Our search for extraterrestrial life might have just got a whole lot easier. Now, if aliens so much as modify a planet in their solar system to make it warmer, we would be able to tell.
That's thanks to a new study from The University of California, Riverside, which has identified the artificial greenhouse gases that would be obvious giveaways of a terraformed planet (one that has been artificially modified to be hospitable for life).
The gases described in the study – fluorinated versions of methane, ethane, and propane, along with gases made of nitrogen and fluorine or sulfur and fluorine – could be detectable using existing technology in the atmospheres of planets outside our own solar system. This means it's possible the James Webb Space Telescope could one day soon spot an alien civilisation.
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In large volumes, such gases would act as pollutants on Earth (further spurring climate change). Sulfur hexafluoride, for example, has 23,500 times the warming power of carbon dioxide – a small amount of this could heat a freezing planet to the stage of creating liquid water persistently.
However, there are potential reasons why extraterrestrials would use them on an exoplanet.
“[They’d] be good for a civilization that perhaps wanted to forestall an impending ice age or terraform an otherwise-uninhabitable planet in their system, as humans have proposed for Mars,” said Edward Schwieterman, an astrobiologist and lead author of the study.
Because these gases are not known to occur in large quantities naturally, they must be manufactured. This means that finding them would imply a sign of intelligent, technology-using life forms – on Earth they're used to make components such as computer chips.
The gases are also exceptionally long-lived and would persist in Earth-like atmospheres for up to 50,000 years. This could be extremely useful to the James Webb telescope as the fluorinated gases on terraformed planets could produce an infrared signature.
While the researchers cannot quantify the likelihood of finding these gases in the near future, they are confident that, if they are there, it is entirely possible to detect them during currently planned missions.
“You wouldn’t need extra effort to look for these signs, if your telescope is already characterising the planet for other reasons,” said Schwieterman. “And it would be jaw-droppingly amazing to find them.”
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