Non-LTE CO limb emission at 4.7 μm in the upper atmosphere of Venus, Mars and Earth: Observations and modeling

We report here on CO limb observations in Mars, Venus and Earth and their model simulations. A comparative study of the CO emission, including the most recent spacecraft observations of the three planets' atmospheres, has been performed. Strong daytime emissions near 4.7μm have been recently observed in the limb of the upper atmosphere of the three terrestrial planets by the Planetary Fourier Spectrometer on Mars Express (Formisano et al., 2005), the Visible and Infrared Thermal Imaging Spectrometer on Venus Express (Drossart et al., 2007), and the Michelson Interferometer for Passive Atmosphere Sounding on Envisat (Fischer et al., 2008). Those emissions are produced by solar pumping of molecular vibrations and non-local thermodynamic equilibrium (non-LTE) models are used to explain them in a consistent framework for the three atmospheres. The maximum of the 4.7μm emission occurs on Venus between 90 and 110 km, on Mars above 60 km, and on Earth around 68 km. The observations show that the fundamental band dominates the CO non-LTE emission on Earth, while on Venus and Mars the larger contribution comes from the first hot band transition. The main goal of this study is to understand those differences and similarities with the help of theoretical simulations with optical thickness considerations, and compare the capability of space instrumentation for the remote sounding of the atmospheres in this spectral region. © 2010 Elsevier Ltd.