LAUREL (Maryland) • The first close-up image of Pluto has revealed mountains as tall as the Rockies, and an absence of craters - discoveries that, to their delight, baffled scientists working on Nasa's New Horizons mission and provided punctuation for a journey 91/2 years in the making.
Only 112 years after the Wright Brothers were barely able to get their airplane off the ground, a machine from Earth has crossed the solar system to a small, icy world 4.8 billion kilometres away. The fly-by on Tuesday, when New Horizons buzzed within 12,552km of the former ninth planet, came 50 years to the day after Nasa's Mariner 4 spacecraft made a similar first pass by Mars.
Pluto until a few weeks ago was a blurry dot. Within the past couple of days, it has been transformed into a dynamic world with varied geography, discoveries that point to the possibility of ice volcanoes and churning tectonics.
All of this new information could provide clues to how planets form and even to the origins of some of the building blocks of life.
"I don't think any one of us could have imagined this could have been a better toy store," Dr S. Alan Stern, the mission's principal investigator, said at a news conference on Wednesday.
"This exceeds what we came for," said Dr Catherine Olkin, the deputy project scientist. Earlier in the day, New Horizons had sent back the first batch of a bountiful trove of data that it had collected during its close fly-by of Pluto.
Dr Stern said the rooms where teams got their first look at the images were "something close to bedlam". A day before, Nasa had released a mesmerising image of the full 2,368km-wide disc of Pluto, highlighted by a bright heart-shaped swath of terrain.
The newer image focused on a much smaller patch, about 240km across, near the bottom of the heart shape, and captured features as small as 800m across.
The first surprise was the rugged topography - mountains up to 3,350m high. But they are almost certainly made of frozen water instead of rock. "There may be higher ones elsewhere," said Dr John Spencer, an investigator on the mission.
That was a surprise because observations of Pluto from Earth have not found any signs of water ice.
A second surprise was the dwarf planet's surface was unmarred by craters. Dr Spencer said the lack of craters suggested this part of its surface was less than 100 million years old, extremely young given that the solar system is 4.5 billion years old.
Pluto's largest moon, Charon, also surprised scientists. The light and dark areas seen from Earth had pointed to some intriguing possibilities on Pluto, but Charon is smaller and thought to be largely inert.
"Originally, I thought Charon might be an ancient terrain covered in craters," said Dr Olkin. "Charon just blew our socks off when we had the new image today. It is a small world with canyons, cliffs and dark areas that are still mysterious to us."
There was also a canyon 6.4km to 9.7km deep, surprising for a body less than 1,290km wide.
Even Hydra, one of the small moons, proved interesting. It is reflective, bouncing back 45 per cent of the light that hits it.
"That can only mean Hydra's surface is composed primarily of water ice," project scientist Harold Weaver said. "It's the only way to get it that bright."
NEW YORK TIMES