>>  You know I can remember back in my late teens and early twenties
>>  when the broken up planet theory accounting for the asteroid belt
>>  was an acceptable idea. It was around for a few years. This would
>>  have been in the 60s [ if you can remember the 60s then you
>>  weren't really there].
> I checked my references, including a prominent astronomy text of
> the 1960s (Baker's). The only reference I can find to a breakup
> theory being taken seriously was shortly after the first asteroid
> observation in the early 1800s (when Bode's Law was still
> considered useful, and a planet between Mars and Jupiter was
> considered essential), but by the '60s all of the origin theories
> are condensation and accretion theories. In the '70s Alfven's
> introduction of plasma and magnetic field considerations into the
> origin problem led him to write with Arrhenius the definitive
> text on origins for NASA.
Well I have a book from 1992 which uses Bode's Law and has the
asteroid belt as an orbit.  As I understand Bode's Law predicts
probable orbits, and those orbits realistically don't need
full formed planets to fill them.
 > Of course, there may have been some popular theories to that
 > effect, but I think its been a long time since any scientist
 > thought a planet could be destroyed by anything other than a
 > collision.
I know there is a very large outer moon that gets routinely
ripped apart and then falls back together again causing a
strange surface of many different sorts of rocks.  I don't see
why planets subjected to great gravitational forces can't
be ripped apart like this, many of the outer moons would be
classified as small planets if they were free in their own
orbit.
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