That famously reddish surface of Mars may hold a rather incredible secret: it may have been an active contributor to the atmosphere as it is today. NASA researchers found this out when they used the Curiosity rover — specifically, its Sample Analysis at Mars (SAM) array of instruments — to measure levels of xenon and krypton in the atmosphere of Mars.

Tracking these gases allows scientists to measure changes in Mars’ atmosphere over time. In particular, researchers were looking at the balance of isotopes int he two gases. The ratios are able to tell them how different elements interacted with each other in the past, and all signs point to the surface of the planet helping to shape the chemical composition of Mars’ atmosphere as we see it today, according to a NASA statement.

“What we found is that earlier studies of xenon and krypton only told part of the story,” said Pamela Conrad, lead author of the report and SAM’s deputy principal investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “SAM is now giving us the first complete in situ benchmark against which to compare meteorite measurements.”

While scientists have long zeroed in on xenon and krypton as a critical measuring tool of the Martian atmosphere, the Curiosity rover has allowed scientists to take an even closer look at the concentrations of isotopes. They found that certain xenon and krypton isotopes were more abundant on Mars than others, which suggests that they may have been released from rocks in a layer of soil near the surface of the Red Planet.

“SAM’s measurements provide evidence of a really interesting process in which the rock and unconsolidated material at the planet’s surface have contributed to the xenon and krypton isotopic composition of the atmosphere in a dynamic way,” said Conrad.