The arrival of NASA’s Mars Reconnaissance Orbiter (MRO) at the Red Planet in 2006 ushered in a whole new era of Mars observation. With its ultrapowerful HiRISE camera, the orbiter has spied on the Martian surface to study curious features, some of them possibly linked to the presence of water, in unprecedented detail. And along the way HiRISE has also uncovered a few new phenomena.

At the top of that list are recurring slope lineae (RSL), which HiRISE scientists discovered in 2011. RSL are dark lines that appear during the warm season on southern slopes, spread gradually downward and then fade as the weather turns cold again. The behavior of RSL suggests that they are caused by flows of briny liquid water, which, if confirmed, would stir new hopes for current life on Mars.

Click here for a slide show of some of Mars’s most interesting surface features, including animated gifs of recurring slope lineae growing and fading from one season to the next, as documented from orbit by the HiRISE camera.

»View the Slide Show