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20150718_wesat_photos_of_pluto_reveal_a_toy_store_of_surprises.mp3?orgId=1&topicId=1060&aggIds=4495795&d=172&p=7&story=423911190&t=progseg&e=424079233&seg=3&ft=nprml&f=423911190

Pluto turns out to be pretty lively.

Not Las Vegas, perhaps, but more vivacious with geologic activity than we've ever known about, and for good reason: Pluto is currently almost 3 billion miles away from Earth, a dwarf planet spinning in the lonely last ring of our solar system.

But this week the New Horizons space probe sent back the first detailed pictures humans have ever been able to see of Pluto and its five moons.

Pluto is also billions of miles from the sun, so it's cold. But according to these first photos, cold with ice, not stone. Mountains of ice as tall as the Rockies, and only about 100 million years old in a solar system that's been around more than 4.5 billion years.

"Who would have supposed that there were ice mountains?" project scientist Hal Weaver asked at a press conference. "It's just blowing my mind."

Imagine what it must take to blow the mind of a space scientist.

Alan Stern of the Southwest Research Institute, the mission's chief scientist, says that icy, soaring peaks on Pluto should "send a lot of geophysicists back to the drawing boards." It's not what the smartest people expected to see.

These pictures also show Pluto to be a relatively unblemished babe among celestial bodies. It has those ice mountains, but no impact craters — as they're called — caused by the crash of meteorites or other flotsam from space. The scientists say this suggests that Pluto could still smolder below its surface, swelling with energy from the decay of radioactive material, or even an underground ocean.

Dr. Stern said, "I don't think any one of us could have imagined that it was this good of a toy store," which is how a great scientist may see a planet of surprises.

Stephen Hawking of Cambridge sent a message to the New Horizons team in which he called Pluto, "a distant icy world on the edge of our solar system. The revelations of New Horizons may help us to understand better how our solar system was formed. We explore because we are human and we long to know."

And New Horizons will go on, sailing deeper and deeper into deep space, and into our imaginations, as long as the plutonium aboard can propel it; perhaps until the 2030s.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.