[ETL]

"a curious cloud formation that appears regularly in the vicinity of the 20 km-high Arsia Mons volcano, close to the planet’s equator."

This digital-image mosaic of Mars’ Tharsis plateau shows the extinct volcano
Arsia Mons. It was assembled from images that NASA’s Viking 1 orbiter took
during its 1976-1980 working life at Mars. Image credit: NASA / JPL / USGS.

[gleeaikin]

Maybe it is just letting off a little water vapor or other gas that is freezing in the cold air.