After serving us with a mystery surrounding odd fluctuations in the levels of methane on Mars, NASA’s Curiosity rover has served another mystery on the Red Planet: oxygen levels are behaving oddly and unexpectedly.

As revealed by a recent statement by NASA, for the first time ever in the history of space explorations have experts managed to measure the seasonal changes in the gasses that exist in the air located above the surface of the so-called Gale Crater on the Red Planet.

These measurements revealed something strange and unexpected: oxygen, one of the most important gases used by living organisms on Earth to Breathe is behaving oddly, so strange that experts have revealed they cannot explain the discrepancy through any known chemical process.

Oxygen has shown “significant seasonal and interannual variability, suggesting an unknown atmospheric or surface process at work,” researchers wrote in a recent study detailing the oxygen spikes on Mars, published in the Journal of Geophysical Research.

Curiosity has been sniffing curious things on Mars ever since landing on the red planet in 2012. Thanks to its laser spectrometer called SAM (Sample Analysis at Mars), NASA’s rover has been able to make some pretty interesting discoveries on Mars.

The new findings come after around six years worth of Curiosity sniffing around Mars, gathering data. The six-wheeled rover studied Mars as the Red Planet went through its seasons. Just like Earth, Mars is tilted on its axis of rotation which means that both the red planet’s northern and southern hemispheres experience seasons like Earth.

Summer on Mars comes when the hemisphere points towards the sun, while winter arrives when it points away.

Over the course of three Martian years (almost six Earth years), Curiosity inhaled the air at the Gale Crater in order to understand the makeup of the Red Planet’s atmosphere at the surface revealed: 95% by volume of carbon dioxide (CO 2 ), 2.6% molecular nitrogen (N 2 ), 1.9% argon (Ar), 0.16% molecular oxygen (O 2 ), and 0.06% carbon monoxide (CO).

Some of the results Curiosity obtained was no biggie’. However, oxygen levels were just crazy.

The scientists wrote in the recent study that “The SAM measurements of [oxygen] in Gale crater do not show the annual stability or seasonal patterns that would be predicted based on the known sources and sinks in the atmosphere.”

In other words, there was simply may more oxygen than expected to exit during the different seasons on Mars. The Rover spotted there was a lot more oxygen then there should be during Mars’ northern hemisphere’s late spring to summer, and a lot less oxygen than there should be during the northern hemisphere’s winter.

Scientists thought about a few explanations but so far none of those satisfy them. The instrument isn’t broken, it is working perfectly fine just like all other systems on the rover.

There could be that the oxygen the rover sniffed out was from carbon dioxide or even water breaking up in the atmosphere, but this would indicate that the red planet has a lot more water on Mars. Another possibility according to NASA is that carbon dioxide breaks up too slowly in order to produce oxygen signatures.

However, experts are reluctant to think the oxygen spikes have something to do with Mars’ atmospheric dynamics.

Melissa Trainer, first author of the study and a planetary scientist at Goddard Space Flight Center explained in a statement: “The fact that the oxygen behavior 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 researchers have revealed that the oxygen story is curiously similar to that of methane story on Mars. Whether or not these two are connected remains to be seen. Whatever the case, Mars is proving to be a much more interesting planet, one that has offered more mystery than we’ve ever bargained for.