How large would an extraterrestrial city have to be for current telescopes to see it? Would it need to be a planet-sized metropolis like Star Wars’ Coruscant? Or could we see an alien equivalent of Earth’s own largest urban areas, like New York City or Tokyo?
A recent preprint by Bhavesh Jaiswal of the Indian Institute of Science suggests that, in fact, we could see cities a mere fraction of that size, using a feature of light known as specular reflection.
Much of the theoretical musings that experts have put into detecting alien techno-signatures have imagined finding large-scale megastructures well beyond current human capabilities, like Dyson spheres or massive orbital rings. These would be akin to enormous solar system spanning neon signs saying ‘intelligent life is here’! Nothing of the sort has ever been found.
But we’ve recently entered an era in which it is possible to directly image exoplanets themselves, opening up opportunities to search for intelligent life in the Universe on more modest scales.
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