Properties of local plasma injections in Saturn's magnetosphere

Burch, J. L.; Goldstein, J.; Hill, T. W.; Young, D. T.; Crary, F. J.; Coates, A. J.; André, Nicolas; Kurth, W. S.; Sittler, E. C.

doi:10.1029/2005gl022611

Cited by 111 publications

(154 citation statements)

References 13 publications

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“…The rapid rotation of the planet confines it to the equatorial plane and forms a magnetodisc. It then diffuses into the outer magnetosphere due to centrifugal instabilities as described by Kivelson and Southwood [2005] and observed by Burch et al [2005] and Hill et al [2005]. Only the ions and electrons with sufficient energy can escape and travel along the field lines to higher latitudes.…”

Section: Introductionmentioning

confidence: 99%

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: Introductionmentioning

confidence: 99%

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

et al. 2014

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“…Third, there are excursions in energy down to approximately 10 eV; these may be associated either with interchange between Saturn's dense, cold inner magnetosphere and the rarer, hot outer magnetosphere (e.g. Burch et al 2005;Hill et al 2005), or with ionospheric material from Titan. Fourth, there is a prominent interaction interval of approximately 14 min in this case, where Cassini is within Titan's ionosphere and exosphere region, covering the interval approximately 15.18-15.32 UT.…”

Section: Introduction: Titan's Space Environmentmentioning

confidence: 99%

Interaction of Titan's ionosphere with Saturn's magnetosphere

Coates

2008

Phil. Trans. R. Soc. A.

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Titan is the only Moon in the Solar System with a significant permanent atmosphere. Within this nitrogen-methane atmosphere, an ionosphere forms. Titan has no significant magnetic dipole moment, and is usually located inside Saturn's magnetosphere. Atmospheric particles are ionized both by sunlight and by particles from Saturn's magnetosphere, mainly electrons, which reach the top of the atmosphere. So far, the Cassini spacecraft has made over 45 close flybys of Titan, allowing measurements in the ionosphere and the surrounding magnetosphere under different conditions. Here we review how Titan's ionosphere and Saturn's magnetosphere interact, using measurements from Cassini low-energy particle detectors. In particular, we discuss ionization processes and ionospheric photoelectrons, including their effect on ion escape from the ionosphere. We also discuss one of the unexpected discoveries in Titan's ionosphere, the existence of extremely heavy negative ions up to 10 000 amu at 950 km altitude.

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“…Based on their 6 analysis of many events, Mitchell et al (2014) found the former usually occur inward of 7 about 12 R S (1 Saturn radius = 60268 km), while the latter are more commonly observed 8 outward of that distance. Interchange injections can be thought of as flux tube bundles 9 (see, for instance, Burch et al 2005) or flow channels (see below). A review of the 10 literature on Saturn injections, including key findings, can be found in Thomsen et al 11 (2013).…”

Section: Introductionmentioning

confidence: 99%

Effects of radial motion on interchange injections at Saturn

Paranicas

Thomsen

Achilleos

et al. 2016

Icarus

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Charged particle injections are regularly observed in Saturn's inner magnetosphere by Cassini. They are attributed to an ongoing process of flux-tube interchange driven by the strong centrifugal force associated with Saturn's rapid rotation. Numerical simulations suggest that these interchange injections can be associated with inward flow channels, in which plasma confined to a narrow range of longitudes moves radially toward the planet, gaining energy, while ambient plasma in the adjacent regions moves more slowly outward. Most previous analyses of these events have neglected this radial motion and inferred properties of the events under the assumption that they appear instantaneously at the spacecraft's L-shell and thereafter drift azimuthally. This paper describes features of injections that can be related to their radial motion prior to observation. We use a combination of phase space density profiles and an updated version of a test-particle model to quantify properties of the injection. We are able to infer the longitudinal width of the injection, the radial travel time from its point of origin, and the starting L shell of the injection. We can also predict which energies can remain inside the channel during the radial transport. To highlight the effects of radial propagation at a finite speed, we focus on those interchange injections without extensive features of azimuthal dispersion. Injections that have traveled radially for one or more hours prior to observation would have been initiated at a different local time than that of the observation. Finally, we describe an injection where particles have drifted azimuthally into a flow channel prior to observation by Cassini.We have made all the changes both referees have suggested. Cassini. They are attributed to an ongoing process of flux-tube interchange driven by the strong centrifugal force associated with Saturn's rapid rotation. Numerical simulations suggest that these interchange injections can be associated with inward flow channels, in which plasma confined to a narrow range of longitudes moves radially toward the planet, gaining energy, while ambient plasma in the adjacent regions moves more slowly outward. Most previous analyses of these events have neglected this radial motion and inferred properties of the events under the assumption that they appear instantaneously at the spacecraft's L-shell and thereafter drift azimuthally. This paper describes features of injections that can be related to their radial motion prior to observation. We use a combination of phase space density profiles and an updated version of a test-particle model to quantify properties of the injection. We are able to infer the longitudinal width of the injection, the radial travel time from its point of origin, and the starting L shell of the injection. We can also predict which energies can remain inside the channel during the radial transport. To highlight the effects of radial propagation at a finite speed, we focus on those interchange injections without extensi...

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Properties of local plasma injections in Saturn's magnetosphere

Cited by 111 publications

References 13 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

Interaction of Titan's ionosphere with Saturn's magnetosphere

Effects of radial motion on interchange injections at Saturn

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