It may only be a large rock, but images like this drive home the significance of the HiRISE instrument on board NASA’s Mars Reconnaissance Orbiter; it enables us to see recent geological activity on a planet we often view as being “dead.”
This boulder (approximately 6 meters-wide) had come to a stop at the bottom of the sloping wall of an impact crater. The path the boulder took is obvious as it left a series of prints in the Martian regolith as it bounced and rolled. The darker material that appears to have flowed around the rock is relatively fresh dry dust and sand that has also been dislodged from the top of the slope, falling as an avalanche, settling as a dark streak. As time goes on, the streak will age and blend in with the surrounding regolith.
It is suspected that seismic activity or a weather event (such as a dust devil) may have triggered the avalanche. As for the boulder, it looks like it rolled down the slope before the sand/dust avalanche, so it may have originated from the same destabilization event, or it happened earlier. As the source of the streak and boulder appear to originate from the same location, I suspect the former might be the case.
Regardless, it goes to show Mars is still active, and the MRO is in the perfect location to capture the Red Planet proving that fact.
Source: HiRISE
astroengine.com 
