Ice V (pronounced "ice five") is a monoclinic crystalline phase of water, formed by cooling water to 253 K at 500 MPa. It has a complicated structure, including 4-membered, 5-membered, 6-membered, and 8-membered rings and a total of 28 molecules in the unit cell. Ganymede's interior probably includes a liquid water ocean with tens to hundreds of kilometers of Ice V at its base.
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Ice V Wikipedia(Text) CC BY-SA