2014/03/31 by Caroline V. Morley, Mark S. Marley, Jonathan J. Fortney +4 · 1 voice · 2 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Scientific Research and Discoveries #Stellar, planetary, and galactic studies #astro-ph.EP #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/787/1/78
openalex publication_date 2014/05/06 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The formation of clouds affects brown dwarf and planetary atmospheres of nearly all effective temperatures. Iron and silicate condense in L dwarf atmospheres and dissipate at the L/T transition. Minor species such as sulfides and salts condense in mid-late T dwarfs. For brown dwarfs below Teff=450 K, water condenses in the upper atmosphere to form ice clouds. Currently over a dozen objects in this temperature range have been discovered, and few previous theoretical studies have addressed the effect of water clouds on brown dwarf or exoplanetary spectra. Here we present a new grid of models that include the effect of water cloud opacity. We find that they become optically thick in objects below Teff=350-375 K. Unlike refractory cloud materials, water ice particles are significantly non-gray absorbers; they predominantly scatter at optical wavelengths through J band and absorb in the infrared with prominent features, the strongest of which is at 2.8 microns. H2O, NH3, CH4, and H2 CIA are dominant opacity sources; less abundant species such as may also be detectable, including the alkalis, H2S, and PH3. PH3, which has been detected in Jupiter, is expected to have a strong signature in the mid-infrared at 4.3 microns in Y dwarfs around Teff=450 K; if disequilibrium chemistry increases the abundance of PH3, it may be detectable over a wider effective temperature range than models predict. We show results incorporating disequilibrium nitrogen and carbon chemistry and predict signatures of low gravity in planetary- mass objects. Lastly, we make predictions for the observability of Y dwarfs and planets with existing and future instruments including the James Webb Space Telescope and Gemini Planet Imager.