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Cascading dunes in a martian crater

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Posted May 15, 2014

A new mosaic from ESA’s Mars Express shows a swirling field of dark dunes cascading into sunken pits within a large impact crater.

The mosaic was created from two images taken on 7 December 2005 and 9 January 2014, and focuses on the 108 km-wide Rabe crater. The region is 320 km to the west of the large Hellas impact basin, about halfway between the planet’s equator and south pole.

Rabe Crater is a 108 km-wide impact crater with an intricately shaped dune field. The dune material likely comprises locally eroded sediments that have been shaped by prevailing winds. Other smaller craters in the region also contain these dark deposits. One relatively young and deep crater can be seen in the upper left; as well as the dark material, channels and grooves are clearly visible in its crater walls. The images used for this mosaic were taken by the High Resolution Stereo Camera on ESA’s Mars Express on 7 December 2005 (orbit 2441) and 9 January 2014 (orbit 12736). The scene is located at 35°E/44°S, about 320 km west of the giant Hellas impact basin in the southern highlands of Mars. The image resolution is about 15 m per pixel. Copyright ESA/DLR/FU Berlin

Rabe Crater is a 108 km-wide impact crater with an intricately shaped dune field. The dune material likely comprises locally eroded sediments that have been shaped by prevailing winds. Other smaller craters in the region also contain these dark deposits. One relatively young and deep crater can be seen in the upper left; as well as the dark material, channels and grooves are clearly visible in its crater walls. The images used for this mosaic were taken by the High Resolution Stereo Camera on ESA’s Mars Express on 7 December 2005 (orbit 2441) and 9 January 2014 (orbit 12736). The scene is located at 35°E/44°S, about 320 km west of the giant Hellas impact basin in the southern highlands of Mars. The image resolution is about 15 m per pixel. Copyright ESA/DLR/FU Berlin

Wind-sculpted dunes and impact craters are common features on Mars but here we can see them combined, creating a stunning vista.

Rabe crater has an interesting topography: its flat floor has a number of smaller craters and large sunken pits within it. The bulk of the dune material sits atop the flat remnant of the original crater floor, but then some of it spills dramatically down into the pits below.

Map showing the 108 km-wide Rabe crater and its surroundings. It is located about 320 km to the west of the large Hellas impact basin, about halfway between the planet’s equator and south pole, at 35°E/44°S. Rabe crater was imaged by Mars Express in two parts, on 7 December 2005 (orbit 2441) and 9 January 2014 (orbit 12736), as outlined on the map. Copyright NASA MGS MOLA Science Team

Map showing the 108 km-wide Rabe crater and its surroundings. It is located about 320 km to the west of the large Hellas impact basin, about halfway between the planet’s equator and south pole, at 35°E/44°S. Rabe crater was imaged by Mars Express in two parts, on 7 December 2005 (orbit 2441) and 9 January 2014 (orbit 12736), as outlined on the map. Copyright NASA MGS MOLA Science Team

The dunes stand some 150-200 m tall and their swirling patterns indicate the prevailing direction of the winds that have whipped across the crater over time.

The dunes are made of basaltic material, a common volcanic rock that was deposited widely across Mars in the past. In the region shown here, it was subsequently covered over by other layers of material, uncovered by erosion within the crater itself.

Rabe Crater is a 108 km-wide impact crater with an intricately shaped dune field. The dune material likely comprises locally eroded sediments that have been shaped by prevailing winds. Other smaller craters in the region also contain these dark deposits. One relatively young and deep crater can be seen in the upper left; as well as the dark material, channels and grooves are clearly visible in its crater walls. Copyright ESA/DLR/FU Berlin

Rabe Crater is a 108 km-wide impact crater with an intricately shaped dune field. The dune material likely comprises locally eroded sediments that have been shaped by prevailing winds. Other smaller craters in the region also contain these dark deposits. One relatively young and deep crater can be seen in the upper left; as well as the dark material, channels and grooves are clearly visible in its crater walls. Copyright ESA/DLR/FU Berlin

Zooming in on the western (top in the main colour image) portion of the crater reveals distinct layers of dark material exposed in the crater walls. One possible interpretation is that the impact crater punched through the top surface to reveal these otherwise hidden layers. Over time, this material has been eroded and swept up by wind to form the dunes seen towards the centre of the crater.

Colour-coded topography map of Rabe crater and its immediate surroundings. White and red show the highest terrains, while blue and purple show the deepest. The image is based on a digital terrain model of the region, from which the topography of the landscape has been derived. Copyright ESA/DLR/FU Berlin

Colour-coded topography map of Rabe crater and its immediate surroundings. White and red show the highest terrains, while blue and purple show the deepest. The image is based on a digital terrain model of the region, from which the topography of the landscape has been derived. Copyright ESA/DLR/FU Berlin

Similar dark material can also be seen in several of the smaller craters surrounding Rabe, with streaks staining the surface in between, most notably in the left-hand side of the image above. It is possible that some of the dune material was lifted out of Rabe by strong winds and spread locally.

Data from the nadir channel and one stereo channel of the High Resolution Stereo Camera on Mars Express have been combined to produce this anaglyph 3D image, which can be viewed using stereoscopic glasses with red–green or red–blue filters. The image focuses on Rabe crater and its intricate dune field, material that has been shaped by prevailing winds. The image was created using data acquired with the High Resolution Stereo Camera on Mars Express on 7 December 2005 (orbit 2441) and 9 January 2014 (orbit 12736).  The scene is located at 35°E/44°S, about 320 km west of the giant Hellas impact basin in the southern highlands of Mars. The image resolution is about 15 m per pixel.  Copyright ESA/DLR/FU Berlin

Data from the nadir channel and one stereo channel of the High Resolution Stereo Camera on Mars Express have been combined to produce this anaglyph 3D image, which can be viewed using stereoscopic glasses with red–green or red–blue filters. The image focuses on Rabe crater and its intricate dune field, material that has been shaped by prevailing winds. The image was created using data acquired with the High Resolution Stereo Camera on Mars Express on 7 December 2005 (orbit 2441) and 9 January 2014 (orbit 12736). The scene is located at 35°E/44°S, about 320 km west of the giant Hellas impact basin in the southern highlands of Mars. The image resolution is about 15 m per pixel. Copyright ESA/DLR/FU Berlin

Other nearby craters look degraded, their once-distinct rims and internal features crumbling over time. This ‘terrain softening’ process is often associated with the presence of ice just below the surface: this can facilitate the slow and steady creep of material downslope, resulting in a smooth appearance.

Material deposited from the atmosphere, perhaps during sand storms, can also contribute to an apparent softening of features over time.

By contrast, one crater to the upper left of Rabe in the main colour, topography and 3D images shown here retains a sharper appearance. A closer examination of this relatively deep crater reveals fresh-looking channels and grooves in the crater walls.

Grooves like these are often associated with erosion by liquid water but, regardless of their formation history, they can also expose underlying layers, such as the dark material common to this region. Furthermore, a dense patch of this material is seen concentrated in the deepest part of the crater floor.

Impact craters like Rabe offer a window into the past by exposing ancient rocks that would otherwise remain hidden from view. Meanwhile, the dunes show the important continuing role played by wind in shaping the martian landscape.

Source: ESA

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