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June 28, 2012

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Water ran deep on ancient Mars, scientists say

June 28 , 2012
Courtesy of ESA
and World Science staff

Ev­i­dence shows liq­uid wa­ter per­sisted deep un­der Mars’ sur­face for long times dur­ing the first bil­lion years of the Red Plan­et’s ex­ist­ence, re­search­ers are re­port­ing.

The sci­en­tists stud­ied rocks blast­ed out of im­pact crat­ers, which they call nat­u­ral win­dows in­to the his­to­ry of plan­e­tary sur­faces. The rocks of­fer a chance to study ma­te­ri­al once hid­den un­der­ground.

A 25 km- (16 mile-) wide crat­er in the fore­ground of this High Res­o­lu­tion Stereo Cam­era view has ex­ca­vat­ed rocks found to have been al­tered by wa­ter in the crust be­fore the im­pact oc­curred. (Cred­its: Mars Ex­press HRSC, ESA/DL­R/FU Ber­lin (G. Neukum); NA­SA/­MOLA Sci­ence Team; D. Loizeau et al.)

The in­ves­ti­ga­tors used in­stru­ments on the Eu­ro­pe­an Space Agen­cy’s Mars Ex­press space­craft and NASA’s Mars Re­con­nais­sance Or­biter to fo­cus on crat­ers in a large zone of the plan­et’s an­cient south­ern high­lands, called Tyrrhena Ter­ra. 

The group as­sessed the chem­is­try of the crat­er rocks and the sur­round­ing, dug-out ma­te­ri­al. They iden­ti­fied 175 sites with min­er­als formed in the pres­ence of wa­ter in that ar­ea, which is about 1,000 by 2,000 km (600 by 1,200 miles) wide.

The com­pounds, called hy­drat­ed sil­i­cates, “were ex­ca­vat­ed from depths of tens of me­ters [yards] to kilome­ters,” said Eu­ro­pe­an Space Agen­cy sci­ent­ist Da­mien Loizeau, lead au­thor of the stu­dy. “The com­po­si­tion of the rocks is such that un­der­ground wa­ter must have been pre­s­ent here for a long pe­ri­od of time in or­der to have al­tered their chem­is­try.”

The or­di­nary sur­face rocks don’t ex­hib­it such ev­i­dence of wa­ter con­tact, the re­search­ers said. 

The 1000 x 2000 km ar­ea re­gion of Tyrrhena Ter­ra (out­lined by the white box in the in­set) sits be­tween two re­gions of low al­ti­tude – Hel­las Plani­tia and Isidis Plani­tia – in Mars’ south­ern hem­i­sphere, as shown in this glob­al to­pog­ra­phy map. "Hydrated" or water-altered min­er­als were found in 175 lo­ca­tions as­so­ci­at­ed with im­pact crat­ers in Tyrrhena Ter­ra, such as in­side the walls of crat­ers, along crat­er rims, or in ma­te­ri­al ex­ca­vat­ed by the im­pact. (Cred­its: NA­SA/MOLA Sci­ence Team /D. Loizeau et al.)

“Wa­ter cir­cula­t­ion oc­curred sev­er­al kilo­me­tres deep in the crust some 3.7 bil­lion years ago, be­fore the ma­jor­ity of crat­ers formed in this re­gion,” said co-au­thor Ni­co­las Man­gold, a sci­ent­ist with NASA’s Mars Sci­ence Lab­o­r­a­to­ry mis­sion. 

“The wa­ter gen­er­at­ed a di­verse range of chem­i­cal changes in the rocks that re­flect low tem­per­a­tures near the sur­face to high tem­per­a­tures at depth, but with­out a di­rect rela­t­ion­ship to the sur­face con­di­tions at that time.”

By con­trast, Mawrth Val­lis, one of the larg­est iden­ti­fied clay-rich re­gions of Mars, dis­plays a more un­iform wa­tery min­er­al­o­gy that in­di­cates a clos­er link with sur­face pro­cesses, re­search­ers said. “The role of liq­uid wa­ter on Mars is of great im­por­tance for its hab­it­abil­ity and this study us­ing Mars Ex­press de­scribes a very large zone where groundwa­ter was pre­s­ent for a long time,” said Oliv­i­er Witasse, proj­ect sci­ent­ist with the Eu­ro­pe­an Space Agen­cy’s Mars Ex­press mis­sion.

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Evidence shows liquid water persisted deep under Mars’ surface for long times during the first billion years of the Red Planet’s existence, researchers are reporting. The scientists studied rocks blasted out of impact craters, which they call natural windows into the history of planetary surfaces. The rocks offer a chance to study material once hidden underground. The investigators used instruments on the European Space Agency’s Mars Express spacecraft and NASA’s Mars Reconnaissance Orbiter to focus on craters in a large zone of the planet’s ancient southern highlands, called Tyrrhena Terra. The group assessed the chemistry of the crater rocks and the surrounding, dug-out material. They identified 175 sites with minerals formed in the presence of water in that area, which is about 1,000 by 2,000 km (600 by 1,200 miles) wide. The compounds, called hydrated silicates, “were excavated from depths of tens of meters [yards] to kilometers,” said European Space Agency scientist Damien Loizeau, lead author of the study. “The composition of the rocks is such that underground water must have been present here for a long period of time in order to have altered their chemistry.” The ordinary surface rocks don’t exhibit such evidence of water contact, the researchers said. “Water circulation occurred several kilometres deep in the crust some 3.7 billion years ago, before the majority of craters formed in this region,” said co-author Nicolas Mangold, a scientist with NASA’s Mars Science Laboratory mission. “The water generated a diverse range of chemical changes in the rocks that reflect low temperatures near the surface to high temperatures at depth, but without a direct relationship to the surface conditions at that time.” By contrast, Mawrth Vallis, one of the largest identified clay-rich regions of Mars, displays a more uniform watery mineralogy that indicates a closer link with surface processes, researchers said. “The role of liquid water on Mars is of great importance for its habitability and this study using Mars Express describes a very large zone where groundwater was present for a long time,” said Olivier Witasse, project scientist with the European Space Agency’s Mars Express mission.