This could have a significant impact on the stress experienced by the icy shells of these moons. Water is much more dense than ice. Therefore, as the Moon’s ocean freezes, its interior will expand, creating outward forces that will push against the gravity that holds the Moon together. The potential for this transition to shape the surface geology of several moons, including Europa and Enceladus, has already been explored. So, the researchers behind the new work decided to look at the opposite issue: What happens when the interior starts to melt?
Instead of focusing on a specific moon, the team created a general model of an ice-covered ocean. This model treated the snowball as an elastic surface, meaning it wouldn’t just break, and placed sticky ice beneath it. Further down, there was a liquid ocean and eventually a rocky core. As the ice melted and the ocean expanded, researchers tracked the stress on the ice sheets and the changes in pressure at the ice-ocean interface. They also tracked the propagation of thermal energy through the ice shell.
pressure drop
Obviously, there are limits to how much the outer shell can bend to accommodate the shrinking of the moon’s molten interior. This creates a low pressure area beneath the shell. Its results depend on the size of the moon. For larger moons – and this includes most of the moons observed by the team, including Europa – there were two options. For some, gravity is strong enough to maintain pressure to the point where water remains liquid at the interface. In others, gravity was enough to fail even an elastic surface, causing the surface to collapse.
However, for smaller moons, this does not work; The pressure becomes so low that water begins to boil even at ambient temperature (just above the freezing point of water). Additionally, the low pressure will likely release any gases dissolved in the water. The result is that gas bubbles should form at the ice-water interface. “Boiling is possible on these bodies – and not on others – because they are small and have relatively low gravitational acceleration,” the researchers concluded. “As a result, less ocean pressure is required to balance [crustal] Pressure.”
<a href