Transient brightening of Jupiter's aurora observed by the Hisaki satellite and Hubble Space Telescope during approach phase of the Juno spacecraft

Abstract

In early 2014, continuous monitoring with the Hisaki satellite discovered transient auroral emission at Jupiter during a period when the solar wind was relatively quiet for a few days. Simultaneous imaging made by the Hubble Space Telescope (HST) suggested that the transient aurora is associated with a global magnetospheric disturbance that spans from the inner to outer magnetosphere. However, the temporal and spatial evolutions of the magnetospheric disturbance were not resolved because of the lack of continuous monitoring of the transient aurora simultaneously with the imaging. Here we report the coordinated observation of the aurora and plasma torus made by Hisaki and HST during the approach phase of the Juno spacecraft in mid‐2016. On day 142, Hisaki detected a transient aurora with a maximum total H2 emission power of ~8.5 TW. The simultaneous HST imaging was indicative of a large “dawn storm,” which is associated with tail reconnection, at the onset of the transient aurora. The outer emission, which is associated with hot plasma injection in the inner magnetosphere, followed the dawn storm within less than two Jupiter rotations. The monitoring of the torus with Hisaki indicated that the hot plasma population increased in the torus during the transient aurora. These results imply that the magnetospheric disturbance is initiated via the tail reconnection and rapidly expands toward the inner magnetosphere, followed by the hot plasma injection reaching the plasma torus. This corresponds to the radially inward transport of the plasma and/or energy from the outer to the inner magnetosphere.

Response of Jupiter's Aurora to Plasma Mass Loading Rate Monitored by the Hisaki Satellite During Volcanic Eruptions at Io

“…The disappearance of the recurrent aurora on DOY −17 could also be associated with the decrease in the mass loading from DOY −34 to DOY 0. These observational results do not contradict implications that the transient aurora and energetic event are likely associated with the mass loading and are basically independent of the solar wind; that is, they are “internally driven” processes, as recently argued in Kimura et al (, ) and other studies.…”

“…This correspondence implies that the transient aurora is, in some cases, forced to occur due to the solar wind disturbance. On DOY 142 in 2017, when Juno detected a solar wind forward shock arriving at Jupiter, Hisaki observed the transient aurora with one of the largest peak powers that has been measured through the entire Hisaki observing period from November 2013 to July 2016 (Kimura et al, ; Nichols et al, ). This solar wind associated brightening was also fragmentally observed by Cassini (Tsuchiya et al, ), supporting the idea suggested by the present study that the transient aurora is correlated with the solar wind disturbance.…”

“…Recently, continuous monitoring of EUV aurora with Hisaki has indicated that auroral brightening with durations of less than 10 h recur at a frequency of every few days (Kimura et al, , ). In this study, a “transient aurora” refers to an impulsive brightening with typical duration less than 10 h. Transient auroral events occurred during periods when the solar wind was relatively quiet.…”

“…In this study, a “transient aurora” refers to an impulsive brightening with typical duration less than 10 h. Transient auroral events occurred during periods when the solar wind was relatively quiet. Kimura et al (, ) argued that the transient auroral is “internally‐driven” by internal plasma supply from Io and Jupiter's rotation. Auroral imaging by the Hubble space telescope during the transient aurora showed enhancement of poleward auroral structures, which is related to the solar wind interaction, and dawn‐storm‐like structure (Clarke et al, , ; Nichols et al, ), which were followed by outer emissions within a few hours (Badman et al, ; Gray et al, ; Kimura et al, ; Nichols et al, ).…”

Juno's first glimpse of Jupiter's complexity

“…Meanwhile, JAXA's Hisaki satellite has been monitoring UV emissions from the Io plasma torus and Jovian auroral emissions since 2013. Kimura et al [] report on Hisaki observations made, while Juno was approaching Jupiter. They show a similar brightening of the aurora on 21 May 2016 as reported by Nichols et al [] in response to a solar wind compression region.…”