Abstract
AbstractRoutine spacecraft encounters with the Saturn current sheet due to the passage of aperiodic waves provide the opportunity to analyze the current sheet structure. The current density is expected to peak where the field strength reaches a minimum if approximated as a Harris current sheet. However, in Earth's magnetotail this is not always the case as the sheet is sometimes bifurcated (having two or more maxima in the current density). We utilize measurements of Saturn's magnetic field to estimate the current density during crossings of the current sheet by time differentiating the Ba component of the field in a current sheet coordinate system, where Ba is perpendicular to both the current and current sheet normal. This is then averaged and organized by the magnitude of Ba. Using this method, we can identify a classical Harris‐style or bifurcated current sheet as a peak at the center or two distinct maxima on either side of Ba=0, respectively. We find that around 10% of current sheet profiles exhibit a bifurcated current sheet signature, which is substantially lower than an ∼25% occurrence rate at Earth.
Highlights
The equatorial current sheet at Saturn is a result of a rotationally dominated system [Southwood & Kivelson, 2001] with internal plasma sources such as Enceladus and the other moons, the rings and even the planet itself [e.g. Pontius et al, 2006; Tokar et al, 2005; Jurac et al, 2002; Felici et al, 2016]
The internal plasma and fast rotation result in centrifugal stresses [Arridge et al, 2007] that cause the planet’s magnetic field to stretch outwards at the equator
The normal vector can be found using either minimum variance analysis (MVA) or coplanarity in 1018 out of 1461 aperiodic wave events, of these events 807 sample an adequate amount of both lobes to build up an acceptable picture of the current density profile
Summary
The equatorial current sheet at Saturn is a result of a rotationally dominated system [Southwood & Kivelson, 2001] with internal plasma sources such as Enceladus and the other moons, the rings and even the planet itself [e.g. Pontius et al, 2006; Tokar et al, 2005; Jurac et al, 2002; Felici et al , 2016]. The internal plasma and fast rotation result in centrifugal stresses [Arridge et al, 2007] that cause the planet’s magnetic field to stretch outwards at the equator. This ballooning forms a washer shaped current sheet (much like Earth’s cross tail current sheet). Sergis et al [2017] mapped the equatorial current density in Saturn’s inner magnetosphere from 5-16 RS , showing that the particle pressure is dominated by hot plasma pressure (hot ions) outside of 12 RS with a number of local time effects. In the middle to outer magnetosphere, the current density increases from pre-midnight to pre-noon and forms a region-2-like current system [Martin & Arridge, 2018]
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