Picture this: A hundred million years ago, an advanced civilization detects strange signatures of life on a blue-green planet not so far away from their home in the Milky Way. They try sending signals, but whatever’s marching around on that unknown world isn’t responding. So, the curious galactic explorers try something different. They send a robotic probe to a small, quiet space rock orbiting near the life-rich planet, just to keep an eye on things.
If a story like this played out at any moment in Earth’s 4.5 billion-year history, it just might have left an archaeological record. At least, that’s the hope behind a new proposal to check Earth’s so-called co-orbitals for signs of advanced alien technology.
Co-orbitals are space objects that orbit the sun at about the same distance that Earth does. “They’re basically going around the sun at the same rate the Earth is, and they’re very nearby,” said James Benford, a physicist and independent SETI (Search for Extraterrestrial Intelligence) researcher who dreamed up the idea that aliens might have bugged Earth via these co-orbitals while he was at a conference in Houston last year. If he’s right, the co-orbitals could be a way to detect alien activity that occurred before humans even evolved, much less turned their attention toward the stars.