![]() "It has very sharp spectral features," says Beatty. In 2021, Beatty calculated that the sodium emitted from such lights could be detectable in a planet's atmosphere. One of the most revealing technosignatures from Earth might not be our atmospheric pollutants or radio signals at all, however, but our city lights. ( Read more about how we might also be able to spot alien life from their pollution.) "We're pretty sure they can only be produced by technology," says Macy Huston, an astronomer at the University of California, Berkeley in the US. "So they might deduce we are burning stuff here."Ĭhlorofluorocarbons from aerosols, refrigerants and other sources could also be a give-away sign of industrial activity on our planet. The gas is "basically a byproduct of combustion", says Hector Socas-Navarro, an astrophysicist at the Institute of Astrophysics of the Canary Islands in Spain. Nitrogen dioxide could also provide some clues that our planet was inhabited by an intelligent lifeform. What life might be like in oceans on other worlds.The best indicator of life on Earth from such observations might be oxygen, nitrogen, and water vapour, says Paul Rimmer, an astrochemist at the University of Cambridge in the UK, which would "be an indication of a stable liquid ocean". In 2021, Faherty found there were nearly 2,000 stars within 300 light-years of Earth that could potentially be able to see such a transit. If they can see our planet pass in front of our Sun, known as a transit, they could see sunlight passing through our atmosphere and pick out its different gases. By 2031, the closest of the stars would have had enough time to receive the signals and send their own message back, perhaps an interesting target for future study.īut what if alien astronomers were more dedicated? They might try and observe our planet before receiving any such signals. "The signal would definitely show up as artificial," says Isaacson. He found four nearby stars and any accompanying planets would have already received the transmissions, with more than 1,000 stars likely to hear the signals by the year 2300. In April, Isaacson calculated whether some of these transmissions, up to 20 kilowatts, might reach other stars as they wash over the remote spacecraft and continue their journey into space. ![]() The furthest of these, Nasa's Voyager 1 spacecraft, is 24 billion kilometres (15 billion miles) from Earth, requiring a powerful network of dishes on Earth known as the Deep Space Network to be communicated with. Across the Solar System we have multiple spacecraft exploring different locales such as Mars, Jupiter, and even the outer reaches of the Sun. "They want to broadcast to the ground." Other more modern forms of communication, like mobile phone signals, are unlikely to be detectable.īut not all of our signals are so faint. "Radio stations don't want to broadcast into space," says Thomas Beatty, an astronomer at the University of Wisconsin in the US. We continue to broadcast radio signals today, from TV shows to satellite communications, but in a less detectable way. "They needed to be more powerful because the radios that people listened to didn't have as sensitive receivers," he says. The most notable period was from 1900 up to World War Two, says Howard Isaacson, an astronomer at the University of California, Berkeley in the US, when our radio transmissions were stronger. Upon some of these worlds we have started to hunt both for the chemical signatures in their atmospheres that might indicate biological activity and even technosignatures that might be emitted by intelligent life forms – radio signals either purposefully or accidentally sent in our direction.Įarth has been unabashedly broadcasting its own presence into the galaxy for about a century now. But such observations are in their infancy – trillions of worlds are likely scattered throughout the Milky Way. ![]() To date, we have found more than 5,500 planets orbiting other stars in our galaxy, called exoplanets. That means other worlds might be looking too." ![]() "Hold the mirror up to yourself in space, and what would they see of us?" says Jacqueline Faherty, an astrophysicist at the American Museum of Natural History in the US. That's a question scientists have had to grapple with in recent years, as we continue to inadvertently broadcast our presence out into the galaxy. But what if there was? And what if they were looking back, trying to find us? Would they know there is life on Earth?
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