NEW MODELS OF JUPITERS MAGNETIC-FIELD CONSTRAINED BY THE IO FLUX TUBEFOOTPRINT

Spherical harmonic models of the planetary magnetic field of Jupiter a re obtained from in situ magnetic field measurements and remote observ ations of the position of the foot of the Io flux tube in Jupiter's io nosphere. The Io flux tube (IFT) footprint locates the ionospheric foo tprint of field lines traced from Io's orbital radial distance in the equator plane (5.9 Jovian radii). The IFT footprint is a valuable cons traint on magnetic field models, providing ''ground truth'' informatio n in a region close to the planet and thus far not sampled by spacecra ft. The magnetic field is represented using a spherical harmonic expan sion of degree and order 4 for the planetary (''internal'') field and an explicit model of the magnetodisc for the field (''external'') due to distributed currents. Models fitting Voyager 1 and Pioneer 11 magne tometer observations and the IFT footprint are obtained by partial sol ution of the underdetermined inverse problem using generalized inverse techniques. Dipole, quadrupole, octupole, and a subset of higher-degr ee and higher-order spherical harmonic coefficients are determined and compared with earlier models.