These barchan-like dunes are formed by the escape of sand-sized material from a deposit inside the crater. There is some dispute over whether the sand was going out of or into the crater, as the shape of the dunes is not diagnostic. In one volume of scientific abstracts, two successive authors prominently displayed this photograph, with opposite interpretations. The view that the dunes are exiting the crater is favored here because it seems very unlikely that Viking happened along at the right moment to catch a group of barchans migrating across a surface and curving out of their way to fall into a crater and collect there.
Latitude –51°, Longitude 8°, near the crater Green between
Argyre and Hellas Planitia. Viking photograph 571B53, NGF orthographic
version, clear filter.