The mantles of Earth and other rocky planets are rich in
magnesium and oxygen. Due to its simplicity, the mineral
magnesium oxide is a good model for studying the nature of
planetary interiors. New work from a team led by Carnegie's
Stewart McWilliams studied how magnesium oxide behaves under the
extreme conditions deep within planets and found evidence that
alters our understanding of planetary evolution. It is published
November 22 by Science Express. Magnesium oxide is particularly
resistant to changes when under intense pressures and
temperatures. Theoretical predictions claim that it has just
three unique states with different structures and properties
present under planetary conditions: solid under ambient
conditions (such as on the Earth's surface), liquid at high
temperatures, and another structure of the solid at high
pressure. The latter structure has never been observed in nature
or in experiments. McWilliams and his team observed magnesium
oxide between pressures of about 3 million times normal at