A rocky and water-rich planet, not much heftier than our own, has been discovered so close to our solar system that astronomers one day may be able to study its atmosphere.

And though astronomers are pretty certain the water exists, they don't know its state, with speculations ranging from liquid water to water ice and an exotic state called a superfluid.

The extrasolar planet, now named GJ 1214b, is about 40 light-years away. It orbits a red dwarf star. It is the only known "Super-Earth" exoplanet — worlds that have masses between Earth and Neptune — with a confirmed atmosphere.

"Astronomically speaking, this [planet] is on our block," meaning it's in our cosmic neighborhood, said study leader David Charbonneau of the Harvard-Smithsonian Center for Astrophysics in Mass. "For perspective, our own TV signals have already passed beyond the distance of this star."

The planet is about three times the size of Earth and about 6.5 times as massive. It is the second smallest planet discovered outside of our solar system to date, trailing behind only CoRoT-7b, which is 1.7 times Earth's size and about five times as massive.