Space.com [space.com]:
For more than a month now, a European orbiter circling Mars [space.com] has been watching a long, plume-like cloud on the Red Planet.
The cloud has remained in place over a mountain called Arsia Mons near the Martian equator since Sept. 13, according to a statement [esa.int] released by the European Space Agency (ESA). But that location is just a coincidence, the agency adds. No volcanic process is producing the cloud — the volcano hasn't been active in about 50 million years [space.com], scientists believe.
What are those rascally Martians up to?