Comet dust collection

At the time of encounter, Wild2 was at 1.86 AU, and thus was very active. Comets release thousands of tons of dust during cometary activity - the dust is there for the taking, the trick is to snatch it without destroying it or the spacecraft. Two technological achievements by scientists at the Jet Propulsion Laboratory made the collection of comet dust possible the clever design of a trajectory that allowed the spacecraft to encounter the comet coma at a relatively modest speed (6.1 kms ), and the development of a capture medium that slowed and trapped the particles without destroying them. 

Brownlee, D. and 181 coauthors ( ) (2006) Comet 81 P/Wild2 under a microscope. Science 314, 1711-1716. This fascinating article, plus the more focused articles that follow it in the same issue, provide the first characterization of comet dust samples collected and returned by the Stardust spacecraft. 

Comets EUV spectroscopy in-situ dust collection (see also IDPs) Cl chondritic meteorites Ar abundance, upper limits for He, Ne. Stem 1999a. Stardust mission Lodders and Osborne 1999 Ehrenfreund et al. 2001. 

A more recent mission, Deep Impact (2005), was designed to understand the Comet Tempel 1, by impacting it with a 370-kg mass Impactor and collect/analyze the Comet dust. The Impactor, also equipped with its own scientific equipment, was successfully powered by Li-SOCI2 batteries for one day, for navigation and science and communication, prior to the impact. The batteries were made by SAFT with 216 D-cells (9S24P) housed within a single mechanically and thermally coupled aluminum structure. 

Stardust February 7, 1999, saw the start of NASA s Stardust mission the cometary probe, the first mission to collect cosmic dust and return the sample to Earth, has a time-of-flight mass spectrometer (CIDA, Cometary and Interstellar Dust Analyser) on board. This analyses the ions which are formed when cosmic dust particles hit the instrument s surface. In June 2004, the probe reached its goal, the comet 8 IPAVild 2, getting as close as 236 km The CIDA instrument, which was developed at the Max Planck Institute for Extraterrestrial Physics in Garching (near Munich), studied both cometary dust and interstellar star dust. 

The solar system formed from a well-mixed collection of gas and dust inherited from its parent molecular cloud. The bulk composition of this material, as best we can know it, is given by the solar system abundances of elements and isotopes (Tables 4.1 and 4.2). From this bulk material, the planets, asteroids, and comets formed, each with its own unique composition. The processes that produced these compositions separated, or fractionated, elements and isotopes from one another. By studying these elemental and isotopic fractionations, we can potentially identify the processes that separated the elements and can leam about the physical conditions involved. This is particularly important for understanding the early solar system, because its processes and conditions are not directly observable. 

In order to consider the processes of dust coagulation in the early Solar System, we first review the characteristics of this material. Of considerable importance is the fact that these samples - represented principally by chondritic meteorites, but also by IDPs and by samples from Comet Wild 2 collected by the Stardust mission - all come from parent bodies of different kinds. As a result, even the most primitive of these materials has been processed, both physically and chemically, to different degrees. The processes that affected Solar System dust may have occurred in different environments such as the solar nebula (e.g. evaporation/condensation, annealing) and asteroidal parent bodies (aqueous alteration and/or thermal processing, mild compaction to extensive lithihcation). A major challenge is to understand the effects of this secondary processing. 

The sizes of the cometary dust grains vary from less than a micron to probably several centimeters. Infrared observations near 10 pm show the silicate spectral features. In addition, there seems to be a black ingredient presumed to be carbon. Due to different accelerations from the solar radiation pressure, the larger particles follow the comet close in its orbit and are more concentrated to the orbital plane. They become sometimes visible in the anti-tails , narrow spikes which point towards the Sun by an effect of projection when the Earth crosses the comet s orbital plane. Non of the meteorites found so far on Earth seem to be of cometary origin. However, very fluffy micron sized interplanetary dust grains (Brownlee particles) which have been collected by high flying aircraft are possibly cometary debris. 

The obvious source of comet samples is by direct collection at a comet with Earth return. Stardust, the first comet sample mission (Brownlee et al., 2000), will collect the positively identified particulate samples from a comet and return them to Earth. Stardust, a NASA Discovery mission, will collect thousands of particles from the coma of SP comet Wild 2 and return them in 2006. Hopefully future sample return missions will, in addition, recover subsurface samples of ice and dust and return them to Earth with cryogenic preservation. 

Information on the chemical composition of active comets is available from two different "reservoirs , viz. solid debris and sublimated volatile species. The former is extracted by IR spectroscopy of the dust tail and dust trails in the comet s orbit, from collected IDPs, possibly a fraction of CI carbonaceous meteorites, and from meteor data. Information on species in the comet coma and plasma tail is obtained by UV-VIS-IR spectroscopy and radio astronomy. 

Interplanetary dust particles, micrometeorites Mass spectrometry, laboratory Dust from asteroids comets, collected in near Earth space, ice, sediments. Nier and Schlutter 1992 Olinger et al. 1990. ... 

Veiy few significant results on the physical properties of cosmic dnst, as revealed by in-situ experiments, may be expected in the coming years. The samples collected by the Stardust (interplanetaiy dust and comet SlPAVild 2 dust) and Hayabnsa (asteroid Itokawa regohth) missions shonld provide information primarily about chemical properties. The ground truth expected from space mission is thus quite far away in the future, with e g. the Rosetta rendezvous with comet 67P/Chuiyumov-Gerasimenko and landing on its nucleus in 2014. 

Artist s rendering ofAnny-Chantal Levasseur-Regourd after leaping off the Rosetta spacecraft onto Comet 67P/Churyumov-Gerasimenko to collect dust samples. Courtesy of F. Castel. 

These results were obtained with mineralogically and morphologically reasonable parameters of cometaiy dust. A mixture of silicates, metals, and carbonaceous materials, random aggregate structures, and submicron CPs are in agreement with characteristics not only the dust in comet IP/Halley, but also interplanetaiy dust particles (IDPs), collected in the Earth s atmosphere [75]. 

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