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September 11, 2007

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Water may still flow on Mars, scientists say

Dec. 6, 2006
Courtesy NASA
and World Science staff

NASA pho­tos have re­vealed bright new de­posits in two gul­lies on Mars that sug­gest wa­ter coursed through these ditches some­time in the past sev­en years, re­search­ers say.

Courtesy NASA
This is “the strongest ev­i­dence to date that wa­ter still flows oc­ca­sion­al­ly on the sur­face of Mars,” said Mi­chael Mey­er, lead sci­ent­ist for NASA’s Mars Ex­plo­ra­tion Pro­gram in Wash­ing­ton. 

Liq­uid wa­ter, as op­posed to the wa­ter ice and va­por known on Mars, is con­sid­ered nec­es­sary for life. The new find­ings height­en in­t­rigue about the po­ten­tial for mi­cro­bi­al life on the pla­net. The Mars Or­biter Cam­era on NASA’s Mars Glob­al Sur­vey­or pro­vid­ed the new ev­i­dence in im­ages from 2004 and 2005. 

“The shapes of these de­posits are what you would ex­pect to see if the ma­te­ri­al were car­ried by flow­ing wa­ter,” said Mi­chael Ma­lin of Ma­lin Space Sci­ence Sys­tems in San Die­go, Ca­lif. 

“They have finger-like branch­es at the down­hill end and eas­i­ly di­vert­ed around small ob­s­ta­cles.” Ma­lin is prin­ci­pal in­ves­ti­ga­tor for the cam­era and lead au­thor of a re­port on the find­ings pub­lished in the re­search jour­nal Sci­ence. 

Mars’ at­mos­phere is so thin and the tem­per­a­ture so cold that liq­uid wa­ter can­not per­sist at the sur­face. It would rap­id­ly eva­porate or freeze. Re­search­ers pro­pose that wa­ter could re­main liq­uid long enough, af­ter break­ing out from an un­der­ground source, to car­ry de­bris downs­lope be­fore to­tal­ly freez­ing. The two fresh de­posits are each sev­er­al hun­dred me­ters or yards long. 

Mars Glob­al Sur­vey­or has dis­cov­ered tens of thou­sands of gul­lies on slopes in­side craters and oth­er de­pres­sions on Mars. Most gul­lies are at lat­i­tudes of 30 de­grees or higher. Ma­lin and his team first re­ported the dis­cov­ery of the gul­lies in 2000. To look for changes that might in­di­cate pre­s­ent-day flow of wa­ter, his cam­era team re­peat­ed­ly im­aged hun­dreds of the sites. One pair of im­ages showed a gul­ly that ap­peared af­ter mid-2002. That site was on a sand dune, and the gul­ly-cutting pro­cess was in­ter­preted as a dry flow of sand. 

To­day’s an­nounce­ment is the first to re­veal new­ly de­posited ma­te­ri­al ap­par­ent­ly car­ried by flu­ids af­ter ear­li­er im­ag­ing of the same gul­lies. The two sites are in­side craters in the Ter­ra Si­re­num and the Cen­tau­ri Mon­tes re­gions of south­ern Mars. 

“These fresh de­posits sug­gest that at some places and times on pre­s­ent-day Mars, liq­uid wa­ter is emerg­ing from be­neath the ground and brief­ly flow­ing down the slopes. This pos­si­bil­i­ty raises ques­tions about how the wa­ter would stay melted be­low ground, how wide­spread it might be, and wheth­er there’s a be­low-ground wet hab­i­tat con­du­cive to life. Fu­ture mis­sions may pro­vide the an­swers,” said Ma­lin. 

Mars Glob­al Sur­vey­or be­gan or­bit­ing Mars in 1997. The space­craft is re­spon­si­ble for many im­por­tant dis­cov­er­ies, but was lost last month.

* * *

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NASA photographs have revealed bright new deposits seen in two gullies on Mars that suggest water moved sediment through them sometime in the past seven years, researchers say. “These observations give the strongest evidence to date that water still flows occasionally on the surface of Mars,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program in Washington. Liquid water, as opposed to the water ice and vapor known to exist at Mars, is considered necessary for life. The new findings heighten intrigue about the potential for microbial life on Mars. The Mars Orbiter Camera on NASA’s Mars Global Surveyor provided the new evidence of the deposits in images taken in 2004 and 2005. “The shapes of these deposits are what you would expect to see if the material were carried by flowing water,” said Michael Malin of Malin Space Science Systems in San Diego, Calif. “They have finger-like branches at the downhill end and easily diverted around small obstacles.” Malin is principal invest igator for the camera and lead author of a report about the findings published in the journal Science. Mars’ atmosphere is so thin and the temperature so cold that liquid water cannot persist at the surface. It would rapidly evaporate or freeze. Researchers propose that water could remain liquid long enough, after breaking out from an underground source, to carry debris downslope before totally freezing. The two fresh deposits are each several hundred meters or yards long. Mars Global Surveyor has discovered tens of thousands of gullies on slopes inside craters and other depressions on Mars. Most gullies are at latitudes of 30 degrees or higher. Malin and his team first reported the discovery of the gullies in 2000. To look for changes that might indicate present-day flow of water, his camera team repeatedly imaged hundreds of the sites. One pair of images showed a gully that appeared after mid-2002. That site was on a sand dune, and the gully-cutting process was interpreted as a dry flow of sand. Today’s announcement is the first to reveal newly deposited material apparently carried by fluids after earlier imaging of the same gullies. The two sites are inside craters in the Terra Sirenum and the Centauri Montes regions of southern Mars. “These fresh deposits suggest that at some places and times on present-day Mars, liquid water is emerging from beneath the ground and briefly flowing down the slopes. This possibility raises questions about how the water would stay melted below ground, how widespread it might be, and whether there’s a below-ground wet habitat conducive to life. Future missions may provide the answers,” said Malin. Mars Global Surveyor began orbiting Mars in 1997. The spacecraft is responsible for many important discoveries, but was lost last month.