New details of Pluto's largest moon Charon are revealed in this image from New Horizons' Long Range Reconnaissance Imager (LORRI), taken late on July 13, 2015 from a distance of 289,000 miles (466,000 kilometers) in a picture released by NASA in Laurel, Maryland, July 15, 2015. [Photo/Agencies]

LAUREL, Md. - The first close-up views of Pluto show mountains made of ice and a surprisingly young, crater-free surface, scientists with NASA's New Horizons mission said on Wednesday.

The results are the first since the piano-sized spacecraft capped a 3 billion mile (4.82 billion km), 9-1/2-year-long journey to pass within 7,800 miles (12,550 km) of Pluto on Tuesday.

New Horizons is now heading deeper into the Kuiper Belt, a region of the solar system beyond Neptune that is filled with thousands of Pluto-like ice-and-rock worlds believed to be remnants from the formation of the solar system, some 4.6 billion years ago.

Scientists do not know how Pluto formed such big mountains, the tallest of which juts almost 11,000 feet (3,350 meters) off the ground, nearly as high as the Canadian Rockies.

Another puzzle is why Pluto has such a young face. The icy body, which is smaller than Earth's moon, should be pocked with impact craters, the result of Kuiper Belt rocks and boulders raining down over the eons.

Instead, New Horizons revealed that the surface of Pluto has somehow been refreshed, activity that may be tied to an underground ocean, ice volcanoes or other geologic phenomenon that gives off heat.

Scientists believe Pluto's mountains likely formed within the last 100 million years, a relative blink compared to the age of the solar system.