Scientists have discovered something strange about the oxygen levels on Mars. Over the course of six years, the Curiosity rover measured gases during different seasons on the planet, and NASA learned that oxygen increases in the Martian atmosphere in the spring and summer. Now, scientists are trying to solve the oxygen mystery and figure out why the levels fluctuate during the year.

The Curiosity rover used its Sample Analysis at Mars (SAM) instrument to measure gases in the Martian atmosphere. It found that 0.16% of the atmosphere was molecular oxygen (O₂). In addition, it discovered that the levels of oxygen increased in the spring and summer by 30% and decreased in the fall.

"This pattern repeated each spring, though the amount of oxygen added to the atmosphere varied, implying that something was producing it and then taking it away," NASA said.

Scientists believe that the Curiosity rover's measurements are accurate and not a fluke. However, they're struggling to explain why oxygen levels would increase and decrease based on the Martian seasons. Now, they're wondering what could create oxygen on Mars.

First, the possibility of water molecules breaking up and releasing oxygen into the atmosphere doesn't make sense because there's not enough water. Second, carbon dioxide can't be responsible for the extra oxygen either, since it takes too long to fall apart.

One possibility is that microbes are making oxygen during different parts of the year. Another option is that chemical processes that involve the soil, rocks or water are affecting atmospheric oxygen on the planet.

"We’re struggling to explain this. 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," NASA's Melissa Trainer said.

Researchers think oxygen's strange behavior on Mars may have something to do with the unusual things they have noticed about methane. Curiosity found that methane makes up 0.00000004% of the atmosphere, but it also fluctuates during the year. In the summer, methane levels increase by 60%.

"With the new oxygen findings in hand, Trainer’s team is wondering if chemistry similar to what’s driving methane’s natural seasonal variations may also drive oxygen’s. At least occasionally, the two gases appear to fluctuate in tandem," NASA said.

It's possible there is a connection between the two gases, and something may be releasing both of them into the air on Mars. Figuring out what could be the source is part of the problem. The Curiosity rover has limitations that prevent the type of exploration scientists would prefer.

On Earth, plants make up most of the oxygen in the air. However, Mars is a desolate planet without any obvious plant life. Its extreme temperatures and weather patterns make it hard to imagine that a common flower or shrub could survive in these conditions.

It's possible a new type of plant that doesn't exist on Earth may be responsible for releasing oxygen on Mars during the warmer months. Considering that it hasn't been spotted, the plant may be tiny or even microscopic. In addition, it may not function or look the way plants do on Earth and may have an unusual structure that gives it the ability to survive harsh conditions. Hopefully, further exploration of the planet will provide more answers.