Inside Ice Giant Planets and Exoplanets

A new method of computer simulation sheds light on the present structure and past evolution of Ice Giant planets like Uranus and Neptune.

Researchers analyzed the conduction of electricity and heat of water under extreme temperature and pressure conditions, such as those that occur inside ice-giant planets as well as in many exo-planets outside of it.

Simulating the atomic scale for fractions of a nanosecond enables an understanding of what happened to enormous masses on time scales of billions of years.

Ice, liquid or superionic: a totally different water

The scholars analyzed three different phases of water: ice, liquid, and superionic, under the extreme temperature-and-pressure conditions typical of the internal layers of these planets. Grasselli and Baroni explain: “In such exotic physical conditions, we cannot think of ice as we are used to. Even water is actually different, denser, with several molecules dissociated into positive and negative ions, thus carrying an electrical charge. Superionic water lies somewhere between the liquid and solid phases: the oxygen atoms of the H2O molecule are organized in a crystalline lattice, while hydrogen atoms diffuse freely like in a charged fluid”. The study of thermal and electrical currents generated by the water in these three different forms is essential to shed light on many unsolved issues.

Transport of heat and electricity to understand the past and present The two scientists also state that “internal electrical currents are at the base of the Planet’s magnetic field. If we understand how the former flow, we can learn a lot more about the latter”. And not only that. “The thermal and electrical transport coefficients dictate the planet’s history, how and when it was formed, how it cooled down. It is therefore crucial to analyze them with the appropriate tools, like the one we have developed.

The electrical conductivity found for the superionic phase is far larger than assumed in previous models of magnetic field generation in Uranus and Neptune. Since superionic water is thought to dominate the dense and sluggish planetary layers below the convective fluid region where their magnetic field is generated, this new evidence could have a great impact on the study of the geometry and evolution of the magnetic fields of the two planets.

Nature Communications – Heat and charge transport in H2O at ice-giant conditions from ab initio molecular dynamics simulations

The impact of the inner structure and thermal history of planets on their observable features, such as luminosity or magnetic field, crucially depends on the poorly known heat and charge transport properties of their internal layers. The thermal and electric conductivities of different phases of water (liquid, solid, and super-ionic) occurring in the interior of ice giant planets, such as Uranus or Neptune, are evaluated from equilibrium ab initio molecular dynamics, leveraging recent progress in the theory and data analysis of transport in extended systems. The implications of our findings on the evolution models of the ice giants are briefly discussed.

SOURCES- Nature Communications, Scuola Internazionale Superiore di Studi Avanzati
Written by Brian Wang,