In new research, scientists have modeled an impact in space that could explain half of Pluto’s iconic heart-shaped Tombaugh Regio. Sputnik Planitia’s basin is shaped like an inverted pear, which researchers say could be caused by an impact with a celestial object up to 400 miles in diameter. According to their proposed model, an “impactor” composed of ice and rock hits Pluto’s icy surface, passes through it, and creates a “splash” (technical term!) that lasts to this day.
Pluto may no longer be one of the official planets in our solar system, but the same eccentricities (literal and otherwise) that ruled it out make it interesting to researchers. Yes, Pluto is a long way from the Sun, with a maximum surface temperature of -360 degrees Fahrenheit, but its peculiar orbit also puts it closer to the Sun than to Neptune. This long cycle also creates and then destroys Pluto’s very thin atmosphere, which forms during the warm (less cold) orbital season and literally freezes out of the air during the cold orbital season.
All of this means that Pluto is cold enough on its surface that an ice disturbance there could simply linger. If ice can never melt, then ice is the new ground. It would be like a crater in the Earth’s crust, which may develop plant life over decades, but which remains visible as a large impact zone in the underlying soil. But Pluto has other craters that have been sanded and filled in for a long time, indicating that tectonic activity may be working behind the scenes to change things. The iconic heart-shaped spot is different, because it shows no signs of being filled in.
Scientists from the University of Arizona and the University of Bern (Switzerland) were encouraged to carry out an impact model to try to find out what really caused the Sputnik Plain. Their peer-reviewed research now appears in Nature Astronomy. Combining existing knowledge in Earth sciences and geology, as well as 2015 discoveries about Pluto’s complex geology, they modeled all the factors using SPHLATCH, an open source code that steps through space impacts like this one.
Full 3D models (4D if you count time) allow scientists to adjust each variable, one by one, to see what happens. The scientists tested impact angles from 0 to 45 degrees, for example, to see which best created the pear shape. If something were to collide at a 90 degree perpendicular angle, the impact would probably just be a circle. Instead, the type of shape suggests that something struck at an angle and created a narrow “drag” that forms the stem end of the pear.
The 2015 exploration of Pluto by the New Horizons probe made this model possible, because previously we knew very little about Pluto’s geology. With more information, this team was able to model Pluto’s composition more accurately. They believe that if an icy impactor were to hit Pluto’s also icy surface, it would initially fall on top, like a splashed snowball. But over time, the rocky part would sink into the mantle.
“It would then extend to form a hidden and deeply buried rock mass at the boundary between the core and the mantle,” they conclude.
Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She’s also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, mathematics of everyday things, and the philosophy of it all.
