Tucson Standard

Billions of years ago, in the distant regions of our solar system, two icy celestial bodies collided. Instead of a destructive impact, they spun together like a snowman and eventually separated while remaining in orbit. This is how Pluto and its largest moon, Charon, formed according to new research from the University of Arizona.

The study was led by Adeene Denton, a NASA postdoctoral fellow at the University of Arizona's Lunar and Planetary Laboratory. It introduces a "kiss and capture" mechanism that may provide insights into planetary formation. By considering the structural strength of cold, icy worlds, researchers discovered a new type of cosmic collision.

Published in Nature Geoscience, the study challenges previous theories that likened Charon's formation to Earth's moon through massive collisions and deformation. This model overlooked the structural integrity of smaller, colder bodies like Pluto and Charon.

"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.

Advanced simulations showed that instead of deforming during collision, Pluto and proto-Charon temporarily stuck together before separating into the binary system observed today. Binary systems involve two celestial bodies orbiting a common center of mass.

"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," added Erik Asphaug, senior author and professor at the Lunar and Planetary Laboratory.

The study suggests both Pluto and Charon remained largely intact during their collision with much original composition preserved. This contradicts previous models suggesting extensive deformation. The process also deposited internal heat which might explain Pluto's subsurface ocean without early solar system conditions troubling scientists.

Future studies will explore tidal forces on early evolution when Pluto and Charon were closer together, analyze geological features alignment with this scenario, and examine if similar processes explain other binary systems.

"We're particularly interested in understanding how this initial configuration affects Pluto's geological evolution," Denton said. "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."