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At least 1,513 records · Page 84

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NASA NTRS1996

The Detection of Water Ice in Comet Hale-Bopp

We present spectra of Comet Hale-Bopp (C/1995 01) covering the range 1.4-2.5 micron that were recorded when the comet was 7 AU from the Sun. These show I)road absorption features at 1.5 and 2.05 micron. We show that some, but not all, of this absorption could be matched by an intimate mixture of water ice and a low albedo material such as carbon on the nucleus. However, we recognize that it is more likely that the ice features are produced by scattering from icy grains in the coma. The absence of absorption at 1.65 micron suggests that this ice is probably in the amorphous state. An unidentified additional component may be required to account for the downward slope at the longwavelength end of the spectrum.

Davies, John K.↗

NASA NTRS1992

g-Factors of the SH (0-0) Band and SH Upper Limit in Comet P/Brorsen-Metcalf (1980o)

Since H2S was detected in Comets Austin (1989cl) and Levy (1990c) in the microwave range, there has been increasing interest in searching for SH, which is the prime dissociative product of H2S. We present g-factors for the A-X (0-0) band of SH as a function of heliocentric velocity at r = 1.0 AU. We derive an upper limit production rate, Q(SH)/Q(H2O) less than 0.017, for Comet Brorsen-Metcalf (1989o) and calculate a dissociative lifetime of 105 sec at a heliocentric distance, r = 1.0 AU, and at a heliocentric velocity, v(r) = -28.5 km/sec.

Kim, Sang J.↗

NASA NTRS1997

Astrometric Observations of Comets and Asteroids and Subsequent Orbital Investigations

An earlier series of photographic observations was made with the 1.5-m reflector from 1972 to 1989. The start of the series to which this report refers occurred shortly before the conversion from photographic to CCD operation in August 1989, at which point there was a dramatic increase in the productivity of the program. This is evident gives a month-by-month summary of the observations; the earlier data refer to the measurement or remeasurement of photographic plates previously taken with the same telescope. The total number of observations made was 24,423, of which 1338 were of comets. Of the 23,085 observations of asteroids, 21,529 referred to asteroids that were unnumbered when the observations were made. Since an important emphasis of the program was to improve knowledge of the orbits to the point where asteroids can be numbered, the fact that only 4262 of the observations refer to asteroids that are still unnumbered is a measure of the program's success, with 30-35 percent of all the new numberings being habitually made solely because of the recent data from the Oak Ridge program, which even at the time of McCrosky's retirement was still the fourth largest comet-asteroid astrometric program in the world.

Marsden, Brian G.↗

NASA NTRS1997

The Population of Small Comets: Optimum Techniques for Detection

The goals of this project were: (1) to present evidence to the scientific community for the importance of the small comet population and (2) to develop techniques for optimum detection in order to characterize the population. Our work on techniques has been to develop algorithms for searching images for SCs based on the distinctive properties of comets; (1) motion with respect to background stars; (2) extended source with most light coming from the coma rather than the nucleus; and characteristic spectral signature.

Brandt, John C.↗

NASA NTRS1997

The infrared spectrum of comet Hale-Bopp

The infrared spectroscopic observations of the comet C/1995 O1 (Hale-Bopp), in April and September-October 1996, are summarized. High resolution spectra were obtained with the long and short wavelength spectrometers of the Infrared Space Observatory (ISO). The results showed that the dust in this comet contains crystalline silicates. The dust of Hale-Bopp is rather similar to that observed in the circumstellar disks of Vega-type stars.

Crovisier, J.↗

NASA NTRS1997

Morphology and Compositional Differentiation of the Surface of Comets

Giotto images reveal many features on the nucleus of Comet Halley, including gas- and dust-producing sources surrounded by an inactive region. In the inactive region, crater-like structures can be seen that may be extinct sources. These structures may develop by surface erosion of an active area and deposition of some excavated material on the periphery, creating crater-like rims. These rims are formed from "clumps" of comet regolith that can be lifted by the escaping gas. The lack of lift caused by the divergence of the gas flow near the boundary of an active region lets them fall back on the nucleus and create a rim. This may be a continuous process during perihelion passage. Supplementing the original concept of investigating the active and inactive regions, we conclude that three compositionally distinct areas should be sampled during the Rosetta mission: (1) The active regions rich in frozen gases and unprocessed dust; (2) The inactive region covered by a thin layer of fine dust enriched in organics that may be sintered. (3) The crater-like rims containing "clumps" of processed organics, silicates, and trapped frozen gases.

Huebner, W. F.↗

NASA NTRS1997

Electron Spin Resonance (ESR) Studies of Returned Comet Nucleus Samples

Electron Spin Resonance (ESR) studies have been carried out on organic and inorganic free radicals generated by gamma-ray and/or UV-irradiation and trapped in ice matrices. It is suggested that the concentration of these free radicals together with their thermal stability can be used as an accurate built-in geothermometer and radiation probe for returned comet nucleus sample studies. ESR studies have also been carried out on paramagnetic (Mn(2+), Ti(3+), and Fe(3+)) and ferromagnetic (ferric oxide and metallic iron) centers known to be present in terrestrial and extraterrestrial samples. The presence or absence of these magnetic centers coupled with their characteristic ESR lineshape can be used to investigate the shock effects, quenching/cooling rate and oxidation-reduction conditions in the formation and subsequent evolution of returned comet nucleus samples.

Tsay, Fun-Dow↗

NASA NTRS1996

Mid-Infrared Spectra of Comets P/Borrelly, P/Faye, and P/Schaumasse

A 10 micron silicate emission feature has been discovered in the spectra of comets P/BorrelIy and P/Faye at R approximately 1.5 AU. These are the first short period comets in which silicate emission has definitely been detected. The broad emission features are about 25% above the continuum. No emission feature was present in the spectrum of P/Schaumasse; it is possible that the nucleus of P/Schaumasse was directly detected. If all of the observed flux originated from the nucleus, then the effective radius is about 3 km; the observed color temperature is consistent with a rapidly rotating nucleus. We present models that show how the shape of the silicate feature can depend on the way in which silicate and absorbing material are mixed in the grains.

Hanner, Martha S.↗

NASA NTRS1995

Changes in Jupiter's 13-cm Synchrotron Radio Emission Following the Impact of Comet Shoemaker-Levy-9

Results of an observing program to monitor the synchrotron radio emission from Jupiter's inner radiation belts before, during and after the impact of Comet SL-9 are reported. The observations were made at 2295 MHz as part of the NASA-JPL Jupiter Patrol, a long-term radio astronomy monitoring program begun in 1971. ne data indicate that the intensity of the synchrotron emission at 13 cm wavelength increased by 27 percent within a few days after the comet impacts; the longitudinal beaming curve was distorted during the week of impacts; the magnetic latitude beaming curves flattened after the week of impacts suggesting an increase in the emission at higher magnetic latitudes; and the decay of the enhanced emission is consistent with an exponential with a time constant of approx. 125 days. The reported changes following the SL-9 impact are unprecedented in the 23-year history of the Jupiter Patrol.

Klein, M. J.↗

NASA NTRS1994

Shoemaker-Levy Comet Impact with Jupiter Press Briefing

A press briefing about the impact of the G fragment of Comet Shoemaker-Levy on the planet Jupiter is presented. The briefing occurred on July 18, 1994 just hours after the impact. Still black and white pictures taken from the Hubble Space Telescope are presented. Eugene Shoemaker, co-discoverer of the Comet, and Heidi Hammel, Principal Investigator for the Hubble Imaging team at MIT present preliminary results of the study of images and answer questions about the impact and the results of the impact on Jupiter.

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NASA NTRS1994

Shoemaker-Levy 9 Comet Impact Briefing

A press conference held on July 21, 1994, about the impact of some of the fragments from Comet Shoemaker Levy is presented. The press conference opened with a still of Jupiter, showing the impact site of several fragments. The following people were on the panel: (1) Hal Weaver, from the Space Telescope Science Institute, (2) Rita Beebe from New Mexico State University, (3) Lucy McFadden from the University of California and the University of Maryland, (4) David Levy, the co-discoverer of the Shoemaker-Levy comet. The moderator was Eugene Shoemaker. The discussion was about the impact of the fragments on Jupiter. There were 21 pieces that were counted from earlier observations. There was some discussion about the further fragmentation of Q into two pieces. There was also some discussion about the impact on the planet of several fragments. These were due to hit ten hours apart on about the same spot. There were reports from the observatories around the world, including a tape from the Lowell Observatory, a summary of the views from the Galileo orbiter, a video of the impacts from the G fragment, and views of the results from the impact of the C and G fragments as viewed from Australia.

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NASA NTRS1994

Comet Shoemaker-Levy Impact: Briefing

A panel discussion held on May 18, 1994, about the impact of the P/Shoemaker-Levy 9 (SL9) comet with Jupiter and its observable effects on Jupiter's atmosphere, rings, satellites, and magnetosphere, is presented. Before the panel discussion animations show the first nuclei impact, collision with Jupiter's night side (5 of the 22 known fragments of P/Shoemaker-Levy 9; N, P2, P1, Q2, and Q1), and simulated views of the Shoemaker-Levy 9 comet impact with Jupiter (from Earth and Galileo spacecraft) were presented. The panelists are: Dr. Eugene Shoemaker (from Lowell Observatory and US Geological Survey), the moderator and Shoemaker-Levy co-discoverer; Dr. Hal Weaver (from Space Telescope Science Institute); Dr. Lucy McFadden (from University of California-San Diego and the University of Maryland); Dr Melissa McGrath (from Space Telescope Science Institute); and Dr. Heidi Hammel (from Massachusetts Institute of Technology). Topics discussed include: interactions of cometary material with Jupiter's atmosphere, dynamical parameters of Jupiter's troposphere and stratosphere, and Hubble Space Telescope (HST) Observations of the SL9 Impacts on Jupiter's Atmosphere.The panel answered some of the audience's questions at the end of the discussion. This video, Part 2 (of 2), is a continuation of Part 1. It presents the second part of the question and answer session and a replay of the animations.

Source record↗

NASA NTRS1994

Comet Shoemaker-Levy Impact: Briefing

A panel discussion held on May 18, 1994, about the impact of the P/Shoemaker-Levy 9 (SL9) comet with Jupiter and its observable effects on Jupiter's atmosphere, rings, satellites, and magnetosphere, is presented. Before the panel discussion animations show the first nuclei impact, collision with Jupiter's night side (5 of the 22 known fragments of P/Shoemaker-Levy 9; N, P2, P1, Q2, and Q1), and simulated views of the Shoemaker-Levy 9 comet impact with Jupiter (from Earth and Galileo spacecraft) were presented. The panelists are: Dr. Eugene Shoemaker (from Lowell Observatory and US Geological Survey), the moderator and Shoemaker-Levy co-discoverer; Dr. Hal Weaver (from Space Telescope Science Institute); Dr. Lucy McFadden (from University of California-San Diego and the University of Maryland); Dr Melissa McGrath (from Space Telescope Science Institute); and Dr. Heidi Hammel (from Massachusetts Institute of Technology). Topics discussed include: interactions of cometary material with Jupiter's atmosphere, dynamical parameters of Jupiter's troposphere and stratosphere, and Hubble Space Telescope (HST) Observations of the SL9 Impacts on Jupiter's Atmosphere.The panel answered some of the audience's questions at the end of the discussion. This video, Part 1 (of 2), presents the panel discussion and part of the question and answer session.

Source record↗

NASA NTRS1999

Detection of CO and Ethane in Comet 21P/Giacobini-Zinner: Evidence for Variable Chemistry in the Outer Solar Nebula

Ethane and carbon monoxide were detected in a short-period comet of probable Kuiper belt origin. Ethane is substantially less abundant compared with Hyakutake and Hale-Bopp, two comets from the giant-planets region of the solar nebula, suggesting a heliocentric gradient in ethane in pre-cometary ices. It is argued that processing by X-rays from the young sun may be responsible.

Mumma, M. J.↗

NASA NTRS2000

The Formation Age of Comets: Predicted Physical and Chemical Trends

The chemical composition of a comet has always been considered to be a function of where it formed in the nebula. We suggest that the most important factor in determining a comet's chemistry might actually be when it formed. We present specific predictions of correlations between the dust and volatile components to test our hypothesis.

Nuth, Joesph A., III↗

NASA NTRS1999

The Ion Propulsion System on NASA's Space Technology 4/Champollion Comet Rendezvous Mission

The ST4/Champollion mission is designed to rendezvous with and land on the comet Tempel 1 and return data from the first-ever sampling of a comet surface. Ion propulsion is an enabling technology for this mission. The ion propulsion system on ST4 consists of three ion engines each essentially identical to the single engine that flew on the DS1 spacecraft. The ST4 propulsion system will operate at a maximum input power of 7.5 kW (3.4 times greater than that demonstrated on DS1), will produce a maximum thrust of 276 mN, and will provide a total (Delta)V of 11.4 km/s. To accomplish this the propulsion system will carry 385 kg of xenon. All three engines will be operated simultaneously for the first 168 days of the mission. The nominal mission requires that each engine be capable of processing 118 kg. If one engine fails after 168 days, the remaining two engines can perform the mission, but must be capable of processing 160 kg of xenon, or twice the original thruster design requirement. Detailed analyses of the thruster wear-out failure modes coupled with experience from long-duration engine tests indicate that the thrusters have a high probability of meeting the 160-kg throughput requirement.

Brophy, John R.↗

NASA NTRS2000

The Deep Space 4/Champollion Comet Rendezvous and Lander Technology Demonstration Mission

The Deep Space 4/Champollion mission is designed to test and validate technologies for landing on and anchoring to small bodies, and sample collection and transfer, in preparation for future sample return missions from comets, asteroids, and satellites. in addition, DS-4 will test technologies for advanced, multi-engine solar electric propulsion (SEP) systems, inflatable-rigidizable solar arrays, autonomous navigation and precision guidance for landing, autonomous hazard detection and avoidance, and advanced integrated avionics and packaging concepts. Deep Space-4/Champollion consists of two spacecraft: an orbiter/carrier vehicle which includes the multi-engine SEP stage, and a lander, called Champollion, which will descend to the surface of the 46P/Tempel 1 cometary nucleus. The spacecraft will launch in April, 2003 and land on the comet in September, 2006 Deep Space 4/Champollion is a joint project between NASA and CNES, the French space agency.

Smythe, William D.↗

NASA NTRS2000

The Formation Age of Comets: Predicted Physical and Chemical Trends

Nuth, J. A., III↗