Here on Earth, where we're focused on looking outward, we scour the universe for potentially habitable planets located outside our solar system. But what if we turned the search around? What exoplanets out there might be looking at Earth for signs of life?
That's the premise behind a new paper published this week in the Monthly Notices of the Royal Astronomical Society. It asks the compelling question, "Which stars can see Earth as a transiting exoplanet?" Cornell University's Lisa Kaltenegger and Lehigh University's Joshua Pepper co-authored the study.
We find exoplanets by looking for a telltale dip in brightness when a planet passes in front of its star. That same principle would work for a sufficiently advanced alien civilization looking at Earth from across space.
The astronomers "identified 1,004 main-sequence stars (similar to our sun) that might contain Earth-like planets in their own habitable zones -- all within about 300 light-years of Earth -- and which should be able to detect Earth's chemical traces of life," Cornell said in a statement on Wednesday.
Planets in these systems could have a good line-of-sight view of Earth. "If observers were out there searching, they would be able to see signs of a biosphere in the atmosphere of our Pale Blue Dot," Kaltenegger said.
The researchers built the list from data and observations made by NASA's planet-hunting Transiting Exoplanet Survey Satellite (TESS).
NASA's next-generation (and much delayed) James Webb Space Telescope should help us learn more about the atmospheres of distant planets. This study could give the telescope some intriguing targets to investigate.
"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," Kaltenegger said.
Imagine an alien world not too wildly different from our own celebrating the discovery of a potentially habitable planet around a distant star: exoplanet Earth.