Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and Low-Mass Dwarf Stars III. Iron, Magnesium, and Silicon

TL;DR

This study models the chemistry of iron, magnesium, and silicon in giant planets, brown dwarfs, and low-mass stars using thermochemical equilibrium calculations, revealing how these elements behave under various conditions.

Contribution

It provides a model-independent analysis of Fe, Mg, and Si chemistry and cloud formation effects in substellar atmospheres across different temperature and pressure regimes.

Findings

Fe metal condensation removes Fe gases from the atmosphere.

Monatomic Fe and Mg dominate their respective gas phases in many atmospheres.

SiO and SiH4 are key silicon-bearing gases in different substellar environments.

Abstract

We use thermochemical equilibrium calculations to model iron, magnesium, and silicon chemistry in the atmospheres of giant planets, brown dwarfs, extrasolar giant planets (EGPs), and low-mass stars. The behavior of individual Fe-, Mg-, and Si-bearing gases and condensates is determined as a function of temperature, pressure, and metallicity. Our results are thus independent of any particular model atmosphere. The condensation of Fe metal strongly affects iron chemistry by efficiently removing Fe-bearing species from the gas phase. Monatomic Fe is the most abundant Fe-bearing gas throughout the atmospheres of EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs. Mg- and Si-bearing gases are effectively removed from the atmosphere by forsterite (Mg2SiO4) and enstatite (MgSiO3) cloud formation. Monatomic Mg is the dominant magnesium gas throughout the atmospheres of EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs. Silicon monoxide (SiO) is the most abundant Si-bearing gas in the deep atmospheres of brown dwarfs and EGPs, whereas SiH4 is dominant in the deep atmosphere of Jupiter and other gas giant planets. Several other Fe-, Mg-, and Si-bearing gases become increasingly important with decreasing effective temperature. In principle, a number of Fe, Mg, and Si gases are potential tracers of weather or diagnostic of temperature in substellar atmospheres.