Planetary Science

The Trail of a Wild Comet

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Science  30 May 2003:
Vol. 300, Issue 5624, pp. 1345
DOI: 10.1126/science.300.5624.1345a

Comets lose mass as they orbit close to the Sun, producing their distinctive coma and tail of gas and very fine particles. Comets also leave a longer trail of larger particles that are harder to see, except when Earth passes through a trail, causing a meteor shower. The Infrared Astronomical Satellite (IRAS) detected trails from eight short-period comets because the trail particles were very hot. Ishiguro et al. have detected a 2.3°(0.14 AU) long trail behind comet 81P/Wild2 at optical wavelengths—the first optical image of a trail without an infrared counterpart.

Wild2 is of particular interest because the Stardust mission will sample it in January 2004. The spacecraft will fly through the trail at a relative velocity of 6.1 km/s and sample the inferred 1-mm-sized particles. These particles may penetrate to the base of the aerogel sample collectors, but the Whipple bumper shields should protect the spacecraft from catastrophic disruption unless the particles are much larger. If all goes well, Stardust will return these samples to Earth in 2006 and we'll really get to see a comet up close.—LR

Astrophys. J. 589, L101 (2003).

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