Why is Mars red?
Mars looks red because its surface is covered in dust and rocks rich in iron oxide, essentially rust. Fine dust in the thin air also gives the sky a reddish tint.
Iron minerals in Martian rocks reacted with small amounts of water and oxygen over billions of years, forming iron oxides. Winds then spread fine rusty dust across the whole planet, coating the surface. Beneath the dust, many rocks are darker and gray.
In 2025, a study suggested that the main dust mineral may be ferrihydrite, an iron oxide that forms with water. If correct, this hints that Mars rusted while it was still wet, earlier than scientists once thought.
The Red Planet in history
Its reddish color made Mars stand out in the night sky. The ancient Greeks and Romans linked it with blood and war and named it after their war gods, Ares and Mars. Mars has two small moons, Phobos and Deimos, meaning fear and dread.
Did You Know?
Martian dust storms can grow so large that they cover the whole planet for weeks, as happened in 2018, ending the mission of NASA's Opportunity rover.