Martian Regolith Analog Experiments

We describe a set of laboratory experiments designed to investigate Martian regolith hydrodynamics and to test the MAGHNUM computer model. A previous study with MAGHNUM (JGR-Planets 108: 8040-8054) indicated that if H2O is present in the Martian regolith, as is widely believed, then liquid water could be present beneath the cryosphere and it should be in a convective state, locally thinning the cryosphere above warm, upwelling hydrothermal plumes. Our experimental system is designed to match the Rayleigh number believed appropriate for the Martian regolith. The tank is 1.5 m wide, 0.5 m tall, 0.1 m thick, insulated on front and back sides. A constant temperature is applied to the bottom, and a chiller maintains the surface at subzero temperatures. The tank is filled with 37% porosity pea gravel. Both de-ionized pure water as well as salt (CaCl2) solutions are used. Qualitatively, experimental results and MAGHNUM simulations agree. In all cases, hydrothermal convection develops beneath a frozen layer. Convection with salt solutions exhibits more time dependence than with pure water, both in the experiments and in numerical simulations. Quantitative comparisons are in progress.