New Evidence for a Mars Water Reservoir
 
Dec. 19, 2014: NASA and an international team of planetary scientists have
found evidence in meteorites on Earth that indicates Mars has a distinct
and global reservoir of water or ice near its surface.
 
Though controversy still surrounds the origin, abundance and history of
water on Mars, this discovery helps resolve the question of where the
"missing Martian water" may have gone. Scientists continue to
study the planet's historical record, trying to understand the apparent
shift from an early wet and warm climate to today's dry and cool surface
conditions.
 
http://www.nasa.gov/sites/default/files/14-337a.png
 
This illustration depicts Martian water reservoirs. Recent research
provides evidence for the existence of a third reservoir that is
intermediate in isotopic composition between the Red Planet's mantle and
its current atmosphere. These results support the hypothesis that a buried
cryosphere accounts for a large part of the initial water budget of Mars.
Image Credit: NASA
 
The reservoir's existence also may be a key to understanding climate
history and the potential for life on Mars. The team's findings are
reported in the journal Earth and Planetary Science Letters.
 
"There have been hints of a third planetary water reservoir in
previous studies of Martian meteorites, but our new data require the
existence of a water or ice reservoir that also appears to have exchanged
with a diverse set of Martian samples," said Tomohiro Usui of Tokyo
Institute of Technology in Japan, lead author of the paper and a former
NASA/Lunar and Planetary Institute postdoctoral fellow. "Until this
study there was no direct evidence for this surface reservoir or
interaction of it with rocks that have landed on Earth from the surface of
Mars."
 
Researchers from the Tokyo Institute of Technology, the Lunar and Planetary
Institute in Houston, the Carnegie Institution for Science in Washington
and NASA's Astromaterials Research and Exploration Science Division,
located at the agency's Johnson Space Center in Houston, studied three
Martian meteorites.
 
The samples revealed water comprised of hydrogen atoms that have a ratio of
isotopes distinct from that found in water in the Red Planet's mantle and
current atmosphere. Isotopes are atoms of the same element with differing
numbers of neutrons.
 
While recent orbiter missions have confirmed the presence of subsurface
ice, and melting ground-ice is believed to have formed some geomorphologic
features on Mars, this study used meteorites of different ages to show that
significant ground water-ice may have existed relatively intact over time.
 
Researchers emphasize that the distinct hydrogen isotopic signature of the
water reservoir must be of sufficient size that it has not reached isotopic
equilibrium with the atmosphere.
 
"The hydrogen isotopic composition of the current atmosphere could be
fixed by a quasi-steady-state process that involves rapid loss of hydrogen
to space and the sublimation from a widespread ice layer," said
coauthor John Jones, a JSC experimental petrologist and member of NASA's
Mars Curiosity rover team.
 
Curiosity's observations in a lakebed, in an area called Mount Sharp,
indicate Mars lost its water in a gradual process over a significant period
of time.
 
"In the absence of returned samples from Mars, this study emphasizes
the importance of finding more Martian meteorites and continuing to study
the ones we have with the ever-improving analytical techniques at our
disposal," said co-author Conel Alexander, a cosmochemist at the
Carnegie Institution for Science.
 
In this investigation, scientists compared water, other volatile element
concentrations and hydrogen isotopic compositions of glasses within the
meteorites, which may have formed as the rocks erupted to the surface of
Mars in ancient volcanic activity or by impact events that hit the Martian
surface, knocking them off the planet.
 
"We examined two possibilities, that the signature for the newly
identified hydrogen reservoir either reflects near surface ice interbedded
with sediment or that it reflects hydrated rock near the top of the Martian
crust," said coauthor and JSC cosmochemist Justin Simon. "Both
are possible, but the fact that the measurements with higher water
concentrations appear uncorrelated with the concentrations of some of the
other measured volatile elements, in particular chlorine, suggests the
hydrogen reservoir likely existed as ice."
 
The information being gathered about Mars from studies on Earth, and data
being returned from a fleet of robotic spacecraft and rovers on and around
the Red Planet, are paving the way for future human missions on a journey
to Mars in the 2030s.
 
These findings can be viewed online in their entirety at: http://go.nasa.gov/1zwSjTa
 
Credits and more information:
Production editor: Dr. Tony Phillips | Credit: Science{at}NASA
 
For more about the ARES Division at JSC, visit: http://ares.jsc.nasa.gov
 
Learn about NASA's Journey to Mars at:
http://www.nasa.gov/content/nasas-journey-to-mars/
 
 
Regards,
 
Roger

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