Are seasonal deposits in spring at the Martian North Pole much shallower than previously thought?

Abstract

The seasonal deposition and sublimation of CO constitute a major element in the Martian volatile cycle. Here, we propose to use the shadow variations of the ice blocks at the foot of the steep scarps of the North Polar Layered Deposits (NPLDs) to infer the vertical evolution of the seasonal deposits at high polar latitudes. We conduct an experiment at a steep scarp centered at (85.0°N, 151.5°E). We show that the average thickness of the seasonal deposits due to snowfalls in Mars Year 31 is 0.97±0.13 m at Ls = 350.7° in late winter, which then gradually decreases in springtime. The large snow depth measured makes us wonder if snowfalls are more frequent and violent than previously thought. Meanwhile, we show that the average frost thickness due to direct condensation in Mars Year 31 reaches 0.64±0.18 m at Ls = 350.7° in late winter and quasi-linearly decreases towards the summer solstice. Combined, the total thickness of the seasonal cover in Mars Year 31 reaches 1.63±0.22 m at Ls = 350.7° in late winter, continuously decreases to 0.45±0.06 m at Ls = 42.8° in middle spring and 0.06±0.05 m at Ls = 69.6° in late spring. These estimates are up to 0.8 m lower than the existing MOLA results during the spring, which can be mainly attributed to MOLA-related biases. In terms of interannual variations, we observe that snow in the very early spring of Mars Year 36 can be 0.36±0.13 m deeper than that in Mars Year 31.

Thickness of the Seasonal Deposits at the Martian North Polar Region From Shadow Variations of Fallen Ice Blocks

“…HiRISE images are available at NASA Planetary Data System (PDS) (McEwen, 2007). The generated HiRISE DEM and scripts to reproduce Figures 9, 11, 13 and 14 are published in Mendeley Data (Xiao et al, 2024). The self-registered MOLA reference DEM and thickness variation time series from at the Martian north polar region are published in Mendeley Data (Xiao, Stark, Schmidt, et al, 2021).…”