, before its latest return in 2010. 2010 was also a special year for Comet 103PIHartley 2 because of the NASA EPOXI comet-flyby mission.

Assessment of the predictive capacity of the optimized in vitro comet assay using HepG2 cells.

PubMed

Hong, Yoon-Hee; Jeon, Hye Lyun; Ko, Kyung Yuk; Kim, Joohwan; Yi, Jung-Sun; Ahn, Ilyoung; Kim, Tae Sung; Lee, Jong Kwon

2018-03-01

Evaluation of DNA damage is critical during the development of new drugs because it is closely associated with genotoxicity and carcinogenicity. The in vivo comet assay to assess DNA damage is globally harmonized as OECD TG 489. However, a comet test guideline that evaluates DNA damage without sacrificing animals does not yet exist. The goal of this study was to select an appropriate cell line for optimization of the in vitro comet assay to assess DNA damage. We then evaluated the predictivity of the in vitro comet assay using the selected cell line. In addition, the effect of adding S9 was evaluated using 12 test chemicals. For cell line selection, HepG2, Chinese hamster lung (CHL/IU), and TK6 cell lines were evaluated. We employed a method for the in vitro comet assay based on that for the in vivo comet assay. The most appropriate cell line was determined by% tail DNA increase after performing in vitro comet assays with 6 test chemicals. The predictivity of the in vitro comet assay using the selected cell line was measured with 10 test chemicals (8 genotoxins and 2 non-genotoxic chemicals). The HepG2 cell line was found to be the most appropriate, and in vitro comet assays using HepG2 cells exhibited a high accuracy of 90% (9/10). This study suggests that HepG2 is an optimal cell line for the in vitro comet assay to assess DNA damage. Copyright © 2018 Elsevier B.V. All rights reserved.

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.

Theories of comets to the age of Laplace

NASA Astrophysics Data System (ADS)

Heidarzadeh, Tofigh

Although the development of ideas about cometary motion has been investigated in several projects, a comprehensive and detailed survey of physical theories of comets has not been conducted. The available works either illustrate relatively short periods in the history of physical cometology or portray a landscape view without adequate details. The present study is an attempt to depict the details of the major physical theories of comets from Aristotle to the age of Laplace. The basic question from which this project originated was simple: how did natural philosophers and astronomers define the nature and place of a new category of celestial objects--the comets--after Brahe's estimation of cometary distances? However, a study starting merely from Brahe without covering classical and medieval thought about comets would be incomplete. Thus, based on the fundamental physical characteristics attributed to comets, the history of cometology may be divided into three periods: from Aristotle to Brahe, in which comets were assumed to be meteorological phenomena; from Brahe to Newton, when comets were admitted as celestial bodies but with unknown trajectories; and from Newton to Laplace, in which they were treated as members of the solar system having more or less the same properties of the planets. By estimating the mass of comets in the 1800s, Laplace diverted cometology into a different direction wherein they were considered among the smallest bodies in the solar system and deprived of the most important properties that had been used to explain their physical constitution during the previous two millennia. Ideas about the astrological aspects of comets are not considered in this study. Also, topics concerning the motion of comets are explained to the extent that is helpful in illustrating their physical properties. The main objective is to demonstrate the foundations of physical theories of comets, and the interaction between observational and mathematical astronomy, and the physical sciences in defining the properties of comets. The number of publications containing ideas about the physical properties of comets shows a radical increase in the third period of our account of cometology. From numerous general astronomy texts or treatises devoted to comets in this period, those were discussed here that either proposed a different theory of comets or criticized the physical aspects of contemporary theories. The survey includes only works published in England and France, and a few in German-speaking countries. Although Laplace's achievement in estimation of cometary masses became the basis of modern cometology, our current ideas about the actual size, mass and composition of comets, and the processes by which the coma and tail are formed have been developed only since the mid twentieth century. Post-Laplacian developments in the study of comets are highlighted in an appendix, which briefly reviews the major achievements in the observational and theoretical study of comets in the nineteenth and the twentieth centuries. Although the present study is mainly focused on the physical theories of comets, its results will be relevant to studies in the history of geology, planetary science, and astrology. On the other hand, those results may initiate new studies about educational practices for physics and astronomy in post- Newtonian Europe, the ways that different parts of Newton's physical, astronomical and cosmological ideas evolved after him, and the influence of cometary studies on the foundation of astrophysics.

Solar-wind velocity measurements from near-Sun comets C/2011 W3 (Lovejoy), C/2011 L4 (Pan-STARRS), and C/2012 S1 (ISON)

NASA Astrophysics Data System (ADS)

Ramanjooloo, Y.; Jones, G. H.; Coates, A.; Owens, M. J.; Battams, K.

2014-07-01

Since the mid-20th century, comets' plasma (type I) tails have been studied as natural probes of the solar wind [1]. Comets have induced magnetotails, formed through the draping of the heliospheric magnetic field by the velocity shear in the mass-loaded solar wind. These can be easily observed remotely as the comets' plasma tails, which generally point away from the Sun. Local solar-wind conditions directly influence the morphology and dynamics of a comet's plasma tail. During ideal observing geometries, the orientation and structure of the plasma tail can reveal large-scale and small-scale variations in the local solar-wind structure. These variations can be manifested as tail condensations, kinks, and disconnection events. Over 50 % of observed catalogued comets are sungrazing comets [2], fragments of three different parent comets. Since 2011, two bright new comets, C/2011 W3 [3] (from hereon comet Lovejoy) and C/2012 S1 [4] (hereon comet ISON) have experienced extreme solar-wind conditions and insolation of their nucleus during their perihelion passages, approaching to within 8.3×10^5 km (1.19 solar radii) and 1.9×10^6 km (2.79 solar radii) of the solar centre. They each displayed a prominent plasma tail, proving to be exceptions amongst the observed group of sungrazing comets. These bright sungrazers provide unprecedented access to study the solar wind in the heretofore unprobed innermost region of the solar corona. The closest spacecraft in-situ sampling of the solar wind by the Helios probes reached 0.29 au. For this study, we define a sungrazing comet as one with its perihelion within the solar Roche limit (3.70 solar radii). We also extend this study to include C/2011 L4 [5] (comet Pan-STARRS), a comet with a much further perihelion distance of 0.302 au. The technique employed in this study was first established by analysing geocentric amateur observations of comets C/2001 Q4 (NEAT) and C/2004 Q2 (Machholz) [7]. These amateur images, obtained with modern equipment and sensors, rival and sometimes arguably exceed the quality of professional images obtained only 2--3 decades ago. Multiple solar-wind velocity estimates were derived from each image and the results compared to observed and modelled near-Earth solar-wind data. Our unique analysis technique [Ramanjooloo et al., in preparation] allows us to determine the latitudinal variations of the solar wind, heliospheric current-sheet sector boundaries and the boundaries of transient features as a comet with an observable plasma tail probes the inner heliosphere. We present solar-wind velocity measurements derived from multiple observing locations of comets Lovejoy from the 14th -- 19th December 2011, comet Pan-STARRS during 11th -- 16th March 2013 and comet ISON from 12th -- 29th November 2013. Observations were gathered from multiple resources, from the SECCHI heliospheric imagers aboard STEREO A and B [8], the LASCO coronagraphs aboard SOHO [9], as well as ground-based amateur and professional observations coordinated by the CIOC. Overlapping observation sessions from the three spacecraft and ground-based efforts provided the perfect opportunity to use these comets as a diagnostic tool to understand solar-wind variability close to the Sun. We plan to compare our observations to results of suitable simulations [10] of plasma conditions in the corona and inner heliosphere during each of the comets' perihelion passage. The correlation of the solar-wind velocity distribution from different observing locations can provide clues towards the morphology and orientation of the plasma tail. We also attempt to determine the difficult-to-determine non-radial components of the measured solar-wind velocities.

Singing comet changes its song

NASA Astrophysics Data System (ADS)

Volwerk, M.; Goetz, C.; Delva, M.; Richter, I.; Tsurutani, B. T.; Eriksson, A.; Odelstad, E.; Meier, P.; Nilsson, H.; Glassmeier, K.-H.

2017-09-01

The singing comet was discovered at the beginning of the Rosetta mission around comet 67P/Churyumov-Gerasimenko. Large amplitude compressional waves with frequencies between 10 and 100 mHz were observed. When the comet became more active this signal was no longer measured. During the so-called tail excursion, late in the mission after perihelion, with again a less active comet, the singing was observed again and interestingly, going from 26 March to 27 March 2016 the character of the singing changed.

A survey of possible missions to the periodic comets in the interval 1974 - 2010

NASA Technical Reports Server (NTRS)

Bender, D. F.

1974-01-01

Catalogs are developed to survey the mission possibilities for the short period comets. In the first the physical and pertinent orbital characteristics are given for 65 short period comets. The second catalog is one containing the predicted perihelia for each of the 65 comets between 1974 and 2010. Geometry is included to indicate feasibility of Earth-based observation and sighting within 100 days of perihelion. The comets are divided on the basis of size and activity into three groups from the data in the first catalog: primary, secondary and low interest. The perihelia are separated into two groups: satisfactory and not satisfactory on the basis of earth-comet distance.

Automated segmentation of comet assay images using Gaussian filtering and fuzzy clustering.

PubMed

Sansone, Mario; Zeni, Olga; Esposito, Giovanni

2012-05-01

Comet assay is one of the most popular tests for the detection of DNA damage at single cell level. In this study, an algorithm for comet assay analysis has been proposed, aiming to minimize user interaction and providing reproducible measurements. The algorithm comprises two-steps: (a) comet identification via Gaussian pre-filtering and morphological operators; (b) comet segmentation via fuzzy clustering. The algorithm has been evaluated using comet images from human leukocytes treated with a commonly used DNA damaging agent. A comparison of the proposed approach with a commercial system has been performed. Results show that fuzzy segmentation can increase overall sensitivity, giving benefits in bio-monitoring studies where weak genotoxic effects are expected.

The comet rendezvous asteroid flyby mission to Comet Kopff - Getting there is half the fun

NASA Technical Reports Server (NTRS)

Sweetser, Theodore H.; Kiedron, Krystyna

1990-01-01

The goal of the Comet Rendezvous Asteroid Flyby mission (CRAF) is to fly 'outward to the beginning', to examine closely what are thought to be remnants of the origins of the solar system. In particular, the CRAF spacecraft will use a two-year delta-V-earth-gravity-assist (delta-V-EGA) trajectory to reach a rendezvous point near the aphelion of the Comet Kopff, flying by the asteroid 449 Hamburga on the way. This paper discusses the trajectory used to get to the comet. Topics covered include the launch period, possible additional asteroid flybys, the earth flyby, the Hamburga flyby, and the rendezvous with Comet Kopff.

A population of comets in the main asteroid belt.

PubMed

Hsieh, Henry H; Jewitt, David

2006-04-28

Comets are icy bodies that sublimate and become active when close to the Sun. They are believed to originate in two cold reservoirs beyond the orbit of Neptune: the Kuiper Belt (equilibrium temperatures of approximately 40 kelvin) and the Oort Cloud (approximately 10 kelvin). We present optical data showing the existence of a population of comets originating in a third reservoir: the main asteroid belt. The main-belt comets are unlike the Kuiper Belt and Oort Cloud comets in that they likely formed where they currently reside and may be collisionally activated. The existence of the main-belt comets lends new support to the idea that main-belt objects could be a major source of terrestrial water.

Book Review: The Origins of Comets

NASA Technical Reports Server (NTRS)

McKay, Christopher P.

1992-01-01

In The Origins of Comets, Bailey, Clube, and Napier propose that the answer to whether the ancient heavens were more interesting is a resounding "yes." The sky, in fact, has changed and is still changing. The authors trace the study of comets back to ancient Babylonian times with a focus on theories of the origins of these enigmatic visitors. The book is really of three distinct parts: the first six chapters provide an excellent and delightfully readable historical account of comet studies up to this century. The next few chapters give a rather detailed treatment of current models for comet origins. The last section treats the authors' own theories about the relationship between giant comets and extinctions on Earth.

Physical processes in comets

NASA Technical Reports Server (NTRS)

Whipple, F. L.; Huebner, W. F.

1976-01-01

The paper discusses physical processes in comets which involve solar and nuclear radial forces that affect the motions of gases and icy grains, gas-phase chemistry very close to the nuclei of large comets near the sun, sublimation of icy grains, dissociation of parent molecules into radicals and of radicals into atoms, and ionization by sunlight and collisions. The composition and dimensions of nuclei are examined along with variations in intrinsic brightness, the nature of volatiles, gas production rates in the coma, characteristics of icy grains in the coma, and the structure of streamers, ion tails, and dust tails. The structure of the coma is described in detail on the basis of spectroscopic observations of several comets. The origin of comets is briefly reviewed together with the relation of comets to earth, the interplanetary complex, and the interstellar medium. Desirable future observations are noted, especially by space missions to comets.

IUE observations of faint comets

NASA Technical Reports Server (NTRS)

Weaver, H. A.; Feldman, P. D.; Festou, M. C.; Ahearn, M. F.; Keller, H. U.

1981-01-01

Ultraviolet spectra of seven comets taken with the same instrument are given. The comets P/Encke (1980), P/Tuttle (1980 h), P/Stephan-Oterma (1980 g), and Meier (1980 q) were observed in November and December 1980 with the IUE satellite, and comets P/Borrelly (1980 i) and Panther (1980 u) were observed with the IUE on March 6, 1981. The spectra of these comets are compared with one another, as well as with comet Bradfield (1978 X), which was extensively studied earlier in 1980 with the IUE. To simplify the interpretation of the data and to minimize the dependence upon a specific model, the spectra are compared at approximately the same value of heliocentric distance whenever possible. Effects arising from heliocentric velocity, geocentric distance, and optical depth are also discussed. All of the cometary spectra are found to be remarkably similar, suggesting that these comets may have a common composition and origin.

IUE observations of faint comets

NASA Astrophysics Data System (ADS)

Weaver, H. A.; Feldman, P. D.; Festou, M.; A'Hearn, M. F.; Keller, H. U.

1981-09-01

Ultraviolet spectra of seven comets taken with the same instrument are given. The comets P/Encke (1980), P/Tuttle (1980 h), P/Stephan-Oterma (1980 g), and Meier (1980 q) were observed in November and December 1980 with the IUE satellite, and comets P/Borrelly (1980 i) and Panther (1980 u) were observed with the IUE on March 6, 1981. The spectra of these comets are compared with one another, as well as with comet Bradfield (1978 X), which was extensively studied earlier in 1980 with the IUE. To simplify the interpretation of the data and to minimize the dependence upon a specific model, the spectra are compared at approximately the same value of heliocentric distance whenever possible. Effects arising from heliocentric velocity, geocentric distance, and optical depth are also discussed. All of the cometary spectra are found to be remarkably similar, suggesting that these comets may have a common composition and origin.

Search for Dormant Comets in Near-Earth Space

NASA Astrophysics Data System (ADS)

Kim, Yoonyoung

2013-06-01

It is considered that comets have been injected into near-Earth space from outer region (e.g. Kuiper-belt region), providing rich volatile and organic compounds to the earth. Some comets are still active while most of them are dormant with no detectable tails and comae. Here we propose to make a multi-band photometric observation of near-Earth objects (NEOs) with comet-like orbits. We select our targets out of infrared asteroidal catalogs based on AKARI and WISE observations. With a combination of taxonomic types by Subaru observation and albedos by AKARI or WISE, we aim to dig out dormant comet candidates among NEOs. Our results will provide valuable information to figure out the dynamical evolution and fate of comets. We would like to emphasize that this is the first taxonomic survey of dormant comets to utilize the infrared data archive with AKARI and WISE.

Stardust: Catching a Comet and Bringing it Home

NASA Technical Reports Server (NTRS)

Brownlee, Donald E.

2007-01-01

The NASA STARDUST mission collected thousands of particles from Comet Wild 2 that are now being studied by two hundred scientists around the world. The spacecraft captured the samples during a close flyby of the comet in 2004 and returned them to Earth with a dramatic entry into the atmosphere early in 2006. The precious cargo of comet dust is being studied to determine new information about the origin of the Sun and planets. The comet formed at the edge of the solar system, beyond the orbit of Neptune, and is a sample of the material from which the solar system was formed. One of the most dramatic early findings from the mission was that a comet that formed in the coldest place in the solar system contained minerals that formed in the hottest place in the solar system. The comet samples are telling stories of fire and ice and they providing fascinating and unexpected information about our origins.

Look--It's a Comet!

ERIC Educational Resources Information Center

Berglund, Kay

1997-01-01

Describes a classroom lesson on comets that uses modeling and guided imagery to spark students' curiosity. Comet models are built using chunks of rock salt, polystyrene balls, and tinsel. Abstract ideas are made more concrete with a guided imagery story called Comet Ride! Includes an introduction to the use of parallax to measure the distance of…

Comet Kohoutek, 1973-1974, A Teachers' Guide with Student Activities.

ERIC Educational Resources Information Center

Chapman, Robert D.

This teacher's guide provides background information, curriculum source materials, and suggested class activities for class discussion and study. Information related to the discovery of the comet is presented as well as photographic and schematic pictures showing the sky through which the comet travels. Historical data regarding comets of the past…

CORSAIR (COmet Rendezvous, Sample Acquisition, Investigation, and Return): A New Frontiers Mission Concept to Collect Samples from a Comet and Return Them to Earth for Study

NASA Astrophysics Data System (ADS)

Sandford, S. A.; Chabot, N. L.; Dello Russo, N.; Leary, J. C.; Reynolds, E. L.; Weaver, H. A.; Wooden, D. H.

2017-07-01

CORSAIR (COmet Rendezvous, Sample Acquisition, Investigation, and Return) is a mission concept submitted in response to NASA's New Frontiers 4 call. CORSAIR's proposed mission is to return comet nucleus samples to Earth for detailed analysis.

Comets and the origin of the solar system - Reading the Rosetta Stone

NASA Technical Reports Server (NTRS)

Mumma, Michael J.; Weissman, Paul R.; Stern, S. A.

1993-01-01

It is argued that, from the measured volatile abundances, comets formed at temperatures near or below about 60 K and possibly as low as about 25 K. Grains in Comet Halley were found to be of two types: silicates and organics. Isotopic evidence shows that Comet Halley formed from material with the same compositional mix as the rest of the solar system, and is consistent with comets having been a major contributor to the volatile reservoirs on the terrestrial planets. A variety of processes have been shown to modify and reprocess the outer layers of comets both during their long residence time in the Oort cloud and following their entry back into the planetary system. The most likely formation site for comets is in the Uranus-Neptune zone or just beyond, with dynamical ejection by the growing protoplanets to distant orbits to form the Oort cloud. A substantial flux of interstellar comets was likely created by the same process, and may be detectable if cometary formation is common in planetary systems around other stars.

Meteoroid Streams from Sunskirter Comet Breakup

NASA Astrophysics Data System (ADS)

Jenniskens, P. M.

2012-12-01

In its first year of operations, the CAMS project (Cameras for Allsky Meteor Surveillance) has measured 47,000 meteoroid orbits at Earth, including some that pass the Sun as close as 0.008 AU. The population density increases significantly above perihelion distance q = 0.037 AU. Meteoroid streams are known with q about 0.1 AU. The Sun has a profound effect on comets that pass at 0.04-0.16 AU distance, called the sunskirter comets. SOHO and STEREO see families of small comets called the Marsden and Kracht groups. Sunlight is efficiently scattered by small 10-m sized fragments, making those fragments visible even when far from Earth. These comet groups are associated with meteor showers on Earth, in particular the Daytime Arietids and Delta Aquariids. All are related to 96P/Machholz, a highly inclined short-period (5.2 year) Jupiter family comet that comes to within 0.12 AU from the Sun, the smallest perihelion distance known among numbered comets. The proximity of the Sun speeds up the disintegration process, providing us a unique window on this important decay mechanism of Jupiter family comets and creating meteoroid streams. These are not the only sunskirting comets, however. In this presentation, we will present CAMS observations of the complete low-q meteoroid population at Earth and review their association with known parent bodies.

Millimetre observations of comets P/Brorsen-Metcalf (1989o) and Austin (1989c1) with the IRAM 30-m radio telescope

NASA Technical Reports Server (NTRS)

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

1990-01-01

Millimeter observations with the IRAM 30 m telescope were conducted in comet P/Brorsen-Metcalf (1989o) on September 1989 and Austin (1989c1) on April and May 1990. The HCN J(1-0) and J(3-2) lines were detected in both comets. The HCN production rate relative to water in P/Brorsen-Metcalf is comparable to that previously measured in comet P/Halley, while that inferred in comet Austin might be smaller by a factor of two. The H2CO(3 sub 12 - 2 sub 11) transition, marginally observed in comet P/Brorsen-Metcalf, was firmly detected in May 1990 in comet Austin. Observations performed at offset positions suggest that the source of H2CO might be distributed. The H2CO abundance is on the order of 0.5 percent that of water for both comets, assuming a scalelength of 10(exp 4) km at 1 AU from the Sun for the distributed source. During the May observing period of comet Austin, two new species were detected for the first time in a comet: hydrogen sulfide (H2S) through its 1(sub 10) - 1(sub 01) ortho line at 169 GHz, and methanol (CH3OH) through J(3-2) delta K = 0 transitions at 145 GHz. Preliminary estimates of their abundances are 1.5 x 10(exp -3) for H2S and 8 x 10(exp -3) for CH3OH.

A new method for determining the mass ejected during the cometary outburst - Application to the Jupiter-family comets

NASA Astrophysics Data System (ADS)

Wesołowski, M.; Gronkowski, P.

2018-07-01

In the present article, we propose a new method of mass estimation which is ejected from a nucleus of a comet during its outburst of brightness. The phenomena of cometary outburst are often reported for both periodic and parabolic comets. The outburst of a comet brightness is a sudden increase in its brightness greater than one magnitude, average by 2-5 mag. This should not be confused with explosions such as outbreak of a bomb. The essence of the phenomenon is only a sudden brightening of the comet. Long-term observations and studies of this phenomenon lead to the conclusion that the very probable direct cause of the many outbursts is the ejection of the some part of surface layer of a comet's nucleus and an increase in the rate of a sublimation (Hughes (1990), Gronkowski (2007), Gronkowski and Wesołowski (2015)). The purpose of this article is presentation of a new simple method of the estimation of the mass which is ejected from the comet's nucleus during considered phenomenon. To estimate the mass released during an outburst, different probable coefficients of extinction for cometary matter was assumed. The scattering cross-sections of cometary grains were precisely calculated on the basis of Mie's theory. This method was applied to the outburst of a hypothetical comet X/PC belonging to the Jupiter-family comets and to the case of the comet 17P/Holmes outburst in 2007.

On the problem of origin of periodic comets.

NASA Astrophysics Data System (ADS)

Guliev, A. S.

The problem of origin of periodic comets is viewed under various aspects. A steady growth of the fraction of these comets in the overall population of comets is emphasized. The number of discovered periodic comets with small eccentricities and with the Jacobi constant close to 3 is also growing eventually. Comparison of maximum magnitudes of the same comets in different apparitions at the same elongations as well as the analysis of exhausted comets indicate that the age of these objects does not exceed 1000 years. Capture is considered as an efficient mechanism for preserving equilibrium over reasonable time intervals. The analysis of the data given by Everhart and the calculations of the evolution of cometary orbits reveal small efficiency of capture. Comparison of the number of well established capture cases with the corresponding time interval shows that the age of the system of periodic comets must be 17000 years within the framework of this mechanism. This is most unlikely. Secular variations in the distributions of semimajor axes, inclinations, longitudes of perihelia, eccentricities of orbits of periodic comets are analysed. On the average, the eccentricities tend to increase, but this conflicts with the capture mechanism. A conclusion is made that the concept of capture in its classical and modern versions is unable to solve the problem of the origin of periodic comets on the whole. Other, more effective sources and mechanisms seem to be also in operation in enlarging the cometary system.

Cytogenetic status and oxidative DNA-damage induced by atorvastatin in human peripheral blood lymphocytes: standard and Fpg-modified comet assay.

PubMed

Gajski, Goran; Garaj-Vrhovac, Vera; Orescanin, Visnja

2008-08-15

To investigate the genotoxic potential of atorvastatin on human lymphocytes in vitro standard comet assay was used in the evaluation of basal DNA damage and to investigate possible oxidative DNA damage produced by reactive oxygen species (ROS) Fpg-modified version of comet assay was also conducted. In addition to these techniques the new criteria for scoring micronucleus test were applied for more complete detection of baseline damage in binuclear lymphocytes exposed to atorvastatin 80 mg/day in different time periods by virtue of measuring the frequency of micronuclei, nucleoplasmic bridges and nuclear buds. All parameters obtained with the standard comet assay and Fpg-modified comet assay were significantly higher in the treated than in control lymphocytes. The Fpg-modified comet assay showed a significantly greater tail length, tail intensity, and tail moment in all treated lymphocytes than did the standard comet assay, which suggests that oxidative stress is likely to be responsible for DNA damage. DNA damage detected by the standard comet assay indicates that some other mechanism is also involved. In addition to the comet assay, a total number of micronuclei, nucleoplasmic bridges and nuclear buds were significantly higher in the exposed than in controlled lymphocytes. Regression analyses showed a positive correlation between the results obtained by the comet (Fpg-modified and standard) and micronucleus assay. Overall, the study demonstrated that atorvastatin in its highest dose is capable of producing damage on the level of DNA molecule and cell.

Testing solar system formation models using Pan-STARRS1 detections of nearly inactive Manx comets

NASA Astrophysics Data System (ADS)

Boe, Benjamin; Jedicke, Robert; Meech, Karen Jean; Morbidelli, Alessandro; Wiegert, Paul

2016-10-01

Newly discovered Manx comets show low levels of sublimation at perihelion indicating significantly lower volatile abundance compared to typical long period comets. The S-class spectrum of Manx comet C/2014 S3 (PANSTARRS) indicates that they may have formed in the inner solar system and were later perturbed to the highly eccentric orbits observed today (Meech et al. 2016). We used the Pan-STARRS1 observation history and its Moving Object Processing System (MOPS) (Denneau et al. 2013) to model Manx detections since Pan-STARRS has been the primary discovery source of Manx comets. A synthetic Manx population was generated according to the Wiegert and Tremaine (1999) model and processed through MOPS to determine the expected Pan-STARRS1 detections and the corresponding detection efficiencies for Manx comets as a function of each orbital parameter and object size. The population of normal long period comets (LPCs) was modeled in the same fashion. Unbiased populations for LPCs and Manx comets were computed by correcting the real comet populations with the detection efficiencies. Finally, the ratio of the bias corrected number of Manx comets to LPCs is compared to the predictions of various solar system formation models.References:Meech, K. J. et al. (2016), Science Advances 2, 4, id. E1600038.Denneau, L. et al. (2013), Publications of the Astronomical Society of the Pacific, 125, 926, 357-395Wiegert, P. and Tremaine, S. (1999), Icarus, 137, 1, 84-121.

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).

Competitive Memory Training (COMET) for low self-esteem in patients with personality disorders: a randomized effectiveness study.

PubMed

Korrelboom, Kees; Marissen, Marlies; van Assendelft, Tanja

2011-01-01

Self-esteem is a major concern in the treatment of patients with personality disorders in general. In patients with borderline personality disorder, low self-esteem is associated with factors contributing to suicidal and self-injurious behaviour. At the moment there are no well-proven interventions that specifically target low self-esteem. Recently, a new approach, Competitive Memory Training or COMET, aimed at the enhancement of retrieving beneficial information from memory, appeared to be successful in addressing low self-esteem in different patient populations. To assess whether COMET for low self-esteem is also an effective intervention for patients with personality disorders. 91 patients with personality disorders who were already in therapy in a regular mental health institution were randomly assigned to either 7 group sessions of COMET in addition to their regular therapy or to 7 weeks of ongoing regular therapy. These latter patients received COMET after their “7 weeks waiting period for COMET”. All patients that completed COMET were contacted 3 months later to assess whether the effects of COMET had remained stable. Compared to the patients who received regular therapy only, patients in the COMET + regular therapy condition improved significantly and with large effect sizes on indices of self-esteem and depression. Significant differential improvements on measures of autonomy and social optimism were also in favour of COMET, but had small to intermediate effect sizes. The therapeutic effects of COMET remained stable after 3 months on three out of the four outcome measures. COMET for low self-esteem seems to be an efficacious trans-diagnostic approach that can rather easily be implemented in the treatment of patients with personality disorders.

Dust environment and dynamical history of a sample of short-period comets . II. 81P/Wild 2 and 103P/Hartley 2

NASA Astrophysics Data System (ADS)

Pozuelos, F. J.; Moreno, F.; Aceituno, F.; Casanova, V.; Sota, A.; López-Moreno, J. J.; Castellano, J.; Reina, E.; Climent, A.; Fernández, A.; San Segundo, A.; Häusler, B.; González, C.; Rodriguez, D.; Bryssinck, E.; Cortés, E.; Rodriguez, F. A.; Baldris, F.; García, F.; Gómez, F.; Limón, F.; Tifner, F.; Muler, G.; Almendros, I.; de los Reyes, J. A.; Henríquez, J. A.; Moreno, J. A.; Báez, J.; Bel, J.; Camarasa, J.; Curto, J.; Hernández, J. F.; González, J. J.; Martín, J. J.; Salto, J. L.; Lopesino, J.; Bosch, J. M.; Ruiz, J. M.; Vidal, J. R.; Ruiz, J.; Sánchez, J.; Temprano, J.; Aymamí, J. M.; Lahuerta, L.; Montoro, L.; Campas, M.; García, M. A.; Canales, O.; Benavides, R.; Dymock, R.; García, R.; Ligustri, R.; Naves, R.; Lahuerta, S.; Pastor, S.

2014-11-01

Aims: This paper is a continuation of the first paper in this series, where we presented an extended study of the dust environment of a sample of short-period comets and their dynamical history. On this occasion, we focus on comets 81P/Wild 2 and 103P/Hartley 2, which are of special interest as targets of the spacecraft missions Stardust and EPOXI. Methods: As in the previous study, we used two sets of observational data: a set of images, acquired at Sierra Nevada and Lulin observatories, and the Afρ data as a function of the heliocentric distance provided by the amateur astronomical association Cometas-Obs. The dust environment of comets (dust loss rate, ejection velocities, and size distribution of the particles) was derived from our Monte Carlo dust tail code. To determine their dynamical history we used the numerical integrator Mercury 6.2 to ascertain the time spent by these objects in the Jupiter family Comet region. Results: From the dust analysis, we conclude that both 81P/Wild 2 and 103P/Hartley 2 are dusty comets, with an annual dust production rate of 2.8 × 109 kg yr-1 and (0.4-1.5) × 109 kg yr-1, respectively. From the dynamical analysis, we determined their time spent in the Jupiter family Comet region as ~40 yr in the case of 81P/Wild 2 and ~1000 yr for comet 103P/Hartley 2. These results imply that 81P/Wild 2 is the youngest and the most active comet of the eleven short-period comets studied so far, which tends to favor the correlation between the time spent in JFCs region and the comet activity previously discussed.

Study of sungrazing comets with space-based coronagraphs: new possibilities offered by METIS on boar Solar Orbiter

NASA Astrophysics Data System (ADS)

Bemporad, Alessandro

Thanks to the launch of SOHO in the end of 1995 and to the continuous monitoring of the white light (WL) corona offered by the LASCO coronagraphs, it was discovered that sungrazing comets are much more common than previously thought. More than 2500 comets have been discovered over about 17 years, hence slightly less than a comet every 2 days is observed by coronagraphs. The white light emission seen by SOHO/LASCO and more recently also by the STEREO/SECCHI instruments provides information not only on the comet orbits (hence on its origin), but also on the dust-tail formation, dust-tail disconnection, occurrence of nucleus fragmentation and nucleus disintegration processes. Very interestingly, a few sungrazing comets have been also observed in the UV spectra by the SOHO UV Coronagraph Spectrometer (UVCS) and the strong emission observed in the H I Lyman-alpha lambda 1216 Å line provided direct information also on the water outgassing rate, tail chemical composition, nucleus size and occurrence of nucleus fragmentations. Moreover, the UV cometary emission provides a new method to estimate physical parameters of the coronal plasma met by the comet (like electron density, proton temperature and solar wind velocity), in a way that these comets can be considered as “local probes” for the solar corona. Unique observations of comets will be provided in the next future by the METIS coronagraph on board the Solar Orbiter mission: METIS will contemporary observe the corona in WL and in UV (HI Lyman-alpha), hence will be a unique instrument to study at the same time the transiting comets and the solar corona being crossed by the comets. Previous results and new possibilities offered by METIS on these topics are summarized and discussed here.

THE PLASMA ENVIRONMENT IN COMETS OVER A WIDE RANGE OF HELIOCENTRIC DISTANCES: APPLICATION TO COMET C/2006 P1 (MCNAUGHT)

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

Shou, Y.; Combi, M.; Gombosi, T.

2015-08-20

On 2007 January 12, comet C/2006 P1 (McNaught) passed its perihelion at 0.17 AU. Abundant remote observations offer plenty of information on the neutral composition and neutral velocities within 1 million kilometers of the comet nucleus. In early February, the Ulysses spacecraft made an in situ measurement of the ion composition, plasma velocity, and magnetic field when passing through the distant ion tail and the ambient solar wind. The measurement by Ulysses was made when the comet was at around 0.8 AU. With the constraints provided by remote and in situ observations, we simulated the plasma environment of Comet C/2006more » P1 (McNaught) using a multi-species comet MHD model over a wide range of heliocentric distances from 0.17 to 1.75 AU. The solar wind interaction of the comet at various locations is characterized and typical subsolar standoff distances of the bow shock and contact surface are presented and compared to analytic solutions. We find the variation in the bow shock standoff distances at different heliocentric distances is smaller than the contact surface. In addition, we modified the multi-species model for the case when the comet was at 0.7 AU and achieved comparable water group ion abundances, proton densities, plasma velocities, and plasma temperatures to the Ulysses/SWICS and SWOOPS observations. We discuss the dominating chemical reactions throughout the comet-solar wind interaction region and demonstrate the link between the ion composition near the comet and in the distant tail as measured by Ulysses.« less

Extrasolar comets: The origin of dust in exozodiacal disks?

NASA Astrophysics Data System (ADS)

Marboeuf, U.; Bonsor, A.; Augereau, J.-C.

2016-11-01

Comets have been invoked in numerous studies as a potentially important source of dust and gas around stars, but none has studied the thermo-physical evolution, out-gassing rate, and dust ejection of these objects in such stellar systems. In this paper we investigate the thermo-physical evolution of comets in exo-planetary systems in order to provide valuable theoretical data required to interpret observations of gas and dust. We use a quasi-3D model of cometary nucleus to study the thermo-physical evolution of comets evolving around a single star from 0.1 to 50 AU, whose homogeneous luminosity varies from 0.1 to 70L⊙. This paper provides thermal evolution, physical alteration, mass ejection, lifetimes, and the rate of dust and water gas mass productions for comets as a function of the distance to the star and stellar luminosity. Results show significant physical changes to comets at high stellar luminosities. The mass loss per revolution and the lifetime of comets depend on their initial size, orbital parameters and follow a power law with stellar luminosity. The models are presented in such a manner that they can be readily applied to any planetary system. By considering the examples of the Solar System, Vega and HD 69830, we show that dust grains released from sublimating comets have the potential to create the observed (exo)zodiacal emission. We show that observations can be reproduced by 1 to 2 massive comets or by a large number of comets whose orbits approach close to the star. Our conclusions depend on the stellar luminosity and the uncertain lifetime of the dust grains. We find, as in previous studies, that exozodiacal dust disks can only survive if replenished by a population of typically sized comets renewed from a large and cold reservoir of cometary bodies beyond the water ice line. These comets could reach the inner regions of the planetary system following scattering by a (giant) planet.

Physical activity of the selected nearly isotropic comets with perihelia at large heliocentric distance

NASA Astrophysics Data System (ADS)

Kulyk, I.; Rousselot, P.; Korsun, P. P.; Afanasiev, V. L.; Sergeev, A. V.; Velichko, S. F.

2018-03-01

Context. The systematic investigation of comets in a wide range of heliocentric distances can contribute to a better understanding of the physical mechanisms that trigger activity at large distances from the Sun and reveals possible differences in the composition of outer solar system bodies belonging to various dynamical groups. Aims: We seek to analyze the dust environment of the selected nearly isotropic comets with a perihelion distance between 4.5 and 9.1 au, where sublimation of water ice is considered to be negligible. Methods: We present results of multicolor broadband photometric observations for 14 distant active objects conducted between 2008 and 2015 with various telescopes. Images obtained with broadband filters were used to investigate optical colors of the cometary comae and to quantify physical activity of the comet nuclei. Results: The activity level was estimated with Afρ parameters ranging between 95 ± 10 cm and 9600 ± 300 cm. Three returning comets were less active than the dynamically new comets. Dust production rates of the comet nuclei were estimated between 1 and 100 kg s-1 based on some assumptions about the physical properties of dust particles populating comae. The measured colors point out reddening of the continuum for all the comets. The mean values of a normalized reflectivity gradient within the group of the comets amount to 14 ± 2% per 1000 Å and 3 ± 2% per 1000 Å in the BV and VR spectral domains, respectively. The comae of the dynamically new comets, which were observed on their inbound legs, may be slightly redder in the blue spectral interval than comae of the comets observed after the perihelion passages. The dynamically new comets observed both pre- and post-perihelion, seem to have higher production rates post-perihelion than pre-perihelion for similar heliocentric distances.

Comet Siding Spring Seen Next to Mars

NASA Image and Video Library

2017-12-08

This composite NASA Hubble Space Telescope Image captures the positions of comet Siding Spring and Mars in a never-before-seen close passage of a comet by the Red Planet, which happened at 2:28 p.m. EDT October 19, 2014. The comet passed by Mars at approximately 87,000 miles (about one-third of the distance between Earth and the Moon). At that time, the comet and Mars were approximately 149 million miles from Earth. The comet image shown here is a composite of Hubble exposures taken between Oct. 18, 8:06 a.m. EDT to Oct. 19, 11:17 p.m. EDT. Hubble took a separate photograph of Mars at 10:37 p.m. EDT on Oct. 18. The Mars and comet images have been added together to create a single picture to illustrate the angular separation, or distance, between the comet and Mars at closest approach. The separation is approximately 1.5 arc minutes, or one-twentieth of the angular diameter of the full Moon. The background starfield in this composite image is synthesized from ground-based telescope data provided by the Palomar Digital Sky Survey, which has been reprocessed to approximate Hubble’s resolution. The solid icy comet nucleus is too small to be resolved in the Hubble picture. The comet’s bright coma, a diffuse cloud of dust enshrouding the nucleus, and a dusty tail, are clearly visible. This is a composite image because a single exposure of the stellar background, comet Siding Spring, and Mars would be problematic. Mars is actually 10,000 times brighter than the comet, and so could not be properly exposed to show detail in the Red Planet. The comet and Mars were also moving with respect to each other and so could not be imaged simultaneously in one exposure without one of the objects being motion blurred. Hubble had to be programmed to track on the comet and Mars separately in two different observations. The images were taken with Hubble’s Wide Field Camera 3. Credit: NASA, ESA, PSI, JHU/APL, STScI/AURA Credit: NASA, ESA, PSI, JHU/APL, STScI/AURA

Mid-infrared observations of sungrazing comet C/2012 S1 (ISON) with the Subaru Telescope

NASA Astrophysics Data System (ADS)

Ootsubo, T.; Usui, F.; Takita, S.; Watanabe, J.; Yanamandra-Fisher, P.; Honda, M.; Kawakita, H.; Furusho, R.

2014-07-01

Comets are the frozen reservoirs of the early solar nebula and are made of ice and dust. The determination of the properties for cometary dust provides us insight into both the early-solar-nebula environment and the formation process of the planetary system. A silicate feature is often observed in comet spectra in the mid-infrared region and may be used for probing the early history of the solar system. In most cases, the feature shows the existence of crystalline silicate (for example, 11.3 microns) together with amorphous silicate [1,2]. Since the crystallization of silicates from amorphous ones generally requires high-temperature annealing above 800 K (e.g., [3,4]), it is believed that the crystalline silicate grains produced at the inner part of the disk were transported to the outer cold regions where the comet nuclei formed. Comet C/2012 S1 (ISON) is a long-period Oort Cloud comet, discovered in September 2012. In particular, comet ISON is a sungrazing comet, which was predicted to pass close by the Sun and the Earth and becoming a bright object. Mid-infrared observations of this new comet and investigation of the 10-micron silicate feature help us understand the formation of crystalline silicate grains in the early solar nebula. We conducted observations of comet ISON in the mid-infrared wavelength region with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru Telescope on Mauna Kea, Hawaii [5,6,7]. The observation of comet ISON was carried out on 2013 October 19 and 21 UT. Since the weather conditions were not so good when we observed, we carried out N-band imaging observations (8.8 and 12.4 microns) and N-band low-resolution spectroscopy. The spectrum of comet ISON can be fit with the 260--265-K blackbody spectrum when we use the regions of 7.8--8.2 and 12.4--13.0 microns as the continuum. The spectrum has only a weak silicate excess feature, which may be able to attribute to small amorphous olivine grains. We could not detect a clear crystalline silicate feature in the spectrum of our observations. We will compare the spectrum with other Oort Cloud comets, such as comets C/2011 L4 (PanSTARRS) and C/2013 R1 (Lovejoy), and discuss the dust properties and the birthplace of comet ISON.

New catalogue of single-apparition comets discovered in the years 1901-1950. Part I

NASA Astrophysics Data System (ADS)

Królikowska, M.; Sitarski, G.; Pittich, E.; Szutowicz, S.; Ziołkowski, K.; Rickman, H.; Gabryszewski, R.; Rickman, B.

2014-07-01

A new catalogue of cometary orbits derived using a completely homogeneous method of data treatment, accurate methods of numerical integration, and modern model of the Solar System is presented. We constructed a sample of near-parabolic comets from the first half of the twentieth century with original reciprocals of semimajor axes less than 0.000130 au^{-1} in the Marsden and Williams Catalogue of Cometary Orbits (2008, hereafter MW08), i.e., comets of original semimajor axes larger than 7700 au. We found 38 such comets in MW08, where 32 have first-quality orbits (class 1A or 1B) and the remaining 6 have second-quality orbits (2A or 2B). We presented satisfactory non-gravitational (hereafter NG) models for thirteen of the investigated comets. The four main features, distinguishing this catalogue of orbits of single- apparition comets discovered in the early twentieth century from other catalogues of orbits of similarly old objects, are the following. 1. Old cometary positional observations require a very careful analysis. For the purpose of this new catalogue, great emphasis has been placed in collecting sets of observations as complete as possible for the investigated comets. Moreover, for many observations, comet-minus-star-type measurements were also available. This type of data was particularly valuable as the most original measurements of comet positions and has allowed us to recalculate new positions of comets using the PPM star catalogue. 2. Old cometary observations were prepared by observers usually as apparent positions in Right Ascension and Declination or as reduced positions for the epoch of the beginning of the year of a given observation. This was a huge advantage of these data, because this allows us to uniformly take into account all necessary corrections associated with the data reduction to the standard epoch. 3. The osculating orbits of single-apparition comets discovered more than sixty years ago have been formerly determined with very different numerical methods and assumptions on the model of the Solar System, including the number of planets taken into account. This new catalogue changes this situation. We offer a new catalogue of cometary orbits derived using completely homogeneous methods of data treatment, accurate methods of numerical integration, and a modern model of the Solar System. 4. The osculating, original, and future sets of orbits are presented for each catalogue comet. In the case of a comet with detectable NG effects, we give both types of orbit: purely gravitational and non- gravitational. We concluded, however, that all thirteen NG orbital solutions given in the catalogue better represent the actual motions of the investigated comets. Surprisingly, the NG effects were detectable in data for five comets of second-quality-class orbits. Among these five are three comets with hyperbolic original, barycentric GR orbits. This publication will be accompanied by an online catalogue available at ssdp.cbk.waw.pl/LPCs, providing entries to orbital elements of considered comets as well as to full swarms of original and future virtual comets that formed the basis for the further analysis of dynamical evolution.

A Comet's Missing Light

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-05-01

On 28 November 2013, comet C/2012 S1 better known as comet ISON should have passed within two solar radii of the Suns surface as it reached perihelion in its orbit. But instead of shining in extreme ultraviolet (EUV) wavelengths as it grazed the solar surface, the comet was never detected by EUV instruments. What happened to comet ISON?Missing EmissionWhen a sungrazing comet passes through the solar corona, it leaves behind a trail of molecules evaporated from its surface. Some of these molecules emit EUV light, which can be detected by instruments on telescopes like the space-based Solar Dynamics Observatory (SDO).Comet ISON, a comet that arrived from deep space and was predicted to graze the Suns corona in November 2013, was expected to cause EUV emission during its close passage. But analysis of the data from multiple telescopes that tracked ISON in EUV including SDO reveals no sign of it at perihelion.In a recent study, Paul Bryans and DeanPesnell, scientists from NCARs High Altitude Observatory and NASA Goddard Space Flight Center, try to determine why ISON didnt display this expected emission.Comparing ISON and LovejoyIn December 2011, another comet dipped into the Suns corona: comet Lovejoy. This image, showingthe orbit Lovejoy took around the Sun, is a composite of SDO images of the pre- and post-perihelion phases of the orbit. Click for a closer look! The dashed part of the curve represents where Lovejoy passed out of view behind the Sun. [Bryans Pesnell 2016]This is not the first time weve watched a sungrazing comet with EUV-detecting telescopes: Comet Lovejoy passed similarly close to the Sun in December 2011. But when Lovejoy grazed the solar corona, it emitted brightly in EUV. So why didnt ISON? Bryans and Pesnell argue that there are two possibilities:the coronal conditions experienced by the two comets were not similar, orthe two comets themselves were not similar.To establish which factor is the most relevant, the authors first demonstrate that both comets experienced very similar radiation fields as they passed perihelion. They also show that the properties of the Suns corona experienced by each comet like its density and magnetic field topology were roughly the same.Bryans and Pesnell argue that, as both comets appear to have encountered similar solar conditions, the most likely explanation for ISONs lack of detectable EUV emission is that it didnt deposit as much material in its orbit as Lovejoy did. They show that this would happen if ISONs nucleus were four times smaller in radius than Lovejoys, spanning a mere 5070 meters in comparison to Lovejoys 200300 meters.This conclusion is consistent with white-light observations of ISON that suggest that, though it might have started out significantly larger than Lovejoy, ISON underwent dramatic mass loss as it approached the Sun. By the time it arrived at perihelion, it was likely no longer large enough to create a strong EUV signal resulting in the non-detection of this elusive comet with SDO and other telescopes.CitationPaul Bryans and W. Dean Pesnell 2016 ApJ 822 77. doi:10.3847/0004-637X/822/2/77

What's Causing the Activity on Comet 67P?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-09-01

Comet 67P/ChuryumovGerasimenko made famous by the explorations of the Rosetta mission has been displaying puzzling activity as it hurtles toward the Sun. However, recent modeling of the comet by a group of scientists from the Cte dAzur University may now explain whats causing 67Ps activity.Shadowed ActivityA model of comet 67P, with the colors indicating the rate of change of the temperature on the comets surface. The most rapid temperature changes are seen at the comets neck, in the same locations as the early activity seen in the Rosetta images. [Al-Lagoa et al. 2015] Between June and September of 2014, Rosetta observed comet 67P displaying early activity in the form of jets of dust emitted from near the neck of the comet (its narrowest point). Such activity is usually driven by the sublimation of volatiles from the comets surface as a result of sun exposure. But the neck of the comet is frequently shadowed as the comet rotates, and it receives significantly less sunlight than the rest of the comet. So why would the early activity originate from the comets neck?The authors of a recent study, led by Victor Al-Lagoa, hypothesize that its precisely because the neck is receiving alternating sunlight/shadows that its displaying activity. They suggest that thermal cracking of the surface of the comet is happening faster in this region, due to the rapid changes in temperature that result from the shadows cast by the surrounding terrain. The cracking exposes subsurface ices in the neck faster than in other regions, and the ensuing sublimation of that ice is what creates the activity were seeing.Temperature Models: To test their hypothesis, the authors study the surface temperatures on comet 67P by means of a thermophysical model a model used to calculate the temperatures on an airless body, both on and below the surface. The model takes into account factors like thermal inertia (how quickly the bodys temperature responds to changes in the incident energy), shadowing, and self-heating between parts of the surface in contact.Plot of the modeled temperature of two typical surfaces on the comet: one from the neck region (solid line) and one from the head region (dashed line). Unlike the head, the neck displays drastic drops in temperature as a result of shadowing. [Al-Lagoa et al. 2015]Using this model, the authors find that the temperatures behaved as they predicted: the shadows falling on the comets neck causes this region to experience very rapid temperature changes relative to the rest of the body. The authors also found a definite correlation between the regions of most rapid temperature variations and the regions of the comet that show signs of activity in Rosetta images. This provides strong evidence that thermal cracking is indeed taking place in the shadowed regions of the neck, gradually eroding away the surface.Should this model prove correct, its a step toward understanding the evolution of comets like 67P. In addition, the results from this study imply that thermal cracking might happen faster than previously estimated in shadowed regions of other atmosphereless bodies, both near Earth and in the asteroid belt.CitationV. Al-Lagoa et al 2015 ApJ 810 L22. doi:10.1088/2041-8205/810/2/L22

Flyby Comet Imaged By Radar

NASA Image and Video Library

2016-03-24

Radar data of comet P/2016 BA14 taken over three days (March 21-23, 2016), when the comet was between 2.5 million miles and 2.2 million miles (4.1 million kilometers and 3.6 million kilometers) from Earth. Radar images from the flyby indicated that the comet is about 3,000 feet (1 kilometer) in diameter.

Infrared Observations of Comets Halley and Wilson and Properties of the Grains

NASA Technical Reports Server (NTRS)

Hanner, Martha S. (Editor)

1988-01-01

The presented papers and discussions at a workshop held at Cornell Univ. are summarized. The infrared observations of Comet Halley and Comet Wilson are reviewed and they are related to optical properties and composition of cometary grains. Relevant laboratory studies are also discussed. Recommendations are made for future infrared comet observations and supporting laboratory investigations.

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.

To Catch A Comet...Learning From Halley's.

ERIC Educational Resources Information Center

National Aeronautics and Space Administration, Washington, DC.

Comet chronicles and stories extend back over thousands of years. A common theme has been that comets are a major cause of catastrophe and tragedy here on earth. In addition, both Aristotle and Ptolemy believed that comets were phenomena within the earth's atmosphere, and it wasn't until the 16th century, when Danish astronomer Tycho Brache…

Comets, carbonaceous chondrites, and interstellar clouds: Condensation of carbon

NASA Technical Reports Server (NTRS)

Field, G. B.

1979-01-01

Comets, carbonaceous chondrites, and interstellar clouds are discussed in relation to information on interstellar dust. The formation and presence of carbon in stars, comets, and meteorites is investigated. The existence of graphite in the interstellar medium, though it is predicted from thermodynamic calculations, is questioned and the form of carbon contained in comets is considered.

Investigation of the phenomenon of the big comet of 1858

NASA Technical Reports Server (NTRS)

Pape, C. F.

1977-01-01

Various aspects of the large comet of 1858 including the luminosity of the core and the shape, intensity and position of the tail with respect to the sun and stars are described and then compared with the large comet of 1744 described by Heinsius and Halley's comet of 1835. The purpose of these observations is to try to gain a clearer understanding of the nature of the polar force from the sun acting on the comet. This force is said to differ from the usual force of gravity.

The anomalous molecular abundances of Comet P/Wolf-Harrington

NASA Technical Reports Server (NTRS)

Schleicher, David G.; Bus, Schelte J.; Osip, David J.

1993-01-01

Production rates of OH, CN, C2, C3, NH, and NH2 were derived from different data sets for the Comet P/Wolf-Harrington, and a dust production measure was calculated. This comet is found to be depleted by more than an order of magnitude in its pure carbon species compared with OH and CN. The data obtained suggest that a nonnegligible fraction of comets or their constituent components formed at a different temperature and thus at a different location and/or time than the majority of comets.

Orbit of Comet C/1850 Q1 (Bond)

NASA Astrophysics Data System (ADS)

Branham, Richard L., Jr.

Comet C/1850 Q1 (Bond) is one of a number of comets catalogued with parabolic orbits. Given that there are sufficient observations, 104in right ascension and 103in declination, it proves possible to calculate a better orbit. Some of the difficulties of working with 19th century observations, which show considerable scatter, are discussed. Rectangular coordinates, both of the comet and the Sun, are interpolated by a recursive version of Aitken's method, rendering unnecessary the need to specify an order for the interpolation. Comet Bond's orbit is slightly hyperbolic.

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.

Anticipated results from dust experiments on cometary missions

NASA Technical Reports Server (NTRS)

Kissel, J.; Fechtig, H.; Grun, E.

1981-01-01

The major scientific objectives of a mission are: to determine the chemical nature and physical structure of comet nuclei, and to characterize the changes that occur as a function of time orbital position; to characterize the chemical and physical nature of the atmospheres and ionospheres of comets as well as the processes that occur in them, and to characterize the development of the atmospheres and ionospheres as functions of time and orbital position; and to determine the nature of comet tails and processes by which they are formed, and to characterize the interaction of comets with the solar wind. Since dust is a major constituent of a comet, the achievement of these goals requires the intensive study of the paticulate emission from a comet.

Opportunities for ballistic missions to Halley's comet

NASA Technical Reports Server (NTRS)

Farquhar, R. W.; Wooden, W. H., II

1977-01-01

Alternative strategies for ballistic missions to Halley's comet in 1985-86 are described. A large scientific return would be acquired from a ballistic Halley intercept in spite of the high flyby speeds that are associated with this mission mode. The possibility of retargeting the cometary spacecraft to additional comets after the Halley intercept also exists. Two cometary spacecraft of identical design would be used to carry out four separate cometary encounters over a 3 year period. One spacecraft would intercept Halley's comet before its perihelion passage in December 1985 and then go on to comet Borrelly with an encounter in January 1988. The other spacecraft would be targeted for a postperihelion Halley intercept in March 1986 before proceeding toward an encounter with comet Tempel 2 in September 1988.

Methods for computing comet core temperatures

NASA Astrophysics Data System (ADS)

McKay, C. P.; Squyres, S. W.; Reynolds, R. T.

1986-06-01

The temperature profile within the comet nucleus provides the key to an understanding of the history of the volatiles within a comet. Certain difficulties arise in connection with current cometary temperature models. It is shown that the constraint of zero net heat flow can be used to derive general analytical expressions which will allow for the determination of comet core temperature for a spherically symmetric comet, taking into account information about the surface temperature and the thermal conductivity. The obtained results are compared with the expression for comet core temperatures considered by Klinger (1981). Attention is given to analytical results, an example case, and numerical models. The formalization developed makes it possible to determine the core temperature on the basis of the numerical models of the surface temperature.

The next three decades of the comet assay: a report of the 11th International Comet Assay Workshop.

PubMed

Koppen, Gudrun; Azqueta, Amaya; Pourrut, Bertrand; Brunborg, Gunnar; Collins, Andrew R; Langie, Sabine A S

2017-05-01

The International Comet Assay Workshops are a series of scientific conferences dealing with practical and theoretical aspects of the Comet Assay (single-cell gel electrophoresis)-a simple method for detecting DNA strand breaks. The first paper describing such an assay was published over 30 years ago in 1984 by Swedish researchers O. Ostling and K. J. Johanson. Appropriately, the theme for the 2015 meeting was looking to the future: 'The Next 3 Decades of the Comet Assay'. The programme included 25 oral and 43 poster presentations depicting the latest advances in technical developments as well as applications of the comet assay in genotoxicity testing (in vitro and in vivo) and biomonitoring of both humans and the environment. Open discussion sessions based on questions from the participants allowed exchange of practical details on current comet assay protocols. This report summarises technical issues of high importance which were discussed during the sessions. We provide information on ways to improve the assay performance, by testing for cytotoxicity, by using reference samples to reduce or allow for inter-experimental variation, and by standardising quantification of the damage, including replicates and scoring enough comets to ensure statistical validity. After 30 years of experimentation with the comet assay, we are in a position to control the important experimental parameters and make the comet assay a truly reliable method with a wealth of possible applications. © The Author 2017. 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.

Collisions with meteoroid streams as one possible mechanism for the formation of hyperbolic cometary orbits

NASA Astrophysics Data System (ADS)

Guliyev, Ayyub; Nabiyev, Shaig

2017-07-01

This paper presents the results of a statistical analysis of the dynamic parameters of 300 comets that have osculating hyperbolic orbits. It is shown that such comets differ from other comets by their large perihelion distances and by a predominance of retrograde motion. It is shown that the values of i, the inclination of the hyperbolic comets, are in comparative excess over the interval 90-120°. The dominance by q, the perihelion distance, renders it difficult to suggest that the excess hyperbolic velocity of these comets can be the result of physical processes that take place in their nuclei. Aspects of the following working hypothesis, that the hyperbolic excess of parameter e might be formed after comets pass through meteoroid streams, are also studied. To evaluate this hypothesis, the distribution of the orbits of hyperbolic comets relative to the plane of motion of 112 established meteoroid streams are analyzed. The number (N) of orbit nodes for hyperbolic comets with respect to the plane of each stream at various distances is calculated. To determine the degree of redundancy of N, a special computing algorithm was applied that provided the expected value nav as well as the standard deviation σ for the number of cometary nodes at the plane of each stream. A comparative analysis of the N and nav values that take σ into account suggests an excess in 40 stream cases. This implies that the passage of comets through meteoroid streams can lead to an acceleration of the comets' heliocentric velocity.

HUBBLE SEES MINI-COMET FRAGMENTS FROM COMET LINEAR

NASA Technical Reports Server (NTRS)

2002-01-01

[lower right] In one stunning Hubble picture the fate of the mysteriously vanished solid nucleus of Comet LINEAR has been settled. The Hubble picture shows that the comet nucleus has been reduced to a shower of glowing 'mini-comets' resembling the fiery fragments from an exploding aerial firework. This is the first time astronomers have ever gotten a close-up look at what may be the smallest building blocks of cometary nuclei, the icy solid pieces called 'cometesimals', which are thought to be less than 100 feet across. The farthest fragment to the left, which is now very faint, may be the remains of the parent nucleus that fragmented into the cluster of smaller pieces to the right. The comet broke apart around July 26, when it made its closest approach to the Sun. The picture was taken with Hubble's Wide Field Planetary Camera 2 on August 5, 2000, when the comet was at a distance of 64 million miles (102 million kilometers) from Earth. Credit: NASA, Harold Weaver (the Johns Hopkins University), and the HST Comet LINEAR Investigation Team [upper left] A ground-based telescopic view (2.2-meter telescope) of Comet LINEAR taken on August 5, at nearly the same time as the Hubble observations. The comet appears as a diffuse elongated cloud of debris without any visible nucleus. Based on these images, some astronomers had concluded that the ices in the nucleus had completely vaporized, leaving behind a loose swarm of dust. Hubble's resolution was needed to pinpoint the remaining nuclei (inset box shows HST field of view as shown in lower right). Credit: University of Hawaii

Ancient Chinese Observations and Modern Cometary Models

NASA Astrophysics Data System (ADS)

Yeomans, D. K.

1995-12-01

Ancient astronomical observations by Chinese, Japanese, and Korean observers represent the only data source for discerning the long-term behavior of comets. The primary source material is derived from Chinese astrologers who kept a vigilant celestial watch in an effort to issue up-to-date astrological forecasts for the reigning emperors. Surprisingly accurate records were kept on cometary apparitions with careful notes being made of an object's position, motion, size, color, and tail length. For comets Halley, Swift-Tuttle, and Tempel-Tuttle, Chinese observations have been used to model their motions over two millennia and to infer their photometric histories. One general result is that active comets must achieve an apparent magnitude of 3.5 or brighter before they become obvious naked-eye objects. For both comets Halley and Swift-Tuttle, their absolute magnitudes and hence their outgassing rates, have remained relatively constant for two millennia. Comet Halley's rocket-like outgassing has consistently delayed the comet's return to perihelion by 4 days so that the comet's spin axis must have remained stable for at least two millennia. Although its outgassing is at nearly the same rate as Halley's, comet Swift-Tuttle's motion has been unaffected by outgassing forces; this comet is likely to be ten times more massive than Halley and hence far more difficult for rocket-like forces to push it around. Although the earliest definite observations of comet Tempel-Tuttle were in 1366, the associated Leonid meteor showers have been identified as early as A.D. 902. The circumstance for each historical meteor shower and storm have been used to guide predictions for the upcoming 1998-1999 Leonid meteor displays.

Cytogenetic status and oxidative DNA-damage induced by atorvastatin in human peripheral blood lymphocytes: Standard and Fpg-modified comet assay

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

Gajski, Goran; Garaj-Vrhovac, Vera; Orescanin, Visnja

2008-08-15

To investigate the genotoxic potential of atorvastatin on human lymphocytes in vitro standard comet assay was used in the evaluation of basal DNA damage and to investigate possible oxidative DNA damage produced by reactive oxygen species (ROS) Fpg-modified version of comet assay was also conducted. In addition to these techniques the new criteria for scoring micronucleus test were applied for more complete detection of baseline damage in binuclear lymphocytes exposed to atorvastatin 80 mg/day in different time periods by virtue of measuring the frequency of micronuclei, nucleoplasmic bridges and nuclear buds. All parameters obtained with the standard comet assay andmore » Fpg-modified comet assay were significantly higher in the treated than in control lymphocytes. The Fpg-modified comet assay showed a significantly greater tail length, tail intensity, and tail moment in all treated lymphocytes than did the standard comet assay, which suggests that oxidative stress is likely to be responsible for DNA damage. DNA damage detected by the standard comet assay indicates that some other mechanism is also involved. In addition to the comet assay, a total number of micronuclei, nucleoplasmic bridges and nuclear buds were significantly higher in the exposed than in controlled lymphocytes. Regression analyses showed a positive correlation between the results obtained by the comet (Fpg-modified and standard) and micronucleus assay. Overall, the study demonstrated that atorvastatin in its highest dose is capable of producing damage on the level of DNA molecule and cell.« less

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.

First Comet Encounter

NASA Image and Video Library

2010-09-09

Dr. Michael A'Hearn, Principal Investigator, EPOXI Comet Encounter Mission, speaks during a symposium commemorating a quarter-century of comet discoveries, Friday, Sept. 10, 2010, in the Knight studio at the Newseum in Washington. The International Sun-Earth Explorer-3 (ISEE-3) spacecraft flew past the comet Giacobini-Zinner on Sept. 11, 1985 which established a foundation of discoveries that continue today. Photo Credit: (NASA/Paul E. Alers)

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.

Cometary crystalline silicate before and after perihelion passage II

NASA Astrophysics Data System (ADS)

Ootsubo, Takafumi

2014-01-01

Crystalline silicate is often observed in comets as an 11.3-micron resonant emission feature, and may be used for probing the early solar nebula. Because the formation of the crystalline silicate requires high temperature, they are thought to have been born from amorphous silicate at the inner region, and then transported toward the outer regions where comets were born. This transportation can produce the difference in the crystalline fraction in the cometary silicate dust between two dynamical types of comets, Oort-cloud comets (OCs) and Ecliptic comets (ECs), due to the different heliocentric distances of their birth places. The study of peak wavelengths in crystalline features is important to investigate the conditions of the crystalline silicate formation as well. Thus far, we don't have enough observational samples of OCs. Fortunately, we can observe comet C/2012 K1 (PanSTARRS) along with C/2013 A1 (Siding Spring) in this semester. In particular, the comet C/2012 K1 (PanSTARRS) is a bright and good target for this silicate peak feature study. Observations at pre- and post-perihelion provide us precious information on the dust evolution of the comet.

A quantitative comet infection assay for influenza virus

PubMed Central

Lindsay, Stephen M.; Timm, Andrea; Yin, John

2011-01-01

Summary The virus comet assay is a cell-based virulence assay used to evaluate an antiviral drug or antibody against a target virus. The comet assay differs from the plaque assay in allowing spontaneous flows in 6-well plates to spread virus. When implemented quantitatively the comet assay has been shown to have an order-of-magnitude greater sensitivity to antivirals than the plaque assay. In this study, a quantitative comet assay for influenza virus is demonstrated, and is shown to have a 13-fold increase in sensitivity to ribavirin. AX4 cells (MDCK cells with increased surface concentration of α2–6 sialic acid, the influenza virus receptor) have reduced the comet size variability relative to MDCK cells, making them a better host cell for use in this assay. Because of enhanced antiviral sensitivity in flow-based assays, less drug is required, which could lead to lower reagent costs, reduced cytotoxicity, and fewer false-negative drug screen results. The comet assay also serves as a readout of flow conditions in the well. Observations from comets formed at varying humidity levels indicate a role for evaporation in the mechanism of spontaneous fluid flow in wells. PMID:22155578

Use of statistical analysis to validate ecogenotoxicology findings arising from various comet assay components.

PubMed

Hussain, Bilal; Sultana, Tayyaba; Sultana, Salma; Al-Ghanim, Khalid Abdullah; Masoud, Muhammad Shahreef; Mahboob, Shahid

2018-04-01

Cirrhinus mrigala, Labeo rohita, and Catla catla are economically important fish for human consumption in Pakistan, but industrial and sewage pollution has drastically reduced their population in the River Chenab. Statistics are an important tool to analyze and interpret comet assay results. The specific aims of the study were to determine the DNA damage in Cirrhinus mrigala, Labeo rohita, and Catla catla due to chemical pollution and to assess the validity of statistical analyses to determine the viability of the comet assay for a possible use with these freshwater fish species as a good indicator of pollution load and habitat degradation. Comet assay results indicated a significant (P < 0.05) degree of DNA fragmentation in Cirrhinus mrigala followed by Labeo rohita and Catla catla in respect to comet head diameter, comet tail length, and % DNA damage. Regression analysis and correlation matrices conducted among the parameters of the comet assay affirmed the precision and the legitimacy of the results. The present study, therefore, strongly recommends that genotoxicological studies conduct appropriate analysis of the various components of comet assays to offer better interpretation of the assay data.

Can 67P/Churyumov-Gerasimenko become the reference for comet research?

NASA Astrophysics Data System (ADS)

Schulz, R.

2014-07-01

After its discovery in 1969, comet 67P/Churyumov-Gerasimenko went almost unnoticed through another five perihelion passages until the year 2003, when it suddenly became the new target of the first comet rendezvous mission, Rosetta. Today, 11 years and 1.5 apparitions later, it has become one of the few Jupiter-family comets that were monitored along its entire orbit, even near aphelion. Huge effort was spent in determining its characteristics. Observations obtained by the largest and most sophisticated telescopes on the Earth and in space were combined with dedicated modelling approaches in order to be best prepared for the space mission. Therefore, at this point time, we have basically determined as much as is achievable for a comet of this brightness without visiting it by spacecraft. A summary of what we already know about 67P/Churyumov-Gerasimenko, hence what we could in principle also determine for the ensemble of Jupiter-family comets, will be provided. The information expected to become available after the comet rendezvous will then be discussed particularly in view of whether and how it can be transferred to other comets for which only remote observations can be collected in the near future.

MAD2-p31comet axis deficiency reduces cell proliferation, migration and sensitivity of microtubule-interfering agents in glioma.

PubMed

Wu, Dang; Wang, Lepeng; Yang, Yanhong; Huang, Jin; Hu, Yuhua; Shu, Yongwei; Zhang, Jingyu; Zheng, Jing

2018-03-25

Mitotic arrest deficient-like-1 (MAD2, also known as MAD2L1) is thought to be an important spindle assembly checkpoint protein, which ensures accurate chromosome segregation and is closely associated with poor prognosis in many cancer. As a MAD2 binding protein, p31 comet counteracts the function of MAD2 and leads to mitotic checkpoint silence. In this study, we explore the function of MAD2-p31 comet axis in malignant glioma cells. Our results showed that disruption of MAD2-p31 comet axis by MAD2 knockdown or p31 comet overexpression suppressed cell proliferation, survival and migration of glioma, indicating that MAD2-p31 comet axis is required for maintaining glioma cells malignancy. It is noted that MAD2 depletion or p31 comet overexpression reduced the sensitivity of glioma cells to microtubule-interfering agents paclitaxel and vinblastine, providing clinical guidance for application of such drugs. Taken together, our findings suggest that MAD2-p31 comet axis may serve as a potential therapeutic target for glioma. Copyright © 2018. Published by Elsevier Inc.

Photometric follow-up of sungrazing comet C/2012 S1 ISON from OAdM and other observatories

NASA Astrophysics Data System (ADS)

Trigo-Rodríguez, J. M.; Moyano-Cambero, C. E.; Meech, K. J.; Rodríguez, D.; Sánchez, A.; Lacruz, J.

2013-09-01

Comet C/2012 S1 ISON was discovered on Sept. 21st, 2012 by Russian amateur astronomers Vitaly Nevski and Artyom Novichonok in the framework of a monitoring program called the International Scientific Optical Network (giving the acronym ISON from which the comet has been named). At discovery the comet was at a heliocentric distance of 6.29 A.U. and its magnitude was +18.8, but the computed orbit indicated that the comet was following a nearly parabolic orbit. The current orbit brings C/2012 S1 ISON to an extremely small perihelion distance of about 1 milion km on Nov. 28th, 2013. We have set up a multiband photometric monitoring of this sungrazing comet using 0.8m Telescope Joan Oró of the Montsec Astronomical Observatory (OAdM: www.oadm.cat) and several medium-size amateur telescopes with dedicated experience in cometary photometry [1, 2]. Comet sungrazers are interesting objects as they probably originate from the dynamical evolution of long period comets that typically end their lives colliding with the Sun [3]. They are though to be fragments of primitive ice-rich bodies gravitationally dispersed during the early stages of solar system evolution [4].

On observing comets for nuclear rotation

NASA Astrophysics Data System (ADS)

Whipple, F. L.

1981-10-01

The prevalent non-gravitational motions among comets demonstrate that the sublimination does not reach a maximum at the instant of maximum insolation on the nucleus. The occurrence of halos or "parabolic" envelopes in the comae of some comets and of jets, rays, fans, streamers and similar phenomena very near the nucleus in the brightest comets demonstrates that the sublimation process is not uniform over the nuclei. In other words, the nuclei of many comets contain relatively small active regions which provide much or most of the sublimation when these areas are turned toward the Sun. The period of rotation can be determind by measurement of the diameters of the halos or of the latus recta of the "parabolic" envelopes, if the expansion velocities are averaged from observations as a function of solar distance. Experience from analyses of some 80 well observed comets shows that the nuclei are "spotted" for more than a third of all comets, regardless of the "age" as measured by the original inverse semimajor axis including correction for planetary perturbations.

Quantification of applied dose in irradiated citrus fruits by DNA Comet Assay together with image analysis.

PubMed

Cetinkaya, Nurcan; Ercin, Demet; Özvatan, Sümer; Erel, Yakup

2016-02-01

The experiments were conducted for quantification of applied dose for quarantine control in irradiated citrus fruits. Citrus fruits exposed to doses of 0.1 to 1.5 kGy and analyzed by DNA Comet Assay. Observed comets were evaluated by image analysis. The tail length, tail moment and tail DNA% of comets were used for the interpretation of comets. Irradiated citrus fruits showed the separated tails from the head of the comet by increasing applied doses from 0.1 to 1.5 kGy. The mean tail length and mean tail moment% levels of irradiated citrus fruits at all doses are significantly different (p < 0.01) from control even for the lowest dose at 0.1 kGy. Thus, DNA Comet Assay may be a practical quarantine control method for irradiated citrus fruits since it has been possible to estimate the applied low doses as small as 0.1 kGy when it is combined with image analysis. Copyright © 2015 Elsevier Ltd. All rights reserved.

Are comets connected to the origin of life

NASA Technical Reports Server (NTRS)

Delsemme, A. H.

1981-01-01

Possible connections between comets and the origin of life on earth are discussed. The orbital evolution of comets and their origin are considered within a framework for the origin of the solar system, with particular attention given to the origin of the biosphere, and the origin of the Oort cloud. Evidence suggesting that cometary nuclei are undifferentiated throughout is considered, and a model of the average composition of a mean new comet is obtained from observational data which is similar to that of an interstellar frost. The chemistry of the model composition giving rise to the species observed in cometary spectra is considered, as well as the relations of cometary to cosmic abundances of oxygen, carbon and sulfur. The characteristics of possible sites for prebiotic chemistry, including interstellar clouds, the protosolar nebula, comets in the Oort cloud, periodic comets and the primitive earth, are examined, and a possible role of comets in bringing the interstellar prebiotic chemistry to earth is suggested.

Solar Sail Application to Comet Nucleus Sample Return

NASA Technical Reports Server (NTRS)

Taylor, Travis S.; Moton, Tryshanda T.; Robinson, Don; Anding, R. Charles; Matloff, Gregory L.; Garbe, Gregory; Montgomery, Edward

2003-01-01

Many comets have perihelions at distances within 1.0 Astronomical Unit (AU) from the sun. These comets typically are inclined out of the ecliptic. We propose that a solar sail spacecraft could be used to increase the inclination of the orbit to match that of these 1.0 AU comets. The solar sail spacecraft would match the orbit velocity for a short period of time, which would be long enough for a container to be injected into the comet's nucleus. The container would be extended from a long durable tether so that the solar sail would not be required to enter into the potentially degrading environment of the comet s atmosphere. Once the container has been filled with sample material, the tether is retracted. The solar sail would then lower its inclination and fly back to Earth for the sample return. In this paper, we describe the selection of cometary targets, the mission design, and the solar sailcraft design suitable for sail-comet rendezvous as well as possible rendezvous scenarios.

Electron plasma environment at comet Grigg-Skjellerup: General observations and comparison with the environment at comet Halley

NASA Technical Reports Server (NTRS)

Reme, H.; Mazelle, C.; Sauvaud, J. A.; D'Uston, C.; Froment, F.; Lin, R. P.; Anderson, K. A.; Carlson, C. W.; Larson, D. E.; Korth, A.

1993-01-01

The three-dimensional electron spectrometer of the Reme plasma analyzer-complete positive ion, electron and ram negative ion measurements near comet Halley (RPA-COPERNIC) experiment aboard the Giotto spacecraft, although damaged during the comet Halley encounter in March 1986, has provided very new results during the encounter on July 10, 1992, with the weakly active comet Grigg-Skjellerup (G-S). The main characteristic features of the highly structured interaction region extending from approximately 26,500 km inbound to approximately 37,200 km outbound are presented. These results are compared to the results obtained by the same instrument during the Giotto comet Halley fly-by. Despite the large difference in the size of the interaction regions (approximately 60,000 km for G-S, approximately 2000,000 km for Halley) due to 2 orders of magnitude difference in cometary neutral gas production rate, there are striking similarities in the solar wind interactions with the two comets.

Groundbased investigation of comet 67p/churyumov- gerasimenko, target of the spacecraft Mission Rosetta

NASA Astrophysics Data System (ADS)

de Almeida, A. A.; Trevisan Sanzovo, D.; Sanzovo, G. C.; Boczko, R.; Miguel Torres, R.

In this work, we make a comparative study of Comet 67P/Churyumov-Gerasimenko, target of Mission Rosetta, with Comets 1P/Halley and Hyakutake(C/1996 B2). Water and gas) release rates are derived from visual magnitudes (mv), determined mostly by amateur astronomers, and listed in several issues of International Comet Quarterly(ICQ). We make a systematic and uniform analysis of continuum fluxes obtained at visual wavelengths and, using the framework of photometric theory of Newburn & Spinrad (1985, 1989), we estimate dust release rates, qd (in g/s), effective particle sizes, a (in micron), and dust-to-gas mass ratios, for this important sample of comets. We also determine the color excess of the dust particles, CE, relative to the Sun at wavelength ranges 477.0-524.0 nm in the 1996 return of Comet 67P/Churyumov-Gerasimenko, and 365.0-484.5 nm for Comets 1P/Halley and C/1996 B2.

Collisional quenching of OH radio emission from comet Hale-Bopp

NASA Technical Reports Server (NTRS)

Schloerb, F. P.; Devries, C. H.; Lovell, A. J.; Irvine, W. M.; Senay, M.; Wootten, H. A.; Ferris, J. P. (Principal Investigator)

1997-01-01

Observations of comets in the 18-cm OH transitions offer a means to probe gas production, kinematics, and OH excitation in comets. We present initial results of OH observations of comet Hale-Bopp obtained with the NRAO 43 m antenna located in Greenbank, WV. Maps of the emission provide strong constraints on the amount of quenching of the inversion of the OH ground state A-doublet in the coma. Analysis of the total radio OH flux and maps of its radial brightness distribution indicate a quenched region on the order of approximately 500,000 km during March and April 1997. This large value is generally consistent with previous observations of radio OH quenching in lower production rate comets when the high production rate of comet Hale-Bopp is considered.

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.

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.

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

SOFIA FORCAST Far-IR Photometry of Comet ISON and Constraints on the Coma Grain Size Distribution

NASA Technical Reports Server (NTRS)

Wooden, D. H.; DeBuizer, J. M.; Kelley, M. S.; Woodward, C. E.; Harker, D. E.; Reach, W. T.; Sitko, M. L.; Russell, R. W.; Gehrz, R. D.; dePater, Imke;

Destruction of Sun-Grazing Comet C-2011 N3 (SOHO) Within the Low Solar Corona

NASA Technical Reports Server (NTRS)

Schrijver, C. J.; Brown, J. C.; Battams, K.; Saint-Hilaire, P.; Liu, W.; Hudson, H.; Pesnell, W. D.

2012-01-01

Observations of comets in Sun-grazing orbits that survive solar insolation long enough to penetrate into the Suns inner corona provide information on the solar atmosphere and magnetic field as well as on the makeup of the comet. On 6 July 2011, the Solar Dynamics Observatory (SDO) observed the demise of comet C2011 N3 (SOHO) within the low solar corona in five wavelength bands in the extreme ultraviolet (EUV). The comet penetrated to within 0.146 solarradius (100,000 kilometers) of the solar surface before its EUV signal disappeared.

On the nature of the anti-tail of Comet Kohoutek /1973f/. I - A working model

NASA Technical Reports Server (NTRS)

Sekanina, Z.

1974-01-01

The model derived for the anti-tail of Comet Kohoutek describes it as a flat formation, confined essentially to the comet's orbit plane and composed of relatively heavy particles (mostly in the size range 0.1-1 mm) whose motions are controlled by solar gravity and solar radiation pressure. Almost all the material was produced by the comet before perihelion at a rate about an order of magnitude higher than for Comets Arend-Roland and Bennett. The latent heat of vaporization of the particle material is estimated at 40-45 kcal/mole or higher.

The constitution of cometary nuclei

NASA Technical Reports Server (NTRS)

Whipple, F. L.

1977-01-01

The nongravitational term in the expression for the total force acting on a comet is calculated, and an upper limit is obtained for the product of the radial nongravitational term times the radius times the square root of the albedo. This condition is satisfied for ten periodic comets with q no greater than 1.5 AU, and the activity of these comets is consistent with control by H2O ice. Some of the comets must be spotty to account for their low albedo values. The effect of cosmic rays on comets, leading to frosting of their surface, is discussed.

Migration of comets to the terrestrial planets

NASA Astrophysics Data System (ADS)

Ipatov, Sergei I.; Mather, John C.

2007-05-01

The orbital evolution of 30,000 objects with initial orbits close to those of Jupiter-family comets (JFCs) and also of 15,000 dust particles was integrated [1-3]. For initial orbital elements close to those of Comets 2P, 10P, 44P, and 113P, a few objects got Earth-crossing orbits with semi-major axes a<2 AU and aphelion distances Q<4.2 AU, or even got inner-Earth (Q<0.983 AU), Aten, or typical asteroidal orbits, and moved in such orbits for more than 1 Myr (up to tens or even hundreds of Myrs). Most of former trans-Neptunian objects that have typical near-Earth object (NEO) orbits moved in such orbits for Myrs, so during most of this time they were extinct comets. From a dynamical point of view, the fraction of extinct comets among NEOs can exceed several tens of percent, but, probably, many extinct comets disintegrated into mini-comets and dust during a smaller part of their dynamical lifetimes if these lifetimes were large. The probability of the collision of Comet 10P with the Earth during a dynamical lifetime of the comet was P[E]≈1.4•10-4, but 80% of this mean probability was due only to one object among 2600 considered objects with orbits close to that of Comet 10P. For runs for Comet 2P, P[E]≈(1-5)•10-4. For most other considered JFCs, 10-6 < P[E] < 10-5. For Comets 22P and 39P, P[E]≈ (1-2)•10-6; and for Comets 9P, 28P and 44P, P[E]≈(2-5)•10-6. For all considered JFCs, P[E]>4•10-6. The Bulirsh-Stoer method of integration and a symplectic method gave similar results. In our runs the probability of a collision of one object with the Earth could be greater than the sum of probabilities for thousands of other objects. The ratios of probabilities of collisions of JFCs with Venus and Mars to the mass of a planet usually were not smaller than that for Earth. For dust particles started from comets and asteroids, P[E ]was maximum for diameters d~100 μm. These maximum values of P [E] were usually (exclusive for 2P) greater at least by an order of magnitude than the values for parent comets. [1] Ipatov S.I. and Mather J.C. (2004) Annals of the New York Acad. of Sci., v. 1017, 46-65. [2] Ipatov S.I. et al. (2004) Annals of the New York Acad. of Sci., v. 1017, 66-80. [3] Ipatov S.I. and Mather J.C. (2006) Adv. in Space Res., v. 37, N 1, 126-137.

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.

Are There Many Inactive Jupiter-Family Comets among the Near-Earth Asteroid Population?

NASA Astrophysics Data System (ADS)

Fernández, Julio A.; Gallardo, Tabaré; Brunini, Adrián

2002-10-01

We analyze the dynamical evolution of Jupiter-family (JF) comets and near-Earth asteroids (NEAs) with aphelion distances Q>3.5 AU, paying special attention to the problem of mixing of both populations, such that inactive comets may be disguised as NEAs. From numerical integrations for 2×10 6 years we find that the half lifetime (where the lifetime is defined against hyperbolic ejection or collision with the Sun or the planets) of near-Earth JF comets (perihelion distances q<1.3 AU) is about 1.5×10 5 years but that they spend only a small fraction of this time (˜ a few 10 3 years) with q<1.3 AU. From numerical integrations for 5×10 6 years we find that the half lifetime of NEAs in "cometary" orbits (defined as those with aphelion distances Q>4.5 AU, i.e., that approach or cross Jupiter's orbit) is 4.2×10 5 years, i.e., about three times longer than that for near-Earth JF comets. We also analyze the problem of decoupling JF comets from Jupiter to produce Encke-type comets. To this end we simulate the dynamical evolution of the sample of observed JF comets with the inclusion of nongravitational forces. While decoupling occurs very seldom when a purely gravitational motion is considered, the action of nongravitational forces (as strong as or greater than those acting on Encke) can produce a few Enckes. Furthermore, a few JF comets are transferred to low-eccentricity orbits entirely within the main asteroid belt ( Q<4 AU and q>2 AU). The population of NEAs in cometary orbits is found to be adequately replenished with NEAs of smaller Q's diffusing outward, from which we can set an upper limit of ˜20% for the putative component of deactivated JF comets needed to maintain such a population in steady state. From this analysis, the upper limit for the average time that a JF comet in near-Earth orbit can spend as a dormant, asteroid-looking body can be estimated to be about 40% of the time spent as an active comet. More likely, JF comets in near-Earth orbits will disintegrate once (or shortly after) they end their active phases.

Comets: Gases, ices, grains and plasma

NASA Technical Reports Server (NTRS)

Wilkening, L. L.

1981-01-01

The program and abstracts of the 97 papers delivered at the colloquium are presented. Cometary nuclei, comet dust, the coma, ion tails, several comet missions, and cometary origin and evolution were discussed.

History of the dust released by comets

NASA Technical Reports Server (NTRS)

Jambor, B. J.

1976-01-01

The Finson-Brobstein theory is used to examine production and history of dust released from periodic comets and to compare dust size distribution in relation to the Zodiacal cloud. Results eliminate all of the bright new comets from contributors to the Zodiacal cloud. Among the periodic comets, all particles of size much smaller than 10 micrometer are also lost. Only the large particles remain as possible contributors.

Giacobini-Zinner comet: Polarimetric and physical observations

NASA Technical Reports Server (NTRS)

Martel, M. T.; Maines, P.; Grudzinska, S.; Stawikowski, A.

1984-01-01

The results of observations of the Giacobini-Zinner comet on 25 and 31 October 1959 are presented. The magnitude of the comet was measured photoelectrically in two spectral regions. The radius is on the order of one kilometer. The photoelectric measurements of comets 1959b and 1957c were used to measure the abundances of the CN and C2 radicals and of solid particles in the heads.

Comet Wild 2 - Stardust Approach Image

NASA Technical Reports Server (NTRS)

2004-01-01

This image was taken during the close approach phase of Stardust's Jan 2, 2004 flyby of comet Wild 2. It is a distant side view of the roughly spherical comet nucleus. One hemisphere is in sunlight and the other is in shadow analogous to a view of the quarter moon. Several large depressed regions can be seen. Comet Wild 2 is about five kilometers (3.1 miles) in diameter.

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.

Near-parabolic comets observed in 2006-2010. The individualized approach to 1/a-determination and the new distribution of original and future orbits

NASA Astrophysics Data System (ADS)

Królikowska, Małgorzata; Dybczyński, Piotr A.

2013-10-01

Dynamics of a complete sample of small perihelion distance near-parabolic comets discovered in the years 2006-2010 are studied (i.e. of 22 comets of qosc < 3.1 au). First, osculating orbits are obtained after a very careful positional data inspection and processing, including where appropriate, the method of data partitioning for determination of pre- and post-perihelion orbit for tracking then its dynamical evolution. The non-gravitational acceleration in the motion is detected for 50 per cent of investigated comets, in a few cases for the first time. Different sets of non-gravitational parameters are determined from pre- and post-perihelion data for some of them. The influence of the positional data structure on the possibility of the detection of non-gravitational effects and the overall precision of orbit determination is widely discussed. Secondly, both original and future orbits were derived by means of numerical integration of swarms of virtual comets obtained using a Monte Carlo cloning method. This method allows us to follow the uncertainties of orbital elements at each step of dynamical evolution. The complete statistics of original and future orbits that includes significantly different uncertainties of 1/a-values is presented, also in the light of our results obtained earlier. Basing on 108 comets examined by us so far, we conclude that only one of them, C/2007 W1 Boattini, seems to be a serious candidate for an interstellar comet. We also found that 53 per cent of 108 near-parabolic comets escaping in the future from the Solar system, and the number of comets leaving the Solar system as so called Oort spike comets (i.e. comets suffering very small planetary perturbations) is 14 per cent. A new method for cometary orbit quality assessment is also proposed by means of modifying the original method, introduced by Marsden, Sekanina & Everhart. This new method leads to a better diversification of orbit quality classes for contemporary comets.

The Rosetta Mission to Comet 67P/ Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Buratti, Bonnie J.

2017-06-01

As remnant bodies left over from the formation of the Solar System, comets offer clues to the physical conditions and architecture of the protosolar nebula. The Rosetta spacecraft, which included an orbiter and a lander that were built and managed by the European Space Agency with NASA contributing four instruments and scientific expertise, was the first mission to orbit and study a comet through a perihelion passage. The targeted Jupiter-family comet 67P/ Churyumov-Gerasimenko, is seemingly two distinct planetesimals stuck together. The comet has not melted or been processed substantially, except for its outer layers, which consist of reaccreted dust and a crust of heated, devolatized, and annealed refractory materials and organics. The exceptionally low density (0.53 gm/cc) of 67P/ implies it is a rubble pile. The comet also appears to contain a hierarchy of building blocks: smaller spherically shaped meter-sized bodies can be seen in its interior, and even smaller cm-sized pebbles were imaged by the camera as the spacecraft made a soft crash landing on the comet’s surface on 30 September 2016. The unexpected discovery of molecular oxygen, nitrogen, and hydrogen imply that 67P/ was formed under cold conditions not exceeding 30K. The discovery of many organic compounds, including the amino acid glycine, lends support to the idea that comets, which originate in the Kuiper Belt and the Oort Cloud, brought the building blocks of life to Earth. More laboratory data on organic compounds would help to identify additional organic compounds on the comet. The differences between cometary and terrestrial D/H ratios suggest that comets are not the primary source of terrestrial water, although data on more comets is needed to confirm this result.Besides being primordial objects offering a window into the formation of solar systems, comets are astrophysical laboratories, ejecting dust and charged particles into the plasma comprising the solar wind. Several unusual phenomena were observed, such as magnetic cavities surrounding the comet, and oscillations in its magnetic field, which led 67P/ to be nicknamed the “singing comet”.NASA funding acknowledged.

Observations of the 18-cm lines of the OH radical in comets

NASA Astrophysics Data System (ADS)

Crovisier, J.; Colom, P.; Biver, N.; Bockelée-Morvan, D.

2015-10-01

Since 1973, the 18-cm lines of the OH radical have been systematically observed in selected comets with the 300×40 m radio telescope at Nançay. Up to now, 133 comets have been observed (counting different returns of short-period comets as different comets), totalling about 6000 individual observations (typically one hour per day for each observation).These observations trace the water production rates (through its photodissociation product OH) and the coma expansion velocity. They are precious for statistical investigations of the evolution of the activity of the comets. These observations are also made as a participation to multi-wavelength observing campaigns of dedicated comets and as a support to cometary space missions. The observations are organized in a database which is progressively made publicly available: http://www.lesia.obspm.fr/planeto/ cometes/basecom/ [1]The most recent observations are listed in Table 1. Here are some recent highlights: 103P/Hartley 2 was observed in support to its fly-by by the EPOXI mission and to observations with Herschel. [2] The outbursts of the sungrazing comet C/2012 S1 (ISON), preceding its demise as it approached the Sun at 0.012 AU on 28 November 2013, were observed. [3] Comet C/2013 A1 (Siding Spring) was detected just before it passed at only 0.001 AU from Mars on 19 October 2014, due to enhanced background radiation as the comet was close to the Galactic plane. [4] The Nançay radio telescope actively participated to the multi-wavelength observing campaigns of the bright comets C/2011 L4 (PANSTARRS), C/2012 F6 (Lemmon), C/2012 X1 (LINEAR), C/2013 R1 (Lovejoy) and C/2014 Q2 (Lovejoy) (Fig. 1), especially in coordination with radio observations with IRAM and ALMA. It should be noted that the Rosetta target 67P/Churyumov-Gerasimenko, which was marginally detected at its 1982 passage due to a relatively close approach to Earth (# = 0.39 AU) [1], is unfavourably placed at its present return for observations at Nançay.

What if chondritic porous interplanetary dust particles are not the real McCoy

NASA Astrophysics Data System (ADS)

Rietmeijer, Frans J. M.

To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.

What if chondritic porous interplanetary dust particles are not the real McCoy

NASA Technical Reports Server (NTRS)

Rietmeijer, Frans J. M.

1989-01-01

To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.

Pre- and Post-equinox ROSINA production rates calculated using a realistic empirical coma model derived from AMPS-DSMC simulations of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Hansen, Kenneth; Altwegg, Kathrin; Berthelier, Jean-Jacques; Bieler, Andre; Calmonte, Ursina; Combi, Michael; De Keyser, Johan; Fiethe, Björn; Fougere, Nicolas; Fuselier, Stephen; Gombosi, Tamas; Hässig, Myrtha; Huang, Zhenguang; Le Roy, Lena; Rubin, Martin; Tenishev, Valeriy; Toth, Gabor; Tzou, Chia-Yu

2016-04-01

We have previously used results from the AMPS DSMC (Adaptive Mesh Particle Simulator Direct Simulation Monte Carlo) model to create an empirical model of the near comet coma (<400 km) of comet 67P for the pre-equinox orbit of comet 67P/Churyumov-Gerasimenko. In this work we extend the empirical model to the post-equinox, post-perihelion time period. In addition, we extend the coma model to significantly further from the comet (~100,000-1,000,000 km). The empirical model characterizes the neutral coma in a comet centered, sun fixed reference frame as a function of heliocentric distance, radial distance from the comet, local time and declination. Furthermore, we have generalized the model beyond application to 67P by replacing the heliocentric distance parameterizations and mapping them to production rates. Using this method, the model become significantly more general and can be applied to any comet. The model is a significant improvement over simpler empirical models, such as the Haser model. For 67P, the DSMC results are, of course, a more accurate representation of the coma at any given time, but the advantage of a mean state, empirical model is the ease and speed of use. One application of the empirical model is to de-trend the spacecraft motion from the ROSINA COPS and DFMS data (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, Comet Pressure Sensor, Double Focusing Mass Spectrometer). The ROSINA instrument measures the neutral coma density at a single point and the measured value is influenced by the location of the spacecraft relative to the comet and the comet-sun line. Using the empirical coma model we can correct for the position of the spacecraft and compute a total production rate based on the single point measurement. In this presentation we will present the coma production rate as a function of heliocentric distance both pre- and post-equinox and perihelion.

Atlas of Secular Light Curves of Comets

NASA Astrophysics Data System (ADS)

Ferrin, Ignacio

2007-12-01

We have completed work on the secular light curves of 30 periodic and non-periodic comets. The objectives and approach of this project has been explained in Ferrin (Icarus, 178, 493-516, 2005). Each comet requires 2 plots. The time plot shows the reduced (to Δ = 1 AU) magnitude of the comet as a function of time, thus displaying the brightness history of the object. The log plot is a reflected double log plot. The reflection takes place at R=1 AU, to allow the determination of the absolute magnitude by extrapolation. 22 photometric parameters are measured from the plots, most of them new. The plots have been collected in a document that constitutes "The Atlas". We have defined a photometric age, P-AGE, that attempts to measure the age of a comet based on its activity. P-AGE has been scaled to human ages to help in its interpretation. We find that comets Hale-Bopp and 29P/SW 1, are baby comets (P-AGE < 3 comet years), while 107P, 162P and 169P are methuselah comets (P-AGE > 100 cy). The secular light curve of 9P/Tempel 1 exhibits sublimation due to H2O and due to CO. Comet 67P/Churyumov-Gerasimento to be visited by the Rossetta spacecraft in 2014 exhibits a photometric anomaly. Comet 65P/Gunn exhibits a lag in maximum brightness of LAG = + 254 days after perihelion. We suggest that the pole is pointing to the sun at that time. The secular light curves will be presented and a preliminary interpretation will be advanced. The secular light curves present complexity beyond current understanding. The observations described in this work were carried out at the National Observatory of Venezuela (ONV), managed by the Center for Research in Astronomy (CIDA), for the Ministry of Science and Technology (MinCyT).

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.

Temporary satellite capture of comets by Jupiter

NASA Astrophysics Data System (ADS)

Emel'yanenko, N. Yu.

2012-05-01

This paper studies the dynamical evolution of 97 Jupiter-family comets over an 800-year time period. More than two hundred encounters with Jupiter are investigated, with the observed comets moving during a certain period of time in an elliptic jovicentric orbit. In most cases this is an ordinary temporary satellite capture of a comet in Everhart's sense, not associated with a transition of the small body into Jupiter's family of satellites. The phenomenon occurs outside the Hill sphere with comets with a high Tisserand constant relative to Jupiter; the comets' orbits have a small inclination to the ecliptic plane. An analysis of 236 encounters has allowed the determination within the planar pair two-body problem of a region of orbits in the plane ( a, e) whose semimajor axes and eccentricities contribute to the phenomenon under study. Comets with orbits belonging to this region experience a temporary satellite capture during some of their encounters; the jovicentric distance function has several minima; and the encounters are characterized by reversions of the line of apsides and some others features of their combination that are intrinsic to comets in this region. Therefore, this region is called a region of comets with specific features in their encounters with Jupiter. Twenty encounters (out of 236), whereby the comet enters an elliptic jovicentric orbit in the Hill sphere, are identified and investigated. The size and shape of the elliptic heliocentric orbits enabling this transition are determined. It is found that in 11 encounters the motion of small bodies in the Hill sphere has features the most important of which is multiple minima of the jovicentric distance function. The study of these 20 encounters has allowed the introduction of the concept of temporary gravitational capture of a small body into the Hill sphere. An analysis of variations in the Tisserand constant in these (20) encounters of the observable comets shows that their motion is unstable in Hill's sense.

Monitoring of comets activity and composition with the TRAPPIST-North telescope

NASA Astrophysics Data System (ADS)

Moulane, Y.; Benkhaldoun, Z.; Jehin, E.; Opitom, C.; Gillon, M.; Daassou, A.

2017-06-01

TRAPPIST-North (TRAnsiting Planets and PlanetesImals Small Telescope) is a 60-cm robotic telescope that was installed in May 2016 at the Oukaimeden Observatory [1]. The project is led by the University of Liège (Belgium) and the Caddi Ayad University of Marrakech (Morocco). This telescope is a twin of the TRAPPIST-South telescope, which was installed at the ESO La Silla Observatory in 2010 [2]. The TRAPPIST telescopes are dedicated to the detection and characterization of planets orbiting stars other than our Sun (exoplanets) and the study of comets and other small bodies in our solar system. For the comets research, these telescopes have very sensitive CCD cameras with complete sets of narrow band filters to measure the production rates of several gases (OH, NH, CN, C3 and C2) and the dust [3]. With TRAPPIST-North we can also observe comets that would not be visible in the southern hemisphere. Therfore, with these two telescopes, we can now observe continuously the comets around their orbit. We project to study individually the evolution of the activity, chemical composition, dust properties, and coma morphology of several comets per year and of different origins (New comets and Jupiter Family comets) over a wide range of heliocentric distances, and on both sides of perihelion. We measure the production rates of each daughter molecules using a Haser model [4], in addition to the Afρ parameter to estimate the dust production in the coma. In this work, we present the first measurements of the production rates of comet C/2013 X1 (PANSTARRS) observed with TN in June 2016, and the measurements of comet C/2013 V5 (Oukaimeden) observed in 2014 with TRAPPIST-South.

Where are the mini Kreutz-family comets?

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

Ye, Quan-Zhi; Wiegert, Paul A.; Hui, Man-To

The Kreutz family of sungrazing comets contains over 2000 known members, many of which are believed to be under ∼100 m sizes (mini comets) and have only been studied at small heliocentric distances (r {sub H}) with space-based SOHO/STEREO spacecraft. To understand the brightening process of mini Kreutz comets, we conducted a survey using CFHT/MegaCam at moderate r {sub H} guided by SOHO/STEREO observations. We identify two comets that should be in our search area but are not detected, indicating that the comets have either followed a steeper brightening rate within the previously reported rapid brightening stage (the brightening burst),more » or the brightening burst starts earlier than expected. We present a composite analysis of the pre-perihelion light curves of five Kreutz comets that cover to ∼1 AU. We observe significant diversity in the light curves that can be used to grossly classify them into two types: C/Ikeya-Seki and C/SWAN follow the canonical r{sub H}{sup −4} while the others follow r{sub H}{sup −7}. In particular, C/SWAN seems to have undergone an outburst (Δm > 5 mag) or a rapid brightening (n ≳ 11) between r {sub H} = 1.06 AU and 0.52 AU, and shows hints of structural/compositional differences compared to other bright Kreutz comets. We also find evidence that the Kreutz comets as a population lose their mass less efficiently than the dynamically new comet, C/ISON, and are relatively devoid of species that drive C/ISON's activity at large r {sub H}. Concurrent observations of C/STEREO in different wavelengths also suggest that a blueward species such as CN may be the main driver for brightening bursts, instead of sodium as previously thought.« less

Rosetta following a living comet

NASA Astrophysics Data System (ADS)

Accomazzo, Andrea; Ferri, Paolo; Lodiot, Sylvain; Pellon-Bailon, Jose-Luis; Hubault, Armelle; Porta, Roberto; Urbanek, Jakub; Kay, Ritchie; Eiblmaier, Matthias; Francisco, Tiago

2016-09-01

The International Rosetta Mission was launched on 2nd March 2004 on its 10 year journey to rendezvous with comet 67P Churyumov-Gerasimenko. Rosetta performed comet orbit insertion on the 6th of August 2014, after which it characterised the nucleus and orbited it at altitudes as low as a few kilometres. In November 2014 Rosetta delivered the lander Philae to perform the first soft landing ever on the surface of a comet. The critical landing operations have been conducted with remarkable accuracy and will constitute one of the most important achievements in the history of spaceflight. After this critical operation, Rosetta began the escort phase of the comet in its journey in the Solar System heading to the perihelion, reached in August 2015. Throughout this period, the comet environment kept changing with increasing gas and dust emissions. A first phase of bound orbits was followed by a sequence of complex flyby segments which allowed the scientific instruments to perform in depth investigation of the comet environment and nucleus. The unpredictable nature of the comet activity forced the mission control team to implement unplanned changes to the flight plan prepared for this mission phase and to plan the whole mission in a more dynamic way than originally conceived. This paper describes the details of the landing operations and of the main comet escort phase. It also includes the mission status as achieved after perihelion and the findings about the evolution of the comet and its environment from a mission operations point of view. The lessons learned from this unique and complex operations phase and the plans for the next mission phases, which include a mission extension into 2016, are also described.

Recommendations for safety testing with the in vivo comet assay.

PubMed

Vasquez, Marie Z

2012-08-30

While the in vivo comet assay increases its role in regulatory safety testing, deliberations about the interpretation of comet data continue. Concerns can arise regarding comet assay publications with limited data from non-blind testing of positive control compounds and using protocols (e.g. dose concentrations, sample times, and tissues) known to give an expected effect. There may be a tendency towards bias when the validation or interpretation of comet assay data is based on results generated by widely accepted but non-validated assays. The greatest advantages of the comet assay are its sensitivity and its ability to detect genotoxicity in tissues and at sample times that could not previously be evaluated. Guidelines for its use and interpretation in safety testing should take these factors into account. Guidelines should be derived from objective review of data generated by blind testing of unknown compounds dosed at non-toxic concentrations and evaluated in a true safety-testing environment, where the experimental design and conclusions must be defensible. However, positive in vivo comet findings with such compounds are rarely submitted to regulatory agencies and this data is typically unavailable for publication due to its proprietary nature. To enhance the development of guidelines for safety testing with the comet assay, and with the permission of several sponsors, this paper presents and discusses relevant data from multiple GLP comet studies conducted blind, with unknown pharmaceuticals and consumer products. Based on these data and the lessons we have learned through the course of conducting these studies, I suggest significant adjustments to the current conventions, and I provide recommendations for interpreting in vivo comet assay results in situations where risk must be evaluated in the absence of carcinogenicity or clinical data. Copyright © 2012 Elsevier B.V. All rights reserved.

PROBING THE SOLAR WIND ACCELERATION REGION WITH THE SUN-GRAZING COMET C/2002 S2

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

Giordano, S.; Raymond, J. C.; Lamy, P.

Comet C/2002 S2, a member of the Kreutz family of sungrazing comets, was discovered in white-light images of the Large Angle and Spectromeric Coronagraph Experiment coronagraph on the Solar and Heliospheric Observatory (SOHO) on 2002 September 18 and observed in H I Lyα emission by the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) instrument at four different heights as it approached the Sun. The H I Lyα line profiles detected by UVCS are analyzed to determine the spectral parameters: line intensity, width, and Doppler shift with respect to the coronal background. Two-dimensional comet images of these parameters are reconstructed at the differentmore » heights. A novel aspect of the observations of this sungrazing comet data is that, whereas the emission from most of the tail is blueshifted, that along one edge of the tail is redshifted. We attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. In order to use the comet to probe the density, temperature, and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a Monte Carlo simulation of the H I Lyα emission of a comet moving through a coronal plasma. From the outgassing rate, we estimate a nucleus diameter of about 9 m. This rate steadily increases as the comet approaches the Sun, while the optical brightness decreases by more than a factor of 10 and suddenly recovers. This indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms, and molecules produced by the comet.« less

New orbit recalculations of comet C/1890 F1 Brooks and its dynamical evolution

NASA Astrophysics Data System (ADS)

Królikowska, Małgorzata; Dybczyński, Piotr A.

2016-08-01

C/1890 F1 Brooks belongs to a group of 19 comets used by Jan Oort to support his famous hypothesis on the existence of a spherical cloud containing hundreds of billions of comets with orbits of semi-major axes between 50 000 and 150 000 au. Comet Brooks stands out from this group because of a long series of astrometric observations as well as a nearly 2-yr-long observational arc. Rich observational material makes this comet an ideal target for testing the rationality of an effort to recalculate astrometric positions on the basis of original (comet-star) measurements using modern star catalogues. This paper presents the results of such a new analysis based on two different methods: (I) automatic re-reduction based on cometary positions and the (comet-star) measurements and (II) partially automatic re-reduction based on the contemporary data for the reference stars originally used. We show that both methods offer a significant reduction in the uncertainty of orbital elements. Based on the most preferred orbital solution, the dynamical evolution of comet Brooks during three consecutive perihelion passages is discussed. We conclude that C/1890 F1 is a dynamically old comet that passed the Sun at a distance below 5 au during its previous perihelion passage. Furthermore, its next perihelion passage will be a little closer than during the 1890-1892 apparition. C/1890 F1 is interesting also because it suffered extremely small planetary perturbations when it travelled through the planetary zone. Therefore, in the next passage through perihelion, it will once again be a comet from the Oort spike.

Comet ISON Approaching the Sun [still

NASA Image and Video Library

2013-11-27

This movie from NASA’s STEREO spacecraft's Heliospheric Imager shows Comet ISON, Mercury, Comet Encke and Earth over a five-day period from Nov. 20 to Nov. 25, 2013. The sun sits right of the field of view of this camera. Comet ISON, which will round the sun on Nov. 28, is what's known as a sungrazing comet, due to its close approach. Foreshortening or the angle at which these images were obtained make Earth appear as if it is closer to the sun than Mercury. If you look closely you will also see a dimmer and smaller comet Encke near comet ISON. A comet’s journey through the solar system is perilous and violent. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. Even if the comet does not survive, tracking its journey will help scientists understand what the comet is made of, how it reacts to its environment, and what this explains about the origins of the solar system. Closer to the sun, watching how the comet and its tail interact with the vast solar atmosphere can teach scientists more about the sun itself. Image Credit: NASA/STEREO NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

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.

Flight of the Comet

NASA Image and Video Library

2010-11-05

Image taken by NASA EPOXI mission spacecraft during its flyby of comet Hartley 2 on Nov. 4, 2010. The spacecraft came within about 700 kilometers 435 miles of the comet nucleus at the time of closest approach.

Lyman-alpha observations of Comet West /1975n/

NASA Technical Reports Server (NTRS)

Opal, C. B.; Carruthers, G. R.

1977-01-01

The rate of hydrogen production of Comet West is studied through rocket observation of solar Lyman-alpha radiation resonantly scattered by the escaping hydrogen atoms. Two sets of Lyman-alpha exposure sequences are used to obtain computer-smoothed brightness contour (isophote) maps covering a density range of 100:1. A simple radial outflow model is applied to the contour maps to determine the rate of hydrogen production (3.2 by 10 to the 30th power atoms/sec.) Discrepancies between the observed shape of the outer isophotes and predicted models may be explained by optical depth effects, or by the presence of small pieces of the comet's nucleus distributed along the orbit. Hydrogen, carbon, and oxygen production for Comet West and Comet Kohoutek are compared; differences may be accounted for by variations in the composition or evolution of the two comets.

Origin and Evolution of Comet Clouds

NASA Astrophysics Data System (ADS)

Higuchi, Arika

2007-01-01

The Oort cloud (comet cloud) is a spherical comet reservoir surrounding a planetary system. We have investigated the comet cloud formation that consists of two dynamical stages of orbital evolution of planetesimals due to (1) planetary perturbation, and (2) the galactic tide. We investigated the first stage by using numerical calculations and obtained the probabilities of the fates of planetesimals as functions of the orbital parameters of the planets and planetesimals. We investigated the second stage by using the secular perturbation theory and showed the evolution of the structure of a comet cloud from a planetesimal disk. We found that (1) massive planets effectively produce comet cloud candidates by scattering and (2) many planetesimals with semimajor axes larger than 1,000 AU rise up their perihelion distances to the outside of the planetary region and become members of the Oort cloud in 5 Gyr.

Origin of Short-Perihelion Comets

NASA Technical Reports Server (NTRS)

Guliyev, A. S.

2011-01-01

New regularities for short-perihelion comets are found. Distant nodes of cometary orbits of Kreutz family are concentrated in a plane with ascending node 76 and inclination 267 at the distance from 2 up to 3 a.u. and in a very narrow interval of longitudes. There is a correlation dependence between q and cos I concerning the found plane (coefficient of correlation 0.41). Similar results are received regarding to cometary families of Meyer, Kracht and Marsden. Distant nodes of these comets are concentrated close three planes (their parameters are discussed in the article) and at distances 1.4; 0.5; 6 a.u. accordingly. It is concluded that these comet groups were formed as a result of collision of parent bodies with meteoric streams. One more group, consisting of 7 comets is identified. 5 comet pairs are selected among sungrazers.

A worldwide photographic network for wide-field observations of Halley's Comet in 1985-1986

NASA Technical Reports Server (NTRS)

Niedner, M. B., Jr.; Brandt, J. C.; Rahe, J.

1982-01-01

A global network of ground-based observatories for the study of Halley's Comet in 1985/1986 is discussed. Recommendations are made with respect to improving coordination between reporting observatories, in order to ensure detailed imaging of such fast-generating cometary phenomena as plasma-tail knots, helices, disconnected tails, rays and condensations. A method for calibrating telescopes is considered by which well-studied objects will be photographed to provide references for images of Halley's Comet. This procedure is expected to reduce errors to approximately 0.05 mag. A coordinated study of Halley's Comet will provide important data on the physical properties of the Comet. Examples of the topics of study related to the plasma physics of the Comet's tail include: magnetic reconnection, rippling and tearing modes, kink instability, Kelvin-Helmholtz instability, and the flute instability.

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.

Comments on the Rotational State and Non-Gravitational Forces of Comet 46/WIRTANEN. Revised

NASA Technical Reports Server (NTRS)

Samarasinha, Nalin H.; Mueller, Beatrice E. A.; Belton, Michael J. S.

1995-01-01

We apply our experience of modeling the rotational state and non-gravitational forces of comet 1 P/Halley and other comets to comet 46P/Wirtanen. While the paucity of physical data on 46P/Wirtanen makes this process somewhat speculative, this comet's place as target for the important Rosetta mission gives significance to such a study. Our arguments are based on the summary of observational data provided by Jorda and Rickman (1995) and a comparative study of the behavior of other periodic comets. We find 46P/Wirtanen to have a level of surface activity relative to its mass that is dynamically more akin to that found in comet 1 P/Halley than in a typical periodic comet. We show through an illustrative numerical example that this apparent fact should likely lead to an excited spin state for this comet and that significant changes in the spin period could occur in a single pass through perihelion. We argue that the available observations are not sufficient to substantiate the claim of Jorda and Rickman (1995) that the nucleus is undergoing retrograde rotation and it is possible that the rotation is either prograde as well as retrograde. The substantial requirements that must be placed on any future observing program necessary to determine the precise rotational state are outlined. We advocate an extended (approx. two month) southern hemisphere observing campaign to determine the nuclear rotational state in 1996 if possible before activity turns on.

DNA Damage Analysis in Children with Non-syndromic Developmental Delay by Comet Assay.

PubMed

Susai, Surraj; Chand, Parkash; Ballambattu, Vishnu Bhat; Hanumanthappa, Nandeesha; Veeramani, Raveendranath

2016-05-01

Majority of the developmental delays in children are non-syndromic and they are believed to have an underlying DNA damage, though not well substantiated. Hence the present study was carried out to find out if there is any increased DNA damage in children with non-syndromic developmental delay by using the comet assay. The present case-control study was undertaken to assess the level of DNA damage in children with non syndromic developmental delay and compare the same with that of age and sex matched controls using submarine gel electrophoresis (Comet Assay). The blood from clinically diagnosed children with non syndromic developmental delay and controls were subjected for alkaline version of comet assay - Single cell gel electrophoresis using lymphocytes isolated from the peripheral blood. The comets were observed under a bright field microscope; photocaptured and scored using the Image J image quantification software. Comet parameters were compared between the cases and controls and statistical analysis and interpretation of results was done using the statistical software SPSS version 20. The mean comet tail length in cases and control was 20.77+7.659μm and 08.97+4.398μm respectively which was statistically significant (p<0.001). Other comet parameters like total comet length and % DNA in tail also showed a statistically significant difference (p < 0.001) between cases and controls. The current investigation unraveled increased levels of DNA damage in children with non syndromic developmental delay when compared to the controls.

Infrared Spectroscopy of the Dust in Comets and Relationships to Interstellar Dust

NASA Technical Reports Server (NTRS)

Hanner, Martha S.

2003-01-01

Infrared spectroscopy of the dust in comets reveals a complex mix of silicate materials, including both crystalline and non-crystalline components of both olivine (forsterite) and pyroxene composition. These various components do not necessarily share a common origin. Since comets formed in cold regions of the solar nebula, pre-solar grains in the nebula could have been accreted into comets with little alteration. Some of the cometary silicates may be of circumstellar (formed in circumstellar outflows of evolved stars) or interstellar (formed in dense region of the interstellar medium) origin. Spectral similarities to both circumstellar and interstellar silicates are seen in comet spectra. the short-period Kuiper Belt comets) show weak or no spectral features. The lack of features is generally explained as a particle size effect: the small silicate grains are embedded in larger, optically thick particles. However, compositional differences cannot be ruled out. For example, no unambiguous signature of forsterite has yet been seen in the spectrum of a short-period comet. Thus, the Stardust sample from short-period comet P/Wild 2 will be extremely valuable. Not only grain by grain composition and isotopic ratios but also grain morphology, irradiation history, and evidence of organic refractory mantles are important for understanding their origin. The relative abundance and distinguishing characteristics of the various crystalline and non-crystalline silicate components needs to be established. While some comets, such as Hale-Bopp, display a rich infrared spectrum, others (particularly

An analysis of the BVRI colors of 22 active comets

NASA Astrophysics Data System (ADS)

Betzler, A. S.; Almeida, R. S.; Cerqueira, W. J.; Araujo, L. A.; Prazeres, C. J. M.; Jesus, J. N.; Bispo, P. A. S.; Andrade, V. B.; Freitas, Y. A. S.; Betzler, L. B. S.

2017-08-01

Our aim was to analyze the variation of Johnson-Kron-Cousins BVRI color indexes of a sample with 22 active comets of various dynamic groups with the time, geometrical, observational and dynamical parameters. We performed photometric observations of 16 comets between 2010 and 2014, using robotic telescopes in three continents. In addition to the sample, we used data of six comets available in the literature. A statistical comparison between the distributions of color indexes was performed using the Kruskal-Wallis H-test. The color indexes of active comets can vary a few tenths up to a magnitude on time scales that range from hours to weeks. Using the B-V colors of the observed comets, we generated a relationship that correlates the cometary visual and CCD magnitudes. We did not identify any relationship between B-V and V-R colors with heliocentric distance and phase angle. The color B-V is correlated with the photometric aperture that can be described by a logarithmic function. We did not identify any differences in the distribution of B-V color among the comets analyzed at a confidence level equal to or greater than 95%. The mean color of active comets are B-R = 1.20 ± 0.24 , B-V = 0.76 ± 0.16 and V-R = 0.42 ± 0.16 . Active comets with V-R colors outside the three standard deviation interval can be considered objects with unusual physical characteristics.

Once a myth, now an object of study - How the perception of comets has changed over the centuries

NASA Astrophysics Data System (ADS)

2004-02-01

In February 2004, Rosetta will be setting off on its long journey through our solar system to meet up with Comet Churyumov-Gerasimenko. It will take the European Space Agency (ESA) space probe ten years to reach its destination. The comet, which moves in an elliptical orbit around the Sun, will at rendezvous be some 675 million kilometres from the Sun, near the point in its orbit farthest from the Sun. The meeting point was not chosen at random: at this point the comet is still barely active, it is still in fact a frozen lump of ice and interplanetary dust, in all probability the matter from which our solar system emerged four and a half billion years ago. Rosetta’s job is to find out more about these strange bodies that travel through our solar system. As it moves on, the comet will begin to change. As it approaches the Sun, it will - like all comets - become active: in the warmth of the Sun’s rays, the ices evaporate, tearing small dust particles from the surface. This produces the comet head (the coma) and tail. Only these two phenomena are visible from Earth. The comet nucleus itself is far too tiny - Churyumov-Gerasimenko measures about 4 kilometres across - to be viewed from Earth. As Dr Uwe Keller of the Max Planck Institute for Aeronomy in Kaltenburg-Lindau, the scientist responsible for the Osiris camera carried by Rosetta, explains, “Formation of the coma and tail during solar flyby skims several metres of matter off the comet’s surface. In the case of a small comet like Churyumov-Gerasimenko, the shrinkage is a good 1% each time round.” As it flies past the Sun every 6.6 years it can look forward to a short future, especially on a cosmic timescale. Comets - a mystical view Visible cometary phenomena have fascinated human beings from time immemorial - and frightened them too. Even today mystical explanations prevail among some of the Earth’s peoples. The Andaman islanders, a primitive people living in the Gulf of Bengal, see comets as burning torches hurled into the air by forest spirits - the more easily to detect humans foolish enough to stay out at night. For some Australian aborigines, comets are flaming sticks ridden by mighty shamans. Efforts to provide a scientific explanation of the ‘cometa aster’ (‘hairy star’) phenomenon stretch back to ancient times. A widely held view was that comets were in some way connected with processes at work in the atmosphere. In Meteorologica, Aristotle (384-322 BC) described how inflammable gases escape from clefts in rocks, collect in the upper layers of the sub-lunar world (‘world under the Moon’) and ignite. Rapid release of such gases produced a shooting star; when let out slowly, they gave rise to a comet. That was Aristotle’s best shot - and he was well aware of his limited insight into the question. As he himself acknowledged: “As we have no demonstrable basis for assertions about comets, I have to settle for an interpretation that does not conflict with established truths.” Admittedly such truths were thin on the ground at the time. Comets - something of a disaster As the centuries unfolded, what could be called the opposite view - that the comets were responsible for intense heat spells - also gained a considerable audience, though there was just as little truth in it. The natural philosophers went one further. They said comets lead to heat, heat to storms and storms to natural disasters. Pliny the Elder for example (born circa 23 AD) listed twelve cometary phenomena according to their external appearances. And he assigned one natural disaster to each class. The Christian Middle Ages no longer saw cometary phenomena as the blind raging of an even blinder nature, preferring to interpret them as signs from God. Theologians such as Saint Hildegard of Bingen (1098-1179) and Albert Magnus (1200-1280) cited holy scripture. The Book of Jeremiah for example (1:11,12), in which God caused a fearsome “rod of an almond tree” to appear in the sky, a symbol of the prophet’s empowerment. Or again Luke 21:11: “And great earthquakes shall be in divers places, and famines, and pestilences; and fearful sights and great signs shall there be from heaven.” In 1066, Halley’s Comet appeared to many as a harbinger of the Norman conquest of Britain, so vividly portrayed in the Bayeux tapestry, with its scenes from the Battle of Hastings. The decisive step towards overturning the view that comets are atmospheric phenomena was taken in 1577 by Danish astronomer, Tycho Brahe. For two and a half months he observed from his observatory in Uranienburg the progress of a comet across the heavens. Relying on the phenomenon of the daily parallax - an apparent “shuddering” motion of heavenly bodies in fact attributable to the observer’s position on the revolving Earth - he was able to establish that the comet had to be located beyond the lunar orbit. Halley discovers an elliptical orbit The scientific description of comets took another major step forward in 1705 thanks to the work of the British astronomer and physicist, Edmond Halley, a friend and patron of Isaac Newton. Investigating recorded comet measurements, he observed that the orbits of a number of bright comets were very similar: his own calculation of the orbit of a comet observed in 1682 coincided with the data recorded by Johannes Kepler in 1607 and by Apianus in 1531. He concluded that various comet observations were attributable to one and the same comet. Halley was proved right when in December 1758, the comet whose return he had predicted, thenceforth named after him, did indeed make a repeat appearance. This confirmed his theory that apparently parabolic comet orbits were in fact “simply” sections of one enormous elliptical orbit. Since then observations recorded in China in 240 BC have been identified as relating to a sighting of Halley’s comet, the oldest known document dealing with this phenomenon. What was described in the Bible as a sign from God was seen by Fred Hoyle, the British astrophysicist, as a possible explanation for the great hiatal breaks in history. He took the view that such extraordinary developments as the extinction of the mammoth were attributable to strikes by comet fragments. His views incorporated the theory advanced by British astronomers Victor Clube and Bill Napier in 1982 that a giant comet was trapped by our solar system 15000 years ago. With the return of that comet every 1600 years, the accompanying debris - so the argument goes - prompted some of the world’s great turning points. This might also be an explanation for such legends as the Flood. A lump of icy sludgew So what does the actual nucleus of a comet look like? One answer was supplied by the Giotto space probe in a mission masterminded by ESA. The probe was named after the major Italian painter Giotto di Bondone, who, in the early 14th century, portrayed a comet in his fresco in the Scrovegni Chapel in Padua. On 14 March 1986, the probe succeeded in taking 100-metre-resolution pictures of the nucleus of Halley’s Comet from only 600 kilometres away. In the words of Uwe Keller: “The mission forced us to revisit our long-standing image of a comet nucleus as a ‘dirty snowball’. The pictures showed that it was more like a lump of icy sludge. The solid part of the nucleus is much larger than the icy part.” Bur hardly had Giotto trained its electronic eye on the heavenly body than the photo opportunity was already over; a dust particle measuring about a millimetre hit the probe. As the velocity differential between probe and comet was at that point 68.4 km per second, the force of the involuntary encounter was enough to put paid to any further snapshots. All the same, despite the damage to the camera, it proved possible to go on with the mission. Following two periods of “hibernation”, Giotto achieved a successful flyby of the Grigg-Skjellerup comet on 10 July 1992. Rosetta should now bring us entirely new knowledge about comet nuclei. It will orbit the comet and deposit a small lander probe on its surface. So for the first time in history a comet travelling sunwards will be investigated from close quarters. For further information on Rosetta and ESA projects, please consult our portal at : http://www.esa.int/science or http:// www.esa.int/rosetta

Comparison of Wave Energy Transport at the Comets p/Halley and p/Giacobini-Zinner

NASA Technical Reports Server (NTRS)

Sding, A.; Glassmeir, K. H.; Fuselier, S. A.; Neubauer, Fritz M.; Tsurutani, B. T.

1995-01-01

Using magnetic field, plasma density and flow observations from spacecraft flybys of two comets, Eler variables are determined in order to study wave propogation directions. We investigate the inbound path of the Giotto spacecraft flyby of comet p/Halley outside the bow shock, and the inbound and outbound path of the ICE spacecraft flyby of comet p/Giacobini-Zinner outsinde of the bow wave.

Comprehensive analysis of sperm DNA fragmentation by five different assays: TUNEL assay, SCSA, SCD test and alkaline and neutral Comet assay.

PubMed

Ribas-Maynou, J; García-Peiró, A; Fernández-Encinas, A; Abad, C; Amengual, M J; Prada, E; Navarro, J; Benet, J

2013-09-01

Sperm DNA fragmentation (SDF) is becoming an important test to assess male infertility. Several different tests are available, but no consensus has yet been reached as to which tests are most predictive of infertility. Few publications have reported a comprehensive analysis comparing these methods within the same population. The objective of this study was to analyze the differences between the five most common methodologies, to study their correlations and to establish their cut-off values, sensitivity and specificity in predicting male infertility. We found differences in SDF between fertile donors and infertile patients in TUNEL, SCSA, SCD and alkaline Comet assays, but none with the neutral Comet assay. The alkaline COMET assay was the best in predicting male infertility followed by TUNEL, SCD and SCSA, whereas the neutral COMET assay had no predictive power. For our patient population, threshold values for infertility were 20.05% for TUNEL assay, 18.90% for SCSA, 22.75% for the SCD test, 45.37% for alkaline Comet and 34.37% for neutral Comet. This work establishes in a comprehensive study that the all techniques except neutral Comet are useful to distinguish fertile and infertile men. © 2013 American Society of Andrology and European Academy of Andrology.

NASA Hubble Sees Comet ISON Intact

NASA Image and Video Library

2013-10-09

This image from NASA Hubble Space Telescope of the sunward plunging comet ISON suggests that the comet is intact despite some predictions that the fragile icy nucleus might disintegrate as the sun warms it. In this NASA Hubble Space Telescope image taken on October 9, 2013 the comet's solid nucleus is unresolved because it is so small. If the nucleus broke apart then Hubble would have likely seen evidence for multiple fragments. Moreover, the coma or head surrounding the comet's nucleus is symmetric and smooth. This would probably not be the case if clusters of smaller fragments were flying along. What's more, a polar jet of dust first seen in Hubble images taken in April is no longer visible and may have turned off. This color composite image was assembled using two filters. The comet's coma appears cyan, a greenish-blue color due to gas, while the tail is reddish due to dust streaming off the nucleus. The tail forms as dust particles are pushed away from the nucleus by the pressure of sunlight. The comet was inside Mars' orbit and 177 million miles from Earth when photographed. Comet ISON is predicted to make its closest approach to Earth on 26 December, at a distance of 39.9 million miles. http://photojournal.jpl.nasa.gov/catalog/PIA18153

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.

Report of Some Comets: The Discovery of Uranus and Comets by William, Caroline, and John Herschel

NASA Astrophysics Data System (ADS)

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

2011-01-01

We report on the discovery and drawings of comets by William, Caroline, and John Herschel. The first discovery, by William Herschel, in 1781 from Bath, published in the Philosophical Transactions of the Royal Society with the title "Report of a Comet," turned out to be Uranus, the first planet ever discovered, Mercury through Saturn having been known since antiquity. William's sister Caroline was given duties of sweeping the skies and turned out to be a discoverer of 8 comets in her own right, in addition to keeping William's notes. Caroline's comets were discovered from Slough between 1786 and 1797. In the process, we also discuss original documents from the archives of the Royal Society and of the Royal Astronomical Society. We conclude by showing comet drawings that we have recently attributed to John Herschel, including Halley's Comet from 1836, recently located in the Ransom Center of the University of Texas at Austin. Acknowledgments: Planetary astronomy at Williams College is supported in part by grant NNX08AO50G from NASA Planetary Astronomy. We thank Peter Hingley of the Royal Astronomical Society and Richard Oram of the Harry Ransom Center of The University of Texas at Austin for their assistance.

A comparative study of the continuum and emission characteristics of comet dust. 1: Are the silicates in Comet Halley and Kohoutek amorphous or crystalline

NASA Technical Reports Server (NTRS)

Nansheng, Zhao; Greenberg, J. Mayo; Hage, J. I.

1989-01-01

A continuum emission was subtracted from the 10 micron emission observed towards comets Halley and Kohoutek. The 10 micron excess emissions were compared with BN absorption and laboratory amorphous silicates. The results show that cometary silicates are predominantly amorphous which is consistent with the interstellar dust model of comets. It is concluded that cometary silicates are predominantly similar to interstellar silicates. For a periodic comet like Comet Halley, it is to be expected that some of the silicate may have been heated enough to convert to crystalline form. But apparently, this is only a small fraction of the total. A comparison of Comet Halley silicates with a combination of the crystalline forms observed in interplanetary dust particles (IPDs) seemed reasonable at first sight (Walker 1988, Brownlee 1988). But, if true, it would imply that the total silicate mass in Comet Halley dust is lower than that given by mass spectrometry data of Kissel and Krueger (1987). They estimated m sub org/m sub sil = 0.5 while using crystalline silicate to produce the 10 micron emission would give m sub org/m sub sil = 5 (Greenberg et al. 1988). This is a factor of 10 too high.

Origin of the ices agglomerated by Comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Mousis, Olivier; Lunine, Jonathan I.; Luspay-Kuti, Adrienn; Guillot, Tristan; Marty, Bernard; Wurz, Peter; Ali-Dib, Mohamad; Altwegg, Kathrin; Hässig, Myrtha; Rubin, Martin; Vernazza, Pierre; Waite, Jack H.

2015-11-01

The nature of the icy material accreted by comets during their formation in the outer regions of the protosolar nebula is a major open question in planetary science. Some scenarios of comet formation predict that these bodies agglomerated from clathrates crystallized in the protosolar nebula. Concurrently, alternative scenarios suggest that comets accreted amorphous ice originating from the interstellar cloud. Here we show that the recent N2/CO and Ar/CO ratios measured in the coma of the Jupiter family comet 67P/Churyumov-Gerasimenko by the ROSINA instrument aboard the European Space Agency's Rosetta spacecraft can help disentangling between these two scenarios.

Comet 81P/wild 2 under a microscope

USGS Publications Warehouse

Brownlee, D.; Tsou, P.; Aleon, J.; O'D, Alexander; Araki, T.; Bajt, S.; Baratta, G.A.; Bastien, R.; Bland, P.; Bleuet, P.; Borg, J.; Bradley, J.P.; Brearley, A.; Brenker, F.; Brennan, S.; Bridges, J.C.; Browning, N.D.; Brucato, J.R.; Bullock, E.; Burchell, M.J.; Busemann, H.; Butterworth, Anna L.; Chaussidon, M.; Cheuvront, A.; Chi, M.; Cintala, M.J.; Clark, B. C.; Clemett, S.J.; Cody, G.; Colangeli, L.; Cooper, G.; Cordier, P.; Daghlian, C.; Dai, Z.; D'Hendecourt, L.; Djouadi, Z.; Dominguez, G.; Duxbury, T.; Dworkin, J.P.; Ebel, D.S.; Economou, T.E.; Fakra, S.; Fairey, S.A.J.; Fallon, S.; Ferrini, G.; Ferroir, T.; Fleckenstein, H.; Floss, C.; Flynn, G.; Franchi, I.A.; Fries, M.; Gainsforth, Z.; Gallien, J.-P.; Genge, M.; Gilles, M.K.; Gillet, P.; Gilmour, J.; Glavin, D.P.; Gounelle, M.; Grady, M.M.; Graham, G.A.; Grant, P.G.; Green, S.F.; Grossemy, F.; Grossman, L.; Grossman, J.N.; Guan, Y.; Hagiya, K.; Harvey, R.; Heck, P.; Herzog, G.F.; Hoppe, P.; Horz, F.; Huth, J.; Hutcheon, I.D.; Ignatyev, K.; Ishii, H.; Ito, M.; Jacob, D.; Jacobsen, C.; Jacobsen, S.; Jones, S.; Joswiak, D.; Jurewicz, A.; Kearsley, A.T.; Keller, L.P.; Khodja, H.; Kilcoyne, A.L.D.; Kissel, J.; Krot, A.; Langenhorst, F.; Lanzirotti, A.; Le, L.; Leshin, L.A.; Leitner, J.; Lemelle, L.; Leroux, H.; Liu, M.-C.; Luening, K.; Lyon, I.; MacPherson, G.; Marcus, M.A.; Marhas, K.; Marty, B.; Matrajt, G.; McKeegan, K.; Meibom, A.; Mennella, V.; Messenger, K.; Messenger, S.; Mikouchi, T.; Mostefaoui, S.; Nakamura, T.; Nakano, T.; Newville, M.; Nittler, L.R.; Ohnishi, I.; Ohsumi, K.; Okudaira, K.; Papanastassiou, D.A.; Palma, R.; Palumbo, M.E.; Pepin, R.O.; Perkins, D.; Perronnet, M.; Pianetta, P.; Rao, W.; Rietmeijer, F.J.M.; Robert, F.; Rost, D.; Rotundi, A.; Ryan, R.; Sandford, S.A.; Schwandt, C.S.; See, T.H.; Schlutter, D.; Sheffield-Parker, J.; Simionovici, A.; Simon, S.; Sitnitsky, I.; Snead, C.J.; Spencer, M.K.; Stadermann, F.J.; Steele, A.; Stephan, T.

2006-01-01

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

Comet Halley returns: A teachers' guide 1985-1986

NASA Technical Reports Server (NTRS)

Chapman, R. D.; Bondurant, R. L.

1985-01-01

This booklet has been put together as an aid for teachers in elementary and secondary schools. It is divided into two distinct parts. The first part is a brief tutorial which introduces some of the most important concepts about comets, including their historical significance. A list of selected readings is provided at the end of the booklet. The second part of the booklet contains a number of suggested activities, built around the comet. These include both classroom exercises and carefully described field work to observe the comet. Guidance is provided on where to look for the comet, how to observe it, and to photograph it.

Cometary Volatiles and the Origin of Comets

NASA Technical Reports Server (NTRS)

A'Hearn, Michael F.; Feaga, Lori M.; Keller, H. Uwe; Kawakita, Hideyo; Hampton, Donald L.; Kissel, Jochen; Klaasen, Kenneth P.; McFadden, Lucy A.; Meech, Karen J.; Schultz, Peter H.;

Comet nuclei and Trojan asteroids - A new link and a possible mechanism for comet splittings

NASA Technical Reports Server (NTRS)

Hartmann, William K.; Tholen, David J.

1990-01-01

Relatively elongated shapes, implied by recent evidence of a greater incidence of high amplitude lightcurves for comet nuclei and Trojan asteroids than for similarly scaled main belt asteroids, are suggested to have evolved among comet nuclei and Trojans due to volatile loss. It is further suggested that such an evolutionary course may account for observed comet splitting; rotational splitting may specifically occur as a result of evolution in the direction of an elongated shape through sublimation. Supporting these hypotheses, the few m/sec separation velocities projected for rotationally splitting elongated nuclei are precisely in the observed range.

Bright Comet ISON

NASA Image and Video Library

2013-11-22

Comet ISON shines brightly in this image taken on the morning of 19 Nov. 2013. This is a 10-second exposure taken with the Marshall Space Flight Center 20" telescope in New Mexico. The camera there is black and white, but the smaller field of view allows for a better "zoom in" on the comet's coma, which is essentially the head of the comet. Credit: NASA/MSFC/MEO/Cameron McCarty -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on April 30 Hubble View of ISON

NASA Image and Video Library

2013-11-22

On April 30, NASA's Hubble Space Telescope observed Comet ISON again. The comet is in the upper middle, showing the long tail. Various galaxies and stars appear behind it. In this image, Hubble trained its telescope on the stars instead of following the comet. The result is that the comet appears fuzzier, but the stars and galaxies are more detailed and precise. These dimmer features don't pop out if the camera is moving, following along with ISON. To see them, you really need to dwell in one place until they emerge from the noise. Credit: NASA/ESA/STScI/AURA -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

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.

Rosetta - ESA's new comet chaser

NASA Astrophysics Data System (ADS)

1999-06-01

The Rosetta orbiter will literally chase comet Wirtanen for two years, sending back valuable data and ensuring Europe retains its lead in comet science. A lander will attach itself to this lump of frozen ice and dust, which is travelling through space at over 130,000 kilometres per hour, and analyse samples. Just as the re-discovery of the Rosetta Stone, 200 years ago, enabled the mysteries of ancient Egyptian hieroglyphics to be unrravelled, so the Rosetta mission will help scientists learn even more about comets, the most primitive objects in the solar system. In 1986, ESA's Giotto spacecraft flew into the tail of Halley's Comet. That was ESA's first interplanetary mission and it was hailed as an outstanding success. The pictures and scientific data that Giotto sent back placed Europe at the forefront of comet science. Notes for Editors : On the day of the press event, the now deactivated Giotto spacecraft will do an Earth flyby 13 years after its encounter with Halley's Comet. The British Museum is celebrating 200-years anniversary of the Rosetta Stone, with an exhibition that includes a model of its modern equivalent, the Rosetta spacecraft.

Observations of ammonia in comets with Herschel

NASA Astrophysics Data System (ADS)

Biver, N.; Bockelée-Morvan, D.; Hartogh, P.; Crovisier, J.; de Val-Borro, M.; Kidger, M.; Küppers, M.; Lis, D.; Moreno, R.; Szutowicz, S.; HssO Team

2014-07-01

Ammonia is the most abundant nitrogen bearing species in comets. However, it has been scarcely observed in comets due to the weakness of the lines observable from the ground at infrared and centimetre wavelengths. Nevertheless, its main photodissociation product NH_2 has been observed in several comets in the visible. The fundamental rotational J_{K}=(1_0-0_0) transition of NH_3 at 572.5 GHz has been observed in comets since 2004, with the Odin satellite (Biver et al. 2007). In the frame of the Herschel guaranteed time key program ''HssO'' (Hartogh et al. 2009), ammonia was detected with the HIFI instrument in comets 10P/Tempel 2 (Biver et al. 2012), 45P/Honda- Mrkos-Pajdusakova, 103P/Hartley 2, and C/2009 P1 (Garradd). The hyperfine structure of the line is resolved. We have built a complete excitation model to interpret these observations, including the radial distribution in comet 103P. The derived abundances relative to water are on the order of 0.5 %, similar to the values inferred from visible observations of NH_2.

Comets and nongravitational forces. IV.

NASA Technical Reports Server (NTRS)

Marsden, B. G.; Sekanina, Z.

1971-01-01

Orbital elements and nongravitational parameters are derived from observations at every apparition of the periodic comets Honda-Mrkos-Pajdusakova, Faye, Tempel 2, Biela, Brorsen, and Tempel-Swift. For all except the first comet, the observations go back a century and more, although the last three comets have failed to reappear for some considerable time. The circumstances of the splitting of P/Biela are studied, and it is shown that the motion of the primary component was scarcely affected; it is also demonstrated that, if the primary still exists, it may pass only 0.05 AU from the earth in November 1971. An up-to-date list of mass-loss rates from comets is presented. It is found that, while most of the reliable determinations indicate that the cometary nongravitational effects decrease with time, there are a few cases where the effects increase slightly. The former situation is discussed in terms of a nuclear core-mantle model, implying that these comets will eventually evolve into inert, asteroidal objects, while the nuclei of the other comets are interpreted as coreless, eventually to disappear completely (or almost completely).

Comets: Cosmic connections with carbonaceous meteorites, interstellar molecules and the origin of life

NASA Technical Reports Server (NTRS)

Chang, S.

1979-01-01

The ions, radicals, and molecules observed in comets may be derived intact or by partial decomposition from parent compounds of the sort found either in the interstellar medium or in carbonaceous meteorites. The early loss of highly reducing primitive atmosphere and its replacement by a secondary atmosphere dominated by H2O, CO2, and N2, as depicted in current models of the earth's evolution, pose a dilemma for the origin of life: the synthesis of organic compounds necessary for life from components of the secondary atmosphere appears to be difficult, and plausible mechanisms have not been evaluated. Both comets and carbonaceous meteorites are implicated as sources for the earth's atmophilic and organogenic elements. A mass balance argument involving the estimated ratios of hydrogen to carbon in carbonaceous meteorites, comets, and the crust and upper mantle suggests that comets supplied the earth with a large fraction of its volatiles. The probability that comets contributed significantly to the earth's volatile inventory suggests a chemical evolutionary link between comets, prebiotic organic synthesis, and the origin of life.

DNA comet Giemsa staining for conventional bright-field microscopy.

PubMed

Osipov, Andreyan; Arkhangelskaya, Ekaterina; Vinokurov, Alexei; Smetaninа, Nadezhda; Zhavoronkov, Alex; Klokov, Dmitry

2014-04-10

This study was undertaken to evaluate the compatibility of Giemsa staining protocol with the comet assay. We showed, for the first time, that DNA comets can be visualized and analyzed using Giemsa staining. We generated DNA damage dose response curves for human peripheral blood lymphocytes exposed to X-ray radiation using the comet assay with either SybrGreen I or Giemsa stain. The dose response curves were fitted by linear regressions (R2>0.977). The SybrGreen I results showed only ~1.2-fold higher slope coefficient (method sensitivity) compared to the Giemsa results. The unexpectedly high sensitivity of Giemsa staining for the comet assay is due to the Romanowsky-Giemsa effect, the stain photo-stability and the higher resolution of bright-field imaging compared to fluorescence imaging. Our results demonstrate that Giemsa staining can effectively be used for measuring DNA damage by the comet assay. The low cost and availability of Giemsa stain makes this method affordable for any low budget research and will facilitate new applications of the comet assay in biology and medicine.

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.

Physical characteristics of Comet Nucleus C/2001 OG 108 (LONEOS)

NASA Astrophysics Data System (ADS)

Abell, Paul A.; Fernández, Yanga R.; Pravec, Petr; French, Linda M.; Farnham, Tony L.; Gaffey, Michael J.; Hardersen, Paul S.; Kušnirák, Peter; Šarounová, Lenka; Sheppard, Scott S.; Narayan, Gautham

2005-12-01

A detailed description of the Halley-type Comet C/2001 OG 108 (LONEOS) has been derived from visible, near-infrared, and mid-infrared observations obtained in October and November 2001. These data represent the first high-quality ground-based observations of a bare Halley-type comet nucleus and provide the best characterization of a Halley-type comet other than 1P/Halley itself. Analysis of time series photometry suggests that the nucleus has a rotation period of 57.2±0.5 h with a minimum nuclear axial ratio of 1.3, a phase-darkening slope parameter G of -0.01±0.10, and an estimated H=13.05±0.10. The rotation period of C/2001 OG 108 is one of the longest observed among comet nuclei. The V- R color index for this object is measured to be 0.46±0.02, which is virtually identical to that of other cometary nuclei and other possible extinct comet candidates. Measurements of the comet's thermal emission constrain the projected elliptical nuclear radii to be 9.6±1.0 km and 7.4±1.0 km, which makes C/2001 OG 108 one of the larger cometary nuclei known. The derived geometric albedo in V-band of 0.040±0.010 is typical for comet nuclei. Visible-wavelength spectrophotometry and near-infrared spectroscopy were combined to derive the nucleus's reflectance spectrum over a 0.4 to 2.5 μm wavelength range. These measurements represent one of the few nuclear spectra ever observed and the only known spectrum of a Halley-type comet. The spectrum of this comet nucleus is very nearly linear and shows no discernable absorption features at a 5% detection limit. The lack of any features, especially in the 0.8 to 1.0 μm range such as are seen in the spectra of carbonaceous chondrite meteorites and many low-albedo asteroids, is consistent with the presence of anhydrous rather than hydrous silicates on the surface of this comet. None of the currently recognized meteorites in the terrestrial collections have reflectance spectra that match C/2001 OG 108. The near-infrared spectrum, the geometric albedo, and the visible spectrophotometry all indicate that C/2001 OG 108 has spectral properties analogous to the D-type, and possibly P-type asteroids. Comparison of the measured albedo and diameter of C/2001 OG 108 with those of Damocloid asteroids reveals similarities between these asteroids and this comet nucleus, a finding which supports previous dynamical arguments that Damocloid asteroids could be composed of cometary-like materials. These observations are also consistent with findings that two Jupiter-family comets may have spectral signatures indicative of D-type asteroids. C/2001 OG 108 probably represents the transition from a typical active comet to an extinct cometary nucleus, and, as a Halley-type comet, suggests that some comets originating in the Oort cloud can become extinct without disintegrating. As a near-Earth object, C/2001 OG 108 supports the suggestion that some fraction of the near-Earth asteroid population consists of extinct cometary nuclei.

Icy Visitor from Beyond

NASA Image and Video Library

2010-10-05

This visitor from deep space, seen here by NASA Wide-field Infrared Survey Explorer, is comet Hartley 2, the destination for NASA EPOXI mission. The comet tail is seen here as a fuzzy streak to the right of the comet.

ScienceCast 96: Sunset Comet

NASA Image and Video Library

2013-03-14

Comet Pan-STARRS has survived its encounter with the sun and is now emerging from twilight in the sunset skies of the northern hemisphere. A NASA spacecraft monitoring the comet has beamed back pictures of a wild and ragged tail.

Airborne observations of methane in Comet Kohoutek

NASA Technical Reports Server (NTRS)

Roche, A. E.; Wells, W. C.

1974-01-01

The experiment is described for airborne observations of Comet Kohoutek using an infrared tilting-filter photometer. Preliminary analysis of the data established an upper limit to the Comet's fluorescence radiation in methane lines at 3.3 microns.

Swarm of Comets Artist Concept

NASA Image and Video Library

2015-11-24

This illustration shows a star behind a shattered comet. Observations of the star KIC 8462852 by NASA's Kepler and Spitzer space telescopes suggest that its unusual light signals are likely from dusty comet fragments, which blocked the light of the star as they passed in front of it in 2011 and 2013. The comets are thought to be traveling around the star in a very long, eccentric orbit. http://photojournal.jpl.nasa.gov/catalog/PIA20053

Visual and infrared observations of the distant Comets P/Stephan-Oterma /1980g/, Panther /1980u/, and Bowell /1980b/

NASA Technical Reports Server (NTRS)

Jewitt, D. C.; Soifer, B. T.; Neugebauer, G.; Matthews, K.; Danielson, G. E.

1982-01-01

The paper reports combined visual imagery and spectroscopy, near-infrared spectroscopy, and broadband infrared photometry of comets P/Stephan-Oterma (1980g), Bowell (1980b), and Panther (1980u) at intermediate heliocentric distances. The visual data indicate the existence of solid grains in extended halos around the nuclei of the three comets. Broadband near-infrared and thermal infrared measurements of Comet Panther suggest the presence of 2-4-micron-radius particles in the coma which most likely contain molecules incorporating the N-H bond, but which are more complex and less volatile than NH3. Such molecules can be produced in the grains by cosmic-ray reprocessing. Near infrared spectral features identical to those seen in comet Panther similary suggest the presence of a molecule incorporating the N-H bond in comet Bowell.

Visual and infrared observations of the distant Comets P/Stephan-Oterma /1980g/, Panther /1980u/, and Bowell /1980b/

NASA Astrophysics Data System (ADS)

Jewitt, D. C.; Soifer, B. T.; Neugebauer, G.; Matthews, K.; Danielson, G. E.

1982-12-01

The paper reports combined visual imagery and spectroscopy, near-infrared spectroscopy, and broadband infrared photometry of comets P/Stephan-Oterma (1980g), Bowell (1980b), and Panther (1980u) at intermediate heliocentric distances. The visual data indicate the existence of solid grains in extended halos around the nuclei of the three comets. Broadband near-infrared and thermal infrared measurements of Comet Panther suggest the presence of 2-4-micron-radius particles in the coma which most likely contain molecules incorporating the N-H bond, but which are more complex and less volatile than NH3. Such molecules can be produced in the grains by cosmic-ray reprocessing. Near infrared spectral features identical to those seen in comet Panther similary suggest the presence of a molecule incorporating the N-H bond in comet Bowell.

Follow-up observations of Comet 17P/Holmes after its extreme outburst in brightness end of October 2007

NASA Astrophysics Data System (ADS)

Mugrauer, M.; Hohle, M. M.; Ginski, C.; Vanko, M.; Freistetter, F.

2009-05-01

We present follow-up observations of comet 17/P Holmes after its extreme outburst in brightness, which occurred end of October 2007. We obtained 58 V-band images of the comet between October 2007 and February 2008, using the Cassegrain-Teleskop-Kamera (CTK) at the University Observatory Jena. We present precise astrometry of the comet, which yields its most recent Keplerian orbital elements. Furthermore, we show that the comet's coma expands quite linearly with a velocity of about 1650 km/s between October and December 2007. The photometric monitoring of comet 17/P Holmes shows that its photometric activity level decreased by about 5.9 mag within 105 days after its outburst. Based on observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.

A search for the millimetre lines of HCN in Comets Wilson 1987 VII and Machholz 1988 XV

NASA Astrophysics Data System (ADS)

Crouvisier, J.; Despois, D.; Bockelee-Morvan, D.; Gerard, E.; Paubert, G.; Johansson, L. E. B.; Ekelund, L.; Winnberg, A.; Ge, W.; Irvine, W. M.; Kinzel, W. M.; Schloerb, F. P.

1990-08-01

The J(1-0) lines of HCN at 89 GHz were searched for in Comet Wilson 1987 VII, with the FCRAO, the SEST and the IRAM radio telescopes between February and June 1987. There was no firm detection, but significant upper limits were obtained, which put severe constraints on the HCN production rate in that comet. A direct comparison with the observations of P/Halley suggests that the HCN abundance relative to water might be smaller in Comet Wilson by at least a factor of two. The J(1-0) and J(3-2) lines of HCN at 89 and 266 GHz were searched for in Comet Machholz 1988 XV when it was close to perihelion at 0.17 AU from the sun. There was no detection. At that moment, the comet was probably no longer active.

COMET Multimedia modules and objects in the digital library system

NASA Astrophysics Data System (ADS)

Spangler, T. C.; Lamos, J. P.

2003-12-01

Over the past ten years of developing Web- and CD-ROM-based training materials, the Cooperative Program for Operational Meteorology, Education and Training (COMET) has created a unique archive of almost 10,000 multimedia objects and some 50 web based interactive multimedia modules on various aspects of weather and weather forecasting. These objects and modules, containing illustrations, photographs, animations,video sequences, audio files, are potentially a valuable resource for university faculty and students, forecasters, emergency managers, public school educators, and other individuals and groups needing such materials for educational use. The COMET Modules are available on the COMET educational web site http://www.meted.ucar.edu, and the COMET Multimedia Database (MMDB) makes a collection of the multimedia objects available in a searchable online database for viewing and download over the Internet. Some 3200 objects are already available at the MMDB Website: http://archive.comet.ucar.edu/moria/

Multiwavelength Observations of Recent Comets

NASA Technical Reports Server (NTRS)

Milam, Stefanie N.; Charnley, Steven B.; Gicquel, Adeline; Cordiner, Martin; Kuan, Yi-Jehng; Chuang, Yo-Ling; Villanueva, Geronimo; DiSanti, Michael A.; Bonev, Boncho P.; Remijan, Anthony J.;

Observational evidence of aging processes in comets

NASA Astrophysics Data System (ADS)

Meech, Karen J.

1991-10-01

Emphasis was on searching for systematic differences among two groups of comets: periodic comets which spend most of their time in the vicinity of the inner Solar System and the new comets which are believed to be passing through the inner Solar System for the first time. Such differences are expected, but have never been observed, in part because there has never been a systematic observational program aimed at addressing this question. Understanding possible physical and compositional differences between these two groups will lead to a better understanding of the cometary formation conditions in the early Solar System. The employed method studies the activity in the comets as a function of distance by obtaining charge coupled device (CCD) observations of the comets at frequent intervals on both the pre- and post-perihelion legs of their orbits in order to ascertain the distances at the onset and turn-off of activity through comparison with sublimation models.

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.

Observational Search for Cometary Aging Processes

NASA Technical Reports Server (NTRS)

Meech, Karen J.

1997-01-01

The scientific objectives of this study were (i) to search for physical differences in the behavior of the dynamically new comets (those which are entering the solar system for the first time from the Oort cloud) and the periodic comets, and (ii) to interpret these differences, if any, in terms of the physical and chemical nature of the comets and the evolutionary histories of the two comet groups. Because outer solar system comets may be direct remnants of the planetary formation processes, it is clear that the understanding of both the physical characteristics of these bodies at the edge of the planet forming zone and of their activity at large heliocentric distances, r, will ultimately provide constraints on the planetary formation process both in our Solar System and in extra-solar planetary systems. A combination of new solar system models which suggest that the protoplanetary disk was relatively massive and as a consequence comets could form at large distances from the sun (e.g. from the Uranus-Neptune region to the vicinity of the Kuiper belt), observations of activity in comets at large r, and laboratory experiments on low temperature volatile condensation, are dramatically changing our understanding of the chemical'and physical conditions in the early solar nebula. In order to understand the physical processes driving the apparent large r activity, and to address the question of possible physical and chemical differences between periodic, non-periodic and Oort comets, the PI has been undertaking a long-term study of the behavior of a significant sample of these comets (approximately 50) over a wide range of r to watch the development, disappearance and changing morphology of the dust coma. The ultimate goal is to search for systematic physical differences between the comet classes by modelling the coma growth in terms of volatile-driven activity. The systematic observations for this have been ongoing since 1986, and have been obtained over the course of approximately 300 nights using the telescopes on Mauna Kea, Kitt Peak, Cerro Tololo, the European Southern Observatory, and several other large aperture facilities. A greater than 2 TB database of broad band comet images has been obtained which follows the systematic development and fading of the cometary coma for the comets in the database. The results to date, indicate that there is a substantial difference in the brightness and the amount of dust as a function of r between the two comet classes. In addition to this major finding, the program has been responsible for several exciting discoveries, including: the P/Halley outburst at r = 14.3 AU, the discovery of Chiron's coma and modelling and observations of the gravitationally bound component, observational evidence that activity continues out beyond r = 17 AU for many dynamically new comets

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.

What is a Sungrazing Comet? [hd video

NASA Image and Video Library

2013-11-27

Sungrazing comets are a special class of comets that come very close to the sun at their nearest approach, a point called perihelion. To be considered a sungrazer, a comet needs to get within about 850,000 miles from the sun at perihelion. Many come even closer, even to within a few thousand miles. Being so close to the sun is very hard on comets for many reasons. They are subjected to a lot of solar radiation which boils off their water or other volatiles. The physical push of the radiation and the solar wind also helps form the tails. And as they get closer to the sun, the comets experience extremely strong tidal forces, or gravitational stress. In this hostile environment, many sungrazers do not survive their trip around the sun. Although they don't actually crash into the solar surface, the sun is able to destroy them anyway. Many sungrazing comets follow a similar orbit, called the Kreutz Path, and collectively belong to a population called the Kreutz Group. In fact, close to 85% of the sungrazers seen by the SOHO satellite are on this orbital highway. Scientists think one extremely large sungrazing comet broke up hundreds, or even thousands, of years ago, and the current comets on the Kreutz Path are the leftover fragments of it. As clumps of remnants make their way back around the sun, we experience a sharp increase in sungrazing comets, which appears to be going on now. Comet Lovejoy, which reached perihelion on December 15, 2011 is the best known recent Kreutz-group sungrazer. And so far, it is the only one that NASA's solar-observing fleet has seen survive its trip around the sun. Comet ISON, an upcoming sungrazer with a perihelion of 730,000 miles on November 28, 2013, is not on the Kreutz Path. In fact, ISON's orbit suggests that it may gain enough momentum to escape the solar system entirely, and never return. Before it does so, it will pass within about 40 million miles from Earth on December 26th. More information on this topic available at: www.nasa.gov/content/goddard/timeline-of-comet-ison-s-dan... Credit: NASA's Goddard Space Flight Center NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Physical properties of asteroids in comet-like orbits in the infrared asteroidal survey catalogs

NASA Astrophysics Data System (ADS)

Kim, Y.; Ishiguro, M.; Usui, F.

2014-07-01

Dormant comet and Infrared Asteroidal Survey Catalogs. Comet nucleus is a solid body consisting of dark refractory material and ice. Cometary volatiles sublimate from subsurface layer by solar heating, leaving behind large dust grains on the surface. Eventually, the appearance could turn into asteroidal rather than cometary. It is, therefore, expected that there would be ''dormant comets'' in the list of known asteroids. Over past decade, several ground-based studies have been performed to dig out such dormant comets. One common approach is applying a combination of optical and dynamical properties learned from active comet nucleus to the list of known asteroids. Typical comet nucleus has (i) Tisserand parameter with respect to Jupiter, T_{J}<3, (ii) low geometric albedo, p_{v}<0.1 and (iii) reddish or neutral spectra, similar to P, D, C-type asteroids. Following past ground-based surveys, infrared space missions gave us an opportunity to work on further study of dormant comets. To the present, three infrared asteroidal catalogs taken with IRAS[1], AKARI[2] and WISE[3] are available, providing information of sizes and albedos which are useful to study the physical properties of dormant comets as well as asteroids. Usui et al. (2014) merged three infrared asteroidal catalogs with valid sizes and albedos into single catalog, what they called I-A-W[4]. We applied a huge dataset of asteroids in I-A-W to investigate the physical properties of asteroids in comet-like orbits (ACOs, whose orbits satisfy Q>4.5 au and T_{J}<3). Here we present a study of ACOs in infrared asteroidal catalogs taken with AKARI, IRAS and WISE. In this presentation, we aim to introduce albedo and size properties of ACOs in infrared asteroidal survey catalogs, in combination with orbital and spectral properties from literature. Results and Implications. We summarize our finding and implication as followings: - are 123 ACOs (Q>4.5 au and T_J<3) in I-A-W catalog after rejection of objects with large orbital uncertainties. - Majority (˜80 %) of ACOs have low albedo (p_{v}<0.1), showing similar albedo distribution to active comet nuclei. - Low-albedo ACOs have the cumulative size distribution shallower than that of active comet nuclei. - High-albedo (p_{v}≥0.1) ACOs consist of small (D<3 km) bodies are concentrated in near-Earth space. - We suggest that such high-albedo, small near-Earth asteroids are susceptible to Yarkovsky effect and injected into comet-like orbits.

May 8 Hubble View of ISON

NASA Image and Video Library

2013-11-22

Superficially resembling a skyrocket, Comet ISON is hurtling toward the Sun at a whopping 48,000 miles per hour. Its swift motion is captured in this image taken May 8, 2013, by NASA's Hubble Space Telescope. At the time the image was taken, the comet was 403 million miles from Earth, between the orbits of Mars and Jupiter. Unlike a firework, the comet is not combusting, but in fact is pretty cold. Its skyrocket-looking tail is really a streamer of gas and dust bleeding off the icy nucleus, which is surrounded by a bright, star-like-looking coma. The pressure of the solar wind sweeps the material into a tail, like a breeze blowing a windsock. As the comet warms as it moves closer to the Sun, its rate of sublimation will increase. The comet will get brighter and the tail grows longer. The comet is predicted to reach naked-eye visibility in November. The comet is named after the organization that discovered it, the Russia-based International Scientific Optical Network. This false-color, visible-light image was taken with Hubble's Wide Field Camera 3. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scienti

April 10 View of ISON

NASA Image and Video Library

2013-11-22

This NASA Hubble Space Telescope image of Comet (C/2012 S1) ISON was photographed on April 10, 2013, when the comet was slightly closer than Jupiter's orbit at a distance of 394 million miles from Earth. Even at that great distance the comet is already active as sunlight warms the surface and causes frozen volatiles to boil off. Astronomers used such early images to try to measure the size of the nucleus, in order to predict whether the comet would stay intact when it slingshots around the sun -- at 700,000 miles above the sun's surface -- on Nov. 28, 2013. The comet's dusty coma, or head of the comet, is approximately 3,100 miles across, or 1.2 times the width of Australia. A dust tail extends more than 57,000 miles, far beyond Hubble's field of view. This image was taken in visible light. The blue false color was added to bring out details in the comet structure. Credit: NASA/ ESA/STScI/AURA -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on April 10 Hubble View of ISON

NASA Image and Video Library

2013-11-22

This NASA Hubble Space Telescope image of Comet (C/2012 S1) ISON was photographed on April 10, 2013, when the comet was slightly closer than Jupiter's orbit at a distance of 394 million miles from Earth. Even at that great distance the comet is already active as sunlight warms the surface and causes frozen volatiles to boil off. Astronomers used such early images to try to measure the size of the nucleus, in order to predict whether the comet would stay intact when it slingshots around the sun -- at 700,000 miles above the sun's surface -- on Nov. 28, 2013. The comet's dusty coma, or head of the comet, is approximately 3,100 miles across, or 1.2 times the width of Australia. A dust tail extends more than 57,000 miles, far beyond Hubble's field of view. This image was taken in visible light. The blue false color was added to bring out details in the comet structure. Credit: NASA/ ESA/STScI/AURA -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Rosetta/ROSINA observations of the volatiles in the coma of comet 67P/Churyumov-Gerasimenko during the nominal mission

NASA Astrophysics Data System (ADS)

Rubin, M.; Altwegg, K.; Balsiger, H. R.; Berthelier, J. J.; Calmonte, U.; De Keyser, J.; Fiethe, B.; Fuselier, S. A.; Gasc, S.; Gombosi, T. I.; Hässig, M.; Jäckel, A.; Le Roy, L.; Mall, U. A.; Rème, H.; Sémon, T.; Tzou, C. Y.; Wurz, P.

2015-12-01

The European Space Agency's Rosetta spacecraft is in close proximity of comet 67P/Churyumov-Gerasimenko for well over a year now. During this time Rosetta followed the comet from almost 3.5 AU through perihelion at 1.25 AU and away from the Sun again. Part of the scientific payload scrutinizing the comet is the ROSINA experiment, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis. The suite of instruments consists of the Double Focusing Mass Spectrometer DFMS, the Reflectron Time-Of-Flight mass spectrometer RTOF, and the COmet Pressure Sensor COPS. From the combined measurements by ROSINA, the composition and dynamics of the volatiles in the coma of the comet are derived. On 13 August 2015, comet 67P/Churyumov-Gerasimenko reached perihelion, the point along its orbits that is closest to the Sun. Furthermore equinox occurred in May 2015 leading to a change in season - the previous summer hemisphere is now in winter and vice versa. One of the goals of ROSINA is to track the activity of the comet during its apparition and to investigate potential changes in the chemical composition as the spacecraft orbits around the nucleus. In this presentation we will summarize some key findings obtained during the first year and a half of the nominal mission and present first results comparing the pre- and post perihelion neutral gas coma. The goal of these observations is to gather information about the formation and the composition of the comet and ultimately our early Solar System.

Constraints on nebular dynamics and chemistry based on observations of annealed magnesium silicate grains in comets and in disks surrounding Herbig Ae/Be stars

PubMed Central

Hill, Hugh G. M.; Grady, Carol A.; Nuth, Joseph A.; Hallenbeck, Susan L.; Sitko, Michael L.

2001-01-01

Understanding dynamic conditions in the Solar Nebula is the key to prediction of the material to be found in comets. We suggest that a dynamic, large-scale circulation pattern brings processed dust and gas from the inner nebula back out into the region of cometesimal formation—extending possibly hundreds of astronomical units (AU) from the sun—and that the composition of comets is determined by a chemical reaction network closely coupled to the dynamic transport of dust and gas in the system. This scenario is supported by laboratory studies of Mg silicates and the astronomical data for comets and for protoplanetary disks associated with young stars, which demonstrate that annealing of nebular silicates must occur in conjunction with a large-scale circulation. Mass recycling of dust should have a significant effect on the chemical kinetics of the outer nebula by introducing reduced, gas-phase species produced in the higher temperature and pressure environment of the inner nebula, along with freshly processed grains with “clean” catalytic surfaces to the region of cometesimal formation. Because comets probably form throughout the lifetime of the Solar Nebula and processed (crystalline) grains are not immediately available for incorporation into the first generation of comets, an increasing fraction of dust incorporated into a growing comet should be crystalline olivine and this fraction can serve as a crude chronometer of the relative ages of comets. The formation and evolution of key organic and biogenic molecules in comets are potentially of great consequence to astrobiology. PMID:11226213

The Extremely Anomalous Molecular Abundances ofComet 96P/Machholz 1 from Narrowband Photometry

NASA Astrophysics Data System (ADS)

Schleicher, David G.

2007-10-01

Narrowband filter photometry of Comet 96P/Machholz 1 was obtained on 4 nights at Lowell Observatory during the comet's 2007 apparition. Production rates of OH, CN, C2, C3, and NH were derived from these data sets, and relative abundances, expressed as ratios of production rates with respect to OH (a measure of the water abundance), were compared to those measured in other comets. Comet Machholz 1 is shown to be depleted in CN by about a factor of 200 from average, while C2 and C3 are also low but "only” by factors of 10-20 from "typical” composition, i.e. comparable to the most strongly carbon-chain depleted comets reported by A'Hearn et al. (1995; Icarus 118, 223). In contrast, NH is near the upper end of its normal range. This extremely low CN-to-OH ratio for Machholz 1 indicates that it is either compositionally associated with Comet Yanaka (1988r; 1988 Y1) which was strongly depleted in CN and C2 but not NH2 (Fink, 1992; Science 257, 1926), or represents a new compositional class of comets, since Yanaka had a much greater depletion of C2 (>100×) than does Machholz 1. It remains unclear if these comets formed at a location in our solar system with unusual conditions and a low probability of being gravitationally perturbed into the inner solar system, or if one or both objects are interstellar interlopers. These and other results will be presented. This research is supported by NASA's Planetary Astronomy Program.

Early evolution of comet 67P studied with the RPC-LAP onboard Rosetta

NASA Astrophysics Data System (ADS)

Miloch, Wojciech; Edberg, Niklas J. T.; Eriksson, Anders I.; Yang, Lei; Paulsson, Joakim J. P.; Wedlund, Cyril Simon; Odelstad, Elias

2016-07-01

The Rosetta mission provides the in-situ measurements of a comet that are closest to a comet's aphelion ever made. The Rosetta Plasma Consortium (RPC) is a set of five instruments on board the spacecraft that specialise in the measurements of the plasma environment of comet 67P. One of the instruments is RPC-LAP, which consists of two Langmuir Probes and can measure the density, temperature, and flow speed of the plasma in the vicinity of the comet. At the early stage of the Rosetta mission, when the spacecraft is far from the nucleus of comet 67P, the ion part of the current-voltage characteristics of RPC-LAP1 is dominated by the photoemission current which surpasses the currents from the dilute solar wind plasma. As Rosetta starts orbiting around the nucleus in September 2014, LAP1 picks up signatures of local plasma density enhancements corresponding to variations of water-group ions observed in the vicinity of the comet. With the help of current-voltage characteristics and the spacecraft potential, we identify and characterise in space and time the entering of this coma-dominated plasma. In particular we determine the transition for entering the ion dominated region characterised by the 6-hour variations in the local plasma density due to the comet rotation. This transition manifests as a steep gradient in the density with respect to the distance to the comet nucleus. We discuss these RPC-LAP results together with the corresponding measurements by other instruments to provide a comprehensive picture of the transition.

WILL COMET ISON (C/2012 S1) SURVIVE PERIHELION?

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

Knight, Matthew M.; Walsh, Kevin J., E-mail: knight@lowell.edu

2013-10-10

On 2013 November 28 Comet ISON (C/2012 S1) will pass by the Sun with a perihelion distance of 2.7 solar radii. Understanding the possible outcomes for the comet's response to such a close passage by the Sun is important for planning observational campaigns and for inferring ISON's physical properties. We present new numerical simulations and interpret them in context with the historical track record of comet disruptions and of sungrazing comet behavior. Historical data suggest that sizes below ∼200 m are susceptible to destruction by sublimation driven mass loss, while we find that for ISON's perihelion distance, densities lower thanmore » 0.1 g cm{sup –3} are required to tidally disrupt a retrograde or non-spinning body. Such low densities are substantially below the range of the best-determined comet nucleus densities, though dynamically new comets such as ISON have few measurements of physical properties. Disruption may occur for prograde rotation at densities up to 0.7 g cm{sup –3}, with the chances of disruption increasing for lower density, faster prograde rotation, and increasing elongation of the nucleus. Given current constraints on ISON's nucleus properties and the typically determined values for these properties among all comets, we find tidal disruption to be unlikely unless other factors (e.g., spin-up via torquing) affect ISON substantially. Whether or not disruption occurs, the largest remnant must be big enough to survive subsequent mass loss due to sublimation in order for ISON to remain a viable comet well after perihelion.« less

Evidence for a First-of-Its-Kind Comet Jet

NASA Image and Video Library

2010-11-04

These three pairs of images from NASA EPOXI mission demonstrate that a dust jet and gaseous carbon dioxide are being released from comet Hartley 2 at the same time, and from the same location on the comet.

Comet Borrelly Varied Landscape

NASA Image and Video Library

2001-11-03

Sunlight illuminates the bowling-pin shaped nucleus from directly below comet Borrelly as seen by NASA Deep Space 1. At this distance, many features become vivid on the surface of the nucleus, including a jagged line between day and night on the comet.

Comet showers and Nemesis, the death star

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

Hills, J.G.

1984-01-01

The recently proposed hypothesis that the periodic extinctions of terrestrial species are the result of comet showers catalyzed by a hypothetical distant solar companion, Nemesis, a tale of global death by comet bombardment of the earth, is discussed. (GHT)

Spectroscopic Observations of the Planets

NASA Technical Reports Server (NTRS)

Owen, Tobias

1998-01-01

During the period under review, the main effort of the research supported by this grant was concentrated on Titan, Iapetus, and two comets, Comet Hyakutake and Comet Hale-Bopp. Significant discoveries were made in each case as summarized in the report.

Polarization imaging of comets at geocentric distances smaller than 0.5 au: Comet 73P/Schwassmann-Wachmann 3

NASA Astrophysics Data System (ADS)

Hadamcik, E.; Levasseur-Regourd, A.-C.

2014-07-01

Remote observations of sunlight scattered by solid particles provide information on the particle properties for a large variety of comets. When comets approach the Sun, solid particles and gases are released from the surface or from the inner layers [1,2]. If the comet is close enough to the Earth, the inner coma may be studied. Different coma regions are observed corresponding to different dust properties, e.g., in jets or fresh ejected dust around the coma. Narrow-band continuum filters or broader-band filters in less contaminated spectral domains (red or near infrared) are currently used to avoid or reduce the contributions from gaseous emission. Comet 73P/Schwassmann-Wachmann 3 is a fascinating fragmenting comet. Different observations in 1995 revealed an increase of activity and at least four fragments of the nucleus. In its 2011 apparition, the fragments were well separated and appeared like small individual comets. In 2006, its apparition was very favorable and allowed high- spatial resolution imaging by different complementary techniques. We observed three fragments of comet 73P/Schwassmann-Wachmann 3 from April 27 to May 3, 2006, by imaging polarimetry with the 80-cm telescope at Observatoire de Haute-Provence. The distance to the Earth was smaller than 0.2 au. Fragment C resembles a classical active comet. Regions of high and lower polarization were observed in the inner coma, appearing to change almost periodically. The variation of polarization in the inner coma was important from one night to the next one, the whole coma polarization being about constant for nucleus distances greater than 2000 km and increasing with the phase angle. Fragment B continued its (sequential) fragmentation, with a region of secondary fragments progressively moving away from the main nucleus in the antisolar direction. The chemical composition has been reported as being similar in all the fragments [3], but differences were observed between them in polarization underlining differences in, e.g., structure or size distribution of the particles during their ejection and fragmentation. The variation of polarization in the coma and around the fragments will be presented. Finally, a comparison to other comets, including split comets observed at small geocentric distances, will be provided.

CoMet: a workflow using contig coverage and composition for binning a metagenomic sample with high precision.

PubMed

Herath, Damayanthi; Tang, Sen-Lin; Tandon, Kshitij; Ackland, David; Halgamuge, Saman Kumara

2017-12-28

In metagenomics, the separation of nucleotide sequences belonging to an individual or closely matched populations is termed binning. Binning helps the evaluation of underlying microbial population structure as well as the recovery of individual genomes from a sample of uncultivable microbial organisms. Both supervised and unsupervised learning methods have been employed in binning; however, characterizing a metagenomic sample containing multiple strains remains a significant challenge. In this study, we designed and implemented a new workflow, Coverage and composition based binning of Metagenomes (CoMet), for binning contigs in a single metagenomic sample. CoMet utilizes coverage values and the compositional features of metagenomic contigs. The binning strategy in CoMet includes the initial grouping of contigs in guanine-cytosine (GC) content-coverage space and refinement of bins in tetranucleotide frequencies space in a purely unsupervised manner. With CoMet, the clustering algorithm DBSCAN is employed for binning contigs. The performances of CoMet were compared against four existing approaches for binning a single metagenomic sample, including MaxBin, Metawatt, MyCC (default) and MyCC (coverage) using multiple datasets including a sample comprised of multiple strains. Binning methods based on both compositional features and coverages of contigs had higher performances than the method which is based only on compositional features of contigs. CoMet yielded higher or comparable precision in comparison to the existing binning methods on benchmark datasets of varying complexities. MyCC (coverage) had the highest ranking score in F1-score. However, the performances of CoMet were higher than MyCC (coverage) on the dataset containing multiple strains. Furthermore, CoMet recovered contigs of more species and was 18 - 39% higher in precision than the compared existing methods in discriminating species from the sample of multiple strains. CoMet resulted in higher precision than MyCC (default) and MyCC (coverage) on a real metagenome. The approach proposed with CoMet for binning contigs, improves the precision of binning while characterizing more species in a single metagenomic sample and in a sample containing multiple strains. The F1-scores obtained from different binning strategies vary with different datasets; however, CoMet yields the highest F1-score with a sample comprised of multiple strains.

Comets and the origin of life; Proceedings of the Fifth College Park Colloquium on Chemical Evolution, University of Maryland, College Park, MD, October 29-31, 1980

NASA Technical Reports Server (NTRS)

Ponnamperuma, C.

1981-01-01

Papers are presented concerning the characteristics of comets and their possible role in the origin of life. Specific topics include the characteristics, origin and structure of the cometary nucleus, cometary chemical abundances, the nature of interplanetary dust and its entry into terrestrial planet atmospheres, and the mechanism of ray closure in comet tails. Attention is also given to chemically evolved interstellar dust as a source of prebiotic material, the relation of comets to paleoatmospheric photochemistry, comets as a vehicle for panspermia, limits to life posed by extreme environments, and the status of cometary space missions as of 1980.

The Meteoroid Fluence at Mars Due to Comet Siding Spring

NASA Technical Reports Server (NTRS)

Moorhead, Althea V.

2014-01-01

Long-period comet C/2013 A1 (Siding Spring) is headed for a close encounter with Mars on 2014 Oct 19. A collision between the comet and the planet has been ruled out, but the comets coma may envelop Mars and its man-made satellites. We present an analytic model of the dust component of cometary comae that describes the spatial distribution of cometary dust and meteoroids and their size distribution. If the coma reaches Mars, we estimate a total incident particle fluence on the planet and its satellites of 0.01 particles per square meter. We compare our model with numerical simulations, data from past comet missions, and recent Siding Spring observations.

The carbon chemistry of meteorites: Relationships to comets

NASA Technical Reports Server (NTRS)

Chang, S.

1989-01-01

The carbonaceous meteorites exhibiting alteration by liquid water bear a strong relationship to comets. Not only is their elemental composition closer to solar in relative abundances than other meteorites, they are water rich; and they contain isotopic compositions among refractory and volatile elements indicative of presolar components. Some of these isotopic anomalies occur in organic compounds and carbonaceous grains signifying the presence of discrete and identifiable carbon components derived from interstellar and circumstellar matter. Insofar as comets and meteorites are ultimately formed from interstellar gas and dust, and comets have been subjected to considerably less aqueous and thermal evolution than carbonaceous meteorites, the interstellar imprint should be much stronger and better preserved in comets.

Chasing a Comet with a Solar Sail

NASA Technical Reports Server (NTRS)

Stough, Robert W.; Heaton, Andrew F.; Whorton, Mark S.

2008-01-01

Solar sail propulsion systems enable a wide range of missions that require constant thrust or high delta-V over long mission times. One particularly challenging mission type is a comet rendezvous mission. This paper presents optimal low-thrust trajectory designs for a range of sailcraft performance metrics and mission transit times that enables a comet rendezvous mission. These optimal trajectory results provide a trade space which can be parameterized in terms of mission duration and sailcraft performance parameters such that a design space for a small satellite comet chaser mission is identified. These results show that a feasible space exists for a small satellite to perform a comet chaser mission in a reasonable mission time.

A new calibration of the semi-empirical photometric theory for Halley and other comets

NASA Technical Reports Server (NTRS)

Newburn, R. L., Jr.

1984-01-01

The semiempirical photometric theory of gas and dust production in comets (Newburn, 1979, 1981, and 1982) is recalibrated on the basis of the 17-comet compilation of spectrophotometric data of Newburn and Spinrad (1984). The results are presented in graphs and tables, and it is shown that no corrections are required for the constant R and the function delta, but that the mixing ratios (obtained as functions of heliocentric distance) can be improved, with implications for the visual-photometric comet model. Recently calculated light curves for comet Halley are compared, and the use of the nearly identical curves of Bortle and Morris (1984) and Marcus (1983) is recommended.

William Herschel and Comets

NASA Astrophysics Data System (ADS)

Sullivan, Woodruff

2018-01-01

I examine the observational and theoretical researches of William Herschel on 21 comets that he observed over the period 1781 to 1812. Herschel's focus, unlike most contemporaries, was on their physical structure, not their orbits. He forged a strong connection between comets and his nebulae with a scheme of cometary "maturation" (1812) involved a comet traveling from star to star after its central "planetary body'; was born from gravitational collapse of a nebula. During close passages of a star, the comet brightened and lost mass from its atmosphere; at other times, when between stars, it encountered nebulae and was rejuvenated by picking up more mass. Laplace soon adopted these ideas to improve his nebula hypothesis for solar system formation.

Comet ISON Streaks Toward the Sun

NASA Image and Video Library

2013-11-22

Date: 19 Nov 2013 Comet ISON shows off its tail in this three-minute exposure taken on 19 Nov. 2013 at 6:10 a.m. EST, using a 14-inch telescope located at the Marshall Space Flight Center. The comet is just nine days away from its close encounter with the sun; hopefully it will survive to put on a nice show during the first week of December. The star images are trailed because the telescope is tracking on the comet, which is now exhibiting obvious motion with respect to the background stars over a period of minutes. At the time of this image, Comet ISON was some 44 million miles from the sun -- and 80 million miles from Earth -- moving at a speed of 136,700 miles per hour. Credit: NASA/MSFC/Aaron Kingery -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on HT-COMET: a novel automated approach for high throughput assessment of human sperm chromatin quality

PubMed Central

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

2016-01-01

STUDY QUESTION Can we make the comet assay (single-cell gel electrophoresis) for human sperm a more accurate and informative high throughput assay? SUMMARY ANSWER 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. WHAT IS KNOWN ALREADY 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. STUDY DESIGN, SIZE, DURATION The study comprised two distinct components: a HT-COMET technical optimization section based on control versus DNAse treatment analyses (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. PARTICIPANTS/MATERIALS, SETTING, METHODS 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. MAIN RESULTS AND THE ROLE OF CHANCE 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. LIMITATIONS, REASONS FOR CAUTION 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. WIDER IMPLICATIONS OF THE FINDINGS 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. STUDY FUNDING/COMPETING INTEREST(S) 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. PMID:26975326

Secular light curves of comets, II: 133P/Elst Pizarro, an asteroidal belt comet

NASA Astrophysics Data System (ADS)

Ferrín, Ignacio

2006-12-01

We present the secular light curve (SLC) of 133P/Elst-Pizarro, and show ample and sufficient evidence to conclude that it is evolving into a dormant phase. The SLC provides a great deal of information to characterize the object, the most important being that it exhibits outburst-like activity without a corresponding detectable coma. 133P will return to perihelion in July of 2007 when some of our findings may be corroborated. The most significant findings of this investigation are: (1) We have compiled from 127 literature references, extensive databases of visual colors (37 comets), rotational periods and peak-to-valley amplitudes (64 comets). 2-Dimensional plots are created from these databases, which show that comets do not lie on a linear trend but in well defined areas of these phase spaces. When 133P is plotted in the above diagrams, its location is entirely compatible with those of comets. (2) A positive correlation is found between cometary rotational periods and diameters. One possible interpretation suggest the existence of rotational evolution predicted by several theoretical models. (3) A plot of the historical evolution of cometary nuclei density estimates shows no trend with time, suggesting that perhaps a consensus is being reached. We also find a mean bulk density for comets of <ρ>=0.52±0.06 g/cm. This value includes the recently determined spacecraft density of Comet 9P/Tempel 1, derived by the Deep Impact team. (4) We have derived values for over 18 physical parameters, listed in the SLC plots, Figs. 6-9. (5) The secular light curve of 133P/Elst-Pizarro exhibits a single outburst starting at +42±4 d (after perihelion), peaking at LAG=+155±10 d, duration 191±11 d, and amplitude 2.3±0.2 mag. These properties are compatible with those of other low activity comets. (6) To explain the large time delay in maximum brightness, LAG, two hypothesis are advanced: (a) the existence of a deep ice layer that the thermal wave has to reach before sublimation is possible, or (b) the existence of a sharp polar active region pointing to the Sun at time = LAG, that may take the form of a polar ice cap, a polar fissure or even a polar crater. The diameter of this zone is calculated at ˜1.8 km. (7) A new time-age is defined and it its found that T-AGE = 80 cy for 133P, a moderately old comet. (8) We propose that the object has its origin in the main belt of asteroids, thus being an asteroid-comet hybrid transition object, an asteroidal belt comet (ABC), proven by its large density. (9) Concerning the final evolutionary state of this object, to be a truly extinct comet the radius must be less than the thermal wave depth, which at 1 AU is ˜250 m (at the perihelion distance of 133P the thermal wave penetrates only ˜130 m). Comets with radius larger than this value cannot become extinct but dormant. Thus we conclude that 133P cannot evolve into a truly extinct comet because it has too large a diameter. Instead it is shown to be entering a dormant phase. (10) We predict the existence of truly extinct comets in the main belt of asteroids (MBA) beginning at absolute magnitude ˜21.5 (diameter smaller than ˜190 m). (11) The object demonstrates that a comet may have an outburst of ˜2.3 mag, and not show any detectable coma. (12) Departure from a photometric R law is a more sensitive method (by a factor of 10) to detect activity than star profile fitting or spectroscopy. (13) Sufficient evidence is presented to conclude that 133P is the first member of a new class of objects, an old asteroidal belt comet, ABC, entering a dormant phase.

Oct. 9 Hubble View of ISON

NASA Image and Video Library

2013-11-22

On Oct. 9, 2013, Hubble observed comet ISON once again, when it was inside the orbit of Mars, about 177 million miles from Earth. This image shows that the comet was still intact despite some predictions that the fragile icy nucleus might disintegrate closer to the sun. The comet will pass closest to the sun on Nov. 28, 2013. If the nucleus had broke apart then Hubble would have likely seen evidence of multiple fragments. Moreover, the coma, or head, surrounding the comet's nucleus is symmetric and smooth. This would probably not be the case if clusters of smaller fragments were flying along. This color composite image was assembled using two filters. The comet's coma appears cyan, a greenish-blue color due to gas, while the tail is reddish due to dust streaming off the nucleus. The tail forms as dust particles are pushed away from the nucleus by the pressure of sunlight. Credit: NASA -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on IUE observations of periodic comets Tempel-2, Kopff, and Tempel-1

NASA Technical Reports Server (NTRS)

Feldman, Paul D.; Festou, Michel C.

1992-01-01

We summarize the results of observations made between 10 Jun. - 18 Dec. 1988 with the International Ultraviolet Explorer (IUS) of comet P/Tempel-2 during its 1988 appearance. The derived water production rate and relative gas/dust ratio are compared with those of P/Halley, observed with IUE in 1985-86, and other potential Comet Rendezvous/Asteroid Flyby (CRAF) target comets, P/Kopff and P/Tempel-1, both observed with IUE in 1983.

Water production in comets C/2011 L4 (PanSTARRS) and C/2012 F6 (Lemmon) from observations with Soho/Swan

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

Combi, M. R.; Aptekar, G.; Bertaux, J.-L.

2014-06-01

Comets C/2011 L4 (PanSTARRS) and C/2012 F6 (Lemmon) were observed throughout their 2012-2013 apparitions with the Solar Wind Anisotropies (SWAN) all-sky hydrogen Lyα camera on board the Solar and Heliosphere Observatory (SOHO) satellite. SOHO has been in a halo orbit around the L1 Earth-Sun Lagrange point since early 1996 and has been observing the interplanetary medium and comets beginning with C/1996 B2 (Hyakutake). The global water production from these comets was determined from an analysis of the SWAN Lyα camera observations. Comet C/2011 L4 (PanSTARRS), which reached its perihelion distance of 0.302 AU on 2013 March 10.17, was observed onmore » 50 days between 2013 January 29 and April 30. Comet C/2012 F6 (Lemmon), which reached its perihelion distance of 0.731 AU on 2013 March 24.51, was observed on 109 days between 2012 November 29 and 2013 June 31. The maximum water production rates were ∼1 × 10{sup 30} molecules s{sup –1} for both comets. The activities of both comets were asymmetric about perihelion. C/2011 L4 (PanSTARRS) was more active before perihelion than after, but C/2012 F6 (Lemmon) was more active after perihelion than before.« less

Manufactured Porous Ambient Surface Simulants

NASA Technical Reports Server (NTRS)

Carey, Elizabeth M.; Peters, Gregory H.; Chu, Lauren; Zhou, Yu Meng; Cohen, Brooklin; Panossian, Lara; Green, Jacklyn R.; Moreland, Scott; Backes, Paul

2016-01-01

The planetary science decadal survey for 2013-2022 (Vision and Voyages, NRC 2011) has promoted mission concepts for sample acquisition from small solar system bodies. Numerous comet-sampling tools are in development to meet this standard. Manufactured Porous Ambient Surface Simulants (MPASS) materials provide an opportunity to simulate variable features at ambient temperatures and pressures to appropriately test potential sample acquisition systems for comets, asteroids, and planetary surfaces. The original "flavor" of MPASS materials is known as Manufactured Porous Ambient Comet Simulants (MPACS), which was developed in parallel with the development of the Biblade Comet Sampling System (Backes et al., in review). The current suite of MPACS materials was developed through research of the physical and mechanical properties of comets from past comet missions results and modeling efforts, coordination with the science community at the Jet Propulsion Laboratory and testing of a wide range of materials and formulations. These simulants were required to represent the physical and mechanical properties of cometary nuclei, based on the current understanding of the science community. Working with cryogenic simulants can be tedious and costly; thus MPACS is a suite of ambient simulants that yields a brittle failure mode similar to that of cryogenic icy materials. Here we describe our suite of comet simulants known as MPACS that will be used to test and validate the Biblade Comet Sampling System (Backes et al., in review).

Introducing a true internal standard for the Comet assay to minimize intra- and inter-experiment variability in measures of DNA damage and repair

PubMed Central

Zainol, Murizal; Stoute, Julia; Almeida, Gabriela M.; Rapp, Alexander; Bowman, Karen J.; Jones, George D. D.

2009-01-01

The Comet assay (CA) is a sensitive/simple measure of genotoxicity. However, many features of CA contribute variability. To minimize these, we have introduced internal standard materials consisting of ‘reference’ cells which have their DNA substituted with BrdU. Using a fluorescent anti-BrdU antibody, plus an additional barrier filter, comets derived from these cells could be readily distinguished from the ‘test’-cell comets, present in the same gel. In experiments to evaluate the reference cell comets as external and internal standards, the reference and test cells were present in separate gels on the same slide or mixed together in the same gel, respectively, before their co-exposure to X-irradiation. Using the reference cell comets as internal standards led to substantial reductions in the coefficient of variation (CoV) for intra- and inter-experimental measures of comet formation and DNA damage repair; only minor reductions in CoV were noted when the reference and test cell comets were in separate gels. These studies indicate that differences between individual gels appreciably contribute to CA variation. Further studies using the reference cells as internal standards allowed greater significance to be obtained between groups of replicate samples. Ultimately, we anticipate that development will deliver robust quality assurance materials for CA. PMID:19828597

Detection of CO and HCN in the coma of Jupiter-family comet 41P/Tuttle-Giacobini-Kresak

NASA Astrophysics Data System (ADS)

Wierzchos, Kacper; Womack, Maria

2017-10-01

Comets are divided into taxonomical groups determined largely by their orbits. Short-period Jupiter Family comets (JFCs) are thought to have formed in a trans-Neptunian disk ˜30 - 100 AU (Kuiper Belt) and then migrated inward (Edgeworth 1949, Kuiper 1951, Duncan et al. 1988). This different classification may be correlated with chemical abundance variations, and super-volatile species like CO can serve as an indicator of the thermal processes to which the precometary ices that led to comets where exposed (DiSainti et al. 2007). The close approach to Earth of comet 41P on the perihelion passage of 2017 was an excellent opportunity to probe the usually well-hidden inner coma of this Jupiter-family comet. We searched for CO (J=2-1) and HCN (J=3-2) emission with the Arizona Radio Observatory (ARO) 10-m Sub-millimeter Telescope (SMT) on 2017 April 1-2, when the comet was 1.1 AU from the Sun and 0.14 AU from Earth. We report the detection of both CO and HCN emission 13 days before perihelion and present column densities and production rates. We also discuss implications for Jupiter-family comets. The SMT is operated by the ARO, the Steward Observatory, and the University of Arizona, with support through the NSF University Radio Observatories program (AST-1140030). M.W. acknowledges support from NSF grant AST-1615917.

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.

EVIDENCE FOR FRESH FROST LAYER ON THE BARE NUCLEUS OF COMET HALE-BOPP AT 32 AU DISTANCE

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

Szabo, Gyula M.; Kiss, Laszlo L.; Pal, Andras

2012-12-10

Here, we report that the activity of comet Hale-Bopp ceased between late 2007 and 2009 March, at about 28 AU distance from the Sun. At that time, the comet resided at a distance from the Sun that exceeded the freeze-out distance of regular comets by an order of magnitude. A Herschel Space Observatory PACS scan was taken in mid-2010, in the already inactive state of the nucleus. The albedo has been found to be surprisingly large (8.1% {+-} 0.9%), which exceeds the value known for any other comets. With re-reduction of archive Hubble Space Telescope images from 1995 and 1996,more » we confirm that the pre-perihelion albedo resembled that of an ordinary comet and was smaller by a factor of two than the post-activity albedo. Our further observations with the Very Large Telescope also confirmed that the albedo increased significantly by the end of the activity. We explain these observations by proposing gravitational redeposition of icy grains toward the end of the activity. This is plausible for such a massive body in a cold environment, where gas velocity is lowered to the range of the escape velocity. These observations also show that giant comets are not just the upscaled versions of the comets we know but can be affected by processes that are yet to be fully identified.« less

Self-esteem treatment in anxiety: A randomized controlled crossover trial of Eye Movement Desensitization and Reprocessing (EMDR) versus Competitive Memory Training (COMET) in patients with anxiety disorders.

PubMed

Staring, A B P; van den Berg, D P G; Cath, D C; Schoorl, M; Engelhard, I M; Korrelboom, C W

2016-07-01

Little is known about treating low self-esteem in anxiety disorders. This study evaluated two treatments targeting different mechanisms: (1) Eye Movement Desensitization and Reprocessing (EMDR), which aims to desensitize negative memory representations that are proposed to maintain low self-esteem; and (2) Competitive Memory Training (COMET), which aims to activate positive representations for enhancing self-esteem. A Randomized Controlled Trial (RCT) was used with a crossover design. Group 1 received six sessions EMDR first and then six sessions COMET; group 2 vice versa. Assessments were made at baseline (T0), end of first treatment (T1), and end of second treatment (T2). Main outcome was self-esteem. We included 47 patients and performed Linear Mixed Models. COMET showed more improvements in self-esteem than EMDR: effect-sizes 1.25 versus 0.46 post-treatment. Unexpectedly, when EMDR was given first, subsequent effects of COMET were significantly reduced in comparison to COMET as the first intervention. For EMDR, sequence made no difference. Reductions in anxiety and depression were mediated by better self-esteem. COMET was associated with significantly greater improvements in self-esteem than EMDR in patients with anxiety disorders. EMDR treatment reduced the effectiveness of subsequent COMET. Improved self-esteem mediated reductions in anxiety and depression symptoms. Copyright © 2016 Elsevier Ltd. All rights reserved.

Long-term orbital evolution of short-period comets found in Project Cosmo-DICE

NASA Technical Reports Server (NTRS)

Nakamura, Tsuko; Yoshikawa, Makoto

1992-01-01

Orbital evolutions of about 160 short-period (SP) comets are numerically integrated for 4400 years in the framework of a realistic dynamical model. By the round-trip error in closure test, a reliable time space of the integrated orbits is estimated for each comet. Majority of the SP comets with their Tisserand's constant(J) between 2.8 and 3.1 are found to evolve within the past 1000-2000 years from the orbits whose perihelia are near the Jovian orbit to the orbits with perihelia of 1-2 AU. This evolution is much more rapid than that expected from Monte Carlo simulations based on symmetric distribution of planetary perturbations, thus suggesting that asymmetry of perturbation distribution play an important role in cometary evolution. Several comets are shown to evolve from the near-Saturn orbits and then to be handed over under the control of Jupiter. We also find that a few comets were captured from long-period orbits (a = 75-125 AU) via only a few close encounters with Jupiter. It is confirmed that the captured SP comets of low-inclination with 2.7 less than J less than 3.1 show more or less strong chaotic behavior. On the other hand, comets with longer orbital period and/or of high inclination reveal slow or quasi-periodic orbital evolution.

"April Fool’s Day" comet to pass by Earth

NASA Image and Video Library

2017-12-08

On April 1, 2017, comet 41P will pass closer than it normally does to Earth, giving observers with binoculars or a telescope a special viewing opportunity. Comet hunters in the Northern Hemisphere should look for it near the constellations Draco and Ursa Major, which the Big Dipper is part of. Whether a comet will put on a good show for observers is notoriously difficult to predict, but 41P has a history of outbursts, and put on quite a display in 1973. If the comet experiences similar outbursts this time, there’s a chance it could become bright enough to see with the naked eye. The comet is expected to reach perihelion, or its closest approach to the sun, on April 12. A member of the Jupiter family of comets, 41P makes a trip around the sun every 5.4 years, coming relatively close to Earth on some of those trips. On this approach, the comet will pass our planet at a distance of about 13 million miles (0.14 astronomical units), or about 55 times the distance from Earth to the moon. This is the comet’s closest approach to Earth in more than 50 years and perhaps more than a century. Read more: go.nasa.gov/2nLNzes Photo caption: In this image taken March 24, 2017, comet 41P/Tuttle-Giacobini-Kresák is shown moving through a field of faint galaxies in the bowl of the Big Dipper. On April 1, the comet will pass by Earth at a distance of about 13 million miles (0.14 astronomical units), or 55 times the distance from Earth to the moon; that is a much closer approach than usual for this Jupiter-family comet. Photo credit: Image copyright Chris Schur©, used with permission NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Results of the International Validation of the in vivo rodent alkaline comet assay for the detection of genotoxic carcinogens: Individual data for 1,2-dibromoethane, p-anisidine, and o-anthranilic acid in the 2nd step of the 4th phase Validation Study under the JaCVAM initiative.

PubMed

Takasawa, Hironao; Takashima, Rie; Narumi, Kazunori; Kawasako, Kazufumi; Hattori, Akiko; Kawabata, Masayoshi; Hamada, Shuichi

2015-07-01

As part of the Japanese Center for the Validation of Alternative Methods (JaCVAM)-initiative International Validation Study of an in vivo rat alkaline comet assay, we examined 1,2-dibromoethane (DBE), p-anisidine (ASD), and o-anthranilic acid (ANT) to investigate the effectiveness of the comet assay in detecting genotoxic carcinogens. Each of the three test chemicals was administered to 5 male Sprague-Dawley rats per group by oral gavage at 48, 24, and 3h before specimen preparation. Single cells were collected from the liver and glandular stomach at 3h after the final dosing, and the specimens prepared from these two organs were subjected to electrophoresis under alkaline conditions (pH>13). The percentage of DNA intensity in the comet tail was then assessed using an image analysis system. A micronucleus (MN) assay was also conducted using these three test chemicals with the bone marrow (BM) cells collected from the same animals simultaneously used in the comet assay, i.e., combination study of the comet assay and BM MN assay. A genotoxic (Ames positive) rodent carcinogen, DBE gave a positive result in the comet assay in the present study, while a genotoxic (Ames positive) non-carcinogen, ASD and a non-genotoxic (Ames negative) non-carcinogen, ANT showed negative results in the comet assay. All three chemicals produced negative results in the BM MN assay. While the comet assay findings in the present study were consistent with those obtained from the rodent carcinogenicity studies for the three test chemicals, we consider the positive result in the comet assay for DBE to be particularly meaningful, given that this chemical produced a negative result in the BM MN assay. Therefore, the combination study of the comet assay and BM MN assay is a useful method to detect genotoxic carcinogens that are undetectable with the BM MN assay alone. Copyright © 2015 Elsevier B.V. All rights reserved.

Potential Jupiter-Family comet contamination of the main asteroid belt

NASA Astrophysics Data System (ADS)

Hsieh, Henry H.; Haghighipour, Nader

2016-10-01

We present the results of "snapshot" numerical integrations of test particles representing comet-like and asteroid-like objects in the inner Solar System aimed at investigating the short-term dynamical evolution of objects close to the dynamical boundary between asteroids and comets as defined by the Tisserand parameter with respect to Jupiter, TJ (i.e., TJ = 3). As expected, we find that TJ for individual test particles is not always a reliable indicator of initial orbit types. Furthermore, we find that a few percent of test particles with comet-like starting elements (i.e., similar to those of Jupiter-family comets) reach main-belt-like orbits (at least temporarily) during our 2 Myr integrations, even without the inclusion of non-gravitational forces, apparently via a combination of gravitational interactions with the terrestrial planets and temporary trapping by mean-motion resonances with Jupiter. We estimate that the fraction of real Jupiter-family comets occasionally reaching main-belt-like orbits on Myr timescales could be on the order of ∼ 0.1-1%, although the fraction that remain on such orbits for appreciable lengths of time is certainly far lower. For this reason, the number of JFC-like interlopers in the main-belt population at any given time is likely to be small, but still non-zero, a finding with significant implications for efforts to use apparently icy yet dynamically asteroidal main-belt comets as tracers of the primordial distribution of volatile material in the inner Solar System. The test particles with comet-like starting orbital elements that transition onto main-belt-like orbits in our integrations appear to be largely prevented from reaching low eccentricity, low inclination orbits, suggesting that the real-world population of main-belt objects with both low eccentricities and inclinations may be largely free of this potential occasional Jupiter-family comet contamination. We therefore find that low-eccentricity, low-inclination main-belt comets may provide a more reliable means for tracing the primordial ice content of the main asteroid belt than the main-belt comet population as a whole.

Rapid evolution of the spin state of comet 41P/Tuttle-Giacobini-Kresak

NASA Astrophysics Data System (ADS)

Bodewits, Dennis; Farnham, Tony; Knight, Matthew M.; Kelley, Michael S.

2017-10-01

Comet nuclei are small, dynamic objects influenced strongly by their individual history, orbit, rotation and inhomogeneity. Mass loss due to sublimation can exert a profound influence on the physical nature of the cometary nucleus, changing the shape, size, and rotation (Jewitt, in Comets II, 2004). The Rosetta mission to comet 67P showed that these effects are all interrelated (Sierks et al., Science 347, 2015).Comet 41P/Tuttle-Giacobini-Kresak passed Earth as close as 0.142 au in April 2017, allowing observations of the inner coma and an assessment of the rotational state of the nucleus. We acquired observations of comet 41P between March and May 2017 using the 4.3-m Discovery Channel Telescope and the UltraViolet-Optical Telescope (UVOT) on board the Earth-orbiting Swift Gamma Ray Burst Mission.Using CN narrowband imaging and aperture photometry we found that the apparent rotation period of comet 41P more than doubled between March and May 2017, increasing from 20 hours to 50 hours. Measurements of the periodicity in late-March by Knight et al. (CBET 4377, 2017) are consistent with this rate of increase. Comet 41P is the ninth comet for which a rotation period change has been observed (c.f. Samarasinha et al., in Comets II, 2004), but both the fractional change and the rate of change of the period far exceed those observed in the other comets. It is presumably the combination of a long rotation period, high surface activity, and a small nucleus that makes 41P highly susceptible to changes in its rotational state.Extrapolating the comet’s rotation period using its current gas production rates and a simple activity model suggests that the nucleus will continue to spin down, possibly leading to an excited spin state in the next few apparitions. Finally, 41P is known for its large outbursts, and our extrapolation suggest that the comet’s rotation period may have been close to the critical period for splitting in 2001, when it exhibited two significant outbursts.

Rapid evolution of the spin state of comet 41P/Tuttle-Giacobini-Kresak

NASA Astrophysics Data System (ADS)

Bodewits, Dennis; Farnham, Tony; Kelley, Michael S. P.; Manning Knight, Matthew

2018-01-01

Cometary outgassing can produce torques that change the spin state of the nucleus, influencing the evolution and lifetimes of comets. If these torques spin up the rotation to the point that centripetal forces exceed the material strength of the nucleus, the comet may fragment. Comet 41P/Tuttle-Giacobini-Kresak passed Earth as close as 0.142 au in April 2017, allowing observations of the inner coma and an assessment of the rotational state of the nucleus. We acquired observations of comet 41P between March and May 2017 using the 4.3-m Discovery Channel Telescope and the UltraViolet-Optical Telescope (UVOT) on board the Earth-orbiting Swift Gamma Ray Burst Mission.We combined CN narrowband imaging and aperture photometry and found that the apparent rotation period of comet 41P more than doubled between March and May 2017, increasing from 20 hours to over 46 hours. Measurements of the periodicity in late-March by Knight et al. (CBET 4377, 2017) are consistent with this rate of increase. Comet 41P is the ninth comet for which a rotation period change has been observed (c.f. Samarasinha et al., in Comets II, 2004), but both the fractional change and the rate of change of the period far exceed those observed in the other comets. It is the combination of a slow rotation, high activity, and a small nucleus that contribute to the rapid changes of the rotation state of 41P. In addition, the active regions on the surface of 41P are likely oriented in a way such that its torques are highly optimized in comparison to many other comets.Extrapolating the comet’s rotation period using its current gas production rates and a simple activity model suggests that the nucleus will continue to spin down, possibly leading to an excited spin state in the next apparitions. Finally, 41P is known for its large outbursts, and our extrapolation suggest that the comet’s rotation period may have been close to the critical period for splitting in 2001, when it exhibited two significant outbursts.

Up Close and Personal with Hartley 2

NASA Image and Video Library

2010-11-04

This image, one of the closest taken of comet Hartley 2 by NASA EPOXI mission, shows many features across the comet surface. The length of the comet is equal to the distance between the Capitol building and the Washington Monument in Washington.

Records of Halley's comet on Babylonian tablets

NASA Astrophysics Data System (ADS)

Stephenson, F. R.; Yau, K. K. C.; Hunger, H.

1985-04-01

The late Babylonian texts in the British Museum are shown to contain probable observations of Halley's comet at both its 164 BC and 87 BC apparitions. These texts have important bearing on the orbital motion of the comet in the ancient past.

ScienceCast 116: Comet ISON to Fly By Mars

NASA Image and Video Library

2013-08-15

Comet ISON is heading for a Thanksgiving Day brush with the sun, but first it's going to pay a visit to Mars. In this week's ScienceCast, researchers discuss what might happen when Comet ISON meets the Red Planet.

Comet ISON Passes Through Virgo

NASA Image and Video Library

2013-11-22

Date: 8 Nov 2013 - Comet ISON shines in this five-minute exposure taken at NASA's Marshall Space Flight Center on Nov. 8, 2013.. The image was captured using a color CCD camera attached to a 14" telescope located at Marshall. At the time of this picture, comet ISON was 97 million miles from Earth, moving ever closer toward the sun. Credit: NASA/MSFC/Aaron Kingery -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Comet ISON Enhanced

NASA Image and Video Library

2013-11-22

Taken on 19 Nov. 2013, this image shows a composite "stacked" image of comet ISON. These five stacked images of 10 seconds each were taken with the 20" Marshall Space Flight Center telescope in New Mexico. This technique allows the comet's sweeping tail to emerge with more detail. Credit: NASA/MSFC/MEO/Cameron McCarty -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Formation and past evolution of the showers of 96P/Machholz complex

NASA Astrophysics Data System (ADS)

Abedin, Abedin; Wiegert, Paul; Janches, Diego; Pokorný, Petr; Brown, Peter; Hormaechea, Jose Luis

2018-01-01

In this work we model the dynamical evolution of meteoroid streams of comet 96P/Machholz, and the largest member of the Marsden sunskirters, comet P/1999 J6. We simultaneously fit the characteristics of eight meteor showers which have been proposed to be linked to the complex, using observations from a range of techniques - visual, video, TV and radar. The aim is to obtain a self-consistent scenario of past capture of a large comet into a short-period orbit, and its subsequent fragmentation history. Moreover, we also aim to constrain the dominant parent of these showers. The fit of our simulated shower characteristics to observations is consistent with the scenario of a capture of a proto-comet 96P/Machholz by Jupiter circa 20000 BCE, and a subsequent major breakup around 100-950 CE which resulted in the formation of the Marsden group of comets. We find that the Marsden group of comets are not the immediate parents of the daytime Arietids and Northern and Southern δ-Aquariids, as previously suggested. In fact, the hypothesis that the Northern δ-Aquariids are related to the Marsden group of comets is not supported by this study. The bulk of the observational characteristics of all eight showers can be explained by meteoroid ejection primarily from comet 96P/Machholz between 10000 BCE and 20000 BCE. Assuming the Marsden group of comets originated between 100 CE-950 CE, we conclude that sunskirting comets contribute mainly to the meteoroid stream near the time of the peak of the daytime Arietids, Southern δ-Aquariids, κ-Velids. Finally, we find that the meteor showers identified by Babadzhanov and Obrubov (1992) as the α-Cetids, the Ursids and Carinids correspond to the daytime λ-Taurids, the November ι-Draconids or December α-Draconids and the θ-Carinids.

Abundant Solar Nebula Solids in Comets

NASA Technical Reports Server (NTRS)

Messenger, S.; Keller, L. P.; Nakamura-Messenger, K.; Nguyen, A. N.; Clemett, S.

2016-01-01

Comets have been proposed to consist of unprocessed interstellar materials together with a variable amount of thermally annealed interstellar grains. Recent studies of cometary solids in the laboratory have shown that comets instead consist of a wide range of materials from across the protoplanetary disk, in addition to a minor complement of interstellar materials. These advances were made possible by the return of direct samples of comet 81P/Wild 2 coma dust by the NASA Stardust mission and recent advances in microscale analytical techniques. Isotopic studies of 'cometary' chondritic porous interplanetary dust particles (CP-IDPs) and comet 81P/Wild 2 Stardust samples show that preserved interstellar materials are more abundant in comets than in any class of meteorite. Identified interstellar materials include sub-micron-sized presolar silicates, oxides, and SiC dust grains and some fraction of the organic material that binds the samples together. Presolar grain abundances reach 1 weight percentage in the most stardust-rich CP-IDPs, 50 times greater than in meteorites. Yet, order of magnitude variations in presolar grain abundances among CP-IDPs suggest cometary solids experienced significant variations in the degree of processing in the solar nebula. Comets contain a surprisingly high abundance of nebular solids formed or altered at high temperatures. Comet 81P/Wild 2 samples include 10-40 micron-sized, refractory Ca- Al-rich inclusion (CAI)-, chondrule-, and ameboid olivine aggregate (AOA)-like materials. The O isotopic compositions of these refractory materials are remarkably similar to their meteoritic counterparts, ranging from 5 percent enrichments in (sup 16) O to near-terrestrial values. Comet 81P/Wild 2 and CP-IDPs also contain abundant Mg-Fe crystalline and amorphous silicates whose O isotopic compositions are also consistent with Solar System origins. Unlike meteorites, that are dominated by locally-produced materials, comets appear to be composed of materials that were formed across a wide swath of the early protoplanetary disk.

A GREAT search for Deuterium in Comets

NASA Astrophysics Data System (ADS)

Mumma, Michael

2012-10-01

Comets are understood to be the most pristine bodies in the Solar System. Their compositions reflect the chemical state of materials at the very earliest evolutionary stages of the protosolar nebula and, as such, they provide detailed insight into the physical and chemical processes operating in planet-forming disks. Isotopic fractionation ratios of the molecular ices in the nucleus are regarded as signatures of formation processes. These ratios provide unique information on the natal heritage of those ices, and can also test the proposal that Earth's water and other volatiles were delivered by cometary bombardment. Measurement of deuterium fractionation ratios is thus a major goal in contemporary cometary science and the D/H ratio of water - the dominant volatile in comets - holds great promise for testing the formation history of cometary matter. The D/H ratio in cometary water has been measured in only seven comets. Six were from the Oort Cloud reservoir and the D/H ratio was about twice that of the Earth's oceans. However, the recent Herschel measurement of HDO/H2O in 103P/Hartley-2 (the first from the Kuiper Belt) was consistent with exogenous delivery of Earth's water by comets. Outstanding questions remain: are cometary HDO/H2O ratios consistent with current theories of nebular chemical evolution or with an interstellar origin? Does the HDO/H2O ratio vary substantially among comet populations? Hartley-2 is the only Kuiper Belt comet with measured HDO/H2O, are there comets with similar ratios in the Oort cloud? These questions can only be addressed by measuring HDO/H2O ratios in many more suitable bright comets. We therefore propose to measure the D/H ratio in water in a suitable target-of-opportunity comet by performing observations of HDO and OH with the GREAT spectrometer on SOFIA. A multi-wavelength, ground-based observing campaign will also be conducted in support of the airborne observations.

A GREAT search for Deuterium in Comets

NASA Astrophysics Data System (ADS)

Mumma, Michael

2013-10-01

Comets are understood to be the most pristine bodies in the Solar System. Their compositions reflect the chemical state of materials at the very earliest evolutionary stages of the protosolar nebula and, as such, they provide detailed insight into the physical and chemical processes operating in planet-forming disks. Isotopic fractionation ratios of the molecular ices in the nucleus are regarded as signatures of formation processes. These ratios provide unique information on the natal heritage of those ices, and can also test the proposal that Earth's water and other volatiles were delivered by cometary bombardment. Measurement of deuterium fractionation ratios is thus a major goal in contemporary cometary science and the D/H ratio of water - the dominant volatile in comets - holds great promise for testing the formation history of cometary matter. The D/H ratio in cometary water has been measured in only eight comets. Seven were from the Oort Cloud reservoir and the D/H ratio was about twice that of the Earth's oceans. However, the recent Herschel measurement of HDO/H2O in 103P/Hartley-2 (the first from the Kuiper Belt) was consistent with exogenous delivery of Earth's water by comets. Outstanding questions remain: are cometary HDO/H2O ratios consistent with current theories of nebular chemical evolution or with an interstellar origin? Does the HDO/H2O ratio vary substantially among comet populations? Hartley-2 is the only Kuiper Belt comet with measured HDO/H2O, are there comets with similar ratios in the Oort cloud? These questions can only be addressed by measuring HDO/H2O ratios in many more suitable bright comets. We therefore propose to measure the D/H ratio in water in a suitable target-of-opportunity comet by performing observations of HDO and OH with the GREAT spectrometer on SOFIA. A multi-wavelength, ground-based observing campaign will also be conducted in support of the airborne observations.

Comet ISON Approaching the Sun [hd video

NASA Image and Video Library

2013-11-27

This movie from NASA’s STEREO spacecraft's Heliospheric Imager shows Comet ISON, Mercury, Comet Encke and Earth over a five-day period from Nov. 20 to Nov. 25, 2013. The sun sits right of the field of view of this camera. Comet ISON, which will round the sun on Nov. 28, is what's known as a sungrazing comet, due to its close approach. Foreshortening or the angle at which these images were obtained make Earth appear as if it is closer to the sun than Mercury. If you look closely you will also see a dimmer and smaller comet Encke near comet ISON. A comet’s journey through the solar system is perilous and violent. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. Even if the comet does not survive, tracking its journey will help scientists understand what the comet is made of, how it reacts to its environment, and what this explains about the origins of the solar system. Closer to the sun, watching how the comet and its tail interact with the vast solar atmosphere can teach scientists more about the sun itself. Image Credit: NASA/STEREO NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Comets, Carbonaceous Meteorites, and the Origin of the Biosphere

NASA Technical Reports Server (NTRS)

Hoover, Richard B.

2005-01-01

The biosphere comprises the Earth s crust, atmosphere, oceans, and ice caps and the living organisms that survive within this habitat. The discoveries of barophilic chemolithoautotrophic thermophiles living deep within the crust and in deep-sea hydrothermal vents, and psychrophiles in permafrost and deep within the Antarctic Ice Sheet indicate the Earth s biosphere is far more extensive than previously recognized. Molecular biomarkers and Bacterial Paleontology provide evidence that life appeared very early on the primitive Earth and the origin of the biosphere is closely linked with the emergence of life. The role of comets, meteorites, and interstellar dust in the delivery of water, organics and prebiotic chemicals has long been recognized. Deuterium enrichment of seawater and comets indicates that comets delivered oceans to the early Earth. Furthermore, the similarity of the D/H ratios and the chemical compositions of CI carbonaceous meteorites and comets indicate that the CI meteorites may be remnants of cometary nuclei with most volatiles removed. Comets, meteorites, and interstellar dust also contain complex organic chemicals, amino acids, macromolecules, and kerogen-like biopolymers and may have played a crucial role in the delivery of complex organics and prebiotic chemicals during the Hadean (4.5-3.8 Gyr) period of heavy bombardment. The existence of indigenous microfossils of morphotypes of cyanobacteria in the CI and CM carbonaceous meteorites suggests that the paradigm that life originated endogenously in the primitive oceans of early Earth may require re-consideration. Recent data on the hot (300-400 K) black crust on comet P/Halley and Stardust images of P/Wild 2 showing depressions, tall cliffs, and pinnacles, indicate the presence of thick, durable, dark crusts on comets. If cavities within the ice and crust sustain vapor pressures in excess of 10 millibar, then localized pools of liquid water and brines could exist within the comet. Since life exists on Earth wherever there is liquid water, it is suggested that comets might also harbour viable and/or cryopreserved microbiota.

Composition and Cosmogonic Parameters of the Chemically Distinct Comet C/2007 N3 (Lulin)

NASA Astrophysics Data System (ADS)

Gibb, Erika L.; Villanueva, G. L.; Bonev, B. P.; DiSanti, M. A.; Mumma, M. J.; Radeva, Y. L.

2012-10-01

Comets are remnants from the early solar system that retain the volatiles (ices) from the cold outer proto-planetary disk (beyond 5 AU) where they formed. Comet nuclei were among the first objects to accrete in the early solar nebula and many of them were subsequently incorporated into the growing giant planets. Gravitational scattering redistributed the remaining comet population by either sending them to the inner solar system, where they may have enriched the early biosphere, or scattering them into their present-day dynamical reservoirs. Since this early time, comets have been orbiting the Sun relatively untouched by processing mechanisms, until their orbits are perturbed towards the inner solar system. As such, they are believed to be among the most primitive objects in the solar system and may be representative of the material from which the solar system formed. Of particular interest is their icy volatile composition since other solar system objects have either lost or have had significant modifications to their volatile compositions since their formation. Many of the volatiles observed in comets are also important prebiotic species. For example, H2CO is a chemical precursor to sugars and HCN and NH3 are precursors of amino acids. Studying comets is therefore a vital link to understanding the origin and evolution of our planetary system and life on Earth. We obtained high-resolution, near-infrared spectroscopic observations of Comet C/2007 N3 (Lulin) on 30 January - 1 February 2009 with NIRSPEC on Keck II. Lulin is an Oort Cloud comet with a very large aphelion distance, suggesting that it may have been dynamically new. We report production rates of H2O, C2H6, HCN, C2H2, CH4, NH3, H2CO, CH3OH, and CO. We also report two cosmogonic parameters: D/H ratio in H2O and CH4, and isomeric spin temperatures. The implications for comet formations scenarios are discussed.

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.

The application of the comet assay to assess the genotoxicity of environmental pollutants in the nematode Caenorhabditis elegans.

PubMed

Imanikia, Soudabeh; Galea, Francesca; Nagy, Eszter; Phillips, David H; Stürzenbaum, Stephen R; Arlt, Volker M

2016-07-01

This study aimed to establish a protocol for cell dissociation from the nematode Caenorhabditis elegans (C. elegans) to assess the genotoxicity of the environmental pollutant benzo[a]pyrene (BaP) using the alkaline version of the single cell electrophoresis assay (comet assay). BaP genotoxicity was assessed in C. elegans (wild-type [WT]; N2, Bristol) after 48h exposure (0-40μM). Induction of comets by BaP was concentration-dependent up to 20μM; comet% tail DNA was ∼30% at 20μM BaP and ∼10% in controls. Similarly, BaP-induced DNA damage was evaluated in C. elegans mutant strains deficient in DNA repair. In xpa-1 and apn-1 mutants BaP-induced comet formation was diminished to WT background levels suggesting that the damage formed by BaP that is detected in the comet assay is not recognised in cells deficient in nucleotide and base excision repair, respectively. In summary, our study provides a protocol to evaluate DNA damage of environmental pollutants in whole nematodes using the comet assay. Copyright © 2016 The Author(s). Published by Elsevier B.V. All rights reserved.

Assessment of gamma ray-induced DNA damage in Lasioderma serricorne using the comet assay

NASA Astrophysics Data System (ADS)

Kameya, Hiromi; Miyanoshita, Akihiro; Imamura, Taro; Todoriki, Setsuko

2012-03-01

We attempted a DNA comet assay under alkaline conditions to verify the irradiation treatment of pests. Lasioderma serricorne (Fabricius) were chosen as test insects and irradiated with gamma rays from a 60Co source at 1 kGy. We conducted the comet assay immediately after irradiation and over time for 7 day. Severe DNA fragmentation in L. serricorne cells was observed just after irradiation and the damage was repaired during the post-irradiation period in a time-dependent manner. The parameters of the comet image analysis were calculated, and the degree of DNA damage and repair were evaluated. Values for the Ratio (a percentage determined by fluorescence in the damaged area to overall luminance, including intact DNA and the damaged area of a comet image) of individual cells showed that no cells in the irradiated group were included in the Ratio<0.1 category, the lowest grade. This finding was observed consistently throughout the 7-day post-irradiation period. We suggest that the Ratio values of individual cells can be used as an index of irradiation history and conclude that the DNA comet assay under alkaline conditions, combined with comet image analysis, can be used to identify irradiation history.

Maria Mitchell's Comet - a Challenge Once More?

NASA Astrophysics Data System (ADS)

Boyce, P. B.; Graham, A. P.; Strelnitski, V.

1997-12-01

This year marks the sesquicentennial of the discovery of a fateful comet by Maria Mitchell (1 October 1847). This was one of the first telescopic comets ever discovered and the first one discovered by a woman. It brought Maria Mitchell the gold medal from the King of Denmark, the first appointment of a woman as professor of Astronomy (at Vassar College) and the fame to be the first (and for ninety years - the only) woman - member of the American Academy of Arts and Sciences. It gave Maria Mitchell an unusually favorable opportunity to struggle for the rights of American women in science. We restore the circumstances of this discovery, and present the results of a modern re-calculation of the orbit of the comet, including its present position in the sky and its ephemeris for the next 50 years. The comet is 32(m) now and will slowly decrease in brightness. Our ability to detect faint objects has improved dramatically over the 150 years since the comet was discovered. By extrapolation, we show that modern technology may catch up with the declining brightness of the comet by the middle of the next century. Another challenge for astronomers!

On the Absence of EUV Emission from Comet C/2012 S1 (ISON)

NASA Technical Reports Server (NTRS)

Bryans, Paul; Pesnell, W. Dean

2016-01-01

When the sungrazing comet C2012 S1 (ISON) made its perihelion passage within two solar radii of the Sun's surface, it was expected to be a bright emitter at extreme ultraviolet (EUV) wavelengths. However, despite solar EUV telescopes repointing to track the orbit of the comet, no emission was detected. This null result is interesting in its own right, offering the possibility of placing limits on the size and composition of the nucleus. We explain the lack of detection by considering the properties of the comet and the solar atmosphere that determine the intensity of EUV emission from sungrazing comets. By comparing these properties with those of sungrazing comet C2011 W3 (Lovejoy), which did emit in the EUV, we conclude that the primary factor resulting in non-detectable EUV emission from C2012 S1 (ISON) was an insufficiently large nucleus. We conclude that the radius of C2012 S1 (ISON) was at least a factor of four less than that of C2011 W3 (Lovejoy). This is consistent with white-light observations in the days before perihelion that suggested the comet was dramatically reducing in size on approach.

New methods for deriving cometary secular light curves: C/1995 O1 (Hale-Bopp) revisited

NASA Astrophysics Data System (ADS)

Womack, Maria; Lastra, Nathan; Harrington, Olga; Curtis, Anthony; Wierzchos, Kacper; Ruffini, Nicholas; Charles, Mentzer; Rabson, David; Cox, Timothy; Rivera, Isabel; Micciche, Anthony

2017-10-01

We present an algorithm for reducing scatter and increasing precision in a comet light curve. As a demonstration, we processed apparent magnitudes of comet Hale-Bopp from 16 highly experienced observers (archived with the International Comet Quarterly), correcting for distance from Earth and phase angle. Different observers tend to agree on the difference in magnitudes of an object at different distances, but the magnitude reported by observer is shifted relative to that of another for an object at a fixed distance. We estimated the shifts using a self-consistent statistical approach, leading to a sharper light curve and improving the precision of the measured slopes. The final secular lightcurve for comet Hale-Bopp ranges from -7 au (pre-perihelion) to +8 au (post-perihelion) and is the best secular light curve produced to date for this “great” comet. We discuss Hale-Bopp’s lightcurve evolution and possibly related physical implications, and potential usefulness of this light curve for comparisons with other future bright comets. We also assess the appropriateness of using secular lightcurves to characterize dust production rates in Hale-Bopp and other dust-rich comets. M.W. acknowledges support from NSF grant AST-1615917.

The outbursts of the comet 29P/Schwassmann-Wachmann 1: A new approach to the old problem

NASA Astrophysics Data System (ADS)

Gronkowski, P.

2014-02-01

As far as outbursts activity is concerned, the 29P/Schwassmann-Wachmann 1 is the exceptional comet. This Centaur object shows quasi-regular flares with periodicities of 50 days eriodicity (Trigo-Rodriguez et al. 2010). In the introductory part of the presented paper the most well-known hypotheses which try to explain this cometary behaviour are reviewed. The second, actual part of this paper presents the new model for the outburst activity of this comet. The model is based on the idea of Ipatov (2012), according to which there are large cavities %%in comets %%with material under gas pressure, below a considerable fraction of the comet's surface containing material under high gas pressure. In favourite conditions the surface layers over the cavities are thrown away and the interior of these cavities is exposed. Consequently, an outburst of the comet's brightness may be observed. The main characteristics of an outburst of this comet, the brightness jump, %%in its brightness is calculated. Numerical simulations were carried out for wide range of possible cometary parameters. The obtained results are in good agreement with the real observations.

MOLECULAR OXYGEN IN OORT CLOUD COMET 1P/HALLEY

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

Rubin, M.; Altwegg, K.; Dishoeck, E. F. van

2015-12-10

Recently, the ROSINA mass spectrometer suite on board the European Space Agency's Rosetta spacecraft discovered an abundant amount of molecular oxygen, O{sub 2}, in the coma of Jupiter family comet 67P/Churyumov–Gerasimenko of O{sub 2}/H{sub 2}O = 3.80 ± 0.85%. It could be shown that O{sub 2} is indeed a parent species and that the derived abundances point to a primordial origin. Crucial questions are whether the O{sub 2} abundance is peculiar to comet 67P/Churyumov–Gerasimenko or Jupiter family comets in general, and also whether Oort cloud comets such as comet 1P/Halley contain similar amounts of molecular oxygen. We investigated mass spectra obtained bymore » the Neutral Mass Spectrometer instrument during the flyby by the European Space Agency's Giotto probe of comet 1P/Halley. Our investigation indicates that a production rate of O{sub 2} of 3.7 ± 1.7% with respect to water is indeed compatible with the obtained Halley data and therefore that O{sub 2} might be a rather common and abundant parent species.« less

ON THE ABSENCE OF EUV EMISSION FROM COMET C/2012 S1 (ISON)

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

Bryans, Paul; Pesnell, W. Dean

2016-05-10

When the sungrazing comet C/2012 S1 (ISON) made its perihelion passage within two solar radii of the Sun’s surface, it was expected to be a bright emitter at extreme ultraviolet (EUV) wavelengths. However, despite solar EUV telescopes repointing to track the orbit of the comet, no emission was detected. This “null result” is interesting in its own right, offering the possibility of placing limits on the size and composition of the nucleus. We explain the lack of detection by considering the properties of the comet and the solar atmosphere that determine the intensity of EUV emission from sungrazing comets. Bymore » comparing these properties with those of sungrazing comet C/2011 W3 (Lovejoy), which did emit in the EUV, we conclude that the primary factor resulting in non-detectable EUV emission from C/2012 S1 (ISON) was an insufficiently large nucleus. We conclude that the radius of C/2012 S1 (ISON) was at least a factor of four less than that of C/2011 W3 (Lovejoy). This is consistent with white-light observations in the days before perihelion that suggested the comet was dramatically reducing in size on approach.« less

Comet 67P's Pitted Surface

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-11-01

High-resolution imagery of comet 67P ChuryumovGerasimenko has revealed that its surface is covered in active pits some measuring hundreds of meters both wide and deep! But what processes caused these pits to form?Pitted LandscapeESAs Rosetta mission arrived at comet 67P in August 2014. As the comet continued its journey around the Sun, Rosetta extensively documented 67Ps surface through high-resolution images taken with the on-board instrument NavCam. These images have revealed that active, circular depressions are a common feature on the comets surface.In an attempt to determine how these pits formed, an international team of scientists led by Olivier Mousis (Laboratory of Astrophysics of Marseille) has run a series of simulations of a region of the comet the Seth region that contains a 200-meter-deep pit. These simulations include the effects of various phase transitions, heat transfer through the matrix of ices and dust, and gas diffusion throughout the porous material.Escaping VolatilesAdditional examples of pitted areas on 67Ps northern-hemisphere surface include the Ash region and the Maat region (both imaged September 2014 by NavCam) [Mousis et al. 2015]Previous studies have already eliminated two potential formation mechanisms for the pits: impacts (the sizes of the pits werent right) and erosion due to sunlight (the pits dont have the right shape). Mousis and collaborators assume that the pits are instead caused by the depletion of volatile materials chemical compounds with low boiling points either via explosive outbursts at the comets surface, or via sinkholes opening from below the surface. But what process causes the volatiles to deplete when the comet heats?The authors simulations demonstrate that volatiles trapped beneath the comets surface either in icy structures called clathrates or within amorphous ice can be suddenly released as the comet warms up. The team shows that the release of volatiles from these two structures can create 200-meter-deep pits within ~800 years and ~2,000 years, respectively. Since comet 67P has been around the inner solar system for about 7,000 years, both of these processes are viable explanations for the pits.The simulations also show that direct sublimation of crystalline ices of water, carbon monoxide, and carbon dioxide can cause deep pits but only in the absence of a surface layer of dust, known as a dust mantle, in that region of the comet. Direct sublimation could be a viable explanation for the pits, then, if dust grains in the area are so small that they are carried away with the released gas, rather than falling back to form a layer on the comets surface.Regardless of the formation mechanism for these pits, the authors conclude that their very existence implies that the physical and chemical properties across the surface and subsurface of the comet cannot be uniform. Further observations from Rosetta will continue to help us understand comet 67P.CitationO. Mousis et al 2015 ApJ 814 L5. doi:10.1088/2041-8205/814/1/L5

Comet 67P Through the Lens of Art

NASA Astrophysics Data System (ADS)

Smirnova, Ekaterina

2017-04-01

My proposal is to share my artistic exploration of a comet through the bodily senses, while finding inspiration in scientific data. I will present my artwork as a slideshow, showcasing: large scale paintings, ceramic sculptures, music and interactive augmented reality. The Rosetta mission of the European Space Agency (ESA) to comet 67P/ Churyumov-Gerasimenko is remarkable. The scientific investigation of the comet's composition, atmosphere, dust, vapor, surface and internal structure are crucial to help researchers understand the origin of the solar system and our own planet. Sight: Paintings Rosetta mission discovered that the water on the comet is different from the water on Earth; as measured with the ROSINA-DFMS instrument on Rosetta, water on 67P contains approximately 3 times more hydrogen­deuterium oxide - HDO, than found in Earth's oceans. In the art studio I re-create water that is close in composition to the water on the comet, by concentrating the level of HDO. With this water I paint large scale watermedia paintings, based on the photographs by Rosetta (OSIRIS, Nav. Cam.). Touch: Sculptures While exploring the comet's three-dimensional form, I focus more deeply on the composition of the comet. Stoneware clay and my choice of a glaze both include iron oxide, a common constituent of meteorites and comets. Hearing: Music An audio piece "A Singing Comet", by Manuel Senfft, based on the Rosetta Plasma Consortium data, inspired me to make a musical piece. In collaboration with clarinetist Lee Mottram (Wales) and composer Takuto Fukuda (Japan) we created an electro­acoustic composition in which we tell the story of comets visiting our Solar System, repeating their cycle, curving around the sun and releasing water, carrying away dust to form their tails. Smell In collaboration with The Open University, UK, postcards with a smell of the comet were created, introducing the chemical components of the comet. The smell was recreated by combining several molecules that were found in the comet's coma with the ROSINA instrument: in particular, hydrogen cyanide, ammonia and hydrogen sulphide. Interactive: Augmented Reality (AR) Inspired by spectroscopic data from OSIRIS, I introduce AR to reveal a "hidden" layer. I am highlighting that some scientific information can only be viewed by using special instruments, in this case - instruments on board the Rosetta spacecraft. Viewers can see a virtual layer on top of my paintings using a readily available instrument - ones cellphone. RGB colors, of a particular wavelength, will be introduced to the generally monochromatic paintings. Through my art I study the relationship between humans and the Universe, understanding the connection, the influence and the effect they have on each other. ESA's example of human scientists ambitiously exploring a distant cosmic object empowers me to create and share my personal exploration. This is the way I would like to share comet 67P with the world. I invite you to look through an artist's eyes and see science with renewed beauty and wonder. To view the artwork: http://www.ekaterina-smirnova.com/67p/ http://www.ekaterina-smirnova.com/67p-sculptures/

Comet Bites the Dust Around Dead Star Artist Concept

NASA Image and Video Library

2006-01-11

This artist concept illustrates a comet being torn to shreds around a dead star, or white dwarf, called G29-38. NASA Spitzer Space Telescope observed a cloud of dust around this white dwarf that may have been generated from comet disruption.

View of Comet Siding Spring from Southern Hemisphere Artist Concept

NASA Image and Video Library

2014-10-09

Comet Siding Spring will have a close approach to Mars on Oct. 19, 2014. This artist concept shows people in the Southern Hemisphere where to look for Mars in the night sky. Mars and the comet may be visible with binoculars.

Mars-Flyby Comet in False Color

NASA Image and Video Library

2014-11-07

This frame from a movie sequence of images from NASA Mars Reconnaissance Orbiter MRO shows comet C/2013 A1 Siding Spring before and after its close pass by Mars in October 2014. False color enhances subtle variations in brightness in the comet coma.

A photometric investigation of Comet P/Encke

NASA Technical Reports Server (NTRS)

Millis, R. L.

1981-01-01

A photometric investigation of Comet P/Encke was undertaken using the 2.2 m telescope and the 0.6 m telescope. The two primary scientific objectives were: (1) measurement of the production rates of OH, CN, C3, and C2 as a function of heliocentric distance; and (2) determination of the comet's rotational period by searching for periodic brightness variations in the inner coma. Synoptic observation in the Canary Islands; Cambridge, Massachusetts; Flagstaff, Arizona; and Mauna Kea were planned for the study of the comet's rotation.

Comets in UV

NASA Astrophysics Data System (ADS)

Shustov, B.; Sachkov, M.; Gómez de Castro, A. I.; Vallejo, J. C.; Kanev, E.; Dorofeeva, V.

2018-04-01

Comets are important "eyewitnesses" of Solar System formation and evolution. Important tests to determine the chemical composition and to study the physical processes in cometary nuclei and coma need data in the UV range of the electromagnetic spectrum. Comprehensive and complete studies require additional ground-based observations and in situ experiments. We briefly review observations of comets in the ultraviolet (UV) and discuss the prospects of UV observations of comets and exocomets with space-borne instruments. A special reference is made to the World Space Observatory-Ultraviolet (WSO-UV) project.

The International Cometary Explorer (ICE) mission to Comets Giacobini-Zinner and Halley

NASA Technical Reports Server (NTRS)

Brandt, J. C.

1986-01-01

Use of the ISEE-3 satellite (renamed ICE) to study the interaction between the solar wind and a cometary atmosphere by passing through the plasma tail by intercepting Comet Giacobini-Zinner on 11 September 1985 is described. Details of the targeting strategy are discussed. Additional scientific objectives following the tail intercept of Comet Giacobini-Zinner include the support of Comet Halley studies through the measurement of solar-wind conditions upstream of P/Halley in October 1985 and March 1986.

EPOXI at Comet Hartley 2

NASA Technical Reports Server (NTRS)

A'Hearn, Michael F.; Belton, Michael J. S.; Delamere, W. Alan; Feaga, Lori M.; Hampton, Donald; Kissel, Jochen; Klaasen, Kenneth P.; McFadden, Jessica M.; Meech, Karen J.; Melosh, H. Jay;

The study of the physics of cometary nuclei

NASA Technical Reports Server (NTRS)

Whipple, F. L.; Marsden, B. G.; Sekanina, Z.

1976-01-01

A semiannual progress report describing the work completed during the period 1 September 1975 to 29 February 1976 on the physics of cometary nuclei was given. The following items were discussed: (1) a paper entitled ""A speculation about comets and the earth'', (2) a chapter entitled"" The physics of comets'' for ""Reviews of Astronomy and Astrophysics'', (3) continuing work on split comets, and (4) results dealing with a new application of nongravitational solar-radial forces as a measure of comet nucleus dimensions and activity.

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.

Origin of organic matter in the protosolar nebula and in comets

NASA Technical Reports Server (NTRS)

Greenberg, J. M.; Shalabiea, O. M.; Mendoza-Gomez, C. X.; Schutte, W.; Gerakines, P. A.

1994-01-01

Comet organics are traced to their origin in interstellar space. Possible sources of comet organics from solar nebula chemistry are briefly discussed. The infrared spectra of interstellar dust are compared with spectra of solar (space) irradiated laboratory organic residues and with meteorites. The spectra compare very favorably. The atomic composition of first generation laboratory organic residues compares favorably with that of comet Halley organics if divided into approrpriate 'volatile' (less refreactory) and 'refractory' (more refractory) complex organics.

Extended atmospheres of outer planet satellites and comets

NASA Technical Reports Server (NTRS)

Smyth, W. H.; Combi, M. R.

1984-01-01

The cometary hydrogen particle-trajectory model was used successfully to analyze observations of Comet P/Encke. The Pioneer Venus Orbiter Ultraviolet Spectrometer observed the comet at 1216A (hydrogen Lyman-alpha) on 15 April 1984, when the comet was .58 AU from the Sun and 1.02 AU from Venus. The analysis implies a production rate at .58 AU of 3.3 x 10 to the 28th power/sec of the water molecules which photodissociate to produce the observed hydrogen.

A generic interface element for COMET-AR

NASA Technical Reports Server (NTRS)

Mccleary, Susan L.; Aminpour, Mohammad A.

1995-01-01

The implementation of an interface element capability within the COMET-AR software system is described. The report is intended for use by both users of currently implemented interface elements and developers of new interface element formulations. Guidance on the use of COMET-AR is given. A glossary is provided as an Appendix to this report for readers unfamiliar with the jargon of COMET-AR. A summary of the currently implemented interface element formulation is presented in Section 7.3 of this report.

The Pro-Am Collaborative Astronomy (PACA) Project

NASA Astrophysics Data System (ADS)

Yanamandra-Fisher, Padma A.

2016-10-01

The PACA Project is an ecosystem of several social media platforms (Facebook, Pinterest, Twitter, Flickr, Vimeo) that takes connects professional and amateur astronomers in a common observing campaign. It takes advantage of immediate connectivity amongst amateur astronomers worldwide, that can be galvanized to participate in a given observing campaign and provide observations/data that helps provide a long temporal backdrop for professional data. To date, The PACA Project has participated in organized campaigns such as NASA Comet ISON Observing Campaign in 2013; NASA Comet Integrated Observations Campaign to observe Comet Siding Spring flyby of Mars on 19 October 2014, and currently is participating in the ESA/Rosetta mission's ground-based amateur observing campaign, soon to finish. With several bright comets well placed in the sky, the PACA Project has focused groups for each comet of interest to its members. The PACA Project is now extending its observing campaigns to include planets, namely, Jupiter, Saturn and Mars. The 2014 observing campaign of comet Siding Spring included both comet and Mars amateur astronomers. With Mars, just past its recent opposition and heading towards its perihelic opposition, when it will be its largest size as viewed from Earth, in 2018; with NASA's JUNO spacecraft arrival at Jupiter on 4 July 2016 and NASA/ESA Cassini mission ending its mission to Saturn in 2017, all three planets are targets of amateur observers. The synergy between The PACA Project goals, amateur and professional astronomers translates well into a cohesive paradigm to monitor and observe comets and planets to increase the data on these targets for crowdsourcing. I shall highlight the results from the various campaigns, including various comets, Jupiter, Saturn and Mars and propose various science observing campaigns, resulting in both scientific research and citizen science.

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.

The Diversity of Carbon in Cometary Refractory Dust Particles

NASA Technical Reports Server (NTRS)

Wooden, D. H.

2018-01-01

When comparing the dark icy surfaces of outer solar system small bodies and the composition of carbonaceous chondrites derived from dark asteroids we find a significant discrepancy in the assessed amounts of elemental carbon: up to 80% amorphous carbon is used to model the dark surfaces of Kuiper Belt Objects and Centaurs whereas at most 5% of elemental carbon is found in carbonaceous chondrites. If we presume that regimes of comet nuclei formation are analogous to disk regimes where other outer solar system ice-rich bodies formed then we can turn to comet dust to gain insights into the diversity in the concentration and forms of carbon available in the outer disk. Comet dust offers important insights into the diversity in the amounts and forms of carbon that were incorporated into aggregate dust particles in the colder parts of the protoplanetary disk out of which comet nuclei accreted. Comet nuclei are amongst the most primitive bodies because they have remained cold and unequilibrated. Comet dust particles reveal the presence of forms of elemental carbon and of soluble and insoluble organic matter, and in a great diversity of concentrations from very little, e.g., Stardust samples of comet 81P/Wild 2, to 80% by volume for Ultra Carbonaceous Antarctic Micro Meteorites (UCAMMs). Cometary outbursts and/or jet activity also demonstrate variations in the concentration of carbon in the grains at different grain sizes within a single comet. We review the diversity of carbon-bearing dust grains in cometary samples, flyby measurements and deduced from remote-sensing to enrich the discussion about the diversity of carbonaceous matter available in the outer ice-rich disk at the time of comet nuclei formation.

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.

Ground-Based Centimeter, Millimeter, and Submillimeter Observations of Recent Comets

NASA Technical Reports Server (NTRS)

Milam, S. N.; Chuang, Y.-L.; Charnley, S. B.; Kuan, Y. -J.; Villanueva, G. L.; Coulson, I. M.; Remijan. A. R.

2012-01-01

Comets provide important clues to the physical and chemical processes that occurred during the formation and early evolution of the Solar System, and could also have been important for initiating prebiotic chemistry on the early Earth [I]. Comets are comprised of molecular ices, that may be pristine interstellar remnants of Solar System formation, along with high-temperature crystalline silicate dust that is indicative of a more thermally varied history in the protosolar nebula [2]. Comparing abundances of cometary parent volatiles, and isotopic fractionation ratios, to those found in the interstellar medium, in disks around young stars, and between cometary families, is vital to understanding planetary system formation and the processing history experienced by organic matter in the so-called interstellar-comet connection [3]. In the classical picture, the long-period comets probably formed in the nebular disk across the giant planet formation region (5-40 AU) with the majority of them originating from the Uranus-Neptune region. They were subsequently scattered out to the Oort Cloud (OC) by Jupiter. The short-period comets (also known as ecliptic or Jupiter Family Comets - JFC) reside mainly in the Edgeworth-Kuiper belt where they were formed. Given the gradient in physical conditions expected across this region of the nebula, chemical diversity in this comet population is to be expected [4,5]. We have conducted observations of comets I 03P/Hartley 2 (JFC) and C/2009 PI (Garradd) (OC), at primarily millimeter and submillimeter wavelengths, to determine important cosmogonic quantities, such as the ortho:para ratio and isotope ratios, as well as probe the origin of cometary organics and if they vary between the two dynamic reservoirs.

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

Jewitt, David, E-mail: jewitt@ucla.edu

Most comets are volatile-rich bodies that have recently entered the inner solar system following long-term storage in the Kuiper belt and the Oort cloud reservoirs. These reservoirs feed several distinct, short-lived “small body” populations. Here, we present new measurements of the optical colors of cometary and comet-related bodies including long-period (Oort cloud) comets, Damocloids (probable inactive nuclei of long-period comets) and Centaurs (recent escapees from the Kuiper belt and precursors to the Jupiter family comets). We combine the new measurements with published data on short-period comets, Jovian Trojans and Kuiper belt objects to examine the color systematics of the comet-relatedmore » populations. We find that the mean optical colors of the dust in short-period and long-period comets are identical within the uncertainties of measurement, as are the colors of the dust and of the underlying nuclei. These populations show no evidence for scattering by optically small particles or for compositional gradients, even at the largest distances from the Sun, and no evidence for ultrared matter. Consistent with earlier work, ultrared surfaces are common in the Kuiper belt and on the Centaurs, but not in other small body populations, suggesting that this material is hidden or destroyed upon entry to the inner solar system. The onset of activity in the Centaurs and the disappearance of the ultrared matter in this population begin at about the same perihelion distance (∼10 AU), suggesting that the two are related. Blanketing of primordial surface materials by the fallback of sub-orbital ejecta, for which we calculate a very short timescale, is the likely mechanism. The same process should operate on any mass-losing body, explaining the absence of ultrared surface material in the entire comet population.« less

Suprathermal electron environment of comet 67P/Churyumov-Gerasimenko: Observations from the Rosetta Ion and Electron Sensor

NASA Astrophysics Data System (ADS)

Clark, G.; Broiles, T. W.; Burch, J. L.; Collinson, G. A.; Cravens, T.; Frahm, R. A.; Goldstein, J.; Goldstein, R.; Mandt, K.; Mokashi, P.; Samara, M.; Pollock, C. J.

2015-11-01

Context. The Rosetta spacecraft is currently escorting comet 67P/Churyumov-Gerasimenko until its perihelion approach at 1.2 AU. This mission has provided unprecedented views into the interaction of the solar wind and the comet as a function of heliocentric distance. Aims: We study the interaction of the solar wind and comet at large heliocentric distances (>2 AU) using data from the Rosetta Plasma Consortium Ion and Electron Sensor (RPC-IES). From this we gain insight into the suprathermal electron distribution, which plays an important role in electron-neutral chemistry and dust grain charging. Methods: Electron velocity distribution functions observed by IES fit to functions used to previously characterize the suprathermal electrons at comets and interplanetary shocks. We used the fitting results and searched for trends as a function of cometocentric and heliocentric distance. Results: We find that interaction of the solar wind with this comet is highly turbulent and stronger than expected based on historical studies, especially for this weakly outgassing comet. The presence of highly dynamical suprathermal electrons is consistent with observations of comets (e.g., Giacobinni-Zinner, Grigg-Skjellerup) near 1 AU with higher outgassing rates. However, comet 67P/Churyumov-Gerasimenko is much farther from the Sun and appears to lack an upstream bow shock. Conclusions: The mass loading process, which likely is the cause of these processes, plays a stronger role at large distances from the Sun than previously expected. We discuss the possible mechanisms that most likely are responsible for this acceleration: heating by waves generated by the pick-up ion instability, and the admixture of cometary photoelectrons.

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.

Constraints on Comet 332P/Ikeya-Murakami

NASA Astrophysics Data System (ADS)

Hui, Man-To; Ye, Quan-Zhi; Wiegert, Paul

2017-01-01

Encke-type comet 332P/Ikeya-Murakami is experiencing cascading fragmentation events during its 2016 apparition. It is likely the first splitting Encke-type comet ever observed. A nongravitational solution to the astrometry reveals a statistical detection of the radial and transverse nongravitational parameters, {A}1=(1.54+/- 0.39)× {10}-8 au day‑2 and {A}2=(7.19+/- 1.92)× {10}-9 au day‑2, respectively, which implies a nucleus erosion rate of (9.1+/- 1.7)‰ per orbital revolution. The mass-loss rate likely has to be supported by a much larger fraction of an active surface area than known cases of short-period comets; it may be relevant to the ongoing fragmentation. We failed to detect any serendipitous pre-discovery observations of the comet in archival data from major sky surveys, whereby we infer that 332P used to be largely inactive, and is perhaps among the few short-period comets that have been reactivated from weakly active or dormant states. We therefore constrain an upper limit to the nucleus size as 2.0 ± 0.2 km in radius. A search for small bodies in similar orbits to that of 332P reveals comet P/2010 B2 (WISE) to be the best candidate. From an empirical generalized Jupiter-family (Encke-type included) comet population model, we estimate the likelihood of a chance alignment of the 332P–P/2010 B2 pair to be 1 in 33, a small number indicative of a genetic linkage between the two comets on a statistical basis. The pair possibly originated from a common progenitor, which underwent a disintegration event well before the twentieth century.

Mid-infrared spectra of comet nuclei

NASA Astrophysics Data System (ADS)

Kelley, Michael S. P.; Woodward, Charles E.; Gehrz, Robert D.; Reach, William T.; Harker, David E.

2017-03-01

Comet nuclei and D-type asteroids have several similarities at optical and near-IR wavelengths, including near-featureless red reflectance spectra, and low albedos. Mineral identifications based on these characteristics are fraught with degeneracies, although some general trends can be identified. In contrast, spectral emissivity features in the mid-infrared provide important compositional information that might not otherwise be achievable. Jovian Trojan D-type asteroids have emissivity features strikingly similar to comet comae, suggesting that they have the same compositions and that the surfaces of the Trojans are highly porous. However, a direct comparison between a comet and asteroid surface has not been possible due to the paucity of spectra of comet nuclei at mid-infrared wavelengths. We present 5-35 μm thermal emission spectra of comets 10P/Tempel 2, and 49P/Arend-Rigaux observed with the Infrared Spectrograph on the Spitzer Space Telescope. Our analysis reveals no evidence for a coma or tail at the time of observation, suggesting the spectra are dominated by the comet nucleus. We fit each spectrum with the near-Earth asteroid thermal model (NEATM) and find sizes in agreement with previous values. However, the NEATM beaming parameters of the nuclei, 0.74-0.83, are systematically lower than the Jupiter-family comet population mean of 1.03 ± 0.11, derived from 16- and 22-μm photometry. We suggest this may be either an artifact of the spectral reduction, or the consequence of an emissivity low near 16 μm. When the spectra are normalized by the NEATM model, a weak 10-μm silicate plateau is evident, with a shape similar to those seen in mid-infrared spectra of D-type asteroids. A silicate plateau is also evident in previously published Spitzer spectra of the nucleus of comet 9P/Tempel 1. We compare, in detail, these comet nucleus emission features to those seen in spectra of the Jovian Trojan D-types (624) Hektor, (911) Agamemnon, and (1172) Aneas, as well as those seen in the spectra of seven comet comae. The comet comae present silicate features with two distinct shapes, either trapezoidal, or more rounded, the latter apparently due to enhanced emission near 8 to 8.5 μm. The surfaces of Tempel 2, Arend-Rigaux, and Hektor best agree with the comae that present trapezoidal features, furthering the hypothesis that the surfaces of these targets must have high porosities in order to exhibit a spectrum similar to a comet coma. An emissivity minimum at 15 μm, present in the spectra of Tempel 2, Arend-Rigaux, Hektor, and Agamemnon, is also described, the origin of which remains unidentified. The compositional similarity between D-type asteroids and comets is discussed, and our data supports the hypothesis that they have similar origins in the early Solar System.

Comets

NASA Astrophysics Data System (ADS)

Brownlee, D. E.

2003-12-01

Comets are surviving members of a formerly vast distribution of solid bodies that formed in the cold regions of the solar nebula. Cometary bodies escaped incorporation into planets and ejection from the solar system and they have been stored in two distant reservoirs, the Oort cloud and the Kuiper Belt, for most of the age of the solar system. Observed comets appear to have formed between 5 AU and 55 AU. From a cosmochemical viewpoint, comets are particularly interesting bodies because they are preserved samples of the solar nebula's cold ice-bearing regions that occupied 99% of the areal extent of the solar nebula disk. All comets formed beyond the "snow line" of the nebula, where the conditions were cold enough for water ice to condense, but they formed from environments that significantly differed in temperature. Some formed in the comparatively "warm" regions near Jupiter where the nebular temperature may have been greater than 120 K and others clearly formed beyond Neptune where temperatures may have been less than 30 K (Bell et al., 1997). Although comets are the best-preserved materials from the early solar system, they should be a mix of nebular and presolar materials that accreted over a vast range of distances from the Sun in environments that differed in temperature, pressure, and accretional conditions such as impact speed.Comets, by conventional definition, are unstable near the Sun; they contain highly volatile ices that vigorously sublime within 2-3 AU of the Sun. When heated, they release gas and solids due to "cometary activity," a series of processes usually detected from afar by the presence of a coma of gas and dust surrounding the cometary nucleus and or elongated tails composed of dust and gas. Active comets clearly have not been severely modified by the moderate to extreme heating that has affected all other solar system materials, including planets, moons, and even the asteroids that produced the most primitive meteorites. Comets have been widely described as the most primitive solar system materials, preserved at cryogenic temperature and low pressure since the formation of the Sun. This is likely to be true, in general, but there is a growing body of recent evidence suggesting that comets are both more physically complex and have had more complex histories than formerly believed. They formed over an order of magnitude range of distances from the Sun; some are fragments of relatively large bodies and collisional effects must have processed at least some comets, as they have processed asteroids (McSween and Weissman, 1989).Comet-like materials are presumed to be the building blocks of Uranus and Neptune (the ice giants); they may have played a role in the formation of Jupiter and Saturn (the gas giants) and they also played some role in transporting outer solar system volatile materials to inner planets (Delsemme, 2000). The inner solar system flux of comets may have been much higher in the past and comets may have played a role in producing the late heavy bombardment on terrestrial planets ( Levison et al., 2001). Comets also exist outside the solar system and there is good evidence that they orbit a major fraction of Sun-like stars. Circumstellar dust, which appears to have been generated by comets, is detected as thermal infrared emission and sometimes as scattered starlight ( Backman et al., 1997; Weissman, 1984; Jewitt and Luu, 1995). It is particularly interesting that the amount of dust around stars declines with stellar age and is highest around stars younger than a few hundred million years. The common presence of what appears to be comet-generated dust around other stars suggests that comet formation is a normal and common consequence of star formation ( Figure 1). (6K)Figure 1. The ratio of infrared excess/stellar luminosity is a measure of the fraction of starlight absorbed by circumstellar dust and re-radiated in the infrared. The plot from Spangler et al. (2001) shows the temporal decline of dust around "Vega-like" stars (points) and stars in clusters with measured ages (circles). At least for the longer ages, the dust is most probably generated by comets.

Kohoutek - A great comet coming.

NASA Technical Reports Server (NTRS)

Maran, S. P.; Hobbs, R. W.

1973-01-01

Passing inside the earth's orbit in late November, the comet Kohoutek will travel through the inner solar system during a unique period in the history of the space program, when Skylab and Mariner Venus-Mercury are in operation and the new C-141 Airborne Infrared Observatory is ready for flight. It is planned to investigate comprehensively the nature and evolution of the coma and tails of the comet. The detailed goals of the investigation include the identification of the parent molecules of the gases observed in comets, the determination of the processes that break down the parent molecules, the study of the physical nature of transient events in the comet, and the measurement of the solar-wind velocity in the inner solar system.

The Possible Interrelation of TNO and Long-Period Comets by MOID Distribution

NASA Astrophysics Data System (ADS)

Guliyev, A. S.; Nabiyev, Sh. A.; Guliyev, R. A.; Dadashov, A. S.

2015-03-01

The study objects of our work were 91 TNO with diameters greater than 200 km. On the other hand, the paper used the data for 1048 and comets with aphelion and perihelion distances Q > 30 AU and q > 0.1AU, respectively, were observed until 2012. Short-perihelion comets (sporadic and concentrated in separate groups) were excluded from the analysis. If some comet split into several parties, we have taken data for only one fragment, which is marked with the letter A. Data for comets are taken from the catalog [4] and the individual Circulars International Astronomical Union, issued in period after 2008. The data for TNO, mostly borrowed from the website [5], as well as the issues of the same circulars.

Groundbased cometary studies

NASA Technical Reports Server (NTRS)

Schleicher, David G.

1991-01-01

The physical properties of comets were studied by applying a wide variety of observational techniques. Emphasis is on simultaneous or coordinated observations in different spectral regions (e.g., visible and thermal IR or visible and far UV) or with different instrumentation (imaging, spectroscopy, and photometry). The aim was to: (1) measure the basic properties of cometary nuclei by studying comets whose comae are so anemic that the signal from the nucleus can be extracted; (2) investigate the group characteristics of comets by narrowband photometry applied uniformly to a large sample of comets; (3) understand the detailed physics and chemistry occurring in cometary comae through wide-field charge coupled device (CCD) imaging using narrow filters and through long-slit CCD spectroscopy; and (4) investigate the rotational states of comets through time-resolution photometry.

The Interaction Between the Magnetosphere of Mars and that of Comet Siding Spring

NASA Astrophysics Data System (ADS)

Holmstrom, M.; Futaana, Y.; Barabash, S. V.

2015-12-01

On 19 October 2014 the comet Siding Spring flew by Mars. This was a unique opportunity to study the interaction between a cometary and a planetary magnetosphere. Here we model the magnetosphere of the comet using a hybrid plasma solver (ions as particles, electrons as a fluid). The undisturbed upstream solar wind ion conditions are estimated from observations by ASPERA-3/IMA on Mars Express during several orbits. It is found that Mars probably passed through a solar wind that was disturbed by the comet during the flyby. The uncertainty derives from that the size of the disturbed solar wind region in the comet simulation is sensitive to the assumed upstream solar wind conditions, especially the solar wind proton density.

SOCCER: Comet Coma Sample Return Mission

NASA Technical Reports Server (NTRS)

Albee, A. L.; Uesugi, K. T.; Tsou, Peter

1994-01-01

Comets, being considered the most primitive bodies in the solar system, command the highest priority among solar system objects for studying solar nebula evolution and the evolution of life through biogenic elements and compounds. Sample Of Comet Coma Earth Return (SOCCER), a joint effort between NASA and the Institute of Space and Astronautical Science (ISAS) in Japan, has two primary science objectives: (1) the imaging of the comet nucleus and (2) the return to Earth of samples of volatile species and intact dust. This effort makes use of the unique strengths and capabilities of both countries in realizing this important quest for the return of samples from a comet. This paper presents an overview of SOCCER's science payloads, engineering flight system, and its mission operations.

Halley's Comet.

ERIC Educational Resources Information Center

Carey, Tom

1985-01-01

Provides tips for viewing Comet Halley in the Northeast including best viewing dates from November 1985-January 1986. Discusses going south to view the comet in March-April 1986 and gives specific information about accommodations for the Halley Rally in Everglades National Park, southernmost site in the contiguous 48 states. (JHZ)

Dark Side of Comet 67P/Churyumov-Gerasimenko Saturated

NASA Image and Video Library

2014-11-06

This image of comet 67P/Churyumov-Gerasimenko was obtained on October 30, 2014 by the OSIRIS scientific imaging system on the Rosetta spacecraft. The saturation of the image allows the viewer to see some surface structures on dark side of the comet.

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.

Where Do Comets Come From?

ERIC Educational Resources Information Center

Van Flandern, Tom

1982-01-01

Proposes a new origin for comets in the solar system, namely, that comets originated in the breakup of a body orbiting the sun in or near the present location of the asteroid belt in the relatively recent past. Predictions related to the theory are discussed. (Author/JN)

Comet Halley and nongravitational forces

NASA Technical Reports Server (NTRS)

Yeomans, D. K.

1977-01-01

The motion of comet Halley is investigated over the 1607-1911 interval. The required nongravitational-force model was found to be most consistent with a rocket-type thrust from the vaporization of water ice in the comet's nucleus. The nongravitational effects are time-independent over the investigated interval.

Documentary Evidence for the Apparition of a Comet in Late 593 and Early 594 AD

NASA Astrophysics Data System (ADS)

Juhl, R. A.; Mardon, E. G.; Mardon, A. A.

2007-03-01

This presentation uses documentary evidence in an attempt to establish a prima facie case for two apparitions of a comet in the sixth century. This comet may also have made apparitions in the seventh century and later.

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.

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.

The path and surviving tail of a comet that fell into the sun

NASA Technical Reports Server (NTRS)

Sekanina, Z.

1982-01-01

A satisfactory orbital solution for Comet Howard-Koomen-Michels 1979 XI is found on the assumption that the comet's line of apsides coincided with that of the Kreutz sungrazing comet group. The derived perihelion distance then shows that this is the first known case of a comet falling into the sun. A dust tail that survived the comet is studied as a particle flow phenomenon controlled by no force other than solar gravity and solar radiation pressure. The tail's outline is interpreted in terms of an onset of dust production, a peak repulsive force on the particles, and a circumsolar dustfree zone due to particle sublimation. It is shown that the surviving debris consisted mostly of absorbing, submicron size particles in hyperbolic trajectories convex to the sun and curving toward the earth. The tail width may be a product of the interaction of charged dust in the tail with a complicated structure of the coronal magnetic field.

Primitive bodies - Molecular abundances in Comet Halley as probes of cometary formation environments

NASA Technical Reports Server (NTRS)

Lunine, Jonathan I.

1989-01-01

The most recent results on abundances of molecules in Halley's comet are examined in the context of various models for the environment in which comets formed. These environments include molecular clouds associated with star-forming regions, the solar nebula, gaseous disks around proto-planets, and combinations of these. Of all constituents in a cometary nucleus, the highly volatile molecules such as methane, ammonia, molecular nitrogen, and carbon monoxide are most sensitive to the final episode of cometary grain formation and incorporation in the comet's nucleus; hence they likely reflect at least some chemical processing in the solar nebula. Proper interpretation requires modeling of a number of physical processes including gas phase chemistry, chemistry on grain surfaces, and fractionation effects resulting from preferential incorporation of certain gases in proto-cometary grains. The abundance of methane in Halley's comet could be a key indicator of where that comet formed, provided the methane abundance on grains in star-forming regions can be observationally constrained.

Relative motions of fragments of the split comets. III - A test of splitting and comets with suspected multiple nuclei

NASA Technical Reports Server (NTRS)

Sekanina, Z.

1979-01-01

A quantitative test of splitting for comets with suspected multiple nuclei has been formulated using a model which assumes the motions of cometary fragments to be due primarily to outgassing. The model expresses the relative motion of the cometary fragments in terms of the time of splitting and the differential force, which are determined by measurements of the position angle and the separation distance between fragments. The test is applied to 18 comets suspected of having multiple nuclei, of which the comets Sawerthal 1888 I, Campbell 1914 IV, Whipple-Fedtke-Tevzadze 1943 I, Honda 1955 V, Wild 1968 III and Tago-Sato-Kosaka 1969 IX were found to be clear cases of split comets and Davidson 1889 IV and Periodic Giacobini 1896 V were judged to be likely candidates. At least three of the secondary nuclei confirmed can be classified as short-lived companions, while only two appear to be persistent.

Mission strategy for cometary exploration in the 1980's

NASA Technical Reports Server (NTRS)

Farquhar, R. W.

1974-01-01

A sequence of ballistic intercept missions to comets is proposed. The mission set is composed of a well-known group of periodic comets whose physical properties are dissimilar. In addition to full descriptions of the nominal mission profiles, earth-based sighting conditions and estimates of cometary ephemeris errors are presented for each target comet. The first mission of the sequence is a slow flyby (approximately 8 km/sec) of Encke's comet near its perihelion in 1980. Because of a near resonance in the orbital periods of Encke and the spacecraft, it is possible to retarget the spacecraft for a second Encke encounter in 1984. The second mission of the sequence also consists of two cometary encounters but in this case different comets are involved; Giacobini-Zinner in 1985 and Borrelly in 1987. The final mission of the sequence calls for a simultaneous launch of two spacecraft towards Halley's comet in 1985. One spacecraft is targeted fo a pre-perihelion intercept at a heliocentric distance of 1.37 AU.

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.

Imaging of the internal structure of comet 67P/Churyumov-Gerasimenko from radiotomography CONSERT Data (Rosetta Mission) through a full 3D regularized inversion of the Helmholtz equations on functional spaces

NASA Astrophysics Data System (ADS)

Barriot, Jean-Pierre; Serafini, Jonathan; Sichoix, Lydie; Benna, Mehdi; Kofman, Wlodek; Herique, Alain

We investigate the inverse problem of imaging the internal structure of comet 67P/ Churyumov-Gerasimenko from radiotomography CONSERT data by using a coupled regularized inversion of the Helmholtz equations. A first set of Helmholtz equations, written w.r.t a basis of 3D Hankel functions describes the wave propagation outside the comet at large distances, a second set of Helmholtz equations, written w.r.t. a basis of 3D Zernike functions describes the wave propagation throughout the comet with avariable permittivity. Both sets are connected by continuity equations over a sphere that surrounds the comet. This approach, derived from GPS water vapor tomography of the atmosphere,will permit a full 3D inversion of the internal structure of the comet, contrary to traditional approaches that use a discretization of space at a fraction of the radiowave wavelength.

Migration of comets to near-Earth space

NASA Astrophysics Data System (ADS)

Ipatov, S. I.

The orbital evolution of more than 21000 Jupiter-crossing objects under the gravitational influence of planets was investigated. For orbits close to that of Comet 2P, the mean collision probabilities of Jupiter-crossing objects with the terrestrial planets were greater by two orders of magnitude than for some other comets. For initial orbital elements close to those of Comets 2P, 10P, 44P, and 113P, a few objects (<0.1%) got Earth-crossing orbits with semi-major axes a<2 AU and aphelion distances Q<4.2 AU and moved in such orbits for more than 1 Myr (up to tens or even hundreds of Myrs). Some of them even got inner-Earth orbits (Q<0.983 AU) and Aten orbits for millions of years. Most former trans-Neptunian objects that have typical near-Earth object orbits moved in such orbits for millions of years, so during most of this time they were extinct comets or disintegrated into mini-comets.

Identification of low level gamma-irradiation of meats by high sensitivity comet assay

NASA Astrophysics Data System (ADS)

Miyahara, Makoto; Saito, Akiko; Ito, Hitoshi; Toyoda, Masatake

2002-03-01

The detection of low levels of irradiation in meats (pork, beef, and chicken) using the new comet assay was investigated in order to assess the capability of the procedure. The new assay includes a process that improves its sensitivity to irradiation and a novel evaluation system for each slide (influence score and comet-type distribution). Samples used were purchased at retailers and were irradiated at 0.5 and 2kGy at 0°C. The samples were processed to obtain comets. Slides were evaluated by typing comets, calculating the influence score and analyzing the comet-type distribution chart of shown on the slide. Influence scores of beef, pork, and chicken at 0kGy were 287(SD=8.0), 305 (SD=12.9), and 320 (SD=21.0), respectively. Those at 500Gy, were 305 (SD=5.3), 347 (SD=10.6), and 364 (12.6), respectively. Irradiation levels in food were successfully determined. Sensitivity to irradiation differed among samples (chicken>pork>beef).

Interpreting sperm DNA damage in a diverse range of mammalian sperm by means of the two-tailed comet assay

PubMed Central

Cortés-Gutiérrez, Elva I.; López-Fernández, Carmen; Fernández, José Luis; Dávila-Rodríguez, Martha I.; Johnston, Stephen D.; Gosálvez, Jaime

2014-01-01

Key Concepts The two-dimensional Two-Tailed Comet assay (TT-comet) protocol is a valuable technique to differentiate between single-stranded (SSBs) and double-stranded DNA breaks (DSBs) on the same sperm cell.Protein lysis inherent with the TT-comet protocol accounts for differences in sperm protamine composition at a species-specific level to produce reliable visualization of sperm DNA damage.Alkaline treatment may break the sugar–phosphate backbone in abasic sites or at sites with deoxyribose damage, transforming these lesions into DNA breaks that are also converted into ssDNA. These lesions are known as Alkali Labile Sites “ALSs.”DBD–FISH permits the in situ visualization of DNA breaks, abasic sites or alkaline-sensitive DNA regions.The alkaline comet single assay reveals that all mammalian species display constitutive ALS related with the requirement of the sperm to undergo transient changes in DNA structure linked with chromatin packing.Sperm DNA damage is associated with fertilization failure, impaired pre-and post- embryo implantation and poor pregnancy outcome.The TT is a valuable tool for identifying SSBs or DSBs in sperm cells with DNA fragmentation and can be therefore used for the purposes of fertility assessment. Sperm DNA damage is associated with fertilization failure, impaired pre-and post- embryo implantation and poor pregnancy outcome. A series of methodologies to assess DNA damage in spermatozoa have been developed but most are unable to differentiate between single-stranded DNA breaks (SSBs) and double-stranded DNA breaks (DSBs) on the same sperm cell. The two-dimensional Two-Tailed Comet assay (TT-comet) protocol highlighted in this review overcomes this limitation and emphasizes the importance in accounting for the difference in sperm protamine composition at a species-specific level for the appropriate preparation of the assay. The TT-comet is a modification of the original comet assay that uses a two dimensional electrophoresis to allow for the simultaneous evaluation of DSBs and SSBs in mammalian spermatozoa. Here we have compiled a retrospective overview of how the TT-comet assay has been used to investigate the structure and function of sperm DNA across a diverse range of mammalian species (eutheria, metatheria, and prototheria). When conducted as part of the TT-comet assay, we illustrate (a) how the alkaline comet single assay has been used to help understand the constitutive and transient changes in DNA structure associated with chromatin packing, (b) the capacity of the TT-comet to differentiate between the presence of SSBs and DSBs (c) and the possible implications of SSBs or DSBs for the assessment of infertility. PMID:25505901

Comet Hyakutake to Approach the Earth in Late March 1996

NASA Astrophysics Data System (ADS)

1996-03-01

Astronomers Prepare for a Rare Event In the early morning of January 31, 1996, Japanese amateur astronomer Yuji Hyakutake made his second comet discovery within five weeks. He found the new comet near the border between the southern constellations of Hydra (The Water-Snake) and Libra (The Scales), amazingly just three degrees from the position where he detected another comet on December 26, 1995. After two weeks of hectic activity among amateur and professional astronomers all over the world, much interesting information has now been gathered about the new comet which has been designated C/1996 B2 (Hyakutake) . In particular, it has been found to move in a near-parabolic orbit that will bring it unusually close to the Earth next month. It is then expected to become bright enough to be seen with the unaided eye and to remain so during several weeks thereafter. Preparations are now made to observe the celestial visitor with a large number of telescopes, on the ground and in space. This event offers a rare opportunity to study the immediate surroundings of a cometary nucleus in detail and the specialists intend to make the most of it. Discovery and orbit Yuji Hyakutake, of profession photoengraver and a well-known amateur astronomer, announced his new discovery without delay, and within 24 hours, it had been sighted by several other observers in Japan and Australia. Experienced comet-watchers described its appearance as `diffuse with central condensation and of magnitude 11-12', i.e. a little more than 100 times fainter than what can be seen with the unaided eye. This brightness is not unusual for a comet discovered by an amateur, although it would probably have been missed, had it been just a little fainter. In the present case, the decisive factors for Hyakutake's success were undoubtedly his very powerful equipment (25 x 150 binoculars) and the advantageous combination of the comet's southern position in the sky and his location in Kagoshima, the southernmost prefecture of Japan. Within three days only, nearly 120 positional measurements of the comet were obtained, mostly by amateur observers in Australia, PR China, the Czech Republic, France, Japan, Spain and the U.S.A. This allowed Brian Marsden of the Central Bureau for Astronomical Telegrams of the International Astronomical Union (Cambridge, Mass., U.S.A.) to compute a preliminary orbit. It showed that the comet moves along a parabola - or at least an extremely elongated ellipse - and that it must therefore have come from far away and may never have been near the Sun before. At the time of discovery, the comet was about 280 million km from the Earth and outside the orbit of Mars. Moreover, the motion of the comet is such that it will continue to approach the Earth with a speed of about 58 km/sec during the next weeks and will pass within 15 million kilometres of our planet in late March. This corresponds to one tenth of the distance between the Earth and the Sun (0.1 AU) and, in cosmical terms, the passage is therefore a very close one. Information about some earlier comet encounters may be found in the Appendix at the end of this Press Release. Continued observations have confirmed this and have also allowed to fix the moment of closest passage as Monday, March 25, at about 7h UT. At that time, the comet will be moving northwards through the northern constellation of Draco (The Dragon) at the exceptional rate of 0.77 deg/hour. The event will be best observable from the northern hemisphere. Two days later, the comet passes within a few degrees of the northern celestial pole. The perihelion (the orbital point closest to the Sun) is reached on May 1, 1996, at a distance of 35 million kilometres from the Sun, far inside the orbit of the innermost planet, Mercury. From then on, the comet will rapidly move south, crossing the celestial equator in mid-May and reaching 70 degrees south in late July. Recent observations Comet Hyakutake obviously comes from far away, maybe even from the very distant `Oort Cloud' of comets that surrounds the solar system. In this sense it is different from the periodical comets which move in closed orbits around the Sun with revolution periods between a few years and some decades. Its `dirty snowball' nucleus of ices and dust has therefore not been heated by the Sun for a very long time, perhaps never, if this is its first visit to the inner regions of the solar system. Hence it is particularly difficult to predict its future performance. Nevertheless, the available observations seem to indicate that it is a quite `active' comet and that it may therefore become comparatively bright when it approaches the Earth and later at perihelion. But how bright ? Imaging as well as spectroscopic observations have been performed in order to better characterize Comet Hyakutake. On CCD-frames obtained of the comet in early February with telescopes at the ESO La Silla Observatory and elsewhere, an elongation is clearly visible (cf. ESO Press Photo 11/96 ) in the anti-sunward direction of the coma (the cloud of gas and dust that surrounds the cometary nucleus). A real tail has not yet developed, but this is expected to happen soon. The size of the coma was measured as at least 7 arcmin, corresponding to a projected diameter of nearly 500,000 kilometres. It is also of interest that until recently the coma otherwise appeared absolutely symmetrical - there was no indication of `jets', i.e. no large vents on the surface of the nucleus had yet become active. However, on images obtained with the ESO 3.6-metre telescope in the morning of February 13, a `jet'-like feature is seen which emerges south-east of the nucleus (i.e. from the sunlit side) and curls counter-clockwise towards the opposite side (the `tail'-direction). This is probably the first evidence of localized dust production on the surface of the nucleus. CCD observations were made on February 9 at the Lowell Observatory (Flagstaff, U.S.A.) through special optical filters which isolate the light from different components of the coma, e.g. the light emitted by the OH-, C2- and CN-molecules in gaseous form and also the reflected sunlight from the dust grains. They show that the gas production rates are almost as high as those measured at famous Comet Halley when it was at about the same distance from the Sun during its approach in late 1985. The dust production of Comet Hyakutake also seems to be quite impressive. The first spectra of the new comet were obtained at La Silla with the Boller and Chivens spectrograph at the ESO 1.52-metre telescope on February 8; they show comparatively strong emission of CN, C2 and C3 molecules, cf. ESO Press Photo 12/96. This is not unusual for a comet at the corresponding heliocentric distance. In conclusion, the recent observations show Comet Hyakutake to be an `active' comet. The evaporation of the ices on the surface of its nucleus, due to the heating of the Sun, is well underway and much dust is being ejected during this process. It is quite likely that this comet will put on a fine display, starting in mid-March and lasting until soon after the perihelion passage in early May. Nevertheless, there have been some cases [1] in recent times when the activity level of new comets did not develop as expected, so some caution is necessary. The encounter on March 25 By a straightforward extrapolation of the current brightness, it would appear that Comet Hyakutake will reach magnitude 1 on March 25, 1996, at the time of the closest approach to the Earth. This is almost as bright as the brightest stars in the sky. However, it is important to consider that this is the `integrated' brightness of the entire comet head which may fill an area of several degrees in diameter in the sky. Thus the comet will appear as a moderately bright, very diffuse object that is best visible in binoculars. There will be a central point of enhanced brightness, corresponding to the innermost part of the coma around the nucleus. The motion is sufficiently fast to be easily perceptible on the stellar background. We do not know the size of the nucleus yet, but assuming - optimistically, from the measured gas and dust production - that the diameter is 10 kilometres, i.e. about as large as that of Comet Halley, then the magnitude of the nucleus alone should be about 11 at the time of the closest encounter. It may therefore be well visible in even small telescopes, as a bright point near the centre of the diffuse coma. However, it will most probably not be possible to obtain resolved images of the nucleus with ground-based telescopes; even if the size turns out to be this large, the nucleus will only subtend an angle of about 0.15 arcsec and thus appear point-like. The comet's extremely rapid motion across the sky at the encounter will constitute a major technical-observational problem for most telescopes. Moreover, it cannot be excluded that the coma is so dense that the nucleus will be completely hidden from view. The only telescope which could possibly image the nucleus as an extended object is the Hubble Space Telescope, for which observations are now being planned. Still, there is no doubt that the upcoming event offers very bright prospects for the investigation of the near-nucleus environment of a comet. Another technique which will most likely be attempted is that of radar soundings; the return time for a signal will only be 100 seconds. In the past, only a handful of comets have been investigated in this way and none in great detail. However, in view of the recent, great technological advances in this field, it should in principle be possible to `image' the nucleus of Comet Hyakutake with some of the largest radio telescopes. Predictions for the appearance of the tail(s) at the encounter are still very uncertain, since their development has not yet started. In the best case, the dust tail may become quite impressive and reach a length of many degrees, and the expected ion tail could also be quite long. The perihel passage The brightness at perihel on May 1 will probably exceed that at the Earth encounter and Comet Hyakutake could then become a very spectacular object. How bright it will actually be is much dependent on the amount of dust released from the nucleus as it approaches the Sun. Unfortunately, the viewing conditions will not be very good and the full moon on May 3 will also adversely influence the sight. Appendix: Comet encounters with the Earth There is no doubt that the close encounter with C/1996 B2 (Hyakutake) is a relatively rare event. According to Brian Marsden (Central Bureau for Astronomical Telegrams of the International Astronomical Union, Cambridge, Mass., U.S.A.): The approach of C/1996 B2 to the Earth on March 25 (0.10 AU) [2] is the closest for any comet since 1983 (when there were two comets coming to 0.06 AU and 0.03 AU within a month of each other), and it is the fifth closest approach of any comet during the past century. What is unique about this comet is that no other comet is known then to have gone on to pass anything like as close to the Sun as this one does (0.23 AU on May 1). One of the 1983 comets had about twice this comet's perihelion distance, but the approach to the Earth was well after perihelion. There was possibly a comet with a perihelion distance comparable to this one that came closer to the Earth after perihelion in the year 400, but that is very uncertain. The time interval between passage near the Earth and subsequent passage near the Sun is longer for C/1996 B2 (37 days) than for any closer Earth approach since that of the famous Lexell comet in 1770 (43 days), that comet holding the record confirmed approach to the Earth (0.015 AU or 2.2 million kilometres). C/1996 B2 is intrinsically the brightest Earth-approacher since the early eighteenth century, and the 55 days between discovery and Earth approach is a record for a pre-perihelic Earth approach. More information about other close encounters and collisions of comets with the Earth may be found in an article by Zdenek Sekanina and Don Yeomans (Jet Propulsion Laboratory, CALTECH, Pasadena, U.S.A.) which appeared in 1984 in the American journal The Astronomical Journal , Volume 89, page 154. Notes: [1] Prominent examples are Comet Kohoutek in 1973 and Comet Austin in 1990. [2] 1 Astronomical Unit (AU) = 149.6 million kilometres (the mean distance between the Earth and the Sun). Note also that ESO has set up a special Home Page for the Comet Hyakutake event ( http://www.eso.org/educnpubrelns/comet-hyakutake.html) where new information from ESO will be brought.

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.

103P/Hartley 2: ground-based monitoring of the EPOXI flyby comet

NASA Astrophysics Data System (ADS)

Tubiana, C.; Snodgrass, C.; Vincent, J.-B.; Barrera, L.; Nowajewski, P.; Retamales, G.; Lister, T.; Boehnhardt, H.

2011-10-01

Comet 103P/Hartley 2 was the fly-by target of the NASA EPOXI mission. Observations of this comet during its previous perihelion passage [1] and in 2008 when it was in its aphelion arc [2, 3] revealed a small and very active nucleus. We observed 103P from March 2010 to January 2011 using the 4m SOAR telescope located at Cerro Pachon, Chile. We took images in UBVRI filters using the SOAR Optical Imager (SOI). In addition, we made use of the large collection of (mostly BVR) images taken of the comet by school pupils using the two robotic 2m Faulkes Telescopes, which cover the same period. At the time of the observations, the comet was moving from 2.8 AU pre-perihelion to 1.6 AU post-perihelion heliocentric distance, when the comet was expected to display the most activity. The main purpose of our observations was the characterization of the activity of comet 103P and its evolution along the perihelion arc. We searched for the presence of dust coma structures and their evolution with changing heliocentric distance and determined gas and dust production rates, the dust color and the variation in these quantities as the comet passed perihelion. While no coma structures were detected between March and July 2010, a clear anisotropy in the coma in the anti-tail direction was detected in images obtained in November 2011 (Fig. 1). At the same place, the Laplace filter detects what might be a jet.

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.

The comet assay: assessment of in vitro and in vivo DNA damage.

PubMed

Bajpayee, Mahima; Kumar, Ashutosh; Dhawan, Alok

2013-01-01

Rapid industrialization and pursuance of a better life have led to an increase in the amount of chemicals in the environment, which are deleterious to human health. Pesticides, automobile exhausts, and new chemical entities all add to air pollution and have an adverse effect on all living organisms including humans. Sensitive test systems are thus required for accurate hazard identification and risk assessment. The Comet assay has been used widely as a simple, rapid, and sensitive tool for assessment of DNA damage in single cells from both in vitro and in vivo sources as well as in humans. Already, the in vivo comet assay has gained importance as the preferred test for assessing DNA damage in animals for some international regulatory guidelines. The advantages of the in vivo comet assay are its ability to detect DNA damage in any tissue, despite having non-proliferating cells, and its sensitivity to detect genotoxicity. The recommendations from the international workshops held for the comet assay have resulted in establishment of guidelines. The in vitro comet assay conducted in cultured cells and cell lines can be used for screening large number of compounds and at very low concentrations. The in vitro assay has also been automated to provide a high-throughput screening method for new chemical entities, as well as environmental samples. This chapter details the in vitro comet assay using the 96-well plate and in vivo comet assay in multiple organs of the mouse.

In-situ investigations of the ionosphere of comet 67P

NASA Astrophysics Data System (ADS)

Eriksson, A. I.; Edberg, N. J. T.; Odelstad, E.; Vigren, E.; Engelhardt, I.; Henri, P.; Lebreton, J.-P.; Galand, M.; Carr, C. M.; Koenders, C.; Nilsson, H.; Broiles, T.; Rubin, M.

2015-10-01

Since arrival of Rosetta at its target comet 67P/Churyumov-Gerasimenko in August 2014, the plasma environment has been dominated by ionized gas emanating from the comet nucleus rather than by solar wind plasma. This was evident early on from the strong modulation seen with Rosetta's position in a reference frame fixed to the rotating nucleus, with higher plasma densities observed when the spacecraft is above the neck region and when the comet exposes maximum area to the sun. In this respect, Rosetta is inside the comet ionosphere, providing excellent in situ investigation opportunities for the instruments of the Rosetta Plasma Consortium (RPC). In contrast to the often modelled scenario for a very active comet, the Langmuir probe instrument (RPC-LAP) finds electron temperatures mainly in the range of tens of thousand kelvin around this less active comet. This can be attributed to the lower density of neutral gas, meaning little cooling of recently produced electrons. A side effect of this is that the spacecraft charges negatively when within about 100 km from the nucleus. Interesting in itself, this also may point to similar charging for dust grains in the coma, with implications for the detection of the smallest particles and possibly for processes like electrostatic fragmentation. The inner coma also proves to be very dynamic, with large variations not only with latitude and longitude in a comet frame, but also with the solar wind and various wave phenomena.

Evidence for geologic processes on comets

NASA Astrophysics Data System (ADS)

Sunshine, Jessica M.; Thomas, Nicolas; El-Maarry, Mohamed Ramy; Farnham, Tony L.

2016-11-01

Spacecraft missions have resolved the nuclei of six periodic comets and revealed a set of geologically intriguing and active small bodies. The shapes of these cometary nuclei are dominantly bilobate reflecting their formation from smaller cometesimals. Cometary surfaces include a diverse set of morphologies formed from a variety of mechanisms. Sublimation of ices, driven by the variable insolation over the time since each nucleus was perturbed into the inner Solar System, is a major process on comets and is likely responsible for quasi-circular depressions and ubiquitous layering. Sublimation from near-vertical walls is also seen to lead to undercutting and mass wasting. Fracturing has only been resolved on one comet but likely exists on all comets. There is also evidence for mass redistribution, where material lifted off the nucleus by subliming gases is deposited onto other surfaces. It is surprising that such sedimentary processes are significant in the microgravity environment of comets. There are many enigmatic features on cometary surfaces including tall spires, kilometer-scale flows, and various forms of depressions and pits. Furthermore, even after accounting for the differences in resolution and coverage, significant diversity in landforms among cometary surfaces clearly exists. Yet why certain landforms occur on some comets and not on others remains poorly understood. The exploration and understanding of geologic processes on comets is only beginning. These fascinating bodies will continue to provide a unique laboratory for examining common geologic processes under the uncommon conditions of very high porosity, very low strength, small particle sizes, and near-zero gravity.

Water production rates of recent comets (2016-2017) by SOHO/SWAN: 2P/Encke, 41P/Tuttle-Giacobini-Kresak, 45P/ Honda-Mrkos-Pajdusakova, and C/2015 ER61 (PanSTARRS)

NASA Astrophysics Data System (ADS)

Combi, Michael R.; Mäkinen, Terhi; Bertaux, Jean-Loup; Quémerais, Eric; Ferron, Stephane

2017-10-01

The all-sky hydrogen Lyman-alpha camera, SWAN (Solar Wind Anisotropies), on the SOlar and Heliospheric Observatory (SOHO) satellite makes observations of the hydrogen coma of comets. Most water molecules produced by comets are ultimately photodissociated into two H atoms and one O atom producing a huge atomic hydrogen coma that is routinely observed in the daily full-sky SWAN images in comets of sufficient brightness. Water production rates are calculated using our time-resolved model (Mäkinen & Combi, 2005, Icarus 177, 217), typically yielding about 1 observation every 2 days on the average for each comet over the brightest part of its apparition. Here we describe the progress in analysis of observations of comets observed in 2016 and 2017. These include comets 2P/Encke, 41P/Tuttle-Giacobini-Sresak, 45P/ Honda-Mrkos-Pajdusakova, and C/2015 ER61 (PanSTARRS). A status update on the entire SOHO/SWAN archive of water production rates in comets will also be given.SOHO is an international cooperative mission between ESA and NASA. Support from grants NNX15AJ81G from the NASA Solar System Observations Planetary Astronomy Program and a previous grant NNX13AQ66G from the NASA Planetary Mission Data Analysis Program are gratefully acknowledged, as is support from CNRS, CNES, and the Finnish Meteorological Institute (FMI).

Creating cometary models using ancient Chinese data

NASA Astrophysics Data System (ADS)

Yeomans, D. K.

For more than two millennia, Chinese court astronomers maintained a rather comprehensive record of cometary sightings. Owing to the significance of comets as portents for the reigning emperor, early sky watchers from China (as well as their counterparts from Korea and Japan) carefully noted each cometary apparition for the purpose of astrological predictions. The dates and corresponding celestial locations and motions were usually recorded and in some cases, the colors, coma sizes, and tail lengths were also noted. These ancient observations represent the only source of information available for modeling the long-term behavior of periodic comets. For comets Halley and Swift-Tuttle, Chinese records have been identified as far back as 240 B.C. and 69 B.C. respectively and these data have been used to define their long-term motions. As a result, heliocentric and geocentric distances for each Chinese sighting of these two comets can be computed and estimates can be made for each comet's intrinsic brightness at various observed returns. Although the earliest identified apparition of comet Tempel-Tuttle is A.D. 1366, the associated Leonid meteor showers were noted back to at least A.D. 902. The Leonid meteor stream is young in the sense that outstanding meteor displays occur only near the time of the parent comet's perihelion passages. The ancient Chinese records of the Leonid meteor showers and storms have been used to map the particle distribution around the parent comet and this information was used to guide predictions for the 1998-1999 Leonid meteor showers.

A tail like no other. The RPC-MAG view of Rosetta's tail excursion at comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Volwerk, Martin; Goetz, Charlotte; Richter, Ingo; Delva, Magda; Ostaszewski, Katharina; Schwingenschuh, Konrad; Glassmeier, Karl-Heinz

2018-06-01

Context. The Rosetta Plasma Consortium (RPC) magnetometer (MAG) data during the tail excursion in March-April 2016 are used to investigate the magnetic structure of and activity in the tail region of the weakly outgassing comet 67P/Churyumov-Gerasimenko (67P). Aims: The goal of this study is to compare the large scale (near) tail structure with that of earlier missions to strong outgassing comets, and the small scale turbulent energy cascade (un)related to the singing comet phenomenon. Methods: The usual methods of space plasma physics are used to analyse the magnetometer data, such as minimum variance analysis, spectral analysis, and power law fitting. Also the cone angle and clock angle of the magnetic field are calculated to interpret the data. Results: It is found that comet 67P does not have a classical draped magnetic field and no bi-lobal tail structure at this late stage of the mission when the comet is already at 2.7 AU distance from the Sun. The main magnetic field direction seems to be more across the tail direction, which may implicate an asymmetric pick-up cloud. During periods of singing comet activity the propagation direction of the waves is at large angles with respect to the magnetic field and to the radial direction towards the comet. Turbulent cascade of magnetic energy from large to small scales is different in the presence of singing as without it.

The asteroid-comet continuum from laboratory and space analyses of comet samples and micrometeorites

NASA Astrophysics Data System (ADS)

Engrand, Cécile; Duprat, Jean; Bardin, Noémie; Dartois, Emmanuel; Leroux, Hugues; Quirico, Eric; Benzerara, Karim; Remusat, Laurent; Dobrică, Elena; Delauche, Lucie; Bradley, John; Ishii, Hope; Hilchenbach, Martin

2016-10-01

Comets are probably the best archives of the nascent solar system, 4.5 Gyr ago, and their compositions reveal crucial clues on the structure and dynamics of the early protoplanetary disk. Anhydrous minerals (olivine and pyroxene) have been identified in cometary dust for a few decades. Surprisingly, samples from comet Wild2 returned by the Stardust mission in 2006 also contain high temperature mineral assemblages like chondrules and refractory inclusions, which are typical components of primitive meteorites (carbonaceous chondrites - CCs). A few Stardust samples have also preserved some organic matter of comet Wild 2 that share some similarities with CCs. Interplanetary dust falling on Earth originate from comets and asteroids in proportions to be further constrained. These cosmic dust particles mostly show similarities with CCs, which in turn only represent a few percent of meteorites recovered on Earth. At least two (rare) families of cosmic dust particles have shown strong evidences for a cometary origin: the chondritic porous interplanetary dust particles (CP-IDPs) collected in the terrestrial stratosphere by NASA, and the ultracarbonaceous Antarctic Micrometeorites (UCAMMs) collected from polar snow and ice by French and Japanese teams. Analyses of dust particles from the Jupiter family comet 67P/Churyumov-Gerasimenko by the dust analyzers on Rosetta orbiter (COSIMA, GIADA, MIDAS) suggest a relationship to interplanetary dust/micrometeorites. A growing number of evidences highlights the existence of a continuum between asteroids and comets, already in the early history of the solar system.

The Composition of Comet C 2012 K1 (PanSTARRS) and the Distribution of Primary Volatile Abundances Among Comets

NASA Technical Reports Server (NTRS)

Roth, Nathan X.; Gibb, Erika; Bonev, Boncho P.; Disanti, Michael A.; Mumma, Michael J.; Villanueva, Geronimo L.; Paganini, Lucas

2017-01-01

On 2014 May 22 and 24 we characterized the volatile composition of the dynamically new Oort cloud comet C2012 K1 (PanSTARRS) using the long-slit, high resolution ( lambda/delta lambda is approximately or equal to 25,000) near-infrared echelle spectrograph (NIRSPEC) at the 10 m Keck II telescope on Maunakea, Hawaii. We detected fluorescent emission from six primary volatiles (H2O, HCN, CH4, C2H6, CH3OH, and CO). Upper limits were derived for C2H2, NH3, and H2CO. We report rotational temperatures, production rates, and mixing ratios (relative to water). Compared with median abundance ratios for primary volatiles in other sampled Oort cloud comets, trace gas abundance ratios in C2012 K1 (PanSTARRS) for CO and HCN are consistent, but CH3OH and C2H6 are enriched while H2CO, CH4, and possibly C2H2 are depleted. When placed in context with comets observed in the near- infrared to date, the data suggest a continuous distribution of abundances of some organic volatiles (HCN, C2H6, CH3OH, CH4) among the comet population. The level of enrichment or depletion in a given comet does not necessarily correlate across all molecules sampled, suggesting that chemical diversity among comets may be more complex than the simple organics-enriched, organics-normal, and organics-depleted framework.

Spitzer June 13 View of ISON

NASA Image and Video Library

2013-11-22

These images from NASA's Spitzer Space Telescope of Comet ISON were taken on June 13, 2013, when ISON was about 310 million miles from the sun. The image on the left shows light in the near infrared wavelengths of 3.6 microns. It shows a tail of fine, rocky dust issuing from the comet and blown back by the pressure of sunlight as the comet speeds towards the sun. The image on the right side shows light with a wavelength of 4.5 microns. It reveals a very different round structure -- the first detection of a neutral gas atmosphere surrounding ISON. In this case, it is most likely created by carbon dioxide that is "fizzing" from the surface of the comet at a rate of about 2.2 million pounds a day. Credit: NASA/JPL-Caltech/JHUAPL/UCF -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is managed by the Keldysh Institute of Applied Mathematics, part of the Russian Academy of Sciences. NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

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)

Discovery of Main-Belt Comet P/2006 VW139 by Pan-STARRS1

NASA Astrophysics Data System (ADS)

Hsieh, H. H.; Yang, B.; Haghighipour, N.; Kaluna, H. M.; Fitzsimmons, A.; Denneau, L.; Novakovic, B.; Jedicke, R.; Wainscoat, R. J.; Armstrong, J. D.; Duddy, S. R.; Lowry, S. C.; Trujillo, C. A.; Micheli, M.; Keane, J. V.; Urban, L.; Riesen, T.; Meech, K. J.; Abe, S.; Cheng, Y. C.; Chen, W. P.; Granvik, M.; Grav, T.; Ip, W. H.; Kinoshita, D.; Kleyna, J.; Lacerda, P.; Lister, T.; Milani, A.; Tholen, D. J.; Veres, P.; Lisse, C. M.; Kelley, M. S.; Fernandez, Y. R.; Bhatt, B. C.; Sahu, D. K.; Kaiser, N.; Chambers, K. C.; Hodapp, K. W.; Magnier, E. A.; Price, P. A.; Tonry, J. L.

2012-05-01

We describe the discovery of comet-like activity in main-belt asteroid (300163) 2006 VW139 (later re-designated as Comet P/2006 VW139) by Pan-STARRS1. We also detail follow-up photometric, spectroscopic, and dynamical analyses of the object.

Asteroids, Comets, Meteors 1991

NASA Technical Reports Server (NTRS)

Harris, Alan W. (Editor); Bowell, Edward (Editor)

1992-01-01

Papers from the conference are presented and cover the following topics with respect to asteroids, comets, and/or meteors: interplanetary dust, cometary atmospheres, atmospheric composition, comet tails, astronomical photometry, chemical composition, meteoroid showers, cometary nuclei, orbital resonance, orbital mechanics, emission spectra, radio astronomy, astronomical spectroscopy, photodissociation, micrometeoroids, cosmochemistry, and interstellar chemistry.

Brightness Rhythm of Mars Flyby Comet Is Clue to Rotation Rate

NASA Image and Video Library

2014-11-07

This graph shows changes in apparent brightness of comet C/2013 A1 Siding Spring as it approached and receded from Mars, as seen by the HiRISE camera on NASA Mars Reconnaissance Orbiter. The pattern suggests the comet rotates once every eight hours.

ScienceCast 120: Amateur Astonomers See Comet ISON Approaching the Sun

NASA Image and Video Library

2013-09-23

To learn how you can help, visit isoncampaign.org. Comet ISON is still more than two months away from its spectacular close encounter with the sun. Already, the brightening comet has become a good target for backyard telescopes in the pre-dawn sky.

The origin of comets - Implications for planetary formation

NASA Technical Reports Server (NTRS)

Weissman, P. R.

1985-01-01

Primordial and episodic theories for the origin of comets are discussed. The implications of the former type for the origin of the solar system are considered. Candidate sites for the formation of comets are compared. The possible existence of a massive inner Oort cloud is discussed.

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

NASA Astrophysics Data System (ADS)

Jones, Geraint H.; Knight, Matthew M.; Battams, Karl; Boice, Daniel C.; Brown, John; Giordano, Silvio; Raymond, John; Snodgrass, Colin; Steckloff, Jordan K.; Weissman, Paul; Fitzsimmons, Alan; Lisse, Carey; Opitom, Cyrielle; Birkett, Kimberley S.; Bzowski, Maciej; Decock, Alice; Mann, Ingrid; Ramanjooloo, Yudish; McCauley, Patrick

2018-02-01

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun's centre, equal to half of Mercury's perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics.

Hubble's Last Look at Comet ISON Before Perihelion

NASA Image and Video Library

2013-11-22

As of mid-November, ISON is officially upon us. Using Hubble, we've taken our closest look yet at the innermost region of the comet, where geysers of sublimating ice are fueling a spectacular tail. Made from observations on November 2nd, the image combines pictures of ISON taken through blue and red filters. As we expect, the round coma around ISON's nucleus is blue and the tail has a redder hue. Ice and gas in the coma reflect blue light from the Sun, while dust grains in the tail reflect more red light than blue light. This is the most color separation we've seen so far in ISON -- that's because the comet, nearer than ever to the Sun, is brighter and more structured than ever before. We've certainly come a long way since Hubble started observing Comet ISON, way back in April. Of course, our eight-month retrospective pales in comparison with ISON's own journey, which started some 10,000 years ago in the Oort cloud. ISON will come closest to the Sun on November 28, a point in its orbit known as perihelion. What's remarkable here is that the entire ISON, this awesome, shimmery space tadpole, is being produced from a dusty ball of ice estimated to be a few kilometers in diameter. Compared to ISON's full extent, Hubble's latest image is tiny. It only shows the very base of the tail. Yet even in this closest closeup we've ever had, a single pixel spans 24 km across the comet. Now that Comet ISON is close, amateur astromers rule the day. But Hubble observations, including this latest image, are still providing key insights into the science and spectacle of a comet we hope will continue to impress. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) -------- More details on Comet ISON: Comet ISON began its trip from the Oort cloud region of our solar system and is now travelling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day -- 28 Nov 2013 -- skimming just 730,000 miles above the sun's surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Catalogued as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is ISON's very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Comet ISON is, like all comets, a dirty snowball made up of dust and frozen gases like water, ammonia, methane and carbon dioxide -- some of the fundamental building blocks that scientists believe led to the formation of the planets 4.5 billion years ago. NASA has been using a vast fleet of spacecraft, instruments, and space- and Earth-based telescope, in order to learn more about this time capsule from when the solar system first formed. The journey along the way for such a sun-grazing comet can be dangerous. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. This collection of images show ISON throughout that journey, as scientists watched to see whether the comet would break up or remain intact. The comet reaches its closest approach to the sun on Thanksgiving Day -- Nov. 28, 2013 -- skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. ISON stands for International Scientific Optical Network, a group of observatories in ten countries who have organized to detect, monitor, and track objects in space. ISON is

Make a Halley's Comet Orbit Model.

ERIC Educational Resources Information Center

Podmore, Francis; Fleet, Richard W.

1985-01-01

Describes a simple three-dimensional model of Halley's Comet orbit (which is much more informative than a two-dimensional drawing) to illustrate spatial relationships and visualize how the comet moves relative to the earth. Instructions for model assembly are given along with a template which can be photocopied and glued to cardboard. (JN)

An Interview with Catherine Comet.

ERIC Educational Resources Information Center

Scanlan, Mary

1992-01-01

Offers an interview with Catherine Comet, music director of the Grand Rapids (Michigan) Symphony. Reviews her childhood and early study in France and her experiences at the Julliard School of Music and on the contest circuit. Explains how she became a professional conductor. Discusses Comet's view of the importance that classical music can have…

Wild 2 Close Look

NASA Image and Video Library

2004-06-17

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. http://photojournal.jpl.nasa.gov/catalog/PIA06285

Mars Orbiters Duck and Cover for Comet Siding Spring Flyby Artist Concept

NASA Image and Video Library

2014-10-09

This artist concept shows NASA Mars orbiters lining up behind the Red Planet for their duck and cover maneuver to shield them from comet dust that may result from the close flyby of comet Siding Spring C/2013 A1 on Oct. 19, 2014.

Spectroscopic observations of comets

NASA Technical Reports Server (NTRS)

1982-01-01

Development of a spectrograph using a microchannel plate intensifier for observing faint comets is described. The spectrograph is capable of obtaining useful spectra of objects as faint as M(2) = 18. The increased guiding efficiency achieved by the optical coupling of the ISIT vidicon of the 154 cm telescope has resulted in a better signal to noise ratio. The ability to take a direct image of the comet aids in the interpretation of the spatial profile of the emissions. Spectra of comets Schwassmann-Wachmann 1, Bradfield, Encke, Tuttle, and Stephen-Oterma are discussed.

The bare nucleus of comet Neujmin 1

NASA Technical Reports Server (NTRS)

Campins, Humberto; A'Hearn, Michael F.; Mcfadden, Lucy-Ann

1987-01-01

Simultaneous visible and infrared observations of comet P/Neujmin 1 1984c are presented which show that the comet has a large (mean radius 10 km), dark (geometric albedo 2-3 percent) nucleus with a surface which is mostly inert material but which still shows a low level of gaseous activity. This is the first physical evidence that cometary nuclei can leave behind an inert body after the coma activity ceases. No asteroid or asteroid class has been found to match the reflectance and albedo of this comet except possibly some D asteroids.

Nucleus model for periodic Comet Tempel 2

NASA Technical Reports Server (NTRS)

Sekanina, Zdenek

1991-01-01

Observational data obtained primarily during 1988 are analyzed and synthesized to develop a comprehensive physical model for the nucleus of Periodic Comet Tempel 2, one of the best studied members of Jupiter's family of short-period comets. It is confirmed that a previous investigation provided reliable information on the comet's spin-axis orientation, which implies and obliquity of 54 degrees of the orbit plane to the equatorial plane and which appears to have varied little - if at all - with time. This conclusion is critical for fitting a triaxial ellipsoid to approximate the figure of the nucleus.

Scientific returns from a program of space missions to comets

NASA Technical Reports Server (NTRS)

Delsemme, A. H.

1979-01-01

A program of cometary missions is proposed. The nature and size of interstellar dust, its origin and evolution; identification of new interstellar molecules; clarification of interstellar chemistry; accretion of grains into protosolar cometesimals; role of a T Tauri wind in the dissipation of the protosolar nebula; record of isotopic anomalies, better preserved in comets than in meteorites; cosmogenic and radiogenic dating of comets; cosmochronology and mineralogy of meteorites, as compared with that of cometary samples; origin of the earth's biosphere, and the origin of life are topics discussed in relation to comet exploration.

Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Hässig, M.; Altwegg, K.; Balsiger, H.; Bar-Nun, A.; Berthelier, J. J.; Bieler, A.; Bochsler, P.; Briois, C.; Calmonte, U.; Combi, M.; De Keyser, J.; Eberhardt, P.; Fiethe, B.; Fuselier, S. A.; Galand, M.; Gasc, S.; Gombosi, T. I.; Hansen, K. C.; Jäckel, A.; Keller, H. U.; Kopp, E.; Korth, A.; Kührt, E.; Le Roy, L.; Mall, U.; Marty, B.; Mousis, O.; Neefs, E.; Owen, T.; Rème, H.; Rubin, M.; Sémon, T.; Tornow, C.; Tzou, C.-Y.; Waite, J. H.; Wurz, P.

2015-01-01

Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface.

The spectral properties of interplanetary dust particles

NASA Technical Reports Server (NTRS)

Sandford, Scott A.

1988-01-01

The observed spectral and mineralogical properties of interplanetary dust particles (IDP) allows the conclusion that: (1) the majority of IDP infrared spectra are dominated by olivine, pyroxene, or layer lattice silicate minerals, (2) to the first order the emission spectra of comets Halley and Kohoutek can be matched by mixtures of these IDP infrared types, implying that comets contain mixtures of these different crystalline silicates and may vary from comet to comet and perhaps even within a single comet, (3) do not expect to observe a single 20 micron feature in cometary spectra, (4) carbonaceous materials dominate the visible spectra properties of the IDPs even though the mass in these particles consists primarily of silicates, and (5) the particle characteristics summarized need to be properly accounted for in future cometary emission models.

Astrometric observations of comets and asteroids and subsequent orbital investigations

NASA Technical Reports Server (NTRS)

Mccrosky, R. E.; Marsden, B. G.

1986-01-01

During the past year some 500 observations were made on 66 nights and published on the MPCs (Minor Planet Circulars/Minor Planets and Comets). In addition, a handful of measurements of earlier plates were completed and published. 121 of the observations published referred to comets. Of special importance were observations of comets (P/Giacobini-Zinner and P/Halley) in connection with the NASA ICE and ESA Giotto missions, but a special effort was made to get good coverage of almost all of the observable comets. Observations were also made of (2060) Chiron and of the earth-approaching objects (1627) Ivar, (1866) Sisyphys, (1943) Anteros, (3362) 1984 QA, 1985 JA, PA, TB and WA, and 1986 DA and EB. 46 minor planets were given permanent numbers entirely as a result of the observations.

Comet Halley: The Curtis Schmidts-Isla de Pascua observations

NASA Technical Reports Server (NTRS)

Miller, Freeman D.; Liller, William

1986-01-01

Halley's comet plasma tail disturbances and attendant tail phenomena were observed. Nearly simultaneous exposures with two telescopes serve to correlate information obtained with the two instruments. Photographs of 14 pre-Halley comets taken on 54 nights were examined with a view to cross-interpretation of phenomena seen in Halley with the earlier comets, as recorded on a homogenous collection of plates taken with the same instrument. The tail of Halley was highly active. This contrasts sharply with pre-Halley comets where undisturbed tails are the rule. During March and April, disturbances appeared in the tail of Halley at an average of 1 new distrubance every 3.7 days. It is considered that 10 of the 11 observed disturbances had common characteristics which allow them to be characterized as disconnections.

Physical mechanism of comet outbursts - An experimental result

NASA Technical Reports Server (NTRS)

Hartmann, William K.

1993-01-01

Attention is given to an experimental investigation of the physical mechanism of comet outbursts which is consistent with the general picture of mantle presence on comets and clarifies the relation of mantles to eruptive activity. The experiment and closeup observation of Comet P/Halley suggest a result different from most mathematical models in that the release of gas pressure does not occur only from uniform gas flow out of the entire surface. In some active comets near perihelion within a few AU of the sun, gas production rates and disturbance of the surface may be so high that the outflow is nearly continuous, with the regolith being entirely stripped away, as in many of the models. The present model provides a cyclic eruption and recharge mechanism which is lacking in most other models.

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.

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.

Plasma-tail activity and the interplanetary medium at Halley's Comet during Armada Week: 6-14 March 1986

NASA Technical Reports Server (NTRS)

Niedner, Malcolm B., Jr.; Schwingenschuh, Konrad; Hoeksema, J. Todd; Dryer, Murray; Mcintosh, Patrick S.

1987-01-01

The encounters of five spacecraft with Halley's Comet during 6-14 March 1986 offered a unique opportunity to calibrate the solar-wind interaction with cometary plasmas as recorded by remote wide-field and narrow-field/narrowband imaging. Perhaps not generally recognized in the comet community is the additional opportunity offered by the Halley Armada to study the structure of the solar-wind and interplanetary magnetic field (IMF) in three dimensions using five sets of data obtained over similar time intervals and heliocentric distances, but at somewhat different heliolatitudes. In fact, the two problems, i.e., comet physics and the structure of the interplanetary medium, are coupled if one wants to understand what conditions pertained at the comet between the encounters. This relationship is discussed.

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.

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.

MULTI-WAVELENGTH OBSERVATIONS OF COMET C/2011 L4 (PAN-STARRS)

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

Yang, Bin; Keane, Jacqueline; Meech, Karen

2014-04-01

The dynamically new comet C/2011 L4 (Pan-STARRS) is one of the brightest comets observed since the great comet C/1995 O1 (Hale-Bopp). Here, we present our multi-wavelength observations of C/2011 L4 during its in-bound passage to the inner solar system. A strong absorption band of water ice at 2.0 μm was detected in the near-infrared spectra, obtained with the 8 m Gemini-North and 3 m Infrared Telescope Facility Telescopes. The companion 1.5 μm band of water ice, however, was not observed. Spectral modeling shows that the absence of the 1.5 μm feature can be explained by the presence of sub-micron-sized fine ice grains.more » No gas lines (i.e., CN, HCN, or CO) were observed pre-perihelion in either the optical or the submillimeter. We derived 3σ upper limits for the CN and CO production rates. The comet exhibited a very strong continuum in the optical and its slope seemed to become redder as the comet approached the Sun. Our observations suggest that C/2011 L4 is an unusually dust-rich comet with a dust-to-gas mass ratio >4.« less

The Rosetta mission orbiter science overview: the comet phase

PubMed Central

Altobelli, N.; Buratti, B. J.; Choukroun, M.

2017-01-01

The international Rosetta mission was launched in 2004 and consists of the orbiter spacecraft Rosetta and the lander Philae. The aim of the mission is to map the comet 67P/Churyumov–Gerasimenko by remote sensing, and to examine its environment in situ and its evolution in the inner Solar System. Rosetta was the first spacecraft to rendezvous with and orbit a comet, accompanying it as it passes through the inner Solar System, and to deploy a lander, Philae, and perform in situ science on the comet's surface. The primary goals of the mission were to: characterize the comet's nucleus; examine the chemical, mineralogical and isotopic composition of volatiles and refractories; examine the physical properties and interrelation of volatiles and refractories in a cometary nucleus; study the development of cometary activity and the processes in the surface layer of the nucleus and in the coma; detail the origin of comets, the relationship between cometary and interstellar material and the implications for the origin of the Solar System; and characterize asteroids 2867 Steins and 21 Lutetia. This paper presents a summary of mission operations and science, focusing on the Rosetta orbiter component of the mission during its comet phase, from early 2014 up to September 2016. This article is part of the themed issue ‘Cometary science after Rosetta’. PMID:28554981

Rocket Detection of Argon in Comet Hale-Bopp

NASA Astrophysics Data System (ADS)

Stern, S. A.; Festou, M. C.; Parker, J. Wm.; Slater, D. C.; Gladstone, G. R.; A'Hearn, M. F.

1998-12-01

The EUVS planetary sounding rocket spectrograph was flown on 30.2 March 1997 (UT) from White Sands, New Mexico to observe comet Hale-Bopp in the bandpass from 830--1120 A. At the time of launch the comet was near perihelion, 0.915 AU from the Sun, 1.340 AU from Earth, and traveling at a heliocentric radial velocity of +0.70 km/s. EUVS obtained its primary spectra of the comet at resolution near 12 A, collecting 9340 counts over approximately 330 seconds of integration time. To our knowledge, the resulting dataset is both the most sensitive and the highest spectral resolution probe of a comet in the UV below 1200 A as yet achieved, and contains signatures of both the 1048.2 A and 1066.7 A Ar I resonance lines. These features represent the first-ever detections of any noble gas in a comet. The spectrum also includes significant detections which we tentatively attribute to due to 834 A 0 II, 972 A Lyman gamma, 989 A O I, the 1026 A H I Lyman beta/O I. We will discuss the Ar features, retrieve the Ar column in the coma, and discuss the implications of the total Ar/O abundance ratio in Hale-Bopp for the comet's origin.

Two-Tailed Comet Assay (2T-Comet): Simultaneous Detection of DNA Single and Double Strand Breaks.

PubMed

Cortés-Gutiérrez, Elva I; Fernández, José Luis; Dávila-Rodríguez, Martha I; López-Fernández, Carmen; Gosálvez, Jaime

2017-01-01

A modification of the original comet assay was developed for the simultaneous evaluation of DNA single strand breaks (SSBs) and double strand breaks (DSBs) in human spermatozoa. The two-dimensional perpendicular tail comet assay (2T-comet) combines non-denaturing and denaturant conditions to the same sperm nucleoid. In this case, the species-specific deproteinized sperm is first subjected to an electrophoretic field under non-denaturing conditions to mobilize isolated free discrete DNA fragments produced from DSBs; this is then followed by a second electrophoresis running perpendicular to the first one but under alkaline conditions to produce DNA denaturation, exposing SSBs on the same linear DNA chain or DNA fragments flanked by DSBs. This procedure results in a two dimensional comet tail emerging from the core where two types of original DNA affected molecule can be simultaneously discriminated. The 2T-comet is a fast, sensitive, and reliable procedure to distinguish between single and double strand DNA damage within the same cell. It is an innovative method for assessing sperm DNA integrity, which has important implications for human fertility and andrological pathology. This technique may be adapted to assess different DNA break types in other species and other cell types.

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.

Vibrational and rotational excitation of CO in comets. Part 1: Non-equilibrium calculations. Part 2: Results of the calculation for standard bright comet, comet Iras-Araki-Alcock and comet Halley

NASA Technical Reports Server (NTRS)

Chin, G.; Weaver, H. A.

1984-01-01

The vibrational and rotational excitation of the CO molecule in cometary comae were investigated using a model which includes IR vibrational pumping by the solar flux, vibrational and rotational radiative decay, and collisional coupling among rotational states. Steady state was not assumed in solving the rate equations. The evolution of a shell of CO gas was monitored as it expanded from the nucleus into the outer coma. Collisional effects were treated using a kinetic temperature profile derived from theoretical work on the coma energy balance. The kinetic temperature was assumed to be extremely cold in the inner coma; this has significant consequences for the CO excitation. If optical depth effects are ignored, only low J transitions will be significantly excited in comets observed at high spatial resolution. Ground-based observations of CO co-vibrational and rotational transitions will be extremely difficult due to lack of sensitivity and/or terrestrial absorption. However, CO should be detectable from a large comet with favorable observing geometry if the CO is a parent molecule present at the 10% level (or greater) relative to H2O. Observations using cooled, spaceborne instruments should be capable of detecting CO emission from even moderately bright comets.

Urania in the Marketplace: The Blue Comet (A Railroad’s Astronomical Heritage)

NASA Astrophysics Data System (ADS)

Rumstay, Kenneth S.

2017-01-01

Between 1929 February 21 and 1941 September 27 the Central New Jersey Railroad operated a luxury passenger train between Jersey City and Atlantic City. Named The Blue Comet, the locomotive, tender, and coaches sported a unique royal blue paint scheme designed to evoke images of celestial bodies speeding through space. Inside each car were etched window panes and lampshades featuring stars and comets. Each coach sported the name of a famous comet on its side; these comets were of course named for their discoverers. Some of the astronomers honored in this unique fashion remain famous to this day, or at least their comets do. The names D’Arrest, Barnard, Encke, Faye, Giacobini, Halley, Olbers, Temple, Tuttle, and Westphal are familiar ones. But Biela, Brorsen, deVico, Spitaler, and Winnecke have now largely faded into obscurity; their stories are recounted here.Although more than seventy years have elapsed since its last run, The Blue Comet, perhaps the most famous passenger train in American history, lives on in the memories of millions of passengers and railfans. This famous train returned to the attention of millions of television viewers on the evening of 2007 June 3, in an episode of the HBO series The Sopranos.This work was supported by a faculty development grant from Valdosta State University.

Determination of the radius of comet 19P/Borrelly in support of the NMP DS1 Flyby

NASA Astrophysics Data System (ADS)

Festou, Michel

1999-07-01

Comet 19P/Borrelly is the ultimate target of the New Mellinium Program {NMP} Deep Space 1 asteroid-comet flyby mission. The size of this comet's nucleus is a critical parameter needed for flyby planning activities. However, as we describe below, P/Borrelly's radius is not well established. We, the NMP DS1 Science Team, request 1 orbit of HST/STIS time in Cycle 8 to refine the nuclear size estimate. This program cannot wait until Cycle 9 because of mission planning constraints and the fact that the comet is likely to be producing a weak but nonetheless enhanced coma by the time of Cycle 9. We therefore propose to observe comet P/Borrelly in Cycle 8 when the activity level of its nucleus is near its minimum, and quite possibly negligible. From a clear separation of the contributions of the coma and the nucleus in the inner part of STIS images, we will extract the cross section of Borrelly's nucleus. In addition to its immediate value for NMP DS1 mission planning, when c oupled to existing data sets, the STIS data will then enable us to model the coma morphology to better infer the effect of the nucleus outgassing on the comet's motion.

Vibrational and rotational excitation of CO in comets. Part 1: Non-equilibrium calculations. Part 2: Results of the calculation for standard bright comet, comet Iras-Araki-Alcock and comet Halley

NASA Astrophysics Data System (ADS)

Chin, G.; Weaver, H. A.

1984-05-01

The vibrational and rotational excitation of the CO molecule in cometary comae were investigated using a model which includes IR vibrational pumping by the solar flux, vibrational and rotational radiative decay, and collisional coupling among rotational states. Steady state was not assumed in solving the rate equations. The evolution of a shell of CO gas was monitored as it expanded from the nucleus into the outer coma. Collisional effects were treated using a kinetic temperature profile derived from theoretical work on the coma energy balance. The kinetic temperature was assumed to be extremely cold in the inner coma; this has significant consequences for the CO excitation. If optical depth effects are ignored, only low J transitions will be significantly excited in comets observed at high spatial resolution. Ground-based observations of CO co-vibrational and rotational transitions will be extremely difficult due to lack of sensitivity and/or terrestrial absorption. However, CO should be detectable from a large comet with favorable observing geometry if the CO is a parent molecule present at the 10% level (or greater) relative to H2O. Observations using cooled, spaceborne instruments should be capable of detecting CO emission from even moderately bright comets.

The Blue Comet: A Railroad's Astronomical Heritage

NASA Astrophysics Data System (ADS)

Rumstay, Kenneth S.

2009-01-01

Between 1929 February 21 and 1941 September 27, the Central New Jersey Railroad operated a luxury passenger train between Jersey City and Atlantic City. Named The Blue Comet, the locomotive, tender, and coaches sported a unique royal blue paint scheme designed to evoke images of celestial bodies speeding through space. Inside each car were etched window panes and lampshades featuring stars and comets. And each coach sported the name of a famous comet on its side; these comets were of course named for their discoverers. Some of the astronomers honored in this unique fashion remain famous to this day, or at least their comets do. The names D'Arrest, Barnard, Encke, Faye, Giacobini, Halley, Olbers, Temple, Tuttle, and Westphal are familiar ones. But Biela, Brorsen, deVico, Spitaler, and Winnecke have now largely faded into obscurity; their stories are recounted here. Although more than sixty years have elapsed since its last run, The Blue Comet, perhaps the most famous passenger train in American history, lives on in the memories of millions of passengers and railfans. This famous train returned to the attention of millions of television viewers on the evening of 2007 June 3, in an episode of the HBO series The Sopranos. This work was supported by a faculty development grant from Valdosta State University.

Geomorphological Mapping on the Southern Hemisphere of Comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Lee, Jui-Chi; Massironi, Matteo; Giacomini, Lorenza; Ip, Wing-Huen; El-Maarry, Mohamed R.

2016-04-01

Since its rendezvous with comet 67P/Churyumov-Gerasimenko on the sixth of August, 2014, the Rosetta spacecraft has carried out close-up observations of the nucleus and coma of this Jupiter family comet. The OSIRIS, the Scientific Imaging Camera System onboard the Rosetta spacecraft, which consists of a narrow-angle and wide-angle camera (NAC and WAC), has made detailed investigations of the physical properties and surface morphology of the comet. From May 2015, the southern hemisphere of the comet became visible and the adaptical resolution was high enough for us to do a detailed analysis of the surface. Previous work shows that the fine particle deposits are the most extensive geomorphological unit in the northern hemisphere. On the contrary, southern hemisphere is dominated by rocky-like stratified terrain. The southern hemisphere of the nucleus surface reveals quite different morphologies from the northern hemisphere. This could be linked to the different insolation condition between northern and southern hemisphere. As a result, surface geological processes could operate with a diverse intensity on the different sides of the comet nucleus. In this work, we provide the geomorphological maps of the southern hemisphere with linear features and geological units identified. The geomorphological maps described in this study allow us to understand the processes and the origin of the comet.

Interaction of Comets and the Solar Wind

NASA Technical Reports Server (NTRS)

Wagner, William (Technical Monitor); Raymond, John C.

2003-01-01

We had originally planned to analyze UVCS observations of Comet Machholz, but we obtained higher quality observations of Comet Kudo-Fujikawa in January 2003 at its 0.19 AU perihelion. Besides a large and rapidly increasing water outgassing rate, we detected a bright tail in doubly ionized carbon. The amount of carbon was greater than could be accounted for by GO photodissociation, and we attribute the carbon to evaporation of organics from dust. A spectacular disconnection event was apparent in the C III tail, and it coincides within the uncertainties with the position of the heliospheric current sheet. A paper is in press in Science, and it will be the subject of a press release. We are also analyzing two sungrazing comets. Comet C/2001 C2 shows evidence for sub-fragments and for a very long lasting source of neutrals, which we tentatively identify as evaporation of pyroxene dust grains. Comet C/2002 S2 shows a sudden 2 magnitude drop in optical brightness and an equally sudden recovery. UVCS observations during that time show a steadily increasing outgassing rate. We have derived solar wind densities for both comets, but we are still sorting out the ambiguities involving the fragmentation and optical behavior. We are collaborating with Philippe Lamy on the LASCO measurements.

Learned modesty and the first lady's comet: a commentary on Caroline Herschel (1787) 'An account of a new comet'.

PubMed

Winterburn, Emily

2015-04-13

Long before women were allowed to become Fellows of the Royal Society, or obtain university degrees, one woman managed to get her voice heard, her discovery verified and her achievement celebrated. That woman was Caroline Herschel, who, as this paper will discuss, managed to find ways to fit comet discoveries into her domestic life, and present them in ways that were socially acceptable. Caroline lived in a time when strict rules dictated how women (and men) should behave and present themselves and their work. Caroline understood these rules, and used them carefully as she announced each discovery, starting with this comet which she found in 1786. Caroline discovered her comets at a time when astronomers were mainly concerned with position, identifying where things were and how they were moving. Since her discoveries, research has moved on, as astronomers, using techniques from other fields, and most recently sending experiments into space, have learned more about what comets are and what they can tell us about our solar system. Caroline's paper marks one small, early step in this much bigger journey to understand comets. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

The global morphology of the solar wind interaction with comet Churyumov-Gerasimenko

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

Mendis, D. A.; Horányi, M.

2014-10-10

The forthcoming Rosetta-Philae mission to comet 67P/Churyumov-Gerasimenko provides a novel opportunity to observe the variable nature of the solar wind interaction with a comet over an extended range of heliocentric distance. We use a simple analytical one-dimensional MHD model to estimate the sizes of the two most prominent features in the global structure of the solar wind interaction with a comet. When the heliocentric distance of the comet reaches d ≤ 1.51 AU, we expect a sharp shock to be observed, whose size would increase monotonically as the comet approaches the Sun, reaching a value ≅ 15, 000 km atmore » perihelion (d ≅ 1.29 AU). Upstream of the shock, we expect the velocity-space distribution of the picked up cometary ions to be essentially gyrotropic. A well-defined ionopause is predicted when d ≤1.61 AU, though its size is expected to be only ≅25 km at perihelion, and it is expected to be susceptible to the 'flute' instability due to its small size. Consequently, we expect the magnetic field to penetrate all the way to the surface of the nucleus. We conclude with a brief discussion of the response of the comet's plasma environment to fast temporal variations in the solar wind.« less

Further characterization of benzo[a]pyrene diol-epoxide (BPDE)-induced comet assay effects.

PubMed

Bausinger, Julia; Schütz, Petra; Piberger, Ann Liza; Speit, Günter

2016-03-01

The present study aims to further characterize benzo[a]pyrene diol-epoxide (BPDE)-induced comet assay effects. Therefore, we measured DNA effects by the comet assay and adduct levels by high-performance liquid chromatography (HPLC) in human lymphocytes and A549 cells exposed to (±)-anti-benzo[a]pyrene-7,8-diol 9,10-epoxide [(±)-anti-BPDE] or (+)-anti-benzo[a]pyrene-7,8-diol 9,10-epoxide [(+)-anti-BPDE]. Both, the racemic form and (+)-anti-BPDE, which is the most relevant metabolite with regard to mutagenicity and carcinogenicity, induced DNA migration in cultured lymphocytes in the same range of concentrations to a similar extent in the alkaline comet assay after exposure for 2h. Nevertheless, (+)-anti-BPDE induced significantly enhanced DNA migration after 16 and 18h post-cultivation which was not seen in response to (±)-anti-BPDE. Combination of the comet assay with the Fpg (formamidopyrimidine-DNA glycosylase) protein did not enhance BPDE-induced effects and thus indicated the absence of Fpg-sensitive sites (oxidized purines, N7-guanine adducts, AP-sites). The aphidicolin (APC)-modified comet assay suggested significant excision repair activity of cultured lymphocytes during the first 18h of culture after a 2 h-exposure to BPDE. In contrast to these repair-related effects measured by the comet assay, HPLC analysis of stable adducts did not reveal any significant removal of (+)-anti-BPDE-induced adducts from lymphocytes during the first 22h of culture. On the other hand, HPLC measurements indicated that A549 cells repaired about 70% of (+)-anti-BPDE-induced DNA-adducts within 22h of release. However, various experiments with the APC-modified comet assay did not indicate significant repair activity during this period in A549 cells. The conflicting results obtained with the comet assay and the HPLC-based adduct analysis question the real cause for BPDE-induced DNA migration in the comet assay and the reliability of the APC-modified comet assay for the determination of DNA excision repair activity in response to BPDE in different cell types. © The Author 2015. Published by Oxford University Press on behalf of the UK Environmental Mutagen Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

The morphology of cometary nuclei

NASA Astrophysics Data System (ADS)

Keller, H. U.; Jorda, L.

The sudden appearance of a bright comet stretching over a large part of the night sky must have been one of the most awesome phenomena for early humans watching the sky. The nature of comets remained obscure well into the Middle Ages. Only with the introduction of astronomical techniques and analyses in Europe was the parallax of a comet determined by Tycho Brahe for the first time. He proved that comets are not phenomena of the Earth's atmosphere but are farther away than the Moon; in other words they are interplanetary objects. Later Kepler first predicted that comets follow straight lines, then Hevelius suggested parabolic orbits roughly a hundred years later. It was Halley who suggested that the comets of the years 1531, 1607 and 1682 were apparitions of one and the same comet that would return again in 1758. The success of this prediction made it clear that comets are members of our Solar System. While it was now established that periodic comets are objects of the planetary system, their origin and nature continued to be debated. Were they formed together with the planets from the solar nebula (Kant) or were they of extrasolar origin as suggested by Laplace? This debate lasted for 200 years until well into the second half of the last century. Öpik (1932) suggested that a cloud of comets surrounded our Solar System. This hypothesis was quantified and compared to the observed distribution of orbital parameters (essentially the semi-major axes) of new comets by Oort (1950) (Section 2.1). Comets are scattered into the inner Solar System by perturbations caused by galactic tides, passing stars and large molecular clouds. The Oort cloud would have a radius of 2 105AU, a dimension comparable to the distances of stars in our neighbourhood. The lifetime (limited by decay due to activity and by perturbations caused by encounters with planets) even of the new comets on almost parabolic orbits and typical periods of the order of 106 years is short compared to the age of the planetary system (4.5 Gy). Therefore, observed comets could only recently have arrived on their orbits dipping inside the inner Solar System. This reservoir of comets must have been established during the formation process of the planetary system itself. Cometesimals were agglomerated from interstellar/interplanetary gas and dust and scattered out of the inner Solar System by the giant outer planets (Section 2.3). This scheme implies that a central part of a comet, its nucleus, is stable enough to survive these perturbations. It must also be stable enough to pass the vicinity of the sun for many times in the case of a short-period comet. Comets are bright and large when they are close to the sun and fade quickly when they recede beyond about 2AU. Only with the advent of photography and large astronomical telescopes could a comet be followed until it becomes a starlike point source. What makes comets active near the Sun, blowing their appearances up to the order of 105 km? Bright comets often develop tails two orders of magnitude longer. In an attempt to explain the cometary appearance, Bredichin (1903) introduced a mechanical model where repulsive forces drive the particles away from a central condensation. Spectroscopy revealed that dust grains reflect the solar irradiation. In addition, simple molecules, radicals and ions were found as constituents of the cometary coma and tail. The nature of the central condensation remained mysterious for a long time because of the observational dilemma. When the comet is close to the Earth and therefore to the Sun the dense coma obscures the view into its centre. When activity recedes the comet is too far away and too dim for detailed observations of its central condensation. During the middle of the nineteenth century the connection between comets and meteor streams was established. Schiaparelli (1866) calculated the dispersion of cometary dust within the orbital plane. From this time on the perception that the central condensations of comets were agglomerations of dust particles prevailed for about a century. The gas coma was explained by desorption of molecules from dust particles with large surfaces (Levin 1943). The storage of highly reactive radicals (most observed species (CN, CH, NH2, etc.) were of this category) posed a major difficulty to be explained. The inference that these radicals should be dissociation products of stable parent molecules (such as (CN)2, CH4, NH3, etc.) by Wurm (1934, 1935, 1943) led to our present understanding that these molecules are stored as ices within the central nucleus of a comet. Whipple (1950a,b) combined the astrometrical observations of changes of the orbital periods of comets with the existence of an icy cometary nucleus. The sublimation of ices cause reactive (rocket) non-gravitational forces that increase or decrease the orbital period of an active comet according to the sense of rotation of its nucleus. Evidence in support of the icy conglomerate nucleus became more and more compelling by the derived high gas production rates that could not be stored by adsorption on dust grains (Biermann and Trefftz 1964, Huebner 1965, Keller 1976a,b) and by the same account by the large quantities of dust moving into the cometary tail (Finson and Probstein 1968b). The `sand bank' model (Lyttleton 1953) was clearly dismissed in favour of a solid icy nucleus. Its formation and origin could now be explored. While there was some knowledge about the chemical composition of the nucleus, its physical properties, even the basic ones like size, shape and mass, remained largely unknown because the nucleus could not be observed. Early attempts to derive the nucleus size from the `nuclear' magnitudes of comets at large heliocentric distances while they are inactive (Roemer 1966a,b) led to a systematic overestimation of the size because their residual activity could not be eliminated. The advent of modern detectors and large ground-based telescopes revealed that most comets display residual activity or clouds of dust grains around their nuclei. Taking the residual signal into account (mostly using simple models for the brightness distribution) the size estimates of the nuclei could be improved. The (nuclear) magnitude of a comet depends on the product of its albedo and cross-section. Only in a few cases could the albedo and size of a cometary nucleus be separated by additional observation of its thermal emission at infrared wavelengths. By comparison with outer Solar System asteroids Cruikshank et al. (1985) derived a surprisingly low albedo of about 0.04. A value in clear contradiction to the perception of an icy surface but fully confirmed by the first resolved images of a cometary nucleus during the flybys of the Vega and Giotto spacecraft of comet Halley (Sagdeev et al. 1986, Keller et al. 1986). The improvements of radar techniques led to the detection of reflected signals and finally to the derivation of nuclear dimensions and rotation rates. The observations, however, are also model dependent (rotation and size are similarly interwoven as are albedo and size) and sensitive to large dust grains in the vicinity of a nucleus. As an example, Kamoun et al. (1982) determined the radius of comet Encke to 1.5 (2.3, 1.0) km using the spin axis determination of Whipple and Sekanina (1979). The superb spatial resolution of the Hubble Space Telescope (HST) is not quite sufficient to resolve a cometary nucleus. The intensity distribution of the inner coma, however, can be observed and extrapolated toward the nucleus based on models of the dust distribution. If this contribution is subtracted from the central brightness the signal of the nucleus can be derived and hence its product of albedo times cross-section (Lamy and Toth 1995, Rembor 1998, Keller and Rembor 1998; Section 4.3). It has become clear that cometary nuclei are dark, small, often irregular bodies with dimensions ranging from about a kilometre (comet Wirtanen, the target of the Rosetta comet rendezvous mission) to about 50 km (comet Hale- Bopp, comet P/Schwassman-Wachmann 1). Their albedos are very low, about 0.04. Their shapes are irregular, axes ratios of 2:1 are often derived. Even though comets are characterized by their activity, in most cases only a small fraction of the nuclear surface (in some cases less than 1%) is active. An exception seems to be comet P/Wirtanen where all its surface is required to be active in order to explain its production rates (Rickman and Jorda 1998). The detection of trans-Neptunian objects (TNOs) in the Kuiper belt (Jewitt and Luu 1993) reveals a new population of cometary bodies with dimensions an order of magnitude bigger (100 km and larger) than the typical comet observed in the inner planetary system. Little is known about the extent, density, size distribution and physical characteristics of these objects. This region is supposedly the reservoir for short-period comets, manly those controlled by Jupiter (Jupiter family comets). Our present concept of a cometary nucleus has been strongly influenced by the first pictures of the nucleus of comet Halley achieved during the Giotto flyby in 1986. While this revelation seems to be confirmed as typical by modern observations it carries the danger of prototyping new observational results and inferences. Missions and spacecraft are already on their way (Deep Space, Contour, Stardust, Deep Impact) or in preparation (Rosetta) to diversify our knowledge. The morphology of cometary nuclei is determined by their formation process in the early solar nebula, their dynamics and evolution. The physics of the processes leading to their apparent activity while approaching the Sun are still obscure in many details but determine the small- and intermediate-scale morphology. The large-scale morphology, the shape, of a cometary nucleus is determined by its fragility and inner structure and by its generally complex rotational state. These topics will be reviewed in the following sections. Chemical and compositional aspects will be only discussed where they are important in the framework of the physical evolution of cometary nuclei. More details are given in Chapter 53. A brief survey of the current modelling efforts is given. The fate of cometary nuclei and their decay products follows. A summary and outlook ends this chapter on the morphology of cometary nuclei.

Small is different: RPC observations of a small scale comet interacting with the solar wind

NASA Astrophysics Data System (ADS)

Nilsson, Hans; Burch, James L.; Carr, Christopher M.; Eriksson, Anders I.; Glassmeier, Karl-Heinz; Henri, Pierre; Rosetta Plasma Consortium Team

2016-10-01

Rosetta followed comet 67P from low activity at more than 3 AU heliocentric distance to peak activity at perihelion and then out again. We study the evolution of the dynamic plasma environment using data from the Rosetta Plasma Consortium (RPC). Observations of cometary plasma began in August 2014, at a distance of 100 km from the comet nucleus and at 3.6 AU from the Sun. As the comet approached the Sun, outgassing from the comet increased, as did the density of the cometary plasma. Measurements showed a highly heterogeneous cold ion environment, permeated by the solar wind. The solar wind was deflected due to the mass loading from newly added cometary plasma, with no discernible slowing down. The magnetic field magnitude increased significantly above the background level, and strong low frequency waves were observed in the magnetic field, a.k.a. the "singing comet". Electron temperatures were high, leading to a frequently strongly negative spacecraft potential. In mid to late April 2015 the solar wind started to disappear from the observation region. This was associated with a solar wind deflection reaching nearly 180°, indicating that mass loading became efficient enough to form a solar wind-free region. Accelerated water ions, moving mainly in the anti-sunward direction, kept being observed also after the solar wind disappearance. Plasma boundaries began to form and a collisionopause was tentatively identified in the ion and electron data. At the time around perihelion, a diamagnetic cavity was also observed, at a surprisingly large distance from the comet. In late 2016 the solar wind re-appeared at the location of Rosetta, allowing for studies of asymmetry of the comet ion environment with respect to perihelion. A nightside excursion allowed us to get a glimpse of the electrodynamics of the innermost part of the plasma tail. Most of these phenomena are dependent on the small-scale physics of comet 67P, since for most of the Rosetta mission the solar wind - comet atmosphere interaction region is smaller than the pickup ion gyroradius in the undisturbed solar wind.

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;

Comets as parent bodies of CI1 carbonaceous meteorites and possible habitats of ice-microbes

NASA Astrophysics Data System (ADS)

Wickramasinghe, N. Chandra; Wickramasinghe, Janaki T.; Wallis, Jamie; Hoover, Richard B.; Rozanov, Alexei Y.

2011-10-01

Recent studies of comets and cometary dust have confirmed the presence of biologically relevant organic molecules along with clay minerals and water ice. It is also now well established by deuterium/hydrogen ratios that the CI1 carbonaceous meteorites contain indigenous extraterrestrial water. The evidence of extensive aqueous alteration of the minerals in these meteorites led to the hypothesis that water-bearing asteroids or comets represent the parent bodies of the CI1 (and perhaps CM2) carbonaceous meteorites. These meteorites have also been shown to possess a diverse array of complex organics and chiral and morphological biomarkers. Stable isotope studies by numerous independent investigators have conclusively established that the complex organics found in these meteorites are both indigenous and extraterrestrial in nature. Although the origin of these organics is still unknown, some researchers have suggested that they originated by unknown abiotic mechanisms and may have played a role in the delivery of chiral biomolecules and the origin of life on Early Earth. In this paper we review these results and investigate the thermal history of comets. We show that permanent as well as transient domains of liquid water can be maintained on a comet under a plausible set of assumptions. With each perihelion passage of a comet volatiles are preferentially released, and during millions of such passages the comet could shed crustal debris that may survive transit through the Earth's atmosphere as a carbonaceous meteorite. We review the current state of knowledge of comets and carbonaceous meteorites. We also present the results of recent studies on the long-term viability of terrestrial ice-microbiota encased in ancient glacial ice and permafrost. We suggest that the conditions which have been observed to prevail on many comets do not preclude either survivability (or even the active metabolism and growth) of many types of eukaryotic and prokaryotic microbial extremophiles-including algae, cyanobacteria, bacteria and archaea. It is argued that the chemical and morphological biomarkers detected on comets and carbonaceous meteorites can be explained by ancient microbial activity without the need to invoke unknown abiotic production mechanisms.

Are Comets 42P/Neujmin 3 and 53P/Van Biesbroeck Parts of one Comet?

NASA Astrophysics Data System (ADS)

Pittichova, J.; Meech, K. J.; Valsecchi, G. B.; Pittich, E. M.

2003-05-01

We want to present preliminary results of the observations of the physical parameters of comets 42P/Neujmin 3 and 53P/Van Biesbroeck: brightness, nucleus activity, rotation period, light-curve and color changes from our first three optical observing runs (March, and May 2003) at Mauna Kea, using UH 2.2m telescope and Tek2048 CCD camera. Comets 42P/Neujmin 3 and 53P/Van Biesbroeck have very well determined orbits, and their orbital histories are very interesting. Their current orbits are not very similar to each other; however, numerical integrations have shown that both comets had a rather close approach to Jupiter in January 1850, and that, before 1850, the two orbits were nearly identical. Given the extremely low probability of a chance coincidence of the six orbital elements at a given time, the natural conclusion is that the two objects are fragments of a single comet that split sometime in the late 1849 or early 1850. Among the known cases of split periodic comets, this one is peculiar for a number of reasons: 1. the splitting was probably not due to tidal stresses, since the 1850 encounter with Jupiter took place well outside the Roche lobe; 2. it is the only case discovered through a dynamical study; 3. in the only other case of splitting of a Jupiter family comet, that of 3D/Biela, the fragments did not survive for more than a couple of revolutions, whereas in the present case both fragments have passed perihelion more than ten times since the splitting. If these two comets are fragments of a single parent body, then they should show a certain degree of physical and chemical similarity, which we would like to obtain from spectroscopic observation in 2004, when both comets are close to their perihelion. Acknowledgments: Support for this work was provided by NASA Grant No. NAG5-12236 and Scientific Grant Agency VEGA of the Slovak Academy of Sciences, grant No. 2/1005/21.

Dormant Comets in the Near-Earth Asteroid Population

NASA Astrophysics Data System (ADS)

Mommert, Michael; Harris, Alan W.; Mueller, Michael; Hora, Joseph L.; Trilling, David E.; Knight, Matthew; Bottke, William F.; Thomas, Cristina; Delbo', Marco; Emery, Josh P.; Fazio, Giovanni; Smith, Howard A.

2015-11-01

The population of near-Earth objects comprises active comets and asteroids, covering a wide range of dynamical parameters and physical properties. Dormant (or extinct) comets, masquerading as asteroids, have long been suspected of supplementing the near-Earth asteroid (NEA) population. We present a search for asteroidal objects of cometary origin based on dynamical and physical considerations. Our study is based on albedos derived within the ExploreNEOs program and is extended by adding data from NEOWISE and the Akari asteroid catalog. We use a statistical approach to identify asteroids on orbits that resemble those of short-period near-Earth comets using the Tisserand parameter with respect to Jupiter, the aphelion distance, and the minimum orbital intersection distance with respect to Jupiter. We identify a total of 23 near-Earth asteroids from our sample that are likely to be dormant short-period near-Earth comets and, based on a de-biasing procedure applied to the cryogenic NEOWISE survey, estimate both magnitude-limited and size-limited fractions of the NEA population that are dormant short-period comets. We find that 0.3-3.3% of the NEA population with H <= 21, and 9(+2/-5)% of the population with diameters d >= 1 km, are dormant short-period near-Earth comets. We also present an observation program that utilizes the 1.8m Vatican Advanced Technology Telescope (VATT) on Mt. Graham, AZ, to identify dormant comet candidates and search for activity in these objects. Our targets are NEAs on comet-like orbits, based on the dynamical criteria derived in the above study, that are accessible with the VATT (V <= 22). We identify dormant comets based on their optical spectral slope, represented by V-R color measurements, as albedo measurements for most of these objects are not available. For each target we measure and monitor its V magnitude in order to reveal activity outbreaks. We also search for extended emission around our targets using deep imaging and a point-spread-function subtraction technique that allows us to obtain an upper limit on the dust production rate in each target. We present preliminary results from this program. This work is supported in part by funding from the Spitzer Science Center.

Comets as Parent Bodies of CI1 Carbonaceous Meteorites and Possible Habitats of Ice-Microbiota

NASA Technical Reports Server (NTRS)

Wickramasinghe, N. Chandra; Wallis, Daryl H.; Rozanov, Alexei Yu.; Hoover, Richard B.

2011-01-01

Recent studies of comets and cometary dust have confirmed the presence of biologically relevant organic molecules along with clay minerals and water ice. It is also now well established by deuterium/hydrogen ratios that the CI1 carbonaceous meteorites contain indigenous extraterrestrial water. The evidence of extensive aqueous alteration of the minerals in these meteorites led to the hypothesis that water-bearing asteroids or comets represent the parent bodies of the CI1 (and perhaps CM2) carbonaceous meteorites. These meteorites have also been shown to possess a diverse array of complex organics and chiral and morphological biomarkers. Stable isotope studies by numerous independent investigators have conclusively established that the complex organics found in these meteorites are both indigenous and extraterrestrial in nature. Although the origin of these organics is still unknown, some researchers have suggested that they originated by unknown abiotic mechanisms and may have played a role in the delivery of chiral biomolecules and the origin of life on Early Earth. In this paper we review these results and investigate the thermal history of comets. We show that permanent as well as transient domains of liquid water can be maintained on a comet under a plausible set of assumptions. With each perihelion passage of a comet volatiles are preferentially released, and during millions of such passages the comet could shed crustal debris that may survive transit through the Earth s atmosphere as a carbonaceous meteorite. We review the current state of knowledge of comets and carbonaceous meteorites. We also present the results of recent studies on the long-term viability of terrestrial ice-microbiota encased in ancient glacial ice and permafrost. We suggest that the conditions which have been observed to prevail on many comets do not preclude either survivability (or even the active metabolism and growth) of many types of eukaryotic and prokaryotic microbial extremophiles-including algae, cyanobacteria, bacteria and archaea. It is argued that the chemical and morphological biomarkers detected on comets and carbonaceous meteorites can be explained by ancient microbial activity without the need to invoke unknown abiotic production mechanisms.

Low encounter speed comet COMA sample return missions

NASA Technical Reports Server (NTRS)

Tsou, P.; Yen, C. W.; Albee, A. L.

1994-01-01

Comets, being considered the most primitive bodies in the solar system, command the highest priority among solar-system objects for studying solar nebula evolution and the evolution of life through biogenic elements and compounds. The study of comets, and more especially, of material from them, provides an understanding of the physical, chemical, and mineralogical processes operative in the formation and earliest development of the solar systems. These return samples will provide valuable information on comets and serve as a rosetta stone for the analytical studies conducted on interplanetary dust particles over the past two decades, and will provide much needed extraterrestrial samples for the planetary materials community since the Apollo program. Lander sample return missions require rather complex spacecraft, intricate operations, and costly propulsion systems. By contrast, it is possible to take a highly simplified approach for sample capture and return in the case of a comet. In the past, we have considered Earth free-return trajectory to the comet, in which passive collectors intercept dust and volatiles from the cometary coma. However, standard short period cometary free-return trajectories results in the comet to the spacecraft encounter speeds in the range of 10 km/s. At these speeds the kinetic energy of the capture process can render significant modification of dust structure, change of solid phase as well as the lost of volatiles components. This paper presents a class of new missions with trajectories with significant reduction of encounter speeds by incorporating gravity assists and deep space maneuvering. Low encounter speed cometary flyby sample return will enable a marked increase in the value of the return science. Acquiring thousands of samples from a known comet and thousands of images of a comet nucleus would be space firsts. Applying new approach in flight mechanics to generate a new class of low encounter speed cometary sample return trajectories opens new possibilities in science. A systematic search of trajectories for the first decade of the twenty-first century will be made. The target encounter speed is for less than 7 km/s to short period comets.

Analysis of Polarimetric, Photometric, and Spectroscopic Observations of Comet C/1996 Q1 (Tabur)

NASA Astrophysics Data System (ADS)

Kiselev, N. N.; Jockers, K.; Rosenbush, V. K.; Korsun, P. P.

2001-11-01

We present the imaging polarimetry and photometry of Comet C/1996 Q1 (Tabur) obtained on October 10, 1996, with a two-channel focal reducer attached to the 2-m Pik Terskol Observatory telescope through blue (λ4430/44 Å) and red (λ6420/26 Å) continuum filters and through a λ6620/59 Å filter that isolated the NH_2(0.7.0) band. We analyze the λ3600-9300 Å long-slit spectrograms of the comet taken on October 5-6, 1996, with the 2.6-m Crimean Astrophysical Observatory telescope. The NH_2(0.8.0) λ6408 Å emission and an unidentified λ6428 Å emission were found to fall within the pass band of the red filter. The blue filter transmits weak unidentified emissions at λ4424-4444 Å and partially C_2(λ4360 Å). Correction for the depolarizing effect of molecular emissions resulted in an increase of the dust polarization by 2-4% in the near-nucleus region and by almost a factor of 2 in the outer coma regions. However, the polarization and color differences between different coma regions remained even after correction for the contribution of emissions. We found no dust polarization difference between the gas comet Tabur and the dust comet C/1988 A1 (Liller), which are believed to be fragments of a common parent comet. The NH_2coma was found to be elongated perpendicular to the comet radius vector. The causes of the spatial asymmetry in the NH_2molecular distribution are yet to be established. We study the evolution of activity and the spatial distribution of dust brightness, polarization, and color in the comet. We consider a taxonomic classification of gas and dust comets according to dust polarization properties. The polarization differences between dust and gas comets at large phase angles are most likely related both to the actual differences in dust and to the effect of molecular emissions, nuclear gas- and dust-production rates and to the evolution of grain properties with distance from the nucleus.

MESSENGER's Special Delivery: Gas and Dust Production from Comets 2P/Encke and C/2012 S1 (ISON) at Small Heliocentric Distances

NASA Astrophysics Data System (ADS)

Fernandez, Y. R.; Vervack, R. J., Jr.; Knight, M. M.; McCandliss, S. R.; Dello Russo, N.; Feldman, P.; Lisse, C. M.; Tamblyn, P.

2017-12-01

Observations of comets when they are close to the Sun can potentially reveal interesting aspects of their behavior, composition, and structure, thanks to the rapid change both of seasons on the nucleus and of the local insolation environment. However this is typically a difficult time to make observations from Earth, so studies of comets that are near the Sun generally require special facilities. In late 2013, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft observed comets C/2012 S1 (ISON) and 2P/Encke from its vantage point at Mercury when both comets were poorly located for most Earth-based telescopes. The observations included visible-wavelength, multi-filter imaging as well as ultraviolet spectroscopy, using the MDIS and MASCS instruments. Both comets were observed down to about 0.3 AU from the Sun. In Encke's case, it was followed through perihelion, which has rarely been done before. In ISON's case, it was observed while rapidly changing in the days preceding its catastrophic breakup just before perihelion. The data let us constrain the dust and gas production rates of both comets over several weeks, and we can investigate how the rates change with time, rotational phase, and heliocentric distance. We will present preliminary analyses of this time-series photometry and spectroscopy, and compare results to other studies of these comets' behavior when they are farther from the Sun. This work is supported by NASA grant NNX16AJ02G, and makes use of data from the Planetary Data System.

Will comet 209P/LINEAR generate the next meteor storm?

NASA Astrophysics Data System (ADS)

Ye, Quanzhi; Wiegert, Paul A.

2014-02-01

Previous studies have suggested that comet 209P/LINEAR may produce strong meteor activity on Earth on 2014 May 24; however, exact timing and activity level is difficult to estimate due to the limited physical observations of the comet. Here, we reanalyse the optical observations of 209P/LINEAR obtained during its 2009 apparition. We find that the comet is relatively depleted in dust production, with Afρ at 1 cm level within eight months around its perihelion. This feature suggested that this comet may be currently transitioning from a typical comet to a dormant comet. Syndyne simulation shows that the optical cometary tail is dominated by larger particles with β ˜ 0.003. Numerical simulations of the cometary dust trails confirm the arrival of particles on 2014 May 24 from some of the 1798-1979 trails. The nominal radiant is at RA 122° ± 1°, Dec. 79° ± 1° (J2000) in the constellation of Camelopardalis. Given that the comet is found to be depleted in dust production, we concluded that a meteor storm (ZHR ≥ 1000) may be unlikely. However, our simulation also shows that the size distribution of the arrived particles is skewed strongly to larger particles. Coupling with the result of syndyne simulation, we think that the event, if detectable, may be dominated by bright meteors. We encourage observers to monitor the expected meteor event as it will provide us with rare direct information on the dynamical history of 209P/LINEAR which is otherwise irretrievably lost.

Where is the Oort Cloud Located?

NASA Astrophysics Data System (ADS)

Fernandez, Julio

2013-05-01

Abstract (2,250 Maximum Characters): The Oort cloud is the outermost population of the solar system. Our knowledge of its size and space structure relies on the single natural probe we have so far available, namely the new comets that are steadily injected by the tidal force of the galactic disk and passing stars. To learn about the places where new comets come from, it is essential to compute good original orbits and to understand how these may be affected by nongravitational (ng) forces. Distant comets (perihelion distance q > ~3 au) are found to be little affected by ng forces, unless they are very small (radii < ~ a few tenths km) and/or hyperactive (due to a highly volatile substance like CO or CO2). We discuss these problems in this presentation, and try to assemble a consistent picture of the Oort cloud, consisting of the inner Oort cloud (IOC) and the outer Oort cloud (OOC). The distribution of original energies of distant new comets (perihelion distances q> ~3 au presumably little affected by nongravitational forces) show that the boundary between the IOC and the OOC lies around an energy 30 × 10-6 au-1 or a semimajor axis ~ 3.3 × 104 au. New comets from the OOC show an uniform distribution of perihelion distances q, as expected for a thermalized Oort cloud comet population, while comets from the IOC show an increase of the rate of perihelion passages with q, as expected for comets whose perihelion distances evolve slowly under the action of external pertubers, and have to overcome the Jupiter-Saturn barrier to reach the inner planetary region.

The end states of long-period comets and the origin of Halley-type comets

NASA Astrophysics Data System (ADS)

Fernández, Julio A.; Gallardo, Tabaré; Young, Juan D.

2016-09-01

We analyse a sample of 73 old long-period comets (LPCs) (orbital periods 200 < P < 1000 yr) with perihelion distances q < 2.5 au, discovered in the period 1850-2014. We cloned the observed comets and also added fictitious LPCs with perihelia in the Jupiter's zone. We consider both a purely dynamical evolution and a physico-dynamical one with different physical lifetimes. We can fit the computed energy distribution of comets with q < 1.3 au to the observed one only within the energy range 0.01 < x < 0.04 au-1 (or periods 125 < P < 1000 yr), where the `energy' is taken as the inverse of the semimajor axis a, namely x ≡ 1/a. The best results are obtained for physical lifetimes of about 200-300 revolutions (for a comet with a standard q = 1 au). We find that neither a purely dynamical evolution, nor a physico-dynamical one can reproduce the long tail of larger binding energies (x ≳ 0.04 au-1) that correspond to most Halley-type comets (HTCs) and Jupiter-family comets. We conclude that most HTCs are not the end states of the evolution of LPCs, but come from a different source, a flattened one that we identify with the Centaurs that are scattered to the inner planetary region from the trans-Neptunian belt. These results also show that the boundary between LPCs and HTCs should be located at an energy x ˜ 0.04 au-1 (P ˜ 125 yr), rather than the conventional classical boundary at P = 200 yr.

Multi-fluid model of a sun-grazing comet in the rapidly ionizing, magnetized low corona

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

Jia, Y.-D.; Russell, C. T.; Liu, W.

2014-11-20

Two Sun-grazing comets were recently imaged in the low solar corona by space telescopes in unprecedented detail, revealing a wide range of new phenomena. This sparked growing interest in the interaction of comets with the coronal plasma and magnetic field and their diagnostic potential as solar probes. However, interpretation of such rich observational data requires profound understanding of relevant physical processes in an unexplored regime. Here advanced numerical modeling can provide critical clues. To this end, we present a prototype, multi-fluid, magnetohydrodynamic model of a steady-state comet in the low solar corona. These simulation results are compared with previously modeledmore » comets in the solar wind environment. By inspecting their projection and column densities, we find a dominance of O{sup 6+} ions in the cometary tail, which can explain the observed extreme ultraviolet emission. The tail is found to be comparable to recent EUV images of these comets. In addition, the comet tail appears wider when the observer's line of sight is perpendicular rather than parallel to the local magnetic field. This is opposite to the trend in the interplanetary space permeated in the solar wind, because the ratio between dynamic pressure and magnetic pressure is an order of magnitude smaller than at 1 AU. On the other hand, we find that iron ions in the comet head build up to a density comparable to that of oxygen ions, but are unlikely to form a visible tail because of the shorter mean free paths of the neutrals.« less

U.S. EPA, Pesticide Product Label, TOUGH STAIN REMOVING INSTITUTIONAL COMET CLEANSER WITH CHLORINOL G, 02/10/1975

EPA Pesticide Factsheets

2011-04-21

... 1i~~~~~M~T"~C~H~~~~R~I~NO~L~~O~~~~~iil i _L~=_===7 USE COMET ~ ~ FOR THESE TOUGH ~ ... t\\t'6\\\\$ , USE COMET FOR THESE TOUGH ...

Changing Speed of Comets

ERIC Educational Resources Information Center

Follows, Mike

2003-01-01

It is shown that highly elliptical orbits, such as those of comets, can be explained well in terms of energy rather than forces. The principle of conservation of energy allows a comet's velocity to be calculated at aphelion and perihelion. An example asks students to calculate whether they can run fast enough to escape from a small asteroid.…

Piece of a Comet

NASA Technical Reports Server (NTRS)

2006-01-01

This image shows a comet particle collected by the Stardust spacecraft. The particle is made up of the silicate mineral forsterite, also known as peridot in its gem form. It is surrounded by a thin rim of melted aerogel, the substance used to collect the comet dust samples. The particle is about 2 micrometers across.

The Geology of Comet 19/P Borrelly

NASA Technical Reports Server (NTRS)

Britt, D. T.; Boice, D. C; Buratti, B. J.; Hicks, M. D.; Nelson, R. M.; Oberst, J.; Sandel, B. R.; Soderblom, L. A.; Stern, S. A.; Thomas, N.

2002-01-01

The Deep Space One spacecraft flew by Comet 19P/Borrelly on September 22, 2001 and returned a rich array of imagery with resolutions of up to 48 m/pixel. These images provide a window into the surface structure, processes, and geological history of a comet. Additional information is contained in the original extended abstract.

Photometry of the comet Halley : solar analogs selected along the path (November 1985 - Mat 1986)

NASA Astrophysics Data System (ADS)

Fracassini, M.; Pasinetti, L. E.

1985-11-01

108 solar analogs are selected within a strip along the path of the comet Halley (Δδ ≅ ±10°) for photometric observations of the comet from November 1985 to May 1986. Some criteria in the UBV and Geneva photometric systems were adopted for this selection.

Lunar and Planetary Science XXXV: Asteroids, Meteors, Comets

NASA Technical Reports Server (NTRS)

2004-01-01

The session Asteroids, Meteors, Comets includes the following topics: 1) Where Some Asteroid Parent Bodies; 2) The Collisional Evolution of the Main Belt Population; 3) On Origin of Ecliptic Families of Periodic Comets; 4) Mineralogy and Petrology of Laser Irradiated Carbonaceous Chondrite Mighei; and 5) Interaction of the Gould Belt and the Earth.

A Meteorite Dropping Superbolide from the Catastrophycally Disrupted Comet C1919Q2 Metcalf: A Pathway for Meteorites from Jupiter Family Comets

NASA Astrophysics Data System (ADS)

Trigo-Rodríguez, J. M.; Madiedo, J. M.; Williams, I. P.; Castro-Tirado, A. J.; Llorca, J.; Vítek, S.; Jelínek, M.

2009-03-01

A meter-sized meteoroid probably produced during the disintegration of comet C1919Q2 Metcalf was observed producing a -18 magn. bolide (MNRAS, in press).The progenitor meteoroid was sufficiently large and of high enough tensile strength to produce meteorites.

Study of Comets Composition and Structure

NASA Astrophysics Data System (ADS)

Khalaf, S. Z.; Selman, A. A.; Ali, H. S.

2008-12-01

The present paper focuses on the nature of the different interactions between cometary nucleus and tail with solar wind. The dynamics of the comet will impose many features that provide unique behavior of the comet when entering the solar system. These features are reviewed in this paper and few investigations are made. The calculations made in this work represent the analysis and interpretation of the different features of the comet, such as perihelion and eccentricity dependence on the gas production rate, and the dependence of the latter on the composition of the comet nucleus. The dependences of the heliocentric, bow shock, contact surface, and stand-off distances with gas production rate for many types of comets that cover linear and non-linear types are studied in this work. Important results are obtained which indicated the different physical interactions between cometary ions and solar wind. Furthermore, the important relation between mean molecular weight and gas production rate are analyzed and studied in this work and a conclusion is made that, as the gas production rate increases, the mean molecular weight will decrease exponentially. A detailed discussion for this unique relation is given.

The enigmatic object 2201 Oljato - Is it an asteroid or an evolved comet?

NASA Technical Reports Server (NTRS)

Mcfadden, Lucy A.; Cochran, Anita L.; Barker, Edwin S.; Cruikshank, Dale P.; Hartmann, William K.

1993-01-01

The orbital properties of near-earth object 2201 have been associated with meteor showers, and its modeled orbital evolution is chaotic - a property which might indicate a history related to comets. Telescopic observations of its visible and near-infrared spectral reflectance, broad-band visible and near-infrared photometry, infrared radiometric measurements, and radar echoes are reported here from two apparitions, 1979 and 1983. This asteroid has a high radiometric albedo, a property not associated with comet nuclei. In certain wavelength regimes it is classified as an S-type asteroid, in others, an E-type, but its overall spectral reflectance is not typical of either taxonomic type, and neither type is thought of as cometlike. Unexpectedly high ultraviolet reflectance at the 1979 apparition was suggested to be the result of residual outgassing as in a comet. The UV photometric data are modeled as fluorescent emission from neutral species found in comets. The resulting calculations indicate a plausible value for OH and CN emission at 0.3085 and 0.38 micron relative to the observed range of active comets.

Comet 252P/LINEAR: Born (Almost) Dead?

NASA Astrophysics Data System (ADS)

Ye, Quan-Zhi; Brown, Peter G.; Wiegert, Paul A.

2016-02-01

Previous studies have revealed Jupiter-family comet 252P/LINEAR as a comet that was recently transported into the near-Earth object (NEO) region in ∼1800 AD yet only being weakly active. In this Letter, we examine the “formed (almost) dead” hypothesis for 252P/LINEAR using both dynamical and observational approaches. By statistically examining the dynamical evolution of 252P/LINEAR over a period of 107 years, we find the median elapsed residency in the NEO region to be 4 × 102 years, which highlights the likelihood of 252P/LINEAR as an (almost) first-time NEO. With available cometary and meteor observations, we find the dust production rate of 252P/LINEAR to be on the order of 106 kg per orbit since its entry to the NEO region. These two lines of evidence support the hypothesis that the comet was likely to have formed in a volatile-poor environment. Cometary and meteor observations during the comet's unprecedented close approach to the Earth around 2016 March 21 would be useful for understanding of the surface and evolutionary properties of this unique comet.

Observations of the Rigollet Comet from Korea and Japan

NASA Astrophysics Data System (ADS)

Lee, Ki-Won; Mihn, Byeong-Hee; Ahn, Young Sook; Kim, Bong-Gyu

2014-03-01

Since Rigollet first discovered a comet in 1939, many follow-up observations have been made, particularly in Europe. It is now known that the Rigollet comet is identical with the one observed by Herschel in 1788, and thus it is now called 35P/1939 O1 or the Herschel-Rigollet comet. Yumi, a Japanese astronomer, also observed the Rigollet comet in Korea using a 6-inch refractor telescope, and published his data in two Japanese journals (Bulletin of the Observatory of the Government-General of Korea and Publication of the Lecture on Meteorology). In his paper, Yumi also referred to observations by Hirose and Kanda in Japan. However, their works have not been given attention by international society. In this study, we analyze the observation data of Yumi and present preliminary orbital elements using it with a modified Gauss method. We expect that this study will be used to refine the orbital elements of the Rigollet comet by orbital-calculation experts. For that reason, we have also transcribed all the observational data presented by Yumi.

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.

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.

VizieR Online Data Catalog: 18-cm OH lines in comets (Crovisier+, 2002)

NASA Astrophysics Data System (ADS)

Crovisier, J.; Colom, P.; Gerard, E.; Bockelee-Morvan, D.; Bourgois, G.

2002-10-01

Since the apparition of comet Kohoutek 1973 XII, the 18-cm lines of the OH radical have been systematically observed in a number of comets with the Nancay radio telescope. Between 1973 and 1999, 52 comets have been successfully detected. This allowed an evaluation of the cometary water production rates and their evolution with time, as well as a study of several physical processes such as the excitation mechanisms of the OH radio lines, the expansion of cometary atmospheres, their anisotropy in relation to non-gravitational forces, and the Zeeman effect in relation to the cometary magnetic field. Part of these observations and their analysis have already been published. The bulk of the results are now organized in a data base. The present paper is a general presentation of the Nancay cometary data base and a more specific description of the observations of 53 cometary apparitions between 1982 and 1999. Comets observed before 1982 are only partly incorporated in the data base. Observations of comets since 2000 have benefited from a major upgrade of the telescope; they will be presented in forthcoming publications. (5 data files).

The 15 years of comet photometry: A comparative analysis of 80 comets

NASA Technical Reports Server (NTRS)

Osip, David J.; Schleicher, David G.; Millis, Robert L.; Ahearn, Michael F.; Birch, Peter V.

1991-01-01

In 1976, a program of narrowband photometry of comets was initiated that has encompassed well over 400 nights of observations. To date, the program has provided detailed information on 80 comets, 11 of which were observed during multiple apparitions. The filters (initially isolating CN, C2, and continuum and later including C3, OH, and NH) as well as the detectors used for the observations were changed over time, and the parameters adopted in the reduction and modeling of the data have likewise evolved. Accordingly, we have re-reduced the entire database and have derived production rates using current values for scalelengths and fluorescence efficiencies. Having completed this task, the results for different comets can now be meaningfully compared. The general characteristics that are discussed include ranges in composition (molecular production rate ratios) and dustiness (gas production compared with Af(rho)). Additionally an analysis of trends on how the production rates vary with heliocentric distance and on pre- and post-perihelion asymmetries in the production rates of individual comets. Possible taxonomic groupings are also described.

Isotopic ratios in outbursting comet C/2015 ER61

NASA Astrophysics Data System (ADS)

Yang, Bin; Hutsemékers, Damien; Shinnaka, Yoshiharu; Opitom, Cyrielle; Manfroid, Jean; Jehin, Emmanuël; Meech, Karen J.; Hainaut, Olivier R.; Keane, Jacqueline V.; Gillon, Michaël

2018-02-01

Isotopic ratios in comets are critical to understanding the origin of cometary material and the physical and chemical conditions in the early solar nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp increase in brightness offered a rare opportunity to measure the isotopic ratios of the light elements in the coma of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017 April 13 and 17. At the time of our observations, the comet was fading gradually following the outburst. We measured the nitrogen and carbon isotopic ratios from the CN violet (0, 0) band and found that 12C/13C = 100 ± 15, 14N/15N = 130 ± 15. In addition, we determined the 14N/15N ratio from four pairs of NH2 isotopolog lines and measured 14N/15N = 140 ± 28. The measured isotopic ratios of C/2015 ER61 do not deviate significantly from those of other comets.

Fabry-Perot Observations of Comet Hale-Bopp H_2O(+) Velocity Fields

NASA Astrophysics Data System (ADS)

Roesler, F. L.; Klinglesmith, D. A., III; Scherb, F.; Mierkiewicz, E. J.; Oliversen, R. J.

1997-07-01

We have obtained Doppler-sliced images of H_2O(+) emission from Comet Hale-Bopp, using a 15-cm, dual-etalon, Fabry-Perot/CCD imaging spectrometer at the McMath-Pierce 0.8-meter west auxiliary telescope of the National Solar Observatory on Kitt Peak. The 6-arcmin field of view was centered on the comet nucleus, and the spectral resolution was 0.4 Angstroms (20km/sec). The observations consisted of ``data cubes,'' i.e., a sequence of images of the 6158 Angstroms emission doublet at velocity steps of 12.5 or 25km/sec, covering a range from -75km/sec to +75km/sec in the comet reference frame. We were able to follow the comet for 1 to 1(1/_2) hours each clear night. We obtained useable data cubes on at least ten nights between February 25 and April 16. These data are being examined to investigate the comet-solar wind interaction. We will present both still images and time-lapse movies showing sequences of ion velocities and accelerations on the plane of the sky.

Laboratory Study on Disconnection Events in Comets

NASA Astrophysics Data System (ADS)

Li, Yan-Fei; Li, Yu-Tong; Wang, Wei-Min; Yuan, Da-Wei; et al.

2018-01-01

When comets interacting with solar wind, straight and narrow plasma tails will be often formed. The most remarkable phenomenon of the plasma tails is the disconnection event, in which a plasma tail is uprooted from the comet's head and moves away from the comet. In this paper, the interaction process between a comet and solar wind is simulated by using a laser-driven plasma cloud to hit a cylinder obstacle. A disconnected plasma tail is observed behind the obstacle by optical shadowgraphy and interferometry. Our particle-in-cell simulations show that the diference in thermal velocity between ions and electrons induces an electrostatic field behind the obstacle. This field can lead to the convergence of ions to the central region, resulting in a disconnected plasma tail. This electrostatic field-induced model may be a possible explanation for the disconnection events of cometary tails.

Assessment of genotoxic effects of flumorph by the comet assay in mice organs.

PubMed

Zhang, T; Zhao, Q; Zhang, Y; Ning, J

2014-03-01

The present study investigated the genotoxic effects of flumorph in various organs (brain, liver, spleen, kidney and sperm) of mice. The DNA damage, measured as comet tail length (µm), was determined using the alkaline comet assay. The comet assay is a sensitive assay for the detection of genotoxicity caused by flumorph using mice as a model. Statistically significant increases in comet assay for both dose-dependent and duration-dependent DNA damage were observed in all the organs assessed. The organs exhibited the maximum DNA damage in 96 h at 54 mg/kg body weight. Brain showed maximum DNA damage followed by spleen > kidney > liver > sperm. Our data demonstrated that flumorph had induced systemic genotoxicity in mammals as it caused DNA damage in all tested vital organs, especially in brain and spleen.

Comparison of comet 81P/Wild 2 dust with interplanetary dust from comets.

PubMed

Ishii, Hope A; Bradley, John P; Dai, Zu Rong; Chi, Miaofang; Kearsley, Anton T; Burchell, Mark J; Browning, Nigel D; Molster, Frank

2008-01-25

The Stardust mission returned the first sample of a known outer solar system body, comet 81P/Wild 2, to Earth. The sample was expected to resemble chondritic porous interplanetary dust particles because many, and possibly all, such particles are derived from comets. Here, we report that the most abundant and most recognizable silicate materials in chondritic porous interplanetary dust particles appear to be absent from the returned sample, indicating that indigenous outer nebula material is probably rare in 81P/Wild 2. Instead, the sample resembles chondritic meteorites from the asteroid belt, composed mostly of inner solar nebula materials. This surprising finding emphasizes the petrogenetic continuum between comets and asteroids and elevates the astrophysical importance of stratospheric chondritic porous interplanetary dust particles as a precious source of the most cosmically primitive astromaterials.

Effect of solar radiation on a swarm of meteoric particles

NASA Technical Reports Server (NTRS)

Lyttleton, R. A.

1980-01-01

The theory of the Poynting-Robertson effect is used to study the motion of meteors relative to a parent comet describing an undisturbed elliptical orbit. It is shown that any emitted particle proceeds to move retrogressively away from the comet to a certain maximum angular distance (as seen from the sun) depending on its sigma-s value, and then undergoes relative motion in the opposite forward direction. The time taken to reach this greatest elongation behind the comet is the same for all particles, and after twice this time the particles will have returned to zero angular displacement relative to the comet. For comet Encke the time for the elongation to return to zero is about 6600 y; for Halley it is about 200,000 y; for Temple-Tuttle (1965 IV) it is just over 100,000 y.

Performance and data interpretation of the in vivo comet assay in pharmaceutical industry: EFPIA survey results.

PubMed

van der Leede, Bas-Jan; Doherty, Ann; Guérard, Melanie; Howe, Jonathan; O'Donovan, Mike; Plappert-Helbig, Ulla; Thybaud, Véronique

2014-12-01

In genotoxicity testing of pharmaceuticals the rodent alkaline comet assay is being increasingly used as a second in vivo assay in addition to the in vivo micronucleus assay to mitigate in vitro positive results as recommended by the ICH S2(R1) guideline. This paper summarizes a survey suggested by the Safety Working Party of European Medicines Agency (EMA), and conducted by the European Federation of Pharmaceutical Industries and Associations (EFPIA) to investigate the experience among European pharmaceutical companies by conducting the in vivo comet assay for regulatory purpose. A special focus was given on the typology of the obtained results and to identify potential difficulties encountered with the interpretation of study data. The participating companies reported a total of 147 studies (conducted in-house or outsourced) and shared the conclusion on the comet assay response for 136 studies. Most of the studies were negative (118/136). Only about 10% (14/136 studies) of the comet assays showed a positive response. None of the positive comet assay results were clearly associated with organ toxicity indicating that the positive responses are not due to cytotoxic effects of the compound in the tissue examined. The number of comet assays with an equivocal or inconclusive response was rare, respectively <1% (1/147 studies) and 2% (3/147 studies). In case additional information (e.g. repeat assay, organ toxicity, metabolism, tissue exposure) would have been available for evaluation, a final conclusion could most probably have been drawn for most or all of these studies. All (46) negative in vivo comet assays submitted alongside with a negative in vivo micronucleus assay were accepted by the regulatory authorities to mitigate a positive in vitro mammalian cell assay following the current ICH S2 guidance. The survey results demonstrate the robustness of the comet assay and the regulatory acceptance of the current ICH S2 guidance. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

Micropatterned comet assay enables high throughput and sensitive DNA damage quantification

PubMed Central

Ge, Jing; Chow, Danielle N.; Fessler, Jessica L.; Weingeist, David M.; Wood, David K.; Engelward, Bevin P.

2015-01-01

The single cell gel electrophoresis assay, also known as the comet assay, is a versatile method for measuring many classes of DNA damage, including base damage, abasic sites, single strand breaks and double strand breaks. However, limited throughput and difficulties with reproducibility have limited its utility, particularly for clinical and epidemiological studies. To address these limitations, we created a microarray comet assay. The use of a micrometer scale array of cells increases the number of analysable comets per square centimetre and enables automated imaging and analysis. In addition, the platform is compatible with standard 24- and 96-well plate formats. Here, we have assessed the consistency and sensitivity of the microarray comet assay. We showed that the linear detection range for H2O2-induced DNA damage in human lymphoblastoid cells is between 30 and 100 μM, and that within this range, inter-sample coefficient of variance was between 5 and 10%. Importantly, only 20 comets were required to detect a statistically significant induction of DNA damage for doses within the linear range. We also evaluated sample-to-sample and experiment-to-experiment variation and found that for both conditions, the coefficient of variation was lower than what has been reported for the traditional comet assay. Finally, we also show that the assay can be performed using a 4× objective (rather than the standard 10× objective for the traditional assay). This adjustment combined with the microarray format makes it possible to capture more than 50 analysable comets in a single image, which can then be automatically analysed using in-house software. Overall, throughput is increased more than 100-fold compared to the traditional assay. Together, the results presented here demonstrate key advances in comet assay technology that improve the throughput, sensitivity, and robustness, thus enabling larger scale clinical and epidemiological studies. PMID:25527723

The development and validation of EpiComet-Chip, a modified high-throughput comet assay for the assessment of DNA methylation status.

PubMed

Townsend, Todd A; Parrish, Marcus C; Engelward, Bevin P; Manjanatha, Mugimane G

2017-08-01

DNA damage and alterations in global DNA methylation status are associated with multiple human diseases and are frequently correlated with clinically relevant information. Therefore, assessing DNA damage and epigenetic modifications, including DNA methylation, is critical for predicting human exposure risk of pharmacological and biological agents. We previously developed a higher-throughput platform for the single cell gel electrophoresis (comet) assay, CometChip, to assess DNA damage and genotoxic potential. Here, we utilized the methylation-dependent endonuclease, McrBC, to develop a modified alkaline comet assay, "EpiComet," which allows single platform evaluation of genotoxicity and global DNA methylation [5-methylcytosine (5-mC)] status of single-cell populations under user-defined conditions. Further, we leveraged the CometChip platform to create an EpiComet-Chip system capable of performing quantification across simultaneous exposure protocols to enable unprecedented speed and simplicity. This system detected global methylation alterations in response to exposures which included chemotherapeutic and environmental agents. Using EpiComet-Chip on 63 matched samples, we correctly identified single-sample hypermethylation (≥1.5-fold) at 87% (20/23), hypomethylation (≥1.25-fold) at 100% (9/9), with a 4% (2/54) false-negative rate (FNR), and 10% (4/40) false-positive rate (FPR). Using a more stringent threshold to define hypermethylation (≥1.75-fold) allowed us to correctly identify 94% of hypermethylation (17/18), but increased our FPR to 16% (7/45). The successful application of this novel technology will aid hazard identification and risk characterization of FDA-regulated products, while providing utility for investigating epigenetic modes of action of agents in target organs, as the assay is amenable to cultured cells or nucleated cells from any tissue. Environ. Mol. Mutagen. 58:508-521, 2017. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Micropatterned comet assay enables high throughput and sensitive DNA damage quantification.

PubMed

Ge, Jing; Chow, Danielle N; Fessler, Jessica L; Weingeist, David M; Wood, David K; Engelward, Bevin P

2015-01-01

The single cell gel electrophoresis assay, also known as the comet assay, is a versatile method for measuring many classes of DNA damage, including base damage, abasic sites, single strand breaks and double strand breaks. However, limited throughput and difficulties with reproducibility have limited its utility, particularly for clinical and epidemiological studies. To address these limitations, we created a microarray comet assay. The use of a micrometer scale array of cells increases the number of analysable comets per square centimetre and enables automated imaging and analysis. In addition, the platform is compatible with standard 24- and 96-well plate formats. Here, we have assessed the consistency and sensitivity of the microarray comet assay. We showed that the linear detection range for H2O2-induced DNA damage in human lymphoblastoid cells is between 30 and 100 μM, and that within this range, inter-sample coefficient of variance was between 5 and 10%. Importantly, only 20 comets were required to detect a statistically significant induction of DNA damage for doses within the linear range. We also evaluated sample-to-sample and experiment-to-experiment variation and found that for both conditions, the coefficient of variation was lower than what has been reported for the traditional comet assay. Finally, we also show that the assay can be performed using a 4× objective (rather than the standard 10× objective for the traditional assay). This adjustment combined with the microarray format makes it possible to capture more than 50 analysable comets in a single image, which can then be automatically analysed using in-house software. Overall, throughput is increased more than 100-fold compared to the traditional assay. Together, the results presented here demonstrate key advances in comet assay technology that improve the throughput, sensitivity, and robustness, thus enabling larger scale clinical and epidemiological studies. © The Author 2014. Published by Oxford University Press on behalf of the Mutagenesis Society. All rights reserved. For permissions, please email: journals.permissions@oup.com.

High-resolution spectroscopy of the CN red system in comet C/2013 R1 (Lovejoy) using WINERED at Koyama Astronomical Observatory

NASA Astrophysics Data System (ADS)

Kawakita, Hideyo; Shinnaka, Yoshiharu; Kondo, Sohei; Hamano, Satoshi; Sameshima, Hiroaki; Nakanishi, Kenshi; Kawanishi, Takafumi; Nakaoka, Tetsuya; Otsubo, Shogo; Kinoshita, Masaomi; Ikeda, Yuji; Yamamoto, Ryo; Izumi, Natsuko; Fukue, Kei; Yasui, Chikako; Mito, Hiroyuki; Sarugaku, Yuki; Matsunaga, Noriyuki; Kobayashi, Naoto

2015-11-01

CN radical has the strong electronic transition moments in optical wavelength region and CN has extensively observed in comets. Especially, the CN violet system (B2Σ+—X2Σ+) has been observed by using high-resolution spectroscopic technique in order to infer the isotopic ratios of carbon and nitrogen in comets via 12C14N, 13C14N and 12C15N. However, the wavelength range for this system (~388 nm) is severely extinct if a comet is close to the Sun (we have to observe the comet at low elevations from the ground-based observatories). On the other hand, CN radical also has the strong electronic transition in near-infrared (~1.1 microns), the CN red system (A2Πi—X2Σ+). Although there are few reports on the high-resolution spectra of this band in comets, this wavelength region is not severely affected by the telluric extinction and considered as the new window for the observations of the carbon and nitrogen isotopic ratios in comets.High resolution near-infrared spectra of comet C/2013 R1 (Lovejoy) using the WINERED (R~3x104) spectrometer mounted on the 1.3-m Araki telescope at Koyama Astronomical Observatory were acquired on UT 2013 Nov 30. The heliocentric and geocentric distances were 0.91 AU and 0.49 AU, respectively. We detected strong emission lines of the CN red system (0,0) at around 1.1 microns. The rotational line intensities of this band approximately follow the Boltzmann distribution at ~300K for our observations. We present the detailed analysis of the CN red system in comet C/2013 R1 (Lovejoy) and discuss about the isotopic ratios in CN.This research program is supported by the MEXT --- Supported Program for the Strategic Research Foundation at Private Universities, 2014 - 2018 and partially supported by JSPS, 15J10864.

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.

The effect of flash-freezing temperature on stallion sperm DNA structure.

PubMed

Serafini, R; Varner, D D; Bissett, W; Blanchard, T L; Teague, S R; Love, C C

2017-06-01

The effect of flash-freezing storage temperature on stallion sperm DNA has not been evaluated. Commonly, sperm are flash-frozen at various temperatures to preserve sperm DNA prior to analysis. It is unclear whether the temperature at which sperm are frozen and stored may affect the results of DNA assays. In this study, the neutral comet assay was used to evaluate the effect of flash-freezing storage temperature (freezer [-60 °C], dry ice [-78.5 °C], liquid nitrogen [-196 °C]) compared to fresh sperm DNA structure. In addition, intra- and inter-assay and intra- and inter-stallion variabilities were determined. All comet tail measures were higher following any flash-freezing method, as compared to fresh sperm DNA (P < 0.05), with no difference among flash-frozen treatments (P > 0.05). For most comet variables, intra- and inter-assay variabilities were <10%. Intra- and inter-stallion variabilities revealed that comet head length (HL) and width (CW) were less variable as compared to comet tail values, i.e., % comet tail DNA (T-DNA), tail length (TL), tail moment (OTM), and tail migration (TM). Certain comet tail values in fresh (% T-DNA, and OTM) and flash-frozen sperm (OTM, % T-DNA, TL, and TM) were correlated to the Sperm Chromatin Structure Assay (SCSA) variable, COMP-α t . The comet tail measures were negatively correlated to % morphologically normal sperm (P < 0.05) and positively correlated to % abnormal heads and premature germ cells (P < 0.05). Variables COMP-α t and % total sperm motility were not correlated to any morphologic sperm feature in this group of stallions (P > 0.05). While significant differences in the structure of the sperm DNA were identified in the flash-frozen as compared to the fresh sperm DNA with the neutral comet assay, it cannot be assumed that these changes are fertility limiting. Copyright © 2017. Published by Elsevier Inc.

Nūr Ud-Dīn Jahāngīr and Father Kirwitzer: the independent discovery of the Great Comets of November 1618 and the first astronomical use of the telescope in India

NASA Astrophysics Data System (ADS)

Kapoor, R. C.

2016-12-01

The year 1618 in astronomy was a unique one in that it presented three bright cometary apparitions in quick succession. The comets created a sensation, and belonged to an era when Galileo's telescopic observations had created a paradigm shift in our perception of the heavens and Johannes Kepler was introducing a fundamental change in mathematical astronomy by redefining orbits of planets around the Sun. This paper is an account of the observations of two of the three great comets of 1618, made from India. This turned out to be a unique occasion because these same targets of opportunity were followed independently by astronomers from two very different 'schools', and their observations were recorded quantitatively. Jahāngīr, the fourth Mughal Emperor of India, recorded in the Tūzūk-i Jahāngīrī (The Memoirs of Jahāngīr), the appearance of two comets during a Royal journey from the town of Dohad in Gujarat to Agra, the capital city of the Empire, in the thirteenth year of his accession. From the recorded dates, Jahāngīr turns out to be an independent discoverer of two great comets that appeared one after the other in November 1618. Meanwhile, Father Venceslaus Kirwitzer and fellow Jesuits observed these comets from Goa, and their first observations also correspond to the discovery dates of the comets. These same comets also were followed by Father Antonius Rubinus from Cochin. Fr. Kirwitzer collated and published these observations in 1620 in a short treatise where he states that he also viewed these comets with a 'tubo optico'. This is the first recorded use of a telescope in India.

Photographic observations of six comets

NASA Astrophysics Data System (ADS)

de Sanctis, G.; Ferreri, W.; Zappala, V.

Sixty-nine positions of six comets are given as obtained from photographic observations made at the Observatory of Torino from October 1980 to September 1982. Positions are given for Comets Encke, Stephan-Oterma, Meier, Bradfield, Panther, and Austin. Plates were measured with a Zeiss two-coordinate measuring machine. The AGK3 catalog was used to obtain the positions of reference stars and the coordinates of an additional cataloged star near the position of the comet on the plate. The mean values of the differences between the cataloged positions were found to be 0.72 arcsec and 0.52 arcsec in right ascension and declination, respectively.

A dynamical study on extrasolar comets

NASA Astrophysics Data System (ADS)

Loibnegger, B.; Dvorak, R.

2017-09-01

Since the detection of absorption features in spectra of beta Pictoris varying on short time scales it is known that comets exist in other stellar systems. We investigate the dynamics of comets in two differently build systems (HD 10180 and HIP 14810). The outcomes of the scattering process, as there are collisions with the planets, captures and ejections from the systems are analysed statistically. Collisions and close encounters with the planets are investigated in more detail in order to conclude about transport of water and organic material. We will also investigate the possibility of detection of comets in other planetary systems.

Terminal navigation analysis for the 1980 comet Encke slow flyby mission

NASA Technical Reports Server (NTRS)

Jacobson, R. A.; Mcdanell, J. P.; Rinker, G. C.

1973-01-01

The initial results of a terminal navigation analysis for the proposed 1980 solar electric slow flyby mission to the comet Encke are presented. The navigation technique employs onboard optical measurements with the scientific television camera, groundbased observations of the spacecraft and comet, and groundbased orbit determination and thrust vector update computation. The knowledge and delivery accuracies of the spacecraft are evaluated as a function of the important parameters affecting the terminal navigation. These include optical measurement accuracy, thruster noise level, duration of the planned terminal coast period, comet ephemeris uncertainty, guidance initiation time, guidance update frequency, and optical data rate.

Study of mass flow distribution and chemical composition of comets from solar induced X-ray fluorescence

NASA Technical Reports Server (NTRS)

Gorenstein, P.

1979-01-01

The expected performance of an X-ray detector as an instrument aboard a mission to a comet was evaluated. The functions of the detector are both nondispersive analysis of chemical composition and measurement of mass flow from the comet nucleus. Measurements are to be carried out at a distance from the comet. The approach distances considered are of the order of 1000 km and 100 km. A new type of X-ray detector, a proportional scintillation detector, is considered as an X-ray counter for nondispersive elemental analysis.

Nonlinear low frequency (LF) waves - Comets and foreshock phenomena

NASA Technical Reports Server (NTRS)

Tsurutani, Bruce T.

1991-01-01

A review is conducted of LF wave nonlinear properties at comets and in the earth's foreshock, engaging such compelling questions as why there are no cometary cyclotron waves, the physical mechanism responsible for 'dispersive whiskers', and the character of a general description of linear waves. Attention is given to the nonlinear properties of LF waves, whose development is illustrated by examples of waves and their features at different distances from the comet, as well as by computer simulation results. Also discussed is a curious wave mode detected from Comet Giacobini-Zinner, both at and upstream of the bow shock/wave.

Extended atmospheres of outer planet satellites and comets

NASA Technical Reports Server (NTRS)

Smyth, W. H.; Combi, M. R.

1985-01-01

Model analysis of the extended atmospheres of outer planet satellites and comets are discussed. Understanding the neutral hydrogen distribution in the Saturn system concentrated on assessing the spatial dependence of the lifetime of hydrogen atoms and on obtaining appropriately sorted Lyman ALPHA data from the Voyager 1 UVS instrument. Progress in the area of the extended cometary atmospheres included analysis of Pioneer Venus Layman alpha observations of Comet P/Encke with the fully refined hydrogen cloud model, development of the basic carbon and oxygen models, and planning for the Pioneer Venus UVS observations of Comets P/Giacobini-Zinner and P/Halley.

Modeling of meteoroid streams: The velocity of ejection of meteoroids from comets (a review)

NASA Astrophysics Data System (ADS)

Ryabova, G. O.

2013-05-01

An analytical review of the models of ejection of meteoroids from cometary nuclei is presented. Different formulas for the ejection velocity of meteoroids and the corresponding parameters are discussed and compared with the use of comet Halley and the Geminids meteoroid stream as examples. The ejection velocities obtained from observations of the dust trails of comets are discussed, and the values for comets 2P/Encke, 4P/Faye, 17P/Holmes, 22P/Kopff, and 67P/Churyumov-Gerasimenko are compared to the velocities yielded by Whipple's model. The uncertainty intervals of the results are estimated.

Charge and Exchange

NASA Technical Reports Server (NTRS)

2008-01-01

Even though comets are basically giant dirty snowballs, a few years ago they surprised astronomers by emitting X-radiation. These X-rays are not produced by multi-million degree gas (as is often the case) but rather by a process called 'charge exchange'. In this process, ionized atoms (which have lost one or more electrons) which are carried within the solar wind collide with neutral atoms in the comet's coma. The solar wind ion can collide with and capture an electron from the neutral comet atom, and in doing so some of the energy of the collision is observed in the form of X-rays. This produces a glow of X-rays on the sunward side of the comet's atmosphere. Charge exchange can occur in a variety of astrophysical settings, and cometary charge exchange provides astronomers a means to study this process up close. The image above is a pretty picture of comet 73P/Schwassmann-Wachmann 3 passing by the Ring Nebula. This image was obtained by the ultraviolet and optical telescope (UVOT) on the Swift gamma-ray burst hunter. The UVOT observations help astronomers to study the structure and chemistry of the comet, while Swift's X-ray Telescope (XRT) simultaneously monitors the charge exchange process. Comet 73P/Schwassmann-Wachmann 3 is currently in the process of breaking up, and the UVOT observations show important details of how this breakup is occurring.

The Water Production Rate of Recent Comets (2013-2014) by SOHO/SWAN: 2P/Encke (2013), C/2013 R1 (Lovejoy), and C/2013 A1 (Siding Spring)

NASA Astrophysics Data System (ADS)

Combi, Michael R.; Mäkinen, J. T.; Bertaux, J. L.; Quémerais, Eric; Ferron, Stéphane

2014-11-01

The all-sky hydrogen Lyman-alpha camera, SWAN (Solar Wind Anisotropies), on the SOlar and Heliospheric Observatory (SOHO) satellite makes observations of the hydrogen comae of comets. Most water vapor produced by the comet is ultimately photodissociated into two H atoms and one O atom producing a huge atomic hydrogen coma that is routinely observed in the daily full-sky SWAN images in comets of sufficient brightness. Water production rates are calculated using our time-resolved model (Mäkinen & Combi, 2005, Icarus 177, 217), typically yielding about 1 observation every 2 days on the average. Here we describe the progress in analysis of observations of comets observed during 2013-2014 and those selected from the archive for analysis. These include comets 2P/Encke (2013), 45P/Honda Mrkos-Pajdusakova (2011), C/2013 R1 (Lovejoy), as well as C/2013 A1 (Siding Spring), for which results are expected. A status report on the entire SOHO/SWAN archive of water production rates in comets will be given. SOHO is an international cooperative mission between ESA and NASA. Support from grants NNX11AH50G from the NASA Planetary Astronomy Program and NNX13AQ66G from the NASA Planetary Mission Data Analysis Program are gratefully acknowledged.

A simple and novel modification of comet assay for determination of bacteriophage mediated bacterial cell lysis.

PubMed

Khairnar, Krishna; Sanmukh, Swapnil; Chandekar, Rajshree; Paunikar, Waman

2014-07-01

The comet assay is the widely used method for in vitro toxicity testing which is also an alternative to the use of animal models for in vivo testing. Since, its inception in 1984 by Ostling and Johansson, it is being modified frequently for a wide range of application. In spite of its wide applicability, unfortunately there is no report of its application in bacteriophages research. In this study, a novel application of comet assay for the detection of bacteriophage mediated bacterial cell lysis was described. The conventional methods in bacteriophage research for studying bacterial lysis by bacteriophages are plaque assay method. It is time consuming, laborious and costly. The lytic activity of bacteriophage devours the bacterial cell which results in the release of bacterial genomic material that gets detected by ethidium bromide staining method by the comet assay protocol. The objective of this study was to compare efficacy of comet assay with different assay used to study phage mediated bacterial lysis. The assay was performed on culture isolates (N=80 studies), modified comet assay appear to have relatively higher sensitivity and specificity than other assay. The results of the study showed that the application of comet assay can be an economical, time saving and less laborious alternative to conventional plaque assay for the detection of bacteriophage mediated bacterial cell lysis. Copyright © 2014 Elsevier B.V. All rights reserved.

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.

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.

Evolving coma abundances and detection of hypervolatiles in Jupiter-family comet 45P/Honda-Mrkos-Pajdusakova

NASA Astrophysics Data System (ADS)

Dello Russo, Neil; DiSanti, Michael A.; Kawakita, Hideyo; Shinnaka, Yoshiharu; Vervack, Ronald J.; Bonev, Boncho P.; Gibb, Erika L.; Roth, Nathan; McKay, Adam J.; Weaver, Harold A.; Cochran, Anita L.

2017-10-01

Two major shortcomings in chemically classifying comets at infrared wavelengths are a lack of hypervolatile (CO and CH4) detections in Jupiter-family comets and incomplete temporal coverage of comet chemistry, particularly at small heliocentric distances (Rh). We report post-perihelion volatile abundances in comet 45P/Honda-Mrkos-Pajdusakova with the high-resolution infrared spectrometer iSHELL at the NASA/IRTF on UT 6 - 8 January when Rh = 0.55 AU (DiSanti et al. 2017, Astron. J., in press), and with NIRSPEC at the Keck Observatory on UT 13 and 19 February when Rh = 1.0 and 1.1 AU, respectively. Favorable comet geocentric velocities enabled the detection of CO and CH4 in early January and 19 February. The relative abundance of CO is severely depleted whereas CH4 is typical to enriched in 45P when compared to comets from the Oort cloud. Significant differences are seen in relative abundances of species between January and February, notably in the ratio of C2H2/HCN. We explore whether the heliocentric distances of the measurements or seasonal changes primarily cause these differences by comparing to observations of C/2012 S1 ISON obtained over a similar range of heliocentric distances. NASA and NSF research grants support this work. We also acknowledge the expert support of the IRTF and Keck support staffs during these observations.

Radio Observations of Organics in Comets

NASA Technical Reports Server (NTRS)

Milam, Stefanie N.; Charnley, Steven B.; Kuan, Yi-Jehng; Chuang, Yo-Ling; Villanueva, Geronimo; Coulson, Iain; Remijan, Anthony J.

2012-01-01

A major observational challenge in cometary science is to quantify the extent to which chemical compounds can be linked to either interstellar or nebular chemistry. Recently, there have been complimentary observations from multiple facilities to try to unravel the chemical complexity of comets and their origins. Incorporating results from various techniques can gain further insight into the abundances, production rates, distributions, and formation mechanisms of molecules in these objects [I]. Such studies have provided great detail towards molecules with a-typical chemistries, such as H2CO [2]. We report multiwavelength spectral observations of comets from two dynamical families including the JFC 103P/Hartley 2 and a long period comet C/2009 PI (Garradd) with the Arizona Radio Observatory's SMT and 12-m telescopes, as well as the NRAO Greenbank telescope, and the James Clerk Maxwell Telescope. Multiple parent volatiles (e.g. HCN, CH30H, CO) as well as daughter products (e.g, CS and 01-1) have been detected in these objects. We will present a comparison of molecular abundances in these comets to those observed in others, supporting a long-term effort of building a comet taxonomy based on composition. Previous work has revealed a range of abundances of parent species (from "organics-poor" to "organics-rich") with respect to water among comets [3,4,5], however the statistics are not well constrained.

A binary main-belt comet.

PubMed

Agarwal, Jessica; Jewitt, David; Mutchler, Max; Weaver, Harold; Larson, Stephen

2017-09-20

Asteroids are primitive Solar System bodies that evolve both collisionally and through disruptions arising from rapid rotation. These processes can lead to the formation of binary asteroids and to the release of dust, both directly and, in some cases, through uncovering frozen volatiles. In a subset of the asteroids called main-belt comets, the sublimation of excavated volatiles causes transient comet-like activity. Torques exerted by sublimation measurably influence the spin rates of active comets and might lead to the splitting of bilobate comet nuclei. The kilometre-sized main-belt asteroid 288P (300163) showed activity for several months around its perihelion 2011 (ref. 11), suspected to be sustained by the sublimation of water ice and supported by rapid rotation, while at least one component rotates slowly with a period of 16 hours (ref. 14). The object 288P is part of a young family of at least 11 asteroids that formed from a precursor about 10 kilometres in diameter during a shattering collision 7.5 million years ago. Here we report that 288P is a binary main-belt comet. It is different from the known asteroid binaries in its combination of wide separation, near-equal component size, high eccentricity and comet-like activity. The observations also provide strong support for sublimation as the driver of activity in 288P and show that sublimation torques may play an important part in binary orbit evolution.

Inventory of the volatiles on comet 67P/Churyumov-Gerasimenko from Rosetta/ROSINA

NASA Astrophysics Data System (ADS)

Le Roy, Léna; Altwegg, Kathrin; Balsiger, Hans; Berthelier, Jean-Jacques; Bieler, Andre; Briois, Christelle; Calmonte, Ursina; Combi, Michael R.; De Keyser, Johan; Dhooghe, Frederik; Fiethe, Björn; Fuselier, Stephen A.; Gasc, Sébastien; Gombosi, Tamas I.; Hässig, Myrtha; Jäckel, Annette; Rubin, Martin; Tzou, Chia-Yu

2015-11-01

Context. The ESA Rosetta spacecraft (S/C) is tracking comet 67P/Churyumov-Gerasimenko in close vicinity. This prolonged encounter enables studying the evolution of the volatile coma composition. Aims: Our work aims at comparing the diversity of the coma of 67P/Churyumov-Gerasimenko at large heliocentric distance to study the evolution of the comet during its passage around the Sun and at trying to classify it relative to other comets. Methods: We used the Double Focussing Mass Spectrometer (DFMS) of the ROSINA experiment on ESA's Rosetta mission to determine relative abundances of major and minor volatile species. This study is restricted to species that have previously been detected elsewhere. Results: We detect almost all species currently known to be present in cometary coma with ROSINA DFMS. As DFMS measured the composition locally, we cannot derive a global abundance, but we compare measurements from the summer and the winter hemisphere with known abundances from other comets. Differences between relative abundances between summer and winter hemispheres are large, which points to a possible evolution of the cometary surface. This comet appears to be very rich in CO2 and ethane. Heavy oxygenated compounds such as ethylene glycol are underabundant at 3 AU, probably due to their high sublimation temperatures, but nevertheless, their presence proves that Kuiper belt comets also contain complex organic molecules.

Exo-comet Detection in Debris Disks Around Young A-type Stars

NASA Astrophysics Data System (ADS)

Welsh, Barry; Montgomery, S. L.

2013-01-01

We present details of the successful search for comet-like bodies (i.e. exo-comets) in orbit around several nearby stars. These objects have been found in young stellar systems that are in the transitional stage of evolution between possession of a gaseous protoplanetary disk to that of a dust-rich debris disk. During this period it is thought that large planetesimals of ~ 1000 km diameter may cause dynamical perturbations in the population of smaller bodies (such as asteroids and comets), such that they are sent on highly eccentric orbits towards their parent star resulting in the liberation of large amounts of evaporating gas and dust. By observing the varying spectral absorption signature of the CaII K-line at 3933Å due to this liberated gas, we have been able to track the trajectory of these exo-comets over a time-frame of several nights as they approach (and sometimes pass around) the central star. The youngest debris disks (1 - 50 Myr) are thought to represent the last stage in the formation of planetary systems and they may resemble our solar system’s own debris disk at the time of the Late Heavy Bombardment when the terrestrial worlds were subject to frequent collisions with asteroids and comets. Collisions with water-rich comets from the outer regions of our solar system may have delivered water to thee Earth’s oceans.

The comet moment as a measure of DNA damage in the comet assay.

PubMed

Kent, C R; Eady, J J; Ross, G M; Steel, G G

1995-06-01

The development of rapid assays of radiation-induced DNA damage requires the definition of reliable parameters for the evaluation of dose-response relationships to compare with cellular endpoints. We have used the single-cell gel electrophoresis (SCGE) or 'comet' assay to measure DNA damage in individual cells after irradiation. Both the alkaline and neutral protocols were used. In both cases, DNA was stained with ethidium bromide and viewed using a fluorescence microscope at 516-560 nm. Images of comets were stored as 512 x 512 pixel images using OPTIMAS, an image analysis software package. Using this software we tested various parameters for measuring DNA damage. We have developed a method of analysis that rigorously conforms to the mathematical definition of the moment of inertia of a plane figure. This parameter does not require the identification of separate head and tail regions, but rather calculates a moment of the whole comet image. We have termed this parameter 'comet moment'. This method is simple to calculate and can be performed using most image analysis software packages that support macro facilities. In experiments on CHO-K1 cells, tail length was found to increase linearly with dose, but plateaued at higher doses. Comet moment also increased linearly with dose, but over a larger dose range than tail length and had no tendency to plateau.

Low-frequency electromagnetic plasma waves at comet P/Grigg-Skjellerup: Analysis and interpretation

NASA Technical Reports Server (NTRS)

Neubauer, Fritz M.; Glassmeier, Karl-Heinz; Coates, A. J.; Johnstone, A. D.

1993-01-01

The propagation and polarization characteristic of low-frequency electromagnetic wave fields near comet P/Grigg-Skjellerup (P/GS) are analyzed using magnetic field and plasma observations obtained by the Giotto magnetometer experiment and the Johnstone plasma analyzer during the encounter at the comet on July 10, 1992. The results have been physically interpreted.

On the origin of comets

NASA Technical Reports Server (NTRS)

Mendis, A.; Alfven, H.

1976-01-01

Physico-chemical processes leading to the dynamic formation and physical evolution of comets are reviewed in relationship to the various theories that propose solar origins, protoplanetary origins, planetary origins and interstellar origins. Evidence points to the origins of comets by the growth and agglomeration of small particles from gas and dust at very low temperatures at undetermined regions in space.

Rosetta - a comet ride to solve planetary mysteries

NASA Astrophysics Data System (ADS)

2003-01-01

Comets are very interesting objects for scientists, since their composition reflects how the Solar System was when it was very young and still 'unfinished', more than 4600 million years ago. Comets have not changed much since then. By orbiting Comet Wirtanen and landing on it, Rosetta will collect essential information to understand the origin and evolution of our Solar System. It will also help discover whether comets contributed to the beginnings of life on Earth. In fact comets are carriers of complex organic molecules, that - delivered to Earth through impacts - perhaps played a role in the origin of living forms. Furthermore, “volatile” light elements carried by comets may have also played an important role in forming the Earth’s oceans and atmopshere. “Rosetta is one of the most challenging missions ever undertaken so far”, says Prof. David Southwood, ESA Director of Science, “No one before attempted a similar mission, unique for its scientific implications as well as for its complex and spectacular interplanetary space manoeuvres”. Before reaching its target in 2011, Rosetta will circle the Sun almost four times on wide loops in the inner Solar System. During its long trek, the spacecraft will have to endure some extreme thermal conditions. Once it is close to Comet Wirtanen, scientists will take it through a delicate braking manoeuvre; then the spacecraft will closely orbit the comet, and gently drop a lander on it. It will be like landing on a small, fast-moving cosmic bullet that still has - at present - an almost unknown 'geography'. An amazing 8-year interplanetary trek Rosetta is a 3-tonne box-type spacecraft about 3 metres high, with two 14-metre long solar panels. It consists of an orbiter and a lander. The lander is approximately 1 metre across and 80 centimetres high. It will be attached to the side of the Rosetta orbiter during the journey to Comet Wirtanen. Rosetta carries 21 experiments in total, 10 of them on the lander. They will be kept in hibernation during most of its 8-year trek towards Wirtanen. What makes Rosetta's cruise so long? To reach Comet Wirtanen, the spacecraft needs to go out in deep space as far from the Sun as Jupiter is. No launcher could possibly get Rosetta there directly. ESA's spacecraft will gather speed from gravitational ‘kicks’ provided by three planetary fly-bys: one of Mars in 2005 and two of Earth in 2005 and 2007. During the trip, Rosetta will also visit two asteroids, Otawara (in 2006) and Siwa (in 2008). During these encounters, scientists will switch on Rosetta's instruments for calibration and scientific studies. Long trips in deep space include many hazards, such as extreme changes in temperature. Rosetta will leave the benign environment of near-Earth space to the dark, frigid regions beyond the asteroid belt. To manage these thermal loads, experts have done very tough pre-launch tests to study Rosetta's endurance. For example, they have heated its external surfaces to more than 150°C, then quickly cooled it to -180°C in the next test. The spacecraft will be fully reactivated prior to the comet rendezvous manoeuvre in 2011. Then, Rosetta will orbit the comet - an object only 1.2 km wide - while it cruises through the inner Solar System at 135 000 kilometres per hour. At that time of the rendezvous - around 675 million km from the Sun - Wirtanen will hardly show any surface activity. It means that the carachteristic coma (the comet’s ‘atmosphere’) and the tail will not be formed yet, because of the large distance from the Sun. The comet's tail is in fact made of dust grains and frozen gases from the comet's surface that vapourise because of the Sun's heat. During 6-month, Rosetta will extensively map the comet surface, prior to selecting a landing site. In July 2012, the lander will self-eject from the spacecraft from a height of just one kilometre. Touchdown will take place at walking speed - less than 1 metre per second. Immediately after touchdown, the lander will fire a harpoon into the ground to avoid bouncing off the surface back into space, since the extremely weak comet’s gravity alone would not hold onto the lander. Operations and scientific observations on the comet surface will last 65 hours as a minimum, but may continue for many months. During and after the lander operations, Rosetta will continue orbiting and studying the comet: Rosetta will be the first spacecraft to witness at close quarters the changes taking place in a comet when the comet approaches the Sun and grows its coma and tail. The trip will end in July 2013, after 10.5 years of adventure, when the comet is closest to the Sun. Studying a comet on the spot Rosetta's goal is to examine the comet in great detail. The instruments on Rosetta orbiter include several cameras, spectrometers, and experiments that work at different wavelengths --infrared, ultraviolet, microwave, radio and a number of sensors. They will provide, among other things, very high-resolution images and information about the shape, density, temperature, and chemical composition of the comet. Rosetta’s instruments will analyse the gases and dust grains in the so-called “coma” that forms when the comet becomes active, as well as the interaction with the solar wind. The 10 instruments on board the lander will do an on-the-spot analysis of the composition and structure of the comet’s surface and subsurface material. A drilling system will take samples down to 30 centimetres below the surface and will feed these to the ‘composition analysers’. Other instruments will measure properties such as near-surface strength, density, texture, porosity, ice phases, and thermal properties. Microscopic studies of individual grains will tell us about the texture. In addition, instruments on the lander will study how the comet changes during the day-night cycle, and while it approaches the Sun. Ground operations Data from the lander are relayed to the orbiter, which stores them for downlink to Earth at the next ground station contact. ESA has installed a new deep-space antenna at New Norcia, near Perth in Western Australia, as the main communications link between the spacecraft and the ESOC Mission Control in Darmstadt, Germany. This 35-metre diameter parabolic antenna allows the radio signal to reach distances of more than 1 million kilometres from Earth. The radio signals, travelling at the speed of light, will take up to 50 minutes to cover the distance between the spacecraft and Earth. Rosetta's Science Operations Centre, which is responsible for collecting and distributing the scientific data, will share a location at ESOC and ESTEC in Noordwijk, The Netherlands. The Lander Control Centre is located in DLR in Cologne, Germany, and the Lander Science Centre in CNES in Toulouse, France. Building Rosetta Rosetta was selected as a mission in 1993. The spacecraft has been built by Astrium Germany as prime contractor. Major subcontractors are Astrium UK (spacecraft platform), Astrium France (spacecraft avionics), and Alenia Spazio (assembly, integration, and verification). Rosetta’s industrial team involves more than 50 contractors from 14 European countries, Canada and the United States. Scientific consortia from institutes across Europe and the United States have provided the instruments on the orbiter. A European consortium under the leadership of the German Aerospace Research Institute (DLR) has provided the lander. Rosetta has cost ESA Euro 701 million at 2000 economic conditions. This amount includes the launch and the entire period of development and mission operations from 1996 to 2013. The lander and the experiments, the so-called 'payload', are not included since they are funded by the member states through the scientific institutes. Note to editors Europe is certainly a pioneer in comet exploration. In 1986, ESA’s spacecraft Giotto performed the closest comet fly-by ever achieved by any spacecraft (at a distance of 600 kilometres of Halley). It sent back wonderful pictures and data that showed that comets contain complex organic molecules. These kinds of compounds are rich in carbon, hydrogen, oxygen, and nitrogen. Intriguingly, these are the elements which make up nucleic acids and amino acids, which are essential ingredients for life as we know it. Giotto continued its successful journey and flew by Comet Grigg-Skjellerup in 1992 within about 200 km distance. Now scientists will be eagerly waiting to be able to answer some of the new intriguing questions that arose from analysing the exciting results from Giotto. Other past missions that have flown by a comet were: NASA’s ICE mission in 1985, the two Russian VEGA spacecraft and the two Japanese spacecraft Suisei and Sakigake that were part of the armada that visited comet Halley in 1986; NASA’s Deep Space 1 flew-by comet Borelly in 2001 and NASA’s Stardust will fly-by comet Wild 2 in early 2004 and will return samples of the comet’s coma in 2006. Unfortunately NASA’s Contour launched in Summer 2002 failed when it was inserted onto its interplanetary trajectory. In 2004 we will see the launch of Deep Impact, a spacecraft that will shoot a massive block of copper into a comet nucleus.

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.

Physical properties and dynamical relation of the circular depressions on comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Ip, W.-H.; Lai, I.-L.; Lee, J.-C.; Cheng, Y.-C.; Li, Y.; Lin, Z.-Y.; Vincent, J.-B.; Besse, S.; Sierks, H.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; Agarwal, J.; A'Hearn, M. F.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Bodewits, D.; Boudreault, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; De Cecco, M.; El-Maarry, M. R.; Fornasier, S.; Fulle, M.; Groussin, O.; Gutiérrez, P. J.; Güttler, C.; Hviid, S. F.; Jorda, L.; Knollenberg, J.; Kovacs, G.; Kramm, J.-R.; Kührt, E.; Küppers, M.; La Forgia, F.; Lara, L. M.; Lazzarin, M.; López-Moreno, J. J.; Lowry, S.; Marchi, S.; Marzari, F.; Michalik, H.; Mottola, S.; Naletto, G.; Oklay, N.; Pajola, M.; Thomas, N.; Toth, E.; Tubiana, C.

2016-06-01

Aims: We aim to characterize the circular depressions of comet 67P/Churyumov-Gerasimenko and investigate whether such surface morphology of a comet nucleus is related to the cumulative sublimation effect since becoming a Jupiter family comet (JFC). Methods: The images from the Rosetta/OSIRIS science camera experiment are used to construct size frequency distributions of the circular depression structures on comet 67P and they are compared with those of the JFCs 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2. The orbital evolutionary histories of these comets over the past 100 000 yr are analyzed statistically and compared with each other. Results: The global distribution of the circular depressions over the surface of 67P is charted and classified. Descriptions are given to the characteristics and cumulative size frequency distribution of the identified features. Orbital statistics of the JFCs visited by spacecraft are derived. Conclusions: The size frequency distribution of the circular depressions is found to have a similar power law distribution to those of 9P/Tempel 1 and 81P/Wild 2. This might imply that they could have been generated by the same process. Orbital integration calculation shows that the surface erosion histories of 81P/Wild 2, and 9P/Tempel 1 could be shorter than those of 67P, 103 P/Hartley 2 and 19P/Borrelly. From this point of view, the circular depressions could be dated back to the pre-JFC phase or the transneptunian phase of these comets. The north-south asymmetry in the distribution of the circular depressions could be associated with the heterogeneous structure of the nucleus of comet 67P and/or the solar insolation history.

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.

Comets 169P/NEAT and P/2003 T12 (SOHO): Two possible fragments of a common ancestor?

NASA Astrophysics Data System (ADS)

Sosa, Andrea; Fernández, Julio Angel

2015-08-01

In a recent work we analyzed the orbit evolution of Jupiter family comets in near-Earth orbits, and found some comets moving on highly stable orbits, like the near-Earth asteroids (Fernández & Sosa 2015). Two of them actually show almost identical orbits; they are the comets 169P/NEAT and P/2003 T12 (SOHO). Comet 169P seems to be a few km-sized, almost inactive body, while P/2003 T12 would be a very small comet, with a sub-km radius nucleus. We performed extended orbital integrations for the past 100,000 yr to further study their dynamical evolution. We found that the orbital parameters remain stable for several thousand years, with a well defined absolute minimum of their relative spatial distance around 2900 yr in the past, coincident with a low value of the relative velocity. This spatial minimum is in a remarkable good agreement with the results obtained by means of other methods to study common origins between pairs of asteroids (Vokrouhlicky & Nesvorny 2008, Southworth & Hawkins 1963), and to test a comet-meteor shower association (Drummond 1981). Our results support the hypothesis of a breakup of a parent body, that ocurred about 2900 yr ago, as the most probable origin for the studied pair of comets. Possible fragmentation mechanisms, like thermal stress, rotational instability, or colisions, are briefly discussed.References:Drumond J.D. 1981. Icarus 45, 545-553.Fernández J.A., & Sosa A. 2015. Submitted to Planetary & Space Science.Southworth R.B., & Hawkins, G.S. 1963. Smithson. Contrib. Astrophys. 7, 261-285Vokrouhlicky D., & Nesvorny D. 2008. Astron. J. 136, 280-290.

Double-stranded DNA breaks hidden in the neutral Comet assay suggest a role of the sperm nuclear matrix in DNA integrity maintenance

PubMed Central

Ribas-Maynou, J.; Gawecka, J.E.; Benet, J.; Ward, W.S.

2014-01-01

We used a mouse model in which sperm DNA damage was induced to understand the relationship of double-stranded DNA (dsDNA) breaks to sperm chromatin structure and to the Comet assay. Sperm chromatin fragmentation (SCF) produces dsDNA breaks located on the matrix attachment regions, between protamine toroids. In this model, epididymal sperm induced to undergo SCF can religate dsDNA breaks while vas deferens sperm cannot. Here, we demonstrated that the conventional neutral Comet assay underestimates the epididymal SCF breaks because the broken DNA ends remain attached to the nuclear matrix, causing the DNA to remain associated with the dispersion halo, and the Comet tails to be weak. Therefore, we term these hidden dsDNA breaks. When the Comet assay was modified to include an additional incubation with sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) after the conventional lysis, thereby solubilizing the nuclear matrix, the broken DNA was released from the matrix, which resulted in a reduction of the sperm head halo and an increase in the Comet tail length, exposing the hidden dsDNA breaks. Conversely, SCF-induced vas deferens sperm had small halos and long tails with the conventional neutral Comet assay, suggesting that the broken DNA ends were not tethered to the nuclear matrix. These results suggest that the attachment to the nuclear matrix is crucial for the religation of SCF-induced DNA breaks in sperm. Our data suggest that the neutral Comet assay identifies only dsDNA breaks that are released from the nuclear matrix and that the addition of an SDS treatment can reveal these hidden dsDNA breaks. PMID:24282283

Double-stranded DNA breaks hidden in the neutral Comet assay suggest a role of the sperm nuclear matrix in DNA integrity maintenance.

PubMed

Ribas-Maynou, J; Gawecka, J E; Benet, J; Ward, W S

2014-04-01

We used a mouse model in which sperm DNA damage was induced to understand the relationship of double-stranded DNA (dsDNA) breaks to sperm chromatin structure and to the Comet assay. Sperm chromatin fragmentation (SCF) produces dsDNA breaks located on the matrix attachment regions, between protamine toroids. In this model, epididymal sperm induced to undergo SCF can religate dsDNA breaks while vas deferens sperm cannot. Here, we demonstrated that the conventional neutral Comet assay underestimates the epididymal SCF breaks because the broken DNA ends remain attached to the nuclear matrix, causing the DNA to remain associated with the dispersion halo, and the Comet tails to be weak. Therefore, we term these hidden dsDNA breaks. When the Comet assay was modified to include an additional incubation with sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) after the conventional lysis, thereby solubilizing the nuclear matrix, the broken DNA was released from the matrix, which resulted in a reduction of the sperm head halo and an increase in the Comet tail length, exposing the hidden dsDNA breaks. Conversely, SCF-induced vas deferens sperm had small halos and long tails with the conventional neutral Comet assay, suggesting that the broken DNA ends were not tethered to the nuclear matrix. These results suggest that the attachment to the nuclear matrix is crucial for the religation of SCF-induced DNA breaks in sperm. Our data suggest that the neutral Comet assay identifies only dsDNA breaks that are released from the nuclear matrix and that the addition of an SDS treatment can reveal these hidden dsDNA breaks.

Improvements in Modeling the Collimated Jets of Comet 19P/Borrelly from the Stereo Images of the Deep Space 1 Flyby

NASA Astrophysics Data System (ADS)

Melville, Kenneth J.; Farnham, T.; Hoban, S.

2010-10-01

On September 22, 2001, the spacecraft Deep Space 1 (DS1), which was primarily designed for testing advanced technologies in space, preformed an extended mission flyby of the comet 19P/Borrelly. This encounter provided scientists with the best images taken of a comet. These images from the DS1 Miniature Integrated Camera and Spectrometer (MICAS) instrument show features of comet Borrelly's surface; collimated dust jets escaping the nucleus, and the coma of gas and dust that surrounds the nucleus. Properties of the jet, such as rate and angle of expansion have been measured accurately due to the jet's geometric structure and position on the rotation axis of the comet. These measurements have been taken for several points along the spacecrafts approach, flyby, and from additional McDonald ground based observatory images. A model of the jet with similar geometry has been constructed in order to reproduce the observational data found in the flyby images. Other proposed models are tested as well. Once these models has been adjusted to replicate the data, they can be used to investigate the collimation mechanism below the comets surface producing the jet. Comet 19P/Borrelly is the idea test for this model due to the simple structure of the jet, as well as the wide variety of angles and observation times. Using information from this model, scientists may be able to make new assumptions on the composition and physical structure of other comets. This research was supported by the NASA Planetary Data System: Small Bodies Node, and College Student Investigator Program at UMBC Goddard Earth Sciences & Technology Center.

Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula

NASA Astrophysics Data System (ADS)

Lorek, S.; Lacerda, P.; Blum, J.

2018-03-01

Context. Comet formation by gravitational instability requires aggregates that trigger the streaming instability and cluster in pebble-clouds. These aggregates form as mixtures of dust and ice from (sub-)micrometre-sized dust and ice grains via coagulation in the solar nebula. Aim. We investigate the growth of aggregates from (sub-)micrometre-sized dust and ice monomer grains. We are interested in the properties of these aggregates: whether they might trigger the streaming instability, how they compare to pebbles found on comets, and what the implications are for comet formation in collapsing pebble-clouds. Methods: We used Monte Carlo simulations to study the growth of aggregates through coagulation locally in the comet-forming region at 30 au. We used a collision model that can accommodate sticking, bouncing, fragmentation, and porosity of dust- and ice-mixed aggregates. We compared our results to measurements of pebbles on comet 67P/Churyumov-Gerasimenko. Results: We find that aggregate growth becomes limited by radial drift towards the Sun for 1 μm sized monomers and by bouncing collisions for 0.1 μm sized monomers before the aggregates reach a Stokes number that would trigger the streaming instability (Stmin). We argue that in a bouncing-dominated system, aggregates can reach Stmin through compression in bouncing collisions if compression is faster than radial drift. In the comet-forming region ( 30 au), aggregates with Stmin have volume-filling factors of 10-2 and radii of a few millimetres. These sizes are comparable to the sizes of pebbles found on comet 67P/Churyumov-Gerasimenko. The porosity of the aggregates formed in the solar nebula would imply that comets formed in pebble-clouds with masses equivalent to planetesimals of the order of 100 km in diameter.

Water production activity of nine long-period comets from SOHO/SWAN observations of hydrogen Lyman-alpha: 2013-2016

NASA Astrophysics Data System (ADS)

Combi, M. R.; Mäkinen, T. T.; Bertaux, J.-L.; Quémerais, E.; Ferron, S.; Avery, M.; Wright, C.

2018-01-01

Nine recently discovered long-period comets were observed by the Solar Wind Anisotropies (SWAN) Lyman-alpha all-sky camera on board the Solar and Heliosphere Observatory (SOHO) satellite during the period of 2013 to 2016. These were C/2012 K1 (PanSTARRS), C/2013 US10 (Catalina), C/2013 V5 (Oukaimeden), C/2013 R1 (Lovejoy), C/2014 E2 (Jacques), C/2014 Q2 (Lovejoy), C/2015 G2 (MASTER), C/2014 Q1 (PanSTARRS) and C/2013 XI (PanSTARRS). Of these 9 comets 6 were long-period comets and 3 were possibly dynamically new. Water production rates were calculated from each of the 885 images using our standard time-resolved model that accounts for the whole water photodissociation chain, exothermic velocities and collisional escape of H atoms. For most of these comets there were enough observations over a broad enough range of heliocentric distances to calculate power-law fits to the variation of production rate with heliocentric distances for pre- and post-perihelion portions of the orbits. Comet C/2014 Q1 (PanSTARRS), with a perihelion distance of only ∼0.3 AU, showed the most unusual variation of water production rate with heliocentric distance and the resulting active area variation, indicating that when the comet was within 0.7 AU its activity was dominated by the continuous release of icy grains and chunks, greatly increasing the active sublimation area by more than a factor of 10 beyond what it had at larger heliocentric distances. A possible interpretation suggests that a large fraction of the comet's mass was lost during the apparition.

Infrared Spectroscopy of Parent Volatiles in Comets: Implications for Astrobiology

NASA Technical Reports Server (NTRS)

DiSanti, Michael A.

2010-01-01

Current cometary orbits provide information on their recent dynamical history. However, determining a given comet's formation region from its current dynamical state alone is complicated by radial migration in the proto-planetary disk and by dynamical interactions with the growing giant planets. Because comets reside for long periods of time in the outer Solar System, the ices contained in their nuclei (native ices) retain a relatively well-preserved footprint of when and where they formed, and this in turn can provide clues to conditions in the formation epoch. As a comet approaches the Sun, sublimation of its native ices releases parent volatiles into the coma where they can be measured spectroscopically. The past to - 15 years have seen the advent of infrared spectrometers with high sensitivity between about 2.8 and 5.0 micron, enabling a taxonomy among comets based on abundances of parent volatiles (e.g., H2O, CO, CH4, C2H6, HCN, CH30H, H2CO, NH3). Such molecules are of keen interest to Astrobiology, as they include important pre-biotic species that likely were required for the emergence of life on Earth and perhaps elsewhere. Approximately 20 comets have thus far been characterized, beginning with C/1996 82 (Hyakutake) in 1996. Molecular production rates are established through comparison of observed emission line intensities with those predicted by quantum mechanical fluorescence models. Abundances of parent volatiles (relative to H2O) vary among even the relatively small number of comets sampled, with the most volatile species (CO and CH4) displaying the largest variations. Techniques developed for measuring parent volatile abundances in comets will be discussed, as will possible implications for their formation.

A Multi-Wavelength Study of Parent Volatile Abundances in Comet C/2006 M4 (SWAN)

NASA Technical Reports Server (NTRS)

DiSanti, Michael A.; Villanueva, Geronimo L.; Milam, Stefanie N.; Zack, Lindsay N.; Bonev, Boncho P.; Mumma, Michael; Ziurys, Lucy M.; Anderson, William M.

2009-01-01

Volatile organic emissions were detected post-perihelion in the long period comet C/2006 M4 (SWAN) in October and November 2006. Our study combines target-of-opportunity, observations using the infrared Cryogenic Echelle Spectrometer (CSHELL) at the NASA-IRTF 3-m telescope, and millimeter wavelength observations using the Arizona Radio Observatory (ARO) 12-m telescope. Five parent volatiles were measured with CSHELL (H2O, CO, CH3OH, CH4, and C2H6), and two additional species (HCN and CS) were measured with the ARID 12-m. These revealed highly depleted CO and somewhat enriched CH3OH compared with abundances observed in the dominant group of long-period (Oort cloud) comets in our sample and similar to those observed recently in Comet 8P/Tuttle. This may indicate highly efficient H-atom addition to CO at very low temperature (approx.10-20 K) on the surfaces of interstellar (pre-cometary) grains. Comet C12006 M4 had nearly "normal" C2H6, and CH4, suggesting a processing history similar to that experienced by the dominant group. When compared with estimated water production at the time of the millimeter observations, HCN was slightly depleted compared with the normal abundance in comets based on 1R observations but was consistent with the majority of values from the millimeter. The ratio CS/HCN in C/2006 M4 was within the range measured in ten comets at millimeter wavelengths. The higher apparent H-atom conversion efficiency compared with most comets may indicate that the icy grains incorporated into C/2006 M4 were exposed to higher H-atom densities, or alternatively to similar densities but for a longer period of time.

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.

HUBBLE DETECTION OF COMET NUCLEUS AT FRINGE OF SOLAR SYSTEM

NASA Technical Reports Server (NTRS)

2002-01-01

This is sample data from NASA's Hubble Space Telescope that illustrates the detection of comets in the Kuiper Belt, a region of space beyond the orbit of the planet Neptune. This pair of images, taken with the Wide Field Planetary Camera 2 (WFPC2), shows one of the candidate Kuiper Belt objects found with Hubble. Believed to be an icy comet nucleus several miles across, the object is so distant and faint that Hubble's search is the equivalent of finding the proverbial needle-in-haystack. Each photo is a 5-hour exposure of a piece of sky carefully selected such that it is nearly devoid of background stars and galaxies that could mask the elusive comet. The left image, taken on August 22, 1994, shows the candidate comet object (inside circle) embedded in the background. The right picture, take of the same region one hour forty-five minutes later shows the object has apparently moved in the predicted direction and rate of motion for a kuiper belt member. The dotted line on the images is a possible orbit that this Kuiper belt comet is following. A star (lower right corner) and a galaxy (upper right corner) provide a static background reference. In addition, other objects in the picture have not moved during this time, indicating they are outside our solar system. Through this search technique astronomers have identified 29 candidate comet nuclei belonging to an estimated population of 200 million particles orbiting the edge of our solar system. The Kupier Belt was theorized 40 years ago, and its larger members detected several years ago. However, Hubble has found the underlying population of normal comet-sized bodies. Credit: A. Cochran (University of Texas) and NASA

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.

Parametric Dielectric Model of Comet Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Heggy, E.; Palmer, E. M.; Kofman, W. W.; Clifford, S. M.; Righter, K.; Herique, A.

2012-12-01

In 2014, the European Space Agency's Rosetta mission is scheduled to rendezvous with Comet 67P/Churyumov-Gerasimenko (Comet 67P). Rosetta's CONSERT experiment aims to explore the cometary nucleus' geophysical properties using radar tomography. The expected scientific return and inversion algorithms are mainly dependent on our understanding of the dielectric properties of the comet nucleus and how they vary with the spatial distribution of geophysical parameters. Using observations of comets 9P/Tempel 1 and 81P/Wild 2 in combination with dielectric laboratory measurements of temperature, porosity, and dust-to-ice mass ratio dependencies for cometary analog material, we have constructed two hypothetical three-dimensional parametric dielectric models of Comet 67P's nucleus to assess different dielectric scenarios of the inner structure. Our models suggest that dust-to-ice mass ratios and porosity variations generate the most significant measurable dielectric contrast inside the comet nucleus, making it possible to explore the structural and compositional hypotheses of cometary nuclei. Surface dielectric variations, resulting from temperature changes induced by solar illumination of the comet's faces, have also been modeled and suggest that the real part of the dielectric constant varies from 1.9 to 3.0, hence changing the surface radar reflectivity. For CONSERT, this variation could be significant at low incidence angles, when the signal propagates through a length of dust mantle comparable to the wavelength. The overall modeled dielectric permittivity spatial and temporal variations are therefore consistent with the expected deep penetration of CONSERT's transmitted wave through the nucleus. It is also clear that changes in the physical properties of the nucleus induce sufficient variation in the dielectric properties of cometary material to allow their inversion from radar tomography.

The asteroid-comet continuum from laboratory and space analyses of comet samples and micrometeorites

NASA Astrophysics Data System (ADS)

Engrand, Cecile; Duprat, Jean; Bardin, Noemie; Dartois, Emmanuel; Leroux, Hugues; Quirico, Eric; Benzerara, Karim; Rémusat, Laurent; Dobrică, Elena; Delauche, Lucie; Bradley, John; Ishii, Hope; Hilchenbach, Martin; COSIMA Team

2015-08-01

Comets are probably the best archives of the nascent solar system, 4.5 Gyr ago, and their compositions reveal crucial clues on the structure and dynamics of the early protoplanetary disk. Anhydrous minerals (olivine and pyroxene) have been identified in cometary dust for a few decades. Surprisingly, samples from comet Wild2 returned by the Stardust mission in 2006 also contain high temperature mineral assemblages like chondrules and refractory inclusions, which are typical components of primitive meteorites (carbonaceous chondrites - CCs). A few Stardust samples have also preserved some organic matter of comet Wild 2 that share some similarities with CCs. Interplanetary dust falling on Earth originate from comets and asteroids in proportions to be further constrained. These cosmic dust particles mostly show similarities with CCs, which in turn only represent a few percent of meteorites recovered on Earth. At least two (rare) families of cosmic dust particles have shown strong evidences for a cometary origin: the chondritic porous interplanetary dust particles (CP-IDPs) collected in the terrestrial stratosphere by NASA, and the ultracarbonaceous Antarctic Micrometeorites (UCAMMs) collected from polar snow and ice by French and Japanese teams. The Rosetta mission currently carries dust analyzers capable of measuring dust flux, sizes, physical properties and compositions of dust particles from the Jupiter family comet 67P/Churyumov-Gerasimenko (COSIMA, GIADA, MIDAS), as well as gas analyzers (ROSINA, PTOLEMY, COSAC). A growing number of evidences highlights the existence of a continuum between asteroids and comets, already in the early history of the solar system. We will present the implications of the analyses of samples in the laboratory and in space to a better understanding of the early protoplanetary disk.

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.

Dust Activity of Comet Hale-Bopp (C/1995 O1) at Rh ~ 3 AU

NASA Astrophysics Data System (ADS)

Tozzi, G. P.; Mannucci, F.; Stanga, R.; Testi, L.

1997-07-01

Observations of comet Hale-Bopp (C/1995 O1) have been performed in the infrared (J, H, K bands) at the Nordic Optical Telescope (NOT), located on Canary islands, with the ARNICA (ARcetri Near Infrared CAmera). The comet was observed during two periods, at the beginning and the end of September 1996, when the comet was at heliocentric distances rh of ~ 3.3 and 2.9 AU, respectively. The data show a relatively large activity of the comet with production of some outbursts, the largest of which happened some time before the start of the second run (24.8 Sept.) and which may be the further evolution of the outburst detected by the HST (Weaver et al., 1997, Science 275, 1900). Here we present the analysis of the data with particular attention to the evolution of the outbursts and the photometric IR color index of the dust released.

NASA/University Joint Venture (JOVE) Program

NASA Technical Reports Server (NTRS)

Magee-Sauer, Karen P.

1999-01-01

Hale-Bopp observations at the NASA IRTF concluded in September 1997. For the post Hale-Bopp period, telescope time was awarded to study comet Giacobini-Zinner in October 1998 at the NASA IRTF. A total of 6 nights were awarded to our team to study the comet where 2 of those 6 nights were awarded to Magee-Sauer as the principal investigator. Other observing trips were awarded to study YSOs (October 1998) and Mars (spring 1999) were Magee-Sauer was a co-investigator. An observing run from July 4 -7 1999 included study of Mars and YSOS. Our group has started to use the NIRSPEC instrument on the Keck II telescope. In collaboration with the development team from UCLA, we obtained images of comet Lee in August 1999. Telescope proposals are submitted each semester for targeted comet observations when a comet is bright enough to observe.

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).

Cometary science. Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko.

PubMed

Hässig, M; Altwegg, K; Balsiger, H; Bar-Nun, A; Berthelier, J J; Bieler, A; Bochsler, P; Briois, C; Calmonte, U; Combi, M; De Keyser, J; Eberhardt, P; Fiethe, B; Fuselier, S A; Galand, M; Gasc, S; Gombosi, T I; Hansen, K C; Jäckel, A; Keller, H U; Kopp, E; Korth, A; Kührt, E; Le Roy, L; Mall, U; Marty, B; Mousis, O; Neefs, E; Owen, T; Rème, H; Rubin, M; Sémon, T; Tornow, C; Tzou, C-Y; Waite, J H; Wurz, P

2015-01-23

Comets contain the best-preserved material from the beginning of our planetary system. Their nuclei and comae composition reveal clues about physical and chemical conditions during the early solar system when comets formed. ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) onboard the Rosetta spacecraft has measured the coma composition of comet 67P/Churyumov-Gerasimenko with well-sampled time resolution per rotation. Measurements were made over many comet rotation periods and a wide range of latitudes. These measurements show large fluctuations in composition in a heterogeneous coma that has diurnal and possibly seasonal variations in the major outgassing species: water, carbon monoxide, and carbon dioxide. These results indicate a complex coma-nucleus relationship where seasonal variations may be driven by temperature differences just below the comet surface. Copyright © 2015, American Association for the Advancement of Science.

A Herschel Study of D/H in Water in the Jupiter-family Comet 45P/Honda-Mrkos-Pajdušáková and Prospects for D/H Measurements with CCAT

NASA Astrophysics Data System (ADS)

Lis, D. C.; Biver, N.; Bockelée-Morvan, D.; Hartogh, P.; Bergin, E. A.; Blake, G. A.; Crovisier, J.; de Val-Borro, M.; Jehin, E.; Küppers, M.; Manfroid, J.; Moreno, R.; Rengel, M.; Szutowicz, S.

2013-09-01

We present Herschel observations of water isotopologues in the atmosphere of the Jupiter-family comet 45P/Honda-Mrkos-Pajdušáková. No HDO emission is detected, with a 3σ upper limit of 2.0 × 10-4 for the D/H ratio. This value is consistent with the earlier Herschel measurement in the Jupiter-family comet 103P/Hartley 2. The canonical value of 3 × 10-4 measured pre-Herschel in a sample of Oort-cloud comets can be excluded at a 4.5σ level. The observations presented here further confirm that a diversity of D/H ratios exists in the comet population and emphasize the need for additional measurements with future ground-based facilities, such as CCAT, in the post-Herschel era.