Scientists have discovered that the distinct heart-shaped feature of Pluto could have formed due to a massive ancient collision.
Pluto's Heart-Shaped Feature
This massive region on the dwarf planet's surface is known as Tombaugh Regio. It serves as Pluto's largest bright surface feature. It spans roughly 1,000 miles and was named after Clyde Tombaugh, an astronomer who discovered Pluto in 1930.
The heart's western lobe is known as the Sputnik Planitia, which has an altitude several miles lower than its surroundings. The Sputnik Planitia is also covered in carbon monoxide, methane, ice, and nitrogen. The ice reflects sunlight, giving Earth observers a bright appearance.
The Tombaugh Regio was first seen in-depth during a 2015 flyby in New Horizons. The area has mystified astronomers for years due to its odd geological composition and shape.
Now, scientists from the University of Bern, the NCCR (National Center for Competence in Research) PlanetS, and the University of Arizona claim to have solved the long-standing mystery. They think the region was formed due to a massive object hitting the dwarf planet at an odd angle. They noted this in the "Sputnik Planitia as an impactor remnant indicative of an ancient rocky mascon in an oceanless Pluto" study.
An Ancient Collision Could Hold the Answers
The Sputnik Planitia's bright appearance is due to its predominant filling of white nitrogen ice that constantly convects and moves to smooth the surface. It is likely that the nitrogen quickly accumulated after the impact due to lower altitude. This was noted by Harry Ballantyne, the study's lead author and a researcher from the University of Bern.
The new paper notes that the Sputnik Planitia could have been created after a substantial cosmic object roughly 435 miles across. Martin Jutzi, a co-author of the study and a researcher from the University of Bern, says that the Sputnik Planitia's elongated shape suggests that the impact was oblique rather than head-on.
As part of the study, the researchers used the SPH (Smoothed Particle Hydrodynamics) simulation software to simulate collisions with the dwarf planet digitally. They accounted for variables like the compositions of the impacting body and Pluto.
Such simulations validated the scientists' theory regarding the slanted angle of impact and helped them identify the impacting object's likely composition.
Ballantyne explains that Pluto's core is icy, and the rocks stayed hard and did not melt despite the impact's heat. Moreover, thanks to the low velocity and impact angle, the impactor's core did not sink into the dwarf planet's core. Instead, it stayed as an intact splat.
The impact's odd angle and slow speed may have also caused the region's strange heart shape. A more direct and faster impact would have made the crater symmetrical.
Erik Asphaug, a study co-author and researcher from the University of Arizona, explains that they are used to thinking that collisions among planets are gravely intense events. However, velocities are lower in the far Solar System, and ice is solid. Hence, it is necessary to be more precise with calculations.
The findings reveal that the dwarf planet's internal composition differs from what was expected. They also suggest that a subsurface ocean is not present, as Pluto has long been theorized to contain a liquid water ocean under its surface. The new theory suggests that the Sputnik Planitia was an impact site and did not need a subsurface ocean.
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