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The November 30, 2005, issue of the journal Earth and Planetary Science Letters, Volume 240, Issue 1, pp. 1-190, has just been published online. It is a special issue entitled "Sedimentary Geology at Meridiani Planum, Mars," edited by Steven W. Squyres and Andrew H. Knoll.

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November 29, 2005

George Deutsch/Erica Hupp
Headquarters, Washington
(202) 358-1324/1237

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

RELEASE: 05-415

NASA ROVER HELPS REVEAL POSSIBLE SECRETS OF MARTIAN LIFE

Life may have had a tough time getting started in the ancient
environment that left its mark in the Martian rock layers examined by
NASA's Opportunity rover. The most thorough analysis yet of the
rover's discoveries reveals the challenges life may have faced in the
harsh Martian environment.

"This is the most significant set of papers our team has published,"
said Dr. Steve Squyres of Cornell University, Ithaca, N.Y. He is
principal investigator for the science instruments on Opportunity and
its twin rover, Spirit. The lengthy reports reflect more thorough
analysis of Opportunity's findings than earlier papers.

Scientists have been able to deduce conditions in the Meridiani Planum
region of Mars were sometimes wet, strongly acidic and oxidizing.
Those conditions probably posed stiff challenges to the origin of
Martian life.

Based on Opportunity's data, nine papers by 60 researchers in volume
240, issue 1 of the journal Earth and Planetary Science Letters
discuss what this part of the Martian Meridiani Planum region was
like eons ago. The papers present comparisons to some harsh habitats
on Earth and examine the ramifications for possible life on Mars.

Dr. Andrew Knoll of Harvard University, Cambridge, Mass., a paper
co-author, said, "Life that had evolved in other places or earlier
times on Mars, if any did, might adapt to Meridiani conditions, but
the kind of chemical reactions we think were important to giving rise
to life on Earth simply could not have happened at Meridiani."

Scientists analyzed data about stacked sedimentary rock layers 23 feet
thick, exposed inside "Endurance Crater." They identified three
divisions within the stack. The lowest, oldest portion had the
signature of dry sand dunes; the middle portion, windblown sheets of
sand with all the particles produced in part by previous evaporation
of liquid water. The upper portion corresponded to layers Opportunity
found earlier inside a smaller crater near its landing site.

Materials in all three divisions were wet both before and after the
layers were deposited by either wind or water. Researchers described
chemical evidence that the sand grains deposited in the layers had
been altered by water before the layers formed. Scientists analyzed
how acidic water moving through the layers after they were in place
caused changes such as the formation of hematite-rich spherules
within the rocks.

Experimental and theoretical testing reinforces the interpretation of
changes caused by acidic water interacting with the rock layers. "We
made simulated Mars rocks in our laboratory then infused acidic
fluids through them," said researcher Nicholas Tosca from the State
University of New York. "Our theoretical model shows the minerals
predicted to form when those fluids evaporate bear a remarkable
similarity to the minerals identified in the Meridiani outcrop."

The stack of layers in Endurance Crater resulted from a changeable
environment perhaps 3.5 to 4 billion years ago. The area may have
looked like salt flats occasionally holding water, surrounded by
dunes. The White Sands region in New Mexico bears a similar physical
resemblance. "For the chemistry and mineralogy of the environment, an
acidic river basin named Rio Tinto, in Spain, provides useful
similarities," said Dr. David Fernandez-Remolar of Spain's Centro de
Astrobiologia.

Many types of microbes live in the Rio Tinto environment, one of the
reasons for concluding that ancient Meridiani could have been
habitable. However, the organisms at Rio Tinto are descended from
populations that live in less acidic and stressful habitats. If
Meridiani had any life, it might have had to originate in a different
habitat.

"You need to be very careful when you are talking about the prospect
for life on Mars," Knoll said. "We've looked at only a very small
parcel of Martian real estate. The geological record Opportunity has
examined comes from a relatively short period out of Mars' long
history."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Mars
Exploration Rover project. Images and information about the rovers
and their discoveries are available at:

http://www.nasa.gov/vision/universe/solars...m/mer_main.html


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