Post contributed by Alex Barrett, Dept. of Physical Sciences, Open University, UK.
The following images show the walls of a two kilometre diameter impact crater in Utopia Planitia on Mars. This region is part of the low lying Northern Plains which have generally flat topography. The main occurrences of steeper hill slopes in this region are impact craters such as the one illustrated below.
On Earth periglacial landscapes develop in permafrost regions, as a result of the repeated freezing and thawing of the upper layer of the ground over seasonal cycles. Consequently their presence on Mars would provide a geomorphic indicator for regions where water may have been thawing in the geologically recent past. Utopia Planitia is a leading candidate for possible periglacial environments on Mars and a variety of studies have focused on the this region (e.g. Soare et al. 2007; Lefort et al. 2009; Séjourné et al. 2011; Haltigin et al. 2014).
This site is interesting as it contains several landforms which appear morphologically similar to those found on hillsides in periglacial environments on Earth. Image one shows a series of lobate structures which have a similar morphology to terrestrial solifluction lobes (Matsuoka 2001). Several banks of lobes can be seen progressing down the hillside. Other instances of similar lobate features on Mars are documented by Johnsson et al. (2012).
On the left hand side of the image are several small lines of metre scale clasts. These run parallel to the direction of slope and may be analogous to the sorted stripes found on hill sides in the terrestrial arctic. Sorted patterned ground occurs over a variety of slopes but stripes are predominantly found in the steepest areas, while polygons and labyrinths of organised clasts occur on flatter ground (Kessler and Werner 2003). Thus the location of these features on a crater wall supports this hypothesis for their formation. Similar assemblages of clastic stripes and lobes have been observed across the northern plains, particularly at high northern latitudes (e.g. Gallagher et al. 2011).
The southern wall of the crater is not the only part of this landscape to exhibit features which may be related to the thaw of water. The northern wall lacks lobate features, but is instead dominated by several large gullies as shown in image three. These structures could also result from the thawing of liquid water, although on a much more dramatic scale (Soare et al. 2007; Aston et al. 2011).
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