With a length of 600 kilometres and a depth of up to two kilometres, Mawrth Vallis is one of the biggest valleys on Mars and a possible landing site for the ESA ExoMars and NASA Mars 2020 missions. It is entrenched in the Arabia Terra highland, which is more than four billion years old, and ends in the great Chryse Planitia lowland region.
The image shown in this article covers an area of around 330,000 square kilometres on the transition from the southern Martian highlands to the northern Martian lowlands. Mawrth Vallis is at the centre of the image. The image shows a bird’s eye view of the region – the perspective from which the High Resolution Stereo Camera (HRSC) on board the European Mars Express spacecraft has been observing the surface of Mars since 2004. It creates image strips that are around 200 to 500 kilometres wide and several hundred to thousands of kilometres long (depending on the altitude of Mars Express). This view of the region around Mawrth Vallis was made possible using a mosaic of nine individual HRSC images. The camera is operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).
It once was a potentially habitable place
Light and dark deposits can be seen in and around the Mawrth Vallis outflow valley. The light deposits are layered and are one of the biggest occurrences of clay minerals (sheet silicates) on Mars. In many places, these clays are covered with a layer of dark rock. The almost black deposits in this region are remains of ancient volcanic ash that have piled up into imposing dunes in many places (primarily in impact craters). Investigations using the OMEGA instrument on Mars Express have led to a better understanding of the clay minerals, which may be rich in either iron and magnesium or aluminium. The differing composition of the clay minerals indicates different ages and levels of erosion. Deposits containing sulphates have also been found on the valley floor of Mawrth Vallis, which in turn point to another formation environment.
Sheet silicates on Mars are a clear indication of the effect of liquid water on the surface. Furthermore, they point to neutral environmental conditions – another sign that habitable (life-supporting) conditions may have once been predominant here on Mars. The water that once flowed through the Mawrth Vallis valley was probably present on the surface until approximately 3.6 billion years ago. It is even possible that traces of life persist in the clay deposits, protected from radiation and erosion by the dark, superposing layer. For this reason, astrobiologists are very interested in this Martian region.