The Dorsa Argentea, Mars: Comparison to 5900 Terrestrial Esker Systems and Statistical Tests for Topographic Relationships

Introduction: We undertake the first large-scale quantitative analysis of the plan view geometries of the Dorsa Argentea [1] in a comparison to >5900 terrestrial esker systems in Canada [2]. Statistical tests for esker-like topographic relationships [1,3-4,5-6] are also completed. The Dorsa Argentea (DA) are an assemblage of ridges in Mars’ southern high latitudes (70°80°S, 56°W-6°E). Glacial eskers and inverted channels remain as active hypotheses for their formation [1,34,7-14]. A growing body of literature uses the esker interpretation as a basis for inferences about meltwater production (and, by extension, habitability) beneath a putative former ice sheet thought to have extended into the region of the DA during Mars’ Hesperian period, despite a lack of rigorous quantitative testing of the esker hypothesis [e.g. 10-11,13,14]. Methods: We digitized DA ridge segments (individual, unbroken ridges) using ~115 and ~230 m/pixel MOLA DEMs and ~6 m/pixel CTX [15] and ~20 m/pixel HRSC [16] images. We conservatively grouped chains of related ridge segments, separated by gaps, into longer ridge systems. Standalone segments <10 km in length were excluded. Plan view ridge geometry: We calculated system length (Li) by linearly interpolating across gaps between segments. We calculated continuity as the ratio between the total length of segments comprising a system and Li,, and sinuosity as the ratio between Li and the shortest linear distance between end points of the system. Longitudinal change in ridge height and bed slope: We obtained Cross Sectional (CS) topographic profiles at ~1 km spacing (within the 115 m/pixel DEM) along four major ridges (A-D) and calculated the percentage down-ridge change in ridge height (dH). We used base elevations (average elevation of two base points on each CS profile) to calculate longitudinal bed slope (θL) between successive CS profiles. Calculations were not performed across ridge gaps or junctions. Results and analysis: In total, we mapped ~7514 km of ridge systems (Fig. 1a, n = 260). Plan view geometry data for systems of the DA are displayed in Table 1. Maximum lengths are consistent with previous workers [7-8,10,13]. Gaps between segments account for ~10% of Li. Some systems are more fragmented, with a minimum continuity of 0.59 ± 0.02. Figure 1. a) DA classified by system sinuosity. MOLA hillshade basemap. Black box delineates Fig. 3b. b) Map of a sample of Canadian eskers [2,17].