Why methane snow covers Pluto’s peaks

Image: Methane on Pluto
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.

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By Alan Boyle

Mastermind of Cosmic Log, contributing editor at GeekWire, author of "The Case for Pluto: How a Little Planet Made a Big Difference," president of the Council for the Advancement of Science Writing. Check out "About Alan Boyle" for more fun facts.

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