Role of carbon dioxide in cooling planetary thermospheres

The role of carbon dioxide in cooling the thermospheres of Earth, Venus, and Mars is well recognized (Gordiets et al, 1982; Dickinson, 1984; Dickinson et al, 1987; Dickinson and Bougher, 1986; Bougher and Dickinson, 1988). During a collision of CO{sub 2} with atomic and molecular species, some of the translational energy of relative motion (heat) is converted into vibrational energy of the lowest-lying mode, the bending mode, {nu}{sub 2}. This vibrational energy is subsequently radiated at 15 {mu}m. Many of these photons escape to space, cooling the atmosphere. A new value of the rate coefficient for the deactivation of the bending mode of carbon dioxide by atomic oxygen at low temperatures is derived from the observation of 15 {mu}m emission from the atmosphere of the Earth. This new value gives a cooling rate for the lower thermosphere that is two to three times the rate previously calculated, and it may resolve a long-standing problem in the Mars-Venus aeronomy.