Giant Planets magnetospheres
Problem description:
Like the Earth?s magnetosphere, the ones of Jupiter and Saturn are also embedded in the dynamic solar wind. However, the magnetospheres of the large planets are rotationally driven, i.e. the bulk of the energy is obtained from the rotation of the planet and the plasma in the magnetosphere comes from the planet or from its satellite (e.g. Io at Jupiter). However, this does not mean that the solar wind does not have any influence on these magnetospheres; it is still a source of energy and plasma for the magnetospheres. The plasma of the solar wind and of the magnetosphere are kept apart by a thin boundary called the magnetopause in which strong currents flow.
The solar wind ?flow channel? around the planet, the magnetosheath, interacts with the magnetosphere through the magnetopause by means of various instabilities that can occur on/in the magnetopause. Galileo observed that at Jupiter the magnetic fields and currents strengths were not axi-symmetric, like at the Earth. This suggests that the solar wind drives a convection system in Jupiter?s magnetosphere, quite like in the Earth?s magnetosphere.
The sizes of the magnetospheres of Jupiter and Saturn are very large, compared to those of the smaller planets and even compared to the size of the sun. Indeed, if one could see magnetic fields, then the Jovian magnetosphere would be the biggest object in the sky. This also means that the magnetotails are much longer. The magnetotail signature of Jupiter was measured at Saturn?s orbit.
- Fig.1: The comparative sized of the planetary magnetospheres. (Figure taken from Russell & Walker, ?The magnetospheres of the outer planets,? Fig. 15.7 in: Kivelson & Russell, Introduction to space physics)
Jupiter?s and Saturn?s magnetic dipoles are oriented oppositely to that of the Earth (g10 = 4.2, 0.2 and −0.3 respectively), which means that, unlike at the Earth, day-side reconnection takes place during northward IMF conditions, which is more prevalent.
Although Jupiter?s auroral activity is mainly driven by the planet?s rotation, the solar wind does have influence on the emissions, created by reconnection in the magnetotail or on the dayside magnetopause. However the detailed mechanisms on how the solar wind influences the aurora are still unclear. It is clear that the solar wind, at the outer planets, mainly influences the aurora through its dynamical pressure.
References:
- Acuña, Connerney and Ness, The Z3 zonal harmonic model of Saturn?s magnetic field: Analyses and implications, J. Geophys. Res., 88, 8771-8778, 1983
- Bagenal, Dowling and McKinnon, Jupiter, the Planet, Satellites and Magnetosphere, Cambridge Universtiy Press, Cambridge, UK, 2004
- Connerney, Acuña and Ness, Voyager 1 assessment of Jupiter?s planetary magnetic field, J. Geophys. Res., 87, 3623-3627, 1982
- Dessler, Physics of the Jovian Magnetosphere, Cambridge University Press, Cambridge, UK, 1983
- Gehrels, Jupiter, University of Arizona Press, Tucson, AZ, USA, 1976
- Khurana, Influenceof solar wind on Jupiter?s magnetosphere deduced from currents in the equatorial plane, J. Geophys. Res., 106, 25999-26016, 2001
- Kivelson and Russell, Introduction to Space Physics, Cambridge University Press, Cambridge, UK, 1995
