A ‘beating heart’ of frozen nitrogen on the surface of Pluto controls its winds and gives rise to the dwarf planet’s features.

New research indicates that Pluto’s nitrogen heart may control its atmospheric circulation and shape its landscape. The structure — known as Tombaugh Regio — nicknamed the ‘heart of Pluto’ due to its distinctive shape, was observed by NASA’s New Horizons mission in 2015, proving that the dwarf-planet is nor as barren as researchers had previously believed.

“Before New Horizons, everyone thought Pluto was going to be a netball — completely flat, almost no diversity,” Tanguy Bertrand, an astrophysicist and planetary scientist at NASA’s Ames Research Center in California. “But it’s completely different. It has a lot of different landscapes and we are trying to understand what’s going on there.”

Pluto’s beating heart of frozen nitrogen. Image credit: NASA

Deciphering how Pluto’s atmosphere is regulated gives scientists more data to compare to Earth, and as such allows us to highlight similarities and differences between our atmosphere and those of other planets — even a dwarf planet much further away from the Sun.

Nitrogen gas comprises the vast majority of Pluto’s atmosphere, with trace elements of carbon monoxide and methane, whilst a heart-shaped patch of frozen nitrogen coats part of the dwarf planet's surface. The majority of this frozen nitrogen is found in the ‘left-lobe’ — a 1,000-kilometre ice sheet sat in a 3 km deep basin — Sputnik Planitia — as a result of this area’s low-elevation. The ‘right-lobe’ of Tombaugh Region has a higher elevation and contains nitrogen-rich glaciers extending into the basin.

During Pluto’s day, a thin layer of this nitrogen is heated and forms vapour. Conversely, at night, this vapour condenses, forming ice. Thus this day-night cycle of freezing and warming can be compared to a ‘heartbeat’ — but rather than pumping blood around a biological system, this heart pumps nitrogen winds across pluto.

‘The heart of Pluto’ or Tombaugh Region as seen by NASA’s New Horizon probe. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The question of how this pumping of nitrogen across the dwarf planet affects its atmosphere is addressed by Bertrand and his co-authors in a new paper published in the Journal of Geophysical Research: Planets. The research suggests that the nitrogen cycle pushes Pluto’s atmosphere in the opposite direction to the dwarf planet’s spin. During this unique phenomenon — known as ‘retro-rotation’ — winds skimming Pluto’s surface transport heat, grains of ice and other particles creating dark wind streaks and plains across the dwarf planet’s north and northwestern areas.

“This highlights the fact that Pluto’s atmosphere and winds — even if the density of the atmosphere is very low — can impact the surface,” says Bertrand.