"Long before it's in the papers"
January 27, 2015


More evidence of flowing water on Mars reported

Aug. 6, 2011
Courtesy of NASA
and World Science staff

Ob­serva­t­ions from NASA’s Mars Re­con­nais­sance Or­biter have re­vealed pos­si­ble flow­ing wa­ter dur­ing the warmest months on Mars, sci­en­tists re­port.

“NASA’s Mars Ex­plora­t­ion Pro­gram keeps bring­ing us clos­er to de­ter­min­ing wheth­er the Red Plan­et could har­bor life in some for­m,” NASA Ad­min­is­tra­tor Charles Bolden said, “and it reaf­firms Mars as an im­por­tant fu­ture des­tina­t­ion for hu­man ex­plora­t­ion.”

An im­age com­bin­ing im­ages from a NA­SA or­biter with 3-D mod­el­ing shows flows that ap­pear in spring and sum­mer on a slope in­side Mars' New­ton crat­er. (Cred­it: NA­SA/JPL-Caltech/U. of Ar­i­zo­na)

Dark, finger-like fea­tures ap­pear and ex­tend down some Mar­tian slopes dur­ing late spring through sum­mer, and fade in win­ter, ac­cord­ing to re­search­ers. Ob­serva­t­ions have tracked these fea­tures on sev­er­al steep slopes in the mid­dle lat­i­tudes of south­ern Mars.

“The best ex­plana­t­ion for these ob­serva­t­ions so far is the flow of briny wa­ter,” said Al­fred McEwen of the Uni­vers­ity of Ar­i­zo­na, Tuc­son. McEwen is the prin­ci­pal in­ves­ti­ga­tor for the or­biter’s High Res­o­lu­tion Im­ag­ing Sci­ence Ex­pe­ri­ment and lead au­thor of a re­port on the find­ings pub­lished in Thurs­day’s edi­tion of the jour­nal Sci­ence.

Some as­pects of the ob­serva­t­ions still puz­zle the re­search­ers, they said, but flows of brine, or salt wa­ter, fit the fea­tures’ char­ac­ter­is­tics bet­ter than oth­er ex­plana­t­ions. Salt­i­ness low­ers wa­ter’s freez­ing tem­per­a­ture. Sites with ac­tive flows are thought to get warm enough, even in the shal­low sub­sur­face, to sus­tain liq­uid wa­ter about as salty as Earth’s oceans, where­as pure wa­ter would freeze.

“These dark linea­t­ions are dif­fer­ent from oth­er types of fea­tures on Mar­tian slopes,” said Mars Re­con­nais­sance Or­biter Proj­ect Sci­ent­ist Rich­ard Zurek of NASA’s Je­t Pro­pul­sion Lab­o­r­a­to­ry in Pas­a­de­na, Ca­lif. “Re­peat­ed ob­serva­t­ions show they ex­tend ev­er far­ther down­hill with time dur­ing the warm sea­son.”

The fea­tures im­aged are only about 0.5 to 5 yards or me­ters wide, with lengths up to hun­dreds of yards. The width is much nar­rower than pre­vi­ously re­ported gul­lies on Mar­tian slopes. Howev­er, some of those loca­t­ions dis­play more than 1,000 in­di­vid­ual flows. Al­so, while gul­lies are abun­dant on cold, pole-facing slopes, these dark flows are on warm­er, equator-facing slopes.

The im­ages show flows length­en and dark­en on rocky equator-facing slopes from late spring to early fall. The sea­son­al­ity, lat­i­tude dis­tri­bu­tion and bright­ness changes sug­gest a vol­a­tile ma­te­ri­al is in­volved, but there is no di­rect de­tec­tion of one. The set­tings are too warm for carbon-dioxide frost and, at some sites, too cold for pure wa­ter, the sci­en­tists said, sug­gesting the ac­tion of brine. Salt de­posits over much of Mars in­di­cate brines were abun­dant in Mars’ past, they added; the new ob­serva­t­ions sug­gest such wa­ters still may form near the sur­face to­day in lim­it­ed times and places.

No sign of wa­ter ap­peared when re­search­ers checked flow-marked slopes with against anoth­er in­stru­ment on the or­biter, the Com­pact Re­con­nais­sance Im­ag­ing Spec­trom­e­ter for Mars. That may be be­cause fea­tures quickly dry on the sur­face or the wa­ter flows slightly be­neath the sur­face, they spec­u­lat­ed. “The flows are not dark be­cause of be­ing wet,” McEwen said. “They are dark for some oth­er rea­son.”

A flow in­i­ti­at­ed by briny wa­ter could re­ar­range grains or change sur­face rough­ness in a way that dark­ens the ap­pearance, he added. How the fea­tures bright­en again when tem­per­a­tures drop is harder to ex­plain. “It’s a mys­tery now, but I think it’s a solv­a­ble mys­tery with fur­ther ob­serva­t­ions and lab­o­r­a­to­ry ex­pe­ri­ments,” McEwen said.

These re­sults are the clos­est sci­en­tists have come to find­ing ev­i­dence of liq­uid wa­ter on the plan­et’s sur­face to­day, ac­cord­ing to McEwen and col­leagues. Fresh-looking gul­lies sug­gest slope move­ments in ge­o­log­ic­ally re­cent times, per­haps aided by wa­ter. Pur­ported droplets of brine al­so ap­peared on struts of the Phoe­nix Mars Lan­der.

* * *

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Observations from NASA’s Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars, scientists report. “NASA’s Mars Exploration Program keeps bringing us closer to determining whether the Red Planet could harbor life in some form,” NASA Administrator Charles Bolden said, “and it reaffirms Mars as an important future destination for human exploration.” Dark, finger-like features appear and extend down some Martian slopes during late spring through summer, fade in winter, and return the next spring, according to researchers. Repeated observations have tracked the seasonal changes in these recurring features on several steep slopes in the middle latitudes of Mars’ southern half. “The best explanation for these observations so far is the flow of briny water,” said Alfred McEwen of the University of Arizona, Tucson. McEwen is the principal investigator for the orbiter’s High Resolution Imaging Science Experiment and lead author of a report on the findings published in Thursday’s edition of the journal Science. Some aspects of the observations still puzzle the researchers, they said, but flows of brine, or salt water, fit the features’ characteristics better than other explanations. Saltiness lowers water’s freezing temperature. Sites with active flows are thought to get warm enough, even in the shallow subsurface, to sustain liquid water about as salty as Earth’s oceans, whereas pure water would freeze. “These dark lineations are different from other types of features on Martian slopes,” said Mars Reconnaissance Orbiter Project Scientist Richard Zurek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Repeated observations show they extend ever farther downhill with time during the warm season.” The features imaged are only about 0.5 to 5 yards or meters wide, with lengths up to hundreds of yards. The width is much narrower than previously reported gullies on Martian slopes. However, some of those locations display more than 1,000 individual flows. Also, while gullies are abundant on cold, pole-facing slopes, these dark flows are on warmer, equator-facing slopes. The images show flows lengthen and darken on rocky equator-facing slopes from late spring to early fall. The seasonality, latitude distribution and brightness changes suggest a volatile material is involved, but there is no direct detection of one. The settings are too warm for carbon-dioxide frost and, at some sites, too cold for pure water, the scientists said, suggesting the action of brine. Salt deposits over much of Mars indicate brines were abundant in Mars’ past, they added; the new observations suggest such waters still may form near the surface today in limited times and places. No sign of water appeared when researchers checked flow-marked slopes with against another instrument on the orbiter, the Compact Reconnaissance Imaging Spectrometer for Mars. That may be because features quickly dry on the surface or the water flows slightly beneath the surface, they speculated. “The flows are not dark because of being wet,” McEwen said. “They are dark for some other reason.” A flow initiated by briny water could rearrange grains or change surface roughness in a way that darkens the appearance, he added. How the features brighten again when temperatures drop is harder to explain. “It’s a mystery now, but I think it’s a solvable mystery with further observations and laboratory experiments,” McEwen said. These results are the closest scientists have come to finding evidence of liquid water on the planet’s surface today, according to McEwen and colleagues. Fresh-looking gullies suggest slope movements in geologically recent times, perhaps aided by water. Purported droplets of brine also appeared on struts of the Phoenix Mars Lander.