Oxygen on Mars behaves in a way that scientists seem unable to explain, according to NASA.
On its website this week, the space agency noted what they had learned from measuring "seasonal changes in gas" above the craters on Mars.
"They noticed something puzzling: oxygen, the gas many Earth creatures use to breathe, behaves in such a way that scientists have so far been unable to explain through any known chemical processes," the post said.
A portable chemistry laboratory inside the Curiosity explorer analyzes the composition of Mars air above the Gale Crater for six Earth years (or three Mars years).
Scientists hope that oxygen behaves predictably, but "it doesn't" – unlike nitrogen and argon, which follow "predictable seasonal patterns."
NASA association administrator Thomas Zurbuchen said on Twitter the plow had "detected seasonal variations in oxygen on Mars which so far cannot be explained through known chemical processes."
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Apparently, oxygen levels rose by up to 30 percent in spring and summer – which they marked as "predictions above" in a chart on NASA's website.
This observation was published in an academic article this week in the Journal of Geophysical Research: Planet.
One co-author – Sushil Atreya, a scientist at the University of Michigan – called it "just confusing" when researchers first looked at measurements.
Another scientist who led the research, Melissa Trainer from Maryland, said at the NASA post that they were "struggling to explain this."
The scientists double-checked the accuracy of the measuring instruments they used, but that was "fine."
They equate the mystery of oxygen with the unsolved methane puzzle on Mars. Methane seems to increase by 60 percent in the summer, for reasons we don't know about.
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Scientist Timothy McConnochie of the University of Maryland – also a co-author of the paper – told the BBC that measurements showed the possibility of a "reservoir" of oxygen close to the surface.
Oxygen and methane can be products of biological processes, but scientists say the plow has no way of knowing whether the source of the gas is either caused by biology or geology.
They lean toward "non-biological explanations," according to NASA.
"The abiotic process looks very promising, so we must put it aside before pursuing the contribution of microbes," Atreya told the BBC.
For now, the researchers let the world know about their observations and asked Martian experts in the scientific community for any and all ideas.
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