Radial migration and dehydration of phyllosilicates in the solar nebula

Abstract

While it is currently thought that Earth's water was delivered by hydrous minerals, the origin of these minerals is still debated. Nebular models suggest that the area where the Earth formed was too hot for these minerals to form, leading many to believe that they were delivered by large planetary embryos which formed in the outer asteroid belt region of the solar nebula. Others have argued that the hydrous minerals were present during the early accretion phase of the Earth in order to explain different aspects of its geochemistry and therefore, must have formed locally, implying that the nebula must have been cooler than the models predict. In this paper we explore a new possibility: that these hydrous minerals were formed in the outer asteroid belt region of the solar nebula and were then brought into the hotter regions of the nebula by gas drag where they were incorporated into the planetesimals which formed there. The hydrated minerals were able to survive for long periods of time in this hot region due to the sluggish dehydration kinetics. We find that this process need not have been efficient, requiring only a small amount (∼few percentages) of the material in the outer asteroid belt region of the nebula to be subject to this process. This delivery mechanism provides a way for hydrous minerals to be incorporated early on into the planetesimals which were accreted by the Earth without having to alter the generally accepted solar nebula models that are consistent with meteoritic and asteroidal observations.