Recurring slope lineae (RSL) are dark streaks that appear on the surface of Mars during warm seasons and fade during cooler seasons. These features are believed to be formed by the downhill flow of water, brine, or a mix of water and salts. RSL have sparked interest among researchers as they provide evidence for the potential presence of liquid water on Mars, which is a key ingredient for the possibility of life. Scientists continue to study RSL to better understand their formation, composition, and implications for the past and present habitability of Mars.