Pluto's surface is dominated by Sputnik Planitia, a giant pear-shaped basin. Although it appears to be of impact origin, modeling has not yet accounted for its unique shape. Planetary scientists at the University of Bern have proposed an impact mechanism that would both recreate the topography of the basin and explain the alignment around the Pluto-Charon axis. According to their research, Sputnik Planum was created by a collision between Pluto and a planet about 700 km (435 miles) in diameter.

In 2015, NASA's New Horizons spacecraft revealed that Pluto's surface is geologically complex.

The region is dominated by a 1,200 x 2,000 km (746 x 1,243 mi) nitrogen ice-filled basin called Sputnik Planitia.

Sputnik Planitia is located in the western part of Pluto's Tombow region, a famous heart-shaped structure.

This basin is 3 to 4 km (1.9 to 2.5 miles) lower in elevation than most of the dwarf planet's surface.

“Sputnik Planitia's bright appearance is due to the fact that it is filled with mainly white nitrogen ice, which moves and convects to constantly smooth the surface,” said Dr. Harry Ballantyne, a planetary scientist at the University of Bern. Ta.

“Due to the low altitude, this nitrogen likely accumulated quickly after the impact.”

“The eastern part of the 'heart' is also covered with a similar but much thinner layer of nitrogen ice, the origin of which is not yet clear to scientists, but is probably related to Sputnik Planum.”

“The elongated shape of Sputnik Planitia strongly suggests that the impact was an oblique impact rather than a direct head-on impact,” said Dr. Martin Jutzi, a planetary scientist at the University of Bern.

This high-resolution image of Pluto was taken by New Horizons on July 14. Pluto's surface boasts an astonishing range of subtle colors, highlighted in this view by a rainbow of pale blues, yellows, oranges, and deep reds. Many landforms have unique colors that tell complex geological and climatological stories that scientists are only beginning to decipher. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

The authors used smoothed particle hydrodynamics (SPH) simulation software to digitally recreate such collisions while varying both the composition of Pluto and its impactors, as well as the speed and angle of the impactors. did.

These simulations confirmed our suspicions about the oblique angle of the impact and determined the configuration of the impactor.

“Pluto's core is so cold that the rocks remain very hard and do not melt despite the heat of the impact, and the angle and low speed of the impact prevents the impactor's core from sinking into Pluto's core, leaving it intact. “It's like a splatter,” Dr. Ballantyne said.

Dr. Eric Asfaug, a planetary scientist at the University of Arizona, added: “Somewhere beneath Sputnik are the remains of the core of another giant object that Pluto was not able to fully digest.”

“The strength and relatively low velocity of this core were the keys to the success of these simulations. At low strengths, the highly symmetrical remnants look nothing like the teardrop shape observed on New Horizons. surface features are obtained.

“We're used to thinking of planetary collisions as incredibly violent events, and we can ignore the details except for things like energy, momentum, and density.”

“But in distant solar systems the velocities are very slow and the solid ice is strong, so the calculations need to be more accurate. That's where the fun begins.”

The research team's findings also shed new light on Pluto's internal structure.

“In fact, a giant impact like the one simulated is much more likely to have occurred very early in Pluto's history,” the researchers said.

“But this poses a problem: giant depressions like Sputnik Planitia are expected by the laws of physics to move slowly towards the dwarf planet's poles over time because of the lack of mass. ” But paradoxically, it is close to the equator. ”

“A previous theoretical explanation was that Pluto, like several other planetary bodies in the outer solar system, has an ocean of liquid water underground.”

“Previous explanations suggest that Pluto's icy crust thins in the Sputnik Planum region, where the oceans swell and liquid water is denser than ice, creating a mass surplus that triggers a shift toward the equator. It will be.”

“But new research offers a different perspective.”

“In our simulations, all of Pluto's primordial mantle is excavated by the collisions, and as the impactor's nuclear material splatters into Pluto's core, it creates a localized overmass that causes the absence of a subsurface ocean. Or, at best, it could be explained as moving toward the equator without the ocean being present, “very thin,'' Dr. Yutzi said.

“This novel and original origin of Pluto's heart-shaped feature may lead to a deeper understanding of Pluto's origins,” said Dr. Adeen Denton, a planetary scientist at the University of Arizona.

of result It was published in the magazine natural astronomy.

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HA Ballantine other. Sputnik Planum as an impact debris showing an ancient rocky mascon on oceanless Pluto. Nat Astron, published online on April 15, 2024. doi: 10.1038/s41550-024-02248-1