Iron planet

An iron planet is a terrestrial planet composed predominantly of iron, with a small silicate mantle or none at all. Its unusually large metallic core distinguishes it from rocky planets with substantial silicate mantles.

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Planetary differentiation: The separation of a young planet's materials into layers according to density and chemical affinity. Differentiation concentrates dense iron at the center, helping produce an iron-dominated interior.
Mercury: The smallest planet in the Solar System, with an unusually large iron-rich core beneath a silicate mantle. Mercury is a nearby example of high metal content, but it is not known to be predominantly iron.
Radial velocity method: A method for detecting planets by measuring the periodic Doppler shifts they induce in a star's spectrum. It supplies planetary mass estimates needed to calculate an iron-rich world's density.
Silicate planet: A terrestrial planet whose mass is dominated by silicate rock rather than metallic iron. It represents the mantle-rich compositional alternative to an iron-dominated world.
Giant impact hypothesis: The hypothesis that a large collision stripped much of a planet's rocky mantle. A mantle-stripping collision could leave a remnant with a disproportionately large iron core.
K2-229 b: A hot, dense exoplanet whose measured mass and radius imply a substantial iron core. Its inferred interior is often discussed as evidence for a possible iron-rich planet.
Transit method: A method for detecting planets by measuring the dimming of a star as a planet crosses its disk. Transit depth yields a planet's radius, complementing mass in composition estimates.
Carbon planet: A hypothetical terrestrial planet whose interior contains unusually abundant carbon-bearing materials. It shows that terrestrial planets can differ through dominant chemistry, not only iron-to-silicate ratio.
Core–mantle boundary: The interface separating a planet's metallic core from its silicate mantle. Iron planets have a large core relative to this boundary's mantle side.
Kepler-107 c: A dense exoplanet in the Kepler-107 system, measured to be much denser than its neighboring planet. Its density contrast has been interpreted as possible evidence of mantle loss after a collision.