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Signs of “ancient stream” on Mars

Sept. 27, 2012
Courtesy of NASA
and World Science staff

NASA’s Cu­ri­os­ity rov­er mis­sion has found ev­i­dence that a stream once ran briskly across the ar­ea on Mars where the rov­er is driv­ing, ac­cord­ing to sci­en­tists.

There is oth­er ev­i­dence for the early pres­ence of wa­ter on Mars, but this ev­i­dence—im­ages of rocks con­tain­ing an­cient streambed grav­els—is the first to point to a flow strong enough to move peb­bles, re­search­ers said. They’re stu­dy­ing the im­ages of stones ce­mented in­to a lay­er of what they call con­glom­er­ate rock. The stones’ sizes and shapes are be­lieved to of­fer clues to the speed and dis­tance of a long-ago stream’s flow.

NASA'sCu­ri­os­i­ty rov­er found what sci­en­tists called ev­i­dence for an an­cient, flow­ing stream on Mars at a few sites, in­clud­ing the rock out­crop pic­tured he­re, which the sci­ence team has named "Hot­tah" af­ter Hot­tah Lake in Canada’s North­west Ter­ri­to­ries. It may look like a bro­ken side­walk, but this ge­o­log­i­cal fea­ture on Mars is ac­tu­al­ly ex­posed bed­rock made up of smaller frag­ments ce­mented to­geth­er, or what ge­ol­o­gists call a sed­i­men­ta­ry con­glom­er­ate. Sci­en­tists the­o­rize that the bed­rock was dis­rupted in the past, giv­ing it the ti­tled an­gle, most like­ly via im­pacts from me­te­orites. The key ev­i­dence for the an­cient stream is thought to come from the size and round­ed shape of the grav­el in and around the bed­rock. Hot­tah has pieces of grav­el em­bed­ded in it, called clasts, up to a cou­ple inches (few cen­time­ters) in size and lo­cat­ed with­in a ma­trix of sand-sized ma­te­ri­al. Some of the clasts are round in shape, lead­ing the sci­ence team to con­clude they were trans­port­ed by a vig­or­ous flow of wa­ter. The grains are too large to have been moved by wind. (Im­age cred­it: NA­SA/JPL-Caltech/MSSS )


“From the size of grav­els it car­ried, we can in­ter­pret the wa­ter was mov­ing about three feet per sec­ond, with a depth some­where be­tween an­kle and hip deep,” said Cu­ri­os­ity sci­ence co-in­ves­ti­ga­tor Wil­liam Die­trich of the Uni­vers­ity of Cal­i­for­nia, Berke­ley. 

“Plenty of pape­rs have been writ­ten about chan­nels on Mars with many dif­fer­ent hy­pothe­ses about the flows in them. This is the first time we’re ac­tu­ally see­ing wa­ter-trans­ported grav­el on Mars. This is a tran­si­tion from spec­ula­t­ion about the size of stream­bed ma­te­ri­al to di­rect ob­serva­t­ion of it.” 

The find­ing site lies be­tween the north rim of Gale Crat­er and the base of Mount Sharp, a moun­tain in­side the crat­er. 

The round­ed shape of some stones in the ar­ea in­di­cates long-dis­tance trans­port from above the rim, the in­ves­ti­ga­tors said. There, a chan­nel named Peace Val­lis feeds in­to an al­lu­vi­al fan, or fan-shaped de­pos­it of ma­te­ri­al left be­hind when flow­ing wa­ter is slowed down by a flat­tened slope. 

The abun­dance of chan­nels in the fan be­tween the rim and con­glom­er­ate sug­gests flows con­tin­ued or re­peat­ed over a long time, the re­search­ers added.

The find­ing comes from ex­am­in­ing two out­crops, called “Hot­tah” and “Link,” with the tel­e­pho­to ca­pa­bil­ity of Cu­ri­os­ity’s mast cam­era dur­ing the first 40 days af­ter land­ing. Those ob­serva­t­ions fol­lowed up on ear­li­er hints from anoth­er out­crop, which was ex­posed by thrust­er ex­haust as Cu­ri­os­ity touched down.

“Hot­tah looks like some­one jack-hammered up a slab of ­city side­walk, but it’s really a tilted block of an an­cient streambed,” said John Grot­zinger of the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy in Pas­a­de­na, a NASA Mars Sci­ence Lab­o­r­a­to­ry Proj­ect scien­tist.

The grav­els in con­glom­er­ates at both out­crops range in size from a grain of sand to a golf ball, the re­search­ers said; some are an­gu­lar, but many are round­ed. “The shapes tell you they were trans­ported and the sizes tell you they could­n’t be trans­ported by wind. They were trans­ported by wa­ter flow,” said Cu­ri­os­ity sci­ence co-in­ves­ti­ga­tor Re­bec­ca Wil­liams of the Plan­e­tary Sci­ence In­sti­tute in Tuc­son, Ariz.

Mem­bers of the sci­en­tif­ic team said they may use Cu­ri­os­ity to learn the com­po­si­tion of the ma­te­ri­al, which holds the con­glom­er­ate to­geth­er, re­veal­ing more char­ac­ter­is­tics of the wet en­vi­ron­ment that formed the de­pos­its.

The slope of Mount Sharp in Gale Crat­er re­mains the rov­er’s main des­tina­t­ion. Clay and sul­fate min­er­als de­tected there from or­bit can be good pre­servers of chem­i­cals that are po­ten­tial in­gre­di­ents for life.

“A long-flow­ing stream can be a hab­it­a­ble en­vi­ron­ment,” said Grot­zinger. “It is not our top choice as an en­vi­ron­ment for pre­serva­t­ion of or­gan­ics [bio­log­ical chem­i­cals], though. We’re still go­ing to Mount Sharp, but this is insur­ance that we have al­ready found our first po­ten­tially hab­it­a­ble en­vi­ron­ment.” Dur­ing the two-year prime mis­sion of the Mars Sci­ence Lab­o­r­a­to­ry, re­search­ers plan to use Cu­ri­os­ity’s 10 in­stru­ments to in­ves­t­i­gate wheth­er ar­e­as in Gale Crat­er have ev­er of­fered con­di­tions fa­vor­a­ble for mi­cro­bi­al life.


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NASA’s Curiosity rover mission has found evidence that a stream once ran briskly across the area on Mars where the rover is driving, according to scientists. There is other evidence for the early presence of water on Mars, but this evidence—images of rocks containing ancient streambed gravels—is the first of its kind, researchers said. They’re studying the images of stones cemented into a layer of what they call conglomerate rock. The stones’ sizes and shapes are believed to offer clues to the speed and distance of a long-ago stream’s flow. “From the size of gravels it carried, we can interpret the water was moving about three feet per second, with a depth somewhere between ankle and hip deep,” said Curiosity science co-investigator William Dietrich of the University of California, Berkeley. “Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them. This is the first time we’re actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it.” The finding site lies between the north rim of Gale Crater and the base of Mount Sharp, a mountain inside the crater. The rounded shape of some stones in the area indicates long-distance transport from above the rim, the investigators said. There, a channel named Peace Vallis feeds into an alluvial fan, or fan-shaped deposit of material left behind when flowing water is slowed down by a flattened slope. The abundance of channels in the fan between the rim and conglomerate suggests flows continued or repeated over a long time, the researchers added. The finding comes from examining two outcrops, called “Hottah” and “Link,” with the telephoto capability of Curiosity’s mast camera during the first 40 days after landing. Those observations followed up on earlier hints from another outcrop, which was exposed by thruster exhaust as Curiosity, the Mars Science Laboratory Project’s rover, touched down. “Hottah looks like someone jack-hammered up a slab of city sidewalk, but it’s really a tilted block of an ancient streambed,” said Mars Science Laboratory Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. The gravels in conglomerates at both outcrops range in size from a grain of sand to a golf ball, the researchers said; some are angular, but many are rounded. “The shapes tell you they were transported and the sizes tell you they couldn’t be transported by wind. They were transported by water flow,” said Curiosity science co-investigator Rebecca Williams of the Planetary Science Institute in Tucson, Ariz. Members of the scientific team said they may use Curiosity to learn the composition of the material, which holds the conglomerate together, revealing more characteristics of the wet environment that formed these deposits. The stones are thought to provide a sampling from above the crater rim, so the group may also examine several of them to learn about broader regional geology. The slope of Mount Sharp in Gale Crater remains the rover’s main destination. Clay and sulfate minerals detected there from orbit can be good preservers of chemicals that are potential ingredients for life. “A long-flowing stream can be a habitable environment,” said Grotzinger. “It is not our top choice as an environment for preservation of organics, though. We’re still going to Mount Sharp, but this is insurance that we have already found our first potentially habitable environment.” During the two-year prime mission of the Mars Science Laboratory, researchers plan to willuse Curiosity’s 10 instruments to investigate whether areas in Gale Crater have ever offered conditions favorable for microbial