5. March 2020
Mars Express mission

Moreux Crater on Mars – dunes and ev­i­dence of glacial pro­cess­es

Colour plan view of Moreux Crater in Protonilus Mensae
Colour plan view of Moreux Crater in Pro­tonilus Men­sae
Image 1/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Colour plan view of Moreux Crater in Protonilus Mensae

The crater, which is ap­prox­i­mate­ly 135 kilo­me­tres across, has been heav­i­ly erod­ed and changed by glacial pro­cess­es. This is par­tic­u­lar­ly vis­i­ble on the rim and cen­tral peak. Its floor has been so deeply filled that the crater now on­ly has a depth of around three-and-a-half kilo­me­tres. A belt of dark dunes forms a cir­cle around the cen­tral peak. In these con­trast-en­hanced colour im­ages, the dune sands ap­pear bluish.
Perspective view of the central peak in Moreux Crater
Per­spec­tive view of the cen­tral peak in Moreux Crater
Image 2/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Perspective view of the central peak in Moreux Crater

A cen­tral peak that has been heav­i­ly mod­i­fied by glacial pro­cess­es ris­es two kilo­me­tres from the floor of Moreux Crater. The for­ma­tion of cen­tral peaks in im­pact craters is de­ter­mined by grav­i­ty, the im­pact speed and – above a cer­tain val­ue – the size of the im­pactor. They are main­ly found in craters with di­am­e­ters in ex­cess of around 100 kilo­me­tres. The large dune field of barchanoidal ridges can be seen to the north­west of the peak (up­per right, in the back­ground). Nu­mer­ous in­di­vid­u­al sick­le dunes (barchans) are dis­tribut­ed in a ring on the crater floor. In this con­trast-en­hanced colour im­age, the black-grey dune sands ap­pear bluish.
Perspective view of a part of the southern crater rim
Per­spec­tive view of a part of the south­ern crater rim
Image 3/6, Credit: ESA/DLR/FU Berlin – CC BY-SA 3.0 IGO

Perspective view of a part of the southern crater rim

A val­ley up to four kilo­me­tres wide cuts through the rim of Moreux Crater. The flow struc­tures run­ning par­al­lel to the val­ley slopes are rem­nants of an­cient glaciers that flowed down the val­ley slopes, met in the mid­dle of the val­ley floor and then ad­vanced fur­ther down the val­ley, in­to the crater in­te­ri­or. The rock mass­es de­posit­ed on the slopes broke up, prob­a­bly due to the gra­di­ent of the sur­face, and left be­hind the frac­ture struc­tures vis­i­ble in the fore­ground of the im­age. A thin lay­er of vol­canic sand (shown here in blue) cov­ers large parts of the crater floor.
Protonilus Mensae – transition zone between highlands and lowlands
Pro­tonilus Men­sae – tran­si­tion zone be­tween high­lands and low­lands
Image 4/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Protonilus Mensae – transition zone between highlands and lowlands

This colour-cod­ed to­po­graph­ic map shows the lo­ca­tion of Moreux Crater, which is ap­prox­i­mate­ly 135 kilo­me­tres across. It is lo­cat­ed in the tran­si­tion zone be­tween the south­ern high­lands, which are heav­i­ly cratered, and the ex­ten­sive low­lands of the north­ern hemi­sphere of Mars. On 30 Oc­to­ber 2019, the High Res­o­lu­tion Stereo Cam­era op­er­at­ed by DLR on bord ESA’s Mars Ex­press or­biter im­aged the area dur­ing or­bit 20,014. The large, white-bor­dered area marks the ex­tent of the en­tire HRSC im­age strip. The land­scape in the im­ages shown here is lo­cat­ed in the small­er, in­ner rect­an­gle.
Topographic image map of Moreux Crater
To­po­graph­ic im­age map of Moreux Crater
Image 5/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Topographic image map of Moreux Crater

Us­ing im­age strips ac­quired by the High Res­o­lu­tion HRSC cam­era sys­tem on Mars Ex­press, which were im­aged from dif­fer­ent an­gles, re­searchers from DLR and Freie Uni­ver­sität Berlin have com­put­ed dig­i­tal ter­rain mod­els of the Mar­tian sur­face, which con­tain el­e­va­tion in­for­ma­tion for each pix­el. The colour cod­ing of the dig­i­tal ter­rain mod­el (leg­end in the top right-hand cor­ner) pro­vides in­for­ma­tion about dif­fer­ences in al­ti­tude. The crater floor is at an al­ti­tude of ap­prox­i­mate­ly mi­nus 4000 me­tres, while the ar­eas sur­round­ing the crater are at around mi­nus 2000 me­tres. The sur­round­ing Pro­tonilus Men­sae re­gion is ap­prox­i­mate­ly at the height of the ‘areoid’ – a cal­cu­lat­ed sur­face of equal grav­i­ta­tion­al at­trac­tion re­ferred to as an ‘equipo­ten­tial sur­face’. On Earth, the equiv­a­lent ref­er­ence sur­face is sea lev­el.
3D view of the Moreux impact crater in Protonilus Mensae
3D view of the Moreux im­pact crater in Pro­tonilus Men­sae
Image 6/6, Credit: ESA/DLR/FU Berlin – CC BY-SA 3.0 IGO

3D view of the Moreux impact crater in Protonilus Mensae

Anaglyph im­ages can be gen­er­at­ed from da­ta ac­quired by the nadir chan­nel of the High Res­o­lu­tion Cam­era Sys­tem (HRSC), which is di­rect­ed per­pen­dic­u­lar­ly to the sur­face of Mars, and one of the four oblique­ly view­ing stereo chan­nels. When us­ing red-blue or red-green glass­es, they pro­vide a re­al­is­tic, three-di­men­sion­al view of the land­scape. North is on the right of the im­age. The im­pact crater, which is ap­prox­i­mate­ly 135 kilo­me­tres across, has a depth of up to 3500 me­tres. The cen­tral peak is about 2000 me­ters high.
  • Moreux Crater is located in Protonilus Mensae on the border between the Martian highlands and lowlands. Extensive deposits of ground ice exist in this region.
  • Ice-rich material has left many traces, particularly around the central peak and along the crater rim. Analyses of the terrain indicate that these glacial processes have continued until very recently.
  • A range of dune formations can also be seen inside the crater, allowing the prevailing wind directions to be determined.
  • Space, planetary research

The images shown here, which were acquired by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express orbiter, reveal the impressive Moreux Crater on Mars. Glaciers have left their mark on the crater rim and floor, and have significantly altered the terrain. This striking view is complemented by a number of distinctive dark dunes. These formations bear witness to the influence of the prevailing wind systems.

HRSC was developed and is operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). The systematic processing of the camera data was carried out at the DLR Institute of Planetary Research in Berlin-Adlershof. The image products shown here were created at the Department of Planetary Sciences and Remote Sensing at the Freie Universität Berlin.

Moreux Crater has a diameter of approximately 135 kilometres and is up to three-and-a-half kilometres deep. It is located in Protonilus Mensae, which lies on the Martian dichotomy boundary. The region has extensive deposits of ground ice, as well as surface ice and snow. The floor of the crater is mostly covered by dark dune fields, which are common on Mars.

Formed by glaciers …

Ice-rich material has left behind a diverse glacial treasure trove, which can be found mainly around the central peak and along the crater rim. This includes numerous valleys that carve into the flanks. Polygonal structures at the bottom of these valleys have been interpreted as patterned ground, or periglacial landforms. Linear valley fillings, such as in the wide valley at the southern crater rim (Image 3), were created by the meeting of ice and scree masses that once slid down the valley slopes and met in the middle of the valley. Tongue-shaped deposits and viscous flow patterns are remnants of rock glaciers that formed almost everywhere along the crater wall.

Dating of these terrain forms has revealed that glacial and periglacial processes occurred here repeatedly during a period that lasted from approximately one billion to 400,000 years ago. Moreux Crater is situated at 41.6 degrees north, in the mid-latitudes of Mars, where glaciation processes occurred mainly when the axis of rotation of Mars was tilted at a greater angle than it is today (currently the inclination is 25.2 degrees) and the poles, with their ice caps, were tilted more directly towards to the Sun. Then, at mid-latitudes, more ice and snow from the atmosphere was deposited on crater edges and plateaus, where it collected and formed glaciers.

… and gone with the wind

The two-kilometre-high central peak in the crater is surrounded by dark, sandy material. Winds have piled it up into groups of individual dunes and also into contiguous dune fields. The grey-black dunes (they only appear bluish in these contrast-enhanced colour images) consist of volcanic sand and fine ash with a basalt composition. This is mainly comprised of the minerals olivine and pyroxene, which cause the dark colouring of basaltic materials. Both minerals are silicates and have a high content of magnesium and iron.

The dune fields in Moreux Crater show slight colour variations, possibly caused by differences in the composition of the dunes. The OMEGA spectrometer on Mars Express can be used to investigate the mineralogical composition of surface materials. The large contiguous dune field to the north of the central peak (right in Image 1) was found to have a significantly higher olivine content than the rest of the dunes, which are predominantly composed of pyroxene.

In addition to the glacial formations, the crater also has aeolian formations that are visible in the different dune shapes. The most common type of dune is crescent-shaped (referred to as a barchan) which, when they grow together and merge, form barchanoidal ridges. The dune fields in Moreux Crater are made up of these ridges. Barchans are generally associated with limited sediment availability and a unimodal wind regime – this is, they are formed by wind that always blows from the same direction.

However, orientation of the dunes varies in different regions of the crater, which indicates a complex system of prevailing wind directions. This is due to the specific topography of the crater and its central peak. The large barchanoidal dune field to the north of the central peak is primarily formed by winds from the northeast. At its southern end, winds from the northwest meet the dunes and create star dunes, which are typically formed by winds from different directions.

If one follows the dune shapes counterclockwise from there, around the central peak, and uses them to discern the wind directions, the winds follow a semicircle. First, they come from the northwest, then the west, and later from the southwest until one reaches the eastern side of the dune ring (bottom of Image 1). Here, downdrafts from the west blowing from the slopes of the central peak meet winds from the east coming from the crater rim. The barchanoidal ridges change into transverse dunes at this point. Moreux Crater is thus a prime example of how local topography can influence wind flows and thereby have an indirect influence on morphological features.

  • Image processing

    The images shown here were acquired by the High Resolution Stereo Camera (HRSC) on 30 October 2019 during Mars Express orbit 20,014. The image resolution is approximately 16 metres per pixel. The centre of the image is at about 44 degrees east and 42 degrees north. The perpendicular colour view was generated from the data acquired by the HRSC nadir channel, which is directed perpendicular to the Martian surface, and the colour channels. The oblique perspective views were computed using a Digital Terrain Model (DTM) and data from the nadir and colour channels of HRSC. The anaglyph image, which gives a three-dimensional impression of the landscape when viewed with red-blue or red-green glasses, was derived from data acquired by the nadir channel and the stereo channels. The colour-coded image map is based on a DTM of the region, from which the topography of the landscape can be derived. The reference body for the HRSC DTM is an equipotential surface of Mars (areoid).

  • The HRSC experiment on Mars Express


    The High Resolution Stereo Camera (HRSC) 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.

Contact
  • Elke Heinemann
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-2867
    Linder Höhe
    51147 Cologne
    Contact
  • Daniela Tirsch
    Ger­man Aerospace Cen­ter (DLR)

    In­sti­tute of Plan­e­tary Re­search
    Linder Höhe
    51147 Köln
    Contact
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
    Contact
  • 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
    Contact

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