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NASA NTRS1994

Comet coma sample return instrument

The sample collection technology and instrument concept for the Sample of Comet Coma Earth Return Mission (SOCCER) are described. The scientific goals of this Flyby Sample Return are to return to coma dust and volatile samples from a known comet source, which will permit accurate elemental and isotopic measurements for thousands of individual solid particles and volatiles, detailed analysis of the dust structure, morphology, and mineralogy of the intact samples, and identification of the biogenic elements or compounds in the solid and volatile samples. Having these intact samples, morphologic, petrographic, and phase structural features can be determined. Information on dust particle size, shape, and density can be ascertained by analyzing penetration holes and tracks in the capture medium. Time and spatial data of dust capture will provide understanding of the flux dynamics of the coma and the jets. Additional information will include the identification of cosmic ray tracks in the cometary grains, which can provide a particle's process history and perhaps even the age of the comet. The measurements will be made with the same equipment used for studying micrometeorites for decades past; hence, the results can be directly compared without extrapolation or modification. The data will provide a powerful and direct technique for comparing the cometary samples with all known types of meteorites and interplanetary dust. This sample collection system will provide the first sample return from a specifically identified primitive body and will allow, for the first time, a direct method of matching meteoritic materials captured on Earth with known parent bodies.

Albee, A. L.↗

NASA NTRS1981

Distribution and activity of discrete emission areas on the nucleus of periodic Comet Swift-Tuttle

A general model is proposed which accounts for the dynamical evolution of the observed jets, envelopes and tail bands of periodic Comet Swift-Tuttle, the parent comet of the Perseid meteor stream, in terms of dust ejection from discrete active regions on the rotating nucleus. High-resolution drawings and measurements of cometary jets made upon the comet's first appearance in 1862 are used to infer a nuclear rotation period of 2.77 days, obliquity of 80 deg, and spin axis orientation with respect to the solar direction of 60 deg. The observed jets are attributed to eight discrete active regions covering not more than 1% of the cometary surface and producing bursts of duration of about 0.1 day. Calculations show that waning dust jets develop into envelopes and that old envelopes in turn become the observed tail bands. No evidence of truly violent explosions is found, and effects of active region outgassing on cometary orbital motion are negligible. Potential applications of the model to periodic Comet Halley and other comets are noted.

Sekanina, Z.↗

NASA NTRS2002

Studies of Transient Meteor Activity

Meteoroids bombard Earth's atmosphere daily, but occasionally meteor rates increase to unusual high levels when Earth crosses the relatively fresh ejecta of comets. These transient events in meteor activity provide clues about the whereabouts of Earth-threatening long-period comets, the mechanisms of large-grain dust ejection from comets, and the particle composition and size distribution of the cometary ejecta. Observations of these transient events provide important insight in natural processes that determine the large grain dust environment of comets, in natural phenomena that were prevalent during the time of the origin of life, and in processes that determine the hazard of civilizations to large impacts and of man-made satellites to the periodic blizzard of small meteoroids. In this proposal, three tasks form a coherent program aimed at elucidating various aspects of meteor outbursts, with special reference to planetary astronomy and astrobiology. Task 1 was a ground-based effort to observe periods of transient meteor activity. This includes: (1) stereoscopic imaging of meteors during transient meteor events for measurements of particle size distribution, meteoroid orbital dispersions and fluxes; and (2) technical support for Global-MS-Net, a network of amateur-operated automatic counting stations for meteor reflections from commercial VHF radio and TV broadcasting stations, keeping a 24h vigil on the level of meteor activity for the detection of new meteor streams. Task 2 consisted of ground-based and satellite born spectroscopic observations of meteors and meteor trains during transient meteor events for measurements of elemental composition, the presence of organic matter in the meteoroids, and products generated by the interaction of the meteoroid with the atmosphere. Task 3 was an airborne effort to explore the 2000 Leonid meteor outbursts, which are anticipated to be the most significant of transient meteor activity events in the remainder of the agreement period. This includes technical support for a multi-instrument aircraft campaign, Leonid MAC.

Jenniskens, Peter M. M.↗

NASA NTRS2013

Community Supported Stardust Compendia

The Stardust cometary and interstellar collections present unprecedented challenges in sample preparation and analysis. The ensemble of approx.80 tracks and dozens of foil craters from the cometary collection for which we have analyses exhibits a bewildering complexity and diversity of materials. The interstellar collection is even more challenging, because of the extremely low fluence of interstellar dust, a relatively large background of secondary ejecta from impacts on the spacecraft, and the small size of interstellar dust, approximately three orders of magnitude smaller in mass than typical cometary particles. Unlike with the other returned sample collections, characterization of these samples beyond basic photo-documentation is not generally practical at JSC. Even among the other small-particle collections, currently the cosmic dust and Hayabusa samples, SEM/EDX can provide basic chemistry. This is not possible with Stardust particles without destructive and invasive sample preparation. Furthermore, SEM/EDX requires isolating small grains from adhering aerogel. A reliable technique to carry out this task does not exist. Complete characterization of particles requires coordinated analyses using synchrotron and electron-beam microprobes, which do not exist at any one lab. Thus, it was recognized since the Stardust Preliminary Examination in 2006 that characterization of the samples would rely on the worldwide community of Stardust Investigators. Here we announce the development of community-editable, wiki-style Stardust compendia that will support this effort. Our intention is that this will facilitate sample requests by providing basic characterization of tracks. We expect that this will also support comprehensive meta-analyses (global syntheses of analyses) of the collections.

Westphal, Andrew J.↗

NASA NTRS1986

Dust distribution of Comet Halley from the Giotto radio science experiment

Measurements from the Giotto radio science experiment representing the Doppler frequency shift and the intensity level of the X-band downlink signal of the Giotto spacecraft during its encounter with comet Halley are shown. Continuous data reception was maintained throughout the encounter. The Doppler shift measured within a time interval of 100 sec is due to drag effects in the cometary atmosphere causing a deceleration of the spacecraft. The total change of velocity of Giotto is 23.2 cm/sec resulting in a best estimate of 0.32 g for the total cometary mass impacting Giotto during the Halley flyby. A dust jet structure for the inner coma of comet Halley is derived. Several sharply confined dust jets are distinguishable; for the most prominent one, characteristic properties are deduced. Features of this jet structure are shown to correlate with measurements from on-board Giotto experiments and with Earth-based observations.

Edenhofer, P.↗

NASA NTRS1994

Cometary Coma Chemical Composition (C4) Mission

Cometary exploration remains of great importance to virtually all of space science. Because comets are presumed to be remnants of the early solar nebula, they are expected to provide fundamental knowledge as to the origin and development of the solar system as well as to be key to understanding of the source of volatiles and even life itself in the inner solar system. Clearly the time for a detailed study of the composition of these apparent messages from the past has come. A comet rendezvous mission, the Cometary Coma Chemical Composition (C4) Mission, is now being studied as a candidate for the new Discovery program. This mission is a highly-focussed and usefully-limited subset of the Cometary Rendezvous Asteroid Flyby (CRAF) Mission. The C4 mission will concentrate on measurements that will produce an understanding of the composition and physical makeup of a cometary nucleus. The core science goals of the C4 mission are 1) to determine the chemical, elemental, and isotopic composition of a cometary nucleus and 2) to characterize the chemical and isotopic nature of its atmosphere. A related goal is to obtain temporal information about the development of the cometary coma as a function of time and orbital position. The four short-period comets -- Tempel 1, Tempel 2, Churyumov-Gerasimenko, and Wirtanen -which all appear to have acceptable dust production rates, were identified as candidate targets. Mission opportunities have been identified beginning as early as 1998. Tempel I with a launch in 1999, however, remains the baseline comet for studies of and planning the C4 mission. The C4 mission incorporates two science instruments and two engineering instruments in the payload to obtain the desired measurements. The science instruments include an advanced version of the Cometary Ice and Dust Experiment (CIDEX), a mini-CIDEX with a sample collection system, an X-ray Fluorescence Spectrometer and a Pyrolysis-Gas Chromatograph, and a simplified version of the Neutral Gas and Ion Mass Spectrometer (NIGMS). Both of these instruments have substantial heritage as they are based on those developed for the CRAF Mission. The engineering instruments include a simplified Comet Dust Environmental Monitor (SCODEM) and a navigational Camera, NAVCAM. While neither of the instruments will be permitted to establish science requirements, it is anticipated that significant science return will be accomplished Radio science will also be included.

Carle, Glenn C.↗

NASA NTRS1989

Electron beam analysis of particulate cometary material

Electron microscopy will be useful for characterization of inorganic dust grains in returned comet nucleus samples. The choice of instrument(s) will depend primarily on the nature of the samples, but ultimately a variety of electron-beam methods could be employed. Scanning and analytical (transmission) electron microscopy are the logical choise for morphological, mineralogical, and bulk chemical analyses of dust grains removed from ices. It may also be possible to examine unmelted ice/dust mixtures using an environmental scanning electron microscope equipped with a cryo-transfer unit and a cold stage. Electron microscopic observations of comet nuclei might include: (1) porosities of dust grains; (2) morphologies and microstructures of individual mineral grains; (3) relative abundances of olivine, pyroxene, and glass; and (4) the presence of phases that might have resulted from aqueous alteration (layer silicates, carbonates, sulfates).

Bradley, John↗

NASA NTRS1994

Carbon in Comet Halley dust particles

Comets are small bodies of the solar system containing primarily a mixture of frozen gases and carbonaceous and mineral grains. They are likely to preserve volatile mineral from cold regions of the protosolar nebula and remnants of interstellar dust and gas. More than 2500 mass spectra of cometary grains with masses in the range 5 x 10 exp -17 to 5 x 10 exp -12 g were measured in situ by PUMA1 and PUMA2 mass spectrometers on board the VEGA spacecraft during flyby missions to Comet Halley. In this paper, we discuss different organic and inorganic C-containing components discovered so far in Comet Halley dust particles, the nature and abundance of which provide information about possible astrophysical sources of C and constrain models of interstellar grains.

Fomenkova, M. N.↗

NASA NTRS1998

Mission goals of a 1998/1999 Leonid storm Multi-instrument Aircraft Campaign (MAC)

In November of 1998 (or in 1999 with about equal probability) will be our one chance in a lifetime to anticipate with some certainty the occurrence of a meteor storm. For a period of up to 2 hours, rates are expected to increase above 1 meteor per second for a naked eye observer. At that time, Earth passes through the outer regimes of the dust trail of comet 55P/Tempel-Tuttle. The high meteor flux offers unprecedented precision in characterizing the dust trail in terms of spatial and particle size distributions of dust grains and allows the measurement of composition, morphology and orbits of individual cometary grains relatively soon after ejection from the comet. By using the Earth's atmosphere as a detector for the dust trains, grains are sampled over a wide mass range, from the typical grain size of zodiacal dust (40 - 200 micron) up until the rare boulders that can still be lifted off the comet nucleus.

Jenniskens, P.↗

NASA NTRS1975

A study of the icy tails of the distant comets

Properties are studied of the icy grain model for the tails of comets Baade 1955 VI and Haro-Chavira 1956 I, which have large perihelion distances. The general profiles and orientations of the tails are compared with a set of synchrones, or theoretical trajectories of particles ejected from a cometary nucleus at given instants of time. Several features observed in these comets are shown to be explained by the icy grain model, including jet activity in the coma and no appreciable broadening of the tail with increasing distance from the nucleus. It is demonstrated that the transition region between 2 and 3 AU, where water snow begins to experience rapid evaporation, has a significant effect on the dynamics of icy tails. It is suggested that the icy grains constituting these cometary tails may carry fine particles of meteoric dust which are released when the grains begin to disintegrate by evaporation.

Sekanina, Z.↗

NASA NTRS1982

The problem of split comets in review

Cometary splitting is investigated from the dynamical and physical standpoints. A simple two-parameter model is proposed in which the rate of recession of the fragments is determined by the momentum from outgassing, so that the net differential force is of the same nature as the nongravitational perturbations detected in the motions of unsplit comets; the two parameters of the model are the differential radial acceleration and the time of splitting. It is shown that the model successfully represents the positional observations of nearly all the 21 known split comets. The following candidate triggering mechanisms for cometary splitting are considered: tidal forces, rotation, dust-mantle dumping, and radioactive heating. A model that fits the dynamical data and physical characteristics is presented which suggests that most fragments must be appreciably nonspherical and rapidly precessing.

Sekanina, Z.↗

NASA NTRS2004

Astrobiology of Comets

We model the thermal history of a cometary body, regarded as an assemblage of boulders, dust, ices and organics, as it approaches a perihelion distance of - IAU. The transfer of incident energy h m sunlight into the interior leads to the melting of ices under tens of meters of stable crust, providing possible habitats for a wide range of microorganisms. We consider the icediatoms, snow algae and cyanobacteria, bacteria and yeast of cryoconite communities which are encountered in liquid wafer pools (meltwater) surrounding dark rocks in glaciers and the polar ice sheets as excellent analogs for the microbial ecosystems that might possibly exist on some comets.

Hoover, Richard B.↗

NASA NTRS1985

Dust emission of Comet Halley at large heliocentric distances

Comet Halley is currently approaching the inner solar system. Four spacecrafts (NASA's spacecraft, two Russian Vega probes and the Japanese MS-T5 spacecraft) have already been launched to encounter the comet in March 1986. Two additional Halley probes (the European Giotto spacecraft and another Japanese Planet-A probe) will be launched in mid-85 to join the armada. Observations of dust emissions from Halley's Comet are discussed. The evaporation of cometary ices causes the emission of particulates from the nucleus. These observations will be used to determine the fly-by strategy of the Giotto spacecraft by taking into account the distribution of dust in the vicinity of the nucleus and the associated hazard for the space mission.

Gruen, E.↗

NASA NTRS2007

Stardust in STARDUST - the C, N, and O Isotopic Compositions of Wild 2 Cometary Matter in Al foil Impacts

In January 2006, the STARDUST mission successfully returned dust samples from the tail of comet 81P/Wild 2 in two principal collection media, low density silica aerogel and Al foil. While hypervelocity impacts at 6.1 km/s, the encounter velocity of STARDUST, into Al foils are generally highly disruptive for natural, silicate-dominated impactors, previous studies have shown that many craters retain sufficient residue to allow a determination of the elemental and isotopic compositions of the original projectile. We have used the NanoSIMS to perform C, N, and O isotope imaging measurements on four large (59-370 microns diameter) and on 47 small (0.32-1.9 microns diameter) Al foil impact craters as part of the STARDUST Preliminary Examination. Most analyzed residues in and around these craters are isotopically normal (solar) in their C, N, and O isotopic compositions. However, the debris in one large crater shows an average 15N enrichment of approx. 450 %, which is similar to the bulk composition of some isotopically primitive interplanetary dust particles. A 250 nm grain in another large crater has an O-17 enrichment with approx. 2.65 times the solar O-17/O-16 ratio. Such an O isotopic composition is typical for circumstellar oxide or silicate grains from red giant or asymptotic giant branch stars. The discovery of this circumstellar grain clearly establishes that there is authentic stardust in the cometary samples returned by the STARDUST mission. However, the low apparent abundance of circumstellar grains in Wild 2 samples and the preponderance of isotopically normal material indicates that the cometary matter is a diverse assemblage of presolar and solar system materials.

Stadermann, Frank J.↗

NASA NTRS1985

Time-dependent dusty gasdynamical flow near cometary nuclei

This paper presents time-dependent solutions to the coupled dusty hydrodynamics equations describing the spherically symmetric expansion of cometary neutral gas in the vicinity of a cometary nucleus. The sublimation process is repressented by gas outflow from a dust-covered reservoir containing stationary gas whose pressure and density values are determined by the sublimating (Ts) and surface (T0) temperatures. The model resolves earlier ambiguities in determining gas production rates and provides analytic relations between Ts, T0, and the gas parameters at the sonic point. The time evolution of a cometary outburst was modeled. It was found that, as a result of the strong gas-dust interaction in the inner coma region, a 'slow' disturbance in both the dust and gas parameters will be created in addition to the familiar gas blast-wave solution. This new 'slow' disturbance, which propagates with a velocity of about 0.2 km/s, might be responsible for some of the observed slowly expanding cometary halos, such as the one which was recently identified using 1910 Mount Wilson high-resolution comet Halley photographs.

Gombosi, T. I.↗

NASA NTRS2005

Comets, Carbonaceous Meteorites, and the Origin of the Biosphere

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.

Hoover, Richard B.↗

NASA NTRS2007

Stardust in STARDUST - the C, N, and O Isotopic Compositions of Wild 2 Cometary Matter in Al Foil Impacts

In January 2006, the Stardust mission successfully returned dust samples from the tail of comet 81P/Wild 2 in two principal collection media, low density silica aerogel and Al foil. While hypervelocity impacts at the Stardust encounter velocity of 6.1 kilometers per second into Al foils are generally highly disruptive for natural, silicate-dominated impactors, previous studies have shown that many craters retain sufficient residue to allow a determination of the elemental and isotopic compositions of the original projectile. We have used two NanoSIMS ion microprobes to perform C, N, and O isotope imaging measurements on four large (59-295 micrometer diameter) and on 47 small (0.32-1.9 micrometer diameter) Al foil impact craters as part of the Stardust Preliminary Examination. Most analyzed residues in and around these craters are isotopically normal (solar) in their C, N, and O isotopic compositions. However, the debris in one large crater shows an average N-15 enrichment of approx. 450%o, which is similar to the bulk composition of some isotopically primitive interplanetary dust particles and to components of some primitive meteorites. A 250 nm grain in another large crater has an O-17 enrichment with approx. 2.65 times the solar O-17/O-16 ratio. Such an O isotopic composition is typical for circumstellar oxide or silicate grains from red giant or asymptotic giant branch stars. The discovery of this circumstellar grain clearly establishes that there is authentic stardust in the cometary samples returned by the Stardust mission. However, the low apparent abundance of circumstellar grains in Wild 2 samples and the preponderance of isotopically normal material indicates that the cometary matter is a diverse assemblage of presolar and solar system materials.

Stadermann, Frank J.↗

NASA NTRS1979

Scientific returns from a program of space missions to comets

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.

Delsemme, A. H.↗