[meteorite-list] Water Detection at Gusev Crater Described

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Sep 7 19:28:11 2005
Message-ID: <200509072310.j87NAwx02758_at_zagami.jpl.nasa.gov>

University Communications
Washington University in St. Louis
St. Louis, Missouri

Media Assistance:
Tony Fitzpatrick, Senior Science Editor
(314) 935-5272

Subject Matter Experts:
Raymond Arvidson, (314) 935-5609
Alian Wang, Senior research scientist, (314) 935-5671

Sept. 7, 2005

Water detection at Gusev crater described

Chemical proof for two wet scenarios

By Tony Fitzpatrick

A large team of NASA scientists, led by earth and planetary scientists at
Washington University in St. Louis details the first solid set of evidence
for water having existed on Mars at the Gusev crater, exploration site of
the rover Spirit.

Using an array of sophisticated equipment on Spirit, Alian Wang, Ph.D.,
Washington University senior research scientist in earth and planetary
sciences in Arts & Sciences, and the late Larry A. Haskin, Ph.D., Ralph E.
Morrow Distinguished University Professor of earth and planetary sciences,
found that the volcanic rocks at Gusev crater near Spirit's landing site
were much like the olivine-rich basaltic rocks on Earth, and some of them
possessed a coating rich in sulfur, bromine, chlorine and hematite, or
oxidized iron. The team examined three rocks and found their most
compelling evidence in a rock named Mazatzal.

The rock evidence indicates a scenario where water froze and melted at
some point in Martian history, dissolving the sulfur, chlorine and bromine
elements in the soil. The small amount of acidic fluids then react with
the rocks buried in the soil and formed these highly oxidized coatings.

Trench-digging rover

During its traverse from landing site to Columbia Hills, the rover Spirit
dug three trenches, allowing researchers to detect relatively high levels
of magnesium sulfate comprising more than 20 percent of the regolith --
soil containing pieces of small rocks -- within one of the trenches, the
Boroughs trench. The tight correlation between magnesium and sulfur
indicates an open hydrologic system -- these ions had been carried by
water to this site and deposited.

Spirit's fellow rover Opportunity earlier had detected a history of water
at another site on Mars, Meridiani planum. This study (by Haskin et al.)
covered the investigation of Spirit rover sols (a sol is a Martian day) 1
through 156, with the major discoveries occurring after sol 80. After the
findings were confirmed, Spirit traversed to the Columbian hills, where it
found more evidence indicating water. The science team is currently
planning for sol 551 operation of Spirit rover, which is only 55 meters
away from the summit of Columbia Hills.

Spirit was on sol 597 on Sept 6 and on the summit of Husband Hill.

"We will stay on the summit for a few weeks to finish our desired
investigations, then go downhill to explore the south inner basin,
especially the so-called 'home-plate,' which could be a feature of older
rock or a filled-in crater," Wang said. "We will name a major geo-feature
in the basin after Larry."

Wang, Haskin, their WUSTL colleague Raymond E. Arvidson, chair of earth
and planetary sciences, and James S. McDonnell Distinguished University
Professor, and Bradley Jolliff, Ph.D., research associate professor in
earth and planetary sciences, and more than two dozen collaborators from
numerous institutions, reported their findings in the July 7, 2005 issue
of Nature magazine (Larry A. Haskin et al. Nature 436, 66-69 (7 July 2005)
doi:10.1038/nature03640). The paper was the last one that lead author
Haskin, a highly regarded NASA veteran and former chair of earth and
planetary sciences at WUSTL, submitted before his death on March 24, 2005.

Buried again and again

"We looked closely at the multiple layers on top of the rock Mazatzal
because it had a very different geochemistry and mineralogy," said Wang.
"This told us that the rock had been buried in the soil and exposed and
then buried again several times over the history. There are chemical
changes during the burial times and those changes show that the soil had
been involved with water.

"The telltale thing was a higher proportion of hematite in the coatings.
We hadn't seen that in any previous Gusev rocks. Also, we saw very high
chlorine in the coating and very high bromine levels inside the rock. The
separation of the sulfur and chlorine tells us that the deposition of
chlorine is affected by water."

While the multilayer coatings on rock Mazatzal indicates a temporal
occurrence of low quantity water associated with freezing and melting of
water, the sulfate deposition at trench sites indicates the involvement of
a large body of water.

"We examined the regolith at different depths within the Big Hole and the
Boroughs trenches and saw an extremely tight correlation between magnesium
and sulfur, which was not observed previously," Wang said. "This tells us
that magnesium sulfate formed in these trench regoliths. The increasing
bromine concentration and the separation of chlorine from sulfur also
suggests the action of water. We don't know exactly how much water is
combined with that. The fact that the magnesium sulfate is more than 20
percent of the examined regolith sample says that the magnesium and sulfur
were carried by water to this area from another place, and then deposited
as magnesium sulfate. A certain amount of water would be needed to
accomplish that action."

Related Links:

* McDonnell Center for Space Sciences
  http://wurtzite.wustl.edu/mcss/admission.htm
* Alian Wang's Web site
  http://epsc.wustl.edu/admin/people/wang.html

IMAGE CAPTIONS:

[Image 1:
http://news-info.wustl.edu/asset/page/normal/3258.html]
Alian Wang in the laboratory.

[Image 2:
http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20050901a/Sol582A_P2299_L456-A590R1_br.jpg
(102KB)]
This mini-panorama was taken by Spirit on Aug. 23, 2005, just as the rover
finally completed its intrepid climb up "Husband Hill." The summit appears
to be a windswept plateau of scattered rocks, little sand dunes and small
exposures of outcrop.
Received on Wed 07 Sep 2005 07:10:58 PM PDT