Researchers have built a detailed interpretation of Charon’s interior to account for the striking surface features, including long canyon-like troughs and indications of past cryovolcanism. The discussion appears in a recent article in Icarus that surveys how a climatic and tectonic history might have shaped this distant moon.
The analysis relies on data gathered by NASA’s New Horizons mission during its 2015 flyby of Pluto. Scientists were surprised to discover signs suggesting cryovolcanic activity on Charon, a body long thought to be geologically extinct. The proposed scenario imagines a long-vanished ocean inside Charon, liquid long enough to influence the crust, which eventually froze. In this model, the liquid consisted of a mixture of water and ammonia, with varying proportions. Ammonia serves as an antifreeze agent, potentially extending the life of a subsurface ocean and altering how it interacts with the surrounding ice shell.
As the subsurface ocean froze, a rising pressure within the interior would push water through cracks in the ice, forcing eruptions that reach the surface and leave a record of cryovolcanic activity. These events, in turn, could drive surface cracking and guide the formation of canyon-like features. Yet current understandings of Charon’s internal evolution suggest the ice crust may have been too thick for the stresses of ocean freezing to produce a complete breakup. The timing of ocean freezing matters as well: Pluto and Charon likely achieved a synchronized, nearly circular orbital configuration early on, limiting tidal heating to the first million years of their history.
One of the study’s key statements notes that if the oceans and surface interactions described are correct, either the ice crust at the eruption moment was far thinner than the widely cited 100 kilometers, or the surface was not in direct contact with the ocean during the eruption. In other words, rethinking the thickness of the crust during the eruptive phase is necessary, or there may be an as yet unknown heat source deep inside Charon. The authors acknowledge the possibility that the canyon-forming activity could have arisen from eruptions of liquid from smaller subsurface openings, rather than a single global event. Overall, the work highlights how future missions and refined modeling could resolve whether the observed canyons are witnesses to an ancient ocean or to a series of localized, episodic vents that left a different imprint on the moon’s surface.