[meteorite-list] Curiosity Rover Finds Evidence of Mars Crust Contributing to Atmosphere

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=6631

Curiosity Finds Evidence of Mars Crust Contributing to Atmosphere
Jet Propulsion Laboratory
September 29, 2016

NASA's Curiosity rover has found evidence that chemistry in the surface 
material on Mars contributed dynamically to the makeup of its atmosphere 
over time. It's another clue that the history of the Red Planet's atmosphere 
is more complex and interesting than a simple legacy of loss.

The findings come from the rover's Sample Analysis at Mars, or SAM, instrument 
suite, which studied the gases xenon and krypton in Mars' atmosphere. 
The two gases can be used as tracers to help scientists investigate the 
evolution and erosion of the Martian atmosphere. A lot of information 
about xenon and krypton in Mars' atmosphere came from analyses of Martian 
meteorites and measurements made 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."

Of particular interest to scientists are the ratios of certain isotopes 
- or chemical variants - of xenon and krypton. The SAM team ran a series 
of first-of-a-kind experiments to measure all the isotopes of xenon and 
krypton in the Martian atmosphere. The experiments are described in a 
paper published in Earth and Planetary Science Letters.

The team's method is called static mass spectrometry, and it's good for 
detecting gases or isotopes that are present only in trace amounts. Although 
static mass spectrometry isn't a new technique, its use on the surface 
of another planet is something only SAM has done.

Overall, the analysis agreed with earlier studies, but some isotope ratios 
were a bit different than expected. When working on an explanation for 
those subtle but important differences, the researchers realized that 
neutrons might have gotten transferred from one chemical element to another 
within the surface material on Mars. The process is called neutron capture, 
and it would explain why a few selected isotopes were more abundant than 
previously thought possible.

In particular, it looks as if some of the barium surrendered neutrons 
that got picked up by xenon to produce higher-than-expected levels of 
the isotopes xenon-124 and 126. Likewise, bromine might have surrendered 
some of its neutrons to produce unusual levels of krypton-80 and krypton-82.

These isotopes could have been released into the atmosphere by impacts 
on the surface and by gas escaping from 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 Earth and Mars exhibit very different patterns of xenon 
and krypton isotopes, particularly for xenon-129. Mars has much more of 
it in the 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."

NASA's Mars Science Laboratory Project is using Curiosity to determine 
if life was possible on Mars and study major changes in Martian environmental 
conditions. NASA studies Mars to learn more about our own planet, and 
in preparation for future human missions to Mars. NASA's Jet Propulsion 
Laboratory, a division of the California Institute of Technology in Pasadena, 
manages the project for NASA's Science Mission Directorate in Washington.

For more information about SAM, visit:

http://ssed.gsfc.nasa.gov/sam

SAM experiment data are archived in the Planetary Data System, online 
at:

http://pds.nasa.gov

For more information about Curiosity, visit:

http://www.nasa.gov/msl

The research paper is available at:

http://dx.doi.org/10.1016/j.epsl.2016.08.028

News Media Contact
Written by Elizabeth Zubritsky

Guy Webster Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster at jpl.nasa.gov

Dwayne Brown / Laurie Cantillo
NASA Headquarters, Washington
202-358-1726 / 202-358-1077
dwayne.c.brown at nasa.gov / laura.l.cantillo at nasa.gov

2016-249