Active Seti writes: "If aliens were hunting life outside their own planet with telescopes a bit bigger than our own, could they peer through the vastness of space and lock onto Earth as a likely home for life? Researchers say with a space telescope larger than the Hubble Space Telescope pointed directly at our sun, observers could measure Earth's 24-hour rotation period, leading to observations of oceans and the chance of life. "They would only be able to see Earth as a single pixel, rather than resolving it to take a picture," said Astronomer Eric Ford. "But that could be enough for them to identify our planet as one that likely contains clouds and oceans of liquid water." Astronomers could infer that anomalies in the pattern were caused by changing weather patterns, most prominently, clouds, Ford said. Although some uninhabitable planets are extremely cloudy, the repeated presence and absence of clouds indicates active weather, so finding similar variability on another planet would be a reasonable indication of liquid water. The research will be useful to astronomers designing the next generation of space telescopes because it provides an outline of the capabilities required for studying the surfaces of Earth-like planets."
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