Mars probably got the nickname, The Red Planet, due to the rusty color of its soil, which is comprised of iron-rich minerals. The Egyptians called it the red one because it appears more reddish in the night sky. What makes it appear reddish is a combination of the fact that its surface is comprised of iron-rich minerals that essentially rust (or oxidize) and that the dust made of these minerals is kicked up into the atmosphere, giving the atmosphere a reddish hue from far away (e.g., from Earth!). The Martian surface is not all rust-colored, however. Depending on the oxidation process, the minerals can be a range of colors from butterscotch to rust. And, believe it or not, some places on Mars might even have a slight greenish tinge due to the presence of olivine...much like the green sand beach in Hawaii.