Uncovering local magnetospheric processes governing the morphology and variability of Ganymede's aurora using three‐dimensional multifluid simulations of Ganymede's magnetosphere

Abstract

We investigate local magnetospheric processes governing the morphology and variability of Ganymede's aurora depending on its position with respect to the center of the Jovian plasma sheet. We couple an existing three-dimensional multifluid simulation to a new aurora brightness model developed for this study. With this, we are able to qualitatively and quantitatively show that the short-and long-period variabilities observed in Ganymede's auroral footprint at Jupiter are also predicted to be present in the brightness and morphology of the aurora at Ganymede. We also examine the relationship between acceleration structures and precipitation of electrons in Ganymede's neutral atmosphere by looking at the component of the electric field parallel to Ganymede's magnetic field. Our results confirm that regions of electron accelerations coincide with regions of brightest auroral emissions, as expected. Finally, we identify the likely source regions of electrons generating the aurora at Ganymede and discuss the plasma dynamic mechanisms likely responsible for these accelerations.

Electron Physics in 3‐D Two‐Fluid 10‐Moment Modeling of Ganymede's Magnetosphere

“…Both bands, particularly the ion band, approximately agree with in situ measurements by HST, reproduced in the bottom panel of Figure . They are also consistent with Figure 4 of Payan et al () from multi‐ion MHD simulations with a more realistic brightness model, particularly the case where the moon is near the center of the Jovian plasma sheet, which is consistent with our simulation setup (flyby G8).…”

“…Paty et al used multi‐ion MHD model to study how different ion species are supplied at the ionosphere and convected and energized in the magnetosphere (Paty & Winglee, , ; Paty et al, ). They further developed a brightness model to understand the morphology of Ganymede's auroral oval (Payan et al, ). Later, Dorelli et al () showed that introduction of Hall effect in an MHD model produced significant asymmetry in plasma flow paths and modified the local field line topology.…”

New Results From Galileo's First Flyby of Ganymede: Reconnection‐Driven Flows at the Low‐Latitude Magnetopause Boundary, Crossing the Cusp, and Icy Ionospheric Escape

“…In the cusp, energetic (∼keV) precipitating ions were observed, and plasma flows became strongly field‐aligned, flowing downward into the surface of the moon. The location of the cusp crossing is consistent with both multifluid simulations by Payan et al () and observations by the Hubble Space Telescope by McGrath et al ().…”

“…Consistent with passage through the cusp, just prior to entering the polar cap, ion flow velocities shifted to become highly field aligned, flowing down toward the surface of the moon, and the energy spectrogram shows signs of energized (∼ keV) precipitating ions. The location of this proposed cusp crossing ( latitude, longitude, G‐Phi‐Omega) is consistent with the of Ganymede's auroral oval in both three‐dimensional multifluid simulations by Payan et al () and observations by the Hubble Space Telescope (McGrath et al, ).…”

Photochemistry-emission coupled model for Europa and Ganymede

“…The observations of the auroral ovals as observed in the UV might also be used to characterize the subsurface ocean (Saur et al 2015). Numerous modeling studies have showed that electron impact is the dominant dissociation mechanism of O 2 (Saur et al 1998;Eviatar et al 2001;Payan et al 2015), leading to the generation of atomic oxygen in the O( Observations of emissions in the visible are also good parameters for determining the different energetic inputs coming in upper planetary atmospheres, i.e. solar UV photons and precipitating particles, with the green (557.7 nm) and reddoublet (630, 636.4 nm) lines coming from the deactivation of oxygen atoms in the O( 1 S) and O( 1 D) states, respectively.…”