Lifetime of a comet

acurno

Hi all,
Just following up from the thread about the Hale-Bop (or however its spelt!). All comets have tails hundreds of thousands (or millions) of km long due to their proximity to the sun heating up the surface and creating a debris tail right? So how much degredation does a comet suffer during a pass of the sun? Comets I'm lead to believe are remnants from the early formation of the solar system so how have they survived this long considering they lose mass after each solar pass?

I remember years ago when Hale-Bop came on the scene some American creationist used this argument, as in, it's impossible comets are 4b+ years old because of this loss of mass.

My only guess is that, similar to water when it freezes it gains mass (something like 20% I think from what I remember from LC Geography class), so that when the comet goes back to deep space it I suppose, re-freezes??

djhaxman

It depends on if they are short or long period comets. Short period comets like Halley's comet return frequently by astronomical standards and everytime they orbit the sun they lose mass. Long period comets can have orbits of hundreds of thousands of years so will last a lot longer.

enda1

acurno wrote: »

snip

My only guess is that, similar to water when it freezes it gains mass (something like 20% I think from what I remember from LC Geography class), so that when the comet goes back to deep space it I suppose, re-freezes??

When water freezes it gains volume. Mass stays the same (actually if you talk about the tiny decimals it actually drops a little bit!) but its density changes and therefore its volume.

Zubeneschamali

acurno wrote: »

Comets I'm lead to believe are remnants from the early formation of the solar system so how have they survived this long considering they lose mass after each solar pass?

Simple answer is that lots of them haven't survived this long.

There's a big cloud of billions of them way out in the cold, dark bits of the solar system. Every now and then, something disturbs an orbit, and a comet sails into the inner system where we see it. Some of them are destroyed the first time they pass the Sun. Some swing around the Sun and back out into the outer system, and we never see them again.

A few are captured into short period orbits in the inner system, and we see them more than once. These are thought to survive for some limited number of orbits, (50-1000 depending on how close they get to the Sun).

Then their ice is all gone, and just a bit of rock and dirt is left.