Mars and Pluto, Compared

People have called Mars the Red Planet for centuries, but Mars might have to share that name. Dwarf planet Pluto also has a reddish hue, but for a very different reason. The surface of Mars contains lots of iron minerals. These minerals oxidize, or rust, in the presence of oxygen, and in the distant past, liquid water. The entire surface of Mars is literally rusty dust! We don’t know yet why Pluto is reddish, but chemistry appears to be the culprit! Sunlight could cause hydrocarbons (e.g., methane and carbon monoxide) on Pluto’s icy surface and in its chilly atmosphere to combine, forming compounds that rain red-hued materials upon the dwarf planet. Whatever the different reasons for their reddish color, Mars and Pluto are two interesting planets in our Solar System that shed some light about how our Solar System formed and continues to develop.