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February 07, 2012

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New, “strong” evidence for ancient ocean on Mars

Feb. 7, 2012
Courtesy of ESA
and World Science staff

The Eu­ro­pe­an Space Agen­cy’s Mars Ex­press space­craft has pick­ed up strong new ev­i­dence that Mars once had an ocean, though this ocean would have been rel­a­tively short-lived, sci­en­tists say.

Us­ing ra­dar, the or­bit­ing space­craft de­tected what re­search­ers called sed­i­ments rem­i­nis­cent of an ocean floor with­in the bounds of pre­vi­ously noted, an­cient shore­lines.

A map of a proposed ocean that would have cov­ered Mars' north­ern plains around three bil­lion years ago. (Credits: ESA, C. Car­reau)
Scouring more than two years of da­ta, sci­en­tists found the Red Plan­et’s north­ern plains are cov­ered in a light ma­te­ri­al that ap­pears to con­sist of “sed­i­men­tary de­posits, may­be ice-rich,” said Jé­ré­mie Moug­i­not, one of the re­sear­chers.

“It is a strong new in­dica­t­ion that there was once an ocean here,” added Moug­inot, of the Plan­etary and As­t­ro­phys­i­cal In­sti­tute of Gre­no­ble and France and the Uni­vers­ity of Cal­i­for­nia, Ir­vine.

The ex­ist­ence of oceans on an­cient Mars has been sus­pected be­fore. Fea­tures rem­i­nis­cent of shore­lines have been ten­ta­tively iden­ti­fied in im­ages from var­i­ous space­craft. But it re­mains a con­tro­ver­sial is­sue. Two oceans have been pro­posed: four bil­lion years ago, when warm­er con­di­tions pre­vailed, and three bil­lion years ago when sub­sur­face ice melted, pos­sibly due to heat-generating pro­cesses un­der­ground. These would have cre­at­ed out­flow chan­nels that drained wa­ter in­to low-lying ar­eas.

Mars Ex­press’s MAR­SIS ra­dar in­stru­ment “pen­e­trates deep in­to the ground, re­veal­ing the first 60-80 me­tres (yards) of the plan­et’s sub­sur­face,” said Wlo­dek Kof­man, lead­er of the ra­dar team at the Gre­no­ble in­sti­tute. “Through­out all of this depth, we see the ev­i­dence for sed­i­men­ta­ry ma­te­ri­al and ice.”

Ra­dar is a sys­tem for map­ping un­seen ob­jects by an­a­lyz­ing short ra­di­o waves that are sent out, then re­flected back from those ob­jects. Ra­dar im­ag­ing can al­so pen­e­trate un­der­ground.

“Pre­vi­ous Mars Ex­press re­sults about wa­ter on Mars came from the study of im­ages and min­er­al­o­gi­cal da­ta, as well as at­mos­pher­ic mea­sure­ments,” said Oliv­i­er Witasse, the space agen­cy’s Mars Ex­press proj­ect sci­ent­ist. “Now we have the view from the sub­sur­face ra­dar,” he added. “This adds new pieces of in­forma­t­ion to the puz­zle but the ques­tion re­mains: where did all the wa­ter go?” Mars Ex­press is sched­uled to con­tin­ue in­ves­ti­gat­ing.

The new­found sed­i­ments show up as ar­eas of low ra­dar re­flec­ti­vity, the re­searchers said, adding that such sed­i­ments are typ­ic­ally light, grainy ma­te­ri­als that have been erod­ed away by wa­ter and car­ried to their des­tina­t­ion.

This lat­er ocean would have been tem­po­rary, though. With­in a mil­lion years or less, Moug­inot es­ti­mates, the wa­ter would have ei­ther fro­zen back in place and been pre­served un­der­ground again, or turned in­to va­por and lifted grad­u­ally in­to the at­mos­phere. “I don’t think it could have stayed as an ocean long enough for life to for­m,” he said, adding that to find ev­i­dence of life sci­en­tists will have to look even fur­ther back in Mars’ his­to­ry when liq­uid wa­ter per­sisted for much long­er pe­ri­ods.

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The European Space Agency’s Mars Express spacecraft has picked up strong new evidence that Mars once had an ocean, but this ocean would have been relatively short-lived, scientists say. Using radar, the orbiting spacecraft detected what researchers called sediments reminiscent of an ocean floor within the boundaries of previously identified, ancient shorelines on the Red Planet. Scouring more than two years of data, scientists found the planet’s northern plains are covered in a light material that appears to consist of “sedimentary deposits, maybe ice-rich,” said Jérémie Mouginot of the Planetary and Astrophysical Institute of Grenoble and France and of the University of California, Irvine. “It is a strong new indication that there was once an ocean here.” The existence of oceans on ancient Mars has been suspected before. Features reminiscent of shorelines have been tentatively identified in images from various spacecraft. But it remains a controversial issue. Two oceans have been proposed: four billion years ago, when warmer conditions prevailed, and three billion years ago when subsurface ice melted, possibly due to heat-generating processes underground. These would have created outflow channels that drained water into low-lying areas. Mars Express’s MARSIS radar instrument “penetrates deep into the ground, revealing the first 60-80 metres (yards) of the planet’s subsurface,” said Wlodek Kofman, leader of the radar team at the Grenoble institute. “Throughout all of this depth, we see the evidence for sedimentary material and ice.” Radar is a system for mapping distant objects by analyzing short radio waves that are reflected back from those objects after initially being sent out. Radar imaging can also penetrate underground. “Previous Mars Express results about water on Mars came from the study of images and mineralogical data, as well as atmospheric measurements,” said Olivier Witasse, the space agency’s Mars Express project scientist. “Now we have the view from the subsurface radar,” he added. “This adds new pieces of information to the puzzle but the question remains: where did all the water go?” Mars Express is scheduled to continue investigating. The newfound sediments appear as areas of low radar reflectivity, the investigators said, adding that such sediments are typically light, grainy materials that have been eroded away by water and carried to their destination. This later ocean would however have been temporary, though. Within a million years or less, Mouginot estimates, the water would have either frozen back in place and been preserved underground again, or turned into vapor and lifted gradually into the atmosphere. “I don’t think it could have stayed as an ocean long enough for life to form,” he said, adding that to find evidence of life scientists will have to look even further back in Mars’ history when liquid water persisted for much longer periods.