New research indicates that Pluto’s largest moon, Charon, may continue to lose rotational energy despite the pair’s long-standing tidal lock, offering scientists a rare glimpse into the hidden interiors of distant icy worlds.
This impressive view of Charon was captured on July 14, 2015. Charon’s color palette is not as diverse as Pluto’s; most striking is the reddish north (top) polar region, informally named Mordor Macula. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
Objects across the Solar System are thought to undergo a process called despinning, where tidal forces may slow a body’s rotation rate, altering its shape and temperature.
Although the mechanism has long been theorized to occur on Pluto’s moon Charon, there has been a lack of clear geological evidence.
Charon is a promising candidate for such evidence because its surface is around 4 billion years old and has experienced relatively limited resurfacing compared with other icy satellites.
“Charon exhibits a topographic dichotomy of rugged northern highlands and smoother southern plains,” said Dr. Hanzhang Chen, a researcher at the University of California, Los Angeles and ETH Zurich.
“Previous studies proposed that Charon has undergone global extension accompanied by cryovolcanism.”
In the study, Dr. Chen and colleagues examined variations in the orientations and types of tectonic features of mountain ranges in a region called Oz Terra, in Charon’s northern hemisphere.
These features extend over 200 km and display asymmetric slopes consistent with compression, rather than extension.
Modeling indicates the presence of an ice shell at least 30-36 km thick at the time of formation and suggests that the crust near the equator became approximately 1% shorter during this time, with this compression being absorbed along existing faultlines and creating the observed ridges.
This modeling leads the authors to estimate that Charon’s early rotation period was approximately 14.3 hours, notably faster than its present tidally locked state of around 153.3 hours.
This provides evidence to support a gradual slowing, or despinning, of its rotation.
The findings suggest that Charon may have begun its evolution in a relatively cold state, forming a thick, rigid ice shell early on.
“Our work suggests that Charon’s surface presents an example that records the planetary despinning history, which predates the proposed global extension and cryovolcanism on Charon,” the scientists said.
“The coevolution of despinning and global contraction favors a cold start for Charon, offering insights into the early thermal evolution of icy satellites in the outer Solar System.”
The team’s paper was published July 14 in the journal Nature Communications.
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H. Chen et al. 2026. Early tidal despinning history recorded in the tectonics of Oz Terra, Charon. Nat Commun 17, 5978; doi: 10.1038/s41467-026-75069-7
