NASA’s Curiosity rover used its Sample Analysis at Mars (SAM) instruments to study the gases of Mars’ atmosphere, yielding important clues about how the Martian crust contributed to form the isotopes present on the planet’s exterior.

Through Curiosity’s SAM, NASA investigators studied xenon and krypton isotopes and discovered that the isotope ratios were different than what they anticipated. This is an indicator of some sort of interaction between surface and atmosphere elements. It is the first time that SAM experiments take place to survey the xenon and krypton isotopes in Mars. The news findings were published in Earth and Planetary Science Letters.

Mars Curiosity Rover
Curiosity rover explores the Martian surface. Image credit: NASA.

A difference in measurements indicates dynamic interaction

The data that resulted from the SAM experiments were compared to those obtained by the NASA Viking mission, which took place in 1975. The Viking 1 and 2 orbiters imaged the geological formations on the Martian surface, among which there are many that are inherent to a large presence of water. There were river valleys, evidence of floods, stream networks, and many other formations linked to the existence of water on Mars.

Combining the atmospheric measurements of krypton and xenon of the Viking mission with isotope ratios in Martian meteorites, researchers found out that the Martian surface had to interact with the atmosphere to alter its composition dynamically. Although the measured meteorites are impure in nature, they served as a mean of comparison with the samples picked up by Curiosity.

Mars Curiosity
“Processes in Mars’ surface material can explain why particular xenon (Xe) and krypton (Kr) isotopes are more abundant in the Martian atmosphere than expected, as measured by NASA’s Curiosity rover. Cosmic rays striking barium (Ba) or bromine (Br) atoms can alter isotopic ratios of xenon and krypton,” said NASA in a press release.

Krypton isotopes in meteorites were defined as having a “solar-like atmospheric composition,” but they appear to be different to the isotopes found in solar wind patterns. The xenon isotopes also show some discrepancies from previous samples, and apparently, the main cause for this is a phenomenon known as “neutron capture.”

Neutron capture occurs when isotopes surrender some of its neutrons to others, which leads to the formation of unusual levels of other isotopes, particularly krypton-80, krypton-82, and xenon-132.

On the Martian surface, the measurements of krypton and xenon came from loose rocks on the most external surface layer, known as regolith. As cosmic rays collide with the planet’s surface, they force barium atoms to lose some of its neutrons, which can be picked up by xenon atoms, thus forming the high levels of isotopes found on the regolith.

The same occurs with bromine, which can yield its neutrons to Krypton, leading to the formation of unusual isotopes. These isotopes can reach high  places into the atmosphere while impacts and gas escapes occur on Mars.

So far, NASA’s Curiosity rover has been on Mars for 1477 sols, which is equivalent to 1518 earth days, since its landing on August 6, 2012.

“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,” stated Dr. Pamela Conrad, lead author of the study at NASA’s Goddard Space Flight Center.

Source: Earth and Planetary Science Letters