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22-Nov-2012

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On other planets, a new kind of magnesium oxide



Photo of a laser-shock experiment in progress. Shown is the center of the target chamber, where a sample of material is struck with several high power laser pulses at once. In a brief instant (one billionth of a second), a material initially at low pressure and temperature, similar to the Earth's surface, is artificially heated and compressed to its natural state deep within a planet. This extreme state is quickly studied using probes and telescopes pointed at the target (shown) before it explodes into a cloud of vapor and dust, as seen in this photo.
[Image courtesy of Eugene Kowaluk, Laboratory for Laser Energetics, University of Rochester]

Magnesium oxide, one of the simplest minerals on Earth, transforms into liquid metal under certain conditions likely to exist inside giant, Earth-like planets known as "super Earths", reports a new study in the journal Science.

The results hint that inside super Earths, the rocky substance of the deep mantle could actually be metallic, blurring the distinction between what is traditionally thought of as core (liquid metal) and mantle (rock). Liquid magnesium oxide may also produce a geodynamo, which is responsible for creating the magnetic field of planets.

On Earth, magnesium oxide is found everywhere, from the Earth's surface to its deepest mantle. Ryan Stewart McWilliams and colleagues found that at the extreme temperatures and pressures found inside large planets, magnesium oxide is completely transformed from a transparent ceramic to a liquid metal.

In their experiment, the researchers fired powerful lasers at a small piece of magnesium oxide. In just 1 billionth of a second, the sample was heated and squeezed to conditions found inside giant planets. The researchers observed the changing properties of the sample, which first morphed into a solid with a new crystal structure, and finally into a liquid metal.

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