Astronomers identify locations from which aliens could spot Earth

The search for intelligent life beyond Earth has most often focused on where we could find potential signs of life beyond our solar system. But two astronomers from Cornell have investigated a different way to approach this issue — looking at how visible Earth is from distant exoplanets from which aliens might be searching for us.

One way in which astronomers here on Earth search for exoplanets is using a technique called the transit method. This is where they observe distant stars and look for periodic dips in their brightness which indicate a planet passing between us and them.

“Let’s reverse the viewpoint to that of other stars and ask from which vantage point other observers could find Earth as a transiting planet,” lead author Lisa Kaltenegger explained. “If observers were out there searching, they would be able to see signs of a biosphere in the atmosphere of our Pale Blue Dot,” she said, “And we can even see some of the brightest of these stars in our night sky without binoculars or telescopes.”

Cornell astronomer Lisa Kaltenegger and Lehigh University’s Joshua Pepper have identified 1,004 main-sequence stars – similar to our sun – that might contain Earth-like planets in their own habitable zones within about 300 light-years of here, which should be able to detect Earth’s chemical traces of life.
Cornell astronomer Lisa Kaltenegger and Lehigh University’s Joshua Pepper have identified 1,004 main-sequence stars – similar to our sun – that might contain Earth-like planets in their own habitable zones within about 300 light-years of here, which should be able to detect Earth’s chemical traces of life. John Munson/Cornell University

The new research aimed to identify which distant planets would be able to detect the presence of Earth using the transit technique, and the researchers came up with a list of the 1,000 nearest stars which could host planets from which Earth could be spotted.

“Only a very small fraction of exoplanets will just happen to be randomly aligned with our line of sight so we can see them transit,” co-author Joshua Pepper said. ”But all of the thousand stars we identified in our paper in the solar neighborhood could see our Earth transit the sun, calling their attention.”

This work could help select potential locations where we could search for life beyond Earth. “If we found a planet with a vibrant biosphere, we would get curious about whether or not someone is there looking at us too,” Kaltenegger said. “If we’re looking for intelligent life in the universe, that could find us and might want to get in touch, we’ve just created the star map of where we should look first.”

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