Seasonal flows on warm Martian slopes

Seasonal flows on warm Martian slopes (also called recurring slope lineae, recurrent slope lineae and RSL) are thought to be salty water flows occurring during the warmest months on Mars.

The flows are narrow (0.5 to 5 meters) and exhibit relatively dark markings on steep (25° to 40°) slopes, appear and incrementally grow during warm seasons and fade in cold seasons. Liquid brines near the surface almost certainly explain this activity, but the exact source of the water and the mechanism behind its motion are not understood. On October 5, 2015, possible RSLs were reported on Mount Sharp near the Curiosity rover.

Research indicates that in the past there was liquid water flowing on the surface of Mars, creating large areas similar to Earth's oceans. However, the question remains as to where the water has gone.

The Mars Reconnaissance Orbiter (MRO) is a multipurpose spacecraft launched in 2005 designed to conduct reconnaissance and exploration of Mars from orbit. The spacecraft is managed by the Jet Propulsion Laboratory (JPL). The HiRISE instrument is at the forefront of the ongoing RSL studies as it helps chart the features with images of closely monitored sites typically taken every few weeks.

Distinctive properties of recurring slope lineae (RSL) include slow incremental growth, formation on warm slopes in warm seasons, and annual fading and recurrence, showing a strong correlation with solar heating. RSL extend down slope from bedrock outcrops often following small gullies about 0.5 to 5 meters (1 ft 8 in to 16 ft 5 in) wide, with lengths up to hundreds of meters, and some of the locations display more than 1,000 individual flows. RSL advance rates are highest at the beginning of each season, followed by much slower lengthening. RSL appear and lengthen in the late southern spring and summer from 48°S to 32°S latitudes that favor equator-facing slopes, which are times and places with peak surface temperatures from −23 °C to 27 °C. Active RSL also occur in equatorial regions (0–15°S), most commonly in the Valles Marineris troughs.

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