Here’s how the idea could work: An object’s brightness varies with distance, but the relationship between those two factors will depend on whether the brightness is due to reflected sunlight or due to illumination from the object itself. For a self-illuminated object, the brightness varies by a factor of 1 over the distance squared, but “if you have an object that reflects light from another source … the flux dies out like 1 over the distance to the fourth power,” Loeb said.

Monitoring the changes in the brightness of an object on the edge of our solar system, in a broad disk of icy material known as the Kuiper Belt, could provide a “very simple test” to determine whether extraterrestrials have turned on the lights, Loeb said. …

How likely is it that E.T. would be found on the edges of our own solar system? Not that likely, but Loeb and Turner speculate that it could happen. “Artificially lit KBOs [Kuiper Belt objects] might have originated from civilizations near other stars,” they write. “In particular, some small bodies may have traveled to the Kuiper Belt through interstellar space after being ejected dynamically from other planetary systems.”