Planetary Material Science

Planetary Material Science

We have obtained various kinds of extraterrestrial materials. They include meteorites, lunar samples, cosmic dust, and returned samples such as Itokawa asteroidal dust and Wild 2 cometary particles. Their sizes span wide ranges, but we are applying micro-area analytical techniques for petrological, mineralogical and isotopic studies to understand when our solar system formed and how it has evolved into the present form.

Isotopic and trace element chemistry for understanding chronology and materials in the early solar system

Chondrites, a group of primitive meteorites, contain various components, such as CAIs, the oldest solids in the solar system, and chondrules, millimeter-sized silicate droplets. They may retain records of their formation processes in the solar nebula before formation of planetesimals. In fact, these components might form in different regions at different times in the solar nebula. We are conducting isotopic and trace element in situ analyses on these components trying to understand early solar system evolution. The techniques we used are secondary ion mass spectrometry (SIMS) and inductively-coupled plasma mass spectrometry (ICP-MS). One of the important applications of isotope analyses is dating. In addition to long-lived chronometers (e.g., U-Pb system), short-lived (extinct) chronometers with half-lives of sub-My to several My can be used to discuss relative ages of these components. Isotopic analyses may also provide important information about the source materials of meteorites and their components (e.g., different formation regions in the solar system). Trace element analyses may provide information about fractionation processes (i.e., gas-dust separation at various temperatures) in the solar nebula. Combining isotopic and trace element analyses using SIMS and ICP-MS, we are studying evolutionary processes of materials in the early solar system.

Cosmic mineralogy: Revealing evolution of planetary materials

Meteorites and returned samples by spacecraft record evolution of planetary materials that happened at various bodies in the solar system. We are trying to understand the rules governing such evolutions by comparing with terrestrial materials and utilizing planetary exploration data. In order to do this, we are paying attention to samples recording important stages of the evolution. These samples include cometary particles returned by the NASA Stardust, Itokawa asteroidal dust returned by JAXA Hayabusa, achondritic meteorites originating from proto-planets, and Martian meteorites. Our major approaches are to obtain chemical compositions and crystal structures of micro-areas employing X-ray and electron beam techniques because most of these materials are solid crystals. The obtained data enable us to reveal what kinds of chemical and physical processes occurred in their parent bodies, which leads us to figure out planetary evolution from planetesimals to planets via proto-planets. This field is called “cosmic mineralogy”.

Petrographic microscopy image of angrite meteorite, the oldest igneous rock in the solar system. Its formation age is 4.564 billion years ago and considered to have originated from crust of a proto-planet.

High resolution transmission electron photomicrograph of olivine in Martian meteorite. Nano-particles were formed by strong shock metamorphism that took place on the Martian surface.