In research for extraterrestrial life, we are usually the ones Make the spying. But Cornell University astronomer Lisa Kaltenegger wanted to know who could watch we. “Who would we be the aliens for?” she asks.
Kaltenegger therefore enlisted the help of Jackie Faherty, an astrophysicist who works at the Hayden Planetarium, part of the American Museum of Natural History, in New York. Together, they set out to identify stars that could host alien worlds where inhabitants – past, present, or future – would have a chance to detect Earth as an exoplanet in transit. This means that their planet would have just the right vantage point to observe a slight drop in the brightness of our sun as the Earth crosses, or transits, in front of it. This is the most efficient method Earth people use to find planets beyond our solar system as they orbit their own host stars, creating tiny specks in the light that we can see with astronomical instruments. .
In June, Kaltenegger and Faherty announced their results in Nature with a large inventory of stars that have had, or will later have, the right orientation to discover our planet. They identified over 2,000 stars, using a period ranging from 5,000 years when civilizations on Earth began to flourish, to 5,000 years in the future. Not only the study providing a resource for exoplanet hunters by identifying which stars they should pay attention to, it also gives a unique – and arguably disturbing – perspective on our visibility to the rest of the universe. “I felt a little bit spied on,” Faherty said, remembering the odd feeling of being overexposed. “Do I want to be on a planet that can be found?” “
“It’s a beautiful piece of scientific poetry, to think about how all of these objects move through space in this elaborate ballet,” says Bruce Macintosh, a Stanford University astronomer who was not involved in the work. As the first such study to take into account the changing views of stars over time, it builds on previous research that only used their current positions in the cosmos. “We can now build movies about how the universe will look 5,000 years from now, imagining all the stars blinking when the planets get in their way,” he says.
The new result was made possible by the latest data release from the European Space Agency’s Gaia mission, an orbiting observatory with the ambitious goal of creating a three-dimensional map of positions and speeds of a billion stars. Combined with the planetarium software Faherty uses to visualize stellar movements, she and Kaltenegger found exactly 2,034 stars in Earth’s transit zone. For almost all of them, any extraterrestrial being living on planets surrounding these stars would, with sufficiently mature technology, be able to detect the presence of Earth for at least a thousand years. “On a cosmic time scale, it’s a hit on the radar,” says Kaltenegger.
But for human lives, she says, it gives astronomers enough time to develop the tools necessary to peer into other worlds. Kaltenegger and Faherty hope astronomers use the catalog to find new planets, especially around stars that are not very well known or well studied. From there, large-scale missions like that of NASA future James Webb space telescope, slated to launch by the end of the year, can be used to study planetary atmospheres and look for signs of life. “It’s a treasure trove of planets just waiting to be discovered,” says Kaltenegger. “I look forward to what people find.