Volume 534, October 2011
|Number of page(s)||9|
|Section||Planets and planetary systems|
|Published online||03 October 2011|
Clouds in the atmospheres of extrasolar planets
III. Impact of low and high-level clouds on the reflection spectra of Earth-like planets
Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
2 Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Rutherfordstr. 2, 12489 Berlin, Germany
Received: 30 May 2011
Accepted: 2 August 2011
Context. Owing to their wavelength dependent absorption and scattering properties, clouds have an important influence on spectral albedos and planetary reflection spectra. In addition, the spectral energy distribution of the incident stellar light determines the detectable absorption bands of atmospheric molecules in these reflection spectra.
Aims. We study the influence of low-level water and high-level ice clouds on low-resolution reflection spectra and planetary albedos of Earth-like planets orbiting different types of stars in both the visible and near infrared wavelength range.
Methods. We use a one-dimensional radiative-convective steady-state atmospheric model coupled with a parametric cloud model, based on observations in the Earth’s atmosphere to study the effect of both cloud types on the reflection spectra and albedos of Earth-like extrasolar planets at low resolution for various types of central stars.
Results. We find that the high scattering efficiency of clouds causes both the amount of reflected light and the related depths of the absorption bands to be substantially larger than in comparison to the respective clear sky conditions. Low-level clouds have a stronger impact on the spectra than the high-level clouds because of their much larger scattering optical depth. The detectability of molecular features in near the UV – near IR wavelength range is strongly enhanced by the presence of clouds. However, the detectability of various chemical species in low-resolution reflection spectra depends strongly on the spectral energy distribution of the incident stellar radiation. In contrast to the reflection spectra the spectral planetary albedos enable molecular features to be detected without a direct influence of the spectral energy distribution of the stellar radiation. Here, clouds increase the contrast between the radiation fluxes of the planets and the respective central star by about one order of magnitude, but the resulting contrast values are still too low to be observable with the current generation of telescopes.
Key words: planets and satellites: atmospheres / atmospheric effects / astrobiology
© ESO, 2011
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