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For centuries, Earthlings have been staring at the sky and wondering about life among the stars. But while humans were searching for the little green men, aliens might be watching us again.
In new research, astronomers shortlisted nearby star systems where any curious inhabitants of orbiting planets would be well placed to monitor life on Earth.
Scientists have identified 1,715 star systems in our cosmic neighborhood where space observers could have discovered Earth in the past 5,000 years by watching it “cross” the face of the Sun.
Of those who are in the right place to observe Earth transits, 46 star systems are close enough for their planets to intercept a clear signal of human presence — radio and television broadcasts that began about 100 years ago.
Researchers estimate that 29 potentially habitable planets are well positioned to watch Earth transits, eavesdropping on human radio and television broadcasts, allowing any observer to infer a modicum of intelligence. Whether broadcasting will force an advanced civilization to make contact is a moot point.
“One of the ways we find planets is by blocking some of the light from their host star,” said Lisa Kaltenegger, professor of astronomy and director of the Carl Sagan Institute at Cornell University in New York. We asked, ‘Who would the aliens be if someone else was looking?’ “There’s this little sliver in the sky where other star systems have a cosmic front seat to finding Earth as a passing planet.”
Terrestrial astronomers have discovered thousands of planets outside the solar system. About 70% are observed when alien worlds pass in front of their host stars and block some of the light that reaches scientists’ telescopes. Future observatories, such as NASA’s James Webb Space Telescope due to launch this year, will look for signs of life on “exoplanets” by analyzing the composition of their atmospheres.
To find out which nearby star systems are well placed to observe Earth transits, Kaltenegger and Dr. Jackie Ferti, an astrophysicist at the American Museum of Natural History, turned to the European Space Agency’s Gaia catalog of the positions and motions of stars. From this, they identified 2,034 star systems within 100 parsecs (326 light years) that could detect Earth transits at any time from 5,000 years ago to 5,000 years in the future.
One star known as Ross 128, a red dwarf in the constellation Virgo, is about 11 light-years away — close enough to receive terrestrial broadcasts — and has a planet roughly twice the size of Earth. Any adequately equipped life on the planet could monitor the transit of the Earth for more than 2,000 years, but it lost its view 900 years ago. If there was intelligent life on any of the known planets orbiting the star Teegarden, 12.5 light-years away, it would be in a prime position to watch Earth pass in 29 years.
45 light-years away, another star called Trappist-1 is also close enough to eavesdrop on human broadcasts. The star hosts at least seven planets, four of which are in the temperate habitable zone, but they will not be in a position to watch Earth transit for another 1,642 years, the scientists write in Nature.
These findings come as the US government prepares to publish a highly anticipated report on Unidentified Flying Objects (UFOs). The report from the Pentagon’s Task Force on Unknown Atmospheric Phenomena, which was set up to gain insight into the nature and origins of unidentified aircraft, is not expected to reveal or rule out evidence of strange behavior.
Professor Beth Beller of the University of Edinburgh’s Institute of Astronomy, who was not involved in the study of nature, said the work could change the way scientists approach Seti, to search for extraterrestrial life. “What was surprising to me,” she said, “was that so few stars within 100 parsecs have seen the transiting Earth.”
The transit method requires very precise alignment between the transiting planet, its star, and the Sun for a particular planet to be detectable, so this result is not surprising. Now I’m curious to know what percentage of stars in Gaia’s catalog of nearby stars have a vantage point for detecting Earth via other exoplanet detection methods, such as the radial velocity method or direct imaging! “
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