If you have the impression that you are being watched, it could be from a much greater distance than you believe.
Astronomers reversed a technique used to search for life on other planets, trying to see what places could see us instead of what was out there.
There is a great deal
According to a study published Wednesday in the journal Nature
, astronomers calculated that 1,715 stars in our galactic neighborhood — as well as hundreds of likely Earth-like planets circling those stars — had an unobstructed view of Earth during human civilization.
“When I look up at the sky, it looks a little friendlier because it appears to be waving,” said study lead author Lisa Kaltenegger
, director of Cornell University
’s Carl Sagan Institute.
Even though some experts, including the late Stephen Hawking, warn against contacting aliens
because they may harm us, Kaltenegger says it doesn't matter because if those planets have advanced life, someone out there could conclude that there is life back here based on oxygen in our atmosphere or radio waves from human sources that have swept over 75 of the nearest stars on her list.
“I don't think hiding is an option,” she explained.
Humans look for potentially habitable planets by watching them pass in front of the star they are orbiting, which dims the star's light slightly. Kaltenegger and astrophysicist Jacqueline Faherty of the American Museum of Natural History
used the European Space Agency
's Gaia space telescope to flip that around, looking to see what star systems could watch Earth as it passes in front of them.
They examined the 331,312 stars within 326 light-years of Earth. One light-year is 5.9 trillion miles, and the angle to see Earth pass in front of the sun is so small that only 1,715 could see Earth at some point in the last 5,000 years, including 313 that can no longer see us because we've moved out of their line of sight.
Another 319 star systems will be able to see Earth in the next 5,000 years, including a few where scientists have already discovered Earth-like planets, prime candidates for contact, bringing the total to more than 2,000.
The red dwarf star Wolf 359, which is 7.9 light-years away and has been able to see us since the disco era in the mid 1970s, is the closest star on Kaltenegger's list.
Alan Boss, a planetary scientist at the Carnegie Institution for Science
who was not involved in the study, called it “provocative,” adding that in addition to seeing Earth move in front of the star, space telescopes nearby could see us even if the cosmic geometry is incorrect: “So intelligent civilizations who build space telescopes could be studying us right now.”
So how come we haven't heard from them?
It takes a long time for messages and life to travel
between stars, and civilizations may not last long, so the combination of those two factors limits the chances of civilizations exchanging “emails and TikTok
videos,” according to Boss in his own email.
Or, as Kaltenneger suggested, life in the universe may simply be uncommon.
The study is exciting because it tells scientists “where to point our instruments,” according to outside astronomer Seth Shostak
of the SETI Institute
, which searches for extraterrestrial intelligence.
@borenbears is Seth Borenstein
The Howard Hughes Medical Institute's Department of Science Education
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