Why is Mars red?

Mars appears red due to the prevalence of rusted iron elements on its surface. The elements blow up into the atmosphere, intensifying the red color.

The iron elements on the surface of Mars became red when they rusted, a process called oxidation. This occurs when the iron chemically reacts with oxygen atoms and becomes iron oxide. Scientists have not reached a consensus on why or when the oxidation occurred, although the oxidized metal provides grist for the belief that Mars once had water. Knowledge of Mars' blood-red tint stretches back to ancient times, when the Romans named the planet after their god of war.