The extreme ultraviolet airglow of N2 Atmospheres

Abstract

Abstract : Extreme ultraviolet (EUV) airglow observations at Titan, Triton and Earth provide a rigorous test for models of N2 atmospheres. This is primarily because the emissions are produced in dramatically different environments. EUV spectra obtained by the Voyager Ultraviolet Spectrometer (UVS) at Titan and Triton are dominated by emission arising from electron impact on N2 and by photodissociative ionization of N2. Spectral analyses of the UVS data originally showed that the N2 Carroll-Yoshino (CY) (0,0) band near 95.86 nm, the (0,1) band near 98.05 nm and the NII 108.5 nm multiplet are the brightest EUV airglow features. But the detailed processes leading to their intensity distribution are only now becoming clear. Model results have shown that the (0,0) band is optically thick and that photoelectron excitation followed by multiple scattering redistributes nearly all (0,0) band emission to the (0, 1) band. Summing all emissions from other N2 bands and NI multiplets near the (0,0) band excited by the solar EUV and X-ray irradiance indicated that the (0,0) band was misidentified. Many of these other emissions are now identified in new high resolution terrestrial airglow spectra. The distribution of EUV airglow intensity at Triton is different than at Titan and new results are presented here from the same multiple scattering model adapted to Triton. It is found that the ratio of the (0,1) band to the blended emission near the (0,0) band is higher at Triton than at Titan and that the integrated intensity between 94.2-99.6 nm is 2.6 R at Triton. all consistent with UVS observations.