Mars has been known as the "Red Planet" for thousands of years, and the reason behind its color is surprisingly familiar. The reddish appearance comes from iron oxide — the same compound that forms rust on old metal here on Earth. The surface of Mars is covered in a fine dust rich in iron, and over an immense span of time that iron reacted with oxygen and turned a rusty red. When sunlight hits this dusty surface, the planet glows with the warm orange-red tone we see from Earth and through telescopes.

The rusting of Mars is the result of chemistry playing out across billions of years. Iron on the Martian surface combined with oxygen to form iron oxide, the powdery red mineral that now coats much of the planet. Scientists are still studying exactly where that oxygen came from. Some of it may have come from ancient water, since Mars is believed to have had rivers and possibly standing water in its distant past. Water can break apart and release oxygen, which then bonds with iron. Sunlight breaking apart molecules in the thin atmosphere may also have contributed. Either way, the end result is a surface gradually transformed into rust.

The red dust of Mars does not stay still. The planet experiences enormous dust storms, some of which can grow large enough to wrap around the entire globe. These storms lift the fine iron-rich particles high into the atmosphere and spread them across every region of the planet. This is why Mars appears uniformly red rather than patchy — the dust is constantly being redistributed. The same dust also gives the Martian sky its distinctive butterscotch tone during the day, a striking contrast to the blue skies of Earth.

The rusty coating of Mars is mostly a surface feature. Beneath the thin layer of red dust, the rock can be quite different in color. Spacecraft and rovers exploring Mars have found grey and darker rocks once the dusty top layer is brushed away or worn down. When rover instruments grind into Martian stones, the freshly exposed material often looks nothing like the red surface above it. This shows that the red color is essentially a thin, weathered shell — a planet-wide layer of oxidized dust sitting on top of rock that never fully rusted.

This article was written using information from Wikipedia.