An iridescent rounded ridge like the backbone of a mythical horse traces a sinuous path starting at upper right in this image. Lustrous striated lines flow from the ridge top, like folds in a crinkled silk scarf. An overlay of turquoise blue turns the pearly-gray surfaces into shimmering yellow-green. We’re looking at Mars’ Russell Crater dune field. It’s covered seasonally by carbon dioxide frost; this image shows the dune field after the frost has evaporated. The faint dark traces that meander across the dunes are actually dust devil tracks.