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Paper: Characterizing Exoplanet Atmospheres and Surfaces
Volume: 430, Pathways Towards Habitable Planets
Page: 65
Authors: Encrenaz, T.
Abstract: After more than twelve years of successful campaigns leading to the detection of several hundreds of exoplanets, it is now possible to determine, for some of them, the spectroscopic properties of their atmospheres. In the present paper, our knowledge of solar system planets is used to try to extrapolate what kind of atmosphere can be expected for a given exoplanet, on the basis of its mass, its asterocentric distance, and the spectral type of its host star. This simple classification leads to three main categories of exoplanets: (1) the rocky planets (less than 10 terrestrial masses and within the snow line), (2) the icy planets (below 10 terrestrial masses and beyond the snow line), and (3) the giant planets (above 10 terrestrial masses). It is shown that the thermal spectrum of an exoplanet critically depends upon the existence (or the absence) of a stratosphere, which itself depends upon the exoplanet’s composition. The icy and giant planets (Jupiter-, Neptune-, or Titan-type) are expected to have a stratosphere as a result of the methane photodissociation. Rocky planets (Mars- and Venus-type) are expected to show no stratosphere except in the case of the presence of ozone (Earth-type). Typical spectra are shown for each class of object and a discussion is given about the resolving power needed for detecting atmospheric species and/or surface features.
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