The Ugly Truth (cont)

• The published works on the late stage of Uranus and Neptune formation are wrong.
  • The authors of these papers now acknowledge that there were problems with their codes.
  • When we attempted to reproduce these, we get very little growth. (Levison & Stewart 2001).
    • In Ip 1989 simulation we got one merger in 10⁸ years!
  • System got too `hot' to form planets.
    • During a simulation, the time to next collision is, .
    • As system heats up, and , but due to gravitational focusing.
    • So, . System must remain cold to allow growth!
  • However, the standard model works for the terrestrial planets! So, what is different?
    • Gravitational varies with heliocentric distance, physical does not.
    • If objects are close to the Sun then ratio is small.
      
    • If objects are far from the Sun then ratio is large.
      
    • At 20AU scatterings are much more common than collisions, so the system gets excited.