Thermal contraction crack polygons on Mars: Classification, distribution, and climate implications from HiRISE observations

Abstract

Documenting the morphology and distribution of polygonally patterned ground on Mars is critical for understanding the age and origin of the Martian latitude‐dependent mantle. Polygonally patterned ground on Mars is analyzed using High Resolution Imaging Science Experiment image data in order to document the variation of polygon morphology within latitude bands 30–80° in both northern and southern hemispheres. Small‐scale (<∼25 m diameter) polygons are classified on the basis of morphological characteristics into seven groups, which are present in both northern and southern hemispheres. Polygon morphology is shown to be consistent with thermal contraction cracking of an ice‐rich mantling unit, consistent with observations of sediment wedge thermal contraction crack polygons forming in ice‐cemented sediment at the Phoenix landing site. Polygon groups are distributed symmetrically in both northern and southern hemispheres, suggesting strong climate controls on polygon morphology. Northern hemisphere polygonally patterned surfaces are found to decrease in age from low to high latitude, spanning surface ages from ∼1 to <0.1 Ma, suggesting more recent deposition of ice‐rich material at high latitudes than at low latitudes. Six of the seven classes of polygons are interpreted to be capable of forming because of the combined effects of thermal contraction cracking and differential sublimation, suggesting that sublimation and sand wedge polygons dominate Martian high latitudes. Gully polygon systems present at midlatitudes suggest that small amounts of liquid water may have been involved in thermal contraction crack polygon processes, producing composite wedge polygons. No evidence is found for the presence of pervasive small‐scale ice wedge polygons.

Polygon pattern geomorphometry on Svalbard (Norway) and western Utopia Planitia (Mars) using high-resolution stereo remote-sensing data

“…By comparing diverse geomorphometric criteria, several points are discussed by analogy (Table 5). The polygonal structures of western UP belong to the category of smallscale patterns, according to classifications of the wide variety of polygonal structures on Mars (e.g., Mangold, 2005;Levy et al, 2009a). Besides the analogy to the terrestrial polygons, the thermal contraction cracking origin is more likely than other origins such as desiccation cracking, as the landscape assemblage in the region points to a dry origin and there is no evidence of former lakes (Ulrich et al, 2010) or water-rich sediments essential for desiccation (El Maarry et al, 2010).…”

“…The small-scale polygons within the scalloped depressions were classified as mixed-center polygons by Levy et al (2009a). Three different types of polygonal networks were identified (UP2, UP3, and UP4) (Table 3) in connection with the internal morphology of the scalloped depression (Fig.…”

“…While medium-sized (N100 m in diameter) and giant polygons (several kilometers) are suggested to originate by tectonic processes (e.g., Hiesinger and Head, 2000;Yoshikawa, 2003) or by desiccation in the case of medium-sized polygons (El Maarry et al, 2010), many authors have inferred that small-scale patterns (b100 m in diameter) are formed as thermal contraction polygons, analogous to terrestrial iceand sand-wedge polygons (e.g., Seibert and Kargel, 2001;Mangold, 2005;Mellon et al, 2008;Levy et al, 2009aLevy et al, , 2010. Recently, it could be shown by mechanical modeling that the maximum size of polygons formed by thermal contraction is limited to a few decameters (El Maarry et al, 2010).…”

“…Although no clear evidence for the processes responsible for the formation of small-scale polygons on Mars can yet be presented, the distribution of these polygons at middle to high latitudes (Mangold, 2005;Levy et al, 2009a) and their spatial relationship to ground ice on Mars (Mangold et al, 2004) suggest that these landforms are formed by thermal contraction cracking, which is controlled by specific periglacial climatic and subsurface conditions (Levy et al, 2010). Furthermore, the relationship of likely active thermal contraction polygons to periglacial landscape features in a geomorphologic context compared to terrestrial analogs allows conclusions to be drawn about small-scale polygon origin on Mars.…”

“…Patterned ground with polygon diameters ranging from meters to tens of kilometers has been described for many years on Mars (e.g., Lucchitta, 1981;Mellon, 1997;Seibert and Kargel, 2001;Mangold, 2005;van Gasselt et al, 2005;Levy et al, 2009aLevy et al, , 2010. While medium-sized (N100 m in diameter) and giant polygons (several kilometers) are suggested to originate by tectonic processes (e.g., Hiesinger and Head, 2000;Yoshikawa, 2003) or by desiccation in the case of medium-sized polygons (El Maarry et al, 2010), many authors have inferred that small-scale patterns (b100 m in diameter) are formed as thermal contraction polygons, analogous to terrestrial iceand sand-wedge polygons (e.g., Seibert and Kargel, 2001;Mangold, 2005;Mellon et al, 2008;Levy et al, 2009aLevy et al, , 2010.…”