EarthSky, Space and other online sites have pointed out the odd occurrence of a persistent cloud on Mars which is quite large. It is emanating from the Arsia Mons volcano but does not appear to be from an eruption. Instead, it is thought to be a cloud formed by orographic flow over the mountain, similar to the clouds seen downwind of the Rockies in the US. You can read more about this at https://earthsky.org/space/mars-express-curious-elongated-cloud-arsia-mons-volcano.
