Diamonds under pressure impersonate exoplanet cores

Researchers have squeezed diamonds to a record-setting pressure — 14 times as high as that inside Earth’s core. The compressed diamond’s properties could reveal the extreme conditions deep inside supersized distant planets, the team reports in the July 17 Nature.

To constrict diamond, the least compressible known material, physicist Ray Smith of Lawrence Livermore National Laboratory in California and colleagues powered up the world’s largest laser, located at the National Ignition Facility (SN: 4/20/13, p. 26).

Smith’s team focused 176 laser beams on hair-thin layers of gold and artificial diamond to induce waves of pressure. The gold layers help disperse heat, Smith says, helping avoid a problem that can mean diamonds aren’t forever: As pressure mounts, diamond can liquefy, ruining the experiment. The team also found that an initial small wave of pressure helps prevent melting before gradually ramping up the compression to 50 million times Earth’s atmospheric pressure at sea level. The entire process lasted 20 billionths of a second.

Smith says the properties of carbon under pressure could help researchers better simulate the insides of Neptune-like gassy exoplanets, which may have diamond cores. To mimic the cores of giant rocky planets, Smith plans to test iron at similar pressures.