Tens of billions of small, rocky planets orbiting red dwarf stars inhabit the Milky Way, and dozens lie within 30 light-years of Earth, according to a new survey. Between February 2003 and April 2009, researchers at the European Southern Observatory's La Silla Observatory in Chile studied 102 Class M, so-called red dwarf, stars less than about 32.6 light-years away—a proximity that allowed researchers to detect subtle wobbles that would be induced by one or more planets orbiting the star. Of the stars they scrutinized, the researchers found that eight hosted 14 planets, including 12 estimated to be "super-Earths," rocky planets with a mass between one and 10 times that of our own. Then, accounting for planets in orbits that wouldn't induce detectable wobbles, such as those not seen edge-on from Earth, and for the orbital periods of those planets around their parent stars, the team estimated that about 41% of red dwarf stars have super-Earths orbiting at a distance at which surface water would be liquid—including Gliese 667 Cc (artist's concept above), a super-Earth orbiting one star in a three-star system about 22 light-years from Earth. Considering that about 80%, or 160 billion, of the Milky Way's stars are red dwarfs, there are likely more than 65 billion stars in our galaxy with a habitable super-Earth, the researchers report in a forthcoming issue of Astronomy & Astrophysics, and about 100 of them lie within 10 parsecs, or 32.6 light-years, of Earth.
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