The study, published in the journal Nature, has revealed that the mysterious red spot in Charon’s North Pole were actually a build-up of carbon-rich complex molecules that came from Pluto’s leaky atmosphere. According to the study, the atmosphere of the dwarf planet drifting into space could be captured by its satellite. However, Pluto’s traveling atmosphere freeze out on its frigid moon Charon. Radiation will then quickly transform the methane and nitrogen ices into a dark-red chemical, known as tholin.

Pluto’s escaping atmosphere is due to the small size of the dwarf planet. While Pluto managed to hold to some of its atmosphere, much of the gas around it leaks into space. As the escaped gas from Pluto lurks around in space, Charon manages to catch a few. However, the warm temperature in Charon’s equator allows less of the material from Pluto to fall to the moon’s surface. The moon’s North Pole seems to be cold enough for methane to stick. Due to this, methane accumulates in the in Charon’s magnetic pole. The lead author of the study explained, “As more and more fragments join up, they build progressively bigger and more carbon-rich, complicated molecules until they are so complex that we don’t even try to give them chemical names, just describe them with generic terms like ‘organic molecules’ or ‘tholins.’These are what produce the reddish color.”