October 13, 2016

Mars – the dichotomous planet

These images, 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 Mars Express spacecraft, show structures that formed as a result of glacial activity in the Colles Nili region. The 'Hills of the Nile' lie directly on the Martian dichotomy – the boundary that separates the northern lowlands from the southern highlands.

The topographic division (Greek: dichotomy) into a northern area with lowlands and the older, southern highlands with numerous impact craters represents one of the most striking features of Earth's planetary neighbour. The cause of this has not yet been determined. Some scientists believe it is possible that the northern hemisphere of Mars was struck by a large asteroid more than four billion years ago, which acted like a 'grazing shot' that caused several kilometres of the young rock crust to be 'shaved off'. In many areas, the dichotomy boundary consists of a several kilometre-high escarpment, which marks a topographical difference between the highlands of the southern hemisphere and the low-lying northern hemisphere of Mars.

Glaciers were active at the dichotomy boundary

The Colles Nili region is located directly at the foot of the dichotomy escarpment and, amidst smooth terrain, contains several 1000 to 2000 metre high mountains that are probably the heavily eroded remains of the adjoining ancient highlands in the south. The hills are distributed across the landscape like inselbergs or 'escarpment outliers' and are surrounded by smooth, undulating deposits, known as lobate debris aprons. These are streams of rock debris and ice that moved downhill, flowing around obstacles in the landscape before coming to a standstill. In addition, deposits can be seen between the hills, which form a linear pattern on the surface and are known as lineated valley fills. These features form when masses of rock, ice and dust slowly slide down opposing slopes, meet on the valley floor and overlap.

It is likely that both lobate debris aprons and lineated valley fills form from debris-covered ice flows known as rock glaciers, and they occur along the entire Martian dichotomy boundary. These glacial deposits may have formed through the collapse of a regional, retreating ice cover, which was then increasingly covered by rock debris sliding onto the ice laterally. There may have been several episodes of glacial activity in this region over the last hundreds of millions of years. The dark material covering the hills and plains in some places is sand of volcanic origin, which can pile up to form dunes such as those within the large impact crater, for example.

  • Image processing

    The data for the images was acquired by the HRSC during Mars Express orbit 15,727 on 29 May 2016. The image resolution is 15 metres per pixel. The centre of the images is at approximately 60 degrees east and 36 degrees north. The colour plan view was created using data from the nadir channel, which is oriented perpendicular to the surface of Mars, and the colour channels. The oblique perspective view was derived from data acquired by the stereo channels. The anaglyph, which gives a three-dimensional impression of the landscape when viewed with red-blue or red-green glasses, was produced using data from the nadir channel and one stereo channel. The colour-coded map is based on a digital terrain model (DTM) of the region, from which the topography of the landscape can be derived.

  • The HRSC experiment

    The High Resolution Stereo Camera was developed at 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 over 40 co-investigators from 33 institutions and ten countries. The camera is operated by the DLR Institute of Planetary Research in Berlin-Adlershof. The images shown here were generated by the Institute of Geological Sciences at FU Berlin in conjunction with the DLR Institute of Planetary Research in Berlin.

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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