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Study points to watery underground past for Mars

Nov. 2, 2011
Courtesy of NASA
and World Science staff

If life ev­er ex­isted on Mars, the longest-last­ing habi­tats were most likely un­der­ground, a NASA study sug­gests.

A new in­ter­preta­t­ion of years of mineral-mapping da­ta, from more than 350 sites on the Red Plan­et ex­am­ined by Eu­ro­pe­an and NASA or­biters, sug­gests Mar­tian en­vi­ron­ments with abun­dant liq­uid wa­ter on the sur­face ex­isted only dur­ing short episodes. These episodes oc­curred to­ward the end of hun­dreds of mil­lions of years dur­ing which warm wa­ter in­ter­acted with subsur­face rocks, sci­en­tists say. This would have im­plica­t­ions about wheth­er life ex­isted on Mars and how its at­mos­phere has changed.

An in­stru­ment called a spect­ro­me­ter on the Eu­ro­pe­an Space Agen­cy's Mars Ex­press space­craft was used to help de­tect clay min­er­als on Mars. The craft or­bits the Red Plan­et, as shown in this col­lage. (Cour­te­sy of ESA)
“The types of clay min­er­als that formed in the shal­low subsur­face are all over Mars,” said John Mus­tard of Brown Uni­vers­ity in Prov­i­dence, R.I., co-au­thor of the study in the jour­nal Na­ture. “The types that formed on the sur­face… are quite rare.”

Disco­very of clay min­er­als on Mars in 2005 in­di­cat­ed the plan­et once hosted warm, wet con­di­tions, the re­search­ers added. But if those con­di­tions ex­isted on the sur­face for a long time, the plan­et would have needed a much thicker at­mos­phere than it has to keep the wa­ter from evap­o­rat­ing or freez­ing. Re­search­ers have sought ev­i­dence of pro­cesses that could cause a thick at­mos­phere to dis­si­pate over time. 

The new work sup­ports an al­ter­na­tive hy­poth­e­sis, that per­sist­ent warm wa­ter was con­fined un­der­ground and many ero­sion­al fea­tures were carved dur­ing brief pe­ri­ods when liq­uid wa­ter was sta­ble at the sur­face.

“If sur­face habi­tats were short-term, that does­n’t mean we should be glum about prospects for life on Mars, but it says some­thing about what type of en­vi­ron­ment we might want to look in,” said the re­port’s lead au­thor, Beth­a­ny Ehlmann of the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy and NASA’s Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na. “The most sta­ble Mars habi­tats over long dura­t­ions ap­pear to have been in the subsur­face. On Earth, un­der­ground ge­o­ther­mal en­vi­ron­ments have ac­tive ecosys­tems.”

Iden­ti­fica­t­ion of clay min­er­als by an in­stru­ment on the Eu­ro­pe­an Space Agen­cy’s Mars Ex­press or­biter added to ear­li­er ev­i­dence of liq­uid Mar­tian wa­ter, the sci­en­tists said. Clays form from the in­ter­ac­tion of wa­ter with rock. Dif­fer­ent types of clay min­er­als re­sult from dif­fer­ent types of wet con­di­tions.

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If life ever existed on Mars, the longest lasting habitats were most likely undergound, a NASA study suggests. A new interpretation of years of mineral-mapping data, from more than 350 sites on the Red Planet examined by European and NASA orbiters, suggests Martian environments with abundant liquid water on the surface existed only during short episodes. These episodes occurred toward the end of hundreds of millions of years during which warm water interacted with subsurface rocks, scientists say. This would have implications about whether life existed on Mars and how its atmosphere has changed. “The types of clay minerals that formed in the shallow subsurface are all over Mars,” said John Mustard of Brown University in Providence, R.I., co-author of the study in the journal Nature. “The types that formed on the surface… are quite rare.” Discovery of clay minerals on Mars in 2005 indicated the planet once hosted warm, wet conditions, the researchers added. But if those conditions existed on the surface for a long time, the planet would have needed a much thicker atmosphere than it has to keep the water from evaporating or freezing. Researchers have sought evidence of processes that could cause a thick atmosphere to dissipate over time. The new work supports an alternative hypothesis, that persistent warm water was confined underground and many erosional features were carved during brief periods when liquid water was stable at the surface. “If surface habitats were short-term, that doesn’t mean we should be glum about prospects for life on Mars, but it said something about what type of environment we might want to look in,” said the report’s lead author, Bethany Ehlmann of the California Institute of Technology and NASA’s Jet Propulsion Laboratory in Pasadena. “The most stable Mars habitats over long durations appear to have been in the subsurface. On Earth, underground geothermal environments have active ecosystems.” Identification of clay minerals by an instrument on the European Space Agency’s Mars Express orbiter added to earlier evidence of liquid Martian water, the scientists said. Clays form from the interaction of water with rock. Different types of clay minerals result from different types of wet conditions.