Alien Satellites and Other Space Junk Could Help Us Find Extraterrestrial Intelligence

Earth is surrounded by a giant bubble of space junk—but similar trash rings around other planets might be a clue as we go hunting for technologically advanced life beyond humans. That's according to a recent paper posted to the physics pre-print site

Its author, Héctor Socas-Navarro, spends most of his time at the Canary Islands Institute of Astrophysics in Spain studying the sun. But he was struck by a weird side effect of the ring of active and retired satellites circling Earth: it's a little bit opaque. And the more satellites we throw up there, the more opaque it gets. He realized that if we—or any technologically advanced aliens out there—build enough satellites, they'll eventually become dense enough to leave a faint shadow around the planet when it passes in front of a star.

Earth is surrounded by a cloud of junk. NASA's Goddard Space Flight Center/JSC

And that's awfully convenient given that one of the best ways we have of spotting alien planets is by staring at their stars and waiting for tiny dips in brightness as planets pass in front of them. Essentially, Socas-Navarro's new paper proposes, if aliens have put enough satellites into orbit around their planet, we'll be able to spot the faintly opaque bubble before and after we spot the brightness dip of the planet itself.

The scale of the endeavor would be a real challenge for the aliens, however, since this idea relies on between 10 billion and one trillion satellites. "It's like building the pyramids," Avi Loeb, an astronomer at Harvard University, told New Scientist. "Each building block is easy, but putting it together is the hard engineering task."

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As grim as it sounds, looking for trash actually makes a lot of sense if we want to find aliens at about our own level of technological savvy. We aren't advanced enough to take on the wildest schemes people have considered as interstellar giveaways, like building a giant energy-harvesting shell around our sun. But making space junk? That we can definitely do.

Here on Earth, we call that bubble the Clarke exobelt—and while there's a good chance we'll slow down, if we do keep adding to it at our current rate, Socas-Navarro calculates that aliens could be able to see it by about 2200.