Scientists have discovered a new type of    alien planet — a steamy waterworld that is larger than  EARTH but smaller than URANUS.

The standard-bearer for this new class of exoplanet is called GJ 1214b, which astronomers first discovered in December 2009. New observations by NASA's Hubble Space Telescope suggest that GJ 1214b is a watery world enshrouded by a thick, steamy atmosphere.