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A huge heart-shaped feature on Pluto’s surface has intrigued astronomers since NASA’s New Horizons spacecraft captured it in an image in 2015. Now researchers think they have solved the mystery of how the distinctive heart formed – and it could reveal new clues about the dwarf planet’s origins.
The feature is called Tombaugh Region, in honor of astronomer Clybe Tombaugh, who discovered Pluto in 1930. But the heart is not just made of one element, scientists say. And for decades, details about Tombaugh Region’s altitude, geological composition and distinct shape, as well as its highly reflective surface that is brighter white than the rest of Pluto, have defied explanation.
A deep basin called Sputnik Planitia, which forms the “left lobe” of the heart, houses much of Pluto’s nitrogen ice.
The basin covers an area of 1,200 by 2,000 kilometers, equivalent to about a quarter of the United States, but it is also 3 to 4 kilometers lower in elevation than the majority of the United States. the surface of the planet. Meanwhile, the right side of the heart also has a layer of nitrogen ice, but it is much thinner.
Through new research on Sputnik Planitia, an international team of scientists has determined that a catastrophic event created the heart. After analyzing with numerical simulations, the researchers concluded that a planetary body with a diameter of about 700 kilometers (about twice the size of Switzerland from east to west) had probably collided with Pluto early in the dwarf planet’s history.
The findings are part of a study of Pluto and its internal structure published Monday in the journal Nature Astronomy.
Recreating an ancient ‘splat’ on Pluto
Previously, the team studied unusual features across the solar system, such as those on the far side of the moon, that were likely created by collisions during the early, chaotic days of the system’s formation.
The researchers created the numerical simulations using software for smoothed particle hydrodynamics, which is considered the basis for a wide range of planetary collision studies, to model different scenarios for possible impacts, velocities, angles and compositions of the planet’s collision theoretical planetary body with Pluto.
The results showed that the planetary body likely collided with Pluto at an oblique angle, rather than head-on.
“Pluto’s core is so cold that it (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 impact angle and low speed, the core of the impactor did . not sinking into Pluto’s core, but remaining intact like a splat on it,” said lead study author Dr. Harry Ballantyne, research associate at the University of Bern in Switzerland, said in a statement.
But what happened to the planetary body after it collided with Pluto?
“Somewhere beneath Sputnik is the remnant core of another massive body, which Pluto never completely digested,” co-author Erik Asphaug, a professor at the University of Arizona’s Lunar and Planetary Laboratory, said in a statement.
Sputnik Planitia’s teardrop shape is a result of the frigidity of Pluto’s core, as well as the relatively slow speed of the impact itself, the team found. Other types of faster and more direct impacts would have created a more symmetrical shape.
“We’re used to thinking of planetary collisions as incredibly intense events where you can ignore the details other than things like energy, momentum and density. But in the distant solar system, speeds are so much slower and solid ice is strong, so you have to be much more accurate in your calculations,” Asphaug said. “That’s where the fun begins.”
The dark origins of Pluto
While studying heart function, the team also focused on Pluto’s internal structure. An impact early in Pluto’s history would have caused a mass deficit, causing 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 located near the dwarf planet’s equator.
Previous research has suggested that Pluto might have a subsurface ocean, and if so, the ice crust above the subsurface ocean would be thinner in the Sputnik Planitia region, creating a dense bulge of liquid water and a migration of mass would be caused to move towards the equator. said study authors.
But the new study offers a different explanation for the location of the feature.
“In our simulations, Pluto’s entire primordial mantle is excavated by the impact, and as core material from the impactor splashes onto Pluto’s core, it creates a local mass surplus that could explain the migration toward the equator without a subsurface ocean, or at most an underground ocean. very thin,” says co-author Dr. Martin Jutzi, senior researcher in space research and planetary sciences at the Physics Institute of the University of Bern.
Kelsi Singer, a principal scientist at the Southwest Research Institute in Boulder, Colorado and co-deputy principal investigator of NASA’s New Horizons mission, who was not involved in the study, said the authors thoroughly examined the models and developed their hypotheses . , although she would have liked to see “a closer connection with the geological evidence.”
“For example, the authors suggest that the southern part of Sputnik Planitia is very deep, but much of the geological evidence has been interpreted as indicating that the south is shallower than the north,” Singer said.
The researchers believe the new theory about Pluto’s heart could shed more light on how the mysterious dwarf planet formed. Pluto’s origins have remained obscure, as it is located on the edge of the solar system and has only been studied up close by the New Horizons mission.
“Pluto is a vast wonderland of unique and fascinating geology, 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 achieve this by sending spacecraft into orbit around Pluto, possibly with a radar that can see through the ice.”
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