Bruce Murray Space Image Library
Mars dunes in false color
From NASA's website:
Though Mars is the Red Planet, false-color 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 center 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. The larger, brighter formations that are roughly parallel are called "Transverse Aeolian Ridges" (TAR). These TAR are covered with very coarse sand.
The mega-ripples appear blue-green on one side of an enhanced color cutout while the TAR appear brighter blue on the other. This could be because the TAR are actively moving under the force of the wind, clearing away darker dust and making them brighter. All of these different features can indicate which way the wind was blowing when they formed. Being able to study such variety so close together allows us to see their relationships and compare and contrast features to examine what they are made of and how they formed.