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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 21 May 2009 14:00:32 -0700 (PDT)
Message-ID: <200905212100.OAA23700_at_zagami.jpl.nasa.gov>

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
        
-end-
Received on Thu 21 May 2009 05:00:32 PM PDT