Unveiling the Mystery of Pluto’s Giant Heart-Shaped Feature

2024-04-17 02:15:45

An artistic representation of the massive, slow impact on Pluto that led to the heart-shaped structure on its surface. Credit: University of Bern, Thibaut Roger, editor

The mystery of how Pluto has a giant heart-shaped feature on its surface has finally been solved by an international team of astrophysicists led by the University of Bern and members of the National Center for Competence in Research (NCCR) PlanetS. The team is the first to reproduce the unusual shape using numerical simulations, and attributes it to a giant, slow impact at an oblique angle.

Since the cameras of NASA’s New Horizons mission discovered a large heart-shaped structure on the surface of the dwarf planet Pluto in 2015, this “heart” has puzzled scientists because of its unique shape, geological composition and height. Scientists from the University of Bern in Switzerland and the University of Arizona used numerical simulations to investigate its origins. of Sputnik Planetia, the teardrop-shaped western part of Pluto’s heart surface feature.

According to their research, Pluto’s early history was marked by a cataclysmic event that created Sputnik Planetia: a collision with a planetary body just over 400 miles in diameter, about the size of Arizona from north to south. The team’s findings, published in Astronomy of natureIt is also suggested that Pluto’s internal structure is different from what was previously assumed, indicating that there is no subsurface ocean.

“The formation of Sputnik Planitia provides a critical window into the earliest periods of Pluto’s history,” said Edin Denton, a planetary scientist at the UArizona Lunar and Stellar Laboratory who co-authored the paper. “By expanding our investigation to include more unusual formation scenarios, we have learned some entirely new possibilities for Pluto’s evolution, which could potentially apply to other Kuiper Belt objects as well.”

A view of Pluto taken by NASA’s New Horizons spacecraft on July 14, 2015. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

split heart

The “Heart”, also known as Tombaugh Regio, caught the public’s attention immediately upon its discovery. But it also immediately caught the interest of scientists because it is covered in high-albedo material that reflects more light from its surroundings, creating its whiter color. However, the heart is not made up of one element. Sputnik Planitia covers an area of ​​about 750 by 1,250 miles, equivalent to a quarter of Europe or the United States. What’s amazing, though, is that this region is about 2.5 miles lower than most of Pluto’s surface.

“While the vast majority of Pluto’s surface consists of methane ice and its derivatives covering a water-ice membrane, the planetia is mostly filled with nitrogen ice, which likely accumulated quickly after the impact due to the lower altitude,” said the lead author. From the study, Harry Ballantyne, research fellow at Bern. The eastern part of the heart is also covered with a similar but much thinner layer of nitrogen ice, the origin of which is still unclear to scientists, but probably related to Sputnik Planetia.

Diagonal effect

Sputnik Planetia’s elongated shape and its equatorial position strongly suggest that the impact was not a direct head-on collision but an oblique collision, according to Martin Joczi of the University of Bern, who initiated the study. Like several others around the world, the team used smooth hydrodynamic particle simulation software to digitally recreate such impacts, changing both the composition of Pluto and its impactor, as well as the speed and angle of the impactor. These simulations confirmed the scientists’ suspicions about the diagonal impact angle and determined the impacting vehicle.

“Pluto’s core was so cold that the rocks remained very hard and did not melt despite the heat of the impact, and thanks to the impact angle and the low speed, the impact core did not sink into Pluto’s core, but remained intact. Like a splash on it,” Ballantine said. This core strength and relatively low speed were key to the success of these simulations: a lower strength would result in a highly symmetric residual surface feature that does not look like the teardrop shape observed by NASA’s New Horizons probe during its flyby of Pluto in 2015.

“We’re used to thinking of planetary collisions as incredibly intense events where you can ignore the details other than things like energy, momentum and density,” said Lunar and Planetary Laboratory professor and study author Eric Espaug, whose team, collaborating with Swiss colleagues since 2011, have explored the idea of ​​planetary “spots” To explain, for example, features on the far side of the Earth’s moon. “In the far solar system, the velocities are much slower than closer to the sun, and the solid ice is strong, so you have to be much more precise in your calculations. That’s where the fun begins.”

There is no underground ocean on Pluto

The current study also sheds new light on the internal structure of Pluto. In fact, an impact as huge as this imaged occurred much earlier in Pluto’s history than in recent times. However, this poses a problem: a giant crater like Sputnik Planetia is expected to drift slowly towards the pole of the dwarf planet over time due to the laws of physics, since it is less massive than its surroundings. However, it remains near the equator. The previous theoretical explanation suggested a subsurface liquid water ocean, similar to several other planetary bodies in the outer solar system. According to this hypothesis, Pluto’s ice sheet would be thinner in the region of Sputnik Planitia, causing the ocean to protrude upwards, and because liquid water is denser than ice, causing an excess of mass that causes it to migrate towards the equator.

The new study offers an alternative perspective, according to the authors, pointing to simulations in which Pluto’s entire primordial mantle was gouged by the impact, and when the impactor’s core material melted onto Pluto’s core, it created a local mass excess that could explain the equatorward migration without an ocean. underground, or at most very thin.

Denton, who has already started a research project to estimate the speed of this migration, said this innovative and creative hypothesis for the origin of Pluto’s heart-shaped feature could lead to a better understanding of the origin of the dwarf planet.