A study ofUniversity of California, Riverside, has identified man-made greenhouse gases that could reveal a planet terraformed by alien civilizations. These gases, if present in the atmosphere of planets outside our solar system, could be detected using existing technology, such as the James Webb Space Telescope or a future European telescope.
A terraformed planet is artificially made habitable for life. According to the study, i gas described would be detectable even at low concentrations in the atmosphere of exoplanets using current technology. These gases include fluorinated versions of methane, ethane, and propane, as well as compounds of nitrogen and fluorine or sulfur and fluorine, used on Earth in industrial applications such as making computer chips.
These gases, highly effective as greenhouse gases, could heat an icy planet enough to allow liquid water to be present on its surface. Sulfide hexafluoride, for example, has 23,500 times the heating capacity of carbon dioxide.
These gases also offer the advantage of being incredibly long-lived, being able to persist in an Earth-like atmosphere for up to 50,000 years, as pointed out by Edward Schwietermanastrobiologist and lead author of the study:
They wouldn’t need to be replaced too often to maintain a hospitable climate.
Unlike CFCs, which destroy the ozone layer and are short-lived, the proposed fluorinated gases are chemically inert and do not damage the ozone layer, making them more advantageous to an alien civilization with an oxygen-rich atmosphere.
Gas detection with space telescopes
To have an impact on the climate, fluorinated gases must absorb infrared radiation, producing an infrared signature detectable with space telescopes. Scientists could detect these gases in nearby exoplanetary systems with current or planned technology. Schwieterman explained:
With an atmosphere like Earth’s, only one molecule in a million could be one of these gases, and it would be potentially detectable.
The team simulated a planet in the TRAPPIST-1 system, about 40 light-years from Earth, to test the detectability of these gases. This system, which contains seven rocky planets, is one of the best-studied and a realistic target for existing space telescopes.
Collaborations and the future of research
The research was conducted in collaboration with Daniel Angerhausen from the Swiss Federal Institute of Technology/PlanetS and with researchers from NASA’s Goddard Space Flight Center, the Blue Marble Space Institute of Science and the University of Paris.
While researchers cannot quantify the likelihood of finding these gases in the near future, they are confident that, if present, they will be detectable during planned missions to characterize planetary atmospheres, as specified by Schwieterman:
You wouldn’t need extra effort to look for these technosignatures if your telescope is already characterizing the planet for other reasons. It would be incredibly surprising to find them.
