[meteorite-list] NASA Mars Rovers Head for New Sites After Studying Layers

[Ron Baalke]

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown/Erica Hupp (202) 358-1726/1237							
NASA Headquarters, Washington 						 

News Release: 2006-054 			April 12, 2006     

NASA Mars Rovers Head for New Sites After Studying Layers
 
NASA's Mars rover Spirit has reached a safe site for the 
Martian winter, while its twin, Opportunity, is making 
fast progress toward a destination of its own. 

The two rovers recently set out on important -- but very 
different -- drives after earlier weeks inspecting sites 
with layers of Mars history.  Opportunity finished 
examining sedimentary evidence of ancient water at a 
crater called "Erebus," and is now rapidly crossing flat 
ground toward the scientific lure of a much larger crater, 
"Victoria." 

Spirit studied signs of a long-ago explosion at a bright, 
low plateau called "Home Plate" during February and March. 
Then one of its six wheels quit working, and Spirit 
struggled to complete a short advance to a north-facing 
slope for the winter. "For Spirit, the priority has been 
to reach a safe winter haven," said Dr. Steve Squyres of 
Cornell University, Ithaca, N.Y., principal investigator 
for the Mars Exploration Rover project. 

The rovers have operated more than eight times as long 
as their originally planned three-month explorations on 
Mars. Each has driven more than 6.8 kilometers (4.2 
miles) about 11 times as far as planned. Combined, they 
have returned more than 150,000 images. Two years ago, 
the project had already confirmed that at least one place 
on Mars had a wet and possibly habitable environment long 
ago. The scientific findings continue.

Opportunity spent most of the past four months at Erebus, 
a highly eroded impact crater about 300 meters (1,000 feet) 
in diameter, where the rover found extensive exposures of 
thin, rippled layering interpreted as a fingerprint of 
flowing water. "What we see at Erebus is a thicker 
interval of wetted sediment than we've seen anywhere 
else," said Dr. John Grotzinger of the California 
Institute of Technology, "The same outcrops also have 
cracks that may have formed from wetting and drying."

In mid-March, Opportunity began a 2-kilometer (1.6-mile) 
trek from Erebus to Victoria, a crater about 800 meters 
(half a mile) across, where a thick sequence of 
sedimentary rocks is exposed. In the past three weeks, 
Opportunity has already driven more than a fourth of 
that distance.

At Home Plate, Spirit found coarse layering overlain by 
finer layering in a pattern that fits accumulation of 
material falling to the ground after a volcanic or 
impact explosion. In one place, the layers are deformed 
where a golfball-size rock appears to have fallen on 
them while they were soft. 

"Geologists call that a 'bomb sag,' and it is strong 
evidence for some kind of explosive origin," Squyres 
said.  "We would like to have had time to study Home 
Plate longer, but we needed to head for a north-facing 
slope before winter got too bad."

Spirit is in Mars' southern hemisphere, where the sun 
is crossing lower in the northern sky each day.  The 
rovers rely on solar power.  The amount available will 
keep dropping until the shortest days of the Mars winter, 
four months from now. To keep producing enough 
electricity to run overnight heaters that protect vital 
electronics, Spirit's solar panels must be tilted toward 
the winter sun by driving the rover onto north-facing 
slopes.  However, on March 13 the right-front wheel's 
drive motor gave out.  Spirit has subsequently driven 
about 80 meters (262 feet) using five wheels and 
dragging the sixth, but an initial route toward a large 
hill proved impassable due to soft ground. Last week, 
the team chose a smaller nearby ridge, dubbed "Low Ridge 
Haven," as the winter destination. Spirit reached the 
ridge Sunday and has a favorable 11-degree tilt toward 
the north.

"We have to use care choosing the type of terrain we 
drive over," Dr. Ashitey Trebi-Ollennu, a rover planner 
at NASA's Jet Propulsion Laboratory, Pasadena, Calif., 
said about the challenge of five-wheel driving. In tests 
at JPL, the team has been practicing a maneuver to gain 
additional tilt by perching the left-front wheel on a 
basketball-size rock.

Spending eight months or so at Low Ridge Haven will 
offer time for many long-duration studies that members 
of the science team have been considering since early 
in the mission, said Dr. Ray Arvidson of Washington 
University in St. Louis, deputy principal investigator.  
These include detailed mapping of rocks and soils; 
in-depth determination of rock and soil composition; 
monitoring of clouds and other atmospheric changes; 
watching for subtle surface changes due to winds; and 
learning properties of the shallow subsurface by 
tracking surface-temperature changes over a span of 
months.

JPL, a division of the California Institute of 
Technology, Pasadena, manages the Mars Exploration 
Rover Project for the NASA Science Mission Directorate.  

For images and information about the rovers, see 

http://www.nasa.gov/rovers or 
http://marsrovers.jpl.nasa.gov .   

For information about NASA and agency programs on the 
Web, visit 

http://www.nasa.gov .

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