The SWIM23 two-layer heterogeneity match (a) and depth (b) maps prior to rejection of low-latitude detections. Both maps are shown in simple cylindrical and polar projections. Both maps were produced by matching model ATI(L_s) calculated via MARSTHERM to ATI(L_s) derived from TES nighttime bolometric temperatures (N. E. Putzig & M. T. Mellon 2007; N. E. Putzig et al. 2023). Model selection was based on a maximum RSD of RSD = 40, and depths were calculated via a linear RSD interpolation between thermal model depth nodes. Only layering scenarios interpreted as potentially icy are shown in (a), where D = dust, S = sand, C = duricrust, R = rock/ice. Locations of recent impacts (C. M. Dundas et al. 2021) are indicated by white circles (icy), white circles with black borders (possible ice), and red X’s (no indication of ice).