The Penetration of Solar Radiation Into Water and Carbon Dioxide Snow, With Reference to Mars

The depth to which solar radiation can penetrate through ice is an important factor in understanding surface-atmosphere interactions for icy planetary surfaces. Mars hosts both water and carbon dioxide ice on the surface and in the subsurface. At high latitudes during autumn and winter carbon dioxide condenses to form the seasonal polar cap. This has been both modeled and observed to, in part, occur as snowfall. As snow accumulates, the thermal properties of the surface are changed, whether the underlying surface was rocky, regolith, or a solid ice sheet. This results in a change (usually increase) in albedo, affecting the proportion of the incident solar energy reflected, or transmitted below the surface of the snow layer. The depth to which light can penetrate through this layer is an important parameter in heat transfer models for the Martian surface and is often quantified using the e-folding scale. We present the first measurements of the e-folding scale in pure carbon dioxide snow for the wavelengths 300 to 1100nm alongside new measurements of water snow. Plain Language Summary The solid-state greenhouse effect is similar to the climatic greenhouse effect. It occurs in solid materials that are translucent to visible light, but opaque in the infrared, such as ices. On Mars, snow and frosts form from both water and carbon dioxide ice. When the Sun shines on the snow or frost, some light is diffusely reflected, some is transmitted through the snow grains, and some is absorbed by the ice. The proportion of light that travels through a material is dependent on its optical properties, which are unique to its composition. Owing, however, to the nature of frost or snow being a very small, granular material, much of the light is scattered at the grain surfaces. In this study we measured the amount of light that can travel through a snowpack of a particular thickness for both water and carbon dioxide snows. This helps determine how much energy can be transported through the snow to the ground below, which warms up the underlying material. This means that more accurate calculations can be made about the temperature profile of the Martian surface when covered in snow and frost, which gives insight into the different surface processes observed on Mars.