Work

A new chemical network to explore the disequilibrium chemistry of silicates and iron in hot gas giants

Year: 2026

Type: article

Abstract: Chemical equilibrium modeling of gas giant planet atmospheres indicates that the production and condensation of silicates plays an important role in shaping their final composition. However, only partial chemical kinetics networks for these species are presently available, which is an impediment to analyzing the impact of chemical disequilibrium processes. In this paper, we present SILANE , a new chemical network that includes Mg, Si, Fe, and 15 carriers of these elements, including MgSiO 3 and Mg 2 SiO 4 , ready for use in the VULCAN code. We compare the results of our network with a chemical equilibrium model and discuss them in relation to previous results from the literature. We then apply our new network to the analysis of a vertically mixed, solar-composition atmosphere with equilibrium temperatures of T eq in the [700, 1600] K range. We found that (i) rock-forming silicates disappears from the upper atmosphere already at 1100 K; (ii) SiH 4 reaches concentrations of 10 −7 in the upper ( P ≤ 1.0 bar) atmosphere for planets with T eq ∈ [800, 1100] K; and (iii) the amount of oxygen in refractories decreases from 21% at T eq =700 K to 6% already at 1100 K. Meanwhile, in the classical equilibrium framework, it remains constant up to T eq =1300 K. By applying our network to the case of the young hot Jupiter YSES-1 c and comparing both the mixing ratios of volatile species and the enstatite fraction in the silicate mix, we find evidence of a well-mixed atmosphere, possibly with an average K zz ≥ 10 10 cm 2 s −1 up to the 10 −4 bar level.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202557060