Aliens on 1,000 nearby stars could see us, new study suggests


There are about 1,000 star systems where aliens, if they existed, could be watching us from afar, new research suggests.

Those 1,004 star systems are in a direct line of sight to our planet, and close enough to us that they could not only detect planet Earth, but also chemical traces of Earthly life. 

Over the course of the last decade, astronomers have found exoplanets orbiting distant stars using a simple formula: Keep an eye on a star and wait for it to suddenly dim. That dimming is a sign of a planet passing between the star and the telescope. Analyzing how the  light changes as the star dims can reveal the chemical contents of the planet's atmosphere. 

But this method works only for planets whose orbits happen to take them between their host stars and Earth. In a new paper, researchers flipped that formula on its head, asking: Which nearby stars are lined up properly for their inhabitants to see Earth transit in front of the sun? Would any life-forms in those star systems be able to detect signs of us, the living things on Earth's surface? The answer is yes, it turns out, for a great number of nearby stars.

"If observers were out there searching, they would be able to see signs of a biosphere in the atmosphere of our Pale Blue Dot," Lisa Kaltenegger, a Cornell University astronomer and lead author of the paper, said in a statement.

Planets, it turns out, are common in space. Since researchers first confirmed finding one transiting in front of its star in 1992, astronomers have found 4,292 confirmed planets beyond our solar system, orbiting 3,185 stars, thanks largely to the planet hunting Transiting Exoplanet Survey Satellite (TESS). The James Webb Space Telescope (JWST), slated to launch at some point this decade, should have the precision to study many of those planets in more detail — possibly detecting gases like methane or oxygen in their atmospheres, which would be likely signs of life.