Astronomers and space enthusiasts are on newsgroups discussing the discovery made Wednesday that they had found a planet composed mostly of water. It is one of the lightest and smallest so-called extrasolar planets found, part of a growing class of planets less than 10 times the mass of Earth. The planet, prosaically named GJ 1214b, is one of more than 400 exoplanets now known to exist in the universe but one of only a handful of “super-Earths,” having a rocky mass up to 10 times that of Earth’s.

Only 2.7 times the size of Earth and 6.6 times as massive, the planet takes 38 hours to circle a dim red star, GJ 1214, in the constellation Ophiuchus – about 40 light-years from here. It orbits so close to its parent star that its surface temperature hovers around 200 Celsius, hot like an oven. The close proximity of GJ1214b should make it possible for the Hubble Telescope to establish the composition of its atmosphere. That planet is lifeless, but finding it strongly increases the likelihood that before long another distant Earth-like planet will be found orbiting another sunlike star and bearing some unknown form of life, says a leading astronomer at the University of California at Berkeley.

Its discovery has encouraged a growing feeling among astronomers on USENET newsgroups that they are on the verge of a breakthrough and getting closer to finding a planet that something could live on. The results come courtesy of the MEarth project (a description is available via the arXiv), which is based on Mount Hopkins in Arizona. The other discoveries are reported in two articles to be published in the Astrophysical Journal by an American-Australian team led by Steven Vogt of UC Santa Cruz, and Paul Butler of the Carnegie Institution in Washington, D.C. The group, which includes astronomers Didier Queloz and Michel Mayor, who discovered the very first extra-solar planet in 1995, found the new exoplanet after scanning 2,000 very small sun-like stars with an automated bank of eight small telescopes.