Accretion is the growth of planetary bodies through collisions and gravitational capture of smaller material, while differentiation is the internal separation of materials by density after a body becomes hot enough for substantial melting or flow. Accretion and differentiation explain why rocky planets have metallic cores and silicate mantles, why giant impacts can alter composition, and why small primitive bodies preserve early Solar-System material better than large geologically processed worlds.
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Accretion is the growth of planetary bodies through collisions and gravitational capture of smaller material, while differentiation is the internal separation of materials by density after a body becomes hot enough for substantial melting or flow.
supportedAs a growing body becomes more massive, gravitational focusing increases the effective collision cross-section and accelerates accretion.
Planet densities, seismic measurements, gravity fields, magnetic fields, meteorites, and returned samples reveal differentiated interiors.
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