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A giant heart-shaped feature on Pluto’s surface has intrigued astronomers since it was captured in an image by NASA’s New Horizons spacecraft in 2015. Now, researchers think they have solved the mystery of how the distinctive core came to be – and it could reveal new clues about the origin of the dwarf planet.
The feature is called Tombaugh Regio in honor of astronomer Clybe Tombaugh, who discovered Pluto in 1930. But the core is not just one feature, scientists say. And for many years, details of Tombaugh Regio’s elevation, geological composition and unique shape, as well as its highly reflective surface that is whiter than the rest of Pluto, have eluded explanation.
Much of Pluto’s nitrogen ice resides in a deep basin called Sputnik Planitia, which makes up the “left lobe” of the heart.
The basin covers an area of 745 miles by 1,242 miles (1,200 kilometers by 2,000 kilometers), equivalent to about one quarter of the United States, but it is also 1.9 to 2.5 miles (3 to 4 kilometers) lower in elevation than the most of the planet’s surface. Meanwhile, there is also a layer of nitrogen ice to the right of the core, but it is much thinner.
Through new research on Sputnik Planitia, an international team of scientists has determined that the core was created by a cataclysmic event. After an analysis involving numerical simulations, the researchers determined that a planetary body about 435 miles (700 kilometers) in diameter, or about twice the size of Switzerland from east to west, had likely collided with Pluto early in the history of the dwarf planet.
The results are part of a study about Pluto and its internal structure published on Monday in the journal Nature Astronomy.
Reconstructing an ancient ‘splat’ on Pluto
Previously, the team studied unusual features throughout the solar system, such as those on the far side of the moon, likely created by collisions during the early, chaotic days of the system’s formation.
The researchers created the numerical simulations using smoothed particle hydrodynamics software, considered the basis for a wide range of planetary collision studies, to model different scenarios for impacts, velocities, angles and possible compositions of the collision of the planetary body with Pluto.
The results showed that the planetary body probably fell into Pluto at an inclined angle, rather than head on.
“Pluto’s core is so cold that the (rocky body that collided with the dwarf planet) remained very hard and did not melt despite the heat of the impact, and thanks to the angle of impact and the low velocity, the core of the collider . “It didn’t spill into Pluto’s core, but it remained intact as a splat,” said lead study author Dr. Harry Ballantyne, research associate at the University of Bern in Switzerland, in a statement.
But what happened to the planetary body after it entered Pluto?
“Somewhere below Sputnik is the remnant of another massive body, which Pluto did not digest sufficiently,” study author Erik Asphaug, a professor at the University of Arizona’s Lunar and Planetary Laboratory, said in a statement.
The teardrop shape of Sputnik Planitia is a result of the frigidity of Pluto’s core, as well as the relatively low velocity of the impact itself, the team found. Other faster and more direct impacts would create a more symmetrical shape.
“We’re used to thinking of planetary collisions as really intense events where you can ignore the details except for things like energy, momentum and density. But in the distant Solar System, the velocities are much slower, and solid ice is strong, so you have to be much more precise in your calculations,” Asphaug said. “That’s where the fun begins.”
Pluto’s pseudo origin
While studying the core aspect, the team also focused on Pluto’s internal structure. An impact early in Pluto’s history created a mass deficit, which would have caused Sputnik Planitia to slowly migrate toward the dwarf planet’s north pole over time while the planet was still forming. This is due to the fact that the basin is less massive than its surroundings, according to the laws of physics, the researchers explained in the study.
However, Sputnik Planitia is near the dwarf planet’s equator.
Previous research has suggested that Pluto may have a subsurface ocean, and if it did, the icy crust over the subsurface ocean would be thinner in the Sputnik Planitia region, creating a dense bulge of liquid water and would result in a mass shift towards the equator, study authors said.
But the new study offers a different explanation for the location of the feature.
“In our simulations, the entire primordial mantle of Pluto is excavated by the impact, and as the core material of the collider spreads over Pluto’s core, it creates a local mass excess that can explain the equatorward migration without Subsurface ocean, or at most. a very thin person,” said study co-author Dr. Martin Jutzi, senior researcher in space research and planetary sciences at the Institute of Physics of the University of Bern.
Kelsi Singer, principal scientist at the Southwest Research Institute in Boulder, Colorado and co-deputy principal investigator on NASA’s New Horizons Mission, who was not involved in the study, said the authors did a thorough job of examining the modeling and develop their hypotheses. , although she would like to see “a closer connection to the geological evidence”.
“For example, the authors suggest that the southern part of Sputnik Planitia is very deep, but much of the geologic evidence has been interpreted to say that the south is shallower than the north,” Singer said.
The researchers believe that the new theory about Pluto’s core could shed more light on how the mysterious dwarf planet was formed. The origin of Pluto is still murky since it exists on the edge of the solar system and has only been closely studied by the New Horizons mission.
“Pluto’s geology is amazingly unique, so more creative hypotheses to explain that geology are always helpful,” Singer said. “What would help distinguish between different hypotheses is more information about Pluto’s subsurface. We can only find that by sending a spacecraft mission to Pluto in orbit, perhaps with a radar that can see through the ice.”
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