Thanks to super-zoom camera work by NASA's Mars Reconnaissance Orbiter (MRO) slope streaks on the red planet can be observed. Shown here is such a feature in an area south of Olympus Mons in the northern hemisphere of Mars, captured by MRO's High Resolution Imaging Science Experiment (HiRISE) instrument.

These features are found along the slopes of impact craters, buttes, knobs, ridges, and troughs on Mars. Streaks generally start at a point source and widen downslope, traveling over and sometimes around various obstacles.

But what causes them to form?

Slope streaks are among the few known processes currently active on Mars. The cause for their formation, what triggers them, is debated and is the stuff of scientific papers. One possibility is that they are most commonly created by downslope movement of extremely dry sand or very fine-grained dust in an almost fluid-like manner (analogous to a terrestrial snow avalanche) exposing darker underlying material.

Another prospect is they are triggered by possible concentrations of near-surface ice or scouring of the surface by running water from aquifers intercepting slope faces, briny liquid flows, dry granular flow, mixed water-dust flows, and/or hydrothermal activity.

• Red Planet Arrival: NASA's MRO Spacecraft Enters Mars Orbit
• SPACE.com Video Player: MRO Trajectory
• Hello Mars, Meet 'MR. O': The Mars Reconnaissance Orbiter

--Leonard David

Credit: NASA/JPL/University of Arizona