2006/02/28 by Curtis S. Cooper, Adam P. Showman · 9 citations
Physics and Astronomy · #Astro and Planetary Science #Scientific Research and Discoveries #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/506312
published as Astrophys.J.649:1048-1063,2006 · 15 pages, 7 figures; accepted for publication in the Astrophysical Journal. Please see [http://www.lpl.arizona.edu/~curtis/research/publications/] for a PDF version with high-resolution figures (about a 2.1MB download)
arxiv created 2006/05/30 · openalex publication_date 2006/09/27 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
Chemical equilibrium considerations suggest that, assuming solar elemental abundances, carbon on HD 209458b is sequestered primarily as carbon monoxide (CO) and methane (CH 4 ). The relative mole fractions of CO(g) and CH 4 (g) in chemical equilibrium are expected to vary greatly according to variations in local temperature and pressure. We show, however, that in the p = 1-1000 mbar range, chemical equilibrium does not hold. To explore disequilibrium effects, we couple the chemical kinetics of CO and CH 4 to a three-dimensional numerical model of HD 209458b's atmospheric circulation. These simulations show that vigorous dynamics caused by uneven heating of this tidally locked planet homogenize the CO and CH 4 concentrations at p < 1 bar, even in the presence of lateral temperature variations of ~500-1000 K. In the 1-1000 mbar pressure range we find that over 98% of the carbon is in CO. This is true even in cool regions where CH 4 is much more stable thermodynamically. Our work shows, furthermore, that planets 300-500 K cooler than HD 209458b can also have abundant CO in their upper layers due to disequilibrium effects. We demonstrate several interesting observational consequences of these results.