Jupiter’s auroras are about to be observed simultaneously by three space observatories—the James Webb Space Telescope, Hubble, and NASA’s Juno probe—in a coordinated campaign that has never been possible before. The project targets a stubborn puzzle: Jupiter’s upper atmosphere is hundreds of degrees hotter than sunlight alone can explain. This “energy crisis” suggests that auroral processes dump far more heat into the planet than current models account for. The key molecule is H3+, which radiates heat away as infrared light, but no one knows how long it survives before decaying. Without that lifetime, the energy budget cannot be closed. The team will also search for a predicted “proton aurora” that Juno’s particle detectors have hinted at but no telescope has seen, and will map how the volcanic moon Io’s interaction with Jupiter’s magnetic field drives auroral flares. This is fundamental planetary science. There is no immediate practical application for Earth. But Jupiter acts as a natural laboratory for magnetosphere-atmosphere physics that applies to gas giants across the galaxy—including exoplanets we cannot yet visit. Understanding how auroral energy flows and dissipates in a planetary atmosphere could eventually inform models of space weather around other worlds, or reveal why some exoplanets glow in infrared wavelengths they should not.
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This project will study the auroras of Jupiter with an entirely new capability provided by the prestigious James Webb Space Telescope (JWST), in combination with the Hubble Space Telescope (HST), obtained in programmes led by the PI, along with further new HST observations from a Large Program on which he is a Co-I, and data from the NASA Juno mission, on which he is a Science Team Member. Using this unique dataset, this programme will yield fundamental discoveries regarding the nature of Jupiter’s auroras, the auroral ionosphere, and coupling with satellites. Jupiter provides an important laboratory for magnetosphere-atmosphere sciences with significance beyond the solar system. However, there remain fundamental gaps in our knowledge of the behaviour of Jupiter’s magnetosphere and auroral ionosphere. We do not understand how auroral energy is dissipated in the ionosphere and the role it plays in contributing to the “energy crisis” by which Jupiter’s non-auroral upper atmosphere is substantially hotter than expectation based on solar insolation alone, nor how Jupiter’s auroras are powered by moon-magnetosphere interactions. This project will target these fundamental questions. The molecular ion H3+ is thought to play a key role as a primary source of cooling via infrared radiation; however, its overall importance in the energy budget cannot be determined until the lifetime of auroral H3+ is well known. Using our powerful combination of simultaneous FUV and NIR H3+ observations, we will first discover and analyse the detailed H3+ emission morphology at an unprecedented spatial and temporal resolution, and then compare with FUV morphology to establish the nature of H3+ emission and its decay rate. We will go on to use H3+ and H2 spectra, in order to produce time-varying multi-altitude ionospheric temperature maps and H3+ densities, and hence determine the lifetime of auroral H3+. Using the H2 spectral scans, we will then either discover the elusive proton aurora that should result from downward proton beams observed by Juno, or place very tight limits on the contribution of protons to the FUV emission. Finally, we will determine the roles of Alfvén waves and magnetospheric currents in driving auroral emission associated with the Io-Jupiter interaction by examining HST FUV images of the Io footprint obtained during Juno Io flybys, and at an unprecedented 3s resolution in the H3+ emission by JWST. Overall, the results will be a dramatic advance in our understanding of Jupiter’s auroral processes, and those of substellar objects in general.
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