The reddish polar region on Pluto‘s giant moon, Charon, is an impact of methane gas escaping from the icy dwarf planet’s atmosphere, described by the scientists who unraveled the enigma behind the coloured area first spotted by NASA‘s New Horizons spacecraft last year.
Methane gas outflows from Pluto’s atmosphere becomes “trapped” by the moon‘s gravity and pierces to the cold, icy surface at Charon’s pole, researchers stated.
This is accompanied by chemical processing by ultraviolet rays from the Sun that converts the methane into heavier hydrocarbons and finally into reddish organic elements called tholins, they said.
“Who would have thought that Pluto is a graffiti artist, spray-painting its companion with a reddish stain that covers an area the size of New Mexico?” said Will Grundy, a New Horizons co-investigator from Lowell Observatory in the US.
“Nature is amazingly inventive in using the basic laws of physics and chemistry to create spectacular landscapes,” Grundy added.
The team joined reviews from detailed Charon pictures obtained by New Horizons with computer models of how ice evolves on Charon’s poles.
Mission scientists had earlier speculated that methane from Pluto’s atmosphere was trapped in Charon’s north pole and gradually converted into the reddish element, but had no photographs to verify that theory.
Researchers dug into the data to discover whether conditions on the moon (with a diameter of 1,212 kilometers) could support the acquisition and processing of methane gas.
The illustrations using Pluto and Charon’s 248-year orbit around the Sun displays some extreme weather conditions at Charon’s poles, where 100 years of constant sunlight alternate with another century of constant darkness.
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Surface temperatures throughout these long winters dip to – 257 degrees Celsius, cold enough to freeze methane gas into a solid.
“The methane molecules bounce around on Charon’s surface until they either escape back into space or land on the cold pole, where they freeze solid, forming a thin coating of methane ice that lasts until sunlight comes back in the spring,” Grundy said.
But although the methane ice quickly sublimates away, the complex hydrocarbons generated from it remain on the surface.
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The models also proposed that in Charon’s springtime, the returning sunlight triggers the conversion of the frozen methane back into gas.
Sunlight moreover irradiates those leftovers into the reddish coloured substance called tholins that have slowly expanded on Charon’s poles over millions of years.
Fresh Horizons’ perceptions of Charon’s other pole, currently in winter darkness and recognized by New Horizons only by light reflecting from Pluto, or “Pluto-shine” – validated that the equivalent action was happening at both the pol