Solving the mystery of Pluto's giant blades of ice. NASA's New Horizons mission revolutionized our knowledge of Pluto when it flew past that distant world in July 2015. Among its many discoveries were images of strange formations resembling giant knife blades of ice, whose origin had remained a mystery. Now, scientists have turned up a fascinating explanation for this "Bladed terrain": the structures are made almost entirely of methane ice, and likely formed as a specific kind of erosion wore away their surfaces. Source 5f.