Signaling greenhouse gases can signal aliens

If aliens modified a planet in their solar system to make it warmer, we’d be able to figure it out. A new UC Riverside study identifies artificial greenhouse gases that would be the gift of a terraformed planet.

A terraformed planet has been artificially made hospitable to life. The gases described in the study could be detected even at relatively low concentrations in the atmospheres of planets outside our solar system using existing technology. This could include the James Webb Space Telescope, or a future European-led space telescope concept.

And while such polluting gases must be controlled on Earth to prevent harmful climate effects, there are reasons they could be used intentionally on an exoplanet.

“These gases are bad for us because we don’t want to increase heating. 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 humans have proposed for Mars,” said the UCR astrobiologist and lead author of study Edward Schwieterman.

Since these gases are not known to occur in significant quantities in nature, they must be produced. Finding them would therefore be a sign of intelligent life forms using the technology. Such signs are called technosignatures.

The five gases proposed by the researchers are used on Earth in industrial applications, such as manufacturing of computer chips. They include fluorinated versions of methane, ethane, and propane, along with gases made of nitrogen and fluorine or sulfur and fluorine. A new one Astrophysical Journal the paper details their merits as terraforming gases.

One advantage is that they are very effective greenhouse gases. Sulfur hexafluoride, for example, has 23,500 times the heating power of carbon dioxide. A relatively small amount can heat a frozen planet to the point where liquid water can persist on its surface.

Another advantage of the proposed gases – at least from an alien perspective – is that they are extremely long-lived and will persist in an Earth-like atmosphere for up to 50,000 years. “They wouldn’t need to be refilled very often to maintain a welcoming climate,” Schwieterman said.

Others have proposed refrigerant chemicals, such as CFCs, as technological gases because they are almost exclusively man-made and visible in the Earth’s atmosphere. However, CFCs may not be useful because they destroy the ozone layer, unlike the fully fluorinated gases discussed in the new paper, which are chemically inert.

“If another civilization had an oxygen-rich atmosphere, they would also have an ozone layer that they would want to protect,” Schwieterman said. “CFCs would be sequestered in the ozone layer even as they catalyzed its destruction.”

Because they break down more easily, CFCs are also short-lived, making them harder to detect.

Finally, fluorinated gases must absorb infrared radiation to have an impact on climate. This absorption produces a corresponding infrared signature that can be detected with space-based telescopes. With current or planned technology, scientists may detect these chemicals in some nearby exoplanetary systems.

“With an atmosphere like Earth’s, only one in every million molecules could be one of these gases and be potentially detectable,” Schwieterman said. “This concentration of gas would also be sufficient to modify the climate.”

To arrive at this calculation, the researchers simulated a planet in the TRAPPIST-1 system, about 40 light-years away from Earth. They chose this system, which contains seven known rocky planets, because it is one of the most studied planetary systems other than our own. It is also a realistic target to be examined by existing space-based telescopes.

The group also examined the ability of the European LIFE mission to detect fluorinated gases. The LIFE mission will be able to image planets directly using infrared light, allowing it to target more exoplanets than the Webb Telescope, which looks at planets as they pass in front of their stars.

This work was done in collaboration with Daniel Angerhausen at the Swiss Federal Institute of Technology/PlanetS and with researchers at NASA’s Goddard Space Flight Center, the Blue Marble Institute of Space Sciences, and the University of Paris.

While the researchers cannot quantify the likelihood of finding these gases in the near future, they are certain that – if they are present – it is entirely possible to detect them during currently planned missions to characterize atmospheres. planetary.

“You won’t need extra effort to look for these technological signatures if your telescope is already characterizing the planet for other reasons,” Schwieterman said. “And it would be incredibly amazing to find them.”

Other members of the research team echo the enthusiasm not only for the potential of finding signs of intelligent life, but also for how close current technology has brought us to that goal.

“Our thought experiment shows how powerful our next-generation telescopes will be. We are the first generation in history to have the technology to systematically search for life and intelligence in our galactic neighborhood,” added Angerhausen.