Mars ferric oxide map
This map, by the OMEGA instrument on ESA’s Mars Express, plots the distribution of ferric oxides, a mineral phase of iron, across the surface of Mars. Ferric oxides (an oxide of iron) are present everywhere on the planet: within the bulk crust, lava outflows and the dust oxidised by chemical reactions with the martian atmosphere. Mars’ atmosphere contains both carbon dioxide and water, both of which provide a source of oxygen to react with the iron in the surface.
The intensity in colour from blue to red represents the degree of oxidation of the surface from low to high, and therefore is related to the abundance of iron-bearing minerals.