26. October 2022
Mars Express mission

A com­plex mar­tian land­scape in the 'Land of the Sirens'

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Vertical plan view in true colour
Ver­ti­cal plan view in true colour
Image 1/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Vertical plan view in true colour

An area ap­prox­i­mate­ly 220 by 70 kilo­me­tres south­east of Pick­er­ing Crater (out­side the scene) in the Ter­ra Sirenum re­gion shows many land­scapes that are typ­i­cal of the an­cient mar­tian high­lands. These in­clude fea­tures that are over three bil­lion years old and thus heav­i­ly erod­ed, and a sed­i­ment-filled im­pact crater mea­sur­ing 115 kilo­me­tres across. Al­so clear­ly vis­i­ble are val­leys formed by run­ning wa­ter and de­bris-laden rock glaciers slow­ly creep­ing over the sur­face, so­lid­i­fied and su­per­im­posed la­va flows, tec­ton­ic fault struc-tures and fea­tures cre­at­ed more re­cent­ly by wind ero­sion. North is to the right of the im-age.
Oblique view of a 20-kilometre-wide crater
Oblique view of a 20-kilo­me­tre-wide crater
Image 2/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Oblique view of a 20-kilometre-wide crater

This crater is lo­cat­ed to the north of the large crater in the scene ob­served by the HRSC Mars cam­era. The dif­fer­ence in al­ti­tude from the high­est point of the crater rim to the low­est point is al­most 1500 me­tres. To the north, the crater rim has ex­pe­ri­enced much stronger ero­sion, due to ma­te­ri­al falling from the rim of the larg­er crater in the back-ground, which is lo­cat­ed a fur­ther 1000 me­tres above the rim of the small­er crater. With­in the crater are de­posits in­ter­spersed with me­an­der­ing lines – the rem­nants of glaciers that once flowed in­to the crater and met at its cen­tre. They are re­ferred to as lo­bate crater fill – glaciers whose ice flow is cov­ered by rock de­bris, and are al­so known as rock glaciers.
Regional overview map of Terra Sirenum
Re­gion­al overview map of Ter­ra Sirenum
Image 3/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Regional overview map of Terra Sirenum

The sec­tion of the glob­al to­po­graph­ic map of Mars marks the lo­ca­tion of the re­gion of the mar­tian high­lands shown in this im­age re­lease. It is lo­cat­ed south­east of the heav­i­ly erod­ed, 115-kilo­me­tre-wide Pick­er­ing Crater. The long stripe framed in white out­lines the en­tire scene cap­tured by the HRSC on Mars Ex­press on 5 April 2022, while the small rec-tan­gle de­notes the im­ages shown here.
Topographic image map
To­po­graph­ic im­age map
Image 4/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Topographic image map

DLR's High Res­o­lu­tion Stereo Cam­era on board 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. From the two stereo chan­nels point­ing for­wards and the two stereo chan­nels point­ing back­wards at an an­gle to the sur­face and the nadir chan­nel point­ing per­pen­dic­u­lar­ly to Mars, teams of sci­en­tists at the DLR In­sti­tute of Plan­e­tary Re­search and the Free Uni­ver­si­ty of Berlin cal­cu­late dig­i­tal ter­rain mod­els that as­sign el­e­va­tion in­for­ma­tion to each pix­el. The colour scale at the top right of the im­age shows the dif­fer­ences in al­ti­tude in the re­gion. In the scene shown here, the change in al­ti­tude from the low­est ar­eas, shown in blue, to the high­est high­land re­gions (red and pink), is ap­prox­i­mate­ly 4500 me­tres.
3D view of the region southeast of Pickering Crater
3D view of the re­gion south­east of Pick­er­ing Crater
Image 5/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

3D view of the region southeast of Pickering Crater

Anaglyph im­ages can be gen­er­at­ed us­ing da­ta ac­quired by the nadir chan­nel (ori­ent­ed per­pen­dic­u­lar­ly to­wards the sur­face of Mars) of the DLR-op­er­at­ed HRSC cam¬era 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. Viewed in this way, it is strik­ing how the dif­fer­ent craters re­sult­ing from as­ter­oid im­pacts ap­pear to have been punched in­to the mar­tian high­lands. The 3D glass­es make the 4500-me­tre dif­fer­ence in al­ti­tude ap­pear steep­er than in re­al­i­ty.
Overview of the highland region
Overview of the high­land re­gion
Image 6/6, Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO

Overview of the highland region

This area in the an­cient south­ern mar­tian high­lands, mea­sur­ing 220 by 70 kilo­me­tres, was im­aged by the DLR HRSC cam­era sys­tem on ESA's Mars Ex­press or­biter on 5 April 2022 and shows sev­er­al ge­o­log­i­cal land­forms that are de­scribed in the text that ac­com­pa­nies these im­ages. From left to right: a riv­er val­ley carved in­to the high­lands by wa­ter flow­ing down-hill ('large val­ley'); a tec­ton­ic rift or large frac­ture; 'wind al­leys' carved in­to the land­scape by dust and sand ('wind-erod­ed sur­face'); lo­bate crater fill ('crater fill') left by rock glaciers; a crater filled with thin, so­lid­i­fied la­va ('la­va-filled crater'); a dense net­work of val­leys erod­ed in­to the land­scape by run-off rain­wa­ter, snow and ice ('den­drit­ic val­leys'); and wrin­kle ridges of la­va sur­face ma­te­ri­al that has been pushed to­geth­er.
  • Image data from DLR's High Resolution Stereo Camera (HRSC) on board ESA's Mars Express mission show a diverse region southeast of the Pickering crater in Terra Sirenum.
  • In the images, a crater about 70 kilometres in diameter dominates the scene.
  • The eastern crater floor features interesting landscape forms that are the re-sult of wind erosion.
  • In the smaller impact crater in the northern part of the large crater, you can see deposits criss-crossed with lines – the remains of former glaciers that flowed down the crater slopes.
  • A different appearance can be seen in an impact crater further north: here the surface indicates that it was filled with thin lava.

Image data from the High Resolution Stereo Camera (HRSC) operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) aboard the ESA Mars Express mission show a diverse region southeast of the Pickering Crater in Terra Sirenum on the boundary with Daedalia Planum. Terra Sirenum (Land of the Sirens) is a vast highland region over 3.5 billion years old in the southwest of the Tharsis volcanic region. Here – and in the southern highlands in general – there are more impact craters on the surface than in the northern lowlands.

The large variety of surface structures can be attributed to a number of processes. The HRSC images acquired on 5 April 2022 (orbit 23,067) tell a complex geological story: the ground resolution of the image data is approximately 15 metres per pixel. The centre of the image is at 232 degrees east and 38 degrees south. Although Pickering, a prominent crater, is not visible in the HRSC images, is has been included in the regional overview map, in the northwest area of the section shown. This 115-kilometre-diameter crater is rather unusual among Mars craters, as it was named after three people: the US astronomer and physicist Edward Charles Pickering (1846–1919), his brother William Henry Pickering (1858–1938), also an astronomer, and the New Zealand-born rocket engineer and former director of NASA's Jet Pro-pulsion Laboratory, William Hayward Pickering (1910–2004).

A nameless crater approximately 70 kilometres across dominates the landscape in the images displayed. A valley measuring up to 1.8 kilometres across snakes across the landscape in the bottom left, southeast of the crater. Meltwater from the sur-rounding highlands could have flowed into the valley, having run into the depression beneath the crater basin (at the bottom edge of the image). Just 10 kilometres to the north of the valley is fracture that runs almost parallel to it and cuts through the southern edge of the basin. Large, canal-like fractures like this are described as tec-tonic grabens. They occur in regions that are subject to tectonic expansion, where the bedrock is pulled apart by stresses in the brittle crust, so that it cracks along the zone of weakness and drops downward between the two fault lines. These features, which are typical of tectonic grabens, occur in many locations on Mars, such as the south-eastern grabens of Icaria Fossae.

Surface structures indicate ice streams

A large impact crater fills the centre of the image. The traces of erosion here indicate that it is extremely old. At its heart is a region that is dark in places. The dark colour-ing is due to a thin layer of volcanic sands that have been carried into the crater by the wind and deposited there. The floor of the crater is very flat and has long ceased to be bowl-shaped, as would have been typical of the indentation made by a 5–10-kilometre asteroid shortly after it hit the planet. This infilling is another indication of the crater's considerable age. Intriguing landscape features due to wind erosion can be seen at the lower (eastern) edge of the crater floor. It has countless small hills that the wind has scoured out of the rock, along with a few elongated ridges all run-ning in the same direction. The latter are called yardangs. The wind, which is some-times very strong on Mars and blows in one direction for long periods of time, scours 'wind alleys' into the rock due to the dust and sand particles it carries. These indicate the dominant wind direction. The long, thin structure than runs transversely is highly likely to be a former valley filled with erosion-resistant material.

Lava-filled craters and branching valleys

A small impact crater measuring just 20 kilometres across is located in the northern (right-hand) part of the large crater. Deposits cut through by lines can be seen within the crater. These are the remains of former glaciers that flowed down the crater slopes and met in the middle. They are marked as 'lobate crater fill' in the annotated plan view. The surface in the immediate vicinity to the north and in the small neighbouring craters is flat and appears smooth, resembling glaciers on Earth where the ice stream is covered by rock debris. In glaciology, such ice streams are called rock glaciers. These flow structures are formed when a mixture of debris and ice flows downhill from a glacier, and the debris then traces the movements of the ice flow, which becomes malleable under the weight of the rock and the pressure exerted by own weight. Such flow structures are clearly visible in the perspective view of the crater.

An old impact crater further north – labelled 'lava-filled crater' in the plan view, has a completely different appearance. Here, the surface suggests a filling of thin lava that has flowed into the bowl-shaped crater structure. The surface pattern differs from the 'periglacial' features typical of polar landscapes – the processes and landforms associated with cold regions that are not covered in ice. Adjacent to the north is a large network of heavily eroded, branching valleys. These ‘dendritic’ valley patterns are typically formed on Earth by the run-off of surface rainwater, so researchers as-sume that these valleys were formed relatively early in martian history by atmospher-ic precipitation (probably snow rather than rain).

Finally, in the bottom right – northeast on the top view – is a large lava field. Wrinkle ridges are visible here. These are formed when, for instance, layered surface mate-rial (in this case, a soft, pliable layer of lava) is compressed by tectonic forces, and its surface area is reduced. These ridges are very typical of lava deposits on Mars and on the Moon. The steeper side of the ridges, which ascend several dozen me-tres, marks their front side, where the material arched upwards and over the 'over-run' lava layer. These landforms all demonstrate the complex history and formation of Mars in a single image.

Image processing

The images shown here were created using data acquired by the High Resolution Stereo Camera (HRSC) on 5 April 2022 during orbit 23,067 of the Mars Express spacecraft around the Red Planet. The image resolution is approximately 15 metres per pixel. The centre of the images is located at approximately 232 degrees east and 38 degrees south. The colour view 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 were computed using data from the stereo 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 created using data from the nadir channel and stereo channels. 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 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 at the German Aerospace Center (DLR) and built in cooperation with industrial partners (EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). The science team, led by Principal Investigator (PI) Dr Thomas Roatsch of the DLR Institute of Planetary Research, consists of 52 co-investigators from 34 institutions and 11 nations. The camera is operated by the DLR Institute of Planetary Research in Berlin-Adlershof.

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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