The Big Break-Up
Everybody’s talking about the big break-up. No, I don’t mean Nick and Jessica. I’m talking about Schwassmann-Wachmann, a comet that supposed to swung by earth next month, after it — according to one report — broke up for no apparent reason ten years ago.
In 1995, Comet 73P/Schwassmann-Wachmann 3 did something unexpected: it fell apart. For no apparent reason, the comet’s nucleus split into at least three "mini-comets" flying single file through space. Astronomers watched with interest, but the view was blurry even through large telescopes. "73P" was a hundred and fifty million miles away.
No apparent reason? Not exactly.
Naturally, I’m not the guy with the answers on this. (Again, I refer you to the screen name.) But Phil over at Bad Astronomy has what seems like a reasonable explanation to me.
The exact cause is a mystery, though there are plenty of reason why a comet would fall apart. Comets are made of rock and ice. When they get near the Sun, the ice sublimates– turns directly into a gas — and flows into space, which is why comets look fuzzy in pictures. The actual nucleus, the solid part, is very small, but the coma, the fuzzy part, can be thousands of miles across.
It makes sense that after repeated passes of the Sun, enough ice is lost to venting that the structure of the comet can be fragile, since the ice in a way is holding the comet nucleus together. Once enough ice is gone, a breakup could occur if the sublimating ice builds up enough pressure to disrupt the structure. But that is just one explanation. The famous comet Shoemaker-Levy 9 broke apart because of the immense tidal forces of Jupiter’s gravity. Most comets don’t break apart; look at comet Halley, which has been circling the Sun for a long, long time (it was seen in ancient times). It goes to show that some comets are very fragile, and some are not.
OK, so it’s just one possible explanation, but it’s one more than I could come up with on my own. But just for the sake of argument, what other explanations could there be? Unless Bruce Willis or Morgan Freeman had an hand in it, I’ll take Phil’s explanation for now. (HubbleSite has the pics.)
