Hey everyone. I am a lurker here, and I have posted once, I think; however, I literally stumbled upon a very interesting question posed here: https://www.physicsforums.com/showthread.php?t=174274/ Anyway, I decided to see if I could expand upon and get a more "exact" solution for this problem. The first problem I encountered in my research was the several different types of ices, their density, and how the pressure/temperature is related to it. The point in my work at the moment is one in which I have a fairly good piecewise representation describing the density of the H2O at various pressures and temperatures. Because I am working under the assumption that I want the surface of my planet to be approximately 17 degrees C, I am using only Ice VI, Ice VII, Ice X, and Ice XI (even though Ice XI may be unnecessary - come on, we aren't in the TPa range here). The problems I am encountering in making my model more accurate for the density of H2O are the following: How do pressure, temperature, and density, affect liquid water, explicitly? I have a model that I am currently using that seems to make some sense at lower temperatures (between 0-200 degrees or so), however, after a certain point, because my function describing density is dependent solely on pressure, I am getting ridiculously high densities for water, which would not be the case, because said properties of water are only in under high pressure, and therefore high temperature, water, which we all know would have a lower density than if it only depended on pressure. There seems to be little research on the nature of the more unusual crystalline ice structures: how do their densities change with pressure and temperature? Is the transition between two structures instantaneous or is it more gradual, and if it is gradual, over what range does the transition occur? I will edit when I come up with more progress, if I come up with my progress. My goal is to see what a model of this planet would look like. Would it have an Ice X core, with an Ice VI/Ice VII mantle, followed by a liquid water crust? How thick would the atmosphere have to be? How massive must the planet be in order to stay together, given the varying masses throughout the planet? What would be the temperature of this planet's core? I hope you guys can help me out with this, it is making for an interesting pursuit!