Planetologists explain how Charon's "red riding hood" was formed

Scientists from the Northwest Research Institute used experiments, computer

modeling and data obtained from spacemission "New Horizons" to study the atmosphere of Charon. The study showed that the satellite's thin methane atmosphere undergoes explosive pulsations, and the polar red spot is formed under the influence of the solar wind.

"Little Red Riding Hood" at the north pole of CharonNew Horizons was first discovered in 2005. Previously, scientists assumed that this shade produces a material similar to tholins, which is formed when methane molecules are destroyed under the influence of ultraviolet Lyman-alpha glow from hydrogen scattered in the interstellar medium. In new papers published in the journals Science Advances and Geophysical Research Letters, the researchers discovered a more complex process.

Planetologists have reproduced surface conditionsCharon in a laboratory experiment to measure the composition and color of hydrocarbons produced on the satellite. During the experiment, methane condensed in an ultra-high vacuum chamber under the influence of Lyman-alpha photons. 

The study showed that methane is indeedbreaks up into remnants at Charon's north polar spot. But mostly ethane is formed, a colorless material that cannot give a reddish tint.

In addition, the researchers found thatThe atmosphere on Pluto's moon is subject to cyclic explosive events every planetary year (258 Earth years). The spring sunrise causes the polar methane, frozen during the centuries-old winter night, to return back to the atmosphere. At the same time, the density of the air shell increases sharply by almost 1000 times, and polar methane caps can suddenly move between north and south, evaporate, and then freeze again.

Unlike methane, ethane is less volatile and morestable, so it does not evaporate during the spring "explosion". Researchers believe that it is ethane, under the influence of ionizing radiation from the solar wind, that synthesizes increasingly complex, redder materials responsible for the unique albedo on this moon.

Cover image: Courtesy of NASA / Johns Hopkins APL / SwRI

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