Astronomers have found a Neptune-size planet outside the solar system that's composed mainly of water—albeit in solid form. With a torrid surface temperature of 600 kelvins, the planet can't support life. But its existence bodes well for finding watery planets that could provide a haven for life, say Frédéric Pont of the Geneva Observatory in Sauverny, Switzerland, and his colleagues, who report the discovery in an upcoming Astronomy & Astrophysics Letters.
This is the first time that researchers have determined the size, mass, and composition of such a small extrasolar planet, only about 22 times as massive as Earth. The planet, which closely orbits the dwarf star GJ 436, has a diameter about four time