Space: How Pluto Landed its Moon With a 'Kiss'

Pluto landed its largest moon, Charon, with a 'kiss'—overturning decades of scientific assumptions about how planetary bodies form and evolve.

This is the conclusion of a new study, conducted at the University of Arizona, which has identified an entirely new kind of cosmic collision.

"Most planetary collision scenarios are classified as 'hit and run' or 'graze and merge'," explained NASA planetary scientist Adeene Denton in a statement.

"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."

In their study, Denton and colleagues considered a factor that planetary scientists appear to have overlooked for decades—just how structurally strong smaller, icy worlds like Pluto are.

It was previously thought that Charon formed in the wake of a massive collision billions of years ago, much like how Earth's moon was born after our planet collided with a Mars-sized world dubbed "Theia."

In the wake of this colossal impact, the colliding bodies behaved like fluids, with the moon forming out of the molten debris which had been ejected into space.

"Pluto and Charon are different—they're smaller, colder and made primarily of rock and ice," Denton explained.

"When we accounted for the actual strength of these materials, we discovered something completely unexpected."

Modeling the impact, the team found that—rather than being stretched like silly putty by the collision—Pluto and its proto-moon instead temporarily stuck together.

The pair maintained this "kiss" for a while, spinning together as a single, snowman-shaped body, before parting again to form the binary pair we can see today.

As a result, it is likely that both Pluto and Charon stayed largely intact across the collision, preserving their original compositions—and avoiding the large-scale deformation predicted by previous models of the collision.

"The compelling thing about this study is that the model parameters that work to capture Charon end up putting it in the right orbit," wrote paper author and University of Arizona planetary scientist professor Erik Asphaug.

"You get two things right for the price of one," he added in his statement.

With their initial study complete, the researchers are now keen to investigate how gravitational forces might have played a role in Pluto and Charon's early evolution.

Tidal friction as the pair separated would have heated up both bodies, the team believe, potentially resolving the mystery of how Pluto could have formed a subsurface ocean without having formed in the more radioactive very early solar system.

The team also wants to explore how the 'kiss and capture' hypothesis might have resulted in the geological features seen on Pluto in the present day—and whether these kind of collisions might explain other known binary systems.

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

She added: "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."

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about space? Let us know via science@newsweek.com.

Reference

Denton, C. A., Asphaug, E., Emsenhuber, A., & Melikyan, R. (2025). Capture of an ancient Charon around Pluto. Nature Geoscience. https://doi.org/10.1038/s41561-024-01612-0