It turns out that Pluto may be responsible for maintaining the highlights on the red head of its biggest moon.
Scientists think Pluto, which was consigned to underdog status when it was demoted to a dwarf planet a decade ago, may actually be more of a bully.
Data published in the journal Nature on Wednesday reinforced the theory that Pluto’s atmosphere is releasing gas captured near Charon’s frigid northern pole, forcing the largest of its five moons to wear a blotchy, reddish-brown dunce cap.
“This is really the first instance that we know about where the atmosphere that’s escaping from one body is influencing another body in the system,” said Will Grundy, the lead author of the paper and a member of the teamworking on the data found by the New Horizons spacecraft when it flew by Pluto last year.
“In a sense, it’s almost like a shared atmosphere because methane from Pluto bounces around in Charon’s surface environment,” he added.
The paper indicates that Pluto is releasing methane, as well as small portions of other gases including nitrogen, from its atmosphere. Those gases, which are colorless when they are first released, become trapped at Charon’s poles where it’s particularly cold, and are exposed to energetic radiation from several sources, including ultraviolet photons and galactic cosmic rays.
The radiation breaks the gases’ chemical bonds, forming radicals, which in turn, are broken apart and recombined by radiation. The pattern repeats over and over, a process that Dr. Grundy referred to as “bombing the rubble until the rubble bounces,” until the heavier, rust-colored organic macromolecules, known as tholins, develop.
The presence of such macromolecules is exciting to researchers, as they are the essential ingredients of life.
“It’s telling that nature doesn’t have any great difficulty making interestingly complicated organic chemistry,” Dr. Grundy said.
He said the color would be familiar to those who used to travel to Los Angeles when the city was more polluted.
“Back in the old days when you’d fly into Los Angeles, there’d be a sea of this orangey-brown muck,” he said. “That’s basically light hydrocarbons that are the product of human activity — like the evaporation of people’s gas tanks — being affected by ultraviolet light from the sun,” a chemical process similar to the one occurring on Charon.
Scientists theorize that Pluto and Charon were formed by the same collision some four and a half billion years ago. And while Pluto’s radius is nearly twice the size of Charon’s, their centers are about 11,800 miles apart, a distance so comparatively small that they move in a lock step rare for celestial bodies, each keeping the same face directed toward its mate at all times.
By contrast, Earth’s moon is an average of 238,855 miles away from our planet, according to NASA, about 20 times as far as the distance between Charon and Pluto.
New Horizons flew past Pluto last summer, and the pictures from that mission provided scientists’ with their first glimpse of Charon’s reddish-brown polar ice cap. It was a notable feature on a body that had previously been thought to be uniformly gray, said Dale Cruikshank, another member of the New Horizons team and a research scientist at NASA.
Though Randy Gladstone, another author and the head of New Horizons’ atmospheres team, said “we always grimace when people anthropomorphize planets,” he quickly recognized Pluto’s bullying behavior.
“I usually just think of it as Pluto’s varnishing Charon, little thin coats of varnish that darken like varnish would over the eons,” he said, getting into the act. “You could say it’s spray-painting, or even defacing Charon.”