ESA’s Mars Express orbiter has photographed a long white cloud lingering eerily over the planet’s surface.
The phenomenon, which was first spotted back in September, is situated next to Arsia Mons – a volcano – leading some to speculate that a volcanic eruption may have been taking place.
As it happens, however, Arsia Mons has not been volcanically active for over 50 million years.
The answer, it turns out, is that the cloud, which is comprised of water ice, was formed from the interaction between the Martian air and the southwest slope of the volcano.
It is a phenomenon known as a ‘lee cloud’ owing to its formation from the volcano’s leeward slope.
“The cloud’s appearance varies throughout the Martian day, growing in length during local morning downwind of the volcano, almost parallel to the equator, and reaching such an impressive size that could make it visible even to telescopes on Earth,” ESA wrote.