TITLE: Jupiter’s Magnetic Field and Magnetosphere Mapped by the Juno Spacecraft

Abstract:

The Juno spacecraft, in polar orbit about Jupiter since July 4, 2016, maps Jupiter’s magnetic and gravitational potential fields and probes its interior in search of clues to the planet’s formation and evolution. Juno races from pole to pole in approximately 2 hours, with a closest approach to within ~1.05 R_j of the center of the planet (one R_j = 71,492 km, Jupiter’s equatorial radius), just a few thousand km above the clouds. Repeated periapsis passes (every 53 days) will eventually encircle the planet with a dense net of observations equally spaced in longitude (<12° at the equator) and optimized for characterization of the Jovian dynamo. Such close passages are sensitive to small spatial scale variations in the magnetic field and therefore many such passes are required to bring the magnetic field into sharp focus. A preliminary degree 10 spherical harmonic model of the field, JRM09, based on 9 orbits, revealed a dramatic hemispheric asymmetry, with a very non-dipolar northern hemisphere contrasting a dipolar southern hemisphere. An equatorial belt of positive radial flux is interrupted by an isolated reverse-polarity patch (the Great Blue Spot, or GBS) near the equator at ~90º "Lambda system 3" west longitude. Here we present a more detailed degree 18 spherical harmonic model of Jupiter’s magnetic field, derived from the first 24 orbits of the giant planet. With the increased spatial resolution that more orbits allow, we observe distortion of the GBS due to the influence of deep zonal winds, as deduced by Moore et al’s analysis of earlier flyby (Voyager, Pioneer) observations and as anticipated by Cao and Stevenson. We present an overview of the magnetometer observations obtained during Juno’s first 4 and ½ years in orbit in context with prior observations and those acquired by Juno’s other science instruments.