Abstract
AbstractWe use magnetopause crossings of the Cassini spacecraft to study the response of Saturn's magnetosphere to changes in external and internal drivers. We explain how solar wind pressure can be corrected to account for the local variability in internal plasma particle pressure. The physics‐based method is applied to perform the most robust estimation of magnetopause compressibility at Saturn to date, using 7 years' worth of magnetometer data from the Cassini mission and accounting for variable internal drivers—particle pressure and azimuthal ring current. The concept of magnetopause compressibility is generalized to quantitatively account for its detailed variation with respect to the position of the magnetopause. An analytical fit is provided to map the compressibility index to values of the stand‐off distance. In particular, the procedure shows that the Kronian system appears to behave similarly to that of Jupiter when expanded outwards and more like the Earth's magnetopause when compressed.
Highlights
The boundary separating the internal magnetospheric plasma around a magnetized planet from the external solar wind plasma within the magnetosheath, known as the magnetopause, has been shown to be a highly dynamic system (Escoubet et al, 2013; Kaufmann & Konradi, 1969; Masters et al, 2011)
Its shape and position are the results of complex interactions between external influences and internal drivers leading to an outward pressure
The long “trailing off” of the crossings towards the top right of the plane illustrates the broad range in both solar wind pressure and plasma β, which prevents a direct determination of magnetopause compressibility over the entire data set
Summary
The boundary separating the internal magnetospheric plasma around a magnetized planet from the external solar wind plasma within the magnetosheath, known as the magnetopause, has been shown to be a highly dynamic system (Escoubet et al, 2013; Kaufmann & Konradi, 1969; Masters et al, 2011). Recent empirical models of the magnetopause at Saturn have shown the dynamical behaviour of its magnetosphere to stand in between the relatively rigid, dipolar case at the Earth and the more elastic, compressible case at Jupiter (Arridge et al, 2006; Kanani et al, 2010; Pilkington et al, 2015; Sorba et al, 2017). Pilkington et al (2015) have notably illustrated how the internal plasma activity can have a large-scale impact on the position and size of the boundary, and Sorba et al (2017) used a 2-D force balance magnetodisk model of the field (Achilleos et al, 2010) to show how the behavior of Saturn's magnetosphere seems to tend towards a more rigid configuration in a plasma-depleted regime and towards a more compressible, Jupiter-like case in a plasma-loaded state.
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