NASA's Curiosity Rover continues to make discoveries that challenge our understanding of the Martian environment. The most recent puzzling puzzle scientists are dealing with is the variation in oxygen levels on the surface of the planet, as found in Curiosity's portable sample analysis at Mars (SAM) chemistry. Composition at the surface of 95 vol% 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). The nitrogen and argon values follow a predictable seasonal pattern that changes relative to the amount of carbon dioxide. The oxygen levels, however, did not meet the expected patterns and increased by up to 30% in the spring and summer.