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On the excitation of Io's atmosphere by the photoelectrons: Application of the analytical yield spectral model of SO 2
Author(s) -
Bhardwaj Anil,
Michael Marykutty
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1998gl900320
Subject(s) - photoelectric effect , brightness , atomic physics , excitation , ionization , airglow , atmosphere (unit) , excited state , atmospheric models , physics , altitude (triangle) , yield (engineering) , ionosphere , intensity (physics) , atmospheric sciences , ion , optics , meteorology , geophysics , geometry , mathematics , quantum mechanics , thermodynamics
The analytical yield spectral model is applied to the calculation of photoelectron fluxes, excitation rates, and photoelectron‐excited intensities of several neutral and ionized S and O UV emissions, and SO (240–265 nm) and SO 2 (264–430) band emissions in the atmosphere of Io. Most of the OI emission intensity is produced in the e‐O direct collisional‐excitation rather than in the e‐SO 2 dissociative excitation process. Using the existing models of Io's atmosphere the calculated brightness of neutral O and S emissions on Io is found to be 2 to 3 orders of magnitude smaller compared to the HST‐observed intensity. We have shown that larger intensities can be produced on increasing the densities of the atmospheric species, particularly the atomic species: a model where O dominates over SO 2 above a few tens of km altitude can explain 10–30% of the HST brightness. Our model calculations have demonstrated that it is possible to explain the HST‐observed brightness provided that (a) the Io's atmospheric densities are much larger (>factor of 10) and more extended in altitude than those predicted by the existing models, and (b) there is a mechanism to accelerate the ionospheric photoelectrons to energies ∼100 eV. Otherwise, there should be some other source of the production of these emissions on Io.