A planet up to 10 Earth masses, but less massive than Uranus and Neptune. Assuming 'size' is defined by linear dimension (or by volume), mesoplanets should be approximately 1,000 to 5,000 km (620 to 3,110 mi) in diameter.Īlso known as a gas dwarf or transitional planet. A term, not commonly used in the astronomical community, coined by Isaac Asimov. Planets of mass similar to Uranus or Neptune smaller than the gas giants, but still much larger than Earth.Ī planetary body with a size smaller than Mercury, but larger than Ceres. Regardless of their bulk compositions, giant planets normally have thick atmospheres of hydrogen and helium. They are most commonly composed primarily of 'gas' (hydrogen and helium) or 'ices' (volatiles such as water, methane, and ammonia), but may also be composed primarily of rock, which would make one a Mega Earth.
