Planetary differentiation

Planetary differentiation is the separation of a planet’s materials into layers with different compositions or densities. It commonly produces a dense metallic core beneath a silicate mantle and crust.

Accretional heating: Heat generated as a growing body gains mass through impacts and gravitational energy release. Impacts during growth supplied heat that could initiate melting and allow dense materials to sink.
Planetary accretion: The growth of planets through collisions and gravitational accumulation of smaller bodies. Differentiation often begins while accretion is still assembling a planet.
Earth's core: Earth’s dense, iron-rich central region, divided into a liquid outer core and solid inner core. It is the clearest large-scale product of metal sinking during terrestrial differentiation.
Planetary magnetic field: A magnetic field generated or retained by a planet, often through motion of electrically conducting material in its interior. Differentiation can create a liquid metallic core capable of sustaining a magnetic dynamo.
Radioactive decay: The spontaneous transformation of unstable atomic nuclei into more stable nuclei, releasing energy. Short-lived radioactive isotopes heated early planetesimals enough to melt and separate.
Chondritic meteorite: A stony meteorite containing rounded chondrules and primitive material that has not undergone extensive melting. Chondrites provide evidence for the broadly undifferentiated ingredients from which rocky planets formed.
Earth's mantle: The thick silicate layer between Earth’s crust and core, composed mainly of solid rock that can flow over time. Its chemistry records what remained after much of Earth’s iron entered the core.
Geodynamo: The process generating Earth’s magnetic field through convection and rotation in its electrically conducting outer core. Core formation established the metallic reservoir whose motion powers Earth’s dynamo.
Iron catastrophe: A proposed early-Earth process in which widespread melting let iron descend rapidly toward the center. It illustrates how large-scale melting can produce a metallic core quickly.
Silicate: A mineral or material built from silicon–oxygen units, forming most of Earth’s mantle and crust. Silicate chemistry determines the composition of the rocky layers left above a metallic core.

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