Imagine discovering an intelligent civilization many light-years away, one we might identify thanks to the greenhouse gases they intentionally emit into their atmosphere.
That’s the fascinating idea proposed by American researchers in The Astrophysical Journal.
Atmosphere
Given the vast number of planets in the universe and the widespread presence of life’s building blocks, it would be expected that life exists elsewhere in the cosmos. Yet, we haven’t found it so far. The search is still ongoing, and an important role in this quest is played by the James Webb Space Telescope, which allows researchers to hunt for biosignatures in the atmospheres of alien worlds. These biosignatures include gases that suggest the presence of life, such as oxygen, methane, and ozone in high concentrations.
However, American researchers now postulate that there are other gases that could reveal the presence of intelligent extraterrestrial life. Their new study demonstrates that it is possible to detect greenhouse gases, intentionally introduced by aliens into their atmosphere, using the James Webb telescope.
Deliberate Action
The idea of intentionally introducing greenhouse gases into an atmosphere might sound counterintuitive, especially considering what we know about the effects of these gases on Earth. Nonetheless, intelligent aliens might choose this approach—many light-years away—to avert an impending ice age or to make a too-cold planet more hospitable for colonization.
Fluorine Compounds
The researchers suggest that aliens could use several gases for this purpose. They are considering fluorine-enriched versions of methane, ethane, propane, nitrogen, and sulfur. These gases do not naturally occur in significant amounts. Therefore, if the James Webb telescope detects them in high concentrations in alien atmospheres, it could strongly indicate the presence of intelligent aliens who have manufactured these gases to modify their environment.
Efficiency and Longevity
But why would aliens use fluorine-enriched versions of gases like methane or sulfur to alter their climate? The researchers propose several advantages. These gases are highly effective as greenhouse gases. For instance, sulfur-hexafluoride—a compound of sulfur with fluorine—is 23,000 times more potent as a greenhouse gas than CO2. Hence, relatively small quantities could cause significant climate change. Another advantage is the longevity of these gases in the atmosphere; they can linger for up to 50,000 years. This means aliens wouldn’t need to continually introduce new gases to maintain their altered climate.
Visibility
There are numerous valid reasons why aliens dissatisfied with their climate might opt for these gases. If they do this on a relatively nearby exoplanet, we could detect it using current instruments, such as the James Webb telescope, according to researcher Edward Schwieterman. “If only 1 in every million molecules in an atmosphere like ours is such a greenhouse gas, we might still be able to detect it. And that concentration would be sufficient to alter the climate,” he adds.
While we can’t conclusively say that aliens are adjusting their climate with these gases, the researchers are confident that if they are, we would likely be able to see it. This is a compelling reason to look for these ‘technosignatures’ – signals of technologically advanced and intelligent extraterrestrial life, in addition to biosignatures. “You don’t need to make an additional effort to search for these technosignatures when you are already characterizing a planet with a telescope for other reasons,” notes Schwieterman. “And it would be breathtaking if we found them.”
