Abstract
AbstractA large set of observations of Jupiter's ultraviolet aurora was collected with the Hubble Space Telescope concurrently with the NASA‐Juno mission, during an eight‐month period, from 30 November 2016 to 18 July 2017. These Hubble observations cover Juno orbits 3 to 7 during which Juno in situ and remote sensing instruments, as well as other observatories, obtained a wealth of unprecedented information on Jupiter's magnetosphere and the connection with its auroral ionosphere. Jupiter's ultraviolet aurora is known to vary rapidly, with timescales ranging from seconds to one Jovian rotation. The main objective of the present study is to provide a simplified description of the global ultraviolet auroral morphology that can be used for comparison with other quantities, such as those obtained with Juno. This represents an entirely new approach from which logical connections between different morphologies may be inferred. For that purpose, we define three auroral subregions in which we evaluate the auroral emitted power as a function of time. In parallel, we define six auroral morphology families that allow us to quantify the variations of the spatial distribution of the auroral emission. These variations are associated with changes in the state of the Jovian magnetosphere, possibly influenced by Io and the Io plasma torus and by the conditions prevailing in the upstream interplanetary medium. This study shows that the auroral morphology evolved differently during the five ~2 week periods bracketing the times of Juno perijove (PJ03 to PJ07), suggesting that during these periods, the Jovian magnetosphere adopted various states.
Highlights
The National Aeronautics and Space Administration (NASA) Juno spacecraft began its prime mission on 4 July 2016 when it started orbiting Jupiter on a highly elliptical 53-day polar trajectory (Bolton et al, 2017; Connerney et al, 2017)
The main objective of the present study is to provide a simplified description of the global ultraviolet auroral morphology that can be used for comparison with other quantities, such as those obtained with Juno
This study shows that the auroral morphology evolved differently during the five ~2 week periods bracketing the times of Juno perijove (PJ03 to PJ07), suggesting that during these periods, the Jovian magnetosphere adopted various states
Summary
The National Aeronautics and Space Administration (NASA) Juno spacecraft began its prime mission on 4 July 2016 when it started orbiting Jupiter on a highly elliptical 53-day polar trajectory (Bolton et al, 2017; Connerney et al, 2017). Juno skims above Jupiter’s atmosphere at an altitude as low as 3,500 km above the cloud tops, while at the most distant point of its orbit, Juno reaches distances in excess of 100 RJ (1 RJ = 1 Jupiter Radius = 71,492 km) On every orbit, it rapidly passes over both polar regions at an altitude of a few Jovian radii, which is providing us with unprecedented viewing geometries of Jupiter’s auroral emissions, while simultaneously measuring the particles and fields from whence the emissions originate. It should be noted that the poleward and equatorward (antipoleward) directions that we are using throughout this study for both hemispheres relate to the position of the magnetic pole, which we consider to be close to the geometric center of the ME contour All these emissions relate to specific processes taking place in Jupiter’s enormous magnetosphere. This HST campaign completes the local in situ information captured by Juno particles and field instruments and complements the Juno remote sensing instruments (see Bagenal et al, 2014; Bolton et al, 2017; Connerney et al, 2017; Mauk et al, 2017, and references therein, for the Magnetometer, Radio and Plasma Wave Sensor, Jovian Auroral Distributions Experiment, Jupiter Energetic particle Detector Instrument, Jupiter Infrared Auroral Mapper, JunoCam, and Microwave Radiometer instruments), the Ultraviolet Spectrograph (UVS) (Gladstone et al, 2014, 2017)
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