ITHACA, N.Y. — It’s been three decades since legendary astronomer Carl Sagan suggested that the Voyager 1 space probe take a picture of Earth from nearly four billion miles away. Inspired by the “Pale Blue Dot” photo, researchers are posing an interesting question: could other planets be looking at us just like we’re looking at them? A study of Earth’s “solar neighborhood” finds over 1,000 solar systems have the perfect angle to view our planet.
Study co-author Lisa Kaltenegger says their list focuses on main-sequence stars similar to the sun. These solar systems may contains exoplanets, Earth-like worlds sitting in the habitable zone for life. All of the prospective systems are within 300 million light-years of Earth, close enough to see our world’s chemical traces.
“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,” says Kaltenegger, the director of Cornell’s Carl Sagan Institute, in a university release. “If observers were out there searching, they would be able to see signs of a biosphere in the atmosphere of our Pale Blue Dot… and we can even see some of the brightest of these stars in our night sky without binoculars or telescopes.”
What makes this list of 1,004 star systems special is they all sit in Earth’s ecliptic. This is the plane of our world’s orbit around the Sun. Exoplanets traveling along this same path would have a view of Earth.
To them, Earth would be a transiting planet. This means one that passes in front of its sun as the observer looks at distant stars. These exoplanets would be able to see Earth crossing the Sun and it would also illuminate our world’s vibrant biosphere.
Researchers say transit observations are an important tool for astronomers examining nearby solar systems and searching for habitable worlds. They will also play a pivotal role in creating a roadmap for the newest space telescopes, including NASA’s James Webb Space telescope, which launched in 2021.
“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,” co-author Joshua Pepper of Lehigh University says. “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.”
“If we’re looking for intelligent life in the universe, that could find us and might want to get in touch,” Kaltenegger adds. “We’ve just created the star map of where we should look first.”
The study appears in the Monthly Notices of the Royal Astronomical Society.
This article was first posted October 22, 2020.