By watching how the light dims as a planet orbits in front of its parent star, NASA’s Kepler spacecraft has discovered more than 1,000 worlds since its launch in 2009. Now, astronomers are flipping that idea on its head in the hope of finding and talking to alien civilizations.

Scientists searching for extraterrestrial intelligence should target exoplanets from which Earth can be seen passing in front of the Sun, says René Heller, an astronomer at the Max Planck Institute for Solar System Research in Göttingen, Germany. By studying these eclipses, known as transits, civilizations on those planets could see that Earth has an atmosphere that has been chemically altered by life. “They have a higher motivation to contact us, because they have a better means to identify us as an inhabited planet,” Heller says.

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