The red spot on Pluto’s moon Charon can be clearly seen in this enhanced color image captured by NASA’s New Horizons spacecraft during just before its closest approach to Pluto on July 14, 2015.
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As they detail this week in the worldwide scientific journal Nature, Charon’s polar coloring comes from Pluto itself – as methane gas that escapes from Pluto’s atmosphere and becomes “trapped” by the moon’s gravity and freezes to the cold, icy surface at Charon’s pole.
Charon’s great red spot, courtesy of New Horizons. Charon is 754 miles (1,214 kilometers) across; this image resolves details as small as 1.8 miles (2.9 kilometers). -Canada border or the English Channel.
Planetary scientist Will Grundy of Lowell Observatory in Flagstaff, Arizona, bases his findings on observations a year ago by NASA’s New Horizons spacecraft.
When the “paint” escapes Pluto’s atmosphere, a chemical transformation takes place via solar radiation, which turns the caps red.
“Every time we explore, we find surprises”.
Similar colors on Pluto’s surface are probably due to organic molecules known as tholins, named after the ancient Greek word for sepia ink. “They are chemically the same stuff as the smog that used to fill Los Angeles basin – they have an orange tint to them”, Grundy said.
“It’s nearly like Pluto is a graffiti artist, spray-painting Charon’s poles with its escaping atmosphere, leaving planet-scale colored spots”, the study’s lead author, planetary scientist Will Grundy of the Lowell Observatory in Flagstaff, Arizona, told ABC News.
To solve the mystery, Grundy and his colleagues first modeled how much gas might escape Pluto.
His study was reported by the journal Nature on Wednesday, 16 months to the day after New Horizons’ historic flyby of Pluto. Methane is the lighter molecule, so it is the main one escaping.
A study of images beamed back by Nasa’s New Horizon’s space probe may now have uncovered what causes the dark red patch that stains the top of the icy moon. They theorized that some of the material could freeze and that, later, radiation could convert it to tholins. Surface temperatures during these long winters dip to -430 Fahrenheit (-257 Celsius), cold enough to freeze methane gas into a solid.
“The calculations in the paper are simple back-of-the-envelope ones”, Grundy said. “That doesn’t prove anything, but this idea has seemed to survive the tests we’ve thrown at it so far”.
The researchers have also modelled for the first time the evolution of the ice cap, to try and explain the formation of Charon’s unique red cap. Although Charon’s south pole is now in winter night, images of that moon’s southern hemisphere lit by “Pluto-shine” – that is, the scant amount of sunlight reflecting off Pluto – that Grundy and his colleagues analyzed reveal that there is evidence of darkening toward the south pole, suggesting a red cap there as well.
“Methane is volatile enough that it can only stick to the surface during the long, cold polar winters”, Will Grundy, lead author of the new study, told Space.com by email. The peaks of those “waves” could mean there are more solar wind particles locally, increasing X-ray emissions near Pluto in spite of the sluggish solar wind.
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Other dwarf planets exist in our solar system, like Pluto’s neighbors Eris and Makemake, which may have a similar relationship.
