Mars Express sees traces of ‘spiders’ in Mars’s Inca City

The dark spots in this image from ESA’s Mars Express are the telltale sign of ‘spiders’ scattered across the southern polar region of Mars. These small features form when carbon dioxide gas warms up in sunlight and breaks through slabs of overlying ice, etching branched grooves into the surface and dragging dark material up to the surface to form dark blotches.

Many such blotches can be seen within the dark region to the left of the frame, which sits at the outskirts of a part of Mars nicknamed Inca City. The reason for this name is clear, with the linear, almost geometric network of ridges being reminiscent of Inca ruins.

This image comprises data gathered by Mars Express’s High Resolution Stereo Camera (HRSC) on 27 February 2024 during orbit 25449. It was created using data from the nadir channel, the field of view aligned perpendicular to the surface of Mars, and the colour channels of the HRSC. The ground resolution is 15 m/pixel and the image is centred at 300°E/79°S.

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[Image description: A rectangular slice of Mars is shown here in tones of brown and tan. The terrain is darker to the left, and becomes smoother and lighter towards the right. Swirling patches of different material deposits can be seen in the middle section of the image. To the left, two key features can be seen: a raised network of linear, grid-like ridges and walls known as Inca City, and a scattering of dark spots that indicate the presence of features known as ‘spiders’ beneath the ice.]