A groundbreaking study reveals that Charon, Pluto’s largest moon, may continue to experience a loss of rotational energy even after years of tidal locking, offering scientists a unique insight into the hidden interior of this distant icy body.
This stunning image of Charon was captured on July 14, 2015. Unlike Pluto, Charon’s color palette is less varied, with its most notable feature being the reddish northern polar region, informally called Mordor Macra. Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.
Celestial objects in the solar system undergo a phenomenon known as despinning, where tidal forces gradually reduce rotation speeds while altering their shapes and temperatures.
This process has long been theorized for Charon, but previously lacked clear geological evidence.
Charon is an ideal candidate for such exploration due to its ancient surface, approximately 4 billion years old, with limited resurfacing compared to other icy moons.
“Charon displays a distinct topographical dichotomy, characterized by rugged northern highlands and smooth southern plains,” stated Dr. Hanjiang Chen, a researcher at the University of California, Los Angeles and ETH Zurich.
“Prior studies suggest that Charon underwent global expansion alongside cryovolcanic activity.”
This research examined the alterations in tectonic features within the mountain range named Oz Terra in Charon’s northern hemisphere.
These features span over 200 km and exhibit asymmetric slopes, indicating compression rather than extension.
Modeling indicates that an ice shell measuring at least 30-36 km thick existed during formation, pointing to an approximate 1% shortening of the equatorial crust and the absorption of this compression along pre-existing fault lines, resulting in the observed ridges.
The authors estimate that Charon’s original rotation period was about 14.3 hours, significantly faster than its current tidally locked state of approximately 153.3 hours.
This finding provides compelling evidence that Charon’s rotation has indeed slowed over time.
The study suggests that Charon may have developed under relatively cold conditions, forming a robust ice shell early in its history.
“Our research indicates that Charon’s surface reflects a history of planetary despinning, predating its proposed global expansion and cryovolcanic activity,” the researchers stated.
“The co-evolution of unspinning and global contraction supports the notion of Charon having a cold start, offering insights into the early thermal evolution of icy moons in the outer Solar System.”
The team’s paper was published in the journal Nature Communications on July 14th.
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H. Chen et al. 2026. Early tidal despin history recorded in Charon, Oz Terra’s tectonics. Nat Commune 17, 5978; doi: 10.1038/s41467-026-75069-7
Source: www.sci.news
