Huge Pressures Melt Diamonds On Planet Neptune

By | February 20, 2009

Marcus Knudson examines the focal point of his team’s effort to characterize materials at extremely high pressures. The fortress-like box sitting atop its support will hold within it a so-called “flyer plate” that — at speeds far faster than a rifle bullet — will smash into multiple targets inserted in the two circular holes. An extensive network of tiny sensors and computers will reveal information on shock wave transmission, mass movement, plate velocity, and other factors.

The enormous pressures needed to melt diamond to slush and then to a completely liquid state have been determined ten times more accurately by Sandia National Laboratories researchers than ever before.

As a bonus to science, researchers Marcus Knudson, Mike Desjarlais, and Daniel Dolan discovered a triple point at which solid diamond, liquid carbon, and a long-theorized but never-before-confirmed state of solid carbon called bc8 were found to exist together.

Accurate knowledge of these changes of state are essential in simulating behaviors of celestial bodies, and to the effort to produce nuclear fusion at Lawrence Livermore National Laboratory’s National Ignition Facility in California.

The changes resemble those undergone by ice as it melts into water, but under much more extreme conditions.

Granted, it’s not immediately obvious why accelerating a projectile about the size of a stick of gum to 25 times the speed of a rifle bullet and smashing it into a target in central New Mexico would say anything about nuclear fusion or the state of diamonds on Neptune (the eighth planet from the sun).

It does because on Neptune, for example, much of the atmosphere is composed of methane (CH4). Under high pressure, methane decomposes, liberating its carbon. One question for astrophysicists in theorizing the planet’s characteristics is knowing the form that carbon takes in the planet’s interior. At what precise pressure does simple carbon form diamond? Is the pressure eventually great enough to liquefy the diamond, or form bc8, a solid that has yet other characteristics?

“Liquid carbon is electrically conductive at these pressures, which means it affects the generation of magnetic fields,” says Desjarlais. “So, accurate knowledge of phases of carbon in planetary interiors makes a difference in computer models of the planet’s characteristics. Thus, better equations of state can help explain planetary magnetic fields that seem otherwise to have no reason to exist.”

via Huge Pressures Melt Diamonds On Planet Neptune.

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