Kepler, the space telescope considered most likely over the next few years to identify an Earth-like planet orbiting another star, has struck solid ground, mission scientists say. Most of the hundreds of extrasolar planets discovered to date - including the eight previ-ously reported by Kepler - are at least as large as Neptune and are mainly gas giants. But astronomers hope that the mission will even-tually yield a trove of terrestrial planets, includ-ing some orbiting their stars at a distance that would allow their surfaces to host liquid water, and possibly life. Now the team is a step nearer to that goal. It has found a Sun-like star 173 parsecs away -relatively close by galactic standards - harbour-ing a planet that is just 40% larger than Earth, although it is uninhabitably hot. Supporting measurements of the planets mass, gathered at the Keck Observatory on Mauna Kea, Hawaii, suggest that the planets density is 1.6 times that of Earth, implying a rocky composition. Although other telescopes have already spot--ted a handful of similar 'super-Earths', the first confirmed rocky planet to fall within Kepler's sights is an encouraging sign for the mission.
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