For decades, humans have researched and wondered about life beyond Earth. Scientists have now created a list of planets where, if they exist, curious aliens could view Earth.
The scientists reported that there are 1,715 star-systems that could have spotted Earth since about 5,000 years ago. In the next 5,000 years, 319 more star systems will be added, according to a peer-reviewed report published Wednesday in the journal Nature.
“From the exoplanets’ point of view, we are the aliens,” said Lisa Kaltenegger, professor of astronomy and director of Cornell University’s Carl Sagan Institute.
Of those, 75 star systems would have been around when commercial radio stations on Earth began broadcasting into space. Scientists say these planets may be able to pick up radio waves; however, just seven of the star systems detected have the ability to host exoplanets, or a planet outside their solar system.
If these exoplanets harbor intelligent life, those beings could observe Earth and see our atmosphere and signs of life.
How do scientists know this? They used positions and motions from the European Space Agency’s Gaia eDR3 catalog, which is a three-dimensional map of the galaxy. With this map, they were able to determine which stars enter and exit the Earth transit zone, and for how long.
“Gaia has provided us with a precise map of the Milky Way galaxy, allowing us to look backward and forward in time, and to see where stars had been located and where they are going,” said astrophysicist Jackie Faherty, a senior scientist at the American Museum of Natural History.
Faherty said our solar neighborhood is a place where stars enter and exit at an ideal vantage point to see Earth orbit the Sun. Over time, some of those stars lose their view of Earth.
One star, known as Ross 128,,with a red dwarf host star in the Virgo constellation, is about 11 light-years away and is the second-closest system with an Earth-size exoplanet. It is about 1.8 times the size of our planet.
Any inhabitants of Ross 128 could have seen Earth orbit our own sun for 2,158 years, starting about 3,057 years ago. But 900 years ago, they lost their vantage point.
At 45 light-years away, another star called Trappist-1 is also close enough to hear human broadcasts. The star hosts at least seven planets, four of them being habitable. They will be able to witness Earth in just another 1,642 years.
“Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point where they can see Earth transit,” Kaltenegger said. “If we assume the reverse to be true, that provides a healthy timeline for nominal civilizations to identify Earth as an interesting planet.”
The scientists’ research on planets and extraterrestrial life doesn’t stop here. Next year, the James Webb Space telescope is expected to launch and observe several atmospheres and search for signs of life.
“One might 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 for which one of our neighbors might be able to find us.”
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