Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2004 June 22
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Unusual Spires Found on Comet Wild 2
Credit: Stardust Team, JPL, NASA

Explanation: How did unusual spires form on comet Wild 2? Close inspection of images taken of Comet Wild 2 by the passing Stardust spacecraft in January show numerous strange pinnacles as long as 100 meters long jutting off the surface. The pinnacles were unexpected - close-ups of other comets and asteroids show no such features. In fact, no other Solar System object besides Earth is known to show such unusual structures. Other unusual Wild 2 surface features including long cliffs, deep pits and craters, and numerous active jets. Together with the spires, these features are hypothesized to be indicative of a very rigid surface sculpted by impacts and explosive sublimation. Initially, Wild 2 was expected by many to be held together only quite loosely. Stardust is scheduled to fly by the Earth in 2006 and drop off a sample of Wild 2 for detailed scrutiny.

Tomorrow's picture: picturesque circle

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