A long ribbon of clouds streams away from the summit of Arsia Mons, a volcano on Mars, in these images from Mars Express, snapped in July 2020. The cloud forms when winds flow over the top of the volcano, which is about 12 miles (20 km) tall. Water vapor in the winds freezes as it hits higher, cooler altitudes, forming the cloud, which can cover more than 1,100 miles (1,800 km). The cloud forms most frequently around the start of summer in Mars's northern hemisphere. The season arrives on September 4. [ESA/GCP/UPV/EHU Bilbao]