High-pressure experiments provide insight into icy planets

Research team determines compression behaviour of water ice in unprecedented detail

An international team of scientists has been using X-rays to take a look inside distant ice planets. At the PETRA III Extreme Conditions Beamline, they investigated how water ice behaves at high pressure, under conditions corresponding to those inside the planet Neptune, for example. At pressures up to almost two million times atmospheric pressure at sea level on Earth, the researchers were able to observe in unparalleled detail how water ice behaves under compression. The team, led by Hauke Marquardt from the University of Oxford, is presenting its findings in the scientific journal Physical Review B.

Planetary ices – such as water ice (H₂O), methane ice (CH₄) and ammonia ice (NH₃) – make up large parts of the ice giants in our solar system and are very likely to occur inside many exoplanets, which are planets outside our solar system. “However, the physical properties and phase diagrams of these compounds are not sufficiently known at the pressures and temperatures that prevail inside planets,” explains Marquardt. “Previous experimental studies using X-ray diffraction in a static diamond anvil cell have contributed a great deal to our understanding of ices at high pressure, but they have been unable to adequately answer numerous questions.”