A new study has revealed that Pluto and its largest moon Charon formed through an unexpected cosmic dance, challenging decades of scientific assumptions about their origins. University of Arizona researchers discovered that rather than violently merging in a catastrophic collision, the two bodies briefly joined together before separating into their current orbital relationship.
“Pluto and Charon are different – they’re smaller, colder and made primarily of rock and ice. When we accounted for the actual strength of these materials, we discovered something completely unexpected,” says Adeene Denton, NASA postdoctoral fellow at the University of Arizona’s Lunar and Planetary Laboratory and lead author of the study published in Nature Geoscience.
Using advanced computer simulations, the research team found that the two icy bodies temporarily stuck together like a cosmic snowman, rotating as one before separating while remaining gravitationally bound. This newly identified “kiss and capture” mechanism differs markedly from previous theories that suggested a more violent collision similar to the one that formed Earth’s moon.
“Most planetary collision scenarios are classified as ‘hit and run’ or ‘graze and merge.’ What we’ve discovered is something entirely different – a ‘kiss and capture’ scenario where the bodies collide, stick together briefly and then separate while remaining gravitationally bound,” Denton explains.
“The compelling thing about this study is that the model parameters that work to capture Charon end up putting it in the right orbit. You get two things right for the price of one,” adds Erik Asphaug, professor in the Lunar and Planetary Laboratory and senior study author.
The findings suggest that both Pluto and Charon retained much of their original composition during the encounter. This challenges previous models that proposed extensive mixing and deformation during impact. The collision process also generated significant internal heat, potentially explaining how Pluto could have developed a subsurface ocean without requiring formation in the very early solar system.
“We’re particularly interested in understanding how this initial configuration affects Pluto’s geological evolution,” notes Denton. “The heat from the impact and subsequent tidal forces could have played a crucial role in shaping the features we see on Pluto’s surface today.”
The research may also help explain the formation of other binary systems in the outer solar system, where similar pairs of icy worlds orbit each other. The team plans to investigate how tidal forces influenced the early evolution of these bodies when they were much closer together, and examine whether similar processes could explain the formation of other binary systems.