The huge bright heart on Pluto’s surface is probably the result of a collision with a chunk of ice. This is the result of simulations by an international research group. The one in the journal Nature Astronomy published study also calls into questionwhether there really is an ocean beneath the surface of the dwarf planet.
The US space probe flew in July 2015 New Horizons After more than nine years of flight, it passed the dwarf planet at the edge of our solar system and delivered high-resolution images and data of Pluto and its moons to Earth for the first time. The images showed a large, bright heart on the surface of the ice dwarf. That structure was named “Tombaugh Regio” – after the US astronomer Clyde Tombaugh, who discovered Pluto almost 100 years ago.
An international group of astrophysicists led by Harry Ballantyne from the University of Bern has now looked into the mystery surrounding the formation and nature of Pluto’s heart. The team focused on “Sputnik Planitia,” the western, teardrop-shaped part of the structure. This part covers an area of 1,200 by 2,000 kilometers, which is a quarter of the area of Europe, and is three to four kilometers deeper than most of the rest of the celestial body’s surface.
Slow collision with a 700 kilometer chunk
“The bright appearance of Sputnik Planitia is due to the fact that it is predominantly filled with white nitrogen ice,” lead author Ballantyne is quoted as saying in a statement from his university. The ice moves and current transport takes place, so that the surface is constantly smoothed. “This nitrogen most likely accumulated quickly after the impact due to the lower altitude,” Ballantyne said.
Using simulation software, the team recreated how “Sputnik Planitia” could have been created. In this way, the researchers calculated that that part of the heart was probably the result of a collision in which a planetary body with a diameter of around 700 kilometers hit the surface at low speed. The boulder probably consisted mainly of ice with a rock core. “The elongated shape of Sputnik Planitia strongly suggests that it was not a direct frontal impact, but an oblique impact,” explains co-author Martin Jutzi – a thesis that was confirmed by the simulations.
“Pluto’s core is so cold that the rock remained very hard and did not melt despite the heat of the impact,” Ballantyne added. Thanks to the oblique impact angle and the low speed, the core of the impactor did not sink into Pluto’s core, but remained on top of it. “Somewhere beneath Sputnik is the remaining core of another massive body that Pluto never fully digested,” says co-author Erik Asphaug from the US University of Arizona, according to the statement.
As the authors note, their study also sheds new light on the internal structure of the ice dwarf, which lost its status as a planet almost 20 years ago. It is currently assumed that Pluto – similar to other celestial bodies in the outer solar system – has an underground ocean of liquid water. The simulations now suggest that there is only a very shallow subsurface ocean on Pluto or no subsurface ocean at all.