Pluto’s famous heart-shaped structure, named Tombaugh Regio, controls winds in the atmosphere of the dwarf planet and may give rise to features on its surface, according to a study led by NASA’s Ames Research Center. Published in the Journal of Geophysical Research: Planets, the new work confirms that despite a frozen surface and a tenuous atmosphere, Pluto’s climate is remarkably active.
This high-resolution image of Pluto was taken by New Horizons on July 14, 2015. Pluto’s surface sports a remarkable range of subtle colors, enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have their own distinct colors, telling a complex geological and climatological story that scientists have only just begun to decode. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
Nitrogen gas comprises most of Pluto’s tenuous atmosphere, along with small amounts of carbon monoxide and methane. Frozen nitrogen also covers part of the dwarf planet’s surface.
Most of Pluto’s nitrogen ice is confined to Tombaugh Regio. Its left ‘lobe’ is a 1,000-km (620 mile) ice sheet located in a 3-km (1.9 mile) deep basin named Sputnik Planitia — an area that holds most of the dwarf planet’s nitrogen ice because of its low elevation. The right ‘lobe’ is comprised of highlands and nitrogen-rich glaciers that extend into the basin.
During the day, a thin layer of nitrogen ice warms and turns into vapor. At night, the vapor condenses and once again forms ice. Each sequence is like a heartbeat, pumping nitrogen winds around the dwarf planet.
According to the new study, this cycle pushes Pluto’s atmosphere to circulate in the opposite direction of its spin — a unique phenomenon called retro-rotation.
As air whips close to the surface, it transports heat, grains of ice and haze particles to create dark wind streaks and plains across the north and northwestern regions.
“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 Dr. Tanguy Bertrand, a researcher at NASA’s Ames Research Center.
Dr. Bertrand and his colleagues set out to determine how circulating air might shape features on the dwarf planet’s surface.
The researchers 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 and assessed how winds blew across the surface.
They discovered Pluto’s winds above 4 km (2.5 miles) blow to the west — the opposite direction from the dwarf planet’s eastern spin — in a retro-rotation during most of its year.
As nitrogen within Tombaugh Regio vaporizes in the north and becomes ice in the south, its movement triggers westward winds. No other place in the Solar System has such an atmosphere, except perhaps Neptune’s moon Triton.
The scientists also found a strong current of fast-moving, near-surface air along the western boundary of the Sputnik Planitia basin.
Atmospheric nitrogen condensing into ice drives this wind pattern. Sputnik Planitia’s high cliffs trap the cold air inside the basin, where it circulates and becomes stronger as it passes through the western region.
These wind patterns stemming from Pluto’s nitrogen heart may explain why it hosts dark plains and wind streaks to the west of Sputnik Planitia.
Winds could transport heat — which would warm the surface — or could erode and darken the ice by transporting and depositing haze particles. If winds on the dwarf planet swirled in a different direction, its landscapes might look completely different.
“Sputnik Planitia may be as important for Pluto’s climate as the ocean is for Earth’s climate,” Dr. Bertrand said.
“If you remove Sputnik Planitia — if you remove the heart of Pluto — you won’t have the same circulation.”
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T. Bertrand et al. Pluto’s beating heart regulates the atmospheric circulation: results from high resolution and multi-year numerical climate simulations. Journal of Geophysical Research: Planets, published online February 4, 2020; doi: 10.1029/2019JE006120
