The influence of ice dynamics on the habitability of ocean worlds

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2023-12

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Abstract

The habitability of Earth and other ocean worlds in our Solar System is partly dependent on the flow of ice masses on their surfaces. Climate-induced acceleration of glaciers and ice sheets on Earth causes sea-level rise, posing threats to the habitability of coastal areas. However, glacier acceleration shows significant variability, and the physical connection between climate warming and glacier dynamic change remains illusive. In our Solar System, internal oceans are enveloped by outer ice shells. The dynamics of these ice shells regulate the material transport into oceans and control the amount of heat that escapes the oceans. Importantly, the longevity of internal oceans is regulated by the thermodynamics of the outer ice shell, which may be conductive or partially convective depending on the ice shell’s properties. Uncertainties in our understanding of ice dynamics contribute to uncertainties in projected sea-level rise, the potential presence of oceans in icy worlds, and the modes of habitability-promoting material transport into those oceans. To physically model the dynamics of ice, I develop a flexible numerical framework based on the Stokes Equations to predict the dynamics of glaciers and ice shells. I apply this framework to analyze the stresses and strains in three neighboring glaciers in Greenland. Despite experiencing similar climate forcings, one glacier continuously retreated, another retreated and then stopped, while the third never retreated. I find that terminus retreat is triggered by a warming ocean, leading to large-scale changes in glacier dynamics. Glaciers with slippery beds exhibit a sustained dynamic response, resulting in continued acceleration even during a pause in ocean warming. As glaciers with slippery beds are prevalent in Greenland, glacier dynamic mass loss will likely be maintained into the future. Turning to other ocean worlds, the outer ice shells of Titan and Pluto are thick and prone to convection. Non-water-ice materials, such as methane and oxygen, are common on the surface of ice shells. Methane is produced during core degassing and forms methane clathrates within the interior of ocean worlds. I find that methane clathrates are entrained into the ice shell by convection. This entrainment slows down convection, limiting the amount of heat leaving the ocean, thus extending the longevity of internal oceans. Additionally, clathrate entrainment thickens the static conductive portion of the ice shell, constraining modes of material transport through the ice shell into oceans. This static near-surface portion of the ice shell occurs on all icy ocean worlds and presents a formidable barrier to the transport of oxygen from the surface into internal oceans. I investigate a novel process on Europa that circumvents this barrier. I model the dynamic evolution of melt chambers formed during non-breaching impacts into the ice shell. I find that impacts that penetrate halfway through the static portion of the ice shell create a melt pocket that sinks to the ocean below. Sinking melt chambers transport any materials entrained from the surface into the ocean. The foundering of impact melt chambers occurs for all ice shell thicknesses explored, suggesting that this process is active on other ocean worlds as well. This transport process provides a frequent means to oxygenate the oceans in our Solar System.

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