It's abundantly clear that we still have a lot to learn about Mars, but one of the most interesting mysteries is the presence of strange, spider-like formations on the planet's surface. NPR explores a prominent scientific theory about the cause of the formations, which appear quite suddenly in the Martian spring, and completely vanish in the winter. To find out where they come from, and see more great photos of the spidery anomalies, check out the full story at the source link below.