the Ice Zone
- Once the planetesimal ~ 1 km in size -- gravity
- universal attractive force
- accelerates growth of planetesimals
- largest planetesimal in neighborhood dominates
- eventually, growth to 10,000 km
- size of terrestrial planets
- provides core for giant planets
- For terrestrial planets, this is the end of the line
- can’t retain H, He gasses and grow further
- too hot, not enough gravity
- Volatile gases added later through outgassing or cometary impacts
- For giant planets, core grows large enough to retain H, He
- low T, high gravity
- Gas molecules have low speeds because of low T
- Escape velocity is high, and exceeds the gas velocities