Scientists combined data from NASA’s New Horizons mission with new lab experiments and extra-atmospheric modeling to reveal the possible makeup of the red mantle on Pluto’s moon Charon and how it 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. “Before New Horizons, the best Hubble images of Pluto revealed a hazy mass of reflected light,” said Randy Gladstone of SwRI, a member of the New Horizons science team. “In addition to all the remarkable features detected on Pluto’s surface, a flyby of Pluto revealed an unusual feature of Charon, a sudden red mantle centered at the North Pole.”
Shortly after the 2015 encounter, New Horizons scientists suggested that a reddish “tholin-like” substance at Charon’s pole could be synthesized by ultraviolet radiation that breaks down methane molecules. It is captured after escaping from Pluto and then frozen in the polar regions of the Moon during the long winter nights. Tholene is a sticky organic residue formed by chemical reactions powered by light, in this case, Lyman’s alpha ultraviolet glow is scattered by interplanetary hydrogen molecules.
“Our findings suggest that intense seasonal elevations in Charon’s thin atmosphere, as well as the light that breaks through the condensing methane frost, are key to understanding the origins of Charon’s red polar region,” said Dr Ujwal Raut of SwRI, lead author of the research paper “The Charon Factory”. for refractories” in Science Advances. “This is one of the most illustrative and clear examples of surface-atmospheric interactions so far observed in a planetary body.”
The team realistically replicated Charon’s surface conditions at SwRI’s new Center for Laboratory Astrophysics and Space Science Experiments (CLASSE) to measure the composition and color of hydrocarbons produced in Charon’s winter hemisphere while methane freezes under the Lyman-alpha glow. The team inserted measurements into a new atmospheric model of Charon to show the decay of methane into residue in the Arctic Charon Spot.
“Our team’s new ‘photodynamic decay’ experiments provided new frontiers for the contribution of interplanetary Lyman-alpha to the composition of red Charon,” said Raut. “Our experiment condensed methane in a vacuum chamber under exposure to Lyman alpha photons to replicate conditions with high precision at the Charon electrodes.”
SwRI scientists have also developed new computer simulations to model Charon’s thin methane atmosphere.
Dr. Ben Thewlis, lead author of a related paper titled “Extreme exosphere dynamics in Charon: Implications for a red spot” said in Geophysical Research Letters.
The team incorporated results from ultra-realistic SwRI experiments into an atmospheric model to estimate the distribution of complex hydrocarbons arising from methane decomposition under the influence of ultraviolet light. The pattern contains polar regions that primarily generate ethane, a colorless substance that does not contribute to the reddish colour.
“We believe that ionizing radiation from the solar wind breaks down the polar frost cooked with Alpha Lymans to create more complex, redder materials responsible for the unique whiteness on this mysterious moon,” said Raut. “Ethane is less volatile than methane and remains frozen on Charon’s surface long after spring sunrise. Exposure to the solar wind may convert ethane into permanent reddish surface deposits that contribute to the red Charon mantle.”
“The team is set to investigate the role of the solar wind in shaping the Red Pole,” said Dr. Josh Kamer of SwRI, who has continued support from NASA’s new Frontier Data Analysis Program.