Are Recurring Slope Lineae Habitable?

Recurring slope lineae (RSL) are dark flows on steep slopes that extend downhill gradually or incrementally and recur each Mars year. RSL activity often occurs at temperatures exceeding 255 K, meeting one requirement for potential habitability. The temperature-dependent activity is consistent with the stability of brines likely on Mars, and hydrated salts are transiently detected from orbit. These may be the most promising locations for habitable conditions on Mars today, especially in equatorial regions. However, topographic evidence strongly points to the formation of RSL as granular flows, not seepage of water, so the water activity value is probably quite low (< 0.5) and habitability remains very challenging. Future spacecraft experiments and laboratory experiments are needed to understand how RSL form and whether they need to be treated like special regions, requiring extra procedures for planetary protection (quarantine).