NASA's Curiosity rover has found evidence that the Martian crust contributes to its atmosphere. The rover made the finding using its suite of instruments known as Sample Analysis at Mars (SAM), which studied the abundance of xenon and krypton, two noble gases that are present in the Martian atmosphere.

Analysis by the rover suggests the surface is leaking xenon and krypton, which then settles in the atmosphere.

"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, in a statement. "SAM is now giving us the first complete in situ benchmark against which to compare meteorite measurements."

SAM looks at the different isotopes of these gases. An isotope is an element that has a few more or less neutrons in the nucleus than the regular version. The chemical properties are the same, but the physical properties are different since the atoms can be heavier or lighter.

When cosmic rays hit the surface of Mars, they hit elements like barium and bromine, dislodging neutrons that are then captured by xenon and krypton atoms, creating the diversity in isotopes found on the Red Planet.

These isotopes are then liberated from the Martian crust by meteorite impacts or through the erosion of the surface of Mars. The findings of this study are reported in a paper published in Earth and Planetary Science Letters.

^{Schematic representation of how the atmospheric composition of Mars is influenced by the crust. NASA/GSFC/JPL-Caltech}

"The unique capability to measure in situ the six and nine different isotopes of krypton and xenon allows scientists to delve into the complex interactions between the Martian atmosphere and crust," said Michael Meyer, lead scientist for the Mars Exploration Program at NASA Headquarters in Washington. "Discovering these interactions through time allows us to gain a greater understanding of planetary evolution."

Curiosity landed on Mars in 2012 and for the last four years has explored the environment in Gale Crater, slowly moving towards its goal of Mount Sharp – a geological feature at the center of the crater.