Check out this amazing picture featuring a boulder that went tumbling down a slope on Mars. The photo was caught by the HiRISe camera located aboard NASA’s Mars Reconnaissance Orbiter.
What started it up? A Marsquake, a nearby impact, the erosion of its underpinning due to the relentless Martian winds?
You can see the boulder at the bottom of the image, its shadow stretching off to the upper right. The rock is not quite large enough to clearly see any shape or features on it; it’s probably only a few of meters across.