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Top space stories of 2015: Pluto and its moons revealed

Everything about Pluto surprised scientists


When NASA’s New Horizons spacecraft flew by Pluto, Earth watched and celebrated. “The target didn’t disappoint,” says Principal Investigator S. Alan Stern. “It’s absolutely stunning.”

And even though the science collection lasted just months, the New Horizons mission had been decades in the making. NASA chose the mission in 2001, the spacecraft launched in 2006, and it reached Pluto on July 14, 2015.

Seeing the pixelated blobs of Pluto and its largest moon, Charon, evolve into complex worlds through the eye of New Horizons was rewarding, satisfying, and awesome, says Stern. That’s because everything about Pluto surprised scientists. They expected a frozen, cratered, and long-dead world with an equally old-looking system of moons. Instead, Pluto’s surface is young, with smooth frozen plains, icy mountains as high as the U.S. Rockies, topography that resemble dunes, a glacial lake, and ice that has recently flowed around other features in the same way that glaciers move on Earth’s surface. The scientists estimate that the uncratered swaths of terrain are 100 million years old, while other regions are billions of years in age.


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