h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Comets journey billions of miles and hundreds or thousands of years from the outer reaches of the solar system or from the Oort Cloud, presumably drawn in by the gravity of the Sun. Why then do the comets, approaching for so long, finally pass harmlessly behind the Sun instead of crashing into it?

Let me begin this by making one thing clear: I AM NOT A PHYSICIST!

In other, less capitalised (but not communist by any stretch of the imagination), words, this is merely MY theory of why it happens.

The sun has a great magnetic pull which pulls objects into orbit. The comet, in being pulled by the gravitational force of the sun, has momentum. As the comet is pulled into orbit, its momentum is sufficient to keep the orbit from decaying to a point where it would crash into the sun. At some point, possibly because of chemical reactions, the comet is able to use this momentum to continue along its path.

Of course I could be totally wrong.

Of course comets crash into the Sun. In fact more
comets are discovered crashing into the sun than
those that don't.
They are known as the Kreutz family of comets (q.v.).
You can watch them approaching the Sun on the SOHO
website.

Thinking about objects crashing into other stella objects, is that asteroid still supposed to be crashing into the Earth in 2012 (or whenever). It would be nice to know so we can have that final boozy night before the dawn of death. ( I would have used a different phrase but I think Beeb Beeb Ceeb (to quote a goon) would have got a trifle upset!