Astrochemical Inheritance of Terrestrial Planets Water from Local Wet Silicates

TL;DR

This study shows that water can be retained on silicate grains during planet formation, potentially explaining Earth's water content without needing outer Solar System delivery.

Contribution

New quantum mechanics calculations reveal water binds more strongly to silicate grains than to amorphous ice, impacting models of water retention in terrestrial planets.

Findings

Water binding energy on silicates is about twice that on amorphous ice.

Increased water retention on silicates raises the temperature at which water can be preserved.

Model predictions align with observed water content in terrestrial planets.

Abstract

The delivery of water to the inner Solar System rocky planets, including Earth, remains debated, as standard models assume that they formed from dry grains, inside the snowline of the protosolar nebula. However, a recent work showed that a not-negligible amount of water formed during the prestellar phase could have been retained by pebbles and planetesimals at the Earth's orbit in enough quantities to reproduce its water content. This study was based based on quantum mechanics (QM) calculations of the binding energy (BE) of water on amorphous ice and on a kinetic approach. Here, we present new QM calculations of the BE of water frozen on the surface of silicate grains, and show that it is on average about twice larger than that on the amorphous ice. The contribution of this first layer of frozen water increases the dust temperature at which frozen water can be retained. This provides a local source of water not only for the Earth, but also for the inner rocky planets. The predictions from our model are in agreement with the available estimates of water content in terrestrial planets. This suggests that water delivery from the outer Solar System may not be required.