Deposition and degradation of a volatile‐rich layer in Utopia Planitia and implications for climate history on Mars

Abstract

[1] We investigate the surface morphology of a study area in western Utopia Planitia, Mars, which is characterized by a variety of landforms that resemble those of terrestrial periglacial landscapes. Polygonally fractured ground and thermokarst-like depressions are found to be located in a young mantling deposit with a thickness of several tens of meters. We observe a latitudinal dependence of the degradation of this mantling deposit. Larger depressions, whose floors reveal the underlying basement rocks, cover a higher fraction of the total terrain in the southern part of the study area than in the northern part, indicating a more intense degradation of the mantle in the south. All depressions have an asymmetric cross section in north-south direction, interpreted to be the result of the different solar radiation on differently oriented slopes. On the basis of our morphological observations, we develop a conceptual model for landscape evolution in western Utopia Planitia. It involves subaerial deposition of a layered, ice-rich mantle and its subsequent degradation by polygon formation and sublimation. A terrestrial analog to the polygonally fractured mantling deposit and its thermokarst-like depressions is the Siberian Ice Complex or ''Yedoma,'' which consists of subaerial ice-rich deposits and is connected to nonglaciated landscapes with highly continental cold-climatic environmental conditions. Our comparison suggests that no unusual or exotic processes need to be invoked to explain the current morphology of western Utopia. However, the young age of the deposition and degradation implies climatic excursions in the very recent past on Mars.

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

“…Other possible explanations exist, such as energy transfer by warmer winds coming from a southern direction during summer (Morgenstern et al, 2007). Winds could possibly increase temperature gradients and thus crack propagation in N-S-trending troughs, resulting in perpendicular secondary cracks forming in the E-W direction.…”

“…Furthermore, various periglacial-like features have been observed in the region, e.g., polygonal structures, scalloped depressions, and small mounds (e.g., Soare et al, 2005;Morgenstern et al, 2007;Burr et al, 2009;de Pablo and Komatsu, 2009;Lefort et al, 2009;Levy et al, 2009b;Ulrich et al, 2010;Séjourné et al, 2011). These landforms are associated in a geomorphological context, suggesting the existence of ice-rich ground (e.g., Morgenstern et al, 2007;Lefort et al, 2009;Ulrich et al, 2010). Present surface temperatures in the region have been detected to range from~180 K in winter to~240 K in summer (Morgenstern et al, 2007), but thermal modeling indicates they could reach~260 K during summer (Ulrich et al, 2010).…”

“…2b). About 24% of this region is covered by scalloped terrain (Morgenstern et al, 2007). Polygonal patterned ground is widespread in western UP (e.g., Seibert and Kargel, 2001;Lefort et al, 2009;Levy et al, 2009b).…”

“…These landforms are associated in a geomorphological context, suggesting the existence of ice-rich ground (e.g., Morgenstern et al, 2007;Lefort et al, 2009;Ulrich et al, 2010). Present surface temperatures in the region have been detected to range from~180 K in winter to~240 K in summer (Morgenstern et al, 2007), but thermal modeling indicates they could reach~260 K during summer (Ulrich et al, 2010). Geologically, the region is characterized by two main units: the Vastitas Borealis interior unit (ABv i ), which underlies the Astapus Colles unit (ABa) (Tanaka et al, 2005).…”

“…The most conspicuous landforms in western UP are asymmetrically-shaped scalloped depressions, which are interpreted as ground ice degradation features (e.g., Morgenstern et al, 2007;Lefort et al, 2009;Ulrich et al, 2010;Séjourné et al, 2011). Isolated depressions (a few hundred meters to several kilometers in diameter) alternate with coalesced scalloped terrain and nested areas of completely removed mantel material (Fig.…”