Details

Autor(en) / Beteiligte

• Connerney, J. E. P.
• Timmins, S.
• Oliversen, R. J.
• Espley, J. R.
• Joergensen, J. L.
• Kotsiaros, S.
• Joergensen, P. S.
• Merayo, J. M. G.
• Herceg, M.
• Bloxham, J.
• Moore, K. M.
• Mura, A.
• Moirano, A.
• Bolton, S. J.
• Levin, S. M.

Titel

A New Model of Jupiter's Magnetic Field at the Completion of Juno's Prime Mission

Ist Teil von

• Journal of geophysical research. Planets, 2022-02, Vol.127 (2), p.n/a

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2022

Link zum Volltext

Quelle

Wiley Online Library

Beschreibungen/Notizen

• A spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during 32 of its first 33 polar orbits. These Prime Mission orbits sample Jupiter's magnetic field nearly uniformly in longitude (∼11° separation) as measured at equator crossing. The planetary magnetic field is represented with a degree 30 spherical harmonic and the external field is approximated near the origin with a simple external spherical harmonic of degree 1. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model (“JRM33”) of the planetary magnetic field with spherical harmonic coefficients reasonably well determined through degree and order 13. Useful information regarding the field extends through degree 18, well fit by a Lowes' spectrum with a dynamo core radius of 0.81 Rj, presumably the outer radius of the convective metallic hydrogen region. This new model provides a most detailed view of a planetary dynamo and evidence of advection of the magnetic field by deep zonal winds in the vicinity of the Great Blue Spot (GBS), an isolated and intense patch of flux near Jupiter's equator. Comparison of the JRM33 and JRM09 models suggests secular variation of the field in the vicinity of the GBS during Juno's nearly 5 years of operation in orbit about Jupiter. The observed secular variation is consistent with the penetration of zonal winds to a depth of ∼3,500 km where a flow velocity of ∼0.04 ms−1 is required to match the observations. Plain Language Summary Characterizing the planetary magnetic field of Jupiter is one of the primary science objectives of the Juno Mission. Is the magnetic field generated within the outer envelope consisting mostly of molecular hydrogen, or is it generated at depth where hydrogen becomes metallic under great pressure? The Juno spacecraft, in polar orbit about Jupiter since July 2016, just completed its baseline mapping mission of 33 orbits, providing global coverage of Jupiter's magnetic field near the planet. A detailed representation of the field has emerged, suggesting that Jupiter's magnetic field is generated by dynamo action at depth (beneath 0.81 Rj) in convective metallic hydrogen. A change in Jupiter's magnetic field over time (“secular variation”) was identified by comparison of the model field with that of an earlier model. The secular variation appeared on the flanks of an isolated magnetic patch (the “Great Blue Spot” (GBS)) and can be explained by the eastward motion of the field of the GBS, carried by zonal winds at a depth (∼3,500 km) where molecular hydrogen is sufficiently electrically conductive to grip the magnetic field. Key Points The Juno spacecraft sampled Jupiter's vector magnetic field along 32 polar passes separated by ∼11° longitude at the equator A degree 18 spherical harmonic model of Jupiter's magnetic field is obtained by partial solution of a degree 30 linear system The new model is consistent with dynamo action in metallic hydrogen, advection of the field by deep zonal winds, and secular variation