Jupiter's aurora in ultraviolet and infrared: Simultaneous observations with the Hubble Space Telescope and the NASA Infrared Telescope Facility

摘要

We compare Jupiter's northern auroral emissions in infrared (IR) and ultraviolet (UV) using ground-based IR observations from the NASA Infrared Telescope Facility and UV observations from Hubble Space Telescope on 16 December 2000, the only date for which simultaneous observations in the two wavelength regions exist. We use polar projections and longitudinal brightness cuts to compare the IR (H3+ ions) and UV (H_2, H, and Lyman-alpha) aurorae, consisting of the main auroral emission, emission regions both poleward and equatorward of the main emission, and those associated with the Io footprint and its extended tail. We demonstrate that (1) the IR main emission and the equatorward diffuse emissions are generally good proxies for the UV and vice versa, (2) the spatial distribution and temporal behavior of UV and IR emissions within the main emission, at high magnetic latitudes, differ substantially, (3) UV and IR emissions associated with the Io interaction appear at the Io footprint and along an extended (downstream) tail but differ in relative brightness. While the UV aurora is excited directly, the IR aurora is a thermal emission, its intensity depends on both the number density of the H3+ions and the temperature. Three main factors may contribute to the observed morphological differences of the simultaneous emissions in the two wavelengths, namely ion transport, local heating, and the energy of the precipitating electrons. We estimate the H3+ ion transport distances, based on the ion lifetime and suggest that ion transport cannot account for large-scale morphological differences between the UV and IR emissions. We propose that neutral gas heating by particle precipitation and Joule heating locally enhances the H3+emission with no UV counterpart. Additionally, we estimate that local temperature variations are reflected in the IR emission with a time lag of several hours with respect to the UV. Finally, high precipitating electron energies exceeding a certain value might lead to chemical loss of the low altitude H3+ ions, suppress the lower IR emitting layers, and contribute to the observed differences of the emissions between the two wavelength regimes. Key Points Simultaneous comparison of UV and IR auroral emissions at JupiterUV main emission is good proxy for IR but it isn't the case for the polar region Joule heating and the precipitating electron energies explain the differences