A dust storm in Olympia Planum's north polar dune fields was triggered by a late Martian summer cold front. As the northern polar cap shrinks fast, it releases cold air that sometimes moves south, like on Earth. These cold fronts strengthen in late summer and early fall due to temperature differences. Occasionally, they cause big dust storms covering large areas or the whole planet. A similar event happened a month later, leading to a global dust storm lasting most of 2018. The image, taken on April 3, 2018, by the Mars Express HRSC camera during orbit, shows natural colors. [ see full image by Aster Cowart ]