In Depth

Pluto: stunning new image unveiled by New Horizons

'Who would have expected a blue sky in the Kuiper Belt?' asks mission leader. 'It's gorgeous'

The New Horizons probe has sent back an extraordinary new image of Pluto, revealing that the dwarf planet has bright blue skies.

The pictures were beamed back by the Nasa spacecraft, which is currently 3.1 billion miles from Earth. The ground-breaking mission has given human beings their first ever close-up view of Pluto.

The first colour image of the planet's atmospheric haze has wowed scientists. "Who would have expected a blue sky in the Kuiper Belt?" asked the mission's principle investigator Alan Stern. "It's gorgeous."

Scientists say the striking blue tint is the result of the way sunlight is scattered by haze particles. "It tells us about the size and composition of [such] particles," said team member Carly Howett.

In another significant finding, scientists discovered numerous ice patches on Pluto's surface, the BBC reports.

"We expected water-ice to be there, but we've searched for water-ice in Pluto's spectrum for decades and not seen it before now," the mission's Alex Parker tweeted.

What have we learned about Pluto?

One of the most surprising discoveries so far is that the surface of Pluto is far younger than previously supposed. Despite being located in the Kuiper Belt – the remote region of our solar system teeming with asteroids and space debris – no impact craters have yet been spotted on the surface, suggesting it has been smoothed over by relatively recent geological activity. Scientists are now putting the surface in the region of 100 million years old – a baby in planetary terms.

Another unexpected finding, announced in a press conference on Wednesday, is the vast ranges of ice mountains of a size comparable to the Rockies. The mountains confirm the presence of water ice on the planet alongside the nitrogen ice and methane ice previously known to cover its surface. "The steep topography means that the bedrock that makes those mountains must be made of H2O – of water ice," principal investigator Alan Stern told the conference. "We can be very sure that the water is there in great abundance."

New images of Pluto's principal moon, Charon, also unveiled a terrain unlike anything the team had expected, filled with troughs, cliffs and a miles-deep canyon. "Charon just blew our socks off when we had the new image today," said mission scientist Cathy Olkin. "There is so much interesting science in this one image alone."

Why is this mission so important?

The Pluto fly-by marks a major milestone for space exploration, as it means mankind has achieved a complete survey of the 'classical' nine planets for the first time ever. The other outer solar system planets – Jupiter, Saturn, Uranus and Neptune – were observed by the Voyager 2 probe between 1977 and 1989.

The probe has been barrelling through space at a rate of 30,000 miles per hour since its launch in 2006, at a projected cost of $720 million (£462 million). Nine years later, the unmanned probe came within 7,770 miles of the last unexplored planet in the solar system, gathering a wealth of data about Pluto and its principal moon, Charon, in the process.

The data stored on the craft will now begin transmission to Earth, a process which may take 16 months to complete. After a journey lasting almost a decade, the probe had a window of just a few hours to gather as much information as possible before it passed Pluto. There was a small but daunting risk that the craft might be destroyed by debris hurtling through space, but mission operations manager Alice Bowman confirmed that no damage had been sustained.

"We have a healthy spacecraft," she said. "We've recorded data of Pluto's system and we're outbound from Pluto… Just like we practised, just like we planned it. We did it."

What will the data be used for?

The mass of data obtained from New Horizons will help scientists understand the composition of Pluto and shed light on the far reaches of the solar system.

The Kuiper Belt objects, of which Pluto is one, are believed to be fragments from an earlier period in the formation of the solar system, and a closer examination could reveal important information about its evolution over billions of years.

Images sent back from the craft have already given scientists an unprecedented view of Pluto. They have also shown that the planet is larger than previously thought, thereby ending the debate about whether or not it is larger than its 'twin planet' Eris.

What next?

Scientists are hoping that New Horizons will now be able venture even further into outer space. If so, it could transmit ground-breaking information about the Kuiper Belt, the vast ring of unexplored ice planets and asteroids which extends out from the fringes of the solar system.

Graphic by Simon Coxall

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