Iron planet

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Comparison of sizes of planets with different compositions

An iron planet is a type of planet that consists primarily of an iron-rich core with little or no mantle. Mercury is the largest celestial body of this type[citation needed] in the Solar System, but larger iron-rich exoplanets may exist. Also known as a Cannonball.[1]


Iron-rich planets may be the remnants of normal metal/silicate rocky planets whose rocky mantles were stripped away by giant impacts. Some are believed to consist of diamond fields. Current planet formation models predict iron-rich planets will form in close-in orbits or orbiting massive stars where the protoplanetary disk presumably consists of iron-rich material.[2]


Iron-rich planets are smaller and more dense than other types of planets of comparable mass.[3] Such planets would have no plate tectonics or strong magnetic field as they cool rapidly after formation.[2]


Some extrasolar planet candidates that may be composed mainly of iron are KOI-1843 b,[4] Kepler-70b and Kepler-10b.

See also[edit]


  1. ^ Gillett, Stephen L. (1996). Ben Bova, ed. World-Building. Cincinnati, Ohio: Writer's Digest Books. p. 173. ISBN 158297134X. 
  2. ^ a b "Characteristics of Terrestrial Planets" by John Chambers, from "The Great Planet Debate: Science as Process", August 14–16, 2008, The Johns Hopkins University Applied Physics Laboratory Kossiakoff Center, Laurel, MD.
  3. ^
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