“You know, our sun looks just like thousands of other stars in the sky. You’d never guess that there are planets going around it, and that one of those planets has people who consider themselves very intelligent. There would be no way of knowing that,” said Cornell University icon, astronomer Carl Sagan, in a 1973 interview with Rolling Stone, long before Michel Mayor and Didier Queloz announced the first discovery of a planet outside our solar system, an exoplanet, orbiting a solar-type star in our home galaxy, the Milky Way in 1995. The planet, 51 Pegasi b, a gaseous ball comparable with the solar system’s biggest gas giant, Jupiter was detected at the Haute-Provence Observatory in southern France, using custom-made instruments.
Search for Planets is the Search for Life
“The search for planets is the search for life,” observed Natalie Batalha, a Kepler mission scientist from NASA’s Ames Research Center. Now, three decades after Sagan suggested that Voyager 1 snap Earth’s picture from billions of miles away—resulting in the iconic Pale Blue Dot photograph—two Cornell astronomers offer another unique cosmic perspective, suggesting that this post’s headline may be a fact, that some distant exoplanets have a direct line of sight to observe Earth’s biological features, and perhaps have been able to infer that our planet harbors a species standing around thinking that they are the smartest species in the universe.
Star Map of Where We Should Look First
“If we found a planet with a vibrant biosphere, we would get curious about whether or not someone is there looking at us too,” Cornell astrophysicist Lisa Kaltenegger said. “If we’re looking for intelligent life in the universe, that could find us and might want to get in touch” she said, “we’ve just created the star map of where we should look first.”
Kaltenegger, associate professor of astronomy and director of Cornell’s Carl Sagan Institute and Joshua Pepper, associate professor of physics at Lehigh University, have identified 1,004 main-sequence stars (similar to our sun) that might contain Earth-like planets in their own habitable zones—all within about 300 light-years of Earth—using NASA’s Transiting Exoplanet Survey Satellite (TESS) star catalog, and which should be able to detect Earth’s chemical traces of life.
Observing Signs of Earth’s Biosphere
“Let’s reverse the viewpoint to that of other stars and ask from which vantage point other observers could find Earth as a transiting planet,” Kaltenegger said. A transiting planet is one that passes through the observer’s line of sight to another star, such as the sun, revealing clues as to the makeup of the planet’s atmosphere.
“If observers were out there searching, they would be able to see signs of a biosphere in the atmosphere of our Pale Blue Dot,” she said, “And we can even see some of the brightest of these stars in our night sky without binoculars or telescopes”.
Transit observations are a crucial tool for Earth’s astronomers to characterize inhabited extrasolar planets, Kaltenegger added, which astronomers will start to use with the launch of NASA’s James Webb Space telescope next year.
Earth’s Ecliptic –The Key
But which stars systems could find us? Holding the key to this science is Earth’s ecliptic—the plane of Earth’s orbit around the Sun. The ecliptic is where the exoplanets with a view of Earth would be located, as they will be the places able to see Earth crossing its own sun—effectively providing observers a way to discover our planet’s vibrant biosphere.
“Only a very small fraction of exoplanets will just happen to be randomly aligned with our line of sight so we can see them transit.” Pepper said. “But all of the thousand stars we identified in our paper in the solar neighborhood could see our Earth transit the sun, calling their attention.”
Source: L Kaltenegger, J Pepper. Which stars can see Earth as a transiting exoplane t?Monthly Notices of the Royal Astronomical Society: Letters, Volume 499, Issue 1, November 2020, Pages L111–L115, Published: 20 October 2020 doi.org/10.1093/mnrasl/slaa161
The Daily Galaxy, Max Goldberg, via Cornell University
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