Ly-α Dayglow on Uranus : Radiative Transfer Modelling

Abstract: Uranus is one of the least explored planets in our solar system. Event though the Uranian Ly-α emission has been a subject of study for decades, there is not a consensus on the sources contribution to the total signal. This thesis aims to analyse the contribution from scattering of the solar flux to the Uranian Ly-α dayglow by solving the radiative transfer equation in a parameter study for the atmosphere. The sources are solar Ly-α resonant scattering and Rayleigh scattering by atomic and molecular hydrogen respectively. The radiative transfer equation is solved using the Feautrier Method Program, a program written by Randall G. Gladstone. The program was adjusted to the Uranian atmosphere and modelled with different variations in parameters, including the atmospheric temperature and particle density of Ly-α scatterers and absorbers. A parameter study is performed to investigate the dependency on the Ly-α signal on these parameters. The results showed a significant Ly-α limb brightening with a maximum intensity located around 400 km outside one planetary radius as seen from the disk center. The contributions to the Ly-α dayglow from Rayleigh scattering by H2 was calculated to be 160 R whereas the contribution from resonant scattering by H was 550 R. One feature that prevents direct comparison to observed data with this thesis is that some sources that contributes to Uranus Ly-α signal are omitted in the simulations.