Scientists have been scanning the cosmos for possibleFor decades, but for more than a century, humans have also been sending signals from Earth that could be picked up by aliens beyond our planet. That is, if you are looking in the right place for us.
New research has determined exactly which star systems have been, or will be, in a position to detect Earth and mark it as a potential home of intelligent life that is worth further investigation (or perhaps avoiding altogether).
“Any civilization with our level of technology could have seen us already,” Cornell astronomy professor Lisa Kaltenegger told me by email.
Kaltenegger and astrophysicist Jackie Faherty of the American Museum of Natural History used data from the European Space Agency.to identify 2,034 nearby systems with promising perches to detect some human aliens.
“We wanted to know which stars have the right vantage point to see Earth, as it blocks the sunlight,” he said. “And because the stars move in our dynamic cosmos, this point of view is won and lost. I was wondering how long that front row seat takes to find Earth through the star’s drop in brightness. Nobody knew. ”
Kaltenegger and Faherty used Gaia’s latest extensive catalog of stars, which contains both the positions and motion of the stars, to find answers.
“Then you can turn your movement into the future and trace it back to the past,” explains Kaltenegger.
They found that 1,715 of the star systems have been in the correct position to have seen the Earth passing in front of or transiting the Sun since human civilization got under way around 5,000 years ago. The other 319 systems will move into position with a line of sight to Earth for the next 5,000 years.
On a paper published online Wednesday in the journal Nature, scientists get even closer to 75 systems that have been in that ideal human detection range, called the Earth Transit Zone, since commercial radio stations began sending broadcast signals into space that travel into the cosmos to The speed of light.
So if someone or something in those systems is operating a radio telescope like one of ours, they may already be enjoying some really old-fashioned Earth radio dramas right now.
“Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point from which they can see the transit of the Earth,” the paper reads. “That provides a long timeline for nominal civilizations to identify Earth as an interesting planet.”
Scientists also identify seven of the 2,034 star systems known to host exoplanets. These include, a red dwarf star just 11 light-years away that is orbited by an Earth-sized planet. The world would have had a view of Earth for just over 3,000 years, but it left the observation zone about 900 years ago.
“Would anyone have concluded that there was intelligent life on Earth 900 years ago?” Kaltenegger wonders.
TheIt’s only 45 light-years from us and is home to a whopping seven Earth-sized planets, including four in the habitable zone, but they’re probably not spying on us. At least not yet: their path will take them to the Earth Transit Zone where they could observe us, but not for 1,642 years.
Three star systems are home to exoplanets that should be able to see Earth right now and for hundreds of years, but all are more than 200 light-years away, which means our commercial radio signals haven’t reached them yet.
On the scale of the entire Milky Way galaxy, this is still pretty much next door. The researchers hope their work will help inform science using an exciting new technology that is just around the corner, like the nextor Breakthrough Starshot’s plan to send a small spacecraft to check out the Alpha Centauri system and its known exoplanet just 4.2 light-years away.
“One could imagine that worlds beyond Earth that have already detected us are making the same plans for our planet and solar system,” Faherty said. “This catalog is an intriguing thought experiment that one of our neighbors could find us for.”
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