Mars is known as the Red Planet because iron minerals in its surface materials create a reddish appearance.
Mars is the fourth planet from the Sun and is much smaller than Earth. Its thin atmosphere consists mostly of carbon dioxide, with smaller amounts of nitrogen and argon. The planet has polar ice caps, immense volcanoes, deep canyons, impact craters, and evidence that liquid water once flowed across parts of its surface.
The reddish color comes largely from oxidized iron, effectively rust, in dust and rocks. Mars has two small moons, Phobos and Deimos. Its most famous volcano, Olympus Mons, is the largest known volcano in the Solar System, while Valles Marineris forms a vast canyon system. Robotic missions have studied Mars since the 1960s, and rovers including Curiosity and Perseverance have examined its geology while searching for signs of ancient habitability.