In a geological scenario reminiscent of Dante's underworld, where subterranean rivers freeze together, a new study co-authored at UC Davis suggests that water could become trapped deep inside aging planets as a form of ice. Such buried ice could have powerful effects on planet-molding phenomena such as volcanism and plate tectonics. Published in the Dec. 14 issue of the journal Nature, the paper was written by Alexandra Navrotsky, interdisciplinary professor of ceramic, earth and environmental materials chemistry at UC Davis, and Craig Bina, professor of geosciences at Northwestern University. It appears at a time when there is widespread interest in the physical evolution of planets and the possibility of life on planets other than Earth, particularly Mars. Water is often considered a prerequisite for the evolution of life. On Earth, we know that water constantly cycles from the planet's surface to its interior via the process of subduction, in which great slabs of the planet's crust, bearing parts of continents and their water-laden sediments, are carried down into the planet. The novel aspect of the new paper is the suggestion that water also could be carried to the deep interior as a high-pressure form of ice, called ice VII. Rather than being returned to the surface by volcanism, such ice could continue to travel downward and be permanently incorporated into minerals at depth. As the amount of water available near the surface would diminish, thermal processes that transform and renew a planet's surface, such as volcanism and earthquakes, might slow down or even cease. The result: "a tectonically dead planet with a dry surface," say the authors.