Dark streaks that may trace water flowing today.
Garni Crater became famous for its Recurring Slope Lineae (RSL) — narrow dark streaks that appear on warm slopes, grow downhill in the Martian summer, then fade in winter. Their discovery here was tied to the detection of hydrated salts, offering some of the strongest evidence for present-day liquid water on Mars.
Claim your plot here →RSL are thin, dark lines that creep down steep, sun-facing slopes when temperatures rise and retreat when they cool — a rhythm that looks tantalizingly like seepage. In 2015 NASA reported hydrated perchlorate salts in the streaks at Garni and other sites, suggesting briny water may be involved in forming them.
The interpretation remains debated: some scientists argue RSL are instead flows of dry, granular sand triggered by seasonal changes. But whether wet or dry, Garni's streaks sit at the centre of the search for liquid water on Mars today — and any water, however salty, is of enormous interest for the question of life.
Like water darkening sand on a beach, RSL darken slopes as they extend downhill in the warm season.
The behaviour mimics briny seeps on Earth, but in air so thin any water would be extremely salty and short-lived.