The discovery comes after the space agency used the Curiosity rover to measure the seasonal changes in the gas that fills the air above the Gale Crater on Mars, for the first time ever.
But the data sent back from the planet has left the scientists who received it stumped. They say there is no known explanation for the unusual fluctuations in the oxygen on the planet.
“The first time we saw that, it was just mind boggling,” said Sushil Atreya, professor of climate and space sciences at the University of Michigan in Ann Arbor
It comes as researchers continue to grapple with the mystery of methane on the red planet. As has now been revealed of oxygen too, the amount of the gas soars and plunges in a way that appears random and for which scientists have no cause.