An explanation for the H Ly α longitudinal asymmetry in the equatorial spectrum of Jupiter: An outcrop of paradoxical energy deposition in the exosphere

An analysis of the Voyager EUV spectra of the Jupiter sunlit equatorial emissions shows no evidence for a substantial dependence of atomic hydrogen abundance on magnetic longitude, required by earlier theories of the H Ly α longitudinal asymmetry. An explanation for the H Ly α bulge phenomenon is advanced in this work that conforms to the observations and does not require a strong asymmetry in atomic hydrogen abundance. It is proposed that the H Ly α bulge is caused by a combination of proton collisional transfer of H(2s) atoms into the H(2p) state, and production through recombination of H 2 + and H 3 + , in an asymmetric ionosphere. The asymmetry in the ionosphere is presumably caused by Jupiter's magnetic anomaly. The processes producing the H Ly α bulge require a negligible amount of directly applied energy. However, the phenomenon is a symptom of a process of substantial deposition of energy in the exosphere, forming the major source for ionospheric particles and contributing substantially to the upper atmospheric temperature. According to the present model a large fraction of the observed H Ly α emission from the equatorial region is electron excited, at least at times of solar maximum. Other related phenomena and quantities required to maintain the H Ly α asymmetry are discussed in the text.