[meteorite-list] Curiosity Sniffs Out History of Martian Atmosphere

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4532

Curiosity Sniffs Out History of Martian Atmosphere
Jet Propulsion Laboratory
March 31, 2015

NASA's Curiosity rover is using a new experiment to better understand 
the history of the Martian atmosphere by analyzing xenon.

While NASA's Curiosity rover concluded its detailed examination of the 
rock layers of the "Pahrump Hills" in Gale Crater on Mars this winter, 
some members of the rover team were busy analyzing the Martian atmosphere 
for xenon, a heavy noble gas.

Curiosity's Sample Analysis at Mars (SAM) experiment analyzed xenon in 
the planet's atmosphere. Since noble gases are chemically inert and do 
not react with other substances in the air or on the ground, they are 
excellent tracers of the history of the atmosphere. Xenon is present in 
the Martian atmosphere at a challengingly low quantity and can be directly 
measured only with on-site experiments such as SAM.

"Xenon is a fundamental measurement to make on a planet such as Mars or 
Venus, since it provides essential information to understand the early 
history of these planets and why they turned out so differently from Earth," 
said Melissa Trainer, one of the scientists analyzing the SAM data.

A planetary atmosphere is made up of different gases, which are in turn 
made up of variants of the same chemical element called isotopes. When 
a planet loses its atmosphere, that process can affect the ratios of remaining 
isotopes.

Measuring xenon tells us more about the history of the loss of the Martian 
atmosphere. The special characteristics of xenon - it exists naturally 
in nine different isotopes, ranging in atomic mass from 124 (with 70 neutrons 
per atom) to 136 (with 82 neutrons per atom) - allows us to learn more 
about the process by which the layers of atmosphere were stripped off 
Mars than using measurements of other gases.

A process removing gas from the top of the atmosphere removes lighter 
isotopes more readily than heavier ones, leaving a ratio higher in heavier 
isotopes than it was originally.

The SAM measurement of the ratios of the nine xenon isotopes traces a 
very early period in the history of Mars when a vigorous atmospheric escape 
process was pulling away even the heavy xenon gas. The lighter isotopes 
were escaping just a bit faster than the heavy isotopes.

Those escapes affected the ratio of isotopes in the atmosphere left behind, 
and the ratios today are a signature retained in the atmosphere for billions 
of years. This signature was first inferred several decades ago from isotope 
measurements on small amounts of Martian atmospheric gas trapped in rocks 
from Mars that made their way to Earth as meteorites.

"We are seeing a remarkably close match of the in-situ data to that from 
bits of atmosphere captured in some of the Martian meteorites," said SAM 
Deputy Principal Investigator Pan Conrad.

SAM previously measured the ratio of two isotopes of a different noble 
gas, argon. The results pointed to continuous loss over time of much of 
the original atmosphere of Mars.

The xenon experiment required months of careful testing at NASA's Goddard 
Space Flight Center in Greenbelt, Maryland, using a close copy of the 
SAM instrument enclosed in a chamber that simulates the Mars environment. 
This testing was led by Goddard's Charles Malespin, who developed and 
optimized the sequence of instructions for SAM to carry out on Mars.

"I'm gratified that we were able to successfully execute this run on Mars 
and demonstrate this new capability for Curiosity," said Malespin.

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

You can follow the mission on Facebook and Twitter at:

http://www.facebook.com/marscuriosity

and

http://www.twitter.com/marscuriosity


Media Contact

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

Dwayne Brown
NASA Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov 

2015-109