In recent years, “water worlds” have become increasingly of interest to astrobiologists due to their high potential for habitability, as the large amount water on their surfaces is not only necessary for life, but also promises long-term climatic stability. However, also necessary for life is the exchange of chemical compounds between the geosphere and the hydrosphere - something which may be ob- structed by the presence of high pressure ices on these ocean planets and icy moons. In order to explore the habitability of bodies with various surface temperatures, water masses, and core radii, this project develops a model of the structure of the hydrosphere on such planets, examining the effects of planetary cooling on the structure of the hydrosphere, and identifying the conditions which are most favorable to producing a liquid ocean in contact with the rocky mantle. It was found that the thickness and complexity of high pressure ice layers increases as a planet cools, and the liquid ocean shrinks. Additionally, high pressures at the mantle-hydrosphere boundary make it unlikely for a liquid ocean to be in contact with the rocky core on most planets, save those with smaller core radii, lower water masses, and warm surface temperatures. It was also determined that, although this model provides proof of concept for a structural model of planetary hydrospheres, the results may only be interpreted as a cold estimate of planetary structure due to the fact that an internal heat source was not included in the model.

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