Mysterious 'Red Cap' on Pluto's Moon Finally Explained


| LAST UPDATE 06/24/2022

By Stanley Wickens
Pluto Charon mysterious discovery

Of all the celestial objects traveling about our solar system, Pluto may be among the most mysterious. One of Pluto's moons has a "red cap" on it, which, until recently, scientists didn't have a solid explanation for. But thanks to the hard work of one team of scientists, we may finally know how it formed.

Until NASA's New Horizons managed to capture a clear picture of Pluto and Charon, the best image we had of them was as a fuzzy blob that reflected sunlight. But thanks to NASA's interplanetary probe, we managed to get a shot of Pluto's moon, and scientists noticed it had a "red cap." A group of researchers from the Southwest Research Institute in San Antonio, Texas, have put forth the conclusion as to what caused the "red cap" on the moon Charon to form. Their research, which was published in the journals Science and Geophysical Research Letters, claims that the red cap is probably a result of chemicals known as tholins. These are sticky organic residues that result from chemical reactions powered by light. After absorbing a specific color of ultraviolet rays from the Sun, these compounds seemingly turned red and gathered near the moon's north pole.

Charon moon methane pluto
NiPlot via Getty Images
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"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 Dr. Ujjwal Raut, of the Southwest Research Institute. "This is one of the most illustrative and stark examples of surface-atmospheric interactions so far observed at a planetary body." But how exactly did they reach their conclusion? 

The team recreated Charon's atmosphere at SwRI's new Center for Laboratory Astrophysics and Space Science Experiments (CLASSE), in an attempt to study the composition and color of hydrocarbons on Charon’s winter hemisphere as methane freezes below the Lyman-alpha glow. They then placed their measurements within a new atmospheric model of Charon to show how methane would break down into residue around the moon's north pole. "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," Raut explained. While the team is certainly fascinated by the conclusion they've arrived at, they don't plan on their research ending there. We'll be staying tuned to find out more about these dark and mysterious areas of our solar system.

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