A team from the University of Arizona has made a startling new discovery about the formation of Pluto and its moon. Published in Nature Geoscience, the study presents a bold explanation for how these two bodies became locked in their unique binary system. Instead of the traditional theories of violent collisions or merging, this new research suggests a “kiss and capture” process.
Pluto and Charon: the Solar System’s Oddest Couple
Pluto and Charon’s relationship has long puzzled scientists. Unlike typical planet-moon systems, Pluto and Charon revolve around a shared point in space, orbiting each other in a delicate, endless dance. This rare formation is what makes them the largest binary system in the trans-Neptunian region of the solar system. The discovery that their unique orbital characteristics may have been the result of a “kiss and capture” event could provide new insight into the dynamics of planetary bodies far from the Sun.
For decades, the leading hypothesis about how Pluto and Charon became a binary system involved an intense collision, similar to the collision believed to have formed Earth’s moon. In that scenario, a violent impact liquefied both Pluto and Charon, causing them to merge or scatter debris that eventually formed Charon. However, this model was based on the assumption that these bodies were similar to Earth’s composition, which is far from the case.
The “Kiss and Capture” Process: A New Theory
The new theory, supported by simulations and advanced computational models, suggests that Pluto and Charon didn’t undergo a violent crash, but instead, their orbits brought them close enough to each other to “graze” and temporarily stick together. This interaction, which researchers have dubbed a “kiss and capture,” led to a gentle locking of their orbits, preserving much of their original composition.
Unlike larger, more massive planets, Pluto and Charon are composed mainly of rock and ice, and this unique mixture allowed them to withstand the low-energy collision that ultimately resulted in their binary status.
How Simulations Changed Everything
The breakthrough came from applying high-performance simulations that took into account the material strength of icy bodies. These simulations showed that when Pluto and proto-Charon collided at a grazing angle of approximately 50–70 degrees, their relative speed was low enough that the impact caused them to briefly stick together.
Adeene Denton, a NASA postdoctoral fellow and one of the lead authors of the study, explained that they’re “particularly interested in how this initial configuration affects Pluto’s geological evolution. The heat from the impact and subsequent tidal forces likely played a crucial role in shaping the features we see on Pluto today.”
The previous models, which assumed that planetary collisions would result in the bodies merging into a molten mass or ejecting debris into space, overlooked the material strength of icy bodies like Pluto and Charon. The new study presents a more realistic simulation that not only explains their current orbital mechanics but also matches the observed size and orbital characteristics of the two bodies.