1. Formation and evolution of asteroids

The C-complex asteroids located in the main asteroid belt are considered to have formed in lower-temperature environments compared with the formation region of rocky planets. These types of small bodies should possess the vital records of ice and organics in the early solar system. The original information on the formation region of C-complex asteroids was recorded in carbonaceous chondrites. By the chemical and isotopic data from bulk carbonaceous chondrites, we can assess the formation environments and evolution of asteroids.

Ryota Fukai and Tetsuya Yokoyama (2019) The Astrophysical Journal
・Tetsuya Yokoyama, Yuichiro Nagai, Ryota Fukai et al. (2019) The Astrophysical Journal

2. Origin of trans-iron elements in Solar System

The elements in the Solar System have been formed by the various types of nucleosynthesis. The elements heavier than iron (Fe) are generally synthesized in the final stage of the stellar evolution. Chondrites possess the tiny grains formed in those stellar environments, which preserved the nucleosynthetic events. It is still unknown that the nucleosynthetic sites for the rapid neutron capture process (forming platinum and gold) and photodissociation process (forming proton-rich nuclides) are. We are developing the mass spectrometric and spectroscopic techniques for measuring the trace elements in the tiny presolar grains.

Ryota Fukai and Tetsuya Yokoyama (2020) JPS Conference Proceedings
Ryota Fukai and Sota Arakawa (2021) The Astrophysical Journal

3. Global melting events in the early Earth + Fractionation in non-traditional stable isotopes

At the birth of the Earth, the global melting events called as "magma ocean" were occurred. This event formed the global layer structure as core and mantle in the Earth. Geochemical data suggests the heterogeneity in the mantle, however, this is apparently inconsistent with the geophysics data. This inconsistency is possibly caused by the characteristics of long-lived radioactive nuclides that records the multiple events through the terrestrial evolution. In contrast, the short-lived radioactive nuclides like 146Sm reflects the fractionation in the early differentiation of the Earth. We can reveal the global melting events by using the radiogenic isotopes of chondrites and early terrestrial rocks.
Also, The isotopic fractionation in the terrestrial and extraterrestrial materials are occurred with the several phenomena such as chemical reactions and phase transitions. The fractionation possibly reflects the important events like water-rock interaction. We found that some types of trace elements (alkali elements, rare earth elements) can be the good tracers, which can distinguish the cause of fractionation. We are developing the high-precision isotopic analysis to assess the fractionation processes in the Archean rocks.

Ryota Fukai and Tetsuya Yokoyama (2017) Earth and Planetary Science Letters
Ryota Fukai et al. (2020) Goldschmidt conference

4. Fragmentation of planetary materials


5. Developments of high-precision analyses

The advent of new-generation mass spectrometers in the last decade has greatly accelerated research in geosciences and analytical chemistry. Isotope ratio measurements at a level of sub–5 ppm analytical precision are now possible with modern instruments of thermal ionization mass spectrometry (TIMS) and inductively coupled plasma-mass spectrometry (ICP-MS). We have improved the analytical precisions by the correction of detector's efficiencies and ion lens conditions.

Ryota Fukai et al. (2017) International Journal of Mass Spectrometry
Ryota Fukai and Tetsuya Yokoyama (2019) Geochemical Journal
・Tetsuya Yokoyama, Ryota Fukai et al. (2020) Geostandards and Geoanalytical Research

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