NASA’s New Horizons Data Helps Identify a Possible Source for Pluto’s Moon Charon’s Red Cap

 SwRI scientists also developed a new computer simulation to model Charon’s thin methane atmosphere.

HIGHLIGHTS

• SwRI scientists conducted novel ‘dynamic photolysis’ experiments
• Drastic seasonal surges in its atmosphere could be key to red polar zone
• Charon is the largest of the five known moons of Pluto

Scientists combined data from NASA’s New Horizons mission with novel laboratory experiments and exospheric modelling to reveal the likely composition of the red cap on Pluto’s moon Charon and how it may have formed. This first-ever description of Charon’s dynamic methane atmosphere using new experimental data provides a fascinating glimpse into the origins of this moon’s red spot as described in two recent articles. “Prior to New Horizons, the best Hubble images of Pluto revealed only a fuzzy blob of reflected light,” said SwRI’s Randy Gladstone, a member of the New Horizons science team. “In addition to all the fascinating features discovered on Pluto’s surface, the flyby revealed an unusual feature on Charon, a surprising red cap centred on its north pole.”

 

Soon after the 2015 encounter, New Horizons scientists proposed that a reddish “tholin-like” material at Charon’s pole could be synthesized by ultraviolet light breaking down methane molecules. These are captured after escaping from Pluto and then frozen onto the moon’s polar regions during their long winter nights. Tholins are sticky organic residues formed by chemical reactions powered by light, in this case, the Lyman-alpha ultraviolet glow is scattered by interplanetary hydrogen molecules.

 

“Our findings indicate that drastic seasonal surges in Charon’s thin atmosphere, as well as light breaking down the condensing methane frost, are key to understanding the origins of Charon’s red polar zone,” said SwRI’s Dr Ujjwal Raut, lead author of a paper titled “Charon’s Refractory Factory” in the journal Science Advances. “This is one of the most illustrative and stark examples of surface-atmospheric interactions so far observed at a planetary body.”