Why Is Mars Red?

Chemistry of Martian Red Color

Planet Mars, Earth visible in background (Digital Composite)
World Perspectives/Photographer's Choice/Getty Images

When you look up in the sky, you can recognize Mars by its red color. Yet, when you see photos of Mars taken on Mars, many colors are present. What makes Mars the Red Planet and why doesn't it always look red close-up?

The short answer for why Mars appears red, or at least red-orange, is because the Martian surface contains a large amount of rust or iron oxide. The iron oxide forms a rust dust that floats in the atmosphere and sits as a dusty coating across much of the landscape.

Why Mars Has Other Colors Up Close

The dust in the atmosphere causes Mars to appear very rusty from space. When viewed from the surface, other colors are apparent, in part because landers and other instruments don't have to peer through the whole atmosphere to see them, and partly because rust exists in colors other than red, plus there are other minerals on the planet. While red is a common rust color, some iron oxides are brown, black, yellow and even green! So, if you see green on Mars, it doesn't mean there are plants growing on the planet. Rather, some of the Martian rocks are green, just like some rocks are green on Earth.

Where Does the Rust Come From?

So, you may be wondering where all this rust comes from since Mars has more iron oxide in its atmosphere than any other planet. Scientists are not completely sure, but many believe the iron was pushed up by the volcanoes that used to erupt. Solar radiation caused atmospheric water vapor to react with the iron to form iron oxides or rust. Iron oxides also may have come from iron-based meteorites, which can react with oxygen under the influence of solar ultraviolet radiation to form iron oxides.


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Helmenstine, Anne Marie, Ph.D. "Why Is Mars Red?" ThoughtCo, Aug. 26, 2020, thoughtco.com/why-mars-is-red-603792. Helmenstine, Anne Marie, Ph.D. (2020, August 26). Why Is Mars Red? Retrieved from https://www.thoughtco.com/why-mars-is-red-603792 Helmenstine, Anne Marie, Ph.D. "Why Is Mars Red?" ThoughtCo. https://www.thoughtco.com/why-mars-is-red-603792 (accessed March 22, 2023).