Statistics on Jupiter’s Current Sheet With Juno Data: Geometry, Magnetic Fields and Energetic Particles

Abstract

Jupiter, the fifth planet from the sun, has the strongest intrinsic magnetic field among planets in the solar system. The interplay between this magnetic field and the solar wind results in a magnetosphere extending from the topside of Jupiter's atmosphere/ionosphere to beyond 𝐴𝐴 𝐴𝐴∼ 100 𝐴𝐴 R𝐽𝐽 (1 𝐴𝐴 R𝐽𝐽 = 𝐴𝐴 ∼ 71,400 km, Jupiter radii; hereinafter, 𝐴𝐴 𝐴𝐴 represents the radial distance to the Jupiter) (Bagenal et al., 2007). Jupiter's magnetosphere is filled with plasma originating from various sources, including the solar wind, Jupiter's atmosphere/ionosphere, and Jupiter's moons. Among these sources, the moon Io, which supplies 𝐴𝐴 ∼ 1 ton plasma per second to the magnetosphere (e.g., Thomas et al., 2004), serves as the dominant one (e.g., Bolton et al., 2015). After entering the magnetosphere, plasma from Io (and other sources) is picked up by the magnetospheric corotating electric fields and corotates with Jupiter with a period of 9.92 hr. The corotation, in turn, induces a centrifugal force on plasma. This force tends to pull plasma radially outward against the magnetic forces, leading to the deformation of Jupiter's dipole-like magnetic fields (e.g., Hill et al., 1974). The deformation is reinforced by the plasma pressure gradient and anisotropy, which, as suggested by later observational and modeling work (e.g., Caudal, 1986;Mauk & Krimigis, 1987;Paranicas et al., 1991), even play a dominant role in balancing the magnetic forces. As a final result of the force balance, a current sheet is formed in Jupiter's middle and outer magnetosphere (Vasyliunas, 1983).Because of Jupiter's dipole tilts ( ∼10 • ), Jupiter's current sheet is generally displaced from Jupiter's rotational equator (Khurana, 1992;Khurana & Schwarzl, 2005;Connerney et al., 1981). As a result of this displacement and Jupiter rotation, a spacecraft in Jupiter's magnetosphere would periodically cross the current sheet. These periodical crossings manifest as a series of magnetic field reversals in magnetic field data (e.g., Connerney et al., 1981;Khurana & Schwarzl, 2005). According to previous observations, magnetic field reversals can be detected from 𝐴𝐴 𝐴𝐴∼ 10 𝐴𝐴 R𝐽𝐽 to almost the magnetopause (e.g., Connerney et al., 1981;Khurana & Schwarzl, 2005), suggesting the existence of the current sheet in the most of the equatorial regions of Jupiter's magnetosphere. Besides its huge size and notability in observations, the current sheet plays a Abstract Jupiter's magnetosphere contains a current sheet of huge size near its equator. The current sheet not only mediates the global mass and energy cycles of Jupiter's magnetosphere, but also provides a site for many localized dynamic processes, such as reconnection and wave-particle interaction. To correctly evaluate its role in these processes, a statistical description of the current sheet is required. To this end, here we conduct statistics on Jupiter's current sheet, by using four-year Juno data obtained in the 20-100 Jupiter radius, 0-6 local time magnetosphere. The statistics show the thickness of th...

Loss of Energetic Ions Comprising the Ring Current Populations of Jupiter's Middle and Inner Magnetosphere

“…While EMIC waves have been observed at Jupiter inside perhaps L = 13 RJ (Lin et al, 1993), we have found no published record of EMIC waves in the trans-Ganymede region. Mauk and Krimigis (1987) using dayside Voyager-1 data, the colored diamonds and circles were determined using the Juno magnetometer data during the nightside perijove 31 (PJ31) using the procedures developed in Mauk and Krimigis (1987), and the blue squares are from an analysis of the statistical results of Liu et al (2021) for the nightside (see text). (b) Alfvénic magnetic turbulence as measured by Galileo and reported by Saur et al (2003) at a reference frequency of 2.4 × 10 −3 Hz.…”

“…(a) Equatorial radius of curvature of Jupiter's magnetic field configuration as a function of radial position normalized by radial position, and the normalized size of the ion gyroradii at the minimum magnetic field position for 100 keV H + , O + , and S + . The black points and curves were determined byMauk and Krimigis (1987) using dayside Voyager-1 data, the colored diamonds and circles were determined using the Juno magnetometer data during the nightside perijove 31 (PJ31) using the procedures developed inMauk and Krimigis (1987), and the blue squares are from an analysis of the statistical results ofLiu et al (2021) for the nightside (see text). (b) Alfvénic magnetic turbulence as measured by Galileo and reported bySaur et al (2003) at a reference frequency of 2.4 × 10 −3 Hz.…”

Energetic Electron Distributions Near the Magnetic Equator in the Jovian Plasma Sheet and Outer Radiation Belt Using Juno Observations

“…The Juno spacecraft has high inclination orbits and observes energetic electron variations from the auroral region to the equator (Bagenal et al, 2017). Previous studies presented energetic electron fluxes at 𝐴𝐴 𝐴𝐴 𝐴 17 (Wang et al, 2021) and 𝐴𝐴 𝐴𝐴 𝐴 20 (Liu et al, 2021) near the magnetic equator, yet a global survey which would capture the two regions together, track the radial profile of electron phase space densities and study electron pitch angle distributions is needed to understand electron transport and acceleration in the plasma sheet and radiation belts. In this paper, we evaluate energetic (>100 MeV/G) electron distributions near the magnetic equator in Jupiter's plasma sheet ( 𝐴𝐴 𝐴𝐴 𝐴 20 ) and outer radiation belt ( 𝐴𝐴 𝐴𝐴 𝐴 20 ) using Juno observation during the first 29 orbits.…”

The Jovian Energetic Ion Environment of Ganymede: Planetary Space Weather Considerations in View of the JUICE Mission

“…Moreover, to compensate for the relative densities at the orbit of Ganymede, following the approach by Kivelson et al (2004), as in Plainaki et al (2020a), we applied a scaling factor of 1:5 to the fluxes above (science case (i)) and below (science case (iii)) the center of the JPS with respect to the denser center of the JPS itself. We note that this scaling factor represents an upper limit since recent studies based on Juno proton and electron data indicate a smoother gradient between omnidirectional energetic ion fluxes near the JPS and above it (e.g., Liu et al 2021). Our approach makes it easier to compare the current results with those in Plainaki et al (2020a); moreover, a change in the scaling of the fluxes as a function of Ganymede's magnetic latitude would only affect the absolute ion fluxes at 500 km and on the surface, not their ratio.…”

“…As shown in Table 2, no dramatic differences in the H + fluxes in the vicinity of Ganymede exist between the calculations in Paranicas et al (1999) and Paranicas et al (2021). Liu et al (2021), however, argued that time variations are anyway large enough to account for changes in the spectra larger than the uncertainty induced by penetrating radiation. Their study reaches only down to 20 R J , slightly outward of Ganymede, but gives a good sense of time variations in the moon's vicinity.…”