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