Mars , or the Red Planet , is the fourth planet from the Sun in the Solar System and Earth's outer neighbor. It is classified as a terrestrial planet, meaning rocky or rocky. Its name in Arabic is derived from the word "amrakh," meaning "having red spots," as in the phrase "a bull with red spots." The Latin name Mars refers to the Roman god of war. The nickname "Red Planet" comes from the planet's reddish hue, caused by the high concentration of iron oxide dust on its surface and in its atmosphere. Mars has a diameter of approximately 6,792 km (4,220 miles), roughly half the diameter of Earth, making it the second smallest planet in the Solar System after Mercury . Its surface area is about one-quarter that of Earth. Mars orbits the Sun at a distance of approximately 228 million km, or about 1.5 times the distance between Earth and the Sun. Its smooth , polar basin covers roughly 40% of the planet's northern hemisphere and may have a significant influence on the planet's geological formation. Mars has two moons, the first called Deimos , meaning terror in Greek, and the second Phobos , meaning fear . They are small and irregularly shaped, and could be asteroids that it captured, similar to 5261 Eureka , which is a Martian Trojan .