Now this is something I would like to post a bit longer about, probably when this talk actually occurs, but the geophysical implications of finding an induced magnetic field at Io are pretty big (particularly since a global magma ocean had pretty much been ruled out...)
Galileo made five successful flybys of Io during which it collected field and particle data from the satellite’s vicinity. We have reanalyzed the magnetic field data obtained from these flybys to assess the contributions of permanent and induced magnetic fields in the observations. We performed 3-D MHD simulations of the interaction of Io with Jupiter’s magnetosphere to determine magnetic perturbations caused by the satellite/plasma interactions.
Our reanalysis of the difference data (observations – MHD perturbations) shows that a strong electromagnetic induction signature is present in the magnetic field observations. We have modeled the difference data using a three-layer model of Io consisting of a perfectly conducting core, a finite conductivity mantle and a non-conducting crust. The modeling results show that a global subsurface conductor is required at depths below 50 km to explain the magnetic field observations. We further show that a conducting core cannot produce the signature observed and that the response requires a conducting layer much closer to the surface. The high conductivity required of the subsurface conductor can only be explained by hypothesizing the presence of a subsurface magma ocean in Io. Finally, we place upper limits on the strengths of the dipolar and quadrupolar harmonics of the permanent internal field.
EDIT 10/24/2009 12:33 PM: Had to edit links to the Abstract website since they don't seem to actually work... Try the AGU Fall Meeting home page, then click the "Fall Meeting Program and Itinerary Planner" link.
Link: 2009 AGU Fall Meeting [www.agu.org]