GURPS Space - assistance

[Whill]

In an eccentric gas giant arrangement where a gas giant formed outside of the snow line and migrated sunward before stablizing into a new orbit, shouldn't one of the outer orbits be left empty of any gas giants to represent the inner gas giant's original orbit before migration?

Or is that not necessary because a cause for the migration could be that the original gas giant orbit was not stable in the long term, which is what may have caused the close encounter that sent the eccentric gas giant inward in the first place?

[Agemegos]

Originally Posted by Whill

In an eccentric gas giant arrangement where a gas giant formed outside of the snow line and migrated sunward before stablizing into a new orbit, shouldn't one of the outer orbits be left empty of any gas giants to represent the inner gas giant's original orbit before migration?

Not necessarily. Migrating gas giants don't necessarily move alone, but dragging things in from outer orbits behind them. In our system Jupiter formed at about 3.5 AU, migrated in to 1.5 AU by interactions with the disk of planetismals, then got into a resonance with Saturn that first dragged Saturn inwards and then pulled both of them outwards. It ended up further out than it formed, but there was an era in which Jupiter had migrated inwards from the distance that it formed at and had pulled Saturn in to a distance less than that which Jupiter formed at.

[Whill]

Originally Posted by Brett

Not necessarily. Migrating gas giants don't necessarily move alone, but dragging things in from outer orbits behind them. In our system Jupiter formed at about 3.5 AU, migrated in to 1.5 AU by interactions with the disk of planetismals, then got into a resonance with Saturn that first dragged Saturn inwards and then pulled both of them outwards. It ended up further out than it formed, but there was an era in which Jupiter had migrated inwards from the distance that it formed at and had pulled Saturn in to a distance less than that which Jupiter formed at.

I hadn't read all of that early migration in and out of Jupiter and Saturn. Cool. But does this mean that the book's formula for calculating snow lines is incorrect or out-of-date? On p.106 it says R = 4.85 x square root of L. According to the chart on p.103 has the L-Min for a G2 as .68. So according to the book, Sol's snow line would be (4.85 x square root of .68), about 4 AU.