The image from the NASA MRO orbiter, received on May 13, 2018 during the winter at the South Pole of the Red Planet, shows an ice cap made of carbon dioxide. It covers the entire region and as the Sun returns in spring, the “spiders” begin to appear on the landscape.
No, these are not real spiders. Here is an “archaic landscape” describing spider mounds similar to spiders. They form when the ice of carbon dioxide under the surface warms up and is released. This is an active seasonal process that you will not see on Earth. The ice sublimates when heated and the gas accumulates in a trap below the surface. Over time, the trapped carbon dioxide creates pressure and becomes strong enough to break through the ice in the form of a jet, spewing dust. Gas sneaks into the atmosphere, and darker dust can be deposited around the vent or be transported by winds to create streaks. The loss of sublimated carbon dioxide leaves arachnid marks imprinted on the surface.
