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Planet hunters are significantly closer to their goal of finding an "Earth twin" with the discovery of two planets similar in size to our own, astronomers with NASA's Kepler mission announced today. The planets, described at a NASA press conference, orbit a sun that's cooler than ours but is at the right distance to allow water to remain liquid, which is considered essential for a planet to support life. (Read about a related discovery in 2011: "NASA's Kepler Finds Two Earth-Size Planets Around Sunlike Star.") And because of their sizes and orbits, the newfound planets are likely either rocky—like Earth—or watery, NASA scientists said. The two planets are located 1,200 light-years away in a five-planet system orbiting a star dubbed Kepler-62... "I would call this a breakthrough discovery." The press conference also introduced another study released today in the Astrophysical Journal, which involves a related discovery of a sun very much like our own named Kepler-69. The newly found extrasolar planets, or exoplanets, are part of a vast menagerie of celestial bodies discovered in recent years. Our Milky Way galaxy alone is now known to have hundreds of billions of planets circling its stars. Scientists also described another recent discovery: Kepler-69. It's "the sun most like our own that we've found that has a planet orbiting in the habitable zone," said study leader Thomas Barclay, a Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, California. Marcy, a co-author of the Kepler-62 study, called the new exoplanet discoveries "profound." That's in part because it dovetails with another recent finding that most of the 200 billion stars in the Milky Way have an Earth-size planet orbiting them. He said he didn't think the importance of the Milky Way discovery has really sunk in with the public. "It's not just that most stars have Earth-sized planets, but some of them—many of them actually—are at a distance from their suns that allow for lukewarm temperatures," Marcy said. "That means they just might support life." He added, "It's a very moving moment in humanity's efforts to understand our home planet and the possibility of other habitable planets in the universe."
