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October 27, 2008

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Salt might have thwarted Martian life

Feb. 15, 2008
Courtesy Jet Propulsion Laboratory
and World Science staff

Sci­en­tists have dreamed of find­ing ev­i­dence for past life on Mars, where they be­lieve there was once plen­ty of liq­uid wa­ter. But now they’re say­ing it might have been too salty.

Mars as seen by the Hub­ble Space Tel­e­scope (cred­it: Li­sa Frat­tare/STScI)
“Not all wa­ter is fit to drink,” said An­drew Knoll, a Har­vard Uni­ver­s­ity bi­olo­g­ist who is on the sci­ence team for the NASA Mars rov­er Op­por­tun­ity. 

High con­centra­t­ions of dis­solved min­er­als as well as ac­ids may have thwar­t­ed mi­crobes from de­vel­op­ing on the red plan­et, he added.

Op­por­tun­ity and its twin, Spir­it, be­gan their fifth year on Mars last month af­ter prov­ing about 16 times longer-lasting than ex­pected, ac­cord­ing to sci­en­tists. 

At a meet­ing of the Amer­i­can As­so­cia­t­ion for the Ad­vance­ment of Sci­ence in Bos­ton on Feb. 15, re­search­ers dis­cussed the rov­ers’ re­cent dis­cov­er­ies.

Op­por­tun­ity spent re­cent months ex­am­in­ing a bright band of rocks around the in­ner wall of a crat­er in the pla­net’s Ter­ra Merid­i­ani re­gion. The cra­ter turned out to lie atop an un­der­ground wa­ter ta­ble, ac­cord­ing to sci­en­tists. Knoll said the rov­er—which serves as a robotic ge­ol­o­gist—found that the wa­ter, which once cov­ered the ar­ea, left be­hind ev­i­dence of its high ac­id­ity and salin­ity.

“This tight­ens the noose on the pos­si­bil­ity of life,” con­si­der­ing salt is a pre­ser­va­tive, he added. Con­di­tions may have been more hospita­ble ear­li­er, with wa­ter less briny, Knoll said. But “life at the Mar­tian sur­face would have been very chal­leng­ing for the last 4 bil­lion years. The best hopes for a sto­ry of life on Mars are at en­vi­ron­ments we haven’t stud­ied yet—older ones, subsur­face ones.”

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Scientists have dreamed of finding evidence for past life on Mars, where they believe there was once plenty of liquid water. But now they’re saying it might have been too salty. “Not all water is fit to drink,” said Andrew Knoll, a Harvard University biologist who is on the science team for the NASA Mars rover Opportunity. High concentrations of dissolved minerals as well as acids may have thwarted any microbes from developing on the red planet, he added. Opportunity and its twin, Spirit, began their fifth year on Mars last month after proving about 16 times longer-lasting than expected, according to scientists. Today, at a meeting of the American Association for the Advancement of Science in Boston, researchers discussed the rovers’ recent discoveries. Opportunity spent recent months examining a bright band of rocks around the inner wall of a crater in Mars’ Terra Meridiani region that turned out to be atop an underground water table, according to scientists. Knoll said the rover—which serves as a robotic geologist—found that water, which once had covered the area, left behind evidence of its high acidity and salinity. “This tightens the noose on the possibility of life,” he added. Conditions may have been more hospitable earlier, with water less briny, Knoll said. But “life at the Martian surface would have been very challenging for the last 4 billion years. The best hopes for a story of life on Mars are at environments we haven’t studied yet—older ones, subsurface ones.”