Observations of the northern seasonal polar cap on Mars II: HiRISE photometric analysis of evolution of northern polar dunes in spring

Evolution of Mars' northern polar seasonal CO2deposits: Variations in surface brightness and bulk density

“…However, it is a natural component of seasonal ice and cannot be dismissed entirely. It is known that the spectrally averaged water‐ice band strength increases over spring on the north cap [ Pommerol et al ., ; Portyankina et al ., ]. Therefore, the brightening of ice in Louth and Dunes could be due to an intimate mixture of water ice that naturally brightens over spring.…”

A New Analysis of Mars “Special Regions”: Findings of the Second MEPAG Special Regions Science Analysis Group (SR-SAG2)

“…However, even the most extreme known brines require temperatures above *200 K, which are unlikely when CO 2 frost still largely covers the adjacent dune surfaces, as confirmed by CRISM observations during the season of streak activity (Pommerol et al, 2013a). An alternative hypothesis is that springtime CO 2 sublimation and gas flow initiate gravity-driven mass wasting of sand and ice down the dune slipfaces (Hansen et al, 2011Portyankina et al, 2013), forming the dark streaks and the small gullies with which they associate in some cases (Fig. 23).…”

Widespread Megaripple Activity Across the North Polar Ergs of Mars

“…Whereas spring ice does not fill in megaripple troughs (estimated to be ∼1 m; e.g., Figure S3 in Supporting Information ), DTR areas appear to be smoothed over, suggesting decimeter‐thick winter frost accumulation (Figure 9). CO 2 frost is typically fully sublimated off sandy surfaces by late spring ( L s ∼ 80°–90°) (Hansen et al., 2013; Portyankina et al., 2013), possibly slightly earlier for sites like Buzzel where slip faces are orientated southward (Pommerol et al., 2013). DTRs and megaripple surfaces may respond to wind and regain mobility promptly around the northern summer solstice.…”