Variability of Lyman-alpha emission from Jupiter

The Jovian Lyman-alpha emission line was reobserved in 1978 March using the high-resolution spectrometer of the Copernicus satellite. An intensity of 8.3 plus or minus 2.9 kilorayleighs was measured. This value represents a significant increase in intensity over previous (1976) Copernicus observations, but is lower than the recent (1979) values obtained by Voyager 1 and IUE. The increase in intensity has been accompanied by a significant increase in line width giving strong support to the theory that the emission results from resonant scattering of the solar Lyman-alpha line by H atoms in the upper Jovian atmossphere. The strength of Jovian Lyman-alpha emission correlates well with the level of solar activity. The solar extreme ultraviolet radiation varies with the solar cycle. This radiation causes the dissociation of H2 and CH4 into H atoms in the Jovian atmosphere. Therefore, in times of high solar activity, the H column density will increase, causing the observed strong Jovian Lyman-alpha emission.