[meteorite-list] NASA Rover Sees Variable Environmental History at Martian Crater

[Ron Baalke]

May 21, 2009

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

Gay Yee Hill 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-0344 
gay.y.hill at jpl.nasa.gov 

RELEASE: 09-117

NASA ROVER SEES VARIABLE ENVIRONMENTAL HISTORY AT MARTIAN CRATER

PASADENA, Calif. -- One of NASA's two Mars rovers has recorded a 
compelling saga of environmental changes that occurred over billions 
of years at a Martian crater. 

The Mars rover, Opportunity, surveyed the rim and interior of Victoria 
Crater on the Red Planet from September 2006 through August 2008. Key 
findings from that work, reported in the May 22 edition of the 
journal Science, reinforce and expand what researchers learned from 
Opportunity's exploration of two smaller craters after landing on 
Mars in 2004. 

The rover revealed the effects of wind and water. The data show water 
repeatedly came and left billions of years ago. Wind persisted much 
longer, heaping sand into dunes between ancient water episodes. These 
activities still shape the landscape today. At Victoria, steep cliffs 
and gentler alcoves alternate around the edge of a bowl about a half 
a mile in diameter. The scalloped edge and other features indicate 
the crater once was smaller than it is today, but wind erosion has 
widened it gradually. 

"What drew us to Victoria Crater is the thick cross-section of rock 
layers exposed there," said Steve Squyres of Cornell University in 
Ithaca, N.Y. Squyres is the principal investigator for the science 
payloads on Opportunity and its twin rover Spirit. "The impact that 
excavated the crater millions of years ago provided a golden 
opportunity, and the durability of the rover enabled us to take 
advantage of it." 

Imaging the crater's rim and interior, Opportunity inspected layers in 
the cliffs around the crater, including layered stacks more than 30 
feet thick. Distinctive patterns indicate the rocks formed from 
shifting dunes that later hardened into sandstone, according to 
Squyres and 33 co-authors of the findings. 

Instruments on the rover's arm studied the composition and detailed 
texture of rocks just outside the crater and exposed layers in one 
alcove called Duck Bay. Rocks found beside the crater include pieces 
of a meteorite, which may have been part of the impacting space rock 
that made the crater. 

Other rocks on the rim of the crater apparently were excavated from 
deep within it when the object hit. These rocks bear a type of 
iron-rich small spheres, or spherules, that the rover team nicknamed 
"blueberries" when Opportunity first saw them in 2004. The spherules 
formed from interaction with water penetrating the rocks. The 
spherules in rocks deeper in the crater are larger than those in 
overlying layers, suggesting the action of groundwater was more 
intense at greater depth. 

Inside Duck Bay, the rover found that, in some ways, the lower layers 
differ from overlying ones. The lower layers showed less sulfur and 
iron, more aluminum and silicon. This composition matches patterns 
Opportunity found earlier at the smaller Endurance Crater, about 4 
miles away from Victoria, indicating the processes that varied the 
environmental conditions recorded in the rocks were regional, not 
just local. 

Opportunity's first observations showed interaction of volcanic rock 
with acidic water to produce sulfate salts. Dry sand rich in these 
salts blew into dunes. Under the influence of water, the dunes 
hardened to sandstone. Further alteration by water produced the 
iron-rich spherules, mineral changes, and angular pores left when 
crystals dissolved away. A rock from space blasted a hole about 2,000 
feet wide and 400 feet deep. Wind erosion chewed at the edges of the 
hole and partially refilled it, increasing the diameter by about 25 
percent and reducing the depth by about 40 percent. 

Since leaving Victoria Crater about eight months ago, Opportunity has 
been on its way to study a crater named Endeavour that is about 20 
times bigger than Victoria. The rover has driven about one-fifth of 
what could be a 10-mile trek to this new destination. 

The twin rovers Spirit and Opportunity continue to produce scientific 
results while operating far beyond their design life. The mission, 
designed to last 90 days, celebrated its fifth anniversary in 
January. Both rovers show signs of aging but are still capable of 
exploration and scientific discovery. 

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Mars 
rovers for NASA's Science Mission Directorate in Washington. 

For more information about Spirit and Opportunity, visit: 

http://www.nasa.gov/rovers 
	
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