Insights on Water Ice‐Induced Cohesion in the Lunar Regolith From Laboratory Experiments

Abstract It remains unknown whether water ice at cold trap temperatures induces mechanical failure of slopes in lunar permanently shadowed regions (PSRs), or if it acts as a cementing agent to enhance slope stability. An incomplete understanding of the mechanical properties of the lunar polar regolith poses a critical risk of safe trafficability and extended mobility in PSRs. The purpose of this study is to investigate the effect of water ice on lunar regolith cohesion via laboratory experiments conducted at cold trap (∼90K) and warmer PSR temperatures (∼220K). We measured the static angle of repose (SAoR), dynamic angle of repose (DAoR), failure modes, and aspect ratio of mixtures of water ice and lunar highland regolith simulant as proxies for lunar regolith cohesion. Experiments at ∼90K show that the SAoR increases only when water ice abundances are >30 wt.%, while the DAoR and mode of failure do not deviate from the dry regolith. In lunar cold traps where water ice detections are likely in the few wt.% range, the effects of ice‐induced cohesion are negligible. If a cold trap contains >30 wt.% ice, enhanced slope stability from ice‐induced cohesion is possible. In experiments with >30 wt.% water ice abundance at >∼220K, ice‐induced cohesion increases SAoR and DAoR, and shifts failure from deep rotational slides (indicative of a cohesionless material) to small, superficial flows that suggest a stabilized bulk heap. Such conditions (e.g., in Tooting Crater, Mars) likely permit steeper, more stable slopes.