Signs of spiders from Mars

Rather than being actual spiders, these small, dark features form when spring sunshine falls on layers of carbon dioxide deposited over the dark winter months. The sunlight causes carbon dioxide ice at the bottom of the layer to turn into gas, which subsequently builds up and breaks through slabs of overlying ice. The gas bursts free in martian springtime, dragging dark material up to the surface as it goes and shattering layers of ice up to a metre thick.

The emerging gas, laden with dark dust, shoots up through cracks in the ice in the form of tall fountains or geysers, before falling back down and settling on the surface. This creates dark spots of between 45 m and 1 km across. This same process creates characteristic ‘spider-shaped’ patterns etched beneath the ice – and so these dark spots are a telltale sign that spiders may be lurking below.

The aforementioned dark spots can be seen all over the Mars Express image, creeping across towering hills and expansive plateaus. However, most can be seen as small spots in the dark region to the left, which sits just at the outskirts of a part of Mars nicknamed Inca City. The reason for this name is no mystery, with the linear, almost geometric network of ridges being reminiscent of Inca ruins. More formally known as Angustus Labyrinthus, Inca City was discovered in 1972 by NASA’s Mariner 9 probe.