While underway, NASA’s tiny New Horizons probe discovered something very mysterious on Pluto’s moon Charon – a red “cap”.
Data from the probe, which is powered by a Star Trek-style ion drive, was combined with data from laboratory experiments this week – and scientists now think they may understand what the .
The red area appears to be sticky organic residue formed when methane is broken down into more complex molecules by the solar wind.
Southwest Research Institute’s Randy Gladstone said: “Prior to New Horizons, the best Hubble images of Pluto showed only a fuzzy blob of reflected light.”
“In addition to all the intriguing features discovered on Pluto’s surface, the flyby revealed an unusual feature on Charon, a surprising red cap centered on its north pole.”
Shortly after the 2015 encounter, New Horizons scientists suggested that a reddish “tholin-like” material at the Charon pole could be synthesized by ultraviolet light breaking down methane molecules.
These are captured by Pluto after their flight and then frozen during their long winter nights on the Moon’s polar regions.
Tholins are sticky organic residues formed by chemical reactions driven by light, in this case the ultraviolet glow of Lyman-alpha scattered by interplanetary hydrogen atoms.
dr Ujjwal Raut of the Southwest Research Institute: “Our results indicate that drastic seasonal variations in Charon’s thin atmosphere, as well as light dissolving the condensing methane frost, are key to understanding the origins of Charon’s red polar zone.
“This is one of the most vivid and blatant examples of surface-atmosphere interactions yet observed on a planetary body.”
The team realistically replicated Charon’s surface conditions at SwRI’s new Center for Astrophysics and Space Experiments (CLASSE) to measure the composition and color of hydrocarbons produced in Charon’s winter hemisphere when methane is released under the Lyman-alpha glow freezes.
The team fed the measurements into a new atmospheric model of Charon to show how methane decays to residues at Charon’s north pole.
Raut said: “Our team’s novel ‘dynamic photolysis’ experiments have revealed new frontiers for the contribution of interplanetary Lyman alpha to the synthesis of Charon’s red material.
Our experiment condensed methane in an ultra-high vacuum chamber under the action of Lyman alpha photons to replicate conditions at Charon’s poles with high fidelity.”
SwRI scientists also developed a new computer simulation to model Charon’s sparse methane atmosphere.
The team fed the results of SwRI’s ultra-realistic experiments into the atmospheric model to estimate the distribution of complex hydrocarbons produced during methane decomposition under the influence of ultraviolet light.
The model has polar zones that primarily produce ethane, a colorless material that does not contribute to a reddish color.
Raut said: “We believe that ionizing radiation from the solar wind is breaking down the Lyman-alpha-boiled polar frost to synthesize increasingly complex, redder materials responsible for the unique albedo on this enigmatic moon.”
“Ethane is less volatile than methane and remains frozen on Charon’s surface long after sunrise. Exposure to solar wind can convert ethane into permanent reddish surface deposits that contribute to Charon’s red cap.”
Behold: NASA created flyby videos of Pluto and Charon