Life may have had a tough time getting started in the ancient
\nenvironment that left its mark in the Martian rock layers examined by
\nNASA’s Opportunity rover. The most thorough analysis yet of the
\nrover’s discoveries reveals the challenges life may have faced in the
\nharsh Martian environment.<\/p>\n
"This is the most significant set of papers our team has published,"
\nsaid Dr. Steve Squyres of Cornell University, Ithaca, N.Y. He is
\nprincipal investigator for the science instruments on Opportunity and
\nits twin rover, Spirit. The lengthy reports reflect more thorough
\nanalysis of Opportunity’s findings than earlier papers.<\/p>\n
Scientists have been able to deduce conditions in the Meridiani Planum
\nregion of Mars were sometimes wet, strongly acidic and oxidizing.
\nThose conditions probably posed stiff challenges to the origin of
\nMartian life.<\/p>\n
\n
\nBased on Opportunity’s data, nine papers by 60 researchers in volume
\n240, issue 1 of the journal Earth and Planetary Science Letters
\ndiscuss what this part of the Martian Meridiani Planum region was
\nlike eons ago. The papers present comparisons to some harsh habitats
\non Earth and examine the ramifications for possible life on Mars.<\/p>\n
Dr. Andrew Knoll of Harvard University, Cambridge, Mass., a paper
\nco-author, said, "Life that had evolved in other places or earlier
\ntimes on Mars, if any did, might adapt to Meridiani conditions, but
\nthe kind of chemical reactions we think were important to giving rise
\nto life on Earth simply could not have happened at Meridiani."<\/p>\n
Scientists analyzed data about stacked sedimentary rock layers 23 feet
\nthick, exposed inside "Endurance Crater." They identified three
\ndivisions within the stack. The lowest, oldest portion had the
\nsignature of dry sand dunes; the middle portion, windblown sheets of
\nsand with all the particles produced in part by previous evaporation
\nof liquid water. The upper portion corresponded to layers Opportunity
\nfound earlier inside a smaller crater near its landing site.<\/p>\n
Materials in all three divisions were wet both before and after the
\nlayers were deposited by either wind or water. Researchers described
\nchemical evidence that the sand grains deposited in the layers had
\nbeen altered by water before the layers formed. Scientists analyzed
\nhow acidic water moving through the layers after they were in place
\ncaused changes such as the formation of hematite-rich spherules
\nwithin the rocks.<\/p>\n
Experimental and theoretical testing reinforces the interpretation of
\nchanges caused by acidic water interacting with the rock layers. "We
\nmade simulated Mars rocks in our laboratory then infused acidic
\nfluids through them," said researcher Nicholas Tosca from the State
\nUniversity of New York. "Our theoretical model shows the minerals
\npredicted to form when those fluids evaporate bear a remarkable
\nsimilarity to the minerals identified in the Meridiani outcrop."<\/p>\n
The stack of layers in Endurance Crater resulted from a changeable
\nenvironment perhaps 3.5 to 4 billion years ago. The area may have
\nlooked like salt flats occasionally holding water, surrounded by
\ndunes. The White Sands region in New Mexico bears a similar physical
\nresemblance. "For the chemistry and mineralogy of the environment, an
\nacidic river basin named Rio Tinto, in Spain, provides useful
\nsimilarities," said Dr. David Fernandez-Remolar of Spain’s Centro de
\nAstrobiologia.<\/p>\n
Many types of microbes live in the Rio Tinto environment, one of the
\nreasons for concluding that ancient Meridiani could have been
\nhabitable. However, the organisms at Rio Tinto are descended from
\npopulations that live in less acidic and stressful habitats. If
\nMeridiani had any life, it might have had to originate in a different
\nhabitat.<\/p>\n
"You need to be very careful when you are talking about the prospect
\nfor life on Mars," Knoll said. "We’ve looked at only a very small
\nparcel of Martian real estate. The geological record Opportunity has
\nexamined comes from a relatively short period out of Mars’ long
\nhistory."<\/p>\n
NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Mars
\nExploration Rover project. Images and information about the rovers
\nand their discoveries are available at:<\/p>\n