Anomalous recurring slope lineae on Mars: Implications for formation mechanisms

Recurring slope lineae (RSL) on Mars are dark linear features which lengthen and fade seasonfcally. The role of water in the processes responsible for their formation remains undetermined. RSL in close proximity (meters to tens of meters apart) are likely to be expressions of the same underlying processes; therefore, differences in behavior between neighbors can provide new constraints on potential mechanisms for initiation, lengthening and fading. We present observations of anomalous RSL, categorized into three types: early faders, collinear RSL, and those which emerge at featureless locations. We conclude that, given currently proposed processes, our observations favor a highly localizable growth mechanism and the possibility of propagation without surface expression. Using the implications of observed anomalous behavior, we evaluate the feasibility of two specific proposed mechanisms: dry granular flow and flow of liquid through porous regolith. Our observations are more immediately compatible with the liquid flow mechanism.

Automated summary

Recurring slope lineae (RSL) on Mars are dark linear features that lengthen and fade seasonally. The role of water in their formation processes is still uncertain. Observations of anomalous RSL suggest a preference for the liquid flow mechanism over dry granular flow for their growth.