'Kiss And Capture': Study Explains How Pluto's Largest Moon Was Formed

The relationship between Pluto and Charon might have begun with a cosmic "kiss." According to new research, billions of years ago, Pluto may have captured its largest moon, Charon, through a brief icy encounter. This theory sheds light on how the dwarf planet managed to acquire a moon nearly half its size.

A study led by Adeene Denton, a NASA postdoctoral fellow who conducted the research at the U of A Lunar and Planetary Laboratory, has revealed this unexpected "kiss and capture" mechanism, which could help scientists better understand how planetary bodies form and evolve. By considering something planetary scientists had overlooked over decades-the structural strength of cold, icy worlds-researchers have discovered an entirely new type of cosmic collision.

The findings were published in the journal Nature Geoscience.

As per a release, for decades, scientists have theorised that Pluto's unusually large moon Charon formed through a process similar to Earth's moon-a massive collision followed by the stretching and deformation of fluid-like bodies, Denton said. This model worked well for the Earth-moon system, where the intense heat and larger masses involved meant the colliding bodies behaved more like fluids. However, when applied to the smaller, colder Pluto-Charon system, this approach overlooked a crucial factor: the structural integrity of rock and ice.

"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," Denton said.

"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," said Denton.

"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," said senior study author Erik Asphaug, a professor in the Lunar and Planetary Laboratory.