Researchers 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 find us just by watching our pale blue dot cross 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.
Exoplanets orbiting these neighboring stars have a cosmic front-row seat to discover if Earth has life, according to researchers who published their findings in Nature today (June 23, 2021).
According to Lisa Kaltenegger, professor of astronomy and director of Cornell’s Carl Sagan Institute in the College of Arts and Sciences, “from the exoplanets’ point of view, we are the aliens.”
“We wanted to know which stars had the best view of Earth because the Sun’s light is blocked,” she explained. “This vantage point is gained and lost because stars migrate in our dynamic cosmos.”
Kaltenegger and astrophysicist Jackie Faherty, a senior scientist at the American Museum of Natural History and co-author of “Past, Present, and Future Stars That Can See Earth As A Transiting Exoplanet,” used data from the European Space Agency’s Gaia eDR3 catalog to figure out which stars enter and exit the Earth Transit Zone and for how long.
“Gaia has given us an accurate picture of the Milky Way galaxy,” Faherty said, “allowing us to look backward and forward in time, and see where stars have been and where they are going.”
117 objects lie within about 100 light-years of the sun, and 75 of these objects have been in the Earth Transit Zone since commercial radio stations on Earth began broadcasting into space about a century ago, of the 2,034 star-systems passing through the Earth Transit Zone over the 10,000-year period examined.
Faherty explained, “Our solar neighbourhood is a dynamic location where stars come and exit that perfect vantage position to witness Earth transit the Sun at a quick speed.”
There are seven known exoplanets among the 2,034 star systems in the list. Each of these worlds has or will have the ability to detect Earth, much as Earth’s scientists have discovered thousands of worlds orbiting other stars using the transit method.
Earth’s astronomers can analyse the atmospheres of faraway exoplanets by watching them transit or cross their own sun. Exoplanets that have intelligent life can see Earth when it is backlit by the sun and see the chemical signs of life in our atmosphere.
The Ross 128 system is roughly 11 light-years away and is the second-closest system with an Earth-size exoplanet, with a red dwarf host star in the Virgo constellation (about 1.8 times the size of our planet). This exoworld’s occupants could have watched Earth transit our own sun for 2,158 years, starting around 3,057 years ago; they lost their vantage point about 900 years ago.
According to Kaltenegger, even the closest stars spend more than 1,000 years at a vantage position where they may watch Earth transit. “If we assume the opposite is true, we have a reasonable timetable for notional civilizations to see Earth as a fascinating planet.”
The James Webb Space Telescope, which is due to launch later this year, will examine numerous transiting worlds in detail in order to describe their atmospheres and, ultimately, look for indications of life.
Breakthrough Starshot is an ambitious project that aims to fly a nano-sized spacecraft toward the closest exoplanet discovered at Proxima Centauri 4.2 light-years away from Earth and completely analyse it.
“It’s possible that worlds beyond Earth that have previously discovered us are plotting the same course for our planet and solar system,” Faherty speculated. “This catalogue is a fascinating mental experiment that one of our neighbours might be able to locate us for.”