The Economist reports on the findings of NASA’s Kepler telescope’s search for habitable planets: “The 833 new planets thus identified bring the total found by Kepler to 3,538. Technically these are only ‘candidate’ planets, whose presence is inferred by the tiny dimming they cause when they pass in front of their host stars. Such candidates must await confirmation by other telescopes before being promoted to full discoveries. But astronomers expect a low rate of false positives.”

The number of potentially habitable planets, though, is probably much larger: “A group led by Erik Petigura of the University of California, Berkeley, having crunched the numbers, told the meeting that around a fifth of sun-like stars in the Milky Way are likely to host planets roughly the size and temperature of Earth. By the researchers’ definition, sun-like stars are a fifth of the total, so that means only about one star in 25 would have such a planet. But the galaxy is a big place, so if they are right there are billions of Earthlike planets in it. The closest is expected to be less than 12 light-years from Earth.”

The telescope’s discoveries have also shaken up some existing theories about planetary formation “by finding all sorts of objects that should not, according to the old theories, exist at all—such as planets the size of Jupiter or bigger orbiting close to their parent stars. Building a new theory to account for these space oddities is a big project.”

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