Fine-structure physical chemistry modeling of Uranus H2 X quadrupole emission

Abstract

A new hydrogen physical chemistry model has been developed at the fine-structure level for application to the giant outer planet thermospheres. The model is applied to Uranus because observations of dayglow H2 X 1∑g+ (v) quadrupole and H3+ vibration-rotation emission made at NASA IRTF and UKIRT provide critical constraints for thermospheric modeling. The observed H3+ vibration-rotation emission infers an H3+ dominant ionosphere, predicted only for non-LTE H2 X (v : J). Excitation mechanisms explored are solar and non-solar electron energy deposition. Non-solar electron forcing is constrained by the EUV H2 Lyman and Werner band emission measured by Voyager UVS. Analysis indicates that non-solar electrons are dominant in the energy budget required to predict the observed thermospheric temperature profile. The modeled H2 X quadrupole emission infers that an additional mechanism is required to excite the H2 X (v = 1) population. Non-thermal H produced in dissociative excitation of H2 X is a primary candidate. Copyright 2005 by the American Geophysical Union.