Disequilibrium Chemistry in a Brown Dwarf’s Atmosphere: Carbon Monoxide in Gliese 229b

The distribution of CO in Gliese 229B’s atmosphere reveals how disequilibrium processes establish the atmospheric composition. The CO abundance derived from its spectral signature exceeds the equilibrium value by several orders of magnitude. Our investigation of the source for CO considers disequilibrium mechanisms common to planetary atmospheres and concludes that the CO abundance is sensitive to atmospheric dynamics. Convection is not required to explain the observed abundance; instead, the vertical transport rate at ∼6 bars may be similar to that in planetary stratospheres. Subject headings: convection — planets and satellites: general — stars: atmospheres — stars: individual (Gliese 229B) — stars: low-mass, brown dwarfs