European astronomers have discovered what may be an Earthlike planet 20 light-years away from here, in the Libra constellation. The planet, named Gliese 518c, is five times more massive than Earth and orbits a red sun at a distance that could support the presence of water and, possibly, life. The Geneva Observatory scientists and their collaborators couldn't observe the planet directly, so its discovery was actually an inferrence. Using a 141-inch-diameter telescope in Chile, they measured the wobble of the parent star, a phenomenon caused by the orbiting planet's gravitational pull. Based on those measurements, they could then deduce the planet's approximate mass and other information. From the New York Times:
“On the treasure map of the universe, one would be tempted to mark this planet with an X,” said Xavier Delfosse, a member of the team from Grenoble University in France, according to a news release from the European Southern Observatory, a multinational collaboration based in Garching, Germany...Link
The most exciting part of the find, Dr. Sasselov said, is that it “basically tells you these kinds of planets are very common.” Because they could stay geologically active for billions of years, he said he suspected that such planets could be even more congenial for life than Earth.