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Question 3:
What evidence do astronomers have for concluding that the object with tails is an asteroid and not a comet?

One of the primary pieces of evidence is the location of the object in the asteroid belt. Another clue is that it appears to have a similar orbit as other pieces of a larger asteroid that broke apart in a collision roughly 200 million years ago. Meteorites from these bodies show evidence of being heated, which means that any ices in the original rock would be driven off, causing changes to the rocks and making them metamorphic rocks.

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