They can also provide a first-order approximation for species abundances as a function of pressure, temperature, and metallicity for a variety of atmospheres (e.g., Lodders & Fegley 2002 Visscher et al.
In general, thermochemical equilibrium governs the composition of the deep atmospheres of giant planets and brown dwarfs, however, in cooler atmospheres, thermoequilibrium calculations are the necessary baseline for further disequilibrium assessment. Thermochemical equilibrium calculations are the starting point for initializing models of any planetary atmosphere. In addition, the exoplanet photospheres that have been observed with current instruments are sampled within the region of the atmosphere dominated by vertical mixing and quenching, but not by photochemistry (Line & Yung 2013). For the hottest planets, Line & Yung ( 2013) show that at a pressure of 100 mbar, CH 4, CO, H 2O, and H 2 should be in thermochemical equilibrium even under a wide range of vertical mixing strengths. 2012) show that in hot exoplanetary atmospheres ( T > 1200 K), disequilibrium effects are so reduced that thermochemical equilibrium prevails. 2010a Marley & Robinson 2015 and references therein). 1996 Lodders & Fegley 2002 Visscher et al. Thermochemistry also governs the atmospheric composition in a vast variety of giant planets, brown dwarfs, and low-mass dwarf stars (Allard & Hauschildt 1995 Tsuji et al. In astrophysics, these calculations have been used to model the solar nebula, the atmospheres and circumstellar envelopes of cool stars, and the volcanic gases on Jupiter’s satellite Io (e.g., Lodders & Fegley 1993 Lauretta et al. Thermochemical equilibrium calculations have been widely used in chemical engineering to model combustion, shocks, detonations, and the behavior of rockets and compressors (e.g., Belford & Strehlow 1969 Miller et al.
#Teacode review free#
In addition, this method only requires knowledge of the free energies of the system, which are well known, have been tabulated, and can be easily interpolated or extrapolated. The advantage of the free energy minimization method is that each species present in the system can be treated independently without specifying complicated sets of reactions a priori, and therefore a limited set of equations needs to be solved (Zeleznik & Gordon 1960). However, at high temperatures where thermochemical equilibrium should prevail, one needs to know the forward and reverse reactions and corresponding reaction rates, which are less well known or conflicted (Visscher et al. This is not an issue at lower temperatures where reaction rates are well known. To obtain an accurate kinetic assessment of the system, one must collect a large number of reactions and associate them with the corresponding rates.
Chemical equilibrium can be calculated almost trivially for several reactions present in the system, but as the number of reactions increases, the set of numerous equilibrium constant relations becomes hard to solve simultaneously. However, using kinetics for high-temperature thermochemical equilibrium calculations can be challenging. The kinetic approach, where the pathway to equilibrium needs to be determined, is applicable for a wide range of temperatures and pressures (Visscher et al. There are two methods to calculate chemical equilibrium: using equilibrium constants and reaction rates, i.e., kinetics, or minimizing the free energy of a system (Bahn & Zukoski 1960 Zeleznik & Gordon 1968).
#Teacode review license#
TEA is available under a reproducible-research, open-source license via.
#Teacode review code#
There is a start guide, a user manual, and a code document in addition to this theory paper. TEA is written in Python in a modular format. We also applied the TEA abundance calculations to models of several hot-Jupiter exoplanets, producing expected results. Using their thermodynamic data, TEA reproduces their final abundances, but with higher precision. We tested the code against the method of Burrows & Sharp, the free thermochemical equilibrium code Chemical Equilibrium with Applications (CEA), and the example given by Burrows & Sharp. Given elemental abundances, TEA calculates molecular abundances for a particular temperature and pressure or a list of temperature–pressure pairs. It applies Gibbs free-energy minimization using an iterative, Lagrangian optimization scheme. The code is based on the methodology of White et al. We present an open-source Thermochemical Equilibrium Abundances (TEA) code that calculates the abundances of gaseous molecular species.
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