Mars is a world with a cold, dead heart.

High over the peak of a long dead volcano on the Martian equator, a feathery white cloud stretches across the sky. At first glance it looks like the plume of an eruption, but Mars is a world with a cold, dead heart.

It has been for some time but since 13 September, ESA’s Mars Express has been observing the evolution of the elongated cloud formation hovering in the vicinity of the 20 km high Arsia Mons volcano, close to the planet’s equator.

In spite of its location, this atmospheric feature is not linked to volcanic activity but is rather a cloud driven by the influence of the volcano’s slope on the air flow something that planetary scientists call it an orographic cloud. Those clouds are typically seen on the downwind side of mountains, forming when dense air close to the surface flows uphill and expands, cooling to a temperature that allows moisture to condense on particles of dust. The cloud's appearance provides an opportunity to gauge the density of particles hanging about in the red planets atmosphere.

Earlier this year, the planet was swamped by a massive dust storm and this cloud may help us refine models on how dust rises and settles on Mars, informing the scope of future missions and research. In the meantime, Mars Express will continue snapping raw images of the cloud until it fades away, so you can follow its progress safely from Earth.

Phedias Hadjicharalambous. Cyprus Astronomy Organisation