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In a new paper published in the Astrophysical Journal, Dr. Ravi Kopparapu of NASA’s Goddard Space Flight Center and colleagues assessed the potential detectability of solar panels made of silicon on an Earth-like exoplanet as a potential technosignature.
Conceptual image of an exoplanet with an advanced extraterrestrial civilization. Structures on the right are orbiting solar panel arrays that harvest light from the parent star and convert it into electricity that is then beamed to the surface via microwaves. The exoplanet on the left illustrates other potential technosignatures: city lights (glowing circular structures) on the night side and multi-colored clouds on the day side that represent various forms of pollution, such as nitrogen dioxide gas from burning fossil fuels or chlorofluorocarbons used in refrigeration. Image credit: NASA / Jay Freidlander.
“The search for extraterrestrial life has primarily focused on detecting biosignatures, which are remote observations of atmospheric or ground-based spectral features that indicate signs of life on an exoplanet,” Dr. Kopparapu and co-authors said.
“More recently, technosignatures referring to any observational manifestations of extraterrestrial technology that could be detected or inferred through astronomical searches has received increased attention.”
“While the search for extraterrestrial intelligence through radio observations has been popular for decades, recent studies have proposed alternate searches for technosignatures in the ultraviolet to mid-infrared part of the spectrum.”
The astronomers assume that extraterrestrials would build solar panels out of silicon 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 other sources of energy are used, such as nuclear fusion, it would reduce the silicon technosignature, making the civilization even harder to detect.
They further assume 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.
For the study, the scientists used computer models and NASA satellite data to simulate an Earth-like planet with varying levels of silicon solar panel coverage.
They then modeled an advanced telescope like the proposed NASA Habitable Worlds Observatory to see if it could detect solar panels on the planet about 30 light-years away, which is relatively nearby in a galaxy that spans over 100,000 light-years.
They found that it would require several hundreds of hours of observing time with that type of telescope 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.
“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,” Dr. Kopparapu said.
The study has implications for the Fermi paradox, postulated by physicist Enrico Fermi, which asks the question that since our Milky Way Galaxy is ancient and vast, and interstellar travel is difficult but possible, why hasn’t an alien civilization spread across the Galaxy by now?
“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,” Dr. Kopparapu said.
“They may expand within their own stellar system, or even within nearby star systems, but a galaxy-spanning civilizations may not exist.”
“Additionally, our own technological expertise may not yet be able to predict what more advanced civilizations could do.”
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Ravi Kopparapu et al. 2024. Detectability of Solar Panels as a Technosignature. ApJ 967, 119; doi: 10.3847/1538-4357/ad43d7
This article is based on a press-release provided by NASA.
