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Pluto Has a Nitrogen Heartbeat

Nitrogen on the dwarf planet’s glacial ‘heart’ becomes vapor each day and freezes each night

The left lobe of Pluto's distinctive heart is called Sputnik Planitia, covered with craterless plains of frozen nitrogen that vaporize each day. (NASA/JHUAPL/SwRI)
smithsonianmag.com

Pluto has a heartbeat of sorts, according to a new study from NASA’s New Horizons team.

Each day, sunlight hits the Sputnik Planitia basin—the left side of the heart—and nitrogen ice vaporizes. At night, Pluto’s temperature drops, and the vaporized nitrogen condenses back to ice. The cycle repeats every Plutonian day, which is about six and a half Earth days long, and powers the winds that shaped the dwarf planet’s landscape, per the study published on February 4 in the Journal of Geophysical Research.

"Before New Horizons, everyone thought Pluto was going to be a netball—completely flat, almost no diversity," NASA astrophysicist and planetary scientist Tanguy Bertrand says in a statement. "But it's completely different. It has a lot of different landscapes and we are trying to understand what's going on there."

Humanity got its best look at Pluto in 2015, when NASA’s New Horizons spacecraft sent back images of craters, glaciers, plains, and dunes. The photographs showed Pluto’s landscape surrounded by the thin haze of its mostly-nitrogen atmosphere.

The smooth features of Sputnik Planitia’s 2-mile-deep basin caught planetary scientists’ eyes that July. The region is covered with "vast craterless plains that have some story to tell," New Horizons co-investigator Jeffrey Moore told NPR’s Scott Neuman in 2015. "I am still having to remind myself to take deep breaths. The geology is just astounding.”

In the new study, the researchers discovered the region’s story. They used a weather forecasting model to test how Sputnik Planitia’s “heartbeat” affects the winds of Pluto’s haze, which is about 100,000 times thinner than Earth’s atmosphere.

They found that two and a half miles above ground, the winds blow westward, opposite the direction of Pluto’s rotation. The only other object in the solar system that might do the same thing is Neptune’s moon Triton. The weather model also showed a strong current of air near ground level at the west side of the Sputnik Planitia basin, where tall cliffs at the basin’s edge trap the air.

“It’s very much the kind of thing that’s due to the topography or specifics of the setting,” says planetary scientist Candice Hansen-Koharcheck, who wasn’t involved with the new study, in the statement. “I’m impressed that Pluto’s models have advanced to the point that you can talk about regional weather.”

The unusual way that the atmosphere flows could have influenced the uneven formation of geological features like Pluto’s Bladed Terrain and the whale-shaped Cthulhu Macula, the paper says. The wind may have carried more heat and haze particles to one region than another, causing the dark streaks and dunes that New Horizon spotted in 2015.

The nitrogen heartbeat of the Sputnik Planitia basin seems as important to Pluto’s weather patterns as the ocean is to Earth’s, Bertrand says in the statement. According to their weather models, it provides enough disturbance to the atmosphere to keep the thin air moving and shaping the landscape.

“Pluto’s atmosphere gives us a new laboratory to explore how atmospheres behave in general,” Bertrand tells New Scientist’s Leah Crane.

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