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 in the Solar System, but larger iron-rich exoplanets may exist. Also known as a Cannonball.
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.
Iron-rich planets are smaller and more dense than other types of planets of comparable mass. Such planets would have no plate tectonics or strong magnetic field as they cool rapidly after formation.
See also