If aliens were blanketing their planets with powerful greenhouse gases, as we do, we might notice.
This is evident from a recent thought experiment in which scientists identified five “artificial” greenhouse gases that, if abundant enough, could be found in the atmosphere of certain areas. exoplanets using existing technology, including the James Webb Space Telescope (JWST).
The gases, which include fluorinated versions of methane, ethane and propane, Soil are known to be among the most potent and persistent heat-trapping gases emitted by humans during various industrial manufacturing processes, such as those used to produce semiconductors. Because these substances do not form naturally in large quantities — at least based on Earth’s chemistry — spotting them in the skies of an exoplanet would signal the presence of technologically advanced species, scientists say.
On Earth, these gases are dangerous pollutants and limiting their emissions is crucial to combating man-made pollution. climate changeHowever, their presence in a strange atmosphere does not necessarily have to be bad news.
“For us, these gases are bad because we don’t want to increase warming,” Edward Schwieterman, lead researcher on the study at the University of California, Riverside, said in a recent report. rack“But they would be good for a civilization that perhaps wanted to prevent an impending ice age or terraform an otherwise uninhabitable planet in their system, as people have proposed before Mars.”
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Such deliberate climate modification to create an Earth-like environment is known as terraforming. The idea of terraforming Mars has cropped up in nearly every science fiction story, and in recent years scientists have also proposed similar approaches to support long-term colonization. Ideas for warming Mars include thawing some of the ice at the planet’s poles and releasing carbon dioxide stored in the surface to support the planet’s thin atmosphere like a warm blanket. Although some remain skeptical of the concept. For example, Paul Sutter, an astrophysicist at SUNY Stony Brook and a Space.com contributor, wrote in a 2021 article that this type of terraforming effort probably won’t workespecially since Mars likely doesn’t contain enough carbon dioxide to cause significant warming.
More recently, Schwieterman and his colleagues have discovered a planet in the TRAPPIST-1 systemthat is a family of seven rocky planets about 40 light years away from Earth in the constellation Aquarius; several of these are considered potentially habitable. The planet TRAPPIST-1f, for example, orbits its host star every nine days within its habitable zone.
If aliens were to terraform such a planet, the researchers found that the JWST could identify five greenhouse gases. One of them, sulfur hexafluoride, has a warming potential 23,500 times greater than carbon dioxide. Tiny amounts of this gas, which has a lifespan of at least 1,000 years, would be enough to thaw an icy planet to the point where life-supporting liquid water flows across its surface, the researchers say. (Life as we know it, to be clear.)
“Their long lifetimes make these gases excellent technosignatures to search for systematically compared to shorter-lived signals,” study co-author Daniel Angerhausen of ETH Zurich said in another paper. rack“These signatures could even outlive their civilization if their geoengineering experiments fail.”
Other similar fluorinated gases can last up to 50,000 years in an atmosphere similar to Earth’s, “so they don’t need to be replaced as often to maintain a comfortable climate,” Schwieterman said in the statement.
This means that if there is alien life on icy planets beyond our own solar system pumps a lot of greenhouse gases into their atmospheres to make their worlds more habitable, our existing telescopes could spot them. Even if just one in a million gas molecules were to soak up infrared radiation from its host star, it would produce a telltale signature detectable by the JWST and other room-based telescopes, Schwieterman and his team discovered.
“You wouldn’t have to go out of your way to look for these technosignatures if your telescope is already characterizing the planet for other reasons,” Schwieterman said. “And it would be mind-bogglingly awesome to find them.”
These findings are described in a paper published June 25 in The Astrophysical Journal.