Pluto gains a heart after collision with planetary body

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The giant heart-shaped feature on Pluto’s surface has intrigued astronomers since NASA’s New Horizons spacecraft captured it in a 2015 image. Now, researchers think they have solved the mystery of how the unique heart forms, and may reveal new clues about the origins of dwarf planets.

This feature is called the “Tombaugh Region” in honor of the astronomer Clay Tombaugh, who discovered Pluto in 1930. Details about Tombaugh Region’s altitude, geological composition and unique shape, as well as its highly reflective surface (brighter white than the rest of Pluto), remained unexplained for decades.

A deep basin called Sputnik Planum forms the left lobe of the heart and is home to most of Pluto’s nitrogen ice.

The basin is 745 miles by 1,242 miles (1,200 kilometers by 2,000 kilometers), which is one-quarter the size of the United States, but its elevation is also 1.9 to 2.5 miles (3 to 4 kilometers) lower than most areas. At the same time, there is also a layer of nitrogen ice on the right side of the heart, 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 numerical simulations, the researchers concluded that a planetary body about 435 miles (700 kilometers) in diameter, roughly twice the size of Switzerland from east to west, likely collided with Pluto early in the dwarf planet’s history. .

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

Recreating ancient impact sounds on Pluto

Previously, the team studied unusual features across the solar system, such as those on the far side of the moon, that may have been caused by collisions during the chaotic early days of the system’s formation.

The researchers created numerical simulations using Smoothed Particle Hydrodynamics software, considered the basis for extensive planetary collision studies, to model different scenarios of the potential impacts, speeds, angles and compositions of a theoretical collision between a planetary body and Pluto.

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

Pluto’s core is so cold that (the rocky bodies that collided with the dwarf planet) remained very hard and did not melt despite the heat generated by the impact, and the impactor’s core did not melt due to the impact angle and low speed. It sank into Pluto’s core but remained intact, author Dr. Harry Ballantine, a research associate at the University of Bern in Switzerland, said in a statement.

But what happened after this planetary body hit Pluto?

Study co-author Erik Asphaug, a professor at the Lunar and Planetary Laboratory at the University of Arizona, said in a statement that somewhere beneath Sputnik is the remnant core of another massive body that Pluto never fully digested.

The team found that Sputnik Planitia’s teardrop shape is the result of the coldness of Pluto’s core and the relatively low speed of the impact itself. Other types of faster, more direct impacts produce more symmetrical shapes.

We’re used to thinking of planetary collisions as extremely violent events, and you can ignore the details other than energy, momentum, and density. But in distant solar systems, velocities are much slower and solid ice is strong, so your calculations have to be more precise, Asphaug said. This is where the fun begins.

The mysterious origin of Pluto

While studying the characteristics of the heart, the team also focused on Pluto’s internal structure. Impacts early in Pluto’s history would have created a mass deficit that caused the 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 has less mass than its surroundings, the researchers explained in the study.

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

Previous research has suggested that Pluto may have a subsurface ocean, and if so, the ice shell on the subsurface ocean in the Sputnik Planitia region would be thinner, creating a dense bulge of liquid water and causing mass to migrate toward the equator, the study authors said.

But new research offers a different explanation for the location of these features.

In our simulations, all of Pluto’s primordial mantle was excavated by the impact, and when the impactor’s core material was splashed onto Pluto’s core, it created a local excess of mass, which could explain the equatorward motion in the absence of a subsurface ocean. of migration, or at most a very large migration.

Kelsi Singer, chief scientist at the Southwest Research Institute in Boulder, Colo., and co-deputy principal investigator of NASA’s New Horizons mission, who was not involved in the study, said the authors were exploring models and developing hypotheses. Did a thorough job.

For example, the authors believe that the southern part of Sputnik Planitia is very deep, but much geological evidence has been interpreted to show that the southern part is shallower than the northern part, Singer said.

Researchers believe a new theory about Pluto’s heart could provide more clues about the formation of the mysterious dwarf planet. Pluto’s origins remain mysterious because it exists at the edge of the solar system and has only been studied up close by the New Horizons mission.

Pluto is a vast wonderland with unique and fascinating geology, so more creative hypotheses to explain the geology are always helpful, Singer said. What could help differentiate between the different hypotheses is more information about Pluto’s subsurface. We can only achieve this by sending a spacecraft mission to Pluto’s orbit, possibly equipped with radar that can see through the ice.

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