Observations and systematic documentation of bright/bluish materials within the cavity and ejecta of recent low-latitude impact craters on Mars

Kurzfassung

Impact craters serve as valuable natural probes for investigating the subsurface composition of Mars and other planetary bodies. Large impact events excavate material from deep within the crust, often exposing that material in central uplifts or pits, and were more prevalent during the earlier stages of Mars’ geologic evolution. In contrast, more recent impacts tend to be smaller in scale but can still expose subsurface materials from the uppermost few meters, depending on the size of the event. High-resolution visible observations of ice in the crater rims and ejecta from a subset of such impacts (e.g., Dundas et al., 2021) supported by measurements from instruments like the Mars Odyssey gamma ray/neutron spectrometer (e.g., Boynton et al., 2002; Pathare et al., 2018) and radar (e.g., Mouginot et al., 2010; Putzig et al., 2014), have provided constraints on the distribution and abundance of shallow subsurface water ice. These studies generally indicate the presence of water ice at depths of a few centimeters to meters, primarily restricted to the high- to mid-latitudes, with the most equatorward confirmed ice-bearing crater located at 35.2°N (Posiolova et al., 2022; Dundas et al., 2023), where ice was excavated from depths of ~2-8m (Dundas et al., 2023; Wojcicka et al. 2024). The High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (McEwen et al., 2007) continues to acquire high-resolution images of small, date-constrained impact craters, including those located equatorward of 35° N/S, often as a follow-up to detections by the Context Camera (CTX; Malin et al., 2007). Some of these impacts also exhibit relatively blue-toned materials within the crater walls or ejecta blankets, although most of these features have not been documented systematically. This work attempts to create a high-resolution inventory of all such equatorial impacts observed by HiRISE, with an aim to help characterize the spectral and morphological properties of the exposed bluish materials and assess their possible compositional origins.