Physical properties of subsurface water ice deposits in Mars’s Mid-Latitudes from the shallow radar

Abstract

Understanding Mars’s water budget and distribution is crucial for evaluating its habitability and studying its evolution and past climate. Evidence for past and present glaciation includes geomorphological features: polar ice caps and subsurface ice. Among the most compelling evidence are Viscous Flow Features (VFFs), which suggest the presence of water ice due to surface patterns similar to Earth’s rock glaciers and debris-covered glaciers. These features, including Lobate Debris Aprons (LDAs), are found in the mid-latitudes (30° and 50°) of both hemispheres.

This study focuses on the composition of LDAs, which are large, ice-rich deposits found on slopes of massifs. Two hypotheses for their formation propose either low water ice content (30%) (“rock glaciers”) or near-pure water ice under a debris layer (“debris-covered glaciers”). Using SHARAD (SHAllow RADar) data, we calculate two key parameters – dielectric constant (${ϵ}^{\prime }$) and loss tangent ($tan\delta$) – to better understand the purity and composition of these deposits. Previous studies suggest LDAs consist of nearly pure water ice. Our work increases global coverage across the northern and southern hemispheres, examining five sites with enhanced data coverage and incorporating both ${ϵ}^{\prime }$ and $tan\delta$ to improve the analysis.

Our results indicate that LDAs are most likely part of a global population of features composed of $>$80% water ice, supporting the debris-covered glacier hypothesis. The results also point to the consistency of the debris cover across the globally distributed sites. This finding suggests that these features formed under similar climatic conditions, such as might occur under a specific orbital configuration. The high purity of the ice in LDAs has significant implications for understanding Mars’s past climate and for future exploration, as LDAs represent accessible reservoirs of water ice at mid-latitudes. Additionally, our findings highlight the need for future radar-based studies to incorporate the calculation of the loss tangent, as this can alleviate the sensitivity to the topography of the LDA base inherent in ${ϵ}^{\prime }$.