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 on 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.

Pluto’s methane has been a suspect ever since researchers first saw Charon’s rust-colored polar cap — not seen anywhere else in the solar system — during the 2015 flyby of the New Horizons spacecraft. Will Grundy, a planetary scientist at Lowell Observatory in Flagstaff, Ariz., and colleagues used images of Charon and calculations to demonstrate that methane from Pluto is a reasonable culprit in forming Charon’s red pole.

Christopher Crockett is a freelance science writer and editor based in Arlington, Va. He has a Ph.D. in astronomy from the University of California, Los Angeles.

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