The Upper Atmosphere of Jupiter

Donald M. Hunten Kilt Peak National Observatory, Tucson, Arig.

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Abstract

The aeronomy of Jupiter's atmosphere at pressures <25 mb is surveyed. Attention is drawn to those areas most in need of further work, including both planetary and laboratory studies. The heat balance is still uncertain at nearly all heights. Potential stratospheric heat sources are under consideration, and their presence is suggested by the probable existence of emission features of methane in the infrared and ammonia at radio wavelengths. The thermal emissivity at the mesopause is highly uncertain, and this uncertainty propagates throughout the thermosphere to the exosphere. The photochemistry of methane and ammonia is beginning to receive serious attention, but many difficulties remain. There is still a strong possibility that local photochemical equilibrium cannot exist, and that exchange with the lower atmosphere is essential for a steady state. The photochemistry of H2 is much more satisfactory; the model can be checked against the observed Lyman-α albedo, and an effective eddy diffusion coefficient can be derived, similar to that for earth. A model ionosphere is given, but there are serious uncertainties connected with the loss processes for H+ and He+.

Abstract

The aeronomy of Jupiter's atmosphere at pressures <25 mb is surveyed. Attention is drawn to those areas most in need of further work, including both planetary and laboratory studies. The heat balance is still uncertain at nearly all heights. Potential stratospheric heat sources are under consideration, and their presence is suggested by the probable existence of emission features of methane in the infrared and ammonia at radio wavelengths. The thermal emissivity at the mesopause is highly uncertain, and this uncertainty propagates throughout the thermosphere to the exosphere. The photochemistry of methane and ammonia is beginning to receive serious attention, but many difficulties remain. There is still a strong possibility that local photochemical equilibrium cannot exist, and that exchange with the lower atmosphere is essential for a steady state. The photochemistry of H2 is much more satisfactory; the model can be checked against the observed Lyman-α albedo, and an effective eddy diffusion coefficient can be derived, similar to that for earth. A model ionosphere is given, but there are serious uncertainties connected with the loss processes for H+ and He+.

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