San Antonio TX (SPX) Jun 22, 2022 Southwest Research Institute scientists combined data from NASA's...
Southwest Research Institute scientists combined data from NASA's New Horizons mission with novel laboratory experiments and exospheric modeling to reveal the likely composition of the red cap on Pluto's moon Charon and how it may have formed.
"In addition to all the fascinating features discovered on Pluto's surface, the flyby revealed an unusual feature on Charon, a surprising red cap centered 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.
"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.
The team realistically replicated Charon surface conditions at SwRI's new Center for Laboratory Astrophysics and Space Science Experiments to measure the composition and color of hydrocarbons produced on Charon's winter hemisphere as methane freezes beneath the Lyman-alpha glow.
The team fed the measurements into a new atmospheric model of Charon to show methane breaking down into residue on Charon's north polar spot.
"Our team's novel 'dynamic photolysis' experiments provided new limits on the contribution of interplanetary Lyman-alpha to the synthesis of Charon's red material," Raut said.
SwRI scientists also developed a new computer simulation to model Charon's thin methane atmosphere.
"The model points to 'explosive' seasonal pulsations in Charon's atmosphere due to extreme shifts in conditions over Pluto's long journey around the Sun," said Dr. Ben Teolis, lead author of a related paper titled "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot" in Geophysical Research Letters.
"Ethane is less volatile than methane and stays frozen to Charon's surface long after spring sunrise. Exposure to the solar wind may convert ethane into persistent reddish surface deposits contributing to Charon's red cap."