21. February 2019
Mars Express mission

Net­works of wa­ter chan­nels formed dur­ing the ear­ly days of Mars

View of a heavily dendritic valley network on Mars
View of a heav­i­ly den­drit­ic val­ley net­work on Mars
Image 1/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

View of a heavily dendritic valley network on Mars

This im­age shows a sys­tem of dried-up, heav­i­ly den­drit­ic riv­er val­leys east of the Huy­gens im­pact crater, which is over 450 kilo­me­tres in di­am­e­ter. Such net­works of val­leys orig­i­nat­ed more than three and a half bil­lion years ago, and there­fore typ­i­cal­ly oc­cur in the old­est, most heav­i­ly cratered re­gions of Mars, lo­cat­ed in the south­ern high­lands. The ex­is­tence of such val­ley net­works pro­vides ev­i­dence that, at least in some pe­ri­ods, the plan­et must have had a dif­fer­ent, most like­ly warmer and wet­ter cli­mate, and prob­a­bly even a wa­ter cy­cle. North is to the right in the im­age.
Oblique perspective view of the valley network east of Huygens Crater
Oblique per­spec­tive view of the val­ley net­work east of Huy­gens Crater
Image 2/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

Oblique perspective view of the valley network east of Huygens Crater

This oblique per­spec­tive view was gen­er­at­ed us­ing da­ta ac­quired by the stereo chan­nels of the DLR-de­vel­oped High Res­o­lu­tion Stereo Cam­era (HRSC). From these da­ta, dig­i­tal ter­rain mod­els have been de­rived; these make it pos­si­ble to pro­duce per­spec­tive views of the Mar­tian land­scape. This view shows a heav­i­ly den­drit­ic val­ley net­work east of the Huy­gens im­pact crater. The name­less crater on the left has a di­am­e­ter of about 20 kilo­me­tres, the steep crater wall at the edge of the im­age is about 1000 me­tres tall. The large val­ley in the mid­dle of the pic­ture is about two kilo­me­tres wide.
Musa Bay
Musa Bay in Iran, show­ing a den­drit­ic val­ley net­work
Image 3/6, Credit: Contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO.

Musa Bay in Iran, showing a dendritic valley network

This im­age of Musa Bay in north­east­ern Iran was ac­quired by the Coper­ni­cus Sen­tinel-2A satel­lite. It clear­ly shows the sim­i­lar­i­ty be­tween the den­drit­ic pat­terns of val­leys on Earth and Mars.
Topographical overview map showing the surroundings of the valley network east of Huygens Crater
To­po­graph­i­cal overview map show­ing the sur­round­ings of the val­ley net­work east of Huy­gens Crater
Image 4/6, Credit: NASA/JPL/MOLA, FU Berlin

Topographical overview map showing the surroundings of the valley network east of Huygens Crater

The im­ages of the val­ley net­work to the east of the Huy­gens im­pact crater de­scribed in this ar­ti­cle were ac­quired over the small­er rect­an­gle with­in the larg­er, marked im­age strip. This strip was ac­quired by the High Res­o­lu­tion Stereo Cam­era (HRSC) dur­ing or­bit 18,831 of ESA’s Mars Ex­press space­craft. North is at the top of this im­age.
Three-dimensional view of a valley network east of Huygens Crater
Three-di­men­sion­al view of a val­ley net­work east of Huy­gens Crater
Image 5/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

Three-dimensional view of a valley network east of Huygens Crater

Anaglyph im­ages can be de­rived from the da­ta ac­quired by the nadir chan­nel of the HRSC cam­era sys­tem, which is aligned per­pen­dic­u­lar to the plan­et’s sur­face, and one of the four oblique-view­ing stereo chan­nels. They pro­vide a re­al­is­tic, three-di­men­sion­al view of the land­scape when us­ing red-blue or red-green glass­es.
Colour-coded topographic map of a valley network east of Huygens Crater
Colour-cod­ed to­po­graph­ic map of a val­ley net­work east of Huy­gens Crater
Image 6/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO.

Colour-coded topographic map of a valley network east of Huygens Crater

Dig­i­tal ter­rain mod­els of the Mar­tian sur­face can be gen­er­at­ed from the im­age strips ac­quired by the HRSC cam­era sys­tem, which are record­ed from dif­fer­ent view­ing an­gles. These con­tain el­e­va­tion in­for­ma­tion of the plan­et’s sur­face for each pix­el. The lev­el to which the el­e­va­tion in­for­ma­tion is ref­er­enced is an areoid (a Mar­tian grav­i­ta­tion­al equipo­ten­tial sur­face). In the map, north is to the right.
  • The system of dried out, strongly dendritic river valleys seen in these HRSC images reveals that Mars must have had a different, probably warmer and more humid climate, at least temporarily, in the past.
  • Climate change is thought to have occurred on Mars some 3.7 to 3.8 billion years ago
  • Today, liquid water cannot be stable on the surface of Mars due to its thin atmosphere, but it still seems to be present in large quantities underground, in the form of water ice.
  • Focus: space, planetary research, Mars

These recent images, acquired by the High Resolution Stereo Camera (HRSC), which is carried on board the ESA Mars Express spacecraft and is operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), show a system of dried-up, heavily dendritic river valleys east of the Huygens impact crater. This crater is over 450 kilometres in diameter. Such networks of valleys originated more than three and a half billion years ago, and therefore are typically found in the oldest, most heavily cratered regions of Mars, located in the southern highlands. The existence of such valley networks provides evidence that, at least in some periods more than 3.7 to four billion years ago, the planet must have had a different, most likely warmer and wetter climate, and probably even a water cycle.

The systematic processing of the camera data took place at the DLR Institute for Planetary Research in Berlin-Adlershof. The working group of Planetary Science and Remote Sensing at Freie Universität Berlin used the data to create the image products shown here.

The images show a network of meandering valleys across the landscape, all of which follow a dendritic, ramified or branched pattern. In hydrology, the term 'dendritic' is derived from 'dendron' (Greek for tree) and describes a valley into which, as one moves upstream, ever-smaller side valleys open, which in turn are fed by even smaller tributaries. This results in a pattern similar to the structure of a tree, with a trunk, branches and twigs. On Earth, this erosion pattern is found in most rivers and is the result of a water cycle with precipitation, runoff, evaporation and re-precipitation. In contrast, there are very few dendritic river valleys on Mars, and they have long since dried up. Most Martian valleys exhibit a different, rather straight structure with few tributaries, and they have a different origin – because they were formed by flowing groundwater.

For such dendritic valleys to form, running water had to have been present on Mars. The various sources of this water – precipitation, groundwater or glacial meltwater – can often be determined by examining the valley structure. Martian valley networks with a dendritic layout were most likely formed by surface runoff of precipitation or meltwater. The heads of the valleys are typically located on a topographical ridge such as a watershed, and the course of the runoff channels follows the local gradient. The term ‘watershed’ refers to the boundary between two adjacent river systems, which usually extend along ridges.

As can be deduced from the colour-coded elevation model (image 6), the water flowed from north (on the right in the image) to south. The largest valleys in the images are up to two kilometres wide, and reach a depth of up to 200 metres. In particular, those that run in an east-west direction show heavily eroded valley edges, scoured by the erosive power of the water flowing down the valley. Dendritic valley systems are also found elsewhere on the crater rim and were recorded by the HRSC for the first time on 20 June 2004 during Orbit 532.

Climate change transforms Mars into a 'salty' planet

Today, it is thought that climate change took place on Mars about 3.7 to 3.8 billion years ago, when environmental conditions changed from a somewhat neutral, potentially life-sustaining and sporadically humid environment to a much more acidic, dry, cold environment that is hostile to life. The main reason for this, according to current knowledge, was the gradual loss of the Martian atmosphere and a change in the planet's volcanic activity. 'This climate change transformed our neighbouring planet from being a one with temporary rivers and lakes that was, so to speak, 'full of hope' as regards the possible emergence and development of life, into a one that was just dry and salty," explains Ralf Jaumann from the DLR Institute of Planetary Research and the Principal Investigator of the HRSC.

One of the reasons why Mars lost its atmosphere is the loss of its magnetic field, which was active during the first 500 million years. As it grew ever weaker the solar wind was able to gradually split the molecules in the atmosphere, and the resultant ions were accelerated and lost to space. As a result, and also due to the declining volcanism, the atmosphere became thinner and thinner. In addition, Mars is only half the size of Earth, so its gravitational force is barely sufficient to bind atmospheric molecules to it. Below a certain atmospheric pressure, water can no longer remain liquid on the surface of a planet – it can remain as ice or gas. The lack of precipitation on Mars ultimately collapsed the water cycle.

Is there still liquid water on the surface of Mars today?

Due to the current, very thin atmosphere, liquid water on the surface of Mars cannot be stable. Even if the temperature was favourable, it would evaporate immediately. However, beneath the surface it still seems to be abundant – in the form of water ice. The two polar ice caps on Mars also consist of a mixture of frozen water and carbon dioxide ice. Under very extreme conditions (for example, in very saline environments), liquid water could theoretically still exist for a short time on Mars.

  • Image processing
    The HRSC data for the images show here were acquired on 19 November 2018 during Mars Express orbit 18,831. The image resolution is 14 metres per pixel. The centre of the images is located at approximately 66 degrees east and 17 degrees south. The colour image was created using data from the nadir channel, which is aligned perpendicular to the surface of Mars, and from the colour channels. The oblique perspective view was generated using data from the HRSC stereo channels. The anaglyph image, which gives a three-dimensional impression of the landscape when viewed using red-blue or red-green glasses, was derived from data acquired by the nadir channel and the stereo channels. The colour-coded image 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 Martian gravitational equipotential surface (an areoid).
  • HRSC 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 51 co-investigators from 35 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
  • 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
  • Daniela Tirsch
    Ger­man Aerospace Cen­ter (DLR)

    In­sti­tute of Plan­e­tary Re­search
    Linder Höhe
    51147 Köln
    Contact

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