Pluto acquired a “heart” after a collision with a planetary body

(CNN) — The enormous heart shape on Pluto’s surface has intrigued astronomers since NASA’s New Horizons spacecraft captured it in an image in 2015. Now researchers believe they have solved the mystery of how the distinctive heart formed, which could provide new clues about the origins of this nucleus. dwarf planet.

This feature is called “Regio Tombo” after astronomer Clybe Tombaugh, who discovered Pluto in 1930. But the heart is not a whole element, scientists say. And for decades, details about the height, geological composition and distinctive shape of the Tombaugh region, as well as its reflective surface, brighter white than the rest of Pluto, defied explanation.

A deep pool called Sputnik Planitia, which makes up the “left lobe” of the heart, contains most of Pluto’s nitrogen ice.

The basin covers an area of ​​1,200 by 2,000 kilometers, equivalent to a quarter of the United States, but is 3 to 4 kilometers lower in elevation than most of the planet’s surface. Meanwhile, on the right side of the heart there is also a layer of nitrogenous ice, but it is much thinner.

Thanks to new research on Sputnik Planitia, an international team of scientists has determined that the heart was created as a result of a cataclysmic event. After an analysis that included numerical modeling, the researchers concluded that a planetary body with a diameter of about 700 kilometers, or about twice the size of Switzerland from east to west, likely collided with Pluto early in the planet’s history.

The results are part of a study of Pluto and its internal structure published this Monday in the journal Nature Astronomy.

Recreating ancient “splashes” on Pluto.

Previously, the team had studied unusual features in the solar system, such as those on the far side of the moon, that were likely created by collisions in the early chaotic days of the system’s formation.

The researchers created numerical simulations using smoothed particle fluid dynamics software, considered the basis for a wide range of planetary impact studies, to simulate different potential impact scenarios, speeds, angles and composition of a theoretical collision of a planetary body with Pluto.

The results showed that the planetary body likely struck Pluto at an oblique angle rather than head-on.

“Pluto’s core is so cold that (the rocky body that collided with the dwarf planet) remained very solid and did not melt despite the heat of the impact, and due to the impact angle and low speed, the impactor core did not sink into Pluto’s core, but remained intact like a splash above him,” lead study author Dr. Harry Ballantyne, a researcher at the University of Bern in Switzerland, said in a statement.

But what happened to the planetary body after the collision with Pluto?

“Somewhere beneath Sputnik lies the remaining core of another massive body that Pluto never fully digested,” Eric Asphaug, study co-author and professor at the University of Arizona’s Lunar and Planetary Laboratory, said in a statement.

The team found that Sputnik Planitia’s teardrop shape is due to the coolness of Pluto’s core and relatively low impact speed. Other types of faster, straighter shots would create a more symmetrical shape.

“We tend to think of planetary collisions as incredibly intense events in which we can ignore the details except for things like energy, momentum and density. But in the distant solar system, the speeds are much slower and the solid ice is strong, so you need to be much more precise in your calculations,” Asphaug explains. “This is where the fun starts.”

Pluto’s Dark Origin

While studying the heart’s features, the team also focused on Pluto’s internal structure. An impact early in Pluto’s history may have resulted in 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 because, according to the laws of physics, the basin is less massive than its surroundings, the researchers explain in the study.

However, Sputnik Planitia is located near the dwarf planet’s equator.

Previous research has suggested that Pluto may have an underground ocean, and if so, the ice crust above the underground ocean would be thinner in the Sputnik Planitia region, creating a dense bulge of liquid water and causing mass migration toward the equator. noted the study authors.

However, new research offers a different explanation for the location of this trait.

“In our simulations, Pluto’s entire early mantle is destroyed by the impact, and as impactor core material sloshes into Pluto’s core, a localized excess mass is created that could explain equatorward migration without an underground ocean or, at best, a very thin one,” said study co-author Dr. Martin Jutzi, senior researcher for space and planetary sciences at the Institute of Physics at the University of Bern.

Kelsey Singer, a senior scientist at the Southwest Research Institute in Boulder, Colorado, and deputy principal investigator for NASA’s New Horizons mission who was not involved in the study, said the authors did a thorough job of studying the modeling and developing their hypotheses. although he 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 most geological data is interpreted to mean that the south is shallower than the north,” Singer said.

Researchers believe a new theory about Pluto’s heart could shed more light on how the mysterious dwarf planet formed. Pluto’s origins remain unclear as it exists at the edge of the solar system and was only thoroughly studied by the New Horizons mission.

“Pluto is a huge wonderland with a unique and fascinating geology, so more creative hypotheses to explain the geology are always useful,” says Singer. “What will help differentiate between different hypotheses is more information about Pluto’s interior. We can only achieve this by sending a space mission to orbit Pluto, perhaps with a radar that can look through the ice.”