New Horizons may have spent nine years travelling nearly three billion miles to reach Pluto in the outer reaches of our solar system, but it may have only got there in the nick of time.

Data sent back by the probe has revealed Pluto's thin atmosphere is far more tenuous than had been previously thought and may actually be in the process of collapsing.

Previous measurements of Pluto's atmosphere had suggested the pressure on the surface would be around 15 microbars.

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New Horizons took dramatic images of the hazy atmosphere surrounding Pluto after passing the planet and found it is divided into two distinct regions, as shown in the image above. Methane seems to form most of the upper region, but ultraviolet light causes this to form heavier hydrocarbons that fall back towards the surface

Measurements taken by New Horizons, however, indicate the pressure is less than half that figure at just seven microbars – 100,000 times less than the surface pressure on Earth.

A new video released by Nasa's New Horizons' team suggests that the atmosphere is collapsing as the gases freeze and fall to the surface.

PLUTO'S ICY PLAINS REVEALED The craterless plain that appears to be no more than 100 million years old. Scientists suggest this means they are being shaped by geologic processes. They resemble frozen mud cracks on Earth - has been informally named 'Sputnik Planum' after the Earth's first artificial satellite. Some of these troughs have darker material within them, while others are traced by clumps of hills that appear to rise above the surrounding terrain. Elsewhere, the surface appears to be etched by fields of small pits that may have formed by a process called sublimation, in which ice turns directly from solid to gas, just as dry ice does on Earth. The irregular shapes may be the result of the contraction of surface materials, similar to what happens when mud dries. Or hey may be a product of convection, similar to wax rising in a lava lamp. Advertisement

It means New Horizons was lucky to obtain its fleeting glimpse of the dwarf planet with its faint ring of hazy atmosphere around it as it passed by.

One image sent back, taken from behind Pluto, revealed two distinct layers of haze – one about 50 miles (80km) above the surface and the other about 30 miles (50km).

Dr Ivan Linscott, a researcher at Stanford University who is part of the New Horizons research team, said: 'For the first time we have ground truth, measuring the surface pressure at Pluto, giving us an invaluable perspective on conditions at the surface of the planet.

'This crucial measurement may be telling us that Pluto is undergoing long-anticipated global change.'

New Horizons made its closest approach to Pluto on July 14 and around one hour after passing the planet the spacecraft turned its REX radio instrument to look back at it.

Two radio dishes on Earth, part of Nasa's Deep Space Network, beamed radio waves towards Pluto which were timed to reach the dwarf planet just as New Horizons passed behind it.

These radio waves travelled through Pluto's atmosphere, bending and refracting due to the gases there.

Researchers were then able to use the amount of refraction to calculate the pressure on the surface of the planet.

This false colour image of Pluto was created by combining four images together. Taken when New Horizons was 280,000 miles away, it reveals the complex geology on the surface of Pluto, including the heart shaped ice sheet in the middle, mountain ranges and impact craters

Data released by scientists working on the New Horizons mission have shown that the surface pressure on Pluto has changed dramatically over time as the ice on the surface has melted, releasing gas. The most recent measurements by New Horizons, shown by the red arrow above, show the pressure has rapidly decreased

Researchers believe around half of Pluto's atmosphere may have recently frozen back onto the planet's surface and more may be about to follow.

Other measurements have suggested this process could also be responsible for Pluto's reddish hue.

Ultraviolet light from the sun is causing methane gas in the atmosphere to combine to produce more complex hydrocarbon gases like ethylene and acetylene.

These heavier hydrocarbons fall to the lower colder parts of the atmosphere where they condense as ice particles.

These are then converted into tholins, dark hydrocarbons that colour Pluto's surface as they fall..

Backlit by the sun, Pluto's hazy atmosphere can be seen like a halo around the dwarf planet in the image above taken by New Horizons. Data sent back by the probe suggest Pluto's atmosphere is falling back to the surface

The first ever high-resolution image of Pluto was beamed back to Earth last week showing water ice and 11,000ft (3,350 metre) mountains. The mountains likely formed n 100 million years ago - mere youngsters relative to the 4.56-billion-year age of the solar system

Michael Summers, a New Horizons co-investigator, said: 'The hazes detected in this image are a key element in creating the complex hydrocarbon compounds that give Pluto's surface its reddish hue.'

It is the latest in a number of discoveries by the space probe, which has provided scienitsts with a detailed view of the icy mountains and plains that cover the surface.

They have found signs of exotic ice, which suggests there were relatively recent signs of geology on the surface within the past 100 million years.

A newly discovered mountain range lies near the southwestern margin of Pluto's Tombaugh Regio, between bright, icy plains and dark, heavily-cratered terrain. This image was taken by New Horizons was taken from a distance of 48,000 miles (77,000km). Features as small as a half-mile (1km) across are visible

New Horizons turned its instruments to look back at Pluto, as illustrated above, after it passed the dwarf planet to make measurements of its atmosphere and to take pictures of it backlit by the sun

Close up images have revealed huge sheets of ice, similar to glaciers on Earth,that may still be moving.

The center of the enormous heart shaped ice sheet Sputnik Planum is rich in nitrogen, carbon monoxide, and methane ices.

In the middle of the heart shaped ice sheet, called Sputnik Planum, two bluish-white 'lobes' that extend to the southwest and northeast of the 'heart' may represent exotic ices being transported away in a flows like glaciers

In the southernmost region of the heart, adjacent to the dark equatorial region, it appears that ancient, heavily-cratered terrain has been invaded by much newer icy deposits.

Astronomers have also discovered a mountain range taller than the Rocky Mountains made of ice and a second range around one mile high.