Title:
Toward understanding chemistry of the water worlds in the Solar system

Abstract:
"Follow the water"―this has been the major theme of Solar System exploration. We now know that there are multiple planetary bodies, such as Mars, Europa, Enceladus, Ceres, Pluto, and Titan, that possess (or possessed) a quantity of liquid water. But, after these findings, what would be the next target toward searching for life there? To address this, we need to expand the horizons of planetary science by including full-scale chemistry and, possibly, biology in its research field.

My decadal goal is to develop "chemistry" on the physics-based theory of the formation and evolution of the water worlds. To this end, I focus on the following four topics in the last decade; 1) to quantify chemical reactions in planetary surface processes, 2) to expand hydrological geochemistry to other planets, 3) to understand the feedback among the atmosphere, oceans, and life in Earth's history, and 4) to apply the above understanding for interpretations of spacecraft data.

In this talk, I will focus on the topics 1) and 4). Concerning the topic 1), we suggest that the surface chemicals on Titan, Pluto, and Ceres support the occurrence of the dynamic orbital evolution of the gas giants and its consequence of large-scale material transports in the early Solar system. As for the topic 4), we show that Enceladus possesses an ongoing hydrothermal environments that sustain chemical disequilibrium in the subsurface ocean and can support chemosynthetic microorganisms. In this talk, I also will discuss future research plans that aim to develop a comprehensive view of the water worlds that can support life. In the future studies, we will experimentally investigate formation reactions of oxidants and reductants on planets and will construct numerical models on hydrological and geochemical cycles. This will allow to predict a flux, potential, and location of disequilibrium bioavailable energy on early Mars, Europa, and Enceladus. As an emergence of life also would be a planetary process that utilizes disequilibrium energy, this knowledge also would be useful to constrain the planetary processes necessary for the origin of Earth's life.