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Title: Constraining the atmospheric composition of the day-night terminators of HD 189733b: Atmospheric retrieval with aerosols

A number of observations have shown that Rayleigh scattering by aerosols dominates the transmission spectrum of HD 189733b at wavelengths shortward of 1 μm. In this study, we retrieve a range of aerosol distributions consistent with transmission spectroscopy between 0.3-24 μm that were recently re-analyzed by Pont et al. To constrain the particle size and the optical depth of the aerosol layer, we investigate the degeneracies between aerosol composition, temperature, planetary radius, and molecular abundances that prevent unique solutions for transit spectroscopy. Assuming that the aerosol is composed of MgSiO{sub 3}, we suggest that a vertically uniform aerosol layer over all pressures with a monodisperse particle size smaller than about 0.1 μm and an optical depth in the range 0.002-0.02 at 1 μm provides statistically meaningful solutions for the day/night terminator regions of HD 189733b. Generally, we find that a uniform aerosol layer provide adequate fits to the data if the optical depth is less than 0.1 and the particle size is smaller than 0.1 μm, irrespective of the atmospheric temperature, planetary radius, aerosol composition, and gaseous molecules. Strong constraints on the aerosol properties are provided by spectra at wavelengths shortward of 1 μm as well as longward of 8more » μm, if the aerosol material has absorption features in this region. We show that these are the optimal wavelengths for quantifying the effects of aerosols, which may guide the design of future space observations. The present investigation indicates that the current data offer sufficient information to constrain some of the aerosol properties of HD189733b, but the chemistry in the terminator regions remains uncertain.« less
Authors:
 [1] ; ; ;  [2] ;  [3]
  1. Institute for Computational Science, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich (Switzerland)
  2. Department of Atmospheric, Oceanic, and Planetary Physics, University of Oxford, OX1 3PU Oxford (United Kingdom)
  3. Center for Space and Habitability, University of Bern, Sidlerstrasse 5, CH-3012 Bern (Switzerland)
Publication Date:
OSTI Identifier:
22356511
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 789; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABUNDANCE; AMBIENT TEMPERATURE; DISTRIBUTION; LAYERS; MAGNESIUM SILICATES; MOLECULES; PARTICLE SIZE; PLANETS; RAYLEIGH SCATTERING; SATELLITE ATMOSPHERES; SPACE; SPECTRA; SPECTROSCOPY; WAVELENGTHS