Pluto and its moon Charon may have united through a kiss rather than a collision, according to a study.
The research could give insight into how the dwarf planet is able to support a subsurface ocean.
No one is sure exactly how Pluto and Charon first came together.
Previous theories held that they formed from the debris of a large impact, in a similar way to how our own Moon is believed to have formed.
"Pluto and Charon are different – they’re smaller, colder and made primarily of rock and ice. When we accounted for the strength of these materials, we discovered something completely unexpected," says Adeene Denton from the University of Arizona, who led the study.
"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."
When the giant snowman-like structure eventually broke apart, Charon remained mostly intact.
Pluto, Charon and a liquid ocean?
The idea also explains another of Pluto’s great mysteries.
When the New Horizons mission flew past the diminutive world in 2015, it saw signs of a liquid water ocean.
Geologists have struggled to explain how Pluto’s interior could be warm enough for such a layer.
The tidal forces from the gravitational tug of war during the kiss-and-capture event, however, would have created internal heat that could have melted the dwarf planet’s frozen heart.
This article appeared in the March 2025 issue of BBC Sky at Night Magazine
