In efforts to understand the potential technosignatures of alien civilizations, a new paper is set to appear in The Astrophysics Journal. The authors propose the idea of looking for artificial greenhouse gases in the atmospheres of planets to indicate intentional climate modification by extraterrestrial life forms. Unlike passive industrial pollution, these gases would be a deliberate attempt to alter a planet’s climate using long-lived, low toxicity gases.
Lead author and astrobiologist Edward Schwieterman outlines two scenarios where artificial greenhouse gases could be detected. The first scenario involves terraforming an uninhabitable planet within a planetary system, similar to humanity’s proposed plans for Mars. The second scenario would be the use of these gases to prevent an ice age on a planet. These technosignatures would be long-lived and could potentially be detected without direct communication from the alien civilization.
Computer models were used to simulate realistic planetary spectra of earth-like planets with varying concentrations of greenhouse gases. Compounds such as C2F6 and SF6 were identified as highly absorptive greenhouse gases with warming potentials thousands of times that of carbon dioxide. The team focused on simulating the detection of these gases in the atmosphere of TRAPPIST-1f, a planet located in the outer habitable zone of the TRAPPIST-1 system, some 40 light years away.
A terraformed planet would appear unusual in the infrared spectrum, with potential size discrepancies in mid-infrared transmission spectroscopy and colder temperatures than expected in emitted light. Detecting such technosignatures would depend on the maintenance of greenhouse gas levels in the atmosphere over time. While the number of potentially terraformed planets within a thousand light-years of Earth may be low, the chances of identifying a planet with deliberately modified climate are higher than finding one undergoing temporary industrial pollution.
Overall, the search for artificial greenhouse gases in the atmospheres of distant planets offers a unique opportunity to detect deliberate climate modification by alien civilizations. By analyzing planetary spectra for these technosignatures, researchers aim to not only answer scientific questions about rocky exoplanets but also potentially uncover evidence of advanced extraterrestrial life forms engaged in planetary engineering for survival or terraforming purposes.
