A morphology-driven duty cycle for lunar surface ice explains patchy detectability in polar cold traps

Abstract Despite cryogenic temperatures in lunar polar cold traps, spacecraft observations indicate that exposed surface water ice is sparse and patchy. We develop a morphology-driven duty-cycle framework that treats surface ice as a transient state governed by competition between impact-driven exposure or supply and sublimation loss. High specific surface area (SSA) ice, including submicron frost and thin films, can exhibit exposure-limited surface lifetimes orders of magnitude shorter than bulk ice, leaving surface expressions short-lived even where thermodynamic stability is predicted. Coupling morphology-dependent sublimation with impact-driven optical-skin renewal yields a mechanically controlled upper bound that limits surface visibility to only a few percent in the coldest microtraps. The resulting temperature-dependent duty cycle produces a broad detectability transition near 110 K and helps reconcile widespread subsurface hydrogen inferred from neutron measurements with sparse near-infrared frost detections. We conclude that cold traps host a dynamic surficial veneer that intermittently reveals more extensive subsurface reservoirs.