Geomorphic Evidence for Post-Impact Modification of a Small Crater in Mare Boreum, Mars

Small impact craters within the Martian north polar layered deposits (NPLDs) provide localized geomorphic records of surface modification within an ice-rich polar environment. We investigate a small crater in Mare Boreum using CTX and multi-temporal HiRISE imagery, HiRISE-derived topography, and regional constraints from MOLA, TES, GRS, SHARAD, and geological mapping. The crater retains a sub-circular planform but exhibits markedly subdued topographic expression, including attenuated rim relief and a shallow interior. HiRISE-derived topography indicates substantially reduced relief relative to fresh-crater morphometric expectations for a feature of comparable scale. The coexistence of a preserved planform and strongly attenuated relief indicates substantial cumulative post-impact modification. Multi-temporal HiRISE observations resolve the crater rim, interior, and illumination-sensitive surface features under broadly comparable seasonal conditions. Regional geological, thermophysical, geochemical, and radar observations constrain the broader ice-rich polar setting but do not resolve crater-scale composition, infill, or subsurface structure. The observed morphology is consistent with cumulative modification that may include depositional infilling, sublimation-related redistribution, rim degradation, and relaxation within the NPLDs, although the relative contributions of these processes cannot be uniquely determined from the available orbital observations.