[meteorite-list] Mars Rovers Probing Water History At Two Sites

[Ron Baalke]

Donald Savage 
Headquarters, Washington                  October 7, 2004 
(Phone: 202/358-1727)

Guy Webster 
Jet Propulsion Laboratory (JPL), Pasadena, Calif.
(Phone: 818/354-6278)

RELEASE: 04-342

MARS ROVERS PROBING WATER HISTORY AT TWO SITES

     NASA's Spirit and Opportunity have been exploring Mars 
about three times as long as originally scheduled. The more 
they look, the more evidence of past liquid water on Mars 
these robots discover. Team members reported the new findings 
at a news briefing today.

New findings raise the possibility Opportunity's work area 
was soaked long ago, before it dried and eroded into a wide 
plain. There are also signs some rocks may have gotten wet 
again, after an impact excavated a stadium-size crater in the 
plain. 

Evidence of this exciting possibility has been identified in 
a flat rock dubbed "Escher" and some neighboring rocks near 
the bottom of the crater. These plate-like rocks bear 
networks of cracks dividing the surface into patterns of 
polygons, somewhat similar in appearance to cracked mud after 
the water has dried up here on Earth.

Alternative histories, such as fracturing by the force of the 
crater-causing impact, or the final desiccation of the 
original wet environment that formed the rocks, might also 
explain the polygonal cracks. Rover scientists hope a lumpy 
boulder nicknamed "Wopmay," Opportunity's next target for 
inspection, may help narrow the list of possible 
explanations. 

"When we saw these polygonal crack patterns, right away we 
thought of a secondary water event significantly later than 
the episode that created the rocks," said Dr. John 
Grotzinger. He is a rover-team geologist from the 
Massachusetts Institute of Technology, Cambridge, Mass. 
Finding geological evidence about watery periods in Mars' 
past is the rover project's main goal, because such 
persistently wet environments may have been hospitable to 
life.

"Did these cracks form after the crater was created? We don't 
really know yet," Grotzinger said. 

If they did, one possible source of moisture could be 
accumulations of frost partially melting during climate 
changes, as Mars wobbled on its axis of rotation, in cycles 
of tens of thousands of years. According to Grotzinger, 
another possibility could be the melting of underground ice 
or release of underground water in large enough quantity to 
pool a little lake within the crater. 

One type of evidence Wopmay could add to the case for wet 
conditions after the crater formed would be a crust of water-
soluble minerals. After examining that rock, the rover team's 
plans for Opportunity are to get a close look at a tall stack 
of layers nicknamed "Burns Cliff" from the base of the cliff. 
The rover will then climb out of the crater and head south to 
the spacecraft's original heat shield and nearby rugged 
terrain, where deeper rock layers may be exposed.

Halfway around Mars, Spirit is climbing higher into the 
"Columbia Hills." Spirit drove more than three kilometers 
(approximately two miles) across a plain to reach them. After 
finding bedrock that had been extensively altered by water, 
scientists used the rover to look for relatively unchanged 
rock as a comparison for understanding the area's full range 
of environmental changes. Instead, even the freshest-looking 
rocks examined by Spirit in the Columbia Hills have shown 
signs of pervasive water alteration. 

"We haven't seen a single unaltered volcanic rock, since we 
crossed the boundary from the plains into the hills, and I'm 
beginning to suspect we never will," said Dr. Steve Squyres 
of Cornell University, Ithaca, N.Y., principal investigator 
for the science payload on both rovers. "All the rocks in the 
hills have been altered significantly by water. We're having 
a wonderful time trying to work out exactly what happened 
here," he added.

More clues to deciphering the environmental history of the 
hills could lie in layered rock outcrops further upslope, 
Spirit's next targets. "Just as we worked our way deeper into 
the Endurance crater with Opportunity, we'll work our way 
higher and higher into the hills with Spirit, looking at 
layered rocks and constructing a plausible geologic history," 
Squyres said.

Jim Erickson, rover project manager at JPL, said, "Both 
Spirit and Opportunity have only minor problems, and there is 
really no way of knowing how much longer they will keep 
operating. However we are optimistic about their conditions, 
and we have just been given a new lease on life for them, a 
six-month extended mission that began Oct. 1. The solar power 
situation is better than expected, but these machines are 
already well past their design life. While they're healthy, 
we'll keep them working as hard as possible."

JPL, a division of the California Institute of Technology in 
Pasadena, manages the Mars Exploration Rover project for 
NASA's Science Mission Directorate, Washington. Images and 
additional information about the project are available from 
JPL and Cornell at: 

http://marsrovers.jpl.nasa.gov
http://athena.cornell.edu

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