Pluto may have captured its moon Charon with a brief kiss

Simulations suggest Pluto and its largest moon may have gently stuck together for a few hours before Charon settled into a stable orbit around the dwarf planet

By Alex Wilkins

6 January 2025

Pluto (right) and its moon Charon, photographed by NASA’s New Horizons probe in 2015

NASA/JHUAPL/SwRI

Pluto and its moon Charon may have been briefly locked together in a cosmic “kiss”, before the dwarf planet released the smaller body and recaptured it in its orbit.

Charon is the largest of Pluto’s five moons, with a radius more than half that of Pluto itself, but the question of how it came to orbit Pluto has puzzled astronomers.

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One prominent theory suggests that Charon formed after a vast object smashed into Pluto, spewing debris into space that later formed Charon, similar to how scientists think Earth’s moon formed. But Charon’s large size and close orbit, at eight times wider than Pluto itself, make this a challenging scenario to explain.

Now, Adeene Denton at the University of Arizona and her colleagues have proposed that Charon may have a less destructive origin story, which they describe as a “kiss and capture”.

Previous simulations have treated Pluto and Charon as fluids – an assumption that works when modelling collisions between larger bodies. But recent research has shown that with objects of lighter mass than Earth’s moon, the material strength of their composition influences the outcome. “Pluto and Charon are quite small, so the assumption that they are fluid bodies probably no longer applies,” says Denton.