Jovian Ion Research Articles

Jovian Periodicities (~10 h, ~40, 20, 15 min) at ACE, Upstream from the Earth’s Bow Shock, on 25–27 November 2003

It is known that Jovian radio and high energy electron emissions are observed near Earth. The question we address in this study is whether the quasi-periodic ~10 h and ~40/15–20 min (QP-10 h, QP-40/15–20 min) energetic particle and magnetic field periodicities observed by Ulysses during its distant encounter with Jupiter in 2003 were also detectable as far as the Earth’s orbit. Surprisingly, we found that at the end of the extreme 2003 Halloween events, during times of a highly disturbed Jovian magnetosphere, as inferred from strong bKOM radio emissions observed by Ulysses, and a magnetic connection of Earth with the Jovian magnetosphere, as suggested by simulation results of the interplanetary magnetic field (IMF), the ACE satellite observed, between at least 25–27 November 2013 at the Lagrangian Point L1 (LPL1), all the characteristic Jovian periodicities. In particular, by using high-time resolution data (1/5 min), we found, for the first time, quasi-permanent electron, and magnetic field QP-10/5 h, QP-40 min and QP-15/20 data variations at LPL1 for at least three days. These observations reasonably suggest that low energy (~50–~300 keV) Jovian electrons reached the Earth’s environment; the observations examined extend the lowest energy limit of the Jovian electron spectrum from 200 keV to ~50 keV. In addition, the ACE satellite observed an impressive series of QP-10/5 h energetic (≤0.05 MeV) ion bursts (EIBs) with strong cross-field intensity gradients at the onset/decay phase of the events and energy-dependent field aligned anisotropy suggesting ion streaming in the anti-sunward direction during their main phase. A comparison of simultaneously obtained measurements by ACE at the LPL1 and by Geotail upstream from the bow shock and in the magnetosphere suggests that the QP-10/5 h EIBs are inconsistent with the concept of a terrestrial origin. On the contrary, the observations indicate that the series of QP-10/5 h EIBs on 25–27 November 2003 was a spatial effect caused by the ~10/5 h quasi-periodic approach of a large-scale sheet to the Earth’s environment. The source of the ion population forming the QP-10/5 h sharp EIBs seems most probably Jovian ions accumulated in the interplanetary space, although a solar ion contribution is possible. Based on the above results, it is reasonable to suggest that the observed QP-10 h, QP-40 min and QP-15/20 periodicities are due to Jovian influence. Further research is needed to study the cause of the QP-10/5 h EIBs. This study presents new data which extend our view on the influence of the QP-10 h/QP-40/QP-15/20 min Jovian emissions from the outer to the inner heliosphere at 1 AU.

Simulations of ion sputtering at Ganymede

Ganymede's surface is subject to constant bombardment by Jovian magnetospheric and Ganymede's ionospheric ions. These populations sputter the surface and contribute to the replenishment of the moon's exosphere.Thus far, estimates for sputtering on the moon's surface have included only the contribution from Jovian ions. In this work, we have used our recent model of Ganymede's ionosphere Carnielli et al., 2019 to evaluate the contribution of ionospheric ions for the first time. In addition, we have made new estimates for the contribution from Jovian ions, including both thermal and energetic components.For Jovian ions, we find a total sputtering rate of 2.2 × 1027 s−1, typically an order of magnitude higher compared to previous estimates. For ionospheric ions, produced through photo- and electron-impact ionization, we find values in the range 2.7 × 1026–5.2 × 1027 s−1 when the moon is located above the Jovian plasma sheet. Hence, Ganymede's ionospheric ions provide a contribution of at least 10% to the sputtering rate, and under certain conditions they dominate the process. This finding indicates that the ionospheric population is an important source to consider in the context of exospheric models.

Thermal and Energetic Ion Dynamics in Ganymede's Magnetosphere

AbstractGanymede is the solar system's only known moon with an intrinsic, global magnetic field. This field is strong enough to stand off the incident Jovian magnetospheric flow to form a small, complex magnetosphere around the satellite. Ganymede's magnetosphere is thought to be responsible for variable surface weathering patterns, the production of a neutral exosphere, and the generation of UV aurorae near Ganymede's open‐closed field line boundaries; however, the exact details and underlying mechanisms are poorly understood. We use results from three‐dimensional hybrid models of Ganymede's magnetosphere and a three‐dimensional particle tracing model to quantify the dynamics of thermal and energetic Jovian ions as they interact with Ganymede's magnetosphere and precipitate to the surface. We identify the formation of quasi‐trapped ionic radiation belts in the model and variable surface weathering. Most of the particle precipitation occurs in Ganymede's polar caps, yet ions also precipitate onto Ganymede's equatorial region in lesser amounts due to particle shadowing of quasi‐trapped ions in Ganymede's ionic radiation belts. Model results predict that within Jupiter's central plasma sheet, total ion fluxes to Ganymede's polar, leading, and trailing hemispheres are 50 × 106, 10 × 106, and 0.06 × 106 cm−2 · s−1, respectively. Finally, convolution of incident ions fluxes with neutral sputtering yields for icy bodies predicts neutral sputtered fluxes in Ganymede's polar, leading, and trailing hemispheres of 1.3 × 109, 4.8 × 108, and 1.2 × 108 neutrals cm−2 · s−1, respectively. Together, we estimate that Ganymede loses 7.5 × 1026 neutral particles per second, or assuming a mean mass of 18 amu, approximately 23 kg/s, half that estimated for Europa.

On the formation of Ganymede's surface brightness asymmetries: Kinetic simulations of Ganymede's magnetosphere

AbstractGanymede possesses strong surface brightness asymmetries both between its polar cap and equatorial regions and between its leading and trailing hemispheres. Here we test the hypothesis that these asymmetries are due to differential Jovian plasma and energetic particle precipitation to the surface with the combination of a hybrid plasma model (kinetic ions and fluid electrons) and a particle tracing model. We describe the hybrid model, the first of its kind applied to Ganymede, and compare the results to both Galileo observations and previous MHD and MHD‐EPIC models of Ganymede. We calculate spatially resolved precipitating Jovian ion fluxes to the surface of Ganymede for energies 1 < E < 104 keV and find (1) precipitating fluxes peak near 100 keV and (2) excellent correlation between the precipitating flux and Ganymede's surface brightness variations. Thus, we conclude that precipitating energetic particle fluxes are the primary driver for altering the surface brightness of Ganymede.

Variability of Jovian ion winds: an upper limit for enhanced Joule heating

Abstract. It has been proposed that short-timescale fluctuations about the mean electric field can significantly increase the upper atmospheric energy inputs at Jupiter, which may help to explain the high observed thermospheric temperatures. We present data from the first attempt to detect such variations in the Jovian ionosphere. Line-of-sight ionospheric velocity profiles in the Southern Jovian auroral/polar region are shown, derived from the Doppler shifting of H3+ infrared emission spectra. These data were recently obtained from the high-resolution CSHELL spectrometer at the NASA Infrared Telescope Facility. We find that there is no variability within this data set on timescales of the order of one minute and spatial scales of 640 km, putting upper limits on the timescales of fluctuations that would be needed to enhance Joule heating.

Boundary layer ion composition at Jupiter during the inbound pass of the Ulysses flyby

During the inbound segment of the Ulysses flyby of Jupiter, there were multiple incursions into the dawnside low-latitude boundary layer, as identified by Bame et al. ( Science 257, 1539–1542, 1992) using plasma electron data. In the present study, ion composition and spectral measurements provide independent collaborative evidence for the existence of distinct boundary layer regions. Measurements are taken in the energy-per-charge range of 0.6–60 keV/e and involve mass as well as mass-per-charge identification by the Ulysses/SWICS experiment. Ion species of Jovian magnetospheric origin (including O +, O 2+, S 2+, S 3+) and sheath origin (including He 2+ and high charge state CNO) have been directly identified for the first time in the Jovian magnetospheric boundary layer. Protons of probably mixed origin and He + of possibly sheath (ultimately interstellar pickup) origin were also observed in the boundary layer. Sheath-like ions are observed throughout the boundary layer; however, the Jovian ions are depleted or absent for portions of two boundary layer cases studied. Ions of solar wind origin are observed within the outer magnetosphere. and ions of magnetospheric origin are found within the sheath, indicating that transport across the magnetopause boundary can work both ways, at least under some conditions. Although their source cannot be uniquely identified, the proton energy spectrum in the boundary layer suggests a sheath origin for the lower energy protons.

Energetic particle events (≥30 keV) of Jovian origin observed by Voyager 1 and 2 in interplanetary space

Short‐lived and long‐lived ion flux increases (E ≥30 keV) of Jovian origin have been observed by the low energy charged particle (LECP) instrument on the Voyager 1 and 2 spacecraft. The short‐lived events are observed more than 860 RJ upstream and more than 1500 RJ downstream of Jupiter. Observations of long‐lived events appear to be confined to ≲200 RJ upstream of Jupiter. The short‐lived events last from a few minutes to a couple of hours, while the long‐lived events last from 8 to 21 hours. Both types of events have sharp onsets and decays, are usually confined to energies below 1 MeV total energy, and show a large general enrichment of Z ≥6 particles relative to proton and helium particles when compared with energetic particle events of solar or interplanetary origin. Many of the events have a noticeable peak in the energy spectrum above 100 keV after the main portion of the event. In addition, the short‐lived events (upstream and downstream) are (1) extremely anisotropic with a flow direction consistent with flow away from Jupiter, (2) display no noticeable velocity dispersion, and (3) display initially steep energy spectra that flatten with time. The peak flux level at the lowest energies in the magnetosheath is similar to that observed during long‐lived events. We conclude that a significant fraction of the particles observed during Jovian ion events originate from within the magnetosphere of Jupiter and simply leak out into the magnetosheath. If the interplanetary magnetic field favorably connects to the bow shock, particles can leak out into the interplanetary medium. Together with the necessary leakage model, the observations presented here cannot rule out the existence of a wave particle acceleration region located immediately upstream of the bow shock.