It's larger than Earth but smaller than Uranus. (Thats what she said). It's enshroaded by a thick atmosphere of steam and a huge fraction of it's mass is water. According to NASA's official Hubble Telescope Site:
"Hazes are more transparent to infrared light than to visible light, so the Hubble observations help tell the difference between a steamy and a hazy atmosphere.
They found the spectrum of GJ1214b to be featureless over a wide range of wavelengths, or colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.
"The Hubble measurements really tip the balance in favor of a steamy atmosphere," Berta said.
Since the planet's mass and size are known, astronomers can calculate the density, of only about 2 grams per cubic centimeter. Water has a density of 1 gram per cubic centimeter, while Earth's average density is 5.5 grams per cubic centimeter. This suggests that GJ1214b has much more water than Earth does, and much less rock."
In Laymen's terms? It looks like Waterworld.
Scientists are currently manning the Hubble Telescope 24/7, in search of a race of wayward post-apocalyptic mariners' played by Kevin Costner. So far, no luck...but I think we all had the hunch that he was an intergalactic traveler when we saw how well he protected that little girl and her mother from outlaw "smokers" despite his reluctancy to do so. At least we know these aliens can be friendly; but only if you are as cute as Napolean Dynamite's love interest when she was a child, Tina Majorino.