Mars glows red even to the naked eye, which is why ancient cultures linked it to war and fire — and why it is “Mangal” in Indian astronomy. The colour comes from rust.
Rusty dust
Mars’s surface is covered in fine dust and rocks rich in iron. Over billions of years that iron reacted with oxygen — from water and the thin atmosphere — to form iron oxides, the same family of compounds as rust on an old bicycle. The fine reddish dust is blown around by winds and coats almost everything.
A watery clue
Research published in 2025 suggested that the dust may contain an iron oxide called ferrihydrite, which forms in the presence of cool water. If correct, Mars rusted while liquid water was still around, early in its history — another sign the planet was once much wetter.
Not red everywhere
Just below the surface, rovers have found grey and bluish rock. The red is a thin dusty coating. Rover wheels and drills often expose darker material underneath.
The Martian sky
Dust in the air makes the daytime sky on Mars a butterscotch or pinkish colour, while sunsets appear bluish — the reverse of Earth, because the fine dust scatters light differently.
Related: why Earth’s sky is blue.
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