ISLAMABAD-A mysteriously long, thin cloud has again appeared over the 20-km (~12 miles / 65,000 feet) high Arsia Mons volcano on Mars. The cloud is made up of water ice, but despite appearances, it is not a plume linked to volcanic activity. Instead, the curious stream forms as airflow is influenced by the volcano’s ‘leeward’ slope − the side that does not face the wind. This image of the cloud, which can reach up to 1800-km in length, was taken by the Visual Monitoring Camera (VMC) on Mars Express, which has been studying the Red Planet from orbit for the past 16 years.

“We have been investigating this intriguing phenomenon and were expecting to see such a cloud form around now,” explains Jorge Hernandez-Bernal, PhD candidate at the University of the Basque Country (Spain) and lead author of the ongoing study.