Scientists from Cornell University and the American Museum of Natural History have discovered 2,034 neighboring star systems - all within 326 light-years of Earth - that may locate us just by observing our pale blue dot crossing our sun.
Since the dawn of human civilization roughly 5,000 years ago, there have been 1,715 star systems that could have sighted Earth, with 319 more expected in the next 5,000 years.
According to researchers who published their findings in Nature, exoplanets orbiting these neighboring stars have a cosmic front-row seat to discover if Earth has life. Their study is titled "Past, Present and Future Stars That Can See Earth as a Transiting Exoplanet."
"Seventy percent of all known exoplanets have been found by transits so far," study lead author Lisa Kaltenegger, an astrophysicist and director of the Carl Sagan Institute at Cornell University in Ithaca, New York, told Space.com.
This finding prompted Kaltenegger to speculate about which stars might be able to observe Earth. Last year, she and her colleagues discovered over 1,000 neighboring stars where the faint blue dot of Earth may currently cross in front of the sun. Next, she began to ponder how Earth's viewpoint points may vary throughout time.
Astronomers Detect Star-Systems That Could Have Spotted Earth
The scientists used the European Space Agency's Gaia database to discover which neighboring stars might have seen Earth pass in front of the sun in the past or might do so in the future. The mission's observations include a map of the locations and motions of more than 331,000 stars within 325 light-years of the sun, which began in 2013 and is still ongoing.
"Our solar neighborhood is a dynamic place where stars enter and exit that perfect vantage point to see Earth transit the sun at a rapid pace," study co-author Jackie Faherty, an astrophysicist and senior scientist at the American Museum of Natural History, said in a statement. "Gaia has provided us with a precise map of the Milky Way galaxy, allowing us to look backward and forward in time, and to see where stars had been located and where they are going."
The researchers discovered 1,715 stars that could have seen Earth transits since around 5,000 years ago when civilizations first emerged on the planet. Although 313 of them are no longer able to witness Earth pass in front of the sun, 1,402 can still. In the next 5,000 years, another 319 should enter this "Earth transit zone."
The scientists discovered that 75 of the 2,034 total stars studied during 10,000 years were within 100 light-years of Earth, close enough for human-made radio waves to have passed over the star since commercial radio stations on Earth began broadcasting almost a century ago.
Other Planets Also Found Within Goldilocks Zone
Other reports claim that rocky planets are not only widespread in the Milky Way. They are also frequently found in the habitable or "Goldilocks" zones, where a planet may keep liquid water on its surface. The researchers calculated that 29 of the 75 stars could have rocky worlds in their habitable zones based on previous studies.
Seven of the 2,034 stars are known to contain exoplanets that have had or will have the opportunity to detect the planet in the same way Earth's scientists have. K2-65, K2-155, and K2-240 are three of the seven exoplanetary systems that can currently observe Earth.
If life arose there as well, and if it did so at a similar technological level to ours, Kaltenegger believes that such insignificant observers could have detected or will spot life on our own globe.
NASA's Transiting Exoplanet Survey Satellite (TESS) and other telescopes will search for exoplanets near the 2,034 stars found by the researchers in the future - hopefully many in the habitable zones. Once such planets are discovered, Kaltenegger's team will model them and. Assuming they have life, determine how much time the James Webb Space Telescope will require to find them, and apply for that time.
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