These spider patterns were observed in 2020 as well.
A recent image released by the European Space Agency shows what appears to be a swarm of spiders crawling across Mars' surface. These "spiders" were recently captured on camera by ESA Mars Express spacecraft near a surface formation known as the Inca City. "No sign of Ziggy Stardust - but ESA's Mars Express has snapped the telltale traces of 'spiders' scattered across the southern polar region of Mars," ESA wrote in a press release.
But of course, these aren't actually spiders. According to the press note, they are really just small, dark-coloured features that begin to be formed when sunshine falls on carbon dioxide deposited during the planet's winter months. The light causes the carbon dioxide ice at the bottom of the deposits to turn into gas, which eventually bursts through ice that can be up to three feet thick, shooting dust out in geyser-like blasts before settling on the surface, the space agency said.
While the spots might look tiny from space, they're actually fairly large, the ESA explained. The space agency said that the patches are as small as 145 feet, at their largest, and might be over half a mile wide. Below those large spots, the arachnid-like pattern is carved beneath the carbon dioxide ice, the ESA said.
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Notably, according to Newsweek, these spider patterns were observed in 2020 as well by the ExoMars Trace Gas Orbiter, which launched in 2016 and has been studying Mars for signs of possible past life. The majority of the dark spots captured by the orbiter appear on the outskirts of a part of Mars nicknamed "Inca City". The area, discovered in 1972 by a NASA probe, is also known as Angustus Labyrinthus, and is near the planet's south polar cap.
It's not clear how the area was formed, the ESA said. Suggestions include sand dunes that turned to stone over time, or material like magma or sand seeping through rock.
Meanwhile, Mars Express arrived at the Red Planet in late 2003. In the two decades since its arrival, the orbiter has mapped Mars' atmosphere, traced the history of water across Mars' surface, studied two small Martian moons in unprecedented detail, and returned breathtaking views of the planet in three dimensions.