If aliens were harnessing solar energy, would we be able to detect it? NASA investigates.

Somewhere in the galaxy, an advanced alien civilization may be harnessing energy from its star.

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

Space agencies have powerful telescopes and are building more. Scientists have increasingly been observing other rocky planets similar to Earth to assess whether they can find signs of widespread solar power plants on such faraway planets. After all, extraterrestrial societies need power, and stars like the Sun provide a nearly inexhaustible supply of energy for billions of years. For example, human civilization progressed from primarily burning wood to using coal, and now increasingly uses modernized energy sources like solar power.

“We argue that this is a natural technological evolution of an advanced civilization,” said Ravi Kopparap, a NASA planetary scientist who led the study published in the journal Nature. Astrophysical JournalMashable said.

Solar panels made from space-abundant silicon are highly reflective, which makes the giant solar arrays potentially attractive targets for NASA, which is trying to determine whether microbial or complex life exists on planets outside our solar system (called exoplanets).

The researchers wondered whether a large space telescope like the under-development Habitable Worlds Observatory could detect such a solar power station on a planet about 30 light-years away (that’s trillions of miles, but still relatively close; the Milky Way galaxy is about 100,000 light-years in diameter). Dubbed “SuperHubble,” the Habitable Worlds Observatory will have a mirror about 6 meters (about 20 feet) in diameter; the legendary Hubble telescope’s mirror is 2.4 meters (7.8 feet) in diameter.

On Earth, researchers estimate that humanity could meet all its energy needs with solar panels covering only about 2.5 percent of the surface (with some energy storage, of course). If the population swelled to 30 billion, that would mean covering 9 percent of the land area. But how much of a distant exoplanet’s surface would need to be covered with these reflective arrays before they could be detected? The team simulated whether a “Super Hubble” could observe the technical signature of these distant solar panels and found that a whopping 23 percent of an Earth-like planet’s surface would need to be covered.

“That’s amazing,” Kopparap said.

And it’s probably an unlikely scenario from the human perspective, although it may not be the case for other species, as we’ll discuss below. Additionally, other civilizations don’t need to generate large amounts of energy, so they don’t need vast energy-generating solar farms and structures. Other civilizations may have very efficient technology or small populations, which makes them less likely to have widespread solar panels.

“Civilization may not require as much energy as we think,” Kopparap says.

A conceptual diagram of what the Habitable World Observatory might look like as it peers into space.
Credit: NASA Scientific Visualization Studio

An artist’s conception of an exoplanet home to a technologically advanced civilization.
Credit: NASA / Jay Friedlander

But it’s conceivable that an intelligent lifeform living on a rocky, desert planet like Mars might choose to cover large swaths of its landmass in solar panels — especially on a planet with little to no hydroelectric power — because it might see that as the best renewable energy option, or for reasons we can’t imagine.

“You can’t judge what a civilization’s motives are,” Kopparap noted.

“You can’t judge what a civilization’s motives are.”

Beyond solar panels, some scientists have been thinking for decades about the possibility of huge structures that could surround a star and harness its vast energy. Of course, these giant energy collectors, called Dyson spheres, might not be the most practical approach for a technologically advanced population.

“Any society capable of putting large structures in space could also use nuclear fusion and other space-efficient methods of generating electricity,” Vincent Coffman, a NASA research scientist who worked on the Tech Signature study, said in a NASA statement. (Humans are exploring the creation of fusion energy, but the technology is still a long way off.)

Conceptual diagram of the TRAPPIST-1 solar system, containing seven rocky planets about 40 light-years from Earth, some of which may be habitable.
Credit: NASA / JPL-Caltech

Future telescopes like the Habitable Worlds Observatory will search for signs of life in great numbers. And such studies will inform scientists what to look for. They will look for signs of pollution, components of the atmosphere produced by life, and perhaps other forms of technology. At this point, detecting solar panels seems unlikely, but the possibility cannot be ruled out. Almost anything is possible in the search for potential civilizations that may be extremely rare or even non-existent in our galaxy.

Who knows what these huge, powerful instruments will detect light years away?

“You might even spot city lights,” Kopparap said.