New close-up images of a region near Pluto's equator reveal a giant surprise: a range of youthful mountains rising as high as 11,000 feet (3,500 meters) above the surface of the icy body (Mount Everest, by comparison, measures about 29,000 feet).
The mountains likely formed no more than 100 million years ago—mere youngsters relative to the 4.56-billion-year age of the solar system—and may still be in the process of building, says Jeff Moore of the New Horizons Geology, Geophysics, and Imaging team. That suggests the close-up region, which covers less than one percent of Pluto's surface, may still be geologically active today.
Moore and his colleagues base the youthful age estimate on the lack of craters in this scene. Like the rest of Pluto, this region would presumably have been pummeled by space debris for billions of years and would have once been heavily cratered—unless recent activity had given the region a facelift, erasing those pockmarks.
"This is one of the youngest surfaces we've ever seen in the solar system," says Moore.
Unlike the icy moons of giant planets, Pluto cannot be heated by gravitational interactions with a much larger planetary body. Some other process must be generating the mountainous landscape.
"This may cause us to rethink what powers geological activity on many other icy worlds," says Geology, Geophysics, and Imaging deputy team leader John Spencer of the Southwest Research Institute in Boulder, Colorado.
The mountains are probably composed of Pluto's water-ice "bedrock."
Although methane and nitrogen ice covers much of the surface of Pluto, these materials are not strong enough to build the mountains. Instead, a stiffer material, most likely water-ice, created the peaks.
"At Pluto's temperatures, water-ice behaves more like rock," said deputy team lead Bill McKinnon of Washington University in St. Louis.
The close-up image was taken about 90 minutes before New Horizons closest approach to Pluto, when the craft was 478,000 miles from the surface of the planet. The image easily resolves structures smaller than a mile across.