Pluto's frozen heart of nitrogen makes its atmosphere go backwards


Pluto has a heart-shaped patch of frozen nitrogen, responsible for gusty winds that push in the opposite direction to the dwarf planet’s rotation, say NASA scientists.

As nitrogen within the heart-shaped ice region, called Tombaugh Regio, vaporises in the north and becomes ice in the south, its movement triggers western winds.

Pluto’s winds above 2.5 miles blow to the west – opposite to the dwarf planet’s spin – in a ‘retro-rotation’ during most of its year, which lasts a hefty 248 Earth years.

The team used data from NASA’s New Horizons spacecraft, which captured observations of Pluto back in 2015, including Tombaugh Regio, which lies just north of the equator.

Pluto's heart (outlined in red) may have once tipped the whole world over. And today, the enormous impact basin may still be slowly shifting Pluto's position

Pluto’s heart (outlined in red) may have once tipped the whole world over. And today, the enormous impact basin may still be slowly shifting Pluto’s position

WHY IS PLUTO NOT A PLANET?

 In 2006, the International Astronomical Union, a global group of astronomy experts, established a definition of a planet that required it to ‘clear’ its orbit, or in other words, be the largest gravitational force in its orbit.

Since Neptune’s gravity influences its neighbouring planet Pluto, and Pluto shares its orbit with frozen gases and objects in the Kuiper belt, that meant Pluto was out of planet status.

Pluto was relegated from its definition as a planet to a dwarf planet, which, despite its name, is not a ‘planet’ as defined by the IAU. 

The main difference between ‘dwarf planet’ and ‘planet’ is that the latter does not dominate its region of space. 

Before 2006, there was never a formal definition for what constituted a planet. 

Scientists argue that this means Pluto’s demotion is unjust and unreasonable. 

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‘Just so you know, in my view, Pluto is a planet,’ said NASA administrator Jim Bridenstine. 

No planet in our Solar System has this unusual retro-rotation, and if winds on Pluto pulled in a different direction, its dramatic landscape of icy valleys and mountains would look very different.

‘This highlights the fact that Pluto’s atmosphere and winds – even if the density of the atmosphere is very low –can impact the surface,’ said Tanguy Bertrand, an astrophysicist and planetary scientist at NASA’s Ames Research Center in California and the study’s lead author. 

The findings pinpoint distinctions between Earth and this dwarf planet 3.7 billion miles away from the sun, whose status as a planet was downgraded in 2006.

Nitrogen gas comprises most of Pluto’s thin atmosphere, along with small amounts of carbon dioxide and methane.

During the plutonian day – which lasts six days, nine hours and 36 minutes in Earth time – a thin layer of this nitrogen warms and turns into vapour, and at night, the vapour condenses and once again forms ice.

Each sequence is like a ‘heartbeat’, pumping nitrogen winds around the planet.

As air whips close to the surface, it transports heat, ice grains and haze particles to create dark wind streaks and plains across the north and north-western regions.

Tombaugh Regio’s eastern ‘lobe’ is comprised of highlands and nitrogen-rich glaciers, while its western side is a 620-mile ice sheet located in a 1.9-mile-deep basin called Sputnik Planitia – which is key to this unusual retro-rotation.

‘Sputnik Planitia may be as important for Pluto’s climate as the ocean is for Earth’s climate,’ Bertrand said.

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‘If you remove Sputnik Planitia – if you remove the heart of Pluto – you won’t have the same circulation.’

The researchers found a strong current of fast-moving near-surface air along the western boundary of the Sputnik Planta basin was driven by atmospheric nitrogen condensing into ice.

Pluto’s atmosphere is made primarily of nitrogen, with traces of methane and carbon monoxide, and temperatures can drop to as low as -238 degrees Celsius. By 2030, scientists estimate its atmosphere will freeze over and condense

Pluto’s atmosphere is made primarily of nitrogen, with traces of methane and carbon monoxide, and temperatures can drop to as low as -238 degrees Celsius. By 2030, scientists estimate its atmosphere will freeze over and condense 

Sputnik Plantitia’s high cliffs trap the cold air inside the basin, where it circulates and becomes stronger as it passes through the western region.

Wind patterns that come from Tombaugh Regio may explain why it hosts dark plains and wind streaks to the west of Sputnik Plantitia.

Winds could transport heat or could erode and darken the ice by transporting and depositing haze particles.

The team pulled data from New Horizons’ 2015 flyby to depict Pluto’s topography and its blankets of nitrogen ice.

They then simulated the nitrogen cycle with a weather forecast model to assess how winds blew across the surface.

‘Before New Horizons, everyone thought Pluto was going to be a netball – completely flat, almost no diversity,’ Bertrand said.

‘But it’s completely different. It has a lot of different landscapes and we are trying to understand what’s going on there.’

The legendary New Horizons interplanetary space probe was launched in 2006 and flew 7,800 miles above the surface of Pluto, capturing detailed images of its surface.

The study has been published in Journal of Geophysical Research: Planets.

WHERE IS NEW HORIZONS?

The spacecraft that gave us the first close-up views of Pluto now has a much smaller object in its sights.

New Horizons is now track to fly past a recently discovered, less than 30-mile-wide object out on the solar system frontier.

The close encounter with what’s known as 2014 MU69 would occur in 2019. It orbits nearly 1 billion miles (1.6 billion kilometers) beyond Pluto.

Nasa and the New Horizons team chose 2014 MU69 in August as New Horizons’ next potential target, thus the nickname PT-1. Like Pluto, MU69 orbits the sun in the frozen, twilight zone known as the Kuiper Belt.

MU69 is thought to be 10 times larger and 1,000 times more massive than average comets, including the one being orbited right now by Europe’s Rosetta spacecraft.

On the other end, MU69 is barely 1 percent the size of Pluto and perhaps one-ten-thousandth the mass of the dwarf planet. So the new target is a good middle ground, according to scientists.

The spacecraft was recently approved for its extended mission, allowing it to continue on its path toward the object deeper in the Kuiper Belt.

It’s expected that New Horizons will make its approach to the ancient object on January 1, 2019.

 



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