The research combined data from spacecraft with new laboratory experiments, models of Pluto’s largest moon – ScienceDaily

Scientists at the Southwest Research Institute combined data from NASA’s New Horizons mission with new laboratory experiments and exosphere modeling to uncover the likely composition of Pluto Charon’s red cap and how it may have formed. This first-ever description of Charon’s dynamic methane atmosphere, using new experimental data, provides a fascinating look at the origin of this moon’s red spot, as described in two recent articles.

“Before New Horizons, Hubble’s best images of Pluto revealed only blurred spots of reflected light,” said Randy Gladstone of SwRI, a member of New Horizons’ research team. “In addition to all the fascinating features found on the surface of Pluto, the flight revealed an unusual feature of Charon, a surprising red hat centered on its North Pole.

Shortly after the 2015 meeting, New Horizons scientists suggested that reddish “toline-like” material at the Charon pole could be synthesized by ultraviolet light, which breaks down methane molecules. They are captured after escaping from Pluto and then frozen in the polar regions of the moon during their long winter nights. Tolins are sticky organic residues formed by chemical reactions driven by light, in this case the ultraviolet glow of Lyman-alpha scattered by interplanetary hydrogen molecules.

“Our findings show that drastic seasonal jumps in Charon’s thin atmosphere, as well as light that breaks down condensing methane frost, are key to understanding the origins of Charon’s red polar zone,” said Dr. Ujjwal Raut of SwRI. author of an article entitled “Charon’s Refractory Factory” in the journal Science Advances. “This is one of the most illustrative and striking examples of surface-atmosphere interactions observed so far 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 when methane freezes under Lyman-alpha glow. The team transferred the measurements to a new atmospheric model of Charon to show that methane decomposes into a residue in the northern polar spot of Charon.

“Our team’s new” dynamic photolysis “experiments have set new limits for the contribution of interplanetary Lyman-alpha to the synthesis of Charon’s red material,” Raut said. “Our experiment condenses methane in an ultra-high vacuum chamber when exposed to Lyman-alpha photons to reproduce Charon’s pole conditions with high accuracy.”

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

“The model shows ‘explosive’ seasonal ripples in Charon’s atmosphere due to extreme changes in conditions during Pluto’s long journey around the Sun,” said Dr. Ben Theolis, lead author of a related article entitled Charon’s Extreme Exospheric Dynamics: Implications for the Red Spot ”c Letters for geophysical research.

The team introduced the results of SwRI’s ultra-realistic experiments into the atmospheric model to estimate the distribution of complex hydrocarbons resulting from the decomposition of methane under ultraviolet light. The model has polar zones, generating mainly ethane, a colorless material that does not contribute to reddish color.

“We believe that ionizing radiation from the solar wind decomposes Lyman’s alpha polar frost to synthesize increasingly complex, redder materials responsible for the unique albedo of this mysterious moon,” Raut said. “Ethane is less volatile than methane and remains frozen on Charon’s surface long after the spring sunrise. Exposure to the solar wind can turn ethane into persistent reddish surface deposits that contribute to Charon’s red hat.”

“The team is set to study the role of the solar wind in the formation of the red pole,” said Dr. Josh Kamer of SwRI, who has received continued support from NASA’s New Frontier data analysis program.

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Materials provided by Southwestern Research Institute. Note: Content can be edited for style and length.

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