Salts as Water Ice Cloud Nuclei on Mars

Abstract:

In recent years, observations of the Martian surface have indicated the presence of chlorine-bearing minerals, including perchlorates, on the surface of Mars. These salt-bearing minerals would potentially be source material for dust lofted from the surface into the Martian atmosphere, thus providing potential nucleation sites for water ice clouds. Considering that salts play an important role in cloud formation on Earth, it is important to have a better understanding of how salt may affect nucleation processes under Mars-like conditions. We perform laboratory experiments to examine water ice nucleation onto salt substrates. We use a vacuum chamber that simulates the temperatures and pressures observed of the Martian atmosphere. Using infrared spectroscopy we measure the onset of nucleation and calculate the temperature-dependent critical saturation ratio (Scrit) for water ice nucleation onto salts, specifically sodium chloride and sodium perchlorate. Preliminary results of Scrit values for water ice nucleation on sodium chloride show a negative temperature dependence, as did other substrates from previous experiments. Values of Scrit are useful for understanding the realistic conditions under which water ice clouds may form on Mars, and can be used in climate models simulating clouds on Mars.