Ring current at Saturn: Energetic particle pressure in Saturn's equatorial magnetosphere measured with Cassini/MIMI

Sergis, N.; Krimigis, S. M.; Mitchell, D. G.; Hamilton, D. C.; Krupp, N.; Mauk, B.; Roelof, E. C.; Dougherty, M. K.

doi:10.1029/2006gl029223

Cited by 89 publications

(130 citation statements)

References 17 publications

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“…The plasma beta measured by the spacecraft for these crossings ranged between 15 and 25 and was exceptional compared to previous studies by Sergis et al [2007Sergis et al [ , 2009 and Masters et al [2012b], who found that the plasma beta just inside the magnetopause can be of the order 10.…”

Section: 1002/2014ja019774mentioning

confidence: 62%

Polar confinement of Saturn's magnetosphere revealed by in situ Cassini observations

et al. 2014

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Plasma rotation plays a large role in determining the size and shape of Saturn's disk-like magnetosphere. A magnetosphere more confined to the equator in the polar regions is expected as a result of the interaction between this type of obstacle and the solar wind. In addition, at times away from equinox, a north-south asymmetry is expected where the magnetopause will be further confined in one hemisphere but less confined in the opposite hemisphere. Examining the extent of this confinement has been limited by a lack of high-latitude spacecraft observations. Here for the first time, direct evidence for polar confinement of Saturn's magnetopause has been observed using in situ data obtained by the Cassini spacecraft during a series of high-inclination orbits between 2007 and 2009. Following techniques established by previous authors, we assume an equilibrium between the solar wind dynamic pressure (which Cassini is generally unable to measure directly), and the magnetic plus plasma pressure inside the magnetosphere. This assumption thus allows us to estimate the upstream solar wind dynamic pressure (D P ) for a series of magnetopause crossings, and hence to determine the expected location and global shape of the magnetopause as a function of D P . A clear divergence from the familiar axisymmetric models of the magnetosphere is observed, which may be characterized by an "apparent flattening parameter" of 0.81+0.03/−0.06 (representing a simple dilation of the nominal axisymmetric boundary along the Z KSM axis such that the extent is reduced by approximately 19% in this direction). This figure is insensitive to variations in D P .

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Section: 1002/2014ja019774mentioning

confidence: 62%

Polar confinement of Saturn's magnetosphere revealed by in situ Cassini observations

et al. 2014

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“…Rhea orbits Saturn at the edge the planet's E-ring (Baum et al, 1981), at location which can be seen as a "transition region" within the magnetosphere: there the magnetic field holds its dipolar configuration to a large extent but the magnetic field magnitude drops to values around 30 nT, while the plasma pressure is almost peaked (Sergis et al, 2007), leading to plasma beta values around unity.…”

Section: Saturn's Moon Rheamentioning

confidence: 99%

Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

et al. 2008

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Abstract. Rhea's magnetospheric interaction is simulated using a three-dimensional, hybrid plasma simulation code, where ions are treated as particles and electrons as a massless, charge-neutralizing fluid. In consistency with Cassini observations, Rhea is modeled as a plasma absorbing obstacle. This leads to the formation of a plasma wake (cavity) behind the moon. We find that this cavity expands with the ion sound speed along the magnetic field lines, resulting in an extended depletion region north and south of the moon, just a few Rhea radii (R Rh ) downstream. This is a direct consequence of the comparable thermal and bulk plasma velocities at Rhea. Perpendicular to the magnetic field lines the wake's extension is constrained by the magnetic field. A magnetic field compression in the wake and the rarefaction in the wake sides is also observed in our results. This configuration reproduces well the signature in the Cassini magnetometer data, acquired during the close flyby to Rhea on November 2005. Almost all plasma and field parameters show an asymmetric distribution along the plane where the corotational electric field is contained. A diamagnetic current system is found running parallel to the wake boundaries. The presence of this current system shows a direct corelation with the magnetic field configuration downstream of Rhea, while the resulting j×B forces on the ions are responsible for the asymmetric structures seen in the velocity and electric field vector fields in the equatorial plane. As Rhea is one of the many plasma absorbing moons of Saturn, we expect that this case study should be relevant for most lunar-type interactions at Saturn.

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“…The inbound magnetospheric leg of the encounter is dominated by the suprathermal and magnetic pressures, the first one being known as, on averaged, the major pressure contribution in the outer magnetosphere (Sergis et al, 2007(Sergis et al, , 2009). The estimated dynamic pressure is of the same order of the magnetic term, whereas the electron thermic pressure is smaller by a factor 10.…”

Section: The Pressure Environmentmentioning

confidence: 99%

“…The last pressure term is given by the energetic particles, deduced from the MIMI CHEMS data (Krimigis et al, 2004) using the method developed by Sergis et al (2007). This suprathermal pressure corresponds to both H + and O + (major plasma components) for energies above 3 keV.…”

Section: The Pressure Environmentmentioning

confidence: 99%

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Titan's ionosphere in the magnetosheath: Cassini RPWS results during the T32 flyby

et al. 2009

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Abstract. The Cassini mission has provided much information about the Titan environment, with numerous low altitude encounters with the moon being always inside the magnetosphere. The only encounter taking place outside the magnetopause, in the magnetosheath, occurred the 13 June 2007 (T32 flyby). This paper is dedicated to the analysis of the Radio and Plasma Wave investigation data during this specific encounter, in particular with the Langmuir probe, providing a detailed picture of the cold plasma environment and of Titan's ionosphere with these unique plasma conditions. The various pressure terms were also calculated during the flyby. The comparison with the T30 flyby, whose geometry was very similar to the T32 encounter but where Titan was immersed in the kronian magnetosphere, reveals that the evolution of the incident plasma has a significant influence on the structure of the ionosphere, with in particular a change of the exo-ionospheric shape. The electrical conductivities are given along the trajectory of the spacecraft and the discovery of a polar plasma cavity is reported.

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Ring current at Saturn: Energetic particle pressure in Saturn's equatorial magnetosphere measured with Cassini/MIMI

Cited by 89 publications

References 17 publications

Polar confinement of Saturn's magnetosphere revealed by in situ Cassini observations

Polar confinement of Saturn's magnetosphere revealed by in situ Cassini observations

Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

Titan's ionosphere in the magnetosheath: Cassini RPWS results during the T32 flyby

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