Weakening of ice by magnesium perchlorate hydrate

► Mg-perchlorate hydrate has a dramatic weakening effect on the strength of water ice. ► Coarse-grained ice with a small amount of perchlorate behaves like fine-grained ice. ► SEM imagery indicates that grain boundary sliding is increased relative to pure ice. ► The presence of Mg-perchlorate may have enhanced flow in the martian polar regions.