Planetary Science, Theory of Crystal Growth

Crystal Growth, Solar System Small Bodies, Astrophysics, Chondrules, Semiconductors, Minerals, Phase-Field Method

(1) Evolution of Solid Matter in the Early Solar System:
Today, a wide variety of crystals exist on Earth. Furthermore, extraterrestrial materials such as meteorites also contain various crystals. However, it is believed that almost all of the interstellar matter from which these crystals originated was amorphous. When, where, and how did this amorphous material crystallise during the formation of the Sun and planetary systems? To address this question, we are conducting research using physical modelling and numerical simulations, focusing primarily on the heating of solid matter caused by interactions between gas discs and solid matter.

(2) The Evolutionary Process of Solar System Small Bodies
Asteroids and comets are types of small bodies in the Solar System. Traditionally, asteroids and comets were clearly distinguished from one another. That is to say, asteroids consist mainly of rock, whilst comets consist mainly of ice. However, in recent years, small bodies possessing characteristics of both asteroids and comets have been discovered. This suggests that asteroids and comets are not entirely distinct types, but rather that comets may have lost their ice during the course of their evolution, taking on an asteroid-like appearance. Such celestial bodies are known as Comet-Asteroid Transition Objects (CAT objects). How do comets become asteroids, and how long does this process take? To address this question, we are investigating the long-term thermal evolution of cometary nuclei heated by solar radiation through numerical analyses based on astrophysics.

(3) Mineral morphology and compositional zonings:
Some of the minerals found in rocks and meteorites formed whilst the magma was cooling. Their morphology and the heterogeneous structure of chemical composition (compositional zonings) reflect the environment in which they were formed. When a mineral with a particular morphology and zonal structure is found, what kind of environment did it form in? To address this question, we are conducting numerical analyses based on a mathematical model (the phase-field method) that takes into account element distribution at solid-liquid interfaces and transient element diffusion.

(4) Step dynamics on crystal surfaces:
Although crystal surfaces appear flat at first glance, they contain steps approximately 1 nm high. Crystals grow as atoms and molecules from the solution are transported to the crystal surface and incorporated into the steps. However, if impurities are present in the solution, the incorporation of atoms and molecules into the steps is inhibited, affecting crystal growth. We are investigating the mechanisms of crystal growth by modelling the movement of steps during crystal growth (step dynamics) using mathematical models.