Astronomers have claimed the existence of a new class of planet: a "water-world" with a thick, steamy atmosphere.
The planet, named GJ 1214b, is bigger than Earth but smaller than a gas giant like Jupiter.
It was discovered in 2009 but finally, scientists using the Hubble Telescope reckon they've proved there's a large amount of water on the surface.
GJ 1214b is about 2.7 times wider than Earth's but with a mass seven times higher. It is much closer to its sun.
That means the temperature there might get up to 200 degrees Celsius and GJ 1214b might contain weird materials like hot ice or 'superfluid water'.
The planet's relatively short (40 light years) distance from Earth means it is in the running for follow-up observations by the James Webb Space Telescope, when it is launched by the end of the decade.