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Image: Pluto snow-capped mountains
The inset pictures show a section of Pluto’s Cthulhu Regio that includes a reddish plain as well as a 260-mile-long mountain range. The far right inset indicates the distribution of methane ice in purple, as observed by New Horizons’ Ralph/MVIC imager during the spacecraft’s flyby on July 14, 2015.

The dark terrain informally known as Cthulhu Regio sweeps nearly halfway around Pluto’s equator, with light-colored peaks sticking up from the surrounding plains. What is that light-colored stuff? Apparently, it’s methane frost.

Evidence for Pluto’s methane meteorology was laid out today by the science team behind NASA’s New Horizons mission.

The piano-sized spacecraft’s cameras zeroed in on Cthulhu when it flew past Pluto last July 14. Most of the region is covered with a layer of dark reddish tholins, a substance that forms when sunlight breaks down hydrocarbons such as methane.

Then there are those bright peaks in southeast Cthulhu: When the scientists looked closely at compositional data collected by New Horizons’ Ralph/Multispectral Visible Imaging Camera, they found that the bright areas on top of Cthulhu’s mountains matched up with the spectral signature of methane ice.

“That this material coats only the upper slopes of the peaks suggests methane ice may act like water in Earth’s atmosphere, condensing as frost at high altitude,” John Stansberry, a member of the New Horizons science team from the Space Telescope Science Institute, said in today’s image advisory.

Pluto isn’t the only world in the solar system with methane-based weather: Saturn’s mysterious cloud-covered moon, Titan, has a meteorological cycle that results in methane rain, mixed in with a hearty helping of tholins.

In Titan’s case, the surface is too chilly for liquid water, but warm enough to speculate about the prospects for methane-based biochemistry. At 380 degrees below zero Fahrenheit, Pluto’s surface temperatures are too cold for that kind of speculation – but just right for speculating about the skiing conditions.

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