A “beating heart” of frozen nitrogen
controls Pluto’s winds and may give rise to features on its surface, according
to a new study.
Pluto’s famous heart-shaped
structure, named Tombaugh Regio, quickly became famous after NASA’s New
Horizons mission captured footage of the dwarf planet in 2015 and revealed it
isn’t the barren world scientists thought it was.
Now, new research shows Pluto’s
renowned nitrogen heart rules its atmospheric circulation. Uncovering how
Pluto’s atmosphere behaves provides scientists with another place to compare to
our own planet. Such findings can pinpoint both similar and distinctive
features between Earth and a dwarf planet billions of miles away.
Nitrogen gas — an element also found
in air on Earth — comprises most of Pluto’s thin atmosphere, along with small
amounts of carbon monoxide and the greenhouse gas methane. Frozen nitrogen also
covers part of Pluto’s surface in the shape of a heart. During the day, a thin
layer of this 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.
New research
in AGU’s Journal of Geophysical Research: Planets suggests
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 Tanguy Bertrand, an astrophysicist and
planetary scientist at NASA’s Ames Research Center in California and the
study’s lead author.
Most of Pluto’s nitrogen ice is
confined to Tombaugh Regio. Its left “lobe” is a 1,000-kilometer (620-mile) ice
sheet located in a 3-kilometer (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 heart’s right “lobe” is comprised of highlands and nitrogen-rich
glaciers that extend into the basin.
“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.”
Western
winds
Bertrand and his colleagues set out
to determine how circulating air — which is 100,000 times thinner than that of
Earth’s — might shape features on the surface. 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 and
assessed how winds blew across the surface.
The group discovered Pluto’s winds
above 4 kilometers (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, according to the new study. No
other place in the solar system has such an atmosphere, except perhaps
Neptune’s moon Triton.
The researchers also found a strong
current of fast-moving, near-surface air along the western boundary of the
Sputnik Planitia basin. The airflow is like wind patterns on Earth, such as the
Kuroshio along the eastern edge of Asia. Atmospheric nitrogen condensing into
ice drives this wind pattern, according to the new findings. 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.
The intense western boundary
current’s existence excited Candice Hansen-Koharcheck, a planetary scientist
with the Planetary Science Institute in Tucson, Arizona who wasn’t involved
with the new study.
“It’s very much the kind of thing
that’s due to the topography or specifics of the setting,” she said. “I’m
impressed that Pluto’s models have advanced to the point that you can talk
about regional weather.”
On the broader scale,
Hansen-Koharcheck thought the new study was intriguing. “This whole concept of
Pluto’s beating heart is a wonderful way of thinking about it,” she added.
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,” Bertrand
said. “If you remove Sputnik Planitia — if you remove the heart of Pluto — you
won’t have the same circulation,” he added.
The new findings allow researchers
to explore an exotic world’s atmosphere and compare what they discover with
what they know about Earth. The new study also shines light on an object 6
billion kilometers (3.7 billion miles) away from the sun, with a heart that
captivated audiences around the globe.
“Pluto has some mystery for
everybody,” Bertrand said.
Journal
article: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JE006120
Source: https://myfusimotors.com/2020/02/05/plutos-icy-heart-makes-winds-blow/
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