Mars has its distinctive red look because of the excess of iron on the surface of the planet. Pure iron itself is not red, but when it reacts with oxygen through a process called oxidation, iron forms iron oxide, also known as rust here on Earth. And like rust and the iron in our blood, Mars has become a distinct hue of red.

Where did all this iron come from? The element generally originates from the gaseous remains given off from long-dead stars, and, along with other elements, gravitationally collapses to form new stars and planets. While much of Earth’s iron sank into its core during Earth’s formation, scientists believe that due to Mars’ smaller size and gravity, much of the iron remained at or near the surface, leaving it available to rust into the red compound we see today.

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Mars is red because the soil contains a lot of iron oxide. Iron oxide is actually something you see every day--rust. Very simply put, the soil on the planet contains a large amount of rust. Even sometimes from Earth, Mars is visibly red, which is why is was used to represent the god of war for civilizations such as Rome.

One of the most common minerals on the surface of Mars is iron oxide (rust). Rust is red, and because of that, so is Mars.

Thank you for the great question! Mars is red for two reasons. The first reason: Mars' surface is covered with rust particles, known as iron oxide, which reflect red light due to the structure and shape of the atoms in it. The strong winds on Mars blow the rust particles around, which leaves the surface relatively evenly covered around the planet. The second reason: these particles are dispersed in the atmosphere, much like dust, and bend red light strongly because of the particle size. This is known as light scattering. On Earth, this type of scattering makes the sky blue. Nobody knows exactly how the rust came to be on Mars. On Earth, most rust comes from a reaction of iron, oxygen, and water, but it is known that rust can be generated through other processes that don't involve water.