The Ugly Truth
Unfortunately, there are two major problems with this model.
- Transition from runaway to late-stage of planet formation:
- Recall that
as long as 
is not affected by M.
- As the big guys grow, they have a larger fraction of system mass
stir small guys.
- So, growth slows. ..............
This phase is known as Oligarchic Growth (Ida et al.).
- Studies at 1AU have shown that:
- The largest few objects at any given time are:
- of comparable mass
- separation is ~10RH ~ f(M,a).
- So, as the system evolves:
- Number of big guys decreases.
- Their masses increase.
- Their separation increases.
- Thommes, Duncan, & Levison (2001) studied this extensively in outer solar system.
- Two phases: before and after the gas goes away. Because gas affects velocities.
- Phase I: For a relatively massive disk, we can:
- make Jupiter and Saturn's cores,
- but nothing at 20AU.
- Phase II: Still cannot build Neptune in a billion years.
