skip to main content

Title: Electron densities and alkali atoms in exoplanet atmospheres

We describe a detailed study on the properties of alkali atoms in extrasolar giant planets, and specifically focus on their role in generating the atmospheric free electron densities, as well as their impact on the transit depth observations. We focus our study on the case of HD 209458b, and we show that photoionization produces a large electron density in the middle atmosphere that is about two orders of magnitude larger than the density anticipated from thermal ionization. Our purely photochemical calculations, though, result in a much larger transit depth for K than observed for this planet. This result does not change even if the roles of molecular chemistry and excited state chemistry are considered for the alkali atoms. In contrast, the model results for the case of exoplanet XO-2b are in good agreement with the available observations. Given these results we discuss other possible scenarios, such as changes in the elemental abundances, changes in the temperature profiles, and the possible presence of clouds, which could potentially explain the observed HD 209458b alkali properties. We find that most of these scenarios cannot explain the observations, with the exception of a heterogeneous source (i.e., clouds or aerosols) under specific conditions, but wemore » also note the discrepancies among the available observations.« less
Authors:
 [1] ; ;  [2]
  1. GSMA, Université de Reims Champagne Ardenne, CNRS UMR 7331, Reims, 51687 France (France)
  2. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85719 (United States)
Publication Date:
OSTI Identifier:
22370203
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 796; 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; AEROSOLS; ALKALI METALS; ASTROPHYSICS; ATOMS; DENSITY; ELECTRON DENSITY; ELEMENT ABUNDANCE; EXCEPTIONS; EXCITED STATES; PHOTOCHEMISTRY; PHOTOIONIZATION; PLANETS; SATELLITE ATMOSPHERES; SATELLITES