Researchers reveal new findings about diamond rain on ice planets

An international team of researchers led by Dr Mungo Frost from the SLAC Research Center in California has gained new insights into the formation of diamond showers on icy planets such as Neptune and Uranus, using the European XFEL X-ray laser at Schenefeld. The results also provide clues to the formation of these planets’ complex magnetic fields.

In previous work with X-ray lasers, scientists found that diamonds should form from carbon compounds located inside large gas planets due to the high pressure there. These would then sink deeper into the interior of the planets in the form of a rain of precious stones coming from the upper layers.

A new experiment conducted at Europe’s XFEL has shown that the formation of diamonds from carbon compounds already begins at lower pressures and temperatures than expected. For gas planets, this means that the diamond shower is already forming at a lower depth than previously thought and could therefore have a stronger influence on the formation of magnetic fields.

In addition, diamond showers would also be possible on gas planets smaller than Neptune and Uranus and called “mini-Neptunes”. Such planets do not exist in our solar system, but they occur as exoplanets outside it.

The research is published in the journal Natural astronomy.

As it passes from the outer to the inner layers of planets, diamond rain can entrain gas and ice, causing conductive ice streams. Currents of conductive fluids act as a kind of dynamo through which the magnetic fields of the planets are formed.

“Diamond rain likely has an influence on the formation of the complex magnetic fields of Uranus and Neptune,” Frost said.

The group used a plastic film made from the hydrocarbon compound polystyrene as a carbon source. Under very high pressure, diamonds are formed from the foil, a process that takes place in the same way as inside planets and which can be reproduced at Europe’s XFEL.

Researchers generated the high pressure and temperature of more than 2,200 degrees Celsius found inside the icy gas giants using diamond pad cells and lasers. The buffer cells work like a mini-vice in which the sample is squeezed between two diamonds. Using European XFEL X-ray pulses, the timing, conditions and sequence of diamond formation in the buffer cell can be precisely observed.

The international research team also includes scientists from the European XFEL, the German DESY research centers in Hamburg and the Helmholtz Center in Dresden-Rossendorf, as well as other research institutes and universities from different countries. The European XFEL HIBEF user consortium, involving the HZDR and DESY research centers, contributed significantly to this work.

“Thanks to this international collaboration, we have made great progress at the European XFEL and gained remarkable new knowledge about icy planets,” explains Frost.