Two Different Sources of Water in Earth’s Accretion Zone of the Solar Nebula

Abstract

The origin of water and the related significance for the early Earth depend on the conditions in the different stages of the solar nebula and the later solar system. With our model we simulate the chemical and hydrodynamic processes of the solar nebula. For that purpose we explicitly consider the evolution of the parental cloud core, its gravitational collapse, and the resulting turbulent disk. As a consequence of the low temperature ( 8 K) in the center of the cloud core thick ice layers are formed on the dust grains. The collapse is simulated using a new semi-analytic multi-zone solution of the hydrodynamic equations which is valid for spherical symmetry. Initially, the density distribution of the inner zone represents a central clump from which the proto-sun and later the T Tauri Sun form. The two outer zones evolve into a disk and a thin but spatially extended envelope. The disk stage is described by a stationary model and considers a weakly coupled gas and dust phase. We have identified two different sources of water for the region of Earth’s accretion. The first source is located in the inner region of the collapsing cloud core where the temperature could reach about 500 K. There, water was produced efficiently by gas phase reactions between neutral molecules. The second source is related to icy mantles of dust grains formed in the cloud core and disk stage. In the course of disk evolution cooling caused an enrichment of the dust phase with water ice beyond the snowline which moved inwards, i.e. into the Earth accretion zone. In addition we present results how water formation is related to the initial abundance ratio between carbon and oxygen in the cloud. This research has been supported by the Helmholtz Association through the research alliance “Planetary Evolution and Life“.