Alien Life Hunt Oxygen Isn’t the Only Possible Sign of Life

August 16, 2018

A new study emphasizes that extraterrestrial life hunters should keep an open mind as they scan the atmospheres of exoplanets.

The long-standing strategy of looking for oxygen is indeed a good one, after all, the research team members say, because it’s hard for that gas to accumulate in a planet’s atmosphere without life stirring there.

“But we don’t want to put all our eggs in one basket,” lead study author Joshua Krissansen-Totton, a doctoral student in Earth and space sciences at the University of Washington in Seattle, said in a statement. 5 Bold Claims for Extraterrestrial Life].

“Even if life is common in the universe, we don’t know if it could be life making oxygen,” Krissansen-Totton added.” The biochemistry of oxygen production is very complex and probably quite rare.”

So he and his colleagues took a broader view, studying Earth’s history to determine combinations of gases that, if observed together by future instruments such as NASA’s James Webb Space Telescope, would be strong evidence for life. They came up with what they believe to be a good candidate: methane (CH4) and carbon dioxide (CO2), without any obvious carbon monoxide (CO).

As their chemical formula shows, methane and CO2 are very different molecules. Their coexistence suggests an “atmospheric imbalance” – a term that has astrobiologists quite excited.

“So you’ve got these extreme levels of oxidation. And it’s very difficult to do that through abiotic processes without also producing carbon monoxide, which is the intermediate step,” Krissansen-Totton says.” For example, planets with volcanoes that eject carbon dioxide and methane will also tend to eject carbon monoxide.”

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In addition, many microbes on Earth voraciously consume carbon monoxide. So the abundance of the stuff in a planet’s air would oppose life for several different reasons, the research team members said.

Proposing to look for compounds that are in disequilibrium is not a novel idea. For example, other astrobiologists have suggested that a combination of methane and oxygen in the air of an exoplanet would be a strong signal for life.

But the new study may help open researchers’ minds to possibilities beyond oxygen, which was undetectable in the Earth’s atmosphere for most of the history of life on Earth. The gas didn’t begin to build up in our air until about 2.5 billion years ago, when photosynthesis really began. And scientists say it probably didn’t reach reasonably high levels until about 600 million years ago).

“The exciting thing is that our proposal is feasible and could lead to the historic discovery of an extraterrestrial biosphere in the near future,” study co-author David Catlin, a professor of earth and space sciences at the University of Washington, said in the same statement.