Curiosity rover reveals oxygen spikes on Mars

By analysing readings from the lander’s Sample Analysis at Mars instruments, scientists found oxygen levels rose by 30% in spring and summer above Mars' 916 mile wide Gale Crater.

Curiosity has been measuring seasonal changes in gases above the surface of the Gale Crater for six Martian years, or nearly four Earth years.

Melissa Trainer, planetary scientist at NASA's Goddard Space Flight Center, said: "We're struggling to explain this. The fact that the oxygen behaviour isn't perfectly repeatable every season makes us think that it's not an issue that has to do with atmospheric dynamics. It has to be some chemical source and sink that we can't yet account for."

The makeup of the Martian atmosphere at the surface is on average 95% by volume of carbon dioxide, 2.6% molecular nitrogen, 1.9% argon, 0.16% molecular oxygen and 0.06% carbon monoxide.

While scientists found nitrogen and argon fluctuate in concentration relative to how much carbon dioxide is in the air, oxygen has been observed to show significant seasonal and year?to?year variability, suggesting an unknown atmospheric or surface process at work.

Methane, meanwhile, was found to increase in abundance by about 60% in summer and also spike randomly and dramatically during the year.

NASA scientists believe the reasons for this are more likely geological than biological as they don't currently have any convincing evidence of biological activity on Mars.

Timothy McConnochie, co-author of the findings, said: "We have not been able to come up with one process yet that produces the amount of oxygen we need, but we think it has to be something in the surface soil that changes seasonally because there aren't enough available oxygen atoms in the atmosphere to create the behaviour we see.”

The findings have been published in detail in the Journal of Geophysical Research: Planets.