[world building] how do asteroid belts form?

[Malenfant]

This question is currently stumping me - is the presence of an asteroid belt defined as a fixed distance from a gas giant (i.e. if a terrestrial planet tries to form within a certain fixed distance from a gas giant then it won't be able to and you end up with an asteroid belt instead?), or is it defined by resonances caused by the gas giant?

I'm wondering if the latter is true since apparently the inner and outer edges of our own asteroid belt are defined by 4:1 and 2:1 resonances with Jupiter. However, if that is true then technically Jupiter can't have formed because it's between Saturn's 4:1 and 2:1 resonances. (migration can't really help either, apparently Jupiter only migrated inwards by about 0.5 AU at most, which means it would have started deeper in Saturn's 'asteroid belt zone').

The only solution I can see is that Jupiter formed before Saturn (I'm sure I've heard someone else suggesting this). Since it formed first, it was safe from disruption but could influence the space within its orbit and define the asteroid belt with its resonances.

Anyone know anything more about this? Does this sound about right given what we know?

[symaski62]

[Malenfant]

I'm wondering if the latter is true since apparently the inner and outer edges of our own asteroid belt are defined by 4:1 and 2:1 resonances with Jupiter.

This sentence in my original post was actually made with that diagram in mind - I already knew about that...

[ajtribick]

Some stuff I've come across (unfortunately I can't find it right now) suggests that material within ~3 Hill radii of a gas giant gets destroyed (ejected or accreted on to the gas giant), and planet formation within 8-10 Hill radii gets disrupted (i.e. planet-sized objects don't form). These numbers are for gas giants on circular orbits - the numbers change for eccentric ones.

[Malenfant]

Some stuff I've come across (unfortunately I can't find it right now) suggests that material within ~3 Hill radii of a gas giant gets destroyed (ejected or accreted on to the gas giant), and planet formation within 8-10 Hill radii gets disrupted (i.e. planet-sized objects don't form). These numbers are for gas giants on circular orbits - the numbers change for eccentric ones.

That sounds like it's related to the papers listed here:
http://www.celestiaproject.net/forum/viewtopic.php?t=9594

Those mention 3 hill radii as the limit for ejection... I don't think they mention 8-10 hill radii for disruption though. But still, it does make sense to use the hill radii to figure out that disruption distance, and that would also scale up or down with distance from the star. Hmm....