"Long before it's in the papers"
March 03, 2016


Huge volcanoes may have twisted whole Martian surface

March 3, 2016
Courtesy of National Centre for 
Scientific Research (France)
and World Science staff

Mars looked very dif­fer­ent long ago, sci­en­tists say based on new re­search.

They claim vol­can­ic ac­ti­vity twisted the whole sur­face of the plan­et around its co­re, like turn­ing the flesh of an ap­ri­cot around its stone. This, they say, shifted the face of the plan­et by 20 to 25 de­grees—a quar­ter of the way to­ward flip­ping it upside-down.

A reconstruction of Mars 4 bill­ion years ago, be­fore what sci­ent­ists call the "Great Tilt." (© Didier Florentz)

This new un­der­stand­ing will have to be tak­en in­to ac­count when stu­dy­ing early Mars to look for traces of life or for an ocean, for in­stance, the re­search­ers say.

Sci­en­tists at­trib­ute the swiv­el­ing event, 3 bil­lion to 3.5 bil­lion years ago, to a gi­gantic struc­ture on Mars called the Thar­sis vol­can­ic dome. A vol­can­ic dome is a mound that forms when la­va piles up around a vol­ca­no in­stead of flow­ing away com­plete­ly.

Thar­sis is the larg­est such dome in the So­lar Sys­tem, and it al­so in­cludes the So­lar Sys­tem’s high­est moun­tain, Olym­pus Mons.

The re­search sug­gests that Thar­sis be­came so heavy that it made the plan­et’s out­er lay­ers, called the crust and man­tle, ro­tate. The di­rec­tion of that rota­t­ion was such that both poles—or more ac­cu­rately the up­per lay­ers of the poles—moved. The plan­et’s over­all ax­is of spin did­n’t change.

This changes our vi­sion of Mars dur­ing the first bil­lion years of its his­to­ry, at a time when life may have emerged, the sci­en­tists say. It al­so pro­vides a so­lu­tion to three puz­zles, they add: why riv­ers formed where they are seen to­day; why un­der­ground reser­voirs of wa­ter ice lie far from the poles of Mars; and why the Thar­sis dome to­day lies on the equa­tor.

The find­ings are pub­lished March 2 in the jour­nal Na­ture.

A diagram shows Mars before and after the "Great Tilt." (Courtesy CNRS)

The find­ings came thanks to the com­bined work of geo­phys­i­cists, cli­ma­tol­o­gists and ge­o­mor­phol­ogists, re­search­ers who study land forms. 

The Thar­sis dome first started to form over 3.7 bil­lion years about 20 de­grees north of the equa­tor, re­search­ers say. Vol­can­ic ac­ti­vity con­tin­ued for sev­er­al hun­dred mil­lion years, form­ing a thick, heavy plat­eau over 5,000 km (3,000 miles) wide. The weight, ac­cord­ing to the find­ings, was so huge (equi­valent to a bill­ion bill­ion tons on Earth) that it made Mars’ crust and man­tle swiv­el around. 

In the stu­dy, ge­o­mor­phol­ogists Syl­vain Bouley of Un­iver­sité Paris-Sud and Da­vid Bara­toux of Un­iver­sité Tou­louse III-Paul Sa­ba­tier, both in France, ar­gued that the riv­ers were orig­i­nally dis­trib­ut­ed along a south trop­i­cal band. 

The study radic­ally changes our per­cep­tion of the sur­face of Mars as it was 4 bil­lion years ago, and al­so al­ters the chro­nol­o­gy of events, ac­cord­ing to the in­ves­ti­ga­tors. Ac­cord­ing to this new sce­nar­i­o, a pe­ri­od of liq­uid wa­ter sta­bil­ity that al­lowed the forma­t­ion of riv­er val­leys is con­tem­po­ra­ry with, and most likely a re­sult of, the vol­can­ic ac­ti­vity of the Thar­sis dome. The great tilt would have hap­pened af­ter this ac­ti­vity ended. 

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Mars looked very different long ago, scientists say based on new research. They claim volcanic activity twisted the whole surface of the planet around its core, like turning the flesh of an apricot around its stone. This, they say, shifted the face of the planet by 20 to 25 degrees—a quarter of the way toward flipping it upside-down. This new understanding will have to be taken into account when studying early Mars to look for traces of life or for an ocean, for instance, the researchers say. Scientists attribute the swiveling event, 3 billion to 3.5 billion years ago, to a gigantic structure called the Tharsis volcanic dome. A volcanic dome is a mound that forms when lava piles up around a volcano instead of flowing away completely. Tharsis is the largest such dome in the Solar System, and it also includes the Solar System’s highest mountain, Olympus Mons. The research suggests that Tharsis became so heavy that it made the planet’s outer layers, called the crust and mantle, to rotate. The direction of that rotation was such that both poles—or more accurately the upper layers of the poles—moved. The planet’s overall axis of spin didn’t change. This changes our vision of Mars during the first billion years of its history, at a time when life may have emerged, the scientists say. It also provides a solution to three puzzles, they add: why rivers formed where they are seen today; why underground reservoirs of water ice lie far from the poles of Mars; and why the Tharsis dome today lies on the equator. These findings are published March 2 in the journal Nature. The findings came thanks to the combined work of geophysicists, climatologists and geomorphologists, researchers who study land forms. The Tharsis dome first started to form over 3.7 billion years about 20 degrees North of the equator, researchers say. Volcanic activity continued for several hundred million years, forming a thick, heavy plateau over 5,000 km (3,000 miles) wide. This weight, according to the findings, was so huge that it made Mars’ crust and mantle swivel around. In the new study, geomorphologists Sylvain Bouley of Université Paris-Sud and David Baratoux of Université Toulouse III – Paul Sabatier, both in France, argued that the rivers were originally distributed along a south tropical band. The study radically changes our perception of the surface of Mars as it was 4 billion years ago, and also alters the chronology of events, according to the investigators. According to this new scenario, the period of liquid water stability that allowed the formation of river valleys is contemporaneous with, and most likely a result of, the volcanic activity of the Tharsis dome. The great tilt happened after this activity ended. claim