The ESA's ExoMars Orbiter Captures Swarms of Dark "Spiders" on the Surface of Mars

SYFY's Resident Alien answers the question of extraterrestrial life once and for all, at least for the fictional residents of Patience, Colorado. When Harry Vanderspeigle (Alan Tudyk) shows up in town, a small group of select humans learn that humanity shares the cosmos with a species of octopus-like aliens, and a few other species to boot.

In the real world, astronomers have found what look like Harry’s relatives, a vast collection of spidery forms scattered across the South Pole of Mars, but they aren’t aliens at all. Instead of hinting at an arachnid invasion, these spider-shaped formations are the sign of interesting geological and chemical processes occurring on the Red Planet.

ESA Orbiter Spies Giant “Spiders” on Mars

We’ve known about these spiders, officially known as araneiform terrain, for years, but they’re getting increased attention thanks to new images from the European Space Agency’s (ESA) ExoMars Trace Gas Orbiter. The images show the South Pole of Mars littered with swarms of black, spider-like shapes. As small as they might look from the orbiter’s high vantage point, each of those spiders measures between 45 meters and a kilometer, or between 147 feet and 0.62 miles across.

They show up only seasonally, in the spring and summer months, and that provides a clue into how they form. Over the course of the Martian winter, carbon dioxide (the prevailing component of the Martian atmosphere) freezes into a sheet of dry ice on the surface. In the spring, sunshine returns and warms the ice, and things get interesting.

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This image from NASA's Mars Reconnaissance Orbiter, acquired May 13, 2018, during winter at the South Pole of Mars, shows a carbon dioxide ice cap covering the region and as the sun returns in the spring, "spiders" begin to emerge from the landscape. Photo: NASA

The ice behaves like a greenhouse, letting sunlight through but trapping heat underneath. Rather than melt into a liquid, the Martian CO2 ice sublimates, transitioning directly from a solid to a gas, creating trapped pockets. Over time, the pressure builds and the ice gives way. Pressurized gas races for the surface, carrying dark dust with it, erupting in a geyser of dirty Martian air.

Along the way, gas and dust carve channels through the ice; after the eruption, the dust falls back to the surface in fans. It’s a seasonal process, but individual spiders can grow and develop over the course of many years. NASA’s HiRISE camera aboard the Mars Reconnaissance Orbiter (MRO) imaged one particular spider in 2009, 2011, and 2015, documenting its transformation from a singular dark spot into something more arachnid in nature. The result is a dark nucleus with sullied cracks and fans stretching out from that center, creating the spiders of Mars.

Sadly, these Martian spiders only build dust piles, not spaceships. If you’re looking for an extraterrestrial friend, you’ll have better luck with Resident Alien, streaming now on Peacock.