Water Desorption as a Mechanism for Recurring Slope Lineae Formation

Understanding water in Martian regolith is important because water affects surface morphology, chemistry, and habitability, and is a valuable resource for future human exploration. Recurring slope lineae (RSL)-seasonal dark streaks that propagate down Martian slopes in the summer and fade in the winter-are strongly linked to water because of their seasonality, but their precise formation mechanism remains unclear. RSL are morphologically similar to dry flows because they terminate on slopes that are similar to the angle of repose of sand. However, even dry RSL hypotheses require some role for water to explain their seasonal activity.

One explanation for seasonal mass wasting is that slopes destabilize in low relative humidity (RH) conditions as they release adsorbed water. In high RH winter conditions, slopes hydrate as the regolith adsorbs water from the atmosphere. Adsorbed water increases the slope's angle of repose by strengthening cohesive forces between grains. In low RH summer conditions, water desorbs from the regolith and the angle of repose decreases. If the angle of repose falls below the actual steepness of the slope, the slope will fail.