The bright, red regions were thought to be caused by molecules known as tholins, which are organic compounds that rain down onto the surface after cosmic rays or ultraviolet light interact with the methane in Pluto’s surface and atmosphere.

Why is Pluto brown and white?

The dark color is believed to be the result methane and nitrogen in the atmosphere interacting with ultraviolet light and cosmic rays, creating the dark particles (“tholins”) common to Pluto. And then there are the “Brass Knuckles”, a series of equatorial dark areas on the leading hemisphere.

What is causing the mountain peaks on Pluto to appear white?

While the peaks of the two-and-a-half-mile high mountaintops are composed of methane, the white methane frost is produced by condensation that takes place at higher, warmer altitudes in Pluto’s atmosphere.