Scientists create supergiant planet core pressures using UV lasers and diamonds

Ultraviolet laser and diamond anvils can generate pressure 100 to 1000 times greater than possible today, reproducing conditions expected in the cores of supergiant planets.

Washington, May 3 : Ultraviolet laser and diamond anvils can generate pressure 100 to 1000 times greater than possible today, reproducing conditions expected in the cores of supergiant planets.

Till now, these pressures have only been available experimentally next to underground nuclear explosions.

"This lets us explore a new regime of chemistry and reproduce the conditions of more extreme planets," said Raymond Jeanloz, professor of astronomy and earth and planetary science at the University of California, Berkeley.

The process involves compressing a tiny sample - either liquid or solid - between the tips of two diamonds. Powerful laser beams zap one of the diamonds, vaporizing it and sending a shock wave through the sample that compresses it even more.

The shock wave compresses the sample for 1 to 2 nanoseconds, enough time to study the properties of the sample, which can range from hydrogen and helium, the stuff of stars and giant planets, and to elements that comprise Earth.

To date, Jeanloz and his colleagues have achieved pressures near 10 million atmospheres using the 30 kilojoule ultraviolet Omega laser at the University of Rochester's Laboratory for Laser Energetics in New York.

They hope to eventually use the two-megajoule laser of LLNL's National Ignition Facility to achieve more than a billion atmospheres of pressure.

The advantage in this process, as Jeanloz said, is that the temperature as well as pressure can be varied, and experimenters can study the compressed samples for long periods.

On the other hand, laser-induced shock waves can produce tens of millions of atmospheres, but only for a split-second and at very high temperatures. This technique also requires lasers the size of a building, said Jeanloz.

"By combining the two, we can get to higher pressures and much higher densities than either of the methods alone.

High density is really important, because we are trying to understand what happens as you bring atoms really close together, and compare our observations to quantum mechanical calculations," said Jeanloz.

According to him, the combined method also allows scientists to tune the temperature over a wide range independent of density, something almost impossible to do with laser-induced shock waves alone.

"When we squeeze materials to a million atmospheres pressure, the chemistry is changed dramatically.

Materials go from being transparent insulators to becoming metallic or even superconducting.

The periodic table is completely changed at high pressures. There is reason to expect that when we go from the million atmosphere range to the billion atmosphere range, again there will be huge changes in chemical bonding and material properties," Jeanloz said.

"The centre of Jupiter is at about 70 million atmospheres, which until now has been inaccessible.

We want to be able to understand the hundreds of planets that have now been found that are massive enough that their central pressures are many hundreds of millions of atmospheres, and maybe a billion atmospheres," he added.

The findings appear online in the Proceedings of the National Academy of Sciences.

ANI