Little Pluto, smaller than Earth's moon, has a least one giant mountain range, with water ice the only available building material, scientists with NASA's New Horizons mission said Wednesday.
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The discovery, which popped out from the first of thousands of high-resolution images taken during New Horizons' close flyby of Pluto and its largest moon Charon on Tuesday, raised immediate questions about how the 11,000-foot (3,350 meters) mountains formed.
"We have no idea at this point," New Horizons scientist John Spencer, with the Southwest Research Institute in Boulder, Colo., told reporters.
"These mountains are quite spectacular. There may be higher ones elsewhere."
Scientists believe the mountains are made of water ice, as nitrogen, methane and other materials available on its surface aren't strong enough to support that amount of mass.
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"We are seeing the bed ice of Pluto. The water ice is strong enough at Pluto's temperatures to hold up big mountains, and that's what we think we are seeing here," Spencer said.
More details will are expected throughout the week, and especially over the next few months, as New Horizons relays back its images and science observations from its nine-day Pluto encounter.
After a journey of nearly a decade, New Horizons passed less than 7,800 miles from Pluto at 7:49 a.m. ET Tuesday. The probe is already more than 1 million miles farther into the Kuiper Belt, a region filled with ice-and-rocky bodies believed to be remnants left over from the formation of the solar system 4.6 billion years ago.
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During the eons, Pluto has not been idle. Another surprise in the New Horizons' first close-up was the complete lack of impact craters in the single frame that so far has been subject to scrutiny.
"We haven't yet found a single impact crater on this image. This means this is a very young surface because Pluto has been bombarded by objects in the Kuiper Belt and craters happen. Just eyeballing it, we think (the surface) has to be probably less than 100 million years, which is a small fraction of the 4.5 billion-year age of the solar system. It might be active right now," Spencer said.