How to spot an alien megastructure: The new search for Dyson spheres

Intelligent extraterrestrials may have built vast solar power plants around their host stars. The hunt for their telltale glow is hotting up

By Mordechai Rorvig

THERE comes a point at which any advanced alien civilisation worth its salt has to dismantle a neighbouring planet for spare parts. This isn’t an act of vandalism, you understand, but rather a precursor to building an enormous solar power plant that surrounds its entire host star. What else would an ambitious alien society do to continue its expansion? How else would it meet its ever-increasing demand for energy?

This scenario, or something like it, is the founding principle of the search for alien megastructures, which in this case would look something like dark embers when viewed through infrared telescopes. The search began in 1960, when physicist Freeman Dyson proposed it as a way of finding alien life. More than 60 years later, the hunt for Dyson spheres, as they are now known, remains a minority sport among those involved in the search for extraterrestrial intelligence (SETI), an enterprise that has focused primarily on listening for radio signals from other worlds.

But astronomers are still prospecting for evidence of alien engineering. In particular, they have been working to put the pursuit of Dyson spheres on a rigorous scientific footing. Now, they are poring over the most precise cosmic cartography ever produced to try to find stars that could be surrounded by swarms of solar panels and distinguish them from naturally occurring infrared herrings. They are already narrowing down candidates. They have even begun to think seriously about the final hurdle: how to tell the difference between an infrared herring and a genuine alien megastructure.

Dyson’s original proposal was quite broad. In a one-page paper, he suggested simply …