How do astronomers know that Comet Hyakutake has been around the Sun before?

Because there are enough sightings to define the elements to its orbit, and its period now seems to be between 10 and 20,000 years. We do not, however, know if this is really its first pass or not. However, its composition and variation in brightness and shape suggest it is a relatively young comet that may not have seen many passes.


Copyright 1997 Dr. Sten Odenwald
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