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Wild 2 (pronounced 'vilt 2') used to be a comet orbiting beyond the orbit of Neptune. In 1974 a close encounter with Jupiter's gravity sent the comet on a new orbit that takes it into the inner Solar System. In January 2004 the Stardust spacecraft took close-up photos (plus samples of comet dust from its halo) and revealed a comet nucleus approximatly 4 to 5.5 km across and 3 km deep. It is approximately the shape of a fully inflated whoopie cushion. Like other comets, this nucleus reflects very little light, only about 3%, and is thus darker than coal (but similar to coal dust). The major suprise is that this comet appears to be a solid rounded (ellipsoidal) block of dirty ice that has enough mechanical strength to preserve craters with steep sides (up to 70° slopes) and pinacles up to 100 meters tall. Unlike the other two examples we've seen, Wild 2's surface has preserved a history of impacts from at least the most recent of its 4.57 billion years of history! Next: Abundant Comets (SOHO)Image credits: Stardust website run by JPL and NASA. Caption information: Science Magazine articles, June 18, 2004 (vol 304, no 5678) |
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