Mars Is Red Because of Rust

For millennia, the fiery hue of Mars earned it the nickname "The Red Planet," inspiring associations with war and bloodshed in ancient cultures. The true culprit behind this color, however, is a chemical reaction familiar to anyone who has seen an old car or a forgotten tool left in the rain. The Martian surface is covered in a fine layer of iron oxide, the very same compound we call rust. This isn't a solid crust of metal, but rather a powdery dust, known as regolith, that blankets the rocks and soil.

The story of this rust begins billions of years ago when Mars was a very different world. Iron, spewed onto the surface by ancient volcanoes, was plentiful in the planet's crust. Back then, Mars likely had a thicker atmosphere and liquid water. This combination of iron and atmospheric oxygen—possibly released by the breakdown of water molecules by solar radiation—triggered a slow, planet-wide oxidation process. Over eons, this transformed the iron-rich landscape, staining it a deep reddish-orange.

This rusty dust didn't stay put. Mars is famous for its colossal dust storms, some of which are powerful enough to engulf the entire planet for weeks. These global tempests have churned up the fine iron oxide particles for ages, distributing them across the vast plains and craters. This process created the uniform crimson color we observe today, making the entire planet a testament to an ancient chemical reaction driven by a long-lost environment.