Observation and feature measurements of cloud and haze in exoplanet atmosphere based on transmission spectra

Abstract

Clouds and hazes are important components of exoplanet atmospheres. This paper generalizes features and applications of exoplanet clouds and hazes in transmission spectra. A transmission spectrum presents a planet atmosphere’s wavelength-dependent absorption ability of host star’s radiation during transit. Effective transit radius model is often adopted to explain the wavelength-dependent absorption. In spectrum processing, the effect of stellar limb darkening and star spots should be taken into consideration. Clouds and hazes change features of planet transmission spectrums considerably, e.g., clouds reduce or eliminate absorption features on all bands observed. Since hazes (with small sizes) produce Rayleigh scattering, their reduction in absorption depth is greater in optical band than in infrared band. As transmission spectrum provides limited data about exoplanet atmospheres, emission and reflection spectrum during secondary transit should receive more observation. JWST will perform well in all forms of atmospheric spectrum observation. Advanced knowledge about clouds and hazes will benefit the confine of exoplanet atmospheres’ chemical composition, biosignatures, meteorology as well as planet evolvement model. These results shed light on guiding further exploration of exoplanets and life possibilities on them.