A

David

Darling

Earth-class planet

Earthlike planet

An Earth-class planet is a planet having a mass 0.5 to 10 times that of the Earth (Me) and a radius 0.8 to 2.2 times that of the Earth. Planets more massive than 10 Me have enough gravity to attract a large hydrogen-helium atmosphere and so become gas giants. Those less massive than 0.5 Me are likely to lose any potentially life-supporting atmosphere because of low gravity and lack of plate tectonics needed to recycle carbon dioxide back into the atmosphere.