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.
What if aliens had their own JWST? Within 326 light-years, the researchers found, there are 1,004 with vantage points to spot Earth. Of those, 508 have viewing angles that would give them at least 10 hours of observational data every time Earth passed between that location and the sun — ideal conditions for spotting this little rocky planet and the signs of life in its atmosphere.
"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." said Lehigh University astrophysicist Joshua Pepper, co-author of the paper, in the statement. "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."
About 5% of the 1,004 stars are likely too young for intelligent life to have evolved, the researchers surmise, even if a planet with habitable conditions orbited them. But the remaining 95% belong to star categories that can sustain life for billions of years, which Earth's experience suggests is long enough for intelligent life to evolve, assuming conditions are right.
Most of the stars on the list are toward the farther end of the 326 light-year range, because the zone where Earth's transit is visible gets smaller as you get closer to our solar system. But the closest star on the list is only 28 light-years away. And there are several more nearby stars that are on track to enter the zone where they might spot Earth within centuries. Some are bright enough in the sky to see from Earth.
Two stars on the list have known exoplanets. And a red dwarf just 12 light-years from Earth with known exoplanets — known as Teegarden's star — does not currently have the right viewing angle to spot Earth but at its current rate of movement will enter the Earth-spotting zone as soon as 2044.
The next step, the researchers wrote, is to focus intelligent life-hunting operations on the 1,004 stars identified in their paper. They specifically mentioned SETI's Breakthrough Listen program, designed to detect communications from advanced alien civilizations.
This research was published Oct. 20 in the journal Monthly Notices of the Royal Astronomical Society.
Originally published on Live Science.