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Alien imposters: Planets with oxygen don't necessarily have life
In their search for life in solar systems near and far, researchers have often accepted the presence of oxygen in a planet's atmosphere as the surest sign that life may be present there. A new Johns Hopkins study, however, recommends a reconsideration of that rule of thumb.
Simulating in the lab the atmospheres of planets beyond the solar system, researchers successfully created both organic compounds and oxygen, absent of life.
The findings, published Dec. 11 by the journal ACS Earth and Space Chemistry, serve as a cautionary tale for researchers who suggest the presence of oxygen and organics on distant worlds is evidence of life there.
"Our experiments produced oxygen and organic molecules that could serve as the building blocks of life in the lab, proving that the presence of both doesn't definitively indicate life," says Chao He, assistant research scientist in the Johns Hopkins University Department of Earth and Planetary Sciences and the study's first author. "Researchers need to more carefully consider how these molecules are produced."
[...] "People used to suggest that oxygen and organics being present together indicates life, but we produced them abiotically in multiple simulations," He says. "This suggests that even the co-presence of commonly accepted biosignatures could be a false positive for life."
(Score: 2) by Immerman on Thursday December 20 2018, @05:25PM
Primarily? Because based on looking at our own planet's history, producing molecular oxygen may be easy, but keeping it around is hard. Oxygen is extremely reactive so to get a build up you must continually produce it faster than it can oxidize exposed minerals, react with other gasses, etc. And while this experiment does provide food for thought, I'm not sure it actually refutes anything on its own, since it looked at atmosphere in isolation, while the primary oxygen-sink is probably geological.
On Earth, that sustained elevated oxygen production was a byproduct of life evolving photosynthesis. Life had been around for at least a billion years before that, and it took 600 million years of photosynthesis before the oceans and seabeds were finally saturated enough that oxygen could start leaking out into the atmosphere in more than trace amounts. It then took another billion years of oxidizing land surfaces before atmospheric oxygen levels began to climb substantially.