"NASA has found “circumstantial evidence” of liquid water flowing on the surface
of Mars at its southern mid-latitudes during the planet’s warmer spring and
summer months.
Images from the agency’s Mars Reconnaissance Orbiter (MRO) show dark features
appearing and extending down steep slopes during the planet’s late spring and
summer, fading in winter, and returning the following spring."
See:
http://www.aviationweek.com/aw/gener...&channel=space