Water detection at Gusev crater described: Chemical proof for twowet scenarios (Forwarded)

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/galle...-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.