Pluto got a “flip” after colliding with a planetary body

(CNN) — A huge heart shape on Pluto's surface has intrigued astronomers since NASA's New Horizons spacecraft captured it in a 2015 image, and researchers now believe they've solved the mystery of how the distinctive heart formed, potentially revealing new clues about the dwarf planet's origins.

This feature is called tombo regio, named after astronomer Caleb Tombaugh, who discovered Pluto in 1930. But scientists say the core is not a complete element. For decades, details about Tombo Reggio's elevation, geology and distinctive shape, as well as its white surface that is brighter and more highly reflective than the rest of Pluto, have eluded explanation.

There is a deep basin called Sputnik Planitia, which forms the “left lobe” of the core, and contains much of Pluto's nitrogen ice.

The basin covers an area of ​​1,200 km by 2,000 km, equivalent to a quarter of the area of ​​the United States, but it is also 3 to 4 km lower than most of the planet's surface. Meanwhile, the right side of the core also contains a layer of nitrogen ice, but it is much thinner.

The New Horizons spacecraft captured an image of Pluto's core on July 14, 2015. (Image source: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/NASA)

Through new research on Sputnik Planitia, an international team of scientists has determined that a cataclysmic event created the core. After an analysis that included numerical simulations, 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 dwarf planet's history.

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

Reproducing an ancient “spot” on Pluto

Previously, the team had 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 system's chaotic early days of formation.

The researchers created numerical simulations using smooth particle hydrodynamics software, which is the basis for a wide range of planetary collision studies, to model different scenarios of the potential impacts, velocities, angles and compositions of a theoretical planetary body collision with Pluto.

The results showed that the planetary body may have collided with 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 collision, and thanks to the impact angle and low speed, the impactor’s core did not sink,” said the study’s lead author, Dr. Harry Ballantyne, a research associate at the University of Bern. In Switzerland, he said in a statement: “In the heart of Pluto, but it remained as intact as the water spray above it.”

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

“Somewhere beneath Sputnik is the remaining core of another massive object, which Pluto never fully digested,” Eric Asfaugh, study co-author and professor at the University of Arizona's Lunar and Planetary Laboratory, said in a statement.

The team discovered that Sputnik Planitia's teardrop shape is due to Pluto's cold core and relatively low impact speed. Other types of faster, more direct effects would have created a more symmetrical look.

“We're used to thinking of planetary collisions as incredibly intense events whose details can be ignored except for things like energy, momentum and density. But in a distant solar system, the speeds are much slower and solid ice is strong, so you have to be more precise in your calculations,” explains Asphaug. . “This is where the fun starts.”

The mysterious origins of Pluto

While studying the heart feature, the team also focused on Pluto's internal structure. An impact early in Pluto's history would have created 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 the basin is less massive than its surroundings, according to the laws of physics, as the researchers explained in the study.

However, Sputnik Planitia is close to the dwarf planet's equator.

Previous research has suggested that Pluto could have a subsurface ocean, and if so, the icy crust above the subsurface ocean would be thinner in the Sputnik Planitia region, creating a dense bulge of liquid water and causing a mass migration toward the equator, the authors note.

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

“In our simulations, Pluto's early mantle has been completely excavated by impact, and as the core material from the impactor is scattered into Pluto's core, excess local mass is created that could explain the migration toward the equator without a subsurface ocean, or at most Sensitive”. “One,” said study co-author Dr. Martin Goetze, a senior researcher in space research and planetary science at the Institute of Physics at the University of Bern.

The authors did a thorough job exploring the modeling and developing their hypotheses, said 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. Although he would have liked to see a “closer correlation 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 to mean that the south is less deep than the north,” Singer said.

Researchers believe that the new theory about Pluto's core could shed more light on how the mysterious dwarf planet formed. Pluto's origins have remained a mystery since it is located at the edge of the solar system and has only been closely studied by the New Horizons mission.

“Pluto is a vast wonderland with unique and fascinating geology, so more creative hypotheses to explain that geology are always helpful,” Singer says. “What might help distinguish between different hypotheses is getting more information about Pluto's subsurface. We can only achieve this by sending a space mission into Pluto's orbit, perhaps using a radar that can look through the ice.”