Each color a different material
The global view of Mars shown here has a spatial resolution of 2 kilometers per pixel, although higher resolution data products are quite possible and are already in the works. This contrast-enhanced mosaic (image 1) reveals an unprecedented variety and detail of colors across the Martian surface, which at the same time provides information about its composition. It is well known that most of Mars is reddish in color, due to the high amount of oxidized iron in the dust on its surface, earning it the nickname "Red Planet." But it is also immediately noticeable that a not small part of Mars is rather dark, on image 1 bluish, colored. In fact, these are grayish-blackish sands, which are of volcanic origin and form far-reaching dark sand layers on Mars, but above all also were piled up by the wind to imposing sand dunes or enormous dune fields on the floor of impact craters. These unweathered sands consist of dark, basaltic minerals, of which also volcanic lava on earth is composed.
Material weathered under the influence of water, on the other hand, tends to take on lighter shades over time. For example, clay and sulfate minerals, the two most common water-weathered minerals on Mars, appear particularly bright on such color composites and are relatively easy to recognize on closer views. One of the largest clay mineral deposit on Mars around the former outflow channel Mawrth Vallis, is not shown in this view but has been observed by HRSC earlier and attest to a long-term existence of liquid water on Mars, with the original, basaltic source rock being altered at neutral pH and relatively warm temperatures weathered to clay minerals. Large occurrences of the likewise light-colored sulfate minerals can be seen in this view of Mars within the Valles Marineris canyon system (image 4). Here, they are covered by a thin veneer of dark sand and thus show their impressive colour variations only on closer look by HRSC. Sulphate minerals indicate less life-friendly environmental conditions at low pH values.
Faint, bright to light blue areas actually show clouds in the atmosphere (image 4), as images containing clouds could not be avoided so far in the creation of this first version of the global mosaic. The depths of Valles Marineris are also covered by atmospheric phenomena. However, these are fogs and hazes (image 4), which are particularly fond of forming in depressions at certain times of the day and year.