04-12-2012, 01:15 PM
Does Io have a dynamo?
Io Dynamo.ppt (Size: 2.34 MB / Downloads: 68)
Overview of Io
The Jupiter’s innermost satellite
The most volcanic body known
Within an intense radiation belt
Io’s interior structure
Io is in hydrostatic equilibrium.
Io almost certainly has a metallic core with a radius between 550 and 900 km for an Fe-FeS core or between 350 and 650 km for an Fe core (Anderson, 2001).
Magnetic signature of Io by Galileo’s first flyby
The Voyage 1 detected magnetic perturbation of ~5% of the ambient jovian magnetic field about 11RIo (RIo =1821km) below Io, which comfirmed the presence of a field-aligned current.
A decrease of nearly 40% of the background jovian field was recorded by Galileo at closest approach (898km) of Io, that is 695 nT decrease in a background of 1835 nT (Kivelson, 1996).
Kivelson’s explanation
Plasma sources alone appear incapable of generating perturbations as large as those observed, which was obtained with the plasma parameters of Voyage.
An intrinsic magnetic field of amplitude consistent with dynamo action at Io would explain the observations (Kivelson, 1996).
Modeling on Io’s interaction
Modeling (Krishan, 1997)
With assumptions of “Long Wake” and Voyage 1 plasma data.
The plasma effects can account for only a fractrion (<30%) of the observed depression and the principle cause of the reduction in the field strength is a source inside of Io.
Plasma observations of Galileo’s first flyby of Io
A plausible thick and dense ionosphere (Frank, 1996)
The measurement of torus mass densities are about two times greater than those inferred from Voyage flyby.
The magnetic perturbation due to the plasma interaction is doubled to ~500nT.
The gradients in the plasma pressure give rise to currents which cause magnetic perturbation between 100 to 200 nT.
No need for a magnetized Io interior.