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Curiosity discovers how Mars’ crust contributes to atmosphere

Artist's concept of NASA's Curiosity Mars rover. Image Credit: NASA/JPL-Caltech.

Artist’s concept of NASA’s Curiosity Mars rover. Image Credit: NASA/JPL-Caltech.

NASA’s Curiosity Mars rover has found evidence that chemical processes within the surface of Mars contribute to the makeup of the planet’s atmosphere over time. The new findings come from the rover’s Sample Analysis at Mars (SAM) instrument suite, which studied the gases xenon and krypton in Mars’ atmosphere. The two gases are used by researchers as tracers to aid their investigation of the evolution and erosion of the Martian atmosphere.

Much of what was previously known about xenon and krypton in Mars’ atmosphere came from the study of Martian meteorites and data gathered by the Viking mission.

“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.”

The scientists were especially interested in the ratios of certain isotopes – chemical variants that have different numbers of neutrons – of xenon and krypton. The researchers ran a series of experiments to measure all of the isotopes of the two gases in Mars’ atmosphere. The team described their experiments in a paper published in Earth and Planetary Science Letters (EPSL).

The scientists used a method called static mass spectrometry, which is excellent for detecting gases that are present in only trace amounts. While this is not a new technique, its use on the surface of a planet other than Earth has only been done by SAM.

While the overall analysis agrees with previous studies, the ratios of some isotopes were slightly different than expected. While trying to understand what caused these subtle but important differences, the scientists realized that neutrons could have been transferred from one element within the crust of Mars to another through a process called neutron capture.

These isotopes may have been released into the atmosphere by impacts on the Martian surface and by gas escaping the regolith – which is the soil and broken rocks of the surface.

“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.

The atmospheres of Mars and Earth have very different patterns of xenon and krypton isotopes. For instance, Mars has much more of the isotope xenon-129 in its atmosphere than does Earth.

“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.”

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.

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. Image Credit: NASA/GSFC/JPL-Caltech



Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.

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