Chapter 2 - Unraveling the Mysteries of Recurring Slope Lineae

Abstract

Recurring slope lineae (RSL) are narrow dark features that incrementally lengthen down dust-poor steep slopes when temperatures are warm. They subsequently fade during cooler seasons and recur annually. Here, we discuss possible formation mechanisms based on observations of 748 candidate and confirmed RSL sites. RSL occur on well-preserved craters, canyon walls, light-toned layer deposits, fractures, central peaks, and pits from 42°N to 53°S. We have constrained the seasonality of five RSL regions as a function of slope orientation showing that RSL are always actively lengthening somewhere on the surface of Mars. Dry granular flow, wet-triggered debris flow, and wet-dominated flow formation mechanisms have been proposed, but no mechanism can adequately describe all the RSL observations. More advanced modeling combined with data from future remote sensing or in situ instrumentation is needed to fully discriminate between these formation mechanisms. Furthermore, we acknowledge that RSL may be formed via multiple mechanisms.