C5 - Early interior–surface–atmosphere interactions on the terrestrial planets

Research areas: Planetary physics, geophysics

Summary

During the early phases of planet building, the atmospheric surface temperature may heavily influence the thermochemical evolution of the magma ocean. For example, whether or not the surface is molten critically affects the entrainment of late accreted material into the interior, thereby affecting internal dynamics and mantle mixing (C4). There is a gap in knowledge however, regarding how long this molten surface phase lasts and the implications for mixing of impacting material into the interior. We address this knowledge gap by coupling a state-of-the-art atmospheric evolution model with an interior outgassing model. This coupling is needed because, outgassing feeds back on atmospheric composition and energy balance, hence affecting the surface temperature. In addition to surface temperature, surface pressure is also a key factor affecting outgassing. During the molten surface phase the atmospheric composition likely changes as it gradually cools from a hot silicate vapor atmosphere (which condenses out in grains), to an light element (H,C,O) atom-rich atmosphere and finally into a molecule-rich (e.g., CO2, H2O) atmosphere, which eventually collapses to form the oceans. Our atmospheric evolution model will be updated to include the effects of silicate vapor clouds, atmospheric escape, and thick, steam atmospheres.

Advancing our knowledge of early terrestrial planet atmospheres will thereby help improve the understanding of variations of the Earth’s atmospheric composition over time and  feedback processes with the interior. In the course of magma ocean solidification and core segregation, feedback between the redox buffer of the mantle and outgassing of water and carbon dioxide into the atmosphere becomes increasingly important. We therefore apply a structural model of the interior that involves equations of state for the density and material properties of distinct geochemical reservoirs (crust, mantle, core), including chemical reactions between silicates, metallic and oxidized iron, and hydrogen- and carbon-based volatile constituents. The interior structure model will in turn be used to constrain oxygen fugacity (fO2), which directly determines outgassing (C4). The structural model will be iterated with the atmospheric model until fO2 conditions (hence outgassing and atmospheric pressure) converge.