NASA's New Horizons spacecraft showed us a part of Charon we'd never seen before: a rusty red section crowning its polar region. It's an intriguing feature, something the mission's ground team hadn't seen before, so they spent the past year studying all the data and images the probe sent back. Now, they have their answer. The red cap is apparently the product of methane gas escaping the dwarf planet itself and freezing solid in the frigid pole. Team leader Will Grundy, likens Pluto to a "graffiti artist, spray-painting its companion with a reddish stain that covers an area the size of New Mexico."