Amr Dalsh / Reuters

For decades, the search for intelligent extraterrestrial life has used giant radio telescopes on the ground to scan the skies, hoping to detect alien broadcasts from somewhere in the Milky Way. (No luck so far.) But the rise of powerful space telescopes capable of observing hundreds of Earth-like planets orbiting distant stars, like the Kepler telescope launched in 2009, changed the game. The right technology, astronomers say, could someday allow humans to see optical evidence of extraterrestrial life.

So, what can astronomers look for? The most popular suggestions are structures built by civilizations, far more advanced than our own. In 1960, Freeman Dyson hypothesized spheres or swarms constructed to harness and harvest the energy of a parent star. In 2005, Luc Arnold proposed artificial objects inserted into a planet’s orbit to serve as a signal of existence to other civilizations. Now, a pair of astronomers suggest looking for shields constructed to protect against deadly cosmic explosions.

Milan Cirkovic and Branislav Vukotic suggest, in a report published this month in the journal Acta Astronautica, that advanced civilizations could lasso objects within their solar system to engineer shields that would dampen the dangerous effects of exploding stars or gamma-ray bursts. After all, no one wants to be wiped out by a supernova—and a sophisticated, space-faring society with enough technological prowess could actually do something to protect itself. Back on Earth, telescopes like Kepler could spot these shields as they transit their stars, creating the dimming effect the spacecraft is built to observe. Powerful infrared telescopes could also detect the shields by the heat they emit.

“We should certainly look for these, as well as all conceivable forms of astro-engineering within the SETI framework,” Cirkovic wrote in an email, referring to the search of extraterrestrial intelligence by its acronym. “The orthodox SETI is narrowly conceived and unlikely to succeed as long as it relies on intentional radio emissions.”

Cirkovic and Vukotic suggest protective shields aren’t as complicated as they sound, and could even be conceived and built by humans between several decades and a century from now. Advanced humans, Cirkovic and Vukotic write, could shoot electron beams into a part of the solar system with plenty of icy objects, like the Kuiper belt, creating electromagnetic fields that would push enough objects together to form a Earth-sized disk around the planet. The disk, they say, could block the worst of a cosmic blast and save the planet. If it seems like science fiction, consider that NASA wants to launch a robotic mission to capture a nearby asteroid and change its orbit in the 2020s.

“As these discussions go, this is a surprisingly easy way to do things,” says Jason Wright, an astronomer from Penn State University, of the protective shields. “It would still be by far the greatest engineering achievement humanity has ever accomplished, by a lot. It’s still future [technology], but not impossible.”

The report’s authors argue that advanced humans could also predict some of the cosmic catastrophes from which they seek protection. Weather forecasting is far from perfect, but humans have managed to predict the strength and trajectory of some hurricane and other storm systems, the astronomers say. Years from now, advanced gravitational-wave detectors could observe collisions of merging neutron stars, meetings that produce dangerous gamma-ray bursts. Astronomers could then check nearby stars for potential protective shields.

For now, they’re still looking for other signs. Last October, Kepler scientists announced they had spotted an unusual light pattern from a star inside the constellation Cygnus, suggesting something was circling the star. The cluster of matter could be a cluster of comets, or something else entirely, like a megastructure built by an advanced civilization, for reasons astronomers can only speculate. After all, the search for extraterrestrial life is the search for the unknown.

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