Source of Charon’s red north pole is probably Pluto

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. Methane gas wafting from Pluto’s surface sticks to the frigid pole during the moon’s decades-long winter; ultraviolet light from the sun then transforms the methane into reddish organic goop known as tholins.

Planetary scientist Will Grundy of Lowell Observatory in Flagstaff, Ariz., and colleagues used images of Charon taken by the New Horizons spacecraft and computational analysis to demonstrate that methane from Pluto is a reasonable culprit for Charon’s rust-colored pole.