Scientists have modeled the depths of Charon to explain the appearance of canyons and cryovolcanoes on it. An article about this was published in Icarus.
The model is based on data obtained by the New Horizons spacecraft during its flyby of Pluto in 2015. Scientists were surprised that Charon had traces of cryovolcanic activity, although it was believed that this body was geologically “dead”. According to the hypothesis that the authors of the work decided to test, in ancient times there was an ocean inside Charon, which froze over time. This was incorporated into the model – the liquid consisted of a mixture of water and ammonia in various configurations. Ammonia can act as an antifreeze and prolong the life of the liquid ocean.
As the ocean freezes and a layer of new ice builds up inside its ice crust, the pressure inside the ocean rises. Because of this, water enters the cracks and splashes out on the surface under pressure, creating a cryovolcano – an analogue of an earthly volcano – and forming a canyon. However, based on current models of Charon’s internal evolution, the ice shells were too thick to completely break apart under the stresses associated with freezing oceans. The timing of the freezing of the ocean is also important. The synchronous and circular orbits of Pluto and Charon stabilized relatively early, so tidal heating only occurred during the first million years of their existence.
“Either Charon’s ice shell was less than 10 km thick at the time of the flow eruption, as opposed to the 100 km accepted in science, or the surface was not in direct communication with the ocean during the eruption,” the scientists explain.
In other words, if we accept as true the hypothesis being tested by the authors about the connection of canyons and volcanism with the ocean, then either the thickness of the ice crust at the time of the eruptions was much thinner than it was thought, or there was some unknown source of heat in the bowels of Charon. Most likely, according to the authors, the hypothesis about the connection of canyons with the ocean is false, and they were formed during eruptions of liquid from smaller cavities.