Bright dunes on Mars

Seasonal changes observed on the surface of Mars can in part: be attributed to the transport of geological materials by wind(1). Images obtained by or biting spacecraft in the 1970s showed large wind-formed features such as du nes, and revealed regional time-varying albedos that could be attributed to the effects of dust erosion and deposition. But the resolution of these im ages was insufficient to identify different types and sources of aeolian ma terials, nor could they reveal aeolian deposits other than large dunes or e xtensive surface coverings that were redistributed by dust storms. Here we present images of Mars with up to 50 times better resolution. These images show that martian dunes include at least two distinct components, the brigh ter of which rye interpret to be composed of relatively soft minerals, poss ibly sulphates. We also find large areas of the martian surface that have s everal metres or more of aeolian mantle lacking obvious bedforms.