Geomorphological Evidence for Shallow Ice in the Southern Hemisphere of Mars

Abstract

The localized loss of near‐surface excess ice on Mars by sublimation (and perhaps melting) can produce thermokarstic collapse features such as expanded craters and scalloped depressions, which can be indicators of the preservation of shallow ice. We demonstrate this by identifying High Resolution Imaging Science Experiment images containing expanded craters south of Arcadia Planitia (25–40°N) and observe a spatial correlation between regions with thermokarst and the lowest‐latitude ice‐exposing impact craters identified to date. In addition to widespread thermokarst north of ~35°N, we observe localized thermokarst features that we interpret as patchy ice as far south as 25°N. Few ice‐exposing craters have been identified in the southern hemisphere of Mars since they are easier to find in dusty, high‐albedo regions, but the relationship among expanded craters, ice‐exposing impacts, and the predicted ice table boundary in Arcadia Planitia allows us to extend this thermokarst survey into the southern midlatitudes (30–60°S) to infer the presence of ice today. Our observations suggest that the southern hemisphere excess ice boundary lies at ~45°S regionally. At lower latitudes, some isolated terrains (e.g., crater fill and pole‐facing slopes) also contain thermokarst, suggesting local ice preservation. We look for spatial relationships between our results and surface properties (e.g., slope and neutron spectrometer water ice concentration) and ice table models to understand the observed ice distribution. Our results show trends with thermal inertia and dust cover and are broadly consistent with ice deposition during a period with a higher relative humidity than today. Shallow, lower‐latitude ice deposits are of interest for future exploration.

Widespread Exposures of Extensive Clean Shallow Ice in the Midlatitudes of Mars

“…Supporting this possibility, the scarps in the southern hemisphere are mostly located in longitudes where neutron spectrometer data show high ice contents (60-90 weight percent) extending to relatively low latitudes (Pathare et al, 2018). The same region also overlaps the location of the largest concentration of scalloped depressions and thermokarst landforms in the southern hemisphere (Viola and McEwen, 2018;Zanetti et al, 2010), also consistent with high ice contents. Scarps and their host mantling units often appear localized near massifs or crater walls, which might help concentrate snow deposition in incipient glaciers, but these correlations with other data sets suggest that the scarp-hosting ice bodies are associated with high regional ice contents.…”

Geomorphological Evidence of Localized Stagnant Ice Deposits in Terra Cimmeria, Mars

“…There are various lines of evidence for both glacial and excess ice in the midlatitudes of Mars (e.g.Bramson et al, , Dundas et al, , Kadish & Head, , Levy et al, , Stuurman et al, , Viola & McEwen, ), both at present and in the past. Modeling the impact of a projectile into an icy stratum under Martian conditions shows that the formation of a midsized impact crater (30–50 km in diameter) results in the origin of a hot water‐bearing central uplift with mean temperatures in the periphery generally remaining below the melting point of water (Ivanov & Pierazzo, ; Pierazzo et al, ; Senft & Stewart, ; Sherburn & Horstemeyer, ).…”

Modern Mars' geomorphological activity, driven by wind, frost, and gravity

“…Scalloped features (e.g., Dundas et al, 2015b;Lefort et al, 2009;Morgenstern et al, 2007;Séjourné et al, 2011;Soare et al, 2007;2011;Ulrich et al, 2010;Zanetti et al, 2010) and expanded craters (e.g., Dundas et al, 2015b;Viola et al, 2015;Viola and McEwen, 2018) are considered to be some of the most iconic examples of ice loss features (Figure 15). Initial interpretations included formation via melting akin to terrestrial thermokarst and alases (Soare et al, 2007;2011), but the present general consensus is that these are formed via sublimation.…”