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Earth-class planet
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.
Related categories
• PLANETS AND MOONS
• ASTROBIOLOGY
Archived news
Plenty of Earths await discovery (Apr 5, 2004)
Smallest 'Earth-like' planet seen (Aug 25, 2004)
Galaxy teeming with Earths argues astrophysicist (Feb 19, 2001)
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