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

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

Scientists have identified the source of the red Mordor pigment in Charon's polar cap

Photo: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

To determine the likely composition of the reddish “cap” on Pluto's moon Charon and how it might have formed, American scientists from the Southwestern Research Institute combined NASA's New Horizons mission data with new laboratory experiments and modeling 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, in combination with light rays that destroy the condensing methane frost in the polar zones. Articles on this topic have been published in    Geophysical Research Letters     Science Advances journals.

“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 articles, Randy Gladstone of the Southwestern Research Institute, a member of the New Horizons science team. — In addition to all the exciting features found on Pluto's surface, the spacecraft's flyby also made it possible to clearly see the unusual feature of Charon — amazing red cap at its north pole".

Shortly after this expedition in 2015, New Horizons scientists suggested that the reddish “tholin-like” material at Charon's pole may 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, are the organic residues of chemical reactions caused by the ultraviolet glow on the Lyman-alpha hydrogen line, due to the scattering of light quanta by interplanetary hydrogen molecules.< /p>

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 has been informally dubbed) a red spot on this satellite.

"Our results show that abrupt seasonal changes in Charon's rarefied atmosphere, as well as radiation that destroys condensing methane frost, may serve as a key to understanding the origin of Charon's red polar zone, — says Ujwal Raut, lead author of an article in the journal Science Advances. — This is one of the most clear and 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 prevailing on with maximum realism  surface of Charon, at Southwest Research Institute's new Center for Laboratory Astrophysical and Space Science Experiments (CLASSE) to study the composition and color of hydrocarbons produced when methane is frozen by cosmic rays, and fed the data into a new model of the atmosphere Charon, thus showing that methane molecules really break down with the formation of a characteristic color spot found at the north pole of Charon.

Prepared by: Sergey Daga