Astronomers have discovered a new planet in our galaxy that is unlike any other found so far: Both the planet and its atmosphere are mostly water, though none of it is liquid.

The planet, GJ1214b, has a diameter 2.7 times that of Earth, and it weighs seven times as much. It probably has much more water than Earth — in the form of steam and a peculiar high-temperature ice that exists at extremely high pressures — and far less rock.

“There’s probably nothing too special about this planet itself,” said Zachory K. Berta, an astronomer at Harvard University who was involved with the research. The main thing, he added, is that “we have the opportunity to really see the density of the planet.”

He and his colleagues report their findings in The Astrophysical Journal.

To estimate the density and diameter, they measured the color of the light from the star that shines through the planet’s atmosphere.