English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We address disequilibrum abundances of some simple molecules in theatmospheres of solar composition brown dwarfs and self-luminous extrasolargiant planets using a kinetics-based 1D atmospheric chemistry model. Ourapproach is to use the full kinetics model to survey the parameter space witheffective temperatures between 500 K and 1100 K. In all of these worldsequilibrium chemistry favors CH4 over CO in the parts of the atmosphere thatcan be seen from Earth, but in most disequilibrium favors CO. The small surfacegravity of a planet strongly discriminates against CH4 when compared to anotherwise comparable brown dwarf. If vertical mixing is like Jupiter's, thetransition from methane to CO occurs at 500 K in a planet. Sluggish verticalmixing can raise this to 600 K; but clouds or more vigorous vertical mixingcould lower this to 400 K. The comparable thresholds in brown dwarfs are$1100\pm100$ K. Ammonia is also sensitive to gravity, but unlike CH4/CO, theNH3/N2 ratio is insensitive to mixing, which makes NH3 a potential proxy forgravity. HCN may become interesting in high gravity brown dwarfs with verystrong vertical mixing. Detailed analysis of the CO-CH4 reaction networkreveals that the bottleneck to CO hydrogenation goes through methanol, inpartial agreement with previous work. Simple, easy to use quenching relationsare derived by fitting to the complete chemistry of the full ensemble ofmodels. These relations are valid for determining CO, CH4, NH3, HCN, and CO2abundances in the range of self-luminous worlds we have studied but may notapply if atmospheres are strongly heated at high altitudes by processes notconsidered here (e.g., wave breaking).

Methane, Carbon Monoxide, and Ammonia in Brown Dwarfs and Self-Luminous Giant Planets