Zachory Berta says that "GJ1214b is like no planet we know of". Like Berta, part of a team at the Harvard-Smithsonian Center for Astrophysics lead by David Charbonneau, his colleagues were surprised when they discovered that this planet is made mostly of water.
Larger than Earth but smaller than Uranus, GJ1214b has a lot more water and a lot less solid material than our home planet. According to their research, this waterworld is entirely covered with an ocean. Even its atmosphere is a thick steam layer. Not just hazy, but a "dense atmosphere of water vapour".
According to Berta, what's happening in this new type of world is something that we can't imagine: "the high temperatures and high pressures would form exotic materials like 'hot ice' or 'superfluid water', substances that are completely alien to our everyday experience."
Their theory is that GJ1214b formed "farther out from its star, where water ice was plentiful" and then it kept getting closer, which started to make all that ice to liquify.
Right now, GJ1214b orbits its red-dwarf star "every 38 hours at a distance of 1.3 million miles." This results in a steam temperature of 450 degrees Fahrenheit, which is not good if you are in the Swedish sauna business. [Hubble]