If aliens harnessed solar power, could we detect them? NASA investigated.

Somewhere in the galaxy, an advanced alien civilization might harness energy from its star.

And NASA wants to know if it could detect this activity.

The space agency has some powerful telescopes — and it's building more. As scientists increasingly peer at other rocky, Earth-like worlds, they evaluated whether it's possible to pick up signs of widespread solar farms on such distant planets. After all, an extraterrestrial society will need power, and a sun-like star provides nearly inexhaustible energy for billions of years. Human civilization, for example, has advanced from largely burning wood to using coal, and now increasingly uses modernized energy sources like solar power.

"We propose it's a natural technological evolution that an advanced civilization could make," Ravi Kopparapu, a NASA planetary scientist who led the research published in the Astrophysical Journal, told Mashable.

Solar panels — made from silicon, which is abundant in the universe — are highly reflective. This makes vast solar arrays a potentially attractive target for NASA, which seeks to identify if life, whether microbial or complex, might exist on planets beyond our solar system (called exoplanets).

The researchers asked whether a large space telescope, like the developing Habitable Worlds Observatory, would be able to detect such solar farms on a world as far as some 30 light-years away (which is many trillions of miles but still relatively close-by — the Milky Way is around 100,000 light-years across). Dubbed the "super-Hubble," the Habitable Worlds Observatory would pack a mirror some six meters (nearly 20 feet) across; the legendary Hubble telescope has a mirror 2.4 meters (7.8 feet) across.

On Earth, the researchers estimate humanity could meet all its energy needs (with energy storage, of course) by covering around two and a half percent of the surface with solar panels. And if the population hypothetically ballooned to 30 billion, this would mean nine percent of land cover. But how much of the surface of a distant exoplanet might need to be blanketed in these reflective arrays to be detectable? The team ran simulations of how a "super-Hubble" could view these far-off solar panel technosignatures, and found a whopping 23 percent of an Earth-like world's surface would need coverage.

"That's huge," Kopparapu said.

And it's perhaps an unlikely scenario from our species' point of view — though as noted below, perhaps not so for another species. What's more, another civilization simply might not need to generate copious amounts of energy, making sprawling energy-creating solar farms or structures unnecessary. Another civilization could have highly efficient technologies, or a low population. This would make widespread solar panel coverage unlikely.

"A civilization may not need as much energy as we think," Kopparapu said.

Yet it's conceivable that an intelligent species on a rocky desert world like Mars may choose to cover a significant swath of its landmass with solar panels. It could view that as the best renewable energy option, especially on a world that might lack much hydroelectric generation. Or it could have reasons we can't imagine.

"We can't judge what a civilization's motives are," Kopparapu noted.

Beyond solar panels, some scientists have for decades mused about the possibility of megastructures that surround a star, harnessing immense amounts of stellar energy. Of course, these behemoth energy harvesters, called Dyson Spheres, might not be the most pragmatic approach for the technologically advanced.

"Surely a society that can place enormous structures in space would be able to access nuclear fusion or other space-efficient methods of generating power," Vincent Kofman, a NASA research scientist who also worked on this technosignature study, noted in an agency statement. (Humanity is on the hunt to make nuclear fusion energy — though realizing this technology is a long, long way off.)

Future telescopes, like the Habitable Worlds Observatory, will sleuth for a number of possible signs of life — and research like this informs scientists of what they might look for. They'll look for signs of pollution, atmospheric ingredients produced by life, and perhaps other forms of technology. Though it currently appears that detecting solar panels is implausible, it can't be ruled out. In the search for potential civilizations — which may be quite rare in any galaxy or maybe not exist — almost anything is possible.

Who knows what the large, powerful instruments will detect, many light-years away.

"They might even find city lights," Kopparapu said.