Types
Several possible classifications for terrestrial planets have been proposed:
- Silicate planet
- The standard type of terrestrial planet seen in the Solar System, made primarily of silicon-based rocky mantle with a metallic (iron) core.
- Iron planet
- 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 believed to form in the high-temperature regions close to a star, like Mercury, and if the protoplanetary disk is rich in iron.
- Coreless planet
- A theoretical type of terrestrial planet that consists of silicate rock but has no metallic core, i.e. the opposite of an iron planet. The Solar System contains no coreless planets, but chondrite asteroids and meteorites are common in it. Coreless planets are believed to form farther from the star where volatile oxidizing material is more common.
- Carbon planet (also called "diamond planet")
- 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.
- Super-Earth
- Super-Earths are planets with masses between Earth's and Neptune's. They may be gas planets or terrestrial, depending on their mass and other parameters. The latter represent the upper-end of the terrestrial-planet mass range.
Read more about this topic: Terrestrial Planet
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