ESA’s Mars Express spacecraft have spotted the telltale traces of ‘spiders’ scattered across the southern polar region of Mars.
This image of the Martian Inca City was captured by the High Resolution Stereo Camera onboard ESA’s Mars Express orbiter on February 27, 2024. Image credit: ESA / DLR / FU Berlin.
“Rather than being actual spiders, the Martian ‘spiders’ form when spring sunshine falls on layers of carbon dioxide deposited over the dark winter months,” members of the Mars Express team said.
“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 meter 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 (148-3,280 feet) 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 dark spots can be seen all over the Mars Express image. 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 researchers said.
“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.
“We’re still not sure exactly how Inca City formed. It could be that sand dunes have turned to stone over time,” the scientists said.
“Perhaps material such as magma or sand is seeping through fractured sheets of Martian rock. Or, the ridges could be ‘eskers,’ winding structures related to glaciers.”
“The ‘walls’ of Inca City appear to trace part of a large circle, 86 km (53.5 miles) in diameter.”
The scientists suspect that Inca City sits within a large crater that itself formed as a rock from space crashed into the planet’s surface.
“This impact likely caused faults to ripple through the surrounding plain, which were then filled with rising lava and have since worn away over time,” they said.