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Ocean covered a third of Mars, study concludes

June 13, 2010
Courtesy of University of Colorado at Boulder
and World Science staff

Some 3.5 bil­lion years ago, a vast ocean like­ly cov­ered more than one-third of Mars and was part of an Earth-like wa­ter cy­cle that probably in­clud­ed rain, ac­cord­ing to a new stu­dy.

Sci­en­tists an­a­lyzed ge­o­log­i­cal fea­tures thought to have been formed by wa­ter, in­clud­ing riv­er val­leys and del­ta de­posits, where riv­ers spill out and dump sed­i­ments. Of 52 del­ta de­posits iden­ti­fied, more than half are at about the same eleva­t­ion, in­di­cat­ing they marked the bound­aries of an ocean, the sci­en­tists in­volved in the study ar­gued.

Map of Mars' pre­sumed ocean some 3.5 bil­lion years ago. (Im­age cour­te­sy U. Col­orado)
The no­tion of a large, an­cient ocean on Mars, where mi­cro­bi­al life could have aris­en, has been re­peat­edly pro­posed and chal­lenged over the past two dec­ades. 

The new work sup­ports the idea of a sus­tained sea on the Red Plan­et dur­ing the so-called No­a­chi­an era more than 3 bil­lion years ago, said the re­search­ers, Ga­e­ta­no Di Achille and Bri­an Hynek, both of the Uni­vers­ity of Col­o­rad­o at Boul­der. Their find­ings are pub­lished in the June 13 is­sue of the jour­nal Na­ture Ge­o­sci­ence.

Riv­er del­tas on Earth quickly bury or­gan­ic car­bon and oth­er mo­lec­u­lar mark­ers of life. Thus riv­er del­tas Mars would would be a prime tar­get for ex­plora­t­ion, said Di Achille: “if life ev­er arose on Mars, del­tas may be the key to un­lock­ing Mars’ bi­o­log­i­cal past.”

Twen­ty-nine of the 52 del­tas were con­nect­ed ei­ther to the an­cient Mars ocean or to the groundwa­ter ta­ble of the ocean and to seve­ral large, ad­ja­cent lakes, he said.

The study is the first to in­te­grate mul­ti­ple da­ta sets of del­tas, val­ley net­works and to­pog­ra­phy from a ca­dre of NASA and Eu­ro­pe­an Space Agen­cy or­bit­ing mis­sions of Mars dat­ing back to 2001, said Hynek. The study im­plies that an­cient Mars probably had an Earth-like glob­al wa­ter cy­cle, in­clud­ing pre­cipita­t­ion, run­off, cloud forma­t­ion, and ice and groundwa­ter ac­cu­mula­t­ion, he added.

Di Achille and Hynek used a ge­o­graph­ic in­forma­t­ion sys­tem to map the Mar­tian ter­rain and con­clude the ocean likely would have cov­ered about 36 per­cent of the plan­et and con­tained about 30 mil­lion cu­bic miles, or 124 mil­lion cu­bic kilo­me­ters, of wa­ter. This about a tenth as much as oceans on Earth, which is twice Mars’ size, hold.

The eleva­t­ion of the del­tas on the edges of the pro­posed ocean was re­markably con­sist­ent around Mars, said Di Achille. Large, an­cient lakes up­s­lope from the an­cient ocean likely formed in­side im­pact craters and would have been filled by the trans­port of groundwa­ter be­tween the lakes and the an­cient sea, ac­cord­ing to the re­search­ers.

A sec­ond study head­ed by Hynek be­ing pub­lished in Jour­nal of Geo­phys­i­cal Re­search – Plan­ets de­tected about 40,000 riv­er val­leys on Mars. That’s about four times the num­ber pre­vi­ously been iden­ti­fied, said Hynek.

These val­leys were the source of the sed­i­ment car­ried down­stream and dumped in­to the del­tas ad­ja­cent the pro­posed ocean, said Hynek. “The abun­dance of these riv­er val­leys re­quired a sig­nif­i­cant amount of pre­cipita­t­ion,” he said. This “puts a nail in the cof­fin re­gard­ing the pres­ence of past rain­fall on Mars.” Hynek said an ocean was likely re­quired for the sus­tained pre­cipita­t­ion.

“One of the main ques­tions we would like to an­swer is where all of the wa­ter on Mars wen­t,” said Di Achille. He said fu­ture Mars mis­sions—in­clud­ing NASA’s $485 mil­lion Mars At­mos­phere and Vol­a­tile Ev­o­lu­tion mis­sion, or MA­VEN, slat­ed to launch in 2013—should help to an­swer such ques­tions and pro­vide new in­sights in­to the his­to­ry of Mar­tian wa­ter.

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A vast ocean likely covered more than one-third of Mars some 3.5 billion years ago, and was part of an Earth-like water cycle that probably included rain, according to a new study. Scientists analyzed geological features thought to have been formed by water, including river valleys and delta deposits, where rivers spill out and dump sediments. Of 52 delta deposits identified, more than half are at about the same elevation, indicating they marked the boundaries of an ocean, the scientists involved in the study argued. The notion of a large, ancient ocean on Mars, which could have provided a setting for microbial life to arise, has been repeatedly proposed and challenged over the past two decades. The new work supports the idea of a sustained sea on the Red Planet during the so-called Noachian era more than 3 billion years ago, said the researchers, Gaetano Di Achille and Brian Hynek, both of the University of Colorado at Boulder. Their findings are published in the June 13 issue of Nature Geoscience. River deltas on Earth quickly bury organic carbon and other molecular markers of life. Thus river deltas Mars would thus be a prime target for exploration, said Di Achille: “if life ever arose on Mars, deltas may be the key to unlocking Mars’ biological past.” Twenty-nine of the 52 deltas were connected either to the ancient Mars ocean or to the groundwater table of the ocean and to several large, adjacent lakes, he said. The study is the first to integrate multiple data sets of deltas, valley networks and topography from a cadre of NASA and European Space Agency orbiting missions of Mars dating back to 2001, said Hynek. The study implies that ancient Mars probably had an Earth-like global water cycle, including precipitation, runoff, cloud formation, and ice and groundwater accumulation, he added. Di Achille and Hynek used a geographic information system to map the Martian terrain and conclude the ocean likely would have covered about 36 percent of the planet and contained about 30 million cubic miles, or 124 million cubic kilometers, of water, about a tenth as much as Earth’s oceans hold. Mars is slightly more than half Earth’s size. The elevation of the deltas on the edges of the proposed ocean was remarkably consistent around the whole planet, said Di Achille. In addition, the large, ancient lakes upslope from the ancient Mars ocean likely formed inside impact craters and would have been filled by the transport of groundwater between the lakes and the ancient sea, according to the researchers. A second study headed by Hynek being published in Journal of Geophysical Research – Planets detected about 40,000 river valleys on Mars. That’s about four times the number previously been identified, said Hynek. These valleys were the source of the sediment carried downstream and dumped into the deltas adjacent the proposed ocean, said Hynek. “The abundance of these river valleys required a significant amount of precipitation,” he said. This effectively “puts a nail in the coffin regarding the presence of past rainfall on Mars.” Hynek said an ocean was likely required for the sustained precipitation. “These results support the existing theories regarding the extent and formation time of an ancient ocean on Mars and imply the surface conditions during the time probably allowed the occurrence of a global and active hydrosphere integrating valley networks, deltas and a vast ocean,” Di Achille and Hynek wrote in Nature Geoscience. “One of the main questions we would like to answer is where all of the water on Mars went,” said Di Achille. He said future Mars missions—including NASA’s $485 million Mars Atmosphere and Volatile Evolution mission, or MAVEN, which is being led by CU-Boulder and is slated to launch in 2013—should help to answer such questions and provide new insights into the history of Martian water.