Alien Life: Weird 'Biosignatures' Help Scientists Hunt for Extraterrestrials

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The team looked back through the history of Earth to identify the best chemical cocktail. The Archean Earth, pictured here, describes a more than billion-year period in the early history of the planet. Francis Reddy/NASA’s Goddard Space Flight Center

Scientists have found a new way to hunt for alien life on distant exoplanets. Clashing gas signatures could mark a planet as habitable from millions of miles away.

Chemicals such as oxygen are hard to produce without some kind of life. If a planet has oxygen in its atmosphere, it may very well harbor microbes. On Earth, however, oxygen has only been produced in large amounts for about an eighth of its history.

By looking for other gas combinations that should only be possible in the presence of life, scientists might have a better shot at finding aliens.

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The James Webb Telescope will investigate the atmospheres of distant planets. Joshua Krissansen-Totton/NASA/Wikimedia Commons

"This idea of looking for atmospheric oxygen as a biosignature has been around for a long time. And it's a good strategy—it's very hard to make much oxygen without life," said study author Joshua Krissansen-Totton, a University of Washington doctoral student, in a statement. "But we don't want to put all our eggs in one basket. Even if life is common in the cosmos, we have no idea if it will be life that makes oxygen. The biochemistry of oxygen production is very complex and could be quite rare."

History of Earth

The team took a longer look the history of Earth to identify other gaseous emissions that might better indicate life in a study published yesterday in Science Advances. By homing in on times of "chemical disequilibrium"—combinations of gases that shouldn't exist without life— on our own planet, the team identified a mix of gases that might signal biological activity elsewhere.

The work led the team to believe that methane, carbon dioxide and a lack of carbon monoxide could be the biosignature to look out for.

Methane can be produced by asteroid impacts, emissions from the inside a planet itself and reactions of rocks and water. However, the team think it is unlikely an Earth-like planet could produce large amounts of methane without life as well.

Processes such as volcanic eruptions spew out carbon monoxide as well as carbon dioxide and methane. Microbes love to munch on carbon monoxide, so—if they exist on a planet—there shouldn't be much of the gas left at all. Krissansen-Totton explained: "If carbon monoxide were abundant, that would be a clue that perhaps you're looking at a planet that doesn't have biology."

Identifying these biosignatures could be key to the search for alien life. Soon, technology like NASA's James Webb Space Telescope will scour the atmospheres of distant planets for these kinds of chemical cocktails. Co-author David Catling, a professor at the University of Washington, said: "What's exciting is that our suggestion is doable, and may lead to the historic discovery of an extraterrestrial biosphere in the not-too-distant future."