Images and data sent back by NASA’s New Horizons spacecraft during its flyby mission to Pluto (and beyond) show a series of regularly spaced linear ridges sandwiched between a mountain range and Sputnik Planitia, a vast plain of nitrogen, carbon monoxide and methane ice. “When we first saw the New Horizons images, we thought instantly that these were dunes, but it was really surprising because we know there is not much of an atmosphere [on Pluto],” said Jani Radebaugh, a planetary scientist at Brigham Young University and co-author of a study in Science announcing the findings, in a statement.