Scientists identify source of red ‘Mordorian’ pigment in Charon’s polar cap

(ORDO NEWS) — To determine the likely composition of the reddish cap on Pluto’s moon Charon and how it might have formed, US scientists at the Southwestern Research Institute combined data from NASA‘s New Horizons mission with new laboratory experiments and simulations of the celestial body’s exosphere.

The new results show that the color of the cap is most likely influenced by seasonal changes in Charon’s rarefied atmosphere, combined with light rays breaking up the condensing methane frost in the polar zones. Articles on this topic have been published in Geophysical Research Letters and Science Advances.

“Before New Horizons, the best images of Pluto taken by the Hubble telescope showed only some kind of fuzzy light spot,” explains one of the authors of these papers, Randy Gladstone of the Southwestern Research Institute, a member of the New Horizons scientific group.

“In addition to all the exciting features found on Pluto’s surface, the spacecraft’s flyby also made it possible to clearly see Charon’s unusual feature, the amazing red cap at its north pole.”

Shortly after this expedition in 2015, New Horizons scientists speculated that the reddish “tholin-like” material at Charon’s pole could be due to ultraviolet light destroying methane molecules. These volatiles, captured from Pluto and then frozen in the polar regions of Charon during the long winter nights,

Now, the first-ever description of Charon’s dynamic methane atmosphere using new experimental data has provided a fresh look at the origin of the “Mordorian” (as it was unofficially dubbed) red spot on this satellite.

“Our results suggest that the dramatic seasonal changes in Charon’s rarefied atmosphere, as well as radiation that breaks down condensing methane frost, may hold the key to understanding the origin of Charon’s polar red zone,” said Ujwal Raut, lead author of the paper in the journal Science Advances.

“This is one of the clearest and most striking examples of the interaction of the surface and the atmosphere of those that have so far been observed on a planetary body.”

The team reproduced the conditions on Charon’s surface with maximum realism at the Southwestern Research Institute’s new Center for Laboratory Astrophysical and Space Science Experiments (CLASSE) to study the composition and color of hydrocarbons formed when methane is frozen by cosmic rays, and introduced these data into a new model of Charon’s atmosphere, thus showing that methane molecules do break down to form the characteristic color spot found at Charon’s north pole.

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