Experiments performed by Laura Robin Benedetti and colleagues at the University of California in Berkeley agreed with theories that the intense pressures and temperatures in the interiors of planets such as Neptune convert methane into diamond -- with one difference. The research group simulated these forces on methane, which may constitute 10 to 15 percent of Neptune's mass, and found that it dissociated at much lower pressures than the 300 GPa that had been theorized.

The researchers used laser-heated diamond anvil cells to compress liquid methane at pressures of 10 to 50 GPa (100,000 to 500,000 atmospheres) to re-create the conditions inside a gas giant. To produce the 2000 K to 3000 K temperatures of the interior, the scientists heated the samples with a 1064-nm Nd:YAG laser from Quantronix Corp. of East Setauket, N.Y. Subsequent x-ray diffraction revealed that the methane had broken down to form diamond crystals and polymeric hydrocarbons.

The results of the experiment, which were published in the Oct. 1 issue of Science, will help astrophysicists understand the luminosity and magnetic fields of gas giants in terms of the internal chemical dynamics that affect their planetary energy budgets.