tp030.html

The 4¹/₂ Steps of Terrestrial Planet Formation in the Solar System. (cont)
Step III: Oligarchic Growth (Kokubo & Ida; Goldreich et al.; Chambers)

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.
- is roughly constant with mass, so .
So, growth slows and smaller oligarchs can catch up with larger ones.
Studies have shown that (Kokubo & Ida):
- The largest few objects at any given time are:
  1. of comparable mass
  2. orbital separation is ~10R_H, (Earth: R_H=0.01AU)
    where R_H is the gravitational sphere of influence and is f(M,a).
- So, as the system evolves:
  1. Number of big guys decreases.
  2. Their masses increase (mainly by eating planetesimals, but some mergers happen).
  3. Their separation increases.
Oligarchic growth stops when small guys or gas can no longer damp big guys.
- Roughly the size of the Moon or Mars at 1AU. (Kenyon & Bromley)
- This takes roughly a million years.