This was Nasa's 'Image of the day' on the 25th July.
Though Mars is the Red Planet, false-colour images can help us learn about its weather and geology. This image shows a variety of wind-related features on the Red Planet near the centre of Gamboa Crater. Larger sand dunes form sinuous crests and individual domes. There are tiny ripples on the tops of the dunes, only several feet from crest-to-crest. These merge into larger mega-ripples about 30 feet apart that radiate outward from the dunes.
More information is available on the 'Image of the day' site.
Image Credit: NASA/JPL-Caltech/University of Arizona