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Sorry, these aren't huge Martians; they're surface features created by carbon-dioxide ice turning to gas below the surface. Unlike water-ice, when warmed by Spring sunshine on the dust above, C02 ice goes straight to gas, forming these amazing patterns as it bursts through the soil. The official NASA designation for these is "cryptic features," but popular names include "lace, lizard-skin, fans, and spiders."
Best,
Chris