Researchers find possible source for charon's red cap

This first-ever depiction of Charon's methane atmosphere using fresh experimental data gives an insight into the origins of this moon's red patch. Scientists combined data from

NASA`s New Horizons mission with novel laboratory experiments and exospheric modelling to reveal the likely composition of the red cap on Pluto`s moon Charon and how it may have 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. ALSO, READ: NASA UNVEILS SWARM OF CELL PHONE-SIZED ROBOTS TO HUNT FOR ALIEN LIFE "Prior to New Horizons, the best Hubble images of Pluto revealed only a fuzzy blob of

reflected light," said SwRI`s Randy Gladstone, a member of the New Horizons science team. "In addition to all the fascinating features discovered on Pluto`s surface, the flyby

revealed an unusual feature on Charon, a surprising red cap centred 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. These are captured after escaping from Pluto and then frozen onto

the moon`s polar regions during their long winter nights. Tholins are sticky organic residues formed by chemical reactions powered by light, in this case, the Lyman-alpha ultraviolet glow

is scattered by interplanetary hydrogen 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. "This is one of the most illustrative and stark examples of surface-atmospheric interactions so far observed at a planetary body." The team realistically

replicated Charon surface conditions at SwRI`s new Center for Laboratory Astrophysics and Space Science Experiments (CLASSE) 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. "Our experiment condensed methane in an ultra-high vacuum chamber under exposure to Lyman-alpha photons to replicate with high fidelity the conditions at

Charon`s poles." 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. The team input the results from SwRI`s ultra-realistic experiments into the atmospheric model to

estimate the distribution of complex hydrocarbons emerging from methane decomposition under the influence of ultraviolet light. The model has polar zones primarily generating ethane, a

colorless material that does not contribute to a reddish color. "We think ionizing radiation from the solar wind decomposes the Lyman-alpha-cooked polar frost to synthesize increasingly

complex, redder materials responsible for the unique albedo on this enigmatic moon," Raut said. "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." "The team is set to investigate the

role of solar wind in the formation of the red pole," said SwRI`s Dr. Josh Kammer, who secured continued support from NASA`s New Frontier Data Analysis Program.Scientists combined data

from NASA`s New Horizons mission with novel laboratory experiments and exospheric modelling to reveal the likely composition of the red cap on Pluto`s moon Charon and how it may have 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. "Prior to New Horizons, the best Hubble images of Pluto revealed only a fuzzy blob of reflected light," said SwRI`s Randy Gladstone, a member of the New Horizons

science team. "In addition to all the fascinating features discovered on Pluto`s surface, the flyby revealed an unusual feature on Charon, a surprising red cap centred 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. These are captured after escaping from Pluto and then frozen onto the moon`s polar regions during their long winter nights. Tholins are sticky organic

residues formed by chemical reactions powered by light, in this case, the Lyman-alpha ultraviolet glow is scattered by interplanetary hydrogen 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. "This is one of the most illustrative and stark examples

of surface-atmospheric interactions so far observed at a planetary body." The team realistically replicated Charon surface conditions at SwRI`s new Center for Laboratory Astrophysics

and Space Science Experiments (CLASSE) 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. "Our experiment condensed methane in an ultra-high

vacuum chamber under exposure to Lyman-alpha photons to replicate with high fidelity the conditions at Charon`s poles." 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. The

team input the results from SwRI`s ultra-realistic experiments into the atmospheric model to estimate the distribution of complex hydrocarbons emerging from methane decomposition under the

influence of ultraviolet light. The model has polar zones primarily generating ethane, a colorless material that does not contribute to a reddish color. "We think ionizing radiation

from the solar wind decomposes the Lyman-alpha-cooked polar frost to synthesize increasingly complex, redder materials responsible for the unique albedo on this enigmatic moon," Raut

said. "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." "The team is set to investigate the role of solar wind in the formation of the red pole," said SwRI`s Dr. Josh Kammer, who secured

continued support from NASA`s New Frontier Data Analysis Program.