Universe

Pluto Has Gorgeous Blue Skies and Flowing Water Ice

October 13, 2015 | Sarah Tse

Pluto Blue Haze
Photo credit: NASA

NASA's new full-color images reveal that Pluto's hazy atmosphere shines a brilliant blue, and beneath that sapphire haze lies several expanses of water ice.

You might expect Pluto to be dark and dull, given its great distance from the sun. But NASA's New Horizons spacecraft has sent back the first color images of Pluto's atmosphere, showing that a striking blue sky hangs above its icy surface.

Scientists believe the blue tint comes from tiny sooty particles called tholins filling up the dwarf planet's atmosphere. Tholins form high in the atmosphere where ultraviolet rays strike nitrogen and methane molecules, turning them into ions that can react and combine into increasingly large and complex compounds. Eventually the compounds accumulate into larger particles cloaked in frost, and they fall back to the surface. Although the particles themselves are likely gray or red, they scatter blue light to give the atmosphere its vivid hue.

New Horizons has also detected many regions of exposed water ice that are normally masked by other gases. Curiously, the regions with the most ice correspond to areas that appear red in recent color close-ups of the dwarf planet's surface. The New Horizons team is working to figure out why the water ice is associated with red-colored tholins on the surface.

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