31. August 2022
Mars Express mission

A vast and mys­te­ri­ous val­ley sys­tem

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Space
Vertical plan view of a part of ‘Holden Basin’ with chaotic terrain
Ver­ti­cal plan view of a part of ‘Hold­en Basin’ with chaot­ic ter­rain
Image 1/7, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Vertical plan view of a part of ‘Holden Basin’ with chaotic terrain

This de­pres­sion, about 270 kilo­me­tres across, is thought to be the rem­nant of a very old im­pact basin on Mars that once con­tained con­sid­er­able amounts of ground ice. Sud­den melt­ing of the ice and drainage of the wa­ter cre­at­ed cav­i­ties in the sub­sur­face, which then col­lapsed, cre­at­ing the chaot­i­cal­ly frac­tured land­scapes in the cen­tre of the im­age. At the south­west­ern edge of this basin is the Hold­en im­pact crater (not pic­tured here), which is why this de­pres­sion is some­times un­of­fi­cial­ly called ‘Hold­en Basin’. North is to the right in the im­age.
Perspective view to the south of the chaotic terrain
Per­spec­tive view to the south of the chaot­ic ter­rain
Image 2/7, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Perspective view to the south of the chaotic terrain

This 'chaot­ic ter­rain' is lo­cat­ed at the low­est point of a large de­pres­sion up to 2000 me­tres deep and mea­sures ap­prox­i­mate­ly 40 by 80 kilo­me­tres. Such frac­tured land­scapes oc­cur when ice reser­voirs in the sub­sur­face melt, due to vol­cani­cal­ly in­duced heat, for ex­am­ple, and con­sid­er­able amounts of wa­ter are sud­den­ly re­leased and flow away. This caus­es the sur­face above the new­ly formed cav­i­ties to col­lapse and the land­scape to fall in on it­self. The ex­act trig­ger for the for­ma­tion of the chaot­ic ter­rain here at this lo­ca­tion is still un­clear to­day.
Hemispheric overview map of the Uzboi-Ladon-Morava outflow system with possible former water level
Hemi­spher­ic overview map of the Uzboi-Ladon-Mora­va out­flow sys­tem with pos­si­ble for­mer wa­ter lev­el
Image 3/7, Credit: NASA/JPL-Caltech/MOLA; FU Berlin – artist's impression

Hemispheric overview map of the Uzboi-Ladon-Morava outflow system with possible former water level

On this glob­al to­po­graph­ic map of Mars, depth con­tours and de­pres­sions are eas­i­ly recog­nised by their light blue colour­ing. In this artis­tic rep­re­sen­ta­tion, a pos­si­ble wa­ter lev­el that might have pre­vailed in the ULM out­flow sys­tem more than three bil­lion years ago has been shad­ed in dark blue. This makes it eas­i­er to imag­ine what this in­ter­con­nect­ed out­flow sys­tem of gi­gan­tic lakes and rivers might once have looked like. The names 'Hold­en Basin' and 'Lan­don Basin' (dashed cir­cles) are not of­fi­cial names en­dorsed by the In­ter­na­tion­al As­tro­nom­i­cal Union (IAU), but are used un­of­fi­cial­ly for these de­pres­sions.
Location of the Uzboi-Ladon-Morava system in the southern highlands of Mars
Lo­ca­tion of the Uzboi-Ladon-Mora­va sys­tem in the south­ern high­lands of Mars
Image 4/7, Credit: NASA/JPL-Caltech/MOLA; FU Berlin

Location of the Uzboi-Ladon-Morava system in the southern highlands of Mars

The ULM out­flow sys­tem ex­tends over more than 2000 kilo­me­tres from the south­ern high­lands of Mars to the north­ern low­lands. The HRSC cam­era on ESA's Mars Ex­press space­craft, op­er­at­ed by the Ger­man Aerospace Cen­ter (Deutsches Zen­trum für Luft- und Raum­fahrt; DLR), pho­tographed the long strip marked in this im­age on 24 April 2022. The im­ages and land­scapes pre­sent­ed here are lo­cat­ed in the small rect­an­gu­lar sec­tion. The name ‘Hold­en Basin’ is not an of­fi­cial name en­dorsed by the In­ter­na­tion­al As­tro­nom­i­cal Union (IAU), but is used un­of­fi­cial­ly for this de­pres­sion.
Perspective view of the southern edge of 'Holden Basin'
Per­spec­tive view of the south­ern edge of 'Hold­en Basin'
Image 5/7, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Perspective view of the southern edge of 'Holden Basin'

Sev­er­al small for­mer riv­er val­leys cut through the south­ern edge of the old im­pact basin, un­of­fi­cial­ly known as 'Hold­en Basin'. These rel­a­tive­ly small val­leys are up to 500 me­tres wide in places. Their en­trained sed­i­ment prob­a­bly con­tribut­ed to the fill­ing of the basin and helped form the large, flat plain that ad­joins the basin rim here. The im­pact crater on the right of the im­age cen­tre has a di­am­e­ter of ap­prox­i­mate­ly 5.5 kilo­me­tres.
Topographic map of 'Holden Basin' with chaotic terrain
To­po­graph­ic map of 'Hold­en Basin' with chaot­ic ter­rain
Image 6/7, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Topographic map of 'Holden Basin' with chaotic terrain

The DLR HRSC in­stru­ment on ESA's Mars Ex­press or­biter us­es nine sen­sors ar­ranged across the north-south flight di­rec­tion to record the sur­face of Mars from dif­fer­ent an­gles and with four colour chan­nels. Teams of sci­en­tists from the DLR In­sti­tute of Plan­e­tary Re­search and the Freie Uni­ver­sität Berlin use the four an­gled stereo chan­nels and the nadir chan­nel, the field of view of which is di­rect­ed per­pen­dic­u­lar to the Mar­tian sur­face, to com­pute dig­i­tal ter­rain mod­els that as­sign al­ti­tude in­for­ma­tion to each pix­el. The colour scale at the top right of the im­age shows the dif­fer­ences in al­ti­tude in the re­gion.The de­pres­sion is up to 2000 me­tres deep in some places, ex­act­ly where the re­gions of chaot­ic ter­rain are lo­cat­ed. In this colour-cod­ed im­age, the be­gin­ning of the Ladon Valles can be seen from the pur­ple struc­tures that cut through the north­east­ern rim of the basin. North is right in the im­age.
Anaglyph image of the 'Holden Basin'
Anaglyph im­age of the 'Hold­en Basin'
Image 7/7, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Anaglyph image of the 'Holden Basin'

Anaglyph im­ages can be gen­er­at­ed us­ing da­ta ac­quired by the nadir chan­nel (ori­ent­ed per­pen­dic­u­lar­ly to­wards the sur­face of Mars) of the DLR-op­er­at­ed HRSC cam­era sys­tem on ESA's Mars Ex­press space­craft and one of the four oblique stereo chan­nels. When used with red-blue or red-green glass­es, they pro­vide a three-di­men­sion­al view of the land­scape and give the view­er a com­pre­hen­si­ble im­pres­sion of the dif­fer­ences in al­ti­tude. For ex­am­ple, it is on­ly here that one can see how ma­jes­ti­cal­ly the south­ern slope of the basin (left in the pic­ture) ris­es above the flat plateau at the edge of the basin and how deeply the rugged ar­eas of the chaot­ic re­gions cut in­to the basin floor. North is to the right in the im­age.
  • On Mars, there are numerous so-called chaotic areas – a random accumulation of boulders of various sizes and mesa-like elevations. These landscapes do not exist on Earth.
  • They are formed when ice reservoirs in the subsurface melt and large amounts of water are suddenly released and run off. This causes the surface to collapse over the new cavities.
  • The area in the images lies in a vast valley system 8000 kilometres long.
  • The images were taken with the DLR High Resolution Stereo Camera (HRSC) on 24 April 2022 during Mars Express orbit 23,133 around Mars.
  • The image resolution is 19 metres per pixel.
  • Focus: Spaceflight, Solar System exploration, Mars, HRSC.

These images, acquired using with DLR High Resolution Stereo Camera (HRSC), reveal a chaotic region on our neighbouring planet. It is located near Holden Crater in the southern Martian highlands and is part of a vast valley system through which considerable masses of water once flowed in a northerly direction.

The HRSC has been mapping the Red Planet on board ESA's Mars Express spacecraft since 2004. 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 in Berlin-Adlershof. The data it acquires are very important for research into the geology and climate history of Mars.

Chaotic Terrain – a Martian speciality

In the centre of the HRSC images (1,2,6,7) lies a disordered accumulation of boulders of various sizes and mesa-like elevations. Such an area is known as chaotic terrain. On Mars, this type of landscape is quite common. It occurs when ice reservoirs in the subsurface melt, due to volcanically induced heat, for example, and considerable amounts of water are suddenly released and flow away. This causes the surface above the newly formed cavities to collapse and the landscape to fall in on itself. However, the exact trigger for the formation of the chaotic terrain at this location remains unclear. There is no comparable landscape formation on Earth.

The chaotic terrain is located at the lowest point of a large depression up to 2000 metres deep (clearly visible on the topographic map (image 6). It is also unofficially known as the 'Holden Basin', as the Holden impact crater occupies roughly a third of it. The Ladon Valley begins at the north-eastern edge of the depression, as can be seen particularly well at the bottom of the topographic map (north is to the right in the image). The eastern slope of the depression can be seen in the left half of the image. Here there are several, relatively ‘fresh’ valleys that flow into the basin, some of which are up to 500 metres wide.

Follow the water! – The Uzboi-Ladon-Morava outflow ystem

For the last two decades, NASA's exploration of Mars has been guided by the motto 'Follow the Water!'. The Holden Basin and the Holden Crater located there, named after the US-American astronomer Edward Singleton Holden (1846-1914), belong to the so-called Uzboi-Ladon-Morava system, or ULM system for short. This is an approximately 8000-kilometre-long drainage system consisting of a multitude of valleys and depressions through which water was transported from the southern Argyre Planitia to Chryse Planitia in the northern Martian lowlands. This is longer than the course of the Nile River, the longest flowing body of water on Earth. The overview map clearly shows how water flowed from the southern Martian highlands into the northern lowlands more than three billion years ago.

Hemispheric overview map of the Uzboi-Ladon-Morava outflow system with possible former water level
Hemispheric overview map of the Uzboi-Ladon-Morava outflow system with possible former water level
On this global topographic map of Mars, depth contours and depressions are easily recognised by their light blue colouring. In this artistic representation, a possible water level that might have prevailed in the ULM outflow system more than three billion years ago has been shaded in dark blue. This makes it easier to imagine what this interconnected outflow system of gigantic lakes and rivers might once have looked like. The names 'Holden Basin' and 'Landon Basin' (dashed circles) are not official names endorsed by the International Astronomical Union (IAU), but are used unofficially for these depressions.
Credit: NASA/JPL-Caltech/MOLA; FU Berlin – artist's impression

Prior to the impact that created the 140-kilometre-wide Holden Crater, the ULM outflow system consisted of a long and continuous series of channels and depressions that emerged from the Argyre Basin and flowed north through the Uzboi Valley into the depression that is now unofficially known as the Holden Basin. From there, it continued through the Ladon Valleys (Ladon Valles) into the, also unofficially named, 'Ladon Basin', which is also thought to represent a very large ancient impact basin (see the dashed lines in the global overview map). Eventually, the drainage continued northwards through the Morava Valles. It is assumed that even Ares Vallis was formed by outflows of the ULM system (see global overview map). The first mobile Mars robot, Sojourner, of the Mars Pathfinder mission landed and operated in Ares Vallis estuary exactly 25 years ago. The investigations in late summer 1997 revealed that episodic and enormous water masses flowing downhill with great energy had shaped the landscape there.

Taken together, the total area drained may have covered up to nine percent of the Martian surface. The impact that created Holden Crater most likely occurred during the Late Noachian (a period from approximately 3.85 to 3.7 billion years ago), after the main activity of the ULM system. The formation of Holden Crater disrupted the ULM drainage system, but the Uzboi valley to the south breached the crater walls, which were up to 900 metres high, and made Holden the terminal basin for the Uzboi and Nirgal valleys. A river delta formed at the confluence of Uzboi Vallis and the crater, providing irrefutable evidence that a lake formed in Holden Crater. A similar, quite well-known river delta can be found directly north of Holden, in the Eberswalde crater (marked on the hemispheric overview map). This bird-foot delta was once proposed as a landing site for the Mars Science Laboratory (MSL) mission, which included the Curiosity rover, but did not win the race against the other candidates.

Although there is no visible outflow valley at Holden, a collapse area can be seen on the east side of the crater. There is no evidence of significant post-impact outflow or throughflow, but some minor outflow may have occurred along the ULM system after Holden Crater was formed. Certainly, the floor of the basin where Holden Crater was formed was then backfilled with large amounts of ejecta.

The complex history of the ULM system coupled with the overprinting by impacts makes the region an interesting target for future exploration (as mentioned above, it has been discussed on and off as a highly interesting landing site for a quarter of a century). In addition, both Ladon Valles and Holden Crater in particular contain layered and clay mineral-rich sediments that could preserve traces of microbial life particularly well, making them potential targets in the search for ancient life on the Red Planet.

Image processing

The images shown here were created using data acquired by the High Resolution Stereo Camera (HRSC) on 24 April 2022 during orbit 23,133 of the Mars Express spacecraft around the Red Planet. The image resolution is approximately 19 metres per pixel. The centre of the images is located at approximately 329 degrees east and 25 degrees south. The colour view (image 1) was created using data from the nadir channel, the field of view of which is directed perpendicular to the Martian surface, and the colour channels of HRSC. The oblique perspective views (images 2 and 5) were computed using data from the stereo channels of HRSC. The anaglyph image (image 7) which gives a three-dimensional impression of the landscape when viewed with red-blue or red-green glasses, was created using data from the nadir channel and stereo channels. The colour-coded topographic view (image 6) 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 an equipotential surface of Mars (areoid). The systematic processing of the camera data was carried out at the DLR Institute of Planetary Research. Personnel in the Department of Planetary Sciences and Remote Sensing at the 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 (now Airbus), Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The science team, which is headed by Principal Investigator (PI) Thomas Roatsch, consists of 52 co-investigators from 34 institutions in 11 countries.

These high-resolution images and more images acquired by HRSC can be found in the Mars Express image gallery on flickr.

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    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
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