A crater with a central depression in Noachis Terra
June 2, 2016
A crater with a central depression in Noachis Terra
Colour plan view of a crater about 50 kilometres wide in Noachis Terra
The HRSC camera system on board Mars Express captures simultaneous images of the surface of Mars in high resolution, in 3D and with four colour filters in visible light for the colours blue, green and red, as well as in the near-infrared wavelengths. This enhanced contrast true-colour representation, created from the nadir channel oriented vertically towards Mars and the colour channels, enables the material differences in the otherwise very monotonous surface of Mars to be clearly distinguished. Particularly striking is a small field of black dunes inside the crater, which are probably made of dust and sand from eroded volcanic rocks that the wind has transported to the interior of the crater.
Traces of erosion in an unnamed crater in Terra Noachis
A distinctive edge in a layer of rock in a crater to the south-east of the Serpentis Terra in the Highlands of Noachis Terra shows the thickness of the blanket of ejecta deposited during the formation of the crater by an asteroid impact in the immediate vicinity. The deposits once scattered across the entire area were presumably kept in the immediate vicinity of the approximately 50-kilometre-wide and four-kilometre-deep crater before the erosion. The loose material was possibly solidified in the vicinity of the crater by the impact and the crater ejecta lay over it like a blanket.
Topographic map of the region south-east of Serpentis Terra
The image shown here is a part of the Noachis Terra region in the southern highlands of Mars. The crater in the small rectangle has a diameter of about 50 kilometres. The image strips were acquired on 29 July 2015 by the HRSC camera system on board the ESA Mars Express spacecraft during orbit 14,680 from an altitude of about 330 kilometres from the surface of Mars.
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 a part of the Noachis Terra region in the southern highlands of Mars. The crater shown is approximately four kilometres deep and has a diameter of roughly 50 kilometres. It has a central depression and drainage valleys at the crater rim. These structures indicate the presence of ice in the subsurface. An unusual dune field reveals that, at present, atmospheric processes shape the landscape.
The, until now unnamed, crater is located southwest of Mare Serpentis, the 'Sea of Serpents', an albedo structure in the Noachis Terra region. Albedo, derived from the Latin word 'alba' for white or bright, is a measure of the reflectivity of surfaces. Dark or rough surfaces reflect less of the incident light than bright or smooth surfaces. Before the space age, the regions of the Moon and Mars with very low or very high albedo values originating from darker or lighter surfaces were identified this way when they were explored by telescope and were then, for example – as in the case of Mare Serpentis – named after seas or lakes because they have a similar albedo.
Approximately 3.9 billion years old, Noachis Terra is amongst the oldest regions of Mars. The Noachian geological era of Mars – covering the period from approximately 4.1 to 3.7 billion years before our time – is also named after this area (Noah's land). Noachis Terra is located in the southern highlands of Mars, west of the large impact basin Hellas Planitia. Numerous impact craters have been formed, altered and degraded in this region over billions of years.
Subsurface ice and rock glaciers in Noachis Terra
The unnamed crater in the images shows a central depression. This type of impact crater is called a 'central pit crater'. They are commonly found on Mars but also occur on Jupiter's moons Ganymede and Callisto. Such a depression in the centre of the crater probably arises during or after impact by the vaporisation of underground ice which then, due to the sudden explosive expansion of the gas, literally tears a hole in the young crater depression.
The remains of an elevated plateau can be seen to the south and east of the crater. In the past the stacked deposits building the plateau were presumably distributed more uniformly over the area. The loose material was possibly solidified in the vicinity of the crater by the impact and the crater ejecta lay over it like a blanket.
Numerous small valleys and valley networks can be seen on the inner crater rim. Investigations of these valleys and gullies suggest that they were carved out both by meltwater and ice-rich debris flowing downslope. From time to time, the ground ice on the sun-exposed slopes in the interior of the crater melted, and the resulting water flowed towards the centre of the crater. The interior of the valleys is filled with ice-rich deposits, referred to as 'lineated valley fill'.
Image processing and the HRSC experiment on Mars Express
The High Resolution Stereo Camera (HRSC) acquired these images during Mars Express Orbit 14,680 on 29 July 2015. The centre of the image lies at 37 degrees east and 35 degrees south. The image resolution is about 14 metres per pixel. The colour plan view 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.
