Abstract
Saturn's magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the system's dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10–15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively “plasma‐loaded” or “plasma‐depleted” states, defined in terms of the internal suprathermal plasma pressure.
Highlights
The interaction between the solar wind and the magnetic field of a planetary body gives rise to the formation of a magnetosphere, which encloses the planet and shields it from direct bombardment by plasma of solar origin
Vasyliunas [2008] showed that Enceladus may be a more significant plasma source to Saturn’s magnetosphere than Io is to Jupiter’s magnetosphere because, in relative terms, it may cause flux tubes to become more heavily loaded with mass and perturb Saturn’s magnetic field more strongly
We found that a2 = 1∕(7.8 ± 0.4), which apparently indicates that the magnetosphere is very “stiff” and relatively unresponsive to changes in dynamic pressure
Summary
The interaction between the solar wind and the magnetic field of a planetary body gives rise to the formation of a magnetosphere, which encloses the planet and shields it from direct bombardment by plasma of solar origin. K = 1 magnetohydrodynamic (MHD) studies of the Kronian magnetosphere [e.g., Zieger et al, 2010] found that internal plasma dynamics can change the geometry of Saturn’s magnetopause significantly under conditions when the solar wind. Imparts a similar degree of variability to the location of Saturn’s magnetopause as does variability in the solar wind pressure.
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