VULCAN: An Open-source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres

Shang Min Tsai, James Lyons, Luc Grosheintz, Paul B. Rimmer, Daniel Kitzmann, Kevin Heng

Research output: Contribution to journalArticle

32 Scopus citations

Abstract

We present an open-source and validated chemical kinetics code for studying hot exoplanetary atmospheres, which we name VULCAN. It is constructed for gaseous chemistry from 500 to 2500 K, using a reduced C-H-O chemical network with about 300 reactions. It uses eddy diffusion to mimic atmospheric dynamics and excludes photochemistry. We have provided a full description of the rate coefficients and thermodynamic data used. We validate VULCAN by reproducing chemical equilibrium and by comparing its output versus the disequilibrium-chemistry calculations of Moses et al. and Rimmer & Helling. It reproduces the models of HD 189733b and HD 209458b by Moses et al., which employ a network with nearly 1600 reactions. We also use VULCAN to examine the theoretical trends produced when the temperature-pressure profile and carbon-to-oxygen ratio are varied. Assisted by a sensitivity test designed to identify the key reactions responsible for producing a specific molecule, we revisit the quenching approximation and find that it is accurate for methane but breaks down for acetylene, because the disequilibrium abundance of acetylene is not directly determined by transport-induced quenching, but is rather indirectly controlled by the disequilibrium abundance of methane. Therefore we suggest that the quenching approximation should be used with caution and must always be checked against a chemical kinetics calculation. A one-dimensional model atmosphere with 100 layers, computed using VULCAN, typically takes several minutes to complete. VULCAN is part of the Exoclimes Simulation Platform (ESP; exoclime.net) and publicly available at https://github.com/exoclime/VULCAN.

Original languageEnglish (US)
Article number20
JournalAstrophysical Journal, Supplement Series
Volume228
Issue number2
DOIs
StatePublished - Feb 2017

Keywords

  • methods: numerical
  • planets and satellites: atmospheres
  • planets and satellites: composition

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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