A mini-Neptune (sometimes known as a gas dwarf or transitional planet) is a planet of up to 10 Earth masses , smaller than Uranus and Neptune, which have about 14.5 and 17 , respectively. Mini-Neptunes have thick hydrogen–helium atmospheres, probably with deep layers of ice, rock or liquid oceans (made of water, ammonia, a mixture of both, or heavier volatiles). These planets have small cores made of low-density volatiles.