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Pluto's Mysterious Floating Hills Are Probably Water Icebergs

Icebergs floating on a weird sea of frozen nitrogen.
Image: NASA

NASA astronomers have determined that the mysterious, floating hills dotting Pluto's vast central nitrogen glacier are most likely icebergs. The suspected bergs, many of them several miles across, are composed of frozen water, leaving us with the peculiar image of ice floating upon ice. This is possible thanks to the higher density of the frozen nitrogen compared to that of the frozen water. Note that the temperature around here is about -390 degrees Fahrenheit.

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The glaciers themselves are a recent discovery. Imagery collected last summer via the New Horizon mission's Long-Range Reconnaissance Imager revealed a Texas-sized plain (dubbed Sputnik Planum) lying near the planet's central heart-shaped region. It seemed clear that the ice of Sputnik Planum was flowing in a manner not unlike the ice floes of Earth. Those same images revealed that the glacier is interrupted regularly by large masses.

Image: NASA

Icebergs would make sense on Sputnik Planum. The glacier is surrounded on one side by large rugged mountains and where this geography meets the slow-moving glacier, chunks are pulled away from the mountains and are left to circulate flowing nitrogen. And since ice of the glacier is really an assortment of interfacing floes in a sort of cellular arrangement—which is how ice behaves in the Arctic Ocean—the result are the congregations or chains of icebergs lining up in accordance with the cracks that can be seen in the image above.

The Challenger Colles marked on the image are thought to be a bunch of beached icebergs having been pushed by the glacier away from its more cellular areas and into shallower nitrogen at the interface between glacier and hills.