For billions of years, Earth has been playing a cosmic game of hide-and-seek. New research published today in Nature posits that roughly 1,700 stars are in the right position to have spotted life on Earth as early as 5,000 years ago. From a report: These stars, within 100 parsecs (or about 326 light-years) of the sun, were found using data from NASA’s Transiting Exoplanet Survey Satellite and the European Space Agency’s Gaia mission. And with thousands of exoplanets already found orbiting other stars in our universe, could we have already seen life on other planets come and go? Might they have seen us? “The universe is dynamic,” says Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell, and lead author of the study. “Stars move, we move. First the Earth moves around the sun, but the sun moves around the center of our galaxy.”
About 70% of exoplanets are found using the transit method: when a planet passes between a star and an observer, the star dims enough to confirm the presence of a previously unseen celestial body. Kaltenegger and coauthor Jackie Faherty of the American Museum of Natural History compiled a list of stars that either will see or already have seen Earth transit in their lifetimes. Of these, they found seven stars with orbiting exoplanets that could potentially be habitable. Statistically, one out of four stars has a planet that exists in the “Goldilocks zone” — not too hot, not too cold, and just far away from a star to support life. But how do we determine whether faraway exoplanets meet these criteria? When transiting exoplanets block stellar light, part of that light filters through the atmosphere. Energy and light interact with the molecules and atoms of that planet, and by the time that light reaches an astronomer’s telescope, scientists can determine whether it has interacted with chemicals like oxygen or methane. A combination of those two, Kaltenegger says, is the fingerprint for life.
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Source: Slashdot – Radio Waves From Earth Have Reached Dozens of Stars