[meteorite-list] NASA's Rovers Continue Martian Missions

[Ron Baalke]

Dolores Beasley
Headquarters, Washington                             May 24, 2005
(Phone: 202/358-1753)

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

RELEASE: 05-133

NASA'S ROVERS CONTINUE MARTIAN MISSIONS 

NASA's Mars rover Opportunity is trying to escape from a sand 
trap, while its twin, Spirit, has been busy finding new clues to 
a wet and violent early Martian history.

"Spirit has finally found the kind of geology you can really sink 
your teeth into," said Dr. Steve Squyres of Cornell University, 
Ithaca, N.Y. He is principal investigator for the Mars rovers' 
science instruments. According to Squyres, multiple layers of 
rock in the hills Spirit is exploring suggest successive 
deposits of water-altered explosive debris.

Spirit, inside Mars' Gusev Crater, had to share the spotlight 
with the drama provided by Opportunity on the Martian Meridiani 
plains. The rover has been hindered by soft sand for nearly 
three weeks. Traction is difficult in the ripple-shaped dune of 
windblown dust and sand Opportunity drove into on April 26. 
Since it began trying to get out, the rover has advanced only 
11 inches. Without the slippage caused by the rover's wheels 
spinning in the soft sand, Opportunity could have driven 
157 feet. 

"If Opportunity gets free, its next task will be examining the 
site to give the rover team a better understanding of how this 
ripple differs from dozens Opportunity easily crossed," said Jim 
Erickson. He is project manager for the Mars Exploration Rover 
Project at NASA's Jet Propulsion Laboratory, Pasadena, Calif. 

The rovers have worked under harsh Martian conditions longer than 
expected. They have been studying geology on opposite sides of Mars 
for more than a year since successfully completing their 
three-month primary missions. Shortly after landing in January 2004, 
Opportunity found layered bedrock bearing geological evidence of a 
shallow ancient sea. More than one year later, Spirit found 
extensive layered bedrock, after driving more than two miles and 
climbing into the "Columbia Hills."

Squyres said, "In the last few weeks, we have gone from a state of 
confusion about the geology of the Columbia Hills to having real 
stratigraphic sequence and a powerful working hypothesis for the 
history of these layers."

For several months, Spirit climbed a flank of Husband Hill, the 
tallest in the range. The slope closely matched the angle of 
underlying rock layers, which made the layering difficult to detect. 
Spirit reached an intermediate destination, dubbed "Larry's Lookout," 
then continued uphill and looked back. "That was the critical moment, 
when it all began falling into place," Squyres said. "Looking back 
downhill, you can see the layering, and it suddenly starts to makes 
sense."

Spirit has been examining rocks in a series of outcrops called 
Methuselah, Jibsheet and Larry's Lookout. Some of the rocks contain 
the mineral Ilmenite, not found previously by Spirit. "Ilmenite is 
a titanium-iron oxide formed during crystallization of magma," said 
Dr. Dick Morris, a rover science-team member at NASA's Johnson Space 
Center, Houston. "Its occurrence is evidence for diversity in the 
volcanic rocks in the Gusev region."

Rocks from different layers share compositional traits, high in 
titanium, and low in chromium, which suggests a shared origin. 
However, the degree to which minerals in rocks have been chemically 
altered by exposure to water or other processes varies greatly from 
outcrop to outcrop. The textures also vary. At Methuselah, rocks have 
thin laminations revealed by Spirit's microscopic imager. At Jibsheet, 
they are built of bulbous grains packed together. At Larry's Lookout, 
the rocks are massive, with little fine-scale structure.

"Our best hypothesis is we're looking at a stack of ash or debris that 
was explosively erupted from volcanoes and settled down in different 
ways," Squyres said. "We can't fully rule out the possibility the 
debris was generated in impact explosions instead of volcanic ones. 
But we can say, once upon a time, Gusev was a pretty violent place. 
Big, explosive events were happening, and there was a lot of water 
around," he explained.

Rover-team scientists described the robot explorers' activities today 
at the spring meetings of the American Geophysical Union in New 
Orleans. For Images and information about the rovers and their 
discoveries on the Web, visit:

http://www.nasa.gov/vision/universe/solarsystem/mer_main.html

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

http://www.nasa.gov/home/index.html

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