Glaciation on Mercury: Accumulation and flow of ice in permanently shadowed circum-polar crater interiors

Abstract

Radar-bright deposits that coincide with regions in permanent shadow typically found within impact craters at and near the poles of Mercury have been interpreted as being composed of water ice. We investigate the dynamic properties of these solid water-ice deposits (glaciers) with the goal of constraining their movement, flow rates, possible deformation, and related structures and deposits. As an end-member, we treat the extreme case of maximum ice accumulation where these deposits fill the crater to the shadow line, an event we would only expect following maximum accumulation conditions such as a large cometary impact or a comet shower. We find that, given the extremely cold conditions and the limited thickness of glaciers, even under the most favorable accumulation conditions, glaciation is cold-based, ice flow velocities are very low (4 × 10−8 m/yr) and, with the exception of a sublimation lag deposit, glaciation is unlikely to leave any significant impact on the terrain. An important accelerator of ice flow is found to be the contribution of lateral heat conduction from the surrounding extremely hot surface terrain (∼225 K average with up to 450 K maximums), which for 55 km craters yields velocities of 10−3 m/yr while for smaller 10 km craters velocities may exceed 1 m/yr, enough to leave a detectable ice deformation imprint such as drop moraines. However given that the observed deposits are substantially below their maximum fill capacities these estimates are unlikely to be attained.