Nasa has presented the first images acquired by the New Horizons probe during its historic flyby of Pluto.
Chief scientist Alan Stern said the new images showed evidence of geological activity and mountains in the Pluto system.
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, grabbing a huge volume of data.
Mission
scientist John Spencer told journalists that one image of Pluto's
surface showed a terrain that had been resurfaced by some geological
process - such as volcanism - in 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. This has only been seen on
icy moons, where it can be explained by "tidal heating" caused by
gravitational interactions with the host planet.
"You do not need
tidal heating to power geological heating on icy bodies. That's a really
important discovery we just made this morning," said Dr Spencer.
Mission scientist Cathy Olkin added: "This exceeds what we came for."
This
same image shows mountains at the edge of the heart-like region that
are up to 11,000ft high and which team members compared to North
America's Rocky Mountains.
Charon has a chasm four to six miles deep
John Spencer said the methane
and nitrogen ice that coats Pluto's surface were not strong enough to
form mountains, so they were probably composed of Pluto's water-ice
bedrock.
The pictures were sent back to Earth during the course of two data downlinks on Wednesday.
Scientists have named the heart-shaped region Tombaugh Regio, after the astronomer who discovered Pluto in 1930.
The new, close-up image of Charon has revealed a chasm 4-6 miles deep and also further evidence of active resurfacing.
Significantly, all these images are at a much higher resolution than anything we have seen so far.
The mission team has told New Horizons this week to send down only a small fraction of the total data it carries.
Part of the reason is that the probe continues to do science, observing Pluto from its night side.
The intention is to keep looking at it for about two more full rotations, or 12 Earth days.
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