Pluto’s moon has a mysterious red north pole, and we may finally know why

(ORDO NEWS) — Pluto’s life partner, Charon, wears a disarming red cap. Ever since New Horizons photographed the moon’s rusty north pole during a flyby in 2015, scientists have speculated about the planetary processes responsible for leaving such a bright landmark.

Scientists initially suspected the iron-colored spot (nicknamed the Mordor Spot) was methane captured from the surface of Pluto, its red color the result of slow baking in the sun’s ultraviolet light. It was a neat idea, just begging for testing.

Now, a combination of simulations and lab experiments has shown that those early assumptions weren’t all that far off the mark, with a slight deviation. The study adds surprising new details to our understanding of Pluto and Charon’s intimate relationship, suggesting there’s more to the moon’s coloration than meets the eye.

Launched back in 2006, NASA’s New Horizons interplanetary space probe has provided researchers with an unprecedented view of the dwarf planetary system Pluto and Charon, more than 5 billion kilometers (3.1 billion miles) from the Sun. fuzzy patch of reflected light,” says Randy Gladstone, a planetary scientist at the Southwestern Research Institute (SwRI) in the US.

“In addition to all the amazing features found on the surface of Pluto, an unusual feature of Charon; amazing red cap centered on its north pole.”

Red may not be unusual on iron-rich worlds like ours, or Mars, for that matter. But all along the frozen suburbs of the solar system, red is much more likely to indicate the presence of a diverse group of tar-like compounds called tholins.

If it helps, just replace the word tholin with ‘garbage’. The brownish-red hodgepodge of chemicals is similar to leftovers left in an oven if the oven used ultraviolet light to bake cakes from simple gases like carbon dioxide or ammonia.

On Pluto, methane would probably be the starting point. To turn into tholin, these tiny hydrocarbons simply need to absorb a very specific color of UV radiation filtered by rotating hydrogen clouds called Lyman-alpha.

Pluto’s pink glow has been the subject of study for decades. . New Horizons just showed the exact patterns of tholins on its surface in gorgeous high resolution. However, the discovery of a rusty hue on the lid of his companion came as an intriguing surprise.

It was assumed that the release of methane from Pluto could drift towards its orbiting moon. But the exact time it takes for the gas to settle and solidify into such a distinctly blurry spot has always been a stumbling block.

Part of the problem lies in the rivalry between Charon’s weak gravity and the cold light of deep space. from the Sun, which warmed its surface. Weak as it is, a spring dawn may be enough to melt the methane frost and push it off the surface again.

To determine what will actually happen, the SwRI researchers simulated the wobble motion of a system of inclined planets. They discovered that the secret of the smear may lie in the explosive nature of the arrival of spring.

The relatively sudden warming of the north pole will occur within a few years – just a moment in the 248-year orbit of the moon. sun. During this short period, a layer of methane frost only a few tens of microns thick will evaporate at one pole and begin to freeze at the other.

Unfortunately, simulations have shown that this fast movement will be too fast. so that most of the frozen methane absorbs enough Lyman-alpha to turn into tholin.

But ethane – the slightly longer hydrocarbon cousin of methane – is a different story.

“Ethane is less volatile than methane and remains frozen on the surface of Charon long after the spring sunrise,” says planetary scientist Ujwal Raut, lead author of the second study, which models changes in evaporation density and freezing of methane.

“The impact of the solar wind can turn ethane into persistent reddish surface deposits that contribute to the formation of Charon’s red cap.”

Together with the results of laboratory experiments, Rauth and his team’s study demonstrated a real way to convert methane to ethane. at the poles.

There was only one problem. Lyman alpha radiation will not turn ethane into a reddish goo.

This does not exclude hydrocarbons. Charged particles emanating from the Sun over a longer period of time can still generate ever longer chains of hydrocarbons that give Charon its characteristic red cap.

“We think that the ionizing radiation from the solar wind is decomposing the Lyman-alpha-cooked polar frost to synthesize ever more complex, redder materials responsible for the unique albedo on this mysterious moon,” says Raut.

Further laboratory testing and simulations may help strengthen the hypothesis that Charon’s ruddy spot is much more complex than we’ve ever realized.

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