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[PPS01-12] Jupiter’s Magnetic Field and Secular Variation: Implications for the Interior, Rotation Rate, and Particle Motion
キーワード：Jupiter, Magnetic field, Jupiter dynamo, Jovian rotation period
The Juno spacecraft, in polar orbit about Jupiter since July 2016, continues to map the gas giant’s magnetic field with ever-increasing resolution in space and time. Juno’s Prime Mission revealed an intense and non-dipolar magnetic field undergoing secular variation. The Lowes’ radius fit to model spherical harmonics through degree 18 yields a putative dynamo radius of 0.807 +/- 0.006 Rj, which we identify as the depth to which helium rain stabilizes the metallic hydrogen-helium mixture against convection. Direct comparison of spherical harmonic models (JRM33 and JRM09) representative of different epochs revealed secular variation of the field near the isolated and intense patch of negative flux near the equator known as the Great Blue Spot (GBS). The feature drifts eastward relative to the deep interior at a rate of a few cm/s in the same direction as that of surface measurements of the zonal winds. This observation suggests that the zonal winds penetrate to depths of ~3000 km where the electrical conductivity of molecular Hydrogen is sufficient to grip the magnetic field. Spherical harmonic analyses of the Juno data allowing for a slight correction to the planet’s rotation period yields an improved planetary rotation period of 9h 55m 29.698s, compared to the IAU-adopted rate (9h 55m 29.711s +/-0.04s) based on observations of its radio emissions (System III (1965)). Measured in the IAU system, Jupiter’s dipole drifts in longitude by 0.12°/yr, as is also evidenced by direct comparison of the JRM33 model with models representing earlier epochs (Voyager in 1979 and Ulysses in 1992). The complexity of Jupiter’s magnetic field just above the surface of the planet leads to some unanticipated considerations for particle motion: field lines without a magnetic equator external to the 1-bar surface as well as field lines with more than one magnetic equator above the 1-bar surface. What’s a drifting charged particle to do?