Mars is the fourth planet from the sun. Befitting the red planet's bloody color, the Romans named it after their god of war. The Romans copied the ancient Greeks, who also named the planet after their god of war, Ares. Other civilizations also typically gave the planet names based on its color — for example, the Egyptians named it "Her Desher," meaning "the red one," while ancient Chinese astronomers dubbed it "the fire star."

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The red planet is home to both the highest mountain and the deepest, longest valley in the solar system. Olympus Mons is roughly 17 miles high, about three times as tall as Mount Everest, while the Valles Marinerissystem of valleys — named after the Mariner 9 probe that discovered it in 1971 — can go as deep as 6 miles and runs east-west for roughly 2,500 miles, about one-fifth of the distance around Mars and close to the width of Australia or the distance from Philadelphia to San Diego.