Could we detect signs of alien terraforming?

Deep space exploration has always captured the human imagination and fueled our curiosity about the possibility of extraterrestrial life. Recently, a fascinating prospect has opened up: detecting signs of technologically advanced civilizations on other planets not through radio signals, but through their effects on their atmospheres. Researchers have identified five “artificial” greenhouse gases that could serve as distinctive markers if they are abundant in the atmospheres of exoplanets.

Greenhouse gases as technosignatures

On Earth, fluorinated gases, such as the fluorinated versions of methane, ethane, and propane, are particularly potent substances in terms of heat retention potential in the atmosphere. Unlike their non-fluorinated counterparts, these compounds are in fact extremely stable and can persist for decades or even centuries once released into the air. Their ability to effectively trap infrared radiation therefore makes them highly effective global warming agents. Furthermore, these fluorinated gases are not produced naturally in significant quantities on Earth. Their increased presence in the atmosphere is in fact mainly attributed to industrial activities advanced human activities, such as semiconductor manufacturing where they are used as process gases for various applications. The presence of significant quantities of these gases in the atmosphere of a distant planet would therefore suggest not only a capacity to produce these complex substances, but also a willingness and a technological mastery sufficient to use them in large-scale applications. This scenario also opens the door to fascinating implications. An extraterrestrial civilization capable of intentionally transforming its climatic environment could indeed seek to terraform an otherwise inhospitable planet to make it habitable using these different gases. As a reminder, the concept of terraforming, often explored in science fiction and among scientists, represents a proactive use of technology to alter planetary conditions and potentially create viable human habitats on distant worlds. Thus, the detection of fluorinated gases as technosignatures on an exoplanet would not only offer clues to the technological capabilities of an extraterrestrial civilization, but also to its motivations and goals in exploring and transforming the surrounding universe.
Artistic interpretation of an exoplanet. Credits: Ed Bell for the Simons Foundation

The Importance of Extraterrestrial Detection with James Webb

In this quest for extraterrestrial life, researchers have recently carried out simulations to explore the potential of the telescope James Webb in the detection of several of these gases. For their simulations, the authors of the study chose five artificial greenhouse gases used in industrial applications such as the manufacture of computer chips: fluorinated versions of methane, ethane and propaneas well as species consisting of nitrogen and fluorine or sulfur and fluorine. One of the reasons why these artificial gases were chosen is their incredibly effective warming power. Sulfur hexafluoride, for example, has a global warming potential 23,500 times greater than that of carbon dioxide. Another advantage of the gases studied by the researchers (at least for the detection of technosignatures) is that they have a exceptionally long lifespanmeaning they could persist in an Earth-like atmosphere for 50,000 years. For this study, the team simulated the presence of these gases on TRAPPIST-1f, a planet in the TRAPPIST system-1, a family of seven rocky worlds located about 40 light-years from Earth in the constellation Aquarius. Researchers then discovered that the instruments aboard JWST would indeed capable of detecting greenhouse gases artificially produced at the level of abundance required for climate engineering. This means that if an alien civilization emits large numbers of greenhouse gases into its atmosphere to make its world more habitable, our current telescopes might be able to spot them. Details of the study are published in The Astrophysical Journal.