by Florentina Pîslan, PhD student
17.01.2025
Credit image: NASA, APL, SwRI
A recent study published in Nature Geoscience introduces a new theory for how Pluto and its largest moon, Charon, came to be a binary system. Instead of the traditional view that Charon formed from a massive collision, much like Earth’s Moon, researchers propose a gentler, more complex process they call "kiss and capture." This fresh perspective offers new insights into the dynamics of planetary formation in the distant Kuiper Belt.
For decades, scientists have believed that Pluto and Charon were created through a high-energy impact, where a proto-Charon slammed into Pluto, ejecting material that later coalesced into the moon. However, this theory has some major challenges, particularly because Pluto and Charon are icy worlds, not molten planets like early Earth. A high-speed collision would likely have destroyed them or led to significant mixing of their interiors, which doesn’t match what we see today.
To investigate a more plausible scenario, researchers from the University of Arizona ran sophisticated computer simulations that factored in the strength of ice and rock—something previous models often overlooked. Their findings suggest that instead of a violent smash, the two bodies initially stuck together in a "snowman-like" shape. For a brief time, they rotated as a single entity before gently pulling apart due to tidal forces, eventually settling into the stable binary system we see today. This "kiss and capture" model not only explains how Pluto and Charon managed to remain largely intact after their encounter, but it also has important implications for Pluto’s internal structure. As Pluto and Charon inched apart, the process probably produced heat through tidal friction — enough to have kept almost all of an underground ocean from freezing. This is an exciting possibility: Pluto may still have liquid water rezoning beneath its icy surface. If true, it could be a key clue in the search for habitable environments in the far reaches of our solar system.
But the implications don't end there, this study also provides new insights as to how other binary systems in the Kuiper Belt may have formed. Many icy bodies in this distant region exist in pairs, and the "kiss and capture" process might help explain their origins as well. This new view of Pluto and Charon’s past is complex and surprising, illustrating the complex planetary evolution of the Solar System's frozen frontier. And so, rather than a destructive collision, their story may have been one of a cosmic embrace that shaped the worlds we see today.
