Latest dispatch from Pluto reveals frozen plains, icy hills and more

New images give shape to moon Nix and hint at dwarf planet’s geology

close-up of Pluto's surface

PLUTO’S PLAINS  A craterless plain etched by a network of shallow troughs lies within Pluto’s “heart,” as seen in this image taken July 14 when New Horizons was 77,000 kilometers from the dwarf planet. 


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Frozen plains, etched with a network of polygons bordered by shallow troughs, stretch away from Pluto’s icy mountains and through Pluto’s “heart.” Some troughs are filled with dark material, possibly irradiated hydrocarbons, while others are home to icy hills, New Horizons mission scientists announced at a July 17 news conference.

As with everything else coming from Pluto, planetary scientists are still at the scratching-their-heads phase.

“When I first saw [the plains], I called it the ‘not-easy-to-explain’ terrain,” said Jeff Moore, a planetary scientist at the NASA Ames Research Center in Moffett Field, Calif.

The polygons are roughly 20 to 30 kilometers across. One idea is that the surface there is like a boiling pot of oatmeal, Moore said. Heat welling up from below might be pushing up bubbles in the ice. Alternatively, they could be more like mud cracks seen on Earth that are formed by a contracting surface.

Within some of the cracks sit clusters of hills. It’s not clear yet how high they are — or how they got there. They might have been thrust up or perhaps they’ve been whittled away by erosion. “We don’t know which is correct,” Moore says.

Images with even higher resolution, along with stereo photography, are yet to come. “This is just a taste of what’s in the unsent data,” Moore says.

The team has also gotten their first good look at the small moon Nix, which the scientists now know to be 40 kilometers across. While it looks round in images, mission leader Alan Stern said that the team suspects the moon is actually elongated and we’re just “looking down the barrel” at one of the poles.

Early atmospheric data also show hints of a nitrogen tail stretching away from Pluto in the direction opposite the sun. The solar wind of electrons and protons could ionize and sweep up nitrogen escaping from the dwarf planet and blow it away, much like how a comet grows a tail as it nears the sun.

FLYING CLOSE  This flyover shows icy mountains and plains on Pluto. Features as small as a kilometer across are visible.     


Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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