🚀 go-pugleaf

In article <327F0356.2AE9@bas.ac.uk>,
A Paul R Cooper  <paul.cooper@bas.ac.uk> wrote:
>> If you look at our solar system we have a missing planet.  This missing
>> planet has left plenty of evidence if we look between the orbits of Mars &
>> Jupiter there should be a planet. However, what we find is called the
>> Asteroid Belt.

>I think that current theory on planetary formation suggests that the 
>asteroids are not the remains of a planet, but that they represent a region 
>where a planet could not aggregate because of gravitational resonances with 
>Jupiter. Can someone more knowledgeable confirm or deny this?

You are correct. The best work on the subject is by Wetheril (sp?)
who has done many numerical simulations of planetary formation.
He starts with a swarm of bodies, between the sizes of large asteroid
and the Moon, spread out through the inner solar system. This is
basically the prediction of other researchers, about what these
"planetesimals" would be like once they got large enough to gravitationally
interact with each other. He then allows the swarm to perturb each
other's orbits, collide and accrete, until there are just a few,
planetary bodies left in stable orbits. When he puts in perturbations
from Jupiter as well, his runs produce 3-5 terrestrial planets and
an asteroid belt. In a few percent of the runs, a small planet does 
form in the asteroid belt, but it is almost always ejected from
solar system by Jupiter, not broken up. In the vast majority of
the runs, no planet ever forms in the asteroid belt. When he does
not include perturbations from Jupiter, he gets a larger number
of planets and no asteroid belt. So according the the best existing
model of (terrestrial) planet formation, the odds of a planet forming
in the asteroid belt and then being broken apart are around 1%. In
addition to the theories, there is also observational data against
the asteroid belt having been the debris from a planet which broke
up: Stable isotope ratios in meteors show that the meteors came
from several parent bodies, while the debris from a single planet
(broken up or not) would have a single, isotopic "fingerprint."

                                                    Frank Crary
                                                    CU Boulder