April 28, 2016

A 'split' crater in Memnonia Fossae

The images presented here, acquired by the High Resolution Stereo Camera (HRSC) operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) on board the European Space Agency (ESA) Mars Express spacecraft, show part of the Memnonia Fossae region on Mars. This chain of faults is located to the west of the Tharsis volcanic region and north of Sirenum Fossae – another large system of rifts and faults similar to Memnonia Fossae. These features are all the result of tectonic stresses in the Martian crust and extend over 1600 kilometres in an east-west direction. Their origin is attributed to the bulging of the Tharsis volcanic region. They have been named the 'Rifts of Memnonia' after a temple complex in the ancient Egyptian city of Thebes.

The Tharsis region on Mars has been uplifted like a bowl the size of Europe that bulges four to five kilometres upwards. Some of the largest volcanoes in the Solar System can be found here. These include Olympus Mons (22 kilometres high) and the three Tharsis volcanoes of Ascraeus Mons (15 kilometres), Pavonis Mons (8 kilometres) and Arsia Mons (11 kilometres). The exact origins of this bulging mechanism are not yet understood. However, it is very likely that large quantities of magma fed from the Martian mantle over billions of years have exerted pressure on the crust from below. Low-viscosity lava then flowed across the region from the volcanic cones and fissures and added layer upon layer of volcanic rock over large areas.

Martian crust under stress

The great weight of these additional layers of dense, iron-rich volcanic rock on the surface caused immense pressure. At the same time, the magma bubbles rising upwards from the Martian mantle were generating pressure from underneath. The Martian crust was therefore exposed to massive expansion stresses in the Tharsis region. This is evident in numerous tectonic rifts, faults and cracks in the bulging Tharsis shield and in the peripheral zones of this region (see also the image publication on Phoenicis Lacus dated 12 November 2010). The majority of these fracture zones extend outwards from the Tharsis region in a star shape and cut through the ancient southern Martian highlands.

This type of expansion stress has given rise to a landscape pattern typical of tectonically stressed regions, known in geological terms as a 'horst and graben structure'. Because of the pressure on the crust, huge blocks of terrain between two fault lines running in parallel collapsed hundreds or even thousands of metres downwards and created the tectonic 'graben', bordered on each side by the 'horsts' that remained standing.

More about volcanism on Mars:

Volcanism on Mars
Video Volcanism on Mars


One very prominent graben is visible in the HRSC images, in an ancient impact crater with an already heavily eroded rim. It has a diameter of 52 kilometres and lies around 70 kilometres northeast of Dejnev Crater. This still unnamed crater is intersected by a graben 1.5 kilometres wide. Additional grabens can be seen to the north and south of the crater that appear to be split in some places and continue with a lateral offset.

Volcanism and wind erosion characterise the landscape today

Also prominent are a number of striking mesas that project several hundred metres above the level crater floor. The larger ones are up to 2.5 kilometres across. Their arrangement is somewhat reminiscent of many other 'chaotic terrains' on Mars – regions characterised by intense erosion. However, this small chaotic region, which appears to be the result of the crater being refilled with lava that presumably came from the deep rift, stabilised and hence protected the mesas from further erosion.

The many wind alleys created by wind erosion – referred to as yardangs – that can be found on the flat floor between the mesas and around the graben (especially in the western part of the crater floor) indicate that a less erosion-resistant material once filled the crater. This might be material that the wind carried in – such as sand or dust – or sediments that were transported and deposited here by water.

More about 'yardangs':

The weather and climate on Mars
Video on the weather and climate on Mars


  • Image processing

    The High Resolution Stereo Camera (HRSC) acquired these images during Mars Express Orbit 14,689 on 1 August 2015. The region lies at 22 degrees south and 197 degrees east. The image resolution is about 14 metres per pixel. The colour plan view (image 1) was acquired using the nadir channel of the HRSC, which is directed vertically down onto the surface of Mars; the perspective oblique view (image 2) was computed using data acquired by the HRSC stereo channels. The anaglyph image (image 3), which creates a three-dimensional impression of the landscape when viewed with red/blue or red/green glasses, was derived from the nadir channel and one stereo channel. The colour-coded aerial view (image 5) is based on a digital terrain model of the region, from which the topography of the landscape can be derived.

  • The HRSC experiment

    The High Resolution Stereo Camera (HRSC) was developed at DLR and built in collaboration with industrial partners (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.

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Elke Heinemann

Digital Communications
German Aerospace Center (DLR)
Corporate Communications
Linder Höhe, 51147 Cologne
Tel: +49 2203 601-1852

Prof. Dr. Ralf Jaumann

Freie Universität Berlin
Institute of Geological Sciences
Planetary Sciences and Remote Sensing
Malteserstr. 74-100, 12249 Berlin

Ulrich Köhler

German Aerospace Center (DLR)
Institute of Planetary Research
Rutherfordstraße 2, 12489 Berlin