On January 14, Youjun Zhang, a research fellow of the Institute of Atomic and Molecular Physics of SCU, and Professor Junfu Lin of the University of Texas published a review paper entitled "Molten iron in Earth-like exoplanet cores" in the top academic journal Science (Science, 375, 146, 2022). Sichuan University is the first work unit of the paper, and Youjun Zhang is the first author and corresponding author. Drawing upon the research progress of the research group in recent years, this article reviews the paper "Measuring the melting curve of iron at super-Earth core conditions" published by Kraus, and looks forward to the research field of planetary interior physics.
The research paper points out that, similar to the Earth, the activities in Earth-like planets play a very important role in the habitability conditions of planets, such as plate movement, mantle convection and core convection.
“Earth, the only known habitable planet in the Universe, has a magnetic field that shields organic life-forms from harmful radiation coming from the Sun and beyond. This magnetic field is generated by the churning of molten iron in its outer core. The habitability of exoplanets orbiting other stars could be gleaned through better understanding of their iron cores and magnetic fields. However, extreme pressure and temperature conditions inside exoplanets that are much heavier than Earth may mean that their cores behave differently. On page 202 of this issue, Kraus et al. used a powerful laser to generate conditions similar to those inside the cores of such “super-Earths” and reveal that even under extreme conditions, molten iron can crystallize similarly to that found at the base of Earth’s outer core.” (Abstract)
The article also points out that if the Earth-like planetary core is composed of iron (or contains a small amount of other elements), according to the latest research results, even if the pressure of the earth's core is several times higher, the melting line slope of iron will still be less than the adiabatic temperature gradient of the planetary core, then the molten planetary core will solidify from the planetary center and form the core under the action of long-term cooling.
The article indicates that the melting line and crystallization mode of planetary core are only one aspect of revealing the relationship between the internal dynamics of terrestrial planets and the habitability of planets. In the future, it is necessary to further understand the secrets of terrestrial planets from the physical properties of terrestrial planetary core and planetary mantle (such as transport, sound velocity, thermodynamic properties, etc.), We hope to uncover the question of "whether we are the unique advanced life in the universe" as soon as possible and find another planet suitable for human survival.
Figure: two typical crystallization modes of exoplanet molten core. On the left is the mode of solid core formation from the earth's core, and on the right is the mode of ferroalloy crystallization in the middle top of the earth's core (Zhang and Lin,Science, 375, 146, 2022）
The research group of Youjun Zhang is mainly engaged in the internal physics of the Earth and planets and the physics of extreme conditions. They have established a dynamic high-pressure experimental platform and a shock wave physics and Geophysics laboratory in the Institute of Atomic and Molecular Physics. In recent years, the research group has made outstanding achievements in relevant fields under the auspices of the National Natural Science Foundation of China and Sichuan University. So far, Youjun Zhang has published, in the capacity of the first author or corresponding author, more than 20 papers in Science, Proc. Natl. Acad. Sci. U.S.A., Phys. Rev. Lett., Sci. Bull., Earth Planet. Sci. Lett., Geophys. Res. Lett., Phys. Rev. B, J. Geophys. Res. and Appl. Phys. Lett., and so forth. His research achievements include the following: determined the melting temperature and crystallization mechanism of the earth core; revealed the thermal convection and evolution of the Earth's core and the driving mechanism of the Earth's generator; systematically studied the stability and physical properties of typical hydrous minerals under mantle conditions as well as the phase transformation, melting, transport and lattice vibration of typical transition metal elements under extreme conditions.
https://www.science.org/doi/10.1126/science.abn2051
