How a freezing ocean cracked the shell of a frozen moon
In short: For years, scientists viewed Pluto's moon Charon as a dead, inert ball of ice. But data from the New Horizons spacecraft revealed a violent geological history. Now, new models suggest the moon's surface is scarred by a massive internal expansion that literally burst through its outer crust.
In 2015, NASA's New Horizons spacecraft provided a shocking first look at the Pluto-Charon system. Instead of the static, inactive bodies researchers expected, they found geologically active features, including a belt of fractures and cryovolcanic flows. This discovery forced scientists to reconsider the moon's history, leading a team led by the Southwest Research Institute (SwRI) to investigate how such activity occurred on a frozen satellite.
The prevailing theory involves a subsurface liquid ocean composed of water and ammonia. According to models authored by Dr. Alyssa Rhoden, this ocean eventually froze. Because water expands as it turns to ice, the freezing process created immense internal pressure and stress. If the moon's outer ice shell was thinner than currently predicted at that point in its history, this expansion could have caused the shell to crack, forming deep, elongated depressions along Charon's midsection.
When these fractures penetrate the entire shell, the pressurized liquid from the subsurface can be pushed upward to erupt onto the surface as cryovolcanism. While ammonia can act as an antifreeze to prolong the life of a liquid ocean, Rhoden's models found that the specific chemical composition didn't significantly alter the results of the fractures. However, current models also suggest that the ice shells may have been too thick to be fully cracked by these stresses, and the specific timing of the freeze remains a critical factor in understanding the moon's evolution.
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Sources
- Summary by Intellect · source: We Finally Found Out Why Pluto's Moon Charon Is Broken
- Also: Cracks on Pluto
- Also: New models explain canyons on Pluto moon
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