Number of Habitable Exoplanets Found by NASA's Kepler May Not Be So High After All

The tally of potentially habitable alien planets may have to be revised downward a bit. To date, NASA's prolific Kepler space telescope has discovered about 30 roughly Earth-size exoplanets in their host stars' "habitable zone" — the range of orbital distances at which liquid water can likely exist on a world's surface. Or so researchers had thought. New observations by the European Space Agency's (ESA) Gaia spacecraft suggest that the actual number is probably significantly smaller — perhaps between two and 12, NASA officials said today (Oct. 26). [Photos: Gaia Spacecraft to Map Milky Way Galaxy]

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