Spectral Albedo of Dusty Martian CO2 Snow and Ice

There is ample evidence to conclude that the ice deposits on solar system bodies—aside from Earth—have complex chemical constitutions. Carbon dioxide ice is prevalent at the poles of Mars and owing to its substantial reflectivity and seasonal variability, it significantly influences the planet's energy budget. Recent evidence of the existence of CO₂ ice glaciers on Mars explains the volumetric distribution and accumulation of CO₂ ice into the curvilinear basins at the south pole of Mars. While spectral measurements of martian ice have been made, no model of the dusty martian firn or CO₂ glacier ice exists at present. Due to their significant effects on snow and ice's albedo reduction, dust and snow metamorphism must be taken into consideration. Here, we adapt the terrestrial Snow, Ice, and Aerosol Radiation (SNICAR) model and apply it to martian glaciers by incorporating CO₂ ice capabilities in the model and validating with the observed remote sensing data. Compared with CO₂ snow, we find that CO₂ glacier ice albedo is much lower in visible and near-infrared (NIR) spectra. CO₂ ice albedo is more sensitive to layer thickness than CO₂ snow. We observe a noticeable transition between snow albedos and firn/glacier ice albedos. In particular, the absorption features at 1.435 µm and 2.0 µm caused by asymmetric stretching overtones and combinations of fundamental vibrational modes become damped. At these two wavelengths, the albedo is very small; the glacier ice has a higher albedo than coarse-grained snow because of specular reflection. We observe that small amounts (<1%) of Martian dust can lower the albedo of CO₂ ice by at least 50%. Once validated, our model can be used to characterize orbital measurements of martian CO₂ ice and refine climate-model predictions of ice stability. In the future, we plan to study the spectral albedo of other exotic ices in the solar system (N₂ and methane ice in case of Pluto, CO ice on Umbriel).