Source of Charon’s red north pole is probably Pluto

Charon, moon of Pluto

Methane from Pluto plus UV light from the sun are responsible for Charon’s red pole, seen in this mosaic of images from the New Horizons spacecraft. 

NASA, JHUAPL, SWRI

The ruddy north pole of Charon, the largest moon of Pluto, is probably a stain from Pluto itself, researchers report online September 14 in Nature.