Seminar – Dr. Yoshinori Miyazaki

Speaker: Dr. Yoshinori Miyazaki, Caltech Center for Comparative Planetary Evolution, California Institute of Technology

Title: Volatile degassing from the planetary interior and its implication for habitability

Abstract: A large amount of volatiles could be stored in the planetary interior, and volatile partitioning between the surface and interior plays a crucial role in characterizing planetary habitability. In this talk, I will consider the geodynamics and mantle degassing during the early stage of planetary evolution, from a magma ocean to the subsequent subsolidus convection stage, to understand how the surface volatile budget is determined on terrestrial planets. We find that, under stagnant-lid convection, a planet is most likely to develop a Venus-like thick CO2 atmosphere, with most of its water inventory retained in the mantle. An atmosphere with a strong greenhouse effect could preclude the formation of water oceans, and the same is expected to be true for many rocky planets larger than Earth. For terrestrial planets to develop a moderate climate, efficient carbon sequestration is crucial, which requires the operation of plate tectonics. In particular, plate velocity should have been very fast on the early Earth because an increasing number of observations suggest that Earth has attained a clement surface environment relatively early in its history (~4 Ga). I will show that mantle differentiation during magma ocean could be the key to rapid plate motion and thus the early emergence of a habitable environment. In addition, a differentiated mantle could also promote a reaction between olivine and ocean water, creating conditions similar to the Lost City hydrothermal field.

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