3 planets discovered with right size, location for life

Dan Vergano, USA TODAY

Earth is looking a little less lonely after NASA astronomers reported Thursday the discovery of three more Earth-sized worlds orbiting nearby stars in ocean-friendly orbits.

Astronomers have spotted more than 800 planets orbiting nearby stars in recent decades, but only a handful have been Earth-sized, "Goldilocks" worlds, not too hot and not too cold for water. Astronomers consider water an essential ingredient for the possibility of life on other planets.

The Kepler space telescope findings reported in the journal Science by a team led by William Borucki of NASA's Ames Research Center in Moffett Field, Calif., add to that total. The report finds that the star, Kepler-62 has two planets, Kepler-62e and Kepler-62f, orbiting in ocean-friendly orbits around the star.

"This appears to be the best example our team has found yet of Earth-like planets in the habitable zone of a sun-like star," said team astrophysicist Alan Boss of the Carnegie Institution for Science in Washington. Kepler-62 is close by astronomical standards at about 1,200 light years away (708,000 trillion miles). It's a star slightly smaller than our sun, so its "habitable zone" for planets is closer in. The two ocean-friendly planets have "years" of 122 days and 267 days — the time it takes to completely orbit the star — for that reason.

Another star spotted by Kepler, dubbed Kepler-69, appears to have a planet in the habitable zone. The planet, Kepler-69c, is 70% larger than Earth and circles its star once every 242 days, an orbit resembling Venus in our solar system.

"Kepler is really delivering. It is frankly amazing that we live at a time when we can talk about Earth-like planets around other stars," says MIT astronomer Sarah Seager, who was not on the discovery team. "The next stage is being able to really see what these planets are like."

The discovery team suggests that the Kepler-62 planets may be anything from solid to water-covered. A separate team of astronomers suggests the worlds are probably covered with water.

"They have endless oceans," said astronomer Lisa Kaltenegger of the Max Planck Institute for Astronomy and the Harvard-Smithsonian Center in a statement on a related analysis of the two planets accepted for publication by The Astrophysical Journal. "There may be life there, but could it be technology-based like ours? Life on these worlds would be under water with no easy access to metals, to electricity or fire for metallurgy."

Kepler, which spots planets by seeing the dip in starlight they cause during passes in front of their stars, can give only size estimates of planets, not determine their composition, Seager says. Future planet-observing satellites, such as the planned Transiting Exoplanet Survey Satellite (TESS) announced this month by NASA for launch in 2017, should provide more information on such worlds. "What we are seeing with all these different orbits of these worlds is that planet formation is a pretty random process," Seager says. "They certainly don't all look like our solar system."