3. September 2020
Mars Express mission

Nerei­dum Montes – a moun­tain land­scape formed by wa­ter, ice and wind

Vertical plan view – part of Nereidum Montes in true colour
Ver­ti­cal plan view – part of Nerei­dum Montes in true colour
Image 1/5, Credit: ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)

Vertical plan view – part of Nereidum Montes in true colour

This ver­ti­cal plan view of an ap­prox­i­mate­ly 130- by 60-kilo­me­tre area of Nerei­dum Montes – cor­re­spond­ing to an area rough­ly half the moun­tain­ous Aus­tri­an state of Tirol – clear­ly shows how the land­scape at the crater edge has been shaped by var­i­ous ge­o­log­i­cal pro­cess­es since the for­ma­tion of the Ar­gyre im­pact basin four bil­lion years ago. Wa­ter, ice (both on and be­neath the sur­face) and, more re­cent­ly, wind have all left their mark. A strik­ing net­work of small, branch­ing val­leys on the right-hand side of the im­age at­tests to wa­ter hav­ing flowed over the sur­face from the 4000-me­tre-high edge of Ar­gyre and down the moun­tain slopes in­to the basin, carv­ing out ero­sion gul­lies and cre­at­ing small val­leys.
Erosion structures and dunes in Nereidum Montes
Ero­sion struc­tures and dunes in Nerei­dum Montes
Image 2/5, Credit: ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)

Erosion structures and dunes in Nereidum Montes

This oblique per­spec­tive view in­to a deeply carved val­ley bor­dered by moun­tains that are over 3000 me­tres tall shows large-scale move­ments of ma­te­ri­al, cre­at­ed by land­slides. This ma­te­ri­al ac­cu­mu­lat­ed on the val­ley floor, where it was ex­posed to fur­ther pro­cess­es of weath­er­ing and ero­sion. A small im­pact crater on the mas­sif at the up­per left of the val­ley is, like many oth­er craters in this area, filled with ma­te­ri­al and ex­hibits a strik­ing con­cen­tric pat­tern on its sur­face. Such mark­ings in­di­cate the for­mer pres­ence of glaciers cov­ered by rock de­bris, known as rock glaciers. The ma­te­ri­al that slipped in­to the val­ley could al­so have cov­ered ice that might still ex­ist to­day. Last but not least, the dark dune fields at the en­trance to the val­ley tes­ti­fy to the pow­er of the wind to trans­port grains of sand over large dis­tances and around ob­sta­cles. The grey­ish-black dune sands com­mon­ly found on Mars are of vol­canic ori­gin.
The Nereidum Montes mountains in the northwest of the Argyre Basin
The Nerei­dum Montes moun­tains in the north­west of the Ar­gyre Basin
Image 3/5, Credit: NASA/JPL/USGS; FU Berlin

The Nereidum Montes mountains in the northwest of the Argyre Basin

Nerei­dum Montes is part of the north­ern rim of the Ar­gyre Basin. With a di­am­e­ter of 1800 kilo­me­tres and a depth of up to five kilo­me­tres, Ar­gyre, whose north­west­ern low­lands can be seen on the low­er right of this to­po­graph­ic overview map, is the sec­ond-largest im­pact basin on Mars. Sim­i­lar to the Alps, the Nerei­dum Montes moun­tain chain ex­tends for over 1100 kilo­me­tres in an elon­gat­ed arc, run­ning par­al­lel to the edge of the basin. As in the moun­tain­ous ar­eas of Eu­rope, there are in­di­vid­u­al mas­sifs that are up to 4000 me­tres high. The High Res­o­lu­tion Stereo Cam­era op­er­at­ed by the DLR on board the ESA Mars Ex­press or­biter im­aged part of Nerei­dum Montes dur­ing or­bit 14,709. The im­ages show the re­gion to the south of the 85-kilo­me­tre-di­am­e­ter Sum­gin Crater, named af­ter the Rus­sian per­mafrost sci­en­tist Mikhail Ivanovich Sum­gin (1873–1942).
Topographic image map of part of Nereidum Montes
To­po­graph­ic im­age map of part of Nerei­dum Montes
Image 4/5, Credit: ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)

Topographic image map of part of Nereidum Montes

Sci­en­tists from DLR and Freie Uni­ver­sität Berlin are com­put­ing dig­i­tal ter­rain mod­els from im­age strips of the Mar­tian sur­face, ac­quired from dif­fer­ent an­gles by the High Res­o­lu­tion Stereo Cam­era on board Mars Ex­press. In this pro­cess, height in­for­ma­tion is as­signed to ev­ery pix­el. The colour cod­ing of the dig­i­tal ter­rain mod­el (see key at top right) pro­vides in­for­ma­tion about height dif­fer­ences in the north-east­ern part of Nerei­dum Montes. North is to the right of the im­age. The red-coloured high plateaus tow­er more than 4000 me­tres over the sur­round­ing low­lands, which are coloured blue. This rep­re­sen­ta­tion ef­fec­tive­ly shows even mi­nor de­tails of the land­scape, which has been formed by dif­fer­ent ero­sion pro­cess­es.
3D view (anaglyph image) of part of Nereidum Montes
3D view (anaglyph im­age) of part of Nerei­dum Montes
Image 5/5, Credit: ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)

3D view (anaglyph image) of part of Nereidum Montes

Anaglyph im­ages can be cre­at­ed us­ing da­ta ac­quired by the nadir chan­nel (the field of view of which is ori­ent­ed aligned per­pen­dic­u­lar to the sur­face of Mars) of the High Res­o­lu­tion Stereo Cam­era op­er­at­ed by DLR on board ESA’s Mars Ex­press space­craft and one of the four oblique-view­ing stereo chan­nels. When viewed with red-blue or red-green glass­es, these im­ages give a three-di­men­sion­al view of the land­scape. North is to the right of the im­age. The high im­age res­o­lu­tion clear­ly cap­tures the di­verse to­pog­ra­phy of this re­gion. The state of ero­sion makes it pos­si­ble to de­ter­mine the ages of the im­pact craters, the drainage chan­nels and small val­leys on the moun­tain slopes, which were cre­at­ed by wa­ter flow­ing over the sur­face.
  • These images of Mars, acquired by the DLR-operated HRSC instrument, show part of the Nereidum Montes mountain range.
  • This region has been shaped by various geological processes, with water, ice (both on and beneath the surface) and, more recently, wind all contributing to the erosion.
  • The HRSC has been mapping the Red Planet with unprecedented resolution, in three dimensions and in colour, since 2004 – as part of ESA’s Mars Express mission.

These images, acquired by the High Resolution Stereo Camera (HRSC), show part of the Nereidum Montes region. Wind, water, ice and tectonic forces have created a highly diverse landscape. The HRSC has been mapping the Red Planet with unprecedented resolution, in three dimensions and in colour, since 2004 as part of ESA's Mars Express mission. It was developed at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and is operated by the DLR Institute of Planetary Research. Mars Express delivers new data about the geology, mineralogy and atmosphere of Mars to shed light on the climate history of the Red Planet and clarify the role of water and determine the location of whatever water is left.

The Martian 'Alps'

Nereidum Montes is part of the northern rim of Argyre Basin. With a diameter of 1800 kilometres and a depth of up to five kilometres, Argyre is the second-largest impact basin on Mars (the biggest being Hellas Planitia). Similar to the Alps, the Nereidum Montes mountain chain extends for over 1100 kilometres in an elongated arc, running parallel to the edge of the basin. Similar to the mountainous areas of Europe, there are individual massifs that are up to 4000 metres high.

However, the Alps were formed by a very different process to the one that created the ring mountains of Nereidum Montes. The latter were originally the result of an extremely large asteroid impact. The impact was so enormous that it not only formed a bowl-shaped basin several kilometres deep, but also created several concentric rings of mountains at the basin edge. These have acquired a terrace-like structure due to tectonic landslide processes, which moved entire blocks of the surface. By contrast, the Alps were formed when the African continental plate collided with the Eurasian plate, crumpling the collision zone into fold mountains almost 5000 metres high. These are still growing by approximately one centimetre per year, although they are being eroded at the same time.

The 'Silver Plain' and the 'Nereid Mountains'

Before Mars could be closely examined by spacecraft, even Earth's most powerful telescopes could only discern major geological formations. These included the Argyre Basin, but scientists were unable to draw any conclusions about its topography on the basis of their observations by telescope.

Chryse and Argyre were two mythical islands that Pliny the Elder (23–79 AD) described as being located where the Indus flows into the Indian Ocean, and which were said to harbour large deposits of gold (in Greek, chrysos) and silver (argyros). These names were incorporated into the earliest cartographic representations of Mars. Giovanni Schiaparelli (1835–1910) made the most of Mars' proximity to Earth in 1877 to conduct extensive observations and map Mars in detail for the first time. At that point, the 'Golden Plain', or Chryse Planitia, further north was also included in the nomenclature. Nereidum Montes, or 'Mountains of the Nereids' (named after the 50 daughters of Nereus, a sea god in Greek mythology, and his consort Doris, the daughter of Oceanos and Tethys), received its name only in the space age, when it became possible to identify smaller regional structures.

The images show a region characterised by an array of geological processes that occurred after the formation of the Argyre Basin four billion years ago. Water, ice (both on and beneath the surface) and, more recently, wind have all contributed to the erosion that has taken place here. Argyre was originally deeper than it is today. Eroded rock was transported into the basin by glaciers and flowing water, so that it gradually became partially filled.

Indications of ice beneath the surface

A striking network of small, branching valleys on the right-hand side of Image 1 attest to water having flowed over the surface from the edge of Argyre and into the basin. This came either from rainfall in the early days of Mars or from melted glacial ice. To this day, these drainage networks document the planet’s water-rich past.

There has been a long and intensive debate as to whether there was actually a significantly warmer climate (warm and wet) in the early days of Mars. This would have enabled a water cycle with precipitation and a network of bodies of water on the surface, either over a longer period or perhaps just episodically. Alternatively, given that the thin atmosphere offered little in the way of a greenhouse effect, the conditions may have been cold and wet, leading to ice age processes with, at most, precipitation of snow and the associated glacial phenomena. Sporadic volcanic activity or impacts events would have triggered thawing processes that melted the ice on the surface and subsurface, thus causing water to flow.

The latest findings show that the many dry river valleys on Mars were formed by at least four different run-off processes: surface run-off due to precipitation, melting glaciers, subglacial run-off beneath glacial ice masses and escaping groundwater (which in turn may have been formed by melting ground ice). Nereidum Montes is considered to be a key region for thoroughly testing these hypotheses. Due to its morphology, which is thought to be of glacial origin, it is likely that its features were formed by melting glacial ice.

Most of the impact craters in this region are filled with a material that has a striking concentric pattern on its surface. Such structures indicate the former presence of glaciers covered by rock debris, known as rock glaciers. The resulting landforms can also be seen as large-scale deposits in valleys between mountain ranges. It is thought that these landforms still contain water ice deep under a layer of debris that prevents sublimation – the vaporisation of ice in the low-pressure Martian atmosphere.

The power of the wind

Last but not least, the dark dune fields on the left-hand side of Image 1 testify to the power of the wind to transport grains of sand over large distances and around obstacles. The greyish-black dune sands that are common on Mars are of volcanic origin. They consist primarily of old, once-buried volcanic ash, which was often brought up from beneath the Martian surface by impact events. These sands often contain fragments of crushed lava rock and volcanic glass. As they were covered by Martian surface materials for a time, they were not transformed into lighter minerals by the action of water.

Based on the dune types, the direction of the wind that has formed the various dunes can easily be determined. In this example, some individual, crescent-shaped dunes, known as barchans, can be seen. These have grown together to form a barchanoid dune field at the end of the valley. In this case, the wind came from the southeast (bottom left in Image 1), blew into the valley, drove the sands before it and deposited most of the material at the foot of the mountains.

  • Image processing

    These images were acquired by the High Resolution Stereo Camera (HRSC) on 7 August 2015 during Mars Express Orbit 14,709. The ground resolution is approximately 15 metres per pixel and the images are centred at roughly 312 degrees east and 39.5 degrees south. The perpendicular colour view was generated using data acquired by the nadir channel, the field of view which is aligned perpendicular to the surface of Mars, and the colour channels of the HRSC. The oblique perspective view was computed using a Digital Terrain Model (DTM) and data acquired by the nadir and colour channels of the 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 color-coded topographic view 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 a Mars equipotential surface (Areoid).

    The HRSC was developed and is operated by the German Aerospace Center (DLR). The systematic processing of the camera data was performed at the DLR Institute of Planetary Research in Berlin-Adlershof. Personnel at the Department of Planetary Sciences and Remote Sensing at Freie Universität Berlin used these data to create the image products shown here.

  • 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)
    Pub­lic Af­fairs and Com­mu­ni­ca­tions
    Telephone: +49 2203 601-2867
    Fax: +49 2203 601-3249

    Contact
  • Daniela Tirsch
    Ger­man Aerospace Cen­ter (DLR)

    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-488
    Fax: +49 30 67055-402
    Linder Höhe
    51147 Köln
    Contact
  • Ulrich Köhler
    Pub­lic re­la­tions co­or­di­na­tor
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-215
    Fax: +49 30 67055-402
    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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