Research Groups

Planetary Imaging Group (PIG)

Mars desiccation experiment

Polygonal cracks and desiccation

The desiccation of water-rich soils and sediments on Mars has probably played an important role in shaping the Martian landscape. Data from HiRISE from various regions on Mars suggests that polygonal cracks, which can be interpreted as direct evidence of desiccation, are much more common than previously thought (Figure below).

Desiccation polygons
Desiccation polygons on Mars range from hundreds of metres (a; HiRISE image) to tens of centimetres (b; image of the Opportunity rover) in size. (c): Global map of desiccation cracks on Mars from one of our recent studies. Colors denote different geological settings.

For example, polygonal cracks with various scales have been reported in many impact craters at all latitudes (El-Maarry et al., 2010), in putative chloride-rich terrains in the southern mid-latitudes (Osterloo et al., 2008, 2010), in regions that display spectral signatures of clay minerals (e.g., Wray et al., 2008), and in the Meridiani plains as imaged by the MER Opportunity (Watters and Squyres, 2012). El-Maarry et al. (2010) developed an analytical model that suggested that the size of the polygonal cracks and their geographical location can be used to distinguish between polygonal cracks created by desiccation and those created by thermal contraction (i.e., periglacial cracks).

polygonal patterns
Variation in size of polygonal patterns with thickness (D) of desiccating material. Polygon size (i.e.. crack separation) is directly dependent on the thickness of the drying soil. The three figures show patterns in lab desiccation experiments carried out in our labs using a clay-rich soil.

We have recently completed a global investigation of desiccation cracks that are associated with chloride-bearing terrains (El-Maarry et al., submitted) and smectite-rich deposits in general (El-Maarry et al., in preparation). The latest study (i.e., paper currently in preparation) represents a review of desiccation processes on Mars from mapping, modeling, field studies, and experiments on analog soils and contains the first ever compiled map of desiccation features on the surface of Mars. Our work shows that desiccation features are more common on the surface of Mars than previously thought, yet is confined to the Noachian-aged terrains. This work has profound implications for the Noachian climate, the history of liquid water on Mars, and possibly landing-site-selection for future in-situ investigations.