Mars is known as the Red Planet because iron-rich minerals in its surface dust oxidize and create a reddish appearance.
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury. Its thin atmosphere is composed mostly of carbon dioxide, and the planet has polar ice caps, volcanoes, impact craters and enormous dust storms.
Mars contains Olympus Mons, the largest known volcano in the Solar System, and Valles Marineris, a canyon system thousands of kilometres long. The planet has two small moons, Phobos and Deimos.
Mars is often confused with Venus in questions about Earth’s neighbouring planets, but Venus is covered by a dense carbon-dioxide atmosphere and has a pale yellow appearance from space. Mars has been explored by orbiters, landers and rovers, including Curiosity and Perseverance, because its ancient surface preserves evidence of past water activity.