Charon’s Rotation Slows Over Billions of Years, Study Finds

A study published in *Nature Communications* by scientists from the United States and Switzerland presents new evidence that Charon, Pluto’s largest moon, has been gradually decelerating its spin over billions of years. Analysis of mountain chains in the Oz Terra region of Charon’s northern hemisphere shows tectonic signatures that record a slowdown from an estimated 14.3‑hour rotation at formation to the current 153.3‑hour period. The researchers attribute the deceleration to tidal forces arising from the gravitational interaction between Charon and Pluto, a process that compresses the surface and has caused a ~1 % equatorial contraction.

The findings suggest that early Charon possessed a thick icy shell (30‑36 km) and may have begun its history in a relatively cold state, developing a rigid crust early on. While uncertainties remain, the geological record captured in the mountain ridges provides a rare physical trace of rotational evolution for a distant icy satellite, offering insights into the thermal and tidal history of other outer‑solar‑system moons.