Morphology of the UV aurorae Jupiter during Juno's first perijove observations

Abstract

On 27 August 2016, the NASA Juno spacecraft performed its first close‐up observations of Jupiter during its perijove. Here we present the UV images and color ratio maps from the Juno‐UVS UV imaging spectrograph acquired at that time. Data were acquired during four sequences (three in the north, one in the south) from 5:00 UT to 13:00 UT. From these observations, we produced complete maps of the Jovian aurorae, including the nightside. The sequence shows the development of intense outer emission outside the main oval, first in a localized region (255°–295° System III longitude) and then all around the pole, followed by a large nightside protrusion of auroral emissions from the main emission into the polar region. Some localized features show signs of differential drift with energy, typical of plasma injections in the middle magnetosphere. Finally, the color‐ratio map in the north shows a well‐defined area in the polar region possibly linked to the polar cap.

Jovian Auroral Ion Precipitation: Field‐Aligned Currents and Ultraviolet Emissions

“…Since these lower‐energy ions do not penetrate very deep in the atmosphere, it is then easier for the secondary electrons produced to escape and contribute to the downward current system close to the planet. This lower‐energy range was not previously considered with the ion precipitation model. Airglow emissions produced by ion precipitation are low compared to the main auroral oval emission (only ~100 kR) but are still significant enough to contribute some of the observed emission. Color ratios computed for ion energies responsible for the X‐ray emissions are ~10, which is comparable to recent color ratio observations of the UV aurora by Juno (Bonfond et al, ). However, polar atmospheric abundances, particularly CH 4 , need to be investigated further, as there have been many attempts from others at modeling this (Gérard et al, ; Grodent et al, ; Moses et al, ).…”

“…Observations made by the Hubble Space Telescope were interpreted using color ratio, which allowed incident electron energies to be estimated (Gérard et al, ). This has been followed by color ratio measurements made by the UV spectrometer on board the Juno spacecraft (Bonfond et al, ; Connerney et al, ; Gladstone et al, ). Both Gérard et al () and Bonfond et al () have shown color ratios between 1 and 20 for the Juno UV observations.…”

“…This has been followed by color ratio measurements made by the UV spectrometer on board the Juno spacecraft (Bonfond et al, ; Connerney et al, ; Gladstone et al, ). Both Gérard et al () and Bonfond et al () have shown color ratios between 1 and 20 for the Juno UV observations. In the current paper, we include color ratio, as well as overall airglow intensity, for both ion and electron precipitation models.…”

Jovian Injections Observed at High Latitude

“…The UVS false‐color image is of the northern ultraviolet aurora. UVS is described by Gladstone et al (), and analysis of UVS images is presented by Bonfond et al (). The different colors correspond to different UVS spectral bands, which are interpreted (see also Gérard et al, ) as corresponding to different energies for the electrons striking the atmosphere, with red corresponding to high energies, green to intermediate energies, and blue to lower energies; white indicates a mix of energies.…”

Intervals of Intense Energetic Electron Beams Over Jupiter's Poles

“…We have found good correlation between the swirl times from UVS and the very intense beams of JEDI (with few or no counterexamples to date). The swirl region has been described as a patchy area of low brightness and high absorption in the polar region that presumably connects to the most “open” magnetic field lines connecting to Jupiter (Bonfond et al, ). But as noted above, more work on the relevant physical processes needs to be done to link these interesting observations.…”