Islands of ice on Mars and Pluto

Abstract

Ice sheets, such as the polar layered deposits (PLDs) of Mars, are of great interest as records of past climate. Smaller outlier ice deposits near the north and south PLDs are likely more sensitive to climate changes and thus may hold information about more recent climate history. However, the southern outlier deposits have largely remained unmapped and unanalyzed. Here, we identify 31 deposits near, but separated from, Mars's south PLDs, all of which are located within impact craters >15 km in diameter. On the basis of morphology, radar analysis, physical similarity to portions of the PLD margin, and overall similarity to previously described deposits in Mars's north polar region, we conclude that these deposits are primarily composed of water ice. An additional 66 craters contain smaller depositional features, some of which may be remnant ice deposits. The 31 outlier ice deposits represent a previously unquantified inventory of water on Mars, with a total volume between 15,000 and 38,000 km3. In addition, we identify five analogous outlier nitrogen ice deposits located within impact craters near Sputnik Planitia, the large nitrogen ice sheet on Pluto. Although important differences exist between Mars and Pluto, broad physical similarities between the two cases suggest that the topography and microclimates of impact craters cause them to be favorable locations for volatile accumulation and/or retention throughout the Solar System.

Can Triton's Internal Heat Be Inferred From Its Ice Cap?

“…Finer meshing was tested and does not significantly change results. This methodology is similar to validated FEM techniques used in previous work to quantify viscous flow of icy domes (Sori et al., 2017, 2019). The stress exponent, 2.2, in Equation has uncertainty of ∼0.1 (Yamashita et al., 2010), so every model was rerun with exponents of 2.1 and 2.3 for robustness.…”

Orbital Forcing of Martian Climate Revealed in a South Polar Outlier Ice Deposit

“…We studied the 49 crater ice deposits inventoried by Conway et al (2012) and Sori et al (2019) and found that one had widespread exposed layering suitable for paleoclimate analysis. This ice deposit is located in Burroughs Crater (Figure 1), a 117-km-diameter impact crater located at 72°S, over 200 km away from the SPLD.…”

“…The total depth of the Burroughs ice deposit is greater than the 188 m of exposed stratigraphy analyzed here. Topographic analysis (Sori et al., 2019 ) and depth‐corrected SHARAD radargrams (Figure 3 in Supporting Information S1 ) both show that the total ice mound thickness is ∼600 m. If the average accumulation rate of the analyzed 188‐m‐thick exposure is representative of the entire stratigraphic column of the Burroughs deposit, then the entire ice deposit was emplaced over 4.5 Myr. If the top of the deposit was emplaced near the present‐day (see Section 4.2 ) and there are no prolonged episodes of net sublimation (i.e., large missing parts of the record), then this emplacement duration would imply an age of the Burroughs ice deposit of 4.5 Ma.…”

“…These deposits may also represent relatively young stratigraphy that has undergone fewer cycles of accumulation and ablation compared to the PLDs. Previous work has identified 18 crater ice deposits in the northern hemisphere (Conway et al., 2012 ) and 31 crater ice deposits in the southern hemisphere (Sori et al., 2019 ). High‐resolution images have been used to study surface morphology and constrain retreat rates of ice exposures in the northern deposits (Bapst et al., 2018 ; Brown et al., 2008 ).…”

Varied Histories of Outlier Polar Ice Deposits on Mars

“…Given the overall low levels of surface roughness, we favor the interpretation that the lack of reflectors suggests relatively homogenous ice composition with no significant dielectric interfaces. Of the four southern crater deposits that do exhibit subsurface reflectors, three were contiguous with the SPLD (“marginal” craters from Sori et al., 2019). We also found five southern outlier deposits with radargrams that contain fog, and two that contain an LRZ.…”