Sulfurization of Iron in the Dynamic Solar Nebula and Implications for Planetary Compositions

TL;DR

This paper models the chemical and dynamical evolution of iron grains in the solar nebula to understand sulfur depletion and its implications for planetary compositions, especially Jupiter's volatile inventory.

Contribution

It provides a quantitative model showing how rapid radial expansion of the nebula can produce sulfur-depleted conditions suitable for clathrate formation.

Findings

Rapid nebula expansion can produce sulfur-depleted gas.

FeS grains can be transported outward, affecting planetesimal composition.

Conditions for sulfur depletion depend on nebula dynamics and grain chemistry.

Abstract

One explanation for the enhanced ratio of volatiles to hydrogen in Jupiter's atmosphere compared to a a gas of solar composition is that the planet accreted volatile-bearing clathrates during its formation. Models, however, suggest that S would be over abundant if clathrates were the primary carrier of Jupiter's volatiles. This led to the suggestion that S was depleted in the outer nebula due to the formation troilite (FeS). Here, this depletion is quantitatively explored by modeling the coupled dynamical and chemical evolution of Fe grains in the solar nebula. It is found that disks that undergo rapid radial expansion from an initially compact state may allow sufficient production of FeS and carry H$_{2}$S-depleted gas outward where ices would form, providing the conditions needed for S-depleted clathrates to form. However, this expansion would also carry FeS grains to this region, which could also be incorporated into planetesimals. Thus for clathrates to be a viable source of volatiles, models must account for the presence of both H$_{2}$S in FeS in the outer solar nebula.