posted on Apr, 26 2011 @ 10:44 PM
One thing that defines a comet is a highly elliptical orbit around the sun by a body with a diameter of around 3 km up to 50 km usually with a lot of
frozen H, O, N, He, and C, and other light gases which define their difference from solid rock metallic asteroids, with less lighter elements left.
Comets approach the sun much closer than asteroids so there is where the heating comes from, not to mention the extreme speed the sun's gravity
swirls them around then, comets are traveling faster than asteroids, due to their extreme orbits.
Some asteroids can be 10 times the size of the largest comets.
We have many meteorite samples on earth, zero from comets, so you know the geology is much more fragile on comets than asteroids, yes they are largely
frozen lighter gas and dust, while asteroids are hard bound metallic dead rocks, even the tiny pebbles.
A big comet impact threat is largely due to its speed, and not its geology, an asteroid at a comet's speed on impact would be much more devastating
to life on earth, given the same physical size.
Comets deteriorate in orbit, asteroids do not unless they collide.