Pluto's Hazy Hydrocarbon Atmosphere Hides Flowing Earth-like Glaciers

As the New Horizons spacecraft sped away from Pluto last week, it captured a stunning sight: an atmospheric haze surrounding the dwarf planet some 80 miles thick. Now, 10 days later, NASA scientists have had some time to properly analyze the surprising find, identifying two distinct layers within the alien atmosphere: one about 30 miles above the surface, and the other 50 miles above. The layers are more than just pretty and unexpected, however, and offer new insights into what's happening on Pluto's surface below.

For one thing, if previous calculations of the planet's surrounding temperatures had been correct, Pluto's haze shouldn't extend much farther than 20 miles above its surface. It seems our estimations have been off and Pluto is quite a bit colder than once assumed. (Being wrong in science is so often more exciting than the alternative.)

Here's how the Plutonian atmospheric process works, according to NASA's models. Ultraviolet light inbound from the Sun meets methane gas particles hanging around in Pluto's atmosphere, which are broken up and recombined into more complex hydrocarbons like ethylene and acetylene, both of which have been detected by New Horizons. These new particles fall downward through the planet's atmosphere and as they meet lower, colder layers, the particles condense into ice. This is the haze.

There's another step. Ultraviolet light also has the effect of converting the lower reaches of this icy hydrocarbon haze into tholins, which are the complex and heavy reddish-brown molecules that wind up on the surfaces of icy planets and moons as hydrocarbons get together with nitrogen. Tholins are often thought to be precursors to biological life as they offer a potential source of carbon nourishment to microbial life; a wide variety of soil bacteria here on Earth are able to obtain carbon and energy from tholins alone.

"The hazes detected in this image are a key element in creating the complex hydrocarbon compounds that give Pluto's surface its reddish hue," offers Michael Summers, a New Horizons co-investigator from George Mason University, in a NASA statement. "We're going to need some new ideas to figure out what's going on."

In the same sets of images collected by the New Horizon's Long Range Reconnaissance Imager (LORRI), scientists have also found evidence of "exotic" ice floes and recent geological activity on Pluto's surface, which had been hoped for but unexpected. On the Texas-sized plain known as Sputnik Planum, evidence of ice sheet movement is clear, though whether it's still occurring or has since ceased is uncertain. The find is exciting in either case just given that such glaciers have otherwise only been observed on Earth and Mars.

"At Pluto's temperatures of minus-390 degrees Fahrenheit, these ices can flow like a glacier," says Bill McKinnon, deputy leader of the New Horizons Geology, Geophysics, and Imaging team at Washington University in St. Louis. "In the southernmost region of the heart, adjacent to the dark equatorial region, it appears that ancient, heavily-cratered terrain has been invaded by much newer icy deposits."

As New Horizons pushes deeper into the Kuiper Belt, where it's now already some 7.6 million miles from Pluto, the craft will continue to send data homeward, at least through late 2016. Stay tuned, in other words, and catch all of Motherboard's Pluto coverage right here.