Water ice nucleation characteristics of JSC Mars-1 regolith simulant under simulated Martian atmospheric conditions.

Water ice clouds in the Martian atmosphere are governed by parameters such as number density and particle size distribution that in turn affect how they influence the climate. With some of the underlying properties of cloud formation well known only for Earth, extrapolations to Mars are potentially misleading. We report here continued laboratory experiments to identify critical onset conditions for water ice formation under Martian cloud forming temperatures and water partial pressures (155–182 K, 7.6 × 10−5 to 7.7 × 10−3 Pa H2O). By observing the 3 μm infrared band to monitor nucleation and growth, we observe significant temperature dependence in the nucleation of ice on JSC Mars-1 regolith simulant, with critical saturation ratios, Scrit, as high as 3.8 at 155 K. At temperatures below ∼180 K, ice nucleation on JSC Mars-1 requires significant supersaturation, potentially impacting the Martian hydrological cycle.