27. June 2019

Au­ro­rae Chaos – ter­rain col­lapse due to wa­ter run-off?

Aurorae Chaos
Au­ro­rae Chaos in colour
Image 1/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Aurorae Chaos in colour

The tran­si­tion zone be­tween the plateaus of the Mar­tian high­lands in Mar­gar­i­tifer Ter­ra and the chaot­ic ar­eas in the Au­ro­rae Chaos de­pres­sion have been shaped by rad­i­cal ge­o­log­i­cal pro­cess­es. Wa­ter stored in cav­i­ties be­neath the sur­face as un­der­ground ice thawed due to heat­ing and es­caped on­to the sur­face. The re­sult­ing cav­i­ties col­lapsed, and much of the rock de­bris was car­ried away by the wa­ter as a sed­i­ment load. In the sur­round­ing area, in­di­vid­u­al ta­ble moun­tains and buttes re­mained as rem­nants of the orig­i­nal plateau, form­ing the Au­ro­rae Chaos land­scape as it ap­pears to­day. The tran­si­tion zone to the high­lands fea­tures fis­sures and grabens formed due to tec­ton­ic ten­sions in the Mar­tian crust. In ad­di­tion, small­er chaos re­gions can be made out to the south of the es­carp­ment (left in the im­age).      
Perspective view of the transition zone between Margaritifer Terra and Aurorae Chaos
Per­spec­tive view of the tran­si­tion zone be­tween Mar­gar­i­tifer Ter­ra and Au­ro­rae Chaos
Image 2/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Perspective view of the transition zone between Margaritifer Terra and Aurorae Chaos

At the tran­si­tion be­tween the Mar­gar­i­tifer Ter­ra high­land re­gion and the Au­ro­rae Chaos de­pres­sion, the plain of the south­ern high­lands is heav­i­ly fur­rowed and char­ac­terised by grabens, val­leys, hol­lows and shat­tered land­scape. The crust was torn apart by ten­sile tec­ton­ic forces, while un­der­ground ice was prob­a­bly stored in cav­i­ties di­rect­ly be­neath the sur­face. This thawed due to a heat source – ris­ing mag­ma from a vol­cano or the heat gen­er­at­ed by a near­by as­ter­oid im­pact – and rose to the sur­face be­fore flow­ing north. The re­sult­ing cav­i­ties col­lapsed, leav­ing a land­scape that is de­scribed as ‘chaot­ic ter­rain’ by plan­e­tary ge­ol­o­gists.
Topographical map of Margaritifer Terra and Aurorae Chaos
To­po­graph­i­cal map of Mar­gar­i­tifer Ter­ra and Au­ro­rae Chaos
Image 3/5, Credit: MOLA Science Team/FU Berlin

Topographical map of Margaritifer Terra and Aurorae Chaos

The Mar­tian high­lands to the east and north­east of the Valles Mariner­is canyon sys­tem are char­ac­terised by large out­flow val­leys. Large amounts of wa­ter must once have flowed through these val­leys in the di­rec­tion of the north­ern low­lands, at least spo­rad­i­cal­ly, dur­ing Mars’ ear­ly his­to­ry. A con­sid­er­able pro­por­tion of the runoff wa­ter must have orig­i­nat­ed from un­der­ground ice, which was stored in large quan­ti­ties in cav­i­ties be­neath the sur­face. Heat melt­ed this ice, which then emerged as wa­ter and flowed north. The emp­ty cav­i­ties cre­at­ed as a re­sult col­lapsed, leav­ing a con­fused pat­tern of iso­lat­ed ta­ble moun­tains be­hind on the sur­face, which ge­ol­o­gists re­fer to as ‘chaot­ic ter­rain’. The fis­sures and val­leys that lie in be­tween show that tec­ton­ic pro­cess­es have al­so played a part in shap­ing the land­scape. ESA’s Mars Ex­press space­craft flew over the re­gion on 31 Oc­to­ber 2018 dur­ing or­bit 18,675 and im­aged the tran­si­tion be­tween the high­land re­gion of Mar­gar­i­tifer Ter­ra and Au­ro­rae Chaos us­ing DLR’s HRSC cam­era sys­tem. The im­ages shown here are tak­en from the small rect­an­gle in the longer strip.      
3D view of the transition zone between Margaritifer Terra and Aurorae Chaos
3D view of the tran­si­tion zone be­tween Mar­gar­i­tifer Ter­ra and Au­ro­rae Chaos
Image 4/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

3D view of the transition zone between Margaritifer Terra and Aurorae Chaos

Anaglyph im­ages can be pro­duced from da­ta ac­quired by the nadir chan­nel of the HRSC cam­era sys­tem, the field of view of which is aligned per­pen­dic­u­lar to the sur­face of Mars, and one of the four oblique-view­ing stereo chan­nels. When viewed with red-blue or red-green glass­es, these im­ages give a re­al­is­tic, three-di­men­sion­al view of the land­scape. North is to the right. In this 3D view, the strong­ly fis­sured and fur­rowed land­scape, which has col­lapsed in­to it­self due to ge­o­log­i­cal pro­cess­es and ero­sion by flow­ing wa­ter, stands out par­tic­u­lar­ly clear­ly. The dif­fer­ences in el­e­va­tion be­tween the strik­ing promon­to­ry that runs from east to west through the cen­tre of the im­age and the deep­est points in the north (on the right of the im­age) are more than 4000 me­tres. This is ap­prox­i­mate­ly the same as the el­e­va­tion dif­fer­ence be­tween the peak of Mont Blanc (4808 me­tres above sea lev­el) and the Po Val­ley in North­ern Italy, which ex­tends east­wards through north­ern Italy (Turin is 239 me­tres above sea lev­el).      
Topographical image map of the southern part of Aurorae Chaos
To­po­graph­i­cal im­age map of the south­ern part of Au­ro­rae Chaos
Image 5/5, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Topographical image map of the southern part of Aurorae Chaos

Im­age strips ac­quired from dif­fer­ent an­gles by the HRSC cam­era sys­tem on board Mars Ex­press were used to gen­er­ate dig­i­tal ter­rain mod­els of the Mar­tian sur­face, con­tain­ing height in­for­ma­tion for each record­ed pix­el. The ref­er­ence lev­el to which the el­e­va­tion da­ta re­fer is an imag­i­nary sur­face that ex­pe­ri­ences the same grav­i­ta­tion­al at­trac­tion as that found at sea lev­el on Earth. Known as an equipo­ten­tial sur­face, this is shaped like a bi­ax­i­al el­lip­soid and is known as an areoid, a name de­rived from Ares, the Greek name for Mars. North is to the right. The colour cod­ing of the dig­i­tal ter­rain mod­el (leg­end top right) in­di­cates the dif­fer­ences in el­e­va­tion. The bot­tom of the Au­ro­rae Chaos de­pres­sion (the blue area on the right in the im­age) lies about 4000 me­tres be­low the lev­el of the high­lands (red, on the left of the im­age). The coloura­tion al­so re­veals tec­ton­ic frac­ture struc­tures and their di­rec­tion. A strik­ing es­carp­ment runs through the mid­dle of the im­age from north­east to south­west, form­ing a con­nec­tion be­tween the high plateau in the south and Au­ro­rae Chaos, which lies thou­sands of me­tres low­er.      
  • These images, acquired by the HRSC camera on board Mars Express, show the southern part of Aurorae Chaos, a region whose surface collapsed following the melting of large quantities of underground ice.
  • There are numerous mineralogical indications of the early presence of water in and around Mars' numerous chaotic regions.
  • The data used to create the images were acquired on 31 October 2018, during Mars Express orbit 18,765. The image resolution is 14 metres per pixel.
  • Focus: Space, planetary research, Mars

At first glance, it looks like brown crocodile skin photographed at close range, but these images actually show the rough, rugged terrain of Aurorae Chaos. The data used to create the images were acquired by the High Resolution Stereo Camera (HRSC) operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) on board ESA’s Mars Express spacecraft, which has been orbiting Mars since 2003.

Aurorae Chaos is one of many areas of 'chaotic terrain' on Mars. Such terrain typically features a random – and thus chaotic – arrangement of table mountains and isolated boulders of various sizes. Aurorae Chaos is located in the highland region of Margaritifer Terra, a few hundred kilometres from the eastern end of the Valles Marineris canyon system. Many of these chaotic areas are found here, near the equator, and at the transition from the southern highlands to the northern lowlands. No geological formations of this type exist on Earth.

There is a morphologically comparable region on Mercury, and some chaotic areas have also been identified on Jupiter's natural satellite Europa, but in both cases, their geological origins are very different to the chaotic areas on Mars. In the case of Europa, the crust is being pulled apart and then compressed again by tidal forces, resulting in complex configurations of broken floes, fissures and ridges. On Mercury, the chaotic areas were caused by seismic movements in the planet's crust following a huge asteroid impact.

A very large chaotic area

Aurorae Chaos is part of an extensive system of fissures, grabens and hills to the northeast of the vast Valles Marineris canyon system. The bottom of the irregularly shaped depression, which measures up to 600 kilometres across, is approximately four kilometres lower than the surrounding plains. The entire chaos region within Margaritifer Terra covers around 1.6 million square kilometres, making it an extremely imposing landscape. Elsewhere on Mars, the chaotic terrains are significantly smaller, barely exceeding the size of an impact crater.

An escarpment runs from northeast to southwest through the centre (images 1, 4 and 5) and connects the high plateau in the south with the lower-lying areas of Aurorae Chaos in the north. The transition zone features fractures and grabens that run parallel with or diagonal to the escarpment. These were caused by tension in the Martian crust due to tectonic forces that stretched and tore apart the brittle crust in this region. In addition, smaller chaos regions can be made out to the south of the escarpment (left in images 1, 4 and 5 ).

Evidence of the complex history of water on Mars

Such chaotic areas bear witness to the complex transport, storage and release of large amounts of water ice and liquid water on Mars in the past.

The theory most widely held by scientists is that chaotic terrain is formed when underground ice reservoirs melt due to heating, suddenly releasing large quantities of water. The heat may have come from nearby volcanoes or been released as the result of major asteroid impacts. Once the water has drained away, the surface collapses into the newly-formed cavities.

Scientists have used crater size and frequency measurements to estimate the age of the bottom of the huge Aurorae Chaos depression at 3.5 billion years. The collapse process occurred a very long time ago. Groundwater and magma may also have escaped during the collapse, in addition to meltwater.

There are numerous mineralogical indications of the early presence of water, which would have flowed in and around Mars' chaotic terrains. Sulphate-containing layers of sediment that have been identified in some of the basins with chaotic structures indicate the formation and accumulation of this mineral due to the evaporation of relatively acidic water. Clay mineral deposits on the plateau areas of Margaritifer Terra, which predate the sulphate-containing deposits, may be related to fissures and groundwater run-off. The formation of clay minerals would have required the presence of standing, pH-neutral water.

  • Image processing
    The High Resolution Stereo Camera (HRSC) acquired the data from which these images were created on 31 October 2018 during Mars Express Orbit 18,765. The ground resolution is about 14 metres per pixel and the centre of the imaged area is located at approximately 327 degrees east and 11 degrees south. The colour image was created using data from the nadir channel, the field of view of which is aligned perpendicular to the surface of Mars, and the colour channels of the HRSC. The colour-coded topographic view is based on a Digital Terrain Model (DTM) of the region, from which the topography of the landscape can be derived. The reference body for the HRSC-DTM is a Mars equipotential surface (Areoid). The oblique perspective view was generated from the DTM and data from the nadir and colour channels of HRSC. The anaglyph, which provides a three-dimensional view of the landscape when viewed using red-green or red-blue glasses, was derived from data acquired by the nadir channel and the stereo channels.
  • The HRSC experiment on Mars Express
    The High Resolution Stereo Camera was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and built in collaboration with partners in industry (EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The science team, which is headed by Principal Investigator (PI) Ralf Jaumann, consists of 52 co-investigators from 34 institutions in 11 countries. The camera is operated by the DLR Institute of Planetary Research in Berlin-Adlershof.
  • Elke Heinemann
    Ger­man Aerospace Cen­ter (DLR)
    Pub­lic Af­fairs and Com­mu­ni­ca­tions
    Telephone: +49 2203 601-2867
    Fax: +49 2203 601-3249

  • Prof.Dr. Ralf Jaumann
    Freie Uni­ver­sität Berlin
    In­sti­tute of Ge­o­log­i­cal Sci­ences
    Plan­e­tary Sci­ences and Re­mote Sens­ing
    Telephone: +49-172-2355864
    Malteserstr. 74-100
    12249 Berlin
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
  • Daniela Tirsch
    Ger­man Aerospace Cen­ter (DLR)

    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-488
    Fax: +49 30 67055-402
    Linder Höhe
    51147 Köln

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