Of the hundreds of extrasolar planets discovered since 1995, not one resembles Earth, America's leading planet hunter says. As astronomers gathered for a conference in Flagstaff, Ariz., this week, Geoff Marcy of the University of California, Berkeley, told the Arizona Daily Sun: "We haven't found any planets that have a rocky surface on which water can puddle, and water serves as a cocktail mixer for life."

Since 51 Pegasi b, a Jupiter-sized gassy giant, was discovered in 1995, more than 500 planets outside the solar system have been found. This week's conference at Northern Arizona University, "Exploring Strange New Worlds," is sponsored by NASA's Jet Propulsion Laboratory at the California Institute of Technology and its PlanetQuest Exoplanet Exploration Program. Marcy is a member of NASA's Kepler Space Telescope team, which has identified more than 1,200 potential planets since its launch in late 2009 and is trying to find the first one like Earth.

Kepler is designed to stare at one sector of space and photograph 150,000 stars without blinking. The data are combed for tiny dips in light that would indicate a planet orbiting its sun. Kepler will examine less than 1 percent of the sky, but is expected to find thousands of planets.