On Wednesday, scientists presented the first pictures acquired by the New Horizons probe during its historic flyby of the dwarf planet, BBC reported.

The team has also named the prominent heart-shaped region on Pluto after the world's discoverer Clyde Tombaugh. The spacecraft sped past the dwarf planet on Tuesday, getting as close as 12,500km and grabbing a huge volume of data. Mission scientist John Spencer told journalists that the first close-up image of Pluto's surface showed a terrain that had been resurfaced by some geological process - such as volcanism - within the last 100 million years.

"We have not found a single impact crater on this image. This means it must be a very young surface," he said.

This active geology needs some source of heat. Previously, such activity has only been seen on icy moons, where it can be explained by "tidal heating" caused by gravitational interactions with a large host planet.

"You do not need tidal heating to power geological activity on icy worlds. That's a really important discovery we just made this morning," said Dr Spencer.

Alan Stern, the mission's chief scientist commented: "We now have an isolated, small planet that's showing activity after 4.5 billion years."

Prof Stern said the discovery would "send a lot of geophysicists back to the drawing boards".

John Spencer said the relatively thin coating of methane, carbon monoxide and nitrogen ice on Pluto's surface was not strong enough to form mountains, so they were probably composed of Pluto's water-ice bedrock. "Water-ice at Pluto temperatures is strong enough to hold up big mountains," he said.