NASA | The study suggests that Pluto's internal structure is different than previously thought

Ever since cameras on NASA's New Horizons mission discovered a large heart-shaped structure on the surface of dwarf planet Pluto in 2015, the feature has puzzled scientists due to its unique shape, geography and height. A team of scientists from the University of Bern, including several members of NCCR Planets and the University of Arizona at Tucson, used numerical simulations to investigate the origin of Sputnik Planitia, the teardrop-shaped western part of the core's surface. of Pluto.

According to their research, Pluto's early history was marked by a cataclysmic event that created Sputnik Planitia: a collision with a planetary body about 700 km in diameter. The team's findings, recently published in the journal Nature Astronomy, indicate that Pluto's internal structure is different than previously thought, indicating that there is no ocean beneath the surface.

The heart, also known as Tombaugh Regio, attracted public attention immediately after its discovery. But it immediately caught the interest of scientists because it is covered in high-albedo material that reflects more light than its surroundings, giving it its white color.

However, the heart is not made of one element. Sputnik Planitia (the western region) has an area between 1,200 and 2,000 kilometers, which is about a quarter of Europe or the United States. Surprisingly, however, this area is three to four kilometers smaller than most of Pluto's surface.

“The bright appearance of Sputnik Planicia is that it is mainly filled with white nitrogen ice, which is constantly moving and warming to soften the surface. This nitrogen may have accumulated soon after the low-altitude impact,” Dr. Harry Ballantine of the University of Bern, lead author of the study, explains in a statement.

The eastern part of the heart is covered by a similar, but much thinner, layer of nitrogen ice, the origin of which is still unclear to scientists, but may be related to Sputnik's plania.

“The elongated shape of Sputnik Planitia clearly suggests that the impact was not a direct impact but an oblique one,” says Dr. Martin Jutzi from the University of Bern, who initiated the study.

So the team, like many others around the world, used its soft particle hydrodynamics (SPH) simulation software to digitally recreate such impacts, varying both the composition of Pluto and its impact, as well as the speed and angle of impact. These simulations confirmed scientists' suspicions about the angle of inclination of the impact and determined the composition of the impact.

“Because Pluto's core is so cold, the rocks were very hard and didn't melt despite the heat of the impact, and because of the impact angle and low speed, the core of the impact didn't sink into Pluto's core, but it stayed put. Like a touch,” Ballantine explains.

“Somewhere beneath Sputnik is the remnant of another massive body that Pluto hasn't completely digested,” says co-author Eric Asbach of the University of Arizona. This central force and relatively low velocity were key to the success of these simulations: a low force would result in a more symmetrical residual surface feature that does not resemble the teardrop shape observed by New Horizons.

“We're used to thinking of interplanetary collisions as incredibly extreme events, where details other than things like energy, momentum and density can be neglected. But in the far solar system, the speed is much slower and the solid ice is stronger, so you have to be very precise in your calculations. That's where the fun starts,” he says. Asphaug.

The two teams have a long history of collaboration since 2011, for example exploring the idea of ​​planetary “splats” to explain the characteristics of the far side of the Moon. After our Moon and Pluto, the University of Bern team plans to explore similar scenarios for other outer solar system systems, such as the Pluto-like dwarf planet Haumea.