Pluto’s largest moon, Charon, underwent a dramatic slow-down in its early rotation rate that left distinct tectonic scars across its northern highlands, according to a University of California, Los Angeles study published in Nature Communications. Researchers used computer models to simulate the outer solar system moon’s early history, concluding that the icy body once spun more than ten times faster than it does today before despinning.
Decoding Charon’s Tectonic History With Computer Models
NASA’s New Horizons spacecraft remains the only probe to visit the Pluto system, completing a historic flyby in July 2015. During that brief encounter, the spacecraft captured troves of data that scientists continue to analyze. According to the UCLA research team, Charon serves as a vital “testbed” for understanding how other outer solar system icy moons formed and evolved.
Unlike other planetary objects in the outer solar system that have been heavily battered by impact craters or internal heating, Charon’s surface has remained relatively undisturbed. Planetary scientists have hypothesized since the 1970s that unique fault patterns around Charon’s equator stemmed from despinning—a process where an object’s initial fast rotation slows down significantly over time.
Did You Know? Charon is the largest moon relative to its parent body in our entire solar system. It measures half of Pluto’s diameter and boasts one-eighth of Pluto’s mass.
Oz Terra and the Evidence for Early Despinning
To test the despinning hypothesis, researchers deployed a series of computer simulations focused on Oz Terra. Located in Charon’s northern hemisphere, Oz Terra features mountainous and fractured terrain that stands in sharp contrast to the much smoother southern hemisphere region known as Vulcan Planitia.
The simulations revealed that Charon initially possessed an ice shell thickness measuring approximately 30 to 36 kilometers (18 to 22 miles). According to the study, the moon’s early rotation period lasted about 14.3 hours. For comparison, Charon’s current rotation period spans roughly 6.4 days, or 153.3 hours.
This means the moon’s early spin rate was more than ten times faster than its present-day pace. Furthermore, the computer models indicated this despinning phase occurred prior to any cryovolcanism on the moon, pointing to a very early timeline for the tectonic shifts.
Pro Tip: When studying planetary structural geology, researchers frequently adapt techniques originally developed for terrestrial settings to quantify stress and strain on icy bodies.
Implications for Other Icy Moons in the Solar System
Christy discovered Charon on June 22, 1978, at the United States Naval Observatory. The International Astronomical Union announced the discovery just weeks later. Decades later, the data returned by New Horizons and interpreted by modern modeling tools continue to expand our understanding of planetary mechanics.
According to the study’s authors, the work “presents an approach for quantifying despinning-induced strain and stress on planetary bodies by adapting structural geology techniques developed for terrestrial settings.” The researchers added that the “distribution of tectonic provinces on Charon suggests that despinning was accompanied by global contraction, supporting a cold start for Charon.”
By establishing how tectonic patterns formed in Charon’s northern highlands, planetary scientists gain a foundational framework that could eventually unlock the evolutionary histories of icy moons orbiting Jupiter, Saturn, Uranus, and Neptune.
Frequently Asked Questions
When was Charon discovered?
Christy discovered Charon on June 22, 1978, at the United States Naval Observatory.
Which spacecraft visited Charon?
NASA’s New Horizons spacecraft is the only probe to visit Charon, completing a historic flyby in July 2015.
How fast did Charon rotate in its early history?
According to UCLA computer simulations, Charon’s early rotation period was about 14.3 hours, which is more than ten times faster than its current 6.4-day rotation period.
Why is Charon considered a testbed for other moons?
Charon’s surface has remained relatively undisturbed compared to other outer solar system moons, making it an ideal model for studying ice shell mechanics and tectonic evolution.