Laboratory analogs of Mars clouds: Critical saturations for water ice nucleation

Understanding the current martian climate and water cycle depends on a thorough understanding of water ice clouds, which are modeled based on extrapolation of data relevant to Earth's atmosphere. These studies show the successful development of a new chamber and experimental protocol for conducting studies of water ice nucleation via vapor deposition. We have performed experiments at cold temperatures and low pressures more representative of Mars. Critical saturation ratios were observed to vary from 1.1 +/- 0.2 at 185.0 K to 3.3 +/- 0.8 at 155.1 K on martian dust analogs. Variation in the temperature dependence among different substrates was also observed. The strong temperature dependences observed here for many analogs under water ice nucleation conditions makes it is clear that extrapolation of terrestrial values to martian temperatures is inappropriate. Adsorption/desorption tests with smectite clay and JSC Mars-1 Regolith Simulant were also undertaken to insure that experiments were preformed under repeatable conditions. This laboratory work is the first to test martian dust analogs for water ice nucleation under temperatures relevant to Mars (T = 140 -- 210 K), and it is the first study to examine critical saturations for water ice nucleation on JSC Mars-1 Regolith Simulant under any conditions.