Scientists with NASA's New Horizons mission are puzzling over how a world that never gets more sun than Earth at twilight is reshaping its surface, filling in craters, cracking its crust and building towering mountains and smooth hills.
With just 1 percent of the 50 gigabytes of data collected during New Horizons' approach and close encounter with Pluto back on the ground, scientists already are rethinking long-held ideas about icy bodies in the outer reaches of the solar system.
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Pluto, for example, appears far from a pristine remnant left over from the formation of the solar system some 4.6 billion years ago. Its surface is brimming with evidence of relatively current, and possibly ongoing, geological processes.
New Horizons was dispatched to study Pluto and other icy bodies in the Kuiper Belt, located beyond Neptune's orbit.
Pluto, and to some extent its big moon Charon, have young and varied terrains, New Horizons found.
"The landscape is just astoundingly amazing," New Horizons scientist Jeffrey Moore, with NASA's Ames Research Center in Moffett Field, Calif., told reporters on a conference call.
A second batch of pictures released on Friday shows that part of Pluto's bright, heart-shaped region (since named "Tombaugh Regio" for Pluto's discoverer Clyde Tombaugh) contains a vast, crater-free plain, estimated to be less than 100 million years old.
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Resembling frozen mud cracks on Earth, the region, nicknamed "Sputnik Planum" is broken into irregular shaped polygons, roughly 12- to 20 miles in diameter, that are boarded by what appear to be shallow troughs.
"Those could be only a week old, for all we know," Moore said.
The polygons could have been formed by convection, patterns etched in Pluto's surface ice like the roiling surface of a pot of boiling oatmeal. What drives the process, however, has yet to be determined.
The polygons also could be like mud cracks, created by contraction of the surface, Moore added.
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New Horizons pictures also show that some of the troughs have dark material in them. Others are encircled by hills that seem to rise above the surface.
"We suspect the hills may have been pushed up from underneath along the cracks," Moore said.
Another theory is that the hills are mounds of more resistant material after the surrounding plains have eroded away.
"We don't know which of those two explanations are correct," he added.