[meteorite-list] Silica on a Mars Volcano Tells of Wet and Cozy Past

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 1 Nov 2010 10:13:19 -0700 (PDT)
Message-ID: <201011011713.oA1HDJN4007405_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-361

Silica on a Mars Volcano Tells of Wet and Cozy Past
Jet Propulsion Laboratory
October 31, 2010

PASADENA, Calif. -- Light-colored mounds of a mineral deposited on a
volcanic cone more than three billion years ago may preserve evidence of
one of the most recent habitable microenvironments on Mars.

Observations by NASA's Mars Reconnaissance Orbiter enabled researchers
to identify the mineral as hydrated silica and to see its volcanic
context. The mounds' composition and their location on the flanks of a
volcanic cone provide the best evidence yet found on Mars for an intact
deposit from a hydrothermal environment -- a steam fumarole, or hot
spring. Such environments may have provided habitats for some of Earth's
earliest life forms.

"The heat and water required to create this deposit probably made this a
habitable zone," said J.R. Skok of Brown University, Providence, R.I.,
lead author of a paper about these findings published online today by
Nature Geoscience. "If life did exist there, this would be a promising
type of deposit to entomb evidence of it -- a microbial mortuary."

No studies have yet determined whether Mars has ever supported life. The
new results add to accumulating evidence that, at some times and in some
places, Mars has had favorable environments for microbial life. This
specific place would have been habitable when most of Mars was already
dry and cold. Concentrations of hydrated silica have been identified on
Mars previously, including a nearly pure patch found by NASA's Mars
Exploration Rover Spirit in 2007. However, none of those earlier
findings were in such an intact setting as this one, and the setting
adds evidence about the origin.

Skok said, "You have spectacular context for this deposit. It's right on
the flank of a volcano. The setting remains essentially the same as it
was when the silica was deposited."

The small cone rises about 100 meters (100 yards) from the floor of a
shallow bowl named Nili Patera. The patera, which is the floor of a
volcanic caldera, spans about 50 kilometers (30 miles) in the Syrtis
Major volcanic region of equatorial Mars. Before the cone formed,
free-flowing lava blanketed nearby plains. The collapse of an
underground magma chamber from which lava had emanated created the bowl.
Subsequent lava flows, still with a runny texture, coated the floor of
Nili Patera. The cone grew from even later flows, apparently after
evolution of the underground magma had thickened its texture so that the
erupted lava would mound up.

"We can read a series of chapters in this history book and know that the
cone grew from the last gasp of a giant volcanic system," said John
Mustard, Skok's thesis advisor at Brown and a co-author of the paper.
"The cooling and solidification of most of the magma concentrated its
silica and water content."

Observations by cameras on the Mars Reconnaissance Orbiter revealed
patches of bright deposits near the summit of the cone, fanning down its
flank, and on flatter ground in the vicinity. The Brown researchers
partnered with Scott Murchie of Johns Hopkins University Applied Physics
Laboratory, Laurel, Md., to analyze the bright exposures with the
Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument
on the orbiter.

Silica can be dissolved, transported and concentrated by hot water or
steam. Hydrated silica identified by the spectrometer in uphill
locations -- confirmed by stereo imaging -- indicates that hot springs
or fumaroles fed by underground heating created these deposits. Silica
deposits around hydrothermal vents in Iceland are among the best
parallels on Earth.

Murchie said, "The habitable zone would have been within and alongside
the conduits carrying the heated water." The volcanic activity that
built the cone in Nili Patera appears to have happened more recently
than the 3.7-billion-year or greater age of Mars' potentially habitable
early wet environments recorded in clay minerals identified from orbit.

NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for
NASA. Johns Hopkins University Applied Physics Laboratory provided and
operates CRISM, one of six instruments on the orbiter. For more
information about the Mars Reconnaissance Orbiter, visit:
http://www.nasa.gov/mro.

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

Richard Lewis 401-863-3766
Brown University, Providence, R.I.
richard_lewis at brown.edu

Geoffrey Brown 240-228-5618
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
geoffrey.brown at jhuapl.edu

2010-361
Received on Mon 01 Nov 2010 01:13:19 PM PDT