Laboratory simulations of Mars RSL formation

We continue simulation efforts into the wet-origin hypothesis [1] of the formation of Recurring Slope Linea (RSLs) on Mars through the subsurface dosing of Mars regolith analogs at Mars pressure. Using the Mars Analog Reflectance Spectroscopy (MARS) chamber at JHUAPL [2], the liquid origin hypothesis for RSL formation is explored for a simulated 1cm deep, 10 cm wide, 20 cm long regolith analog.. The hypothesis being explored is the possibility that wetting and drying under Mars conditions can both reproduce the morphology of RSLs and lead to sufficient microscopic surface roughness and thus formation of shadows for explaining the lower albedo of RSLs [e.g. 3, 4]. Dosing with distilled water from a ¼" diameter source simulates a spatially constrained subsurface liquid water source, either from a long-lived aquifer or melt of near surface ice. The observed relatively slow growth of RSLs compared to laboratory timescales is a new capability that is simulated through slow continual dosing instead of rapid saturation of the regolith simulant. The slow dosing is effective for not overly disturbing the sample and for preventing mass movement due to regolith saturation. Dosing of sample occurs with the regolith simulant held at an angle of 37 degrees, consistent with slope angles observed for RSLs [5]. During the dosing portion of the experiment, images are collected approximately once/minute to capture the formation and growth of any resulting RSL analog. Subsequent to the completion of the dosing and drying, the sample holder is moved to a horizontal position while Mars pressure is maintained for collection of reflectance spectra. The dosing and drying results in a slight darkening of the sample. However, the linear morphology of RSL is not reproduced and instead only circular wetting has been observed. Further experiments using improved Mars surface material compositional analogs need to be conducted, and possible dependencies on dosing at cooler temperatures, closer to the triple of water where surface wetting may persist for longer periods enabling downslope movement, need to be explored.