Why technosignatures from solar panels might be unlikely

• Technosignatures are signs of alien technology. Astronomers have spoken of trying to detect large-scale solar panel arrays on an alien planet’s surface, or star-energy-gathering megastructures in space (Dyson spheres).
• But a new study suggests it’s unlikely we’ll find technosignatures from solar panels or megastructures built by an advanced alien civilizations.
• That’s partly due to modest energy needs of even a large civilization. For example, the study calculated that a population of 30 billion at a high-living standard would need only about 8.9% coverage of their planet with solar panels. And such relatively small solar panel coverage would be difficult to detect, even across just a few tens of light-years of space.

NASA published this original article by William Steigerwald on August 2, 2024. Edits by EarthSky.

Technosignatures from solar panels on other worlds

One of NASA’s key priorities is understanding the potential for life elsewhere in the universe. So far, NASA has not found any credible evidence of extraterrestrial life. But NASA is exploring the solar system and beyond to help us answer fundamental questions, including whether we are alone in the universe.

Astronomers have long been trying to determine the likelihood of microbial life versus complex life versus a civilization so advanced that we can spot signs of it from here at home. Signs from an advanced civilization are called technosignatures. These studies can help guide suggestions on new telescopes or missions to emphasize the most likely places and ways to look for life.

A smaller technosignature due to modest needs

Now a recent paper published May 24, 2024, in the Astrophysical Journal says if advanced extraterrestrial civilizations exist, one reason they might be hard to detect is because their energy requirements may be relatively modest. If their culture, technology and population size do not need vast amounts of power, they would not be required to build enormous stellar-energy harvesting structures that could be detected by current or proposed telescopes.

Enormous stellar-energy harvesting structures, based on our own earthly experience, might be solar panel arrays that cover a significant portion of their planet’s surface. Or they could be orbiting megastructures to harness most of their parent star’s energy. Both of which we might be able to spot from our own solar system.

Lead author Ravi Kopparapu of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said:

We found that even if our current population of about 8 billion stabilizes at 30 billion with a high standard of living, and we only use solar energy for power, we still use way less energy than that provided by all the sunlight illuminating our planet.

Fermi paradox or ‘Where is everybody?’

The study has implications for the Fermi paradox. Physicist Enrico Fermi proposed this paradox, which asks the question: Where is everybody? In other words, because our galaxy is ancient and vast, and interstellar travel is difficult but possible, why haven’t alien civilizations spread across the galaxy by now? Kopparapu said:

The implication is that civilizations may not feel compelled to expand all over the galaxy because they may achieve sustainable population and energy-usage levels even if they choose a very high standard of living. They may expand within their own stellar system, or even within nearby star systems, but galaxy-spanning civilizations may not exist.

Additionally, our own technological expertise may not yet be able to predict what more advanced civilizations could do. Co-author Vincent Kofman of NASA Goddard and American University, Washington, D.C., added:

Large-scale stellar-energy harvesting structures may especially be obsolete when considering technological advances. 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.

Modeling technosignatures from aliens

The researchers used computer models and NASA satellite data to simulate an Earth-like planet with varying levels of silicon solar panel coverage. The team then modeled an advanced telescope like the proposed NASA Habitable Worlds Observatory. They wanted to see if it could detect solar panels on a planet about 30 light-years away. That’s relatively nearby in a galaxy that spans over 100,000 light-years. They found that type of telescope would require several hundreds of hours of observing time to detect signatures from solar panels covering about 23% of the land area on an Earth-like exoplanet. However, the requirement for 30 billion humans at a high-living standard was only about 8.9% solar-panel coverage.

Looking for extraterrestrial civilizations with advanced technology using technosignatures – observational manifestations of ET technology – is not new. For decades, scientists have been using radio telescopes to look for potential extraterrestrial radio transmissions. More recently, astronomers have proposed using a telescope like the Habitable Worlds Observatory to look for other kinds of technosignatures. They propose looking for chemical fingerprints in exoplanet atmospheres. They also suggest looking for specific characteristics in the light reflected by an exoplanet. Those characteristics might announce the presence of vast silicon solar arrays.

Making assumptions

The new study assumes aliens would build solar panels out of silicon. That’s because it’s relatively abundant compared to other elements used in solar power, such as germanium, gallium or arsenic. Also, silicon is good at converting the light emitted by sun-like stars into electricity. And it’s cost-effective to mine and manufacture into solar cells.

The researchers also assume that a hypothetical extraterrestrial civilization would rely exclusively on solar energy. However, if they used other sources of energy, such as nuclear fusion, it would reduce the silicon technosignature. Therefore it would make the civilization even harder to detect. The study further assumes that the civilization’s population stabilizes at some point. If this doesn’t happen for whatever reason, perhaps they will be driven to expand ever-father into deep space. Finally, it’s impossible to know if an advanced civilization may be using something we haven’t imagined yet that requires immense amounts of power.

Bottom line: Technosignatures – signs of an advanced alien civilization – in the form of solar panels may be difficult to detect, a new study says.

Source: Detectability of Solar Panels as a Technosignature

Via NASA