Differential Rotation in Jupiter's Interior Revealed by Simultaneous Inversion for the Magnetic Field and Zonal Flux Velocity

• Published in: Journal of geophysical research. Planets 2022-05, Vol.127 (5), p.n/a
• Main Authors: Bloxham, Jeremy, Moore, Kimberly M., Kulowski, Laura, Cao, Hao, Yadav, Rakesh K., Stevenson, David J., Connerney, John E. P., Bolton, Scott J.
• Format: Article
• Language: English
• Subjects: Differential rotation; Drift rate; Equator; Jupiter; Jupiter magnetic field; Jupiter probes; Magnetic fields; Magnetometers; Planetary interiors; Planetary magnetic fields; Secular variations; Space missions; Spacecraft; Time dependence
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2021JE007138

A key objective of the current Juno mission (Bolton et al., 2017, https://doi.org/10.1126/science.aal2108) is the direct determination of the secular variation (time dependency) of Jupiter's internal magnetic field in order to further understand the dynamics of Jupiter's interior. Here, we find that the residuals to a static, baseline model of the magnetic field are consistent with the effects of secular variation, specifically secular variation arising from zonal drift of the field. We present a technique for simultaneously inverting for the main magnetic field and secular variation due to zonal drift of the field. We explore the required drift systematically and argue that although the drift is dominated by a prograde super‐rotation, corresponding to approximately 1 part in 106 relative to System IIIa (1965), there is also evidence for differential drift of the field. We compare the resultant secular variation with that determined by Moore et al. (2019, https://doi.org/10.1038/s41550-019-0772-5) and Connerney et al. (2022, https://doi.org/10.1029/2021je007055) and find good agreement. This suggests that the drift rate of Jupiter's magnetic field is steady over time periods of several decades, though short period secular variation (such as that resulting from torsional oscillations) superimposed on this steady secular variation is still possible. Plain Language Summary Magnetometer data from the Juno spacecraft in the orbit around Jupiter show clear signs of time‐dependency in Jupiter's magnetic field. Although a large part of the time‐dependency can be explained by a small change in the rotation rate of the reference frame, there remains a signal of time‐dependency after solving for such a correction. This remaining time‐dependency represents true secular variation of the magnetic field, instead of an apparent secular variation resulting from a slightly incorrect choice of rotation rate. The true secular variation results from a simple latitude‐dependent zonal drift of the field, and includes an equatorial jet that is symmetric about the equator. Key Points Magnetometer data from the Juno spacecraft exhibit clear indications of secular variation of Jupiter's magnetic field Although a large part of the apparent secular variation can be explained by a solid body prograde rotation of approximately 0.1°/yr, there is evidence of latitude‐dependent zonal drift of the magnetic field The recent secular variation we find agrees well with that determined over much