NASA/Jet Propulsion Laboratory/University of Arizona. Satellite images have been combined with elevation data to give the impression of height.

A slope in Horowitz Crater, above, is lined with dark streaks 100 yards long. The streaks are thought to be formed by briny water flowing downhill in warmer months. The bright walls of Garni Crater, below, have similar streaks, which are also known as recurrent slope linae, or R.S.L.s.

NASA/Jet Propulsion Laboratory/University of Arizona

A time-lapse animation of Palikir Crater, below, shows how the streaks extend and darken during warmer months on Mars, then gradually fade as temperatures cool.