The red color of the planet Mars, often called the "Red Planet," comes from the presence of iron oxide (commonly known as rust) on its surface. The iron minerals on Mars have oxidized, forming iron oxide, which coats the dust and rocks on the planet, giving it its distinctive reddish hue. Recent research suggests that the specific type of iron oxide contributing to Mars' red color is primarily ferrihydrite, an iron oxide mineral that forms in the presence of cool water. This contrasts with earlier beliefs that hematite was the main iron oxide. Ferrihydrite likely formed when liquid water was present on Mars' surface billions of years ago, indicating Mars' wetter history. Over time, this rusted iron broke down into fine dust, which is spread around the planet by Martian winds, coloring much of its surface red. Thus, the red coloration of Mars is essentially rust from iron minerals that oxidized due to interactions with water and/or the atmosphere in the planet's past.