Berkeley researchers find ‘superionic’ state of water

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Scientists from the Lawrence Livermore National Laboratory published a paper in the journal Nature Physics confirming that “superionic” water exists on Uranus and Neptune.

Superionic matter is neither solid nor liquid — it is somewhere in between. Though prior theories have predicted the presence of this form of matter on Uranus and Neptune for years, new technology enabled lab researchers to confirm its existence, according to Marius Millot, a former UC Berkeley postdoctoral researcher and a co-author of the study.

“This is a pretty surprising state of matter, and for several decades, no one was able to characterize it,” Millot said.

Shock compression technology — which involves creating a highly pressurized environment —  has been used to re-create the state of matter on Earth for further study, according to Millot. The technique is very unique, though Millot said similar tactics have been adopted by other researchers at the École Polytechnique in France.

A water molecule can change states of matter under extreme amounts of pressure because its structure permits hydrogen to jump from one molecule to the other, according to the study. While the oxygen keeps its crystal-solid lattice, the hydrogen molecules jump from one position to the other, resulting in superionic water.

“Water ice at planetary interior conditions has been predicted to become superionic with fast-diffusing (that is, liquid-like) hydrogen ions moving within a solid lattice of oxygen,” the paper’s abstract reads.

This state of matter is present on Uranus and Neptune but not on other planets because of Uranus and Neptune’s sizes and subsequent high pressures and high temperatures, Millot said. On smaller planets, including Earth, planetary pressure is not high enough for superionic water to occur naturally.

The 10-person team consists of Millot and campus professor of earth and planetary science Raymond Jeanloz, along with their colleagues from the Livermore lab and from University of Rochester. The study has been underway for four years, and according to Millot, the team is enthusiastic about the information that these findings provide.

Millot says the next step for his team will likely be to try to understand whether or not water can act in this way when it is mixed with additive substances including ammonia and methane, as it would be on Uranus and Neptune. So far, the researchers have only tested water without any additional substances.

Knowing the chemical makeup of the planets provides a building block toward understanding the origins of Uranus, Neptune and the solar system at large.

”People are trying to understand the origin of the solar system, and one way that we can peer into the past is to look at the gravity fields and magnetic fields by looking at graphs, so the existence of superionic fields,” Millot said. “It’s a good building block to understanding Uranus and Neptune.”

Contact Isabella Sabri and Michele Meltzer at [email protected].

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