by If aliens blanket their planets with strong greenhouse gases like we do, we’d be able to tell.
That’s according to a recent thought experiment in which scientists identified five “artificial” greenhouse gases that can be seen, if abundant enough, in certain atmospheres. exoplanet using existing technology, including the James Webb Space Telescope (JWST).
The gases, including fluorinated versions of methane, ethane, propane, etc World they are known to be some of the most powerful and persistent heat-trapping gases emitted by humans during various industrial manufacturing processes, such as those used to produce semiconductors, for example. Because these substances do not form naturally in large quantities – at least if we are going by Earth’s chemistry – seeing them in the air of an exoplanet would indicate the presence of a technologically advanced species, the scientists say.
On Earth, these gases are dangerous pollutants, and limiting their emissions is essential to combat human climate change. Their presence in an alien atmosphere may not necessarily be bad news, however.
“For us, these gases are bad because we don’t want to increase warming,” study lead author Edward Schwieterman of the University of California, Riverside, said in a recent statement. statement. “But they could be good for a civilization that might want to prevent an impending ice age or set up an otherwise uninhabitable planet in their system, as people have suggested. Mars.”
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Deliberate climate modification to create an Earth-like environment is called terraforming. The idea of landscaping Mars has cropped up in almost every sci-fi story, and, in recent years, scientists have also proposed similar approaches to support long-term colonization. Ideas for warming Mars include melting some of the ice in the planet’s poles and releasing carbon dioxide trapped in their surface to invigorate the planet’s thin atmosphere like a warm blanket. Although, some are skeptical about 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 workparticularly important because Mars is unlikely to host enough carbon dioxide to trigger a significant warming trend.
Later, Schwieterman and his colleagues simulated a planet in the TRAPPIST-1 systemwho is a family of seven rocky planets about 40 light year off Earth in the constellation Aquarius; some are thought to be potentially habitable. The planet TRAPPIST-1f, for example, circles 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 detect all five greenhouse gases. One of them, sulfur hexafluoride, has a heating capacity that exceeds that of carbon dioxide by 23,500 times. Small amounts of this gas, which has a lifetime of at least 1,000 years, are enough to melt an icy planet to the point where life-supporting liquid water flows on its surface, the researchers say. (Life as we know it, to be clear).
“The long lifetime of these gases makes them excellent technosignatures to systematically search for compared to shorter signals,” study co-author Daniel Angerhausen from ETH Zürich said in another. statement. “These signatures could be beyond their civilization if their geoengineering experiments fail.”
Other such fluorinated gases could hang around in an Earth-like atmosphere for up to 50,000 years, so “they wouldn’t need to be replenished too often to maintain a hospitable climate,” he said. Schwieterman in the statement.
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That means if there is extraterrestrial life in frigid planets beyond ours Solar system pumping large amounts of greenhouse gases into their atmospheres to make their worlds more habitable, our current telescopes might be able to see them. Even if only one in a million gas molecules absorbed the infrared radiation from its host star, it would offer a faint signature detectable by the JWST and others. space-based telescope, found Schwieterman and his team.
“Looking for these technosignatures would not require any additional effort, if your telescope has already characterized the planet for other reasons,” Schwieterman said. “And it would be jaw-droppingly great to get them.”
These results are described in a paper published June 25 in The Astrophysical Journal.
