Researchers discover a potential cause for Charon's crimson crown. New laboratory experiments, simulations of Pluto's biggest moon, and data from satellites were merged in research.



Researchers at the Southwest Research Institute used information from NASA's New Horizons mission, cutting-edge lab tests, and exospheric modeling to determine the red cap's composition and its formation on Pluto's moon Charon. The origins of this moon's red patch as reported in two previous articles are fascinatingly revealed in this first-ever explanation of Charon's dynamic methane atmosphere using fresh experimental data.

According to SwRI's Randy Gladstone, a member of the New Horizons research team, "Prior to New Horizons, the finest Hubble photos of Pluto revealed just a fuzzy blob of reflected light." The flyby revealed an unexpected feature on Charon, a startling crimson cap centered on its north pole, in addition to all the remarkable features observed on Pluto's surface.

Soon after the 2015 flyby, New Horizons scientists hypothesized that a reddish "tholin-like" substance near Charon's pole may be created by the breakdown of methane molecules by UV radiation. These are caught after eluding Pluto and are then frozen onto the poles of the moon during its lengthy winter nights.

Dr. Ujjwal Raut of SwRI is the lead author of a paper titled "Charon's Refractory Factory" that was published in the journal Science Advances. "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," he said. This is one of the most striking and instructive examples of surface-atmospheric interactions ever seen at a planetary body, according to researchers.

To analyze the composition and color of hydrocarbons formed on Charon's winter hemisphere when methane freezes beneath the Lyman-alpha light, the team created a realistic simulation of Charon's surface conditions at SwRI's new Center for Laboratory Astrophysics and Space Science Experiments (CLASSE). The results were included into a fresh model of Charon's atmosphere to demonstrate methane decomposition into residue on the planet's north polar point.

The new limitations on the contribution of extraterrestrial Lyman-alpha to the synthesis of Charon's red material were supplied by our team's innovative "dynamic photolysis" tests, according to Raut. In order to accurately recreate the circumstances at Charon's poles, our experiment condensed methane in an ultra-high vacuum chamber while being exposed to Lyman-alpha photons.

Additionally, SwRI researchers created a fresh computer simulation to represent Charon's tenuous methane atmosphere.

Dr. Ben Teolis, lead author of a related paper titled "Extreme Exospheric Dynamics at Charon: Implications for the Red Spot" in Geophysical Research Letters, stated that 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."

To predict the distribution of complex hydrocarbons originating from methane breakdown under the influence of UV light, the researchers entered the outcomes of SwRI's ultra-realistic tests into the atmospheric model. According to the hypothesis, ethane, a colorless substance that does not contribute to a reddish hue, is the main substance produced by polar zones.

In order to create increasingly complex, redder minerals, Lyman-alpha-cooked polar frost is thought to be decomposed by ionizing radiation from the solar wind, according to Raut. These components are what give this mysterious moon its distinctive albedo. "Ethane is less flammable than methane and remains firmly frozen to Charon's surface well after the first signs of spring. Ethane may be transformed by solar wind exposure into enduring reddish surface deposits that contribute to Charon's crimson cap."

According to Dr. Josh Kammer of SwRI, who was able to maintain funding from NASA's New Frontier Data Analysis Program, "the team is ready to examine the role of solar wind in the creation of the red pole."