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On-and-off floods formed Mars valleys, study finds

Sept. 8, 2008
Courtesy University of California - Santa Cruz
and World Science staff

An­cient net­works of val­leys on Mars were carved by re­cur­rent floods over a long per­i­od when the cli­mate may have been much like that of some ar­id or semiar­id re­gions on Earth, a new study sug­gests.

The re­sults don’t sup­port an al­ter­na­tive the­o­ry that the val­leys were carved by cat­a­stroph­ic flood­ing over a shorter time, the re­search­ers said.

The European Space Agen­cy's Mars Ex­press space­craft took snap­shots of Can­dor Chas­ma, a valley on Mars, on July 6, 2006.
Of­ten cit­ed as ev­i­dence that Mars once had a warm en­vi­ron­ment with liq­uid wa­ter on the sur­face, val­ley net­works are dis­tinc­tive fea­tures of the Mar­tian land­scape. In the new stu­dy, sci­en­tists used com­put­er mod­els to sim­u­late the pro­cesses that formed these fea­tures.

“Our re­sults ar­gue for liq­uid wa­ter be­ing sta­ble at the sur­face of Mars for pro­longed per­i­ods,” said Charles Barn­hart, a grad­u­ate stu­dent in Earth and plan­e­tary sci­ences at the Uni­ver­s­ity of Cal­i­for­nia, San­ta Cruz.

Barn­hart con­ducted the study as a Grad­u­ate Stu­dent Re­search Pro­gram schol­ar at NASA Ames Re­search Cen­ter, work­ing with plan­e­tary sci­ent­ist Jef­frey Moore at the agen­cy and Al­an How­ard of the Uni­ver­s­ity of Vir­gin­ia. 

A pa­per de­scrib­ing their find­ings has been ac­cept­ed for pub­lica­t­ion in the Jour­nal of Geo­phys­i­cal Re­search—Planets. 

“For sev­er­al dec­ades, sci­en­tists worked to de­ter­mine wheth­er or not there had ev­er been pre­cipita­t­ion on Mars. Only in the last 10 years has NASA ac­quired high-res­o­lu­tion top­o­graph­ic da­ta that cinched the case for mas­sive an­cient ero­sion from pre­cipita­t­ion and runof­f,” Moore said.

Sci­en­tists es­ti­mate that the val­ley net­works were carved out more than 3.5 bil­lion years ago. Stud­ies based on cli­mate mod­els have sug­gested that cat­a­stroph­ic events such as as­ter­oid im­pacts could have cre­at­ed warm, wet con­di­tions on Mars, caus­ing del­uges and flood­ing for per­i­ods of hun­dreds to thou­sands of years. 

The new study found that those con­di­tions would re­sult in fea­tures not seen in the Mar­tian land­scape, Barn­hart said. That is be­cause wa­ter would ac­cu­mu­late in­side crat­ers and overflow, carv­ing ex­it breaches that cut through the crat­er walls. “The pre­cipita­t­ion needs to be sea­son­al or per­i­odic, so that there are per­i­ods of evapora­t­ion and in­filtra­t­ion. Oth­er­wise the crat­ers overflow.”

The re­sults sug­gest the net­works formed dur­ing a semiar­id to ar­id cli­mate that per­sisted for tens of thou­sands to hun­dreds of thou­sands of years, the re­search­ers said: flood­ing al­ter­nat­ed with long dry spells when wa­ter could evap­o­rate or soak in­to the ground. Rain­fall may have been sea­son­al, or wet in­ter­vals may have oc­curred over long­er cy­cles, but con­di­tions al­lowing for liq­uid sur­face wa­ter must have lasted for at least 10,000 years, Barn­hart said.

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Ancient networks of valleys on Mars were carved by recurrent floods over a long period when the climate may have been much like that of some arid or semiarid regions on Earth, a new study suggests. The results don’t support an alternative theory that the valleys were carved by catastrophic flooding over a shorter time, the researchers said. Often cited as evidence that Mars once had a warm environment with liquid water on the surface, valley networks are distinctive features of the Martian landscape. In the new study, scientists used computer models to simulate the processes that formed these features. “Our results argue for liquid water being stable at the surface of Mars for prolonged periods,” said Charles Barnhart, a graduate student in Earth and planetary sciences at the University of California, Santa Cruz. Barnhart conducted the study as a Graduate Student Research Program scholar at NASA Ames Research Center, working with planetary scientist Jeffrey Moore at the agency and Alan Howard of the University of Virginia. A paper describing their findings has been accepted for publication in the Journal of Geophysical Research—Planets. “For several decades, scientists worked to determine whether or not there had ever been precipitation on Mars. Only in the last 10 years has NASA acquired high-resolution topographic data that cinched the case for massive ancient erosion from precipitation and runoff,” Moore said. Scientists estimate that the valley networks were carved out more than 3.5 billion years ago. Studies based on climate models have suggested that catastrophic events such as asteroid impacts could have created warm, wet conditions on Mars, causing deluges and flooding for periods of hundreds to thousands of years. The new study found that those conditions would result in features not seen in the Martian landscape, because water would accumulate inside craters and overflow, carving exit breaches that cut through the crater walls, Barnhart said. “These catastrophic anomalies would be so humid and wet there would be breaching of the craters, which we don’t see on Mars,” he said. “The precipitation needs to be seasonal or periodic, so that there are periods of evaporation and infiltration. Otherwise the craters overflow.” The results suggest that valley networks formed on Mars during a semiarid to arid climate that persisted for tens of thousands to hundreds of thousands of years, the researchers said. Episodic flooding alternated with long dry periods when water could evaporate or soak into the ground. Rainfall may have been seasonal, or wet intervals may have occurred over longer cycles. But conditions that allowed for the presence of liquid water on the surface of Mars must have lasted for at least 10,000 years, Barnhart said.