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Comet Dust Seems More Asteroidy

The NASA Stardust mission sampled dust from a comet and brought it back to earth--where the now studied dust seems more like what asteroids should be made of. Chelsea Wald reports.

Remember the good old days when we understood our solar system? Then we found out Pluto wasn’t a planet. And now a new study puts comets in question. The data come from NASA’s Stardust mission—that’s the one that scooped up particles from comet Wild 2 and returned to earth two years ago. The conventional wisdom is that comets originated in the outer solar system, then the sun or a planet nudged them into weird orbits.

Well, this study in the journal Science contradicts that wisdom. Turns out that the particles from Wild 2 look like they belong not to a comet but to an asteroid from the inner solar system. In fact, Stardust didn’t capture any of the pre-solar-system stuff that comets should be made of. This means that the distinction between asteroids and comets may be surprisingly blurry. Some comets might have migrated out from the inner solar system. Or there could be lots of inner solar system stuff in the outer solar system. Either way, it’s time to start rewriting those astronomy textbooks…again.

—Chelsea Wald

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