<Dd> A theoretical type of terrestrial planet that consists almost entirely of iron and therefore has a greater density and a smaller radius than other terrestrial planets of comparable mass . Mercury in the Solar System has a metallic core equal to 60--70% of its planetary mass . Iron planets are thought to form in the high - temperature regions close to a star, like Mercury, and if the protoplanetary disk is rich in iron . </Dd> <Dd> A theoretical type of terrestrial planet that consists of silicate rock but has no metallic core, i.e. the opposite of an iron planet . Although the Solar System contains no coreless planets, chondrite asteroids and meteorites are common in the Solar System . Coreless planets are thought to form farther from the star where volatile oxidizing material is more common . </Dd> <Dt> Carbon planet (also called "diamond planet") </Dt> <Dd> A theoretical class of planets, composed of a metal core surrounded by primarily carbon - based minerals . They may be considered a type of terrestrial planet if the metal content dominates . The Solar System contains no carbon planets, but does have carbonaceous asteroids . </Dd>

Which terrestrial planet has an atmosphere similar to earth's