A NON-LTE MODEL FOR THE JOVIAN METHANE INFRARED EMISSIONS AT HIGH-SPECTRAL-RESOLUTION

High resolution spectra of Jupiter in the 3.3 mum region have so far failed to reveal either the continuum or the line emissions that can be unambiguously attributed to the nu3 band of methane (Drossart et al. 1993; Kim et al. 1991). nu3 line intensities predicted with the help of two simple non-LTE models-a two-level model and a three-level model, using experimentally determined relaxation coefficients, are shown to be one to three orders of magnitude respectively below the 3sigma noise level of these observations. Predicted nu4 emission intensities are consistent with observed values. If the methane mixing ratio below the homopause is assumed as 2 x 10(-3), a value of about 300 K is derived as an upper limit to the temperature of the high stratosphere at microbar levels.