Pluto gained a “heart” after colliding with a planetary body; understand

A huge heart-shaped mark on the surface of Pluto has intrigued astronomers since the NASA's New Horizons probe captured it in a 2015 image. Now, researchers believe they have solved the mystery of how the distinctive heart came to be — and this could reveal new clues about the origins of the dwarf planet .

The brand is called Tombaugh Region in honor of the astronomer Clyde Tombaugh, who discovered Pluto in 1930 . But the heart is not made up of a single element, scientists say. And for decades, details about Tombaugh Regio's elevation, geological composition and distinctive shape, as well as its highly reflective surface that is a brighter white than the rest of Pluto, have defied explanation.

A deep basin called Sputnik Planitia, which forms the left side of the heart, houses most of Pluto's nitrogen ice.

The basin covers an area of ​​1,200 kilometers by 2,000 kilometers, equivalent to about a quarter of the United States, but is also 3 to 4 kilometers lower in elevation than most of the planet's surface. 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 determined that a cataclysmic event created the heart of Pluto . After an analysis involving numerical simulations, the researchers concluded that a planetary body about 700 kilometers in diameter or roughly twice the size of Switzerland, 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 in Nature Astronomy magazine.

Recreating an ancient crash on Pluto

Previously, the team studied unusual features throughout the Solar System, such as those on the far side of the Moon, which were likely created by collisions during the chaotic early 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 potential impacts, speeds, angles and compositions of the theoretical planetary body's collision with Pluto.

The results showed that the planetary body likely collided with Pluto at a tilted 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. Thanks to the impact angle and low speed, the object's core did not sink into Pluto's core, but remained intact as a speck on it,” said study lead author Harry Ballantyne, a research associate at the University of Bern in Switzerland.

But what happened to the planetary body after it hit Pluto?

“Somewhere beneath Sputnik Planitia is the remnant core of another massive body, which Pluto never completely digested,” said study co-author Erik Asphaug, professor at the University of Arizona's Lunar and Planetary Laboratory.

Sputnik Planitia's teardrop shape is a result of the frigidity of Pluto's core, as well as the relatively low speed of the impact itself, the team concluded. Other types of faster, 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 except for things like energy, momentum and density. But in the distant Solar System, speeds are much slower and solid ice is strong, so you need to be much more precise in your calculations,” said Asphaug. “That’s where the fun begins.”

Pluto's Dark Origins

While studying the heart's 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, 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 ice crust over 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 study authors said.

But the new study offers a different explanation for the feature's location.

“In our simulations, Pluto's entire primordial mantle is excavated by the impact, and as material from the impactor's core spreads into Pluto's core, it creates a local excess mass that could explain the equatorward migration without an underground ocean, or at most a very thin one,” said study co-author Dr. Martin Jutzi, senior researcher for space research and planetary sciences at the Institute of Physics at 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 exploring the modeling and developing their hypotheses, although she would have liked to have seen “a closer link with the geological evidence”.