Characterizing Mercury’s South Polar Volatile Deposits with Arecibo Radar and Enhanced Topography

Mercury’s radar-bright polar deposits provide some of the strongest evidence for volatile accumulation on the innermost planet. Ground-based radar observations first identified highly reflective features associated with permanently shadowed regions, and MESSENGER later confirmed that many of these cold traps host water ice and other volatile-bearing materials. However, while recent work has shown that Mercury’s north polar deposits are heterogeneous at local scales, a comparable analysis of the south polar deposits has remained limited by the quality of available topographic, illumination, thermal, and radar data.

Here we present ongoing work focused on a selected set of Mercury’s south polar craters, combining newly recovered Arecibo S-band radar datasets with refined and enhanced local digital elevation models derived from MESSENGER MDIS NAC images. A key component of this effort is the recovery of individual same-circular and opposite-circular polarization images, enabling an analogous  analysis to recent north-polar work in which the two polarizations were used independently to characterize radar-bright deposits, scattering behavior, and local-scale heterogeneity. Additionally, high-resolution DEMs can now be used to measure the local radar incidence angle, allowing for radar scattering modeling that can be used to further constrain the properties of the deposits. 

A major challenge is the lack of MESSENGER altimetry at southern latitudes, leaving many scientifically important areas, including permanently shadowed regions, poorly sampled or unsampled. Rather than relying on simple interpolation, which can produce unrealistic crater morphologies, we apply inpainting techniques to recover plausible local topography while preserving consistency with the surrounding terrain. These enhanced DEMs support modeling of illumination, radar viewing geometry, and thermal environments, allowing us to examine how radar-bright deposits relate to local topography, incidence geometry, shadowing, and predicted temperatures, and to assess whether south polar deposits show spatial patterns comparable to those identified in the north.

This work also provides a timely framework for the BepiColombo era. The refined DEMs, recovered Arecibo radar products, and combined radar–illumination–thermal analysis developed here can provide local context for future BepiColombo observations of Mercury’s south polar cold traps. New BepiColombo measurements will also offer an opportunity to test, refine, and extend these methods, enabling more detailed characterization of Mercury’s polar volatile inventory and its relationship to surface geology, thermal environment, and volatile delivery or preservation processes.