Equilibrium Condensation Model
• Start with material of solar composition material
–   (H, He, C, N, O, Ne, Mg, Si, S, Fe ...)
• Material starts out hot enough that everything is a gas
– May not be exactly true but is simplest starting point
• As gas cools, different chemicals condense
– First high temperature chemicals, then intermediate ones, then ices
• Solids begin to stick together or accrete
– snowflakes snowballs (“Velcro Effect”)
• Once large enough gravity pulls solids together into planetesimals
– planetesimals grow with size
• At some point wind from sun expels all the gas from the system
– Only the solid planetesimals remain to build planets
– Composition depends on temperature at that point (in time and space)
– Gas can only remain if trapped in the gravity of a large enough planet