The NASA rover Curiosity returned some truly amazing data to the Earth at the beginning of the year, with readings of high methane levels that were difficult to explain. Subsequent tests have attempted to identify the cause of the higher than expected readings, but scientists have yet to find a definitive answer.
Now, while the questions about methane continue to swirl, scientists studying the behavior of gas on Mars have noticed that even the oxygen on the Red Planet acts in a very different way from the Earth. The observations were made in the Gale Crater, which the rover has called home since he landed there in 2012.
Curiosity "breathes" air into Mars and analyzes it to determine the levels of various types of gas present. On Earth, the background levels of some gases increase and decrease with the seasons, and the same seems to be true on Mars, but only up to a certain point.
The air on Mars is largely carbon dioxide. In fact, a full 95% of the gas that Curiosity breathes during its tests is CO2. The remaining 5% is a mixture of nitrogen, argon, oxygen and carbon monoxide. By tracking the levels of these gases over a whole Martian year, scientists have noticed anomalies regarding the amount of oxygen compared to other gases.
Within this environment, scientists have discovered that nitrogen and argon follow a predictable seasonal pattern, growing and decreasing in concentration in the Gale crater throughout the year with respect to the quantity of CO2 present in the air. They expected oxygen to do the same. But it was not so. Instead, the amount of gas in the air has increased by about 30% during the spring and summer, and then returned to the levels predicted by the known chemical in autumn.
The fact that oxygen levels vary equally wildly is significant because it hints at processes not yet discovered on the planet's surface. In order for oxygen levels to see a significant peak towards the top and then a drastic drop, something must create it and then another something is using it.
"We are struggling to explain it," says Melissa Trainer of NASA's Goddard Space Flight Center. "The fact that the behavior of the oxygen is not perfectly repeatable every season makes us think that it is not a problem that has to do with atmospheric dynamics. It must be a chemical source and a well that we cannot yet explain."
Before starting to dream of an underground breed of Martian monsters, it is important to know that this is not a smoking gun for life on Mars. In reality, it is all else. There are natural processes that can generate oxygen in the absence of life, and since we have not yet found evidence of life on the Red Planet, but we cannot exclude it, scientists are considering all possible options.