What makes an asteroid an asteroid and not a comet

raknath

Hi all


Have been thinking about this for sometime, what is the fundamental difference that makes an asteroid an object orbitting around the star at a lesser speed and not a comet?

Hope my question is clear, framing it otherwise why do asteroids not turn into raging comets or comets into sedate asteroids?

Thanks again

Nabeshin

Comets are almost exclusively in highly elliptical orbits (why we only see them every hundred years). This is thought to be because they were objects ejected (by some form of gravitational pertubation) from the Kuiper belt or Oort Cloud. An object in such a highly elliptical orbit spends a comparatively low amount of its life near enough to the sun to remove any gasses and melt any ices (what we observe as the comet's tail). An asteroid close enough to the sun would be stripped of these elements within a fairly short period of time.

Though, the distinction is based almost solely on their appearance. Certainly an asteroid in the outer solar system could have the same composition as a comet which streaks through the solar system with a fairly long period. The difference is, because the asteroid is in a (much more) circular orbit, there is no perceptible change in its appearance (increase in luminosity), so they go undiscovered. If someone were to magically throw it towards the inner solar system, it would appear the same.

raknath

What you are basically saying is that random gravitational perturbances cause the asteroid/stellar body to assume some extra velocity which in turn is added on by the gravitational pull of the star near it and hence it becomes a comet

Am i correct then in assuming that the flip-flop between an asteroid and comet is a matter of pure chance?

mgb_phys

It's an arbitrary definition, like the split between a planet and an asteroid.
Any rock can become either depending on it's interactions.

ray b

comets have more ice or frozen gas to form a tail
and fewer hard high melting stuff in them
a rocky or metal asteroid will not form a tail
unless it gets so close to the sun to melt
the rock or metal

has there ever been a rock or metal comet without ice

mgb_phys

what does a comet become when all it's ice has evaporated?

Most of them, it only takes a few 1000s orbits for most to lose all their volatiles.

ray b

but at that point it is no longer a comet!!!!!!!!!!!!
but a asteroid with a odd orbit

Chronos

The Oort cloud, as Nabeshin noted, is the short answer. An asteroid is essentially a comet with little or no volatiles on its surface [such as ice]. Asteroids typically have orbits within the confines of Jupiter's orbit. See
http://nasm.si.edu/research/ceps/etp...et_orbits.html

raknath

Any rock IMO can become an ice ball far enough into space, which possibly explains why comets originate at the Oort cloud?