Spontaneous Axisymmetry Breaking of the External Magnetic Field at Saturn
Feb 7, 2007
3:30PM to 4:30PM
Date(s) - 07/02/2007
3:30 pm - 4:30 pm
Title: Spontaneous Axisymmetry Breaking of the External Magnetic Field at Saturn
Speaker: Dr. Peter Goldreich
Institute: School of Natural Sciences Institute of Advanced Study – Princeton
Location: ABB 102
Saturn’s magnetic field is unique in that it is remarkably axisymmetric. For many years, periodic radio bursts discovered by the Voyager spacecraft were the only evidence we had for any non-axisymmetry. Subsequently, the Ulysses spacecraft found that the radio burst period varies by of order a percent on a timescale of years. Thus it cannot be that of the rotation of Saturn’s interior. More recently, the Cassini spacecraft detected a small non-axisymmetric component of the magnetic field which rotates at the period of the radio bursts. Surprisingly, its magnitude declines only weakly with distance from the planet. This implies that the non-axisymmetric field components are generated by currents that flow outside the planet. I will describe how such currents arise in response to mass being ejected from Saturn’s satellite, Enceladus. Then I will connect the pattern of mass loss to both the nonaxisymmetric magnetic field components and the radio bursts. This theoretical model will be compared with the latest data from the Cassini spacecraft.
In addition to explaining how the axisymmetry of the external magnetic field at Saturn is broken, my lecture will raise the following questions:
Â·How do dynamos function in fully convective bodies?
Â·Why is Saturn’s magnetic field so axisymmetric?
Â·What energy source is responsible for mass ejection by Enceladus?