Imagine a world where a single day lasts more than six days by our standards. That's the reality today on Charon, the giant moon orbiting Pluto at the edge of our solar system. But billions of years ago, Charon spun much faster — a day lasted just over 14 hours. Scientists have now found solid evidence that this spin has been gradually slowing down, and the proof is written in the moon's wrinkled face.
A team led by researcher Hanzhang Chen studied Charon's surface and discovered patterns in mountain ranges that tell a story of dramatic change. In a region called Oz Terra, located in Charon's northern hemisphere, they found tectonic features stretching more than 124 miles — longer than the distance from Boston to Washington, D.C. These ridges and faults show signs of compression, as if the moon's crust was squeezed together.
The scientists used computer models to understand what happened. Their analysis suggests that when Charon was young, it had a thick outer shell of ice at least 18 to 22 miles deep. As the moon's rotation slowed over time, the changing forces squeezed its equatorial crust, making it about 1 percent shorter. This compression created the ridges we see today, similar to wrinkles forming on an apple as it dries out.
By studying these geological features, Chen's team calculated that Charon originally completed a rotation in roughly 14.3 hours. Today, it takes about 153.3 hours — more than six days — because Charon and Pluto are tidally locked, meaning they always show the same face to each other, just like our Moon does with Earth.
Charon's surface is roughly 4 billion years old, making it an unusually well-preserved record of cosmic history. Unlike more active moons, its surface hasn't been smoothed over by volcanic activity or asteroid impacts, so the evidence of this slowing spin has remained visible.
The findings, published in the journal Nature Communications, give scientists a rare window into how icy moons evolve over billions of years. Understanding Charon's story could help researchers predict what other distant moons in our solar system look like on the inside — and what their futures might hold.