Finding the temperature tipping point at which diamonds melt has been very important to scientists at the Sandia National Laboratories, for a few important reasons. First off, it has pointed to a state of carbon where three of its forms (solid diamond, liquid carbon and bc8) exist together. Secondly, it has given clues as to how planets move and why, and thirdly, it could help with understanding nuclear fusion at the Lawrence Livermore National Laboratory's National Ignition Facility in California.
Until now, scientists have known approximately what amount of pressure is needed to melt diamonds, but the new study has determined those amounts ten times more accurately than before.
Through their work, investigators Marcus Knudson, Mike Desjarlais, and Daniel Dolan have managed to bring the understanding of how celestial bodies behave and why even closer to the scientific community, while at the same time providing a potential solution to solving the riddle of nuclear fusion as well.
The machine the scientists have built to test their hypothesis is a sort of micro-accelerator, but unlike those used to move particles in a smasher. The device they have accelerates tiny projectiles to approximately 25 times the speed of a rifle bullet. This innovation offers them insight into how carbon is formed on Neptune. For a long time, astronomers have known that the eight planet's atmosphere is made up from methane (CH4), a compound that can release its composing carbon under extreme pressure.
Now, the strife is to determine what type of carbon the core of the planet consists of. Also, scientists need to know at what pressure carbon forms diamonds, when diamond liquefies, and when the elusive bc8 compound (a state of carbon hinted at theoretically, but never actually created or seen) is formed.
“Liquid carbon is electrically conductive at these pressures, which means it affects the generation of magnetic fields. 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,” Mike Desjarlais explains.
“These experiments are much more accurate than ones previously performed with laser beams. Our flyer plates, with precisely measured velocities, strike several large diamond samples, which enables very accurate shock wave velocity measurements,” Marcus Knudson adds. “Flyer plates” is the name given to a small part of their device, the one responsible with accelerating the tiny pieces of material.