The planet GJ 1214b, shown here in an artist's conception with two hypothetical moons, orbits a "red dwarf" star 40 light-years from Earth. GJ 1214b has a radius of about 2.7 times that of Earth and is about 6.5 times as massive, putting it squarely into the class of exoplanets known as super-Earths.

Astronomers have confirmed that this alien world has a thick atmosphere, but can't yet determine whether the atmosphere is primarily hydrogen or a steamy soup of water vapor.