Jupiter's magnetic field morphology and implications for its interior

As of late 2017, Juno had collected magnetic field data from 8 perijove passes. With its near polar orbit around Jupiter, the roughly equal longitudinal spacing of the orbits and, most importantly, the close approach of Juno to Jupiter's dynamo (within about 20% of the planetary radius) these data provide an unprecedented view of an active dynamo. The initial results are unexpected. While these data might have been expected to reveal progressively smaller-scale structure in the field, instead what is seen is different.

First, at the top of the nominal dynamo region, we see large-scale field organization. Flux emerges from Jupiter's northern hemisphere in a relatively narrow band around 45 degrees N, and stretches across about 270 degrees of longitude. In contrast, in the southern hemisphere we see flux re-enter over a large diffuse region, in which the maximum radial flux is only a third of that seen in the northern hemisphere. Elsewhere (except near the equator), the radial field is much weaker, including at high northern latitudes.

Second, at the equator we see an extraordinarily intense and localized spot of negative flux, in which the radial flux is three times stronger than any other negatively signed flux. These inferences are robust, even at this early stage of analysis, though there may be unmodeled auroral field aligned currents, and other field sources presently under study.

Although the full 32 orbits planned for Juno will be necessary to reveal these features more fully, we will discuss the initial implications of these features for Jupiter's dynamo and deep interior.