Towards a Laboratory Determination of Microphysical Properties of H2O Ice Clouds Under Mars Atmospheric Conditions

Recent observations by the Mars Global Surveyor (MGS) and Mars Odyssey (MO) suggest that water ice clouds have a fundamental role within the Mars climate system, which caused the Mars modeling community to include water ice clouds in global climate studies. However, simulation results depend strongly on cloud properties such as cloud particle size and number. These properties depend on the nucleation, which is dependent on the contact parameter, m, and the saturation ratio, S. As homogenous nucleation of most vapors requires very high levels of saturation, it is believed that heterogeneous nucleation is the most important microphysical process for water ice clouds in Martian atmospheric conditions. The proposed experiment will assess important cloud properties in order to improve models of both the current and past Martian hydrological cycles to be modeled. S, defined as the ratio of the partial vapor pressure to the equilibrium pressure, will be determined using IR spectrometry and pressure. This will allow m, the contact parameter between the water cluster and the simulated Mars dust, to be calculated. A contact parameter of m = 0.95 between the aerosol and water vapor has been assumed in some models. Typical values of m between liquid water and soil in terrestrial conditions range from m = 0.36 to 0.42. Water ice formed between 110 K and 150 K can either be amorphous or crystalline. These two phases of ice are spectrally distinct in the infrared, so the ice phase will be measured under these temperature conditions. The experimental design and parameters for six scenarios, representing the observed regional and seasonal where water ice cloud formation occurs, will be presented.