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What processes during the formation of Pluto's largest moon, Charon, potentially led to it having cryovolcanism, and even an internal ocean? This is what a presented at the 56th Lunar and Planetary Science Conference () hopes to address as a team of researchers investigated the formation and evolution of Charon to ascertain whether it once possessed an internal ocean during its history and if this could have led to cryovolcanism based on images obtained by NASA's New Horizons probe.

For the study, the researchers used a series of computer models to simulate the early conditions on Charon that could have resulted in creating an internal ocean and potentially cryovolcanism, resulting in the southern hemisphere, known as Vulcan Planitia, being resurfaced from cryovolcanism. It is currently hypothesized that Charon collided with Pluto and one goal of this work was to ascertain if Charon first formed before the collision or after.

While only a portion of Charon's surface was briefly imaged by NASA's New Horizons spacecraft in July 2015, this limited dataset has provided planetary scientists with intriguing insights into its formation and evolution. This includes kilometers-high scarps that run along the moon's equator, with the southern hemisphere being more cratered than the northern hemisphere. In the end, the models estimated that Charon's subsurface ocean likely formed between 370 million and 400 million years ago and fully froze between 2.12 billion years ago and 2.2 billion years ago.

The study notes, "Crucially, in no simulation across any parameter studied so far did the ocean fully freeze in a timeframe consistent with massive cryovolcanic eruptions before 4 Gyr ago. These results strongly suggest that if ocean freezing is the cause of the resurfacing of Vulcan Planitia at 4 Gyr ago, the details of the impact matter."

Discovered in 1978, Charon is one of the most intriguing moons in the solar system due to being approximately half the diameter of Pluto, which is the largest known satellite relative to its parent body it's orbiting. For context, Earth's moon is approximately one-quarter the diameter of Earth. Several hypotheses regarding Charon's formation and evolution have been proposed, with the most recent being both Pluto and Charon collided billions of years ago, were stuck together, and eventually came apart and formed the two planetary bodies we see today.

Given the enormous distance from Earth at just under 3.2 billion miles, traveling to the Pluto system takes many years, with NASA's New Horizons taking more than 9.5 years to reach Pluto and Charon for its brief flyby in July 2015. This brief flyby provided scientists with enough data about Pluto and Charon that continues to be pored over today, with scientists continuing to learn more about this intriguing system and how both planetary bodies formed and evolved.

Both planetary bodies are part of the Kuiper Belt, which is a donut-shaped region of icy, rocky objects beyond the orbit of Neptune. While Pluto is the most well-known dwarf planet in the Kuiper Belt, other dwarf planets include Haumea, Makemake, and Eris.

While no follow-up missions to Pluto are currently being planned, are in development, ranging from an orbiter to a lander on Charon's surface. If a subsurface ocean on Charon is confirmed, even a frozen one, this could challenge our understanding of how planetary bodies form and evolve, especially so far from the sun.