The 4¹/₂ Steps of Terrestrial Planet Formation in the Solar System. (cont)
Step III: Oligarchic Growth (Kokubo & Ida 1998)

• 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.
  
  
• Studies have shown that (Kokubo & Ida):
  • The largest few objects at any given time are:
    1. of comparable mass
    2. 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.
    3. Their separation increases.