Matt_dk writes "Does a twin Earth exist someplace in our galaxy? Astronomers are getting closer and closer to finding an Earth-sized planet in an Earth-like orbit. NASA's Kepler spacecraft just launched to find such worlds. Once the search succeeds, the next investigate driving fishing expedition* will be: Is that planet habitable? Does it have an Earth-like atmosphere? message service those quiz will not be easy. 'We'll have to be really lucky to decipher an Earth-like planet's atmosphere during a transit event so that we can tell it is Earth-like,' said Kaltenegger. 'We will need to add up many transits to do so — hundreds of them, even for stars as close as 20 light-years away.'" The abstract of their paper offers a link to the unmitigated paper as a 17-page PDF; here is a short breed from 2007 of the same researchers' work, outlining the type of spectral signature that an Earth-like atmosphere would be anticipated to show.

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