Recently the Hubble Space Telescope discovered a new class of planet, a "Waterworld" if you will. The new (dense) planet is larger than Earth, but smaller than Uranus.
From Hubble's office website:
Observations by NASA's Hubble Space Telescope have come up with a new class of planet, a waterworld enshrouded by a thick, steamy atmosphere. It's smaller than Uranus but larger than Earth.
Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA) and colleagues made the observations of the planet GJ1214b. "GJ1214b is like no planet we know of," Berta said. "A huge fraction of its mass is made up of water." The ground-based MEarth Project, led by CfA's David Charbonneau, discovered GJ1214b in 2009. This super-Earth is about 2.7 times Earth's diameter and weighs almost seven times as much. It orbits a red-dwarf star every 38 hours at a distance of 1.3 million miles, giving it an estimated temperature of 450 degrees Fahrenheit.
"The Hubble measurements really tip the balance in favor of a steamy atmosphere," Berta said.
It looks like they're still working out the atmospheric pressure present on GJ1214b (which from now on I'm referring to as "Geoff"*). But 450°F is healthily in the steam side of water, using Earth's atmospheric pressure as a basis. Even without the water being in liquid state, this is a pretty huge discovery. Geoff could be a good place to start pointing SETI radio telescopes at and could be a good basis for modifying the current model for what can support life. Scientists believe it did exist in the commonly accepted habitable zone at some point in its history, how long or when is still to be determined.
Source -> http://hubblesite.org/newscenter/archive/releases/2012/13/full/ via http://gizmodo.com/5887003/hubble-discovers-a-new-type-of-world-made-of-water
*If you get that joke, I'm impressed