Planetary core

A planetary core is the central, densest region of a planet, typically composed largely of iron and other metals. Its composition and physical state shape a planet’s magnetic field, heat flow, and interior evolution.

Planetary differentiation: The separation of a planet’s materials into layers according to density and chemical affinity. Dense metals sank toward planetary centers, forming cores during early differentiation.
Planetary interior: The internal structure and material of a planet beneath its surface. A core is the deepest major layer in many differentiated planetary interiors.
Earth's core: Earth’s iron-rich interior region, consisting of a liquid outer core and a solid inner core. It is the best-studied planetary core and provides the clearest model of layered metallic interiors.
Earth's inner-core anisotropy: The direction-dependent speed of seismic waves passing through Earth’s solid inner core. Its origin may record crystal alignment, growth, or changing conditions within the core.
Core accretion: The growth of a planetary core as dense material gathers at a growing body’s center. This process describes how metallic cores formed inside many early planetary bodies.
Iron-nickel alloy: A metallic mixture of iron and nickel found in planetary cores and meteorites. Iron and nickel are major constituents of Earth’s core and many planetary cores.
Mercury's core: Mercury’s unusually large metallic core, which occupies a substantial fraction of the planet’s interior. Its size distinguishes Mercury from other terrestrial planets and constrains its formation history.
Earth's inner-core age: The estimated time when Earth’s solid inner core began to crystallize from its liquid outer core. Different age estimates imply different histories for the geodynamo and core cooling.
Iron catastrophe: A proposed rapid sinking of molten iron through a young planet’s silicate mantle toward its center. It offers a mechanism for rapid core formation in early Earth.
High-pressure mineral physics: The study of how materials behave under the extreme pressures found inside planets. Laboratory measurements constrain which core materials remain solid or liquid at depth.

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