Time variation of Jupiter’s internal magnetic field consistent with zonal wind advection

Abstract

Determination of the time dependency (secular variation) of a planet’s magnetic field provides a window into understanding the dynamo responsible for generating its field. However, of the six Solar System planets with active dynamos, secular variation has been firmly established only for Earth. Here, we compare magnetic field observations of Jupiter from the Pioneer 10 and 11, Voyager 1 and Ulysses spacecraft (acquired 1973–1992) with a new Juno reference model (JRM09)1. We find a consistent, systematic change in Jupiter’s field over this 45-year time span, which cannot be explained by changes in the magnetospheric field or by changing the assumed rotation rate of Jupiter. Through a simplified forward model, we find that the inferred change in the field is consistent with advection of the field by Jupiter’s zonal winds, projected down to 93–95% of Jupiter’s radius (where the electrical conductivity of the hydrogen envelope becomes sufficient to advect the field). This result demonstrates that zonal wind interactions with Jupiter’s magnetic field are important and lends independent support to atmospheric and gravitational-field determinations of the profile of Jupiter’s deep winds.

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Fig. 1: Inferred change in Jupiter’s internal magnetic field between Juno (2017) and Pioneer 10 (1973), Pioneer 11 (1974), Voyager 1 (1979) and Ulysses (1992).
Fig. 2: Jupiter’s zonal winds and magnetic field.
Fig. 3: Models of Jupiter’s magnetic secular variation.
Fig. 4: ZWA model of Jupiter’s secular variation.

Data availability

All data and models used in this study are publicly available. The Pioneer 10 and 11, Voyager 1 and Ulysses magnetometer data used in this study are available online on the Planetary Data System. The Jupiter Juno magnetic field model we use is publicly available1. More information regarding the figures and results of this study is available from the corresponding author upon reasonable request.

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Acknowledgements

All authors acknowledge support from the NASA Juno Mission. K.M.M. is supported by the Department of Defense (DoD) through the National Defense Science and Engineering Graduate Fellowship (NDSEG) programme, and the Harvard Graduate School of Arts and Sciences (GSAS) Merit Fellowship. We thank Richard Holme for helpful comments.

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Contributions

K.M.M, H.C. and J.B. designed the study and wrote the manuscript. K.M.M. performed the data analysis, while H.C. performed the zonal wind calculations. All authors contributed to discussions, as well as editing and revising the manuscript. J.E.P.C. is the principal investigator of the Juno magnetometer investigation, and S.J.B. is the principal investigator of the Juno Mission.

Corresponding author

Correspondence to K. M. Moore.

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The authors declare no competing interests.

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Journal peer review information: Nature Astronomy thanks Richard Holme and Chris Jones for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–6, Supplementary Tables 1 and 2, captions of Supplementary Datasets 1–3, Supplementary references

Supplementary Dataset 1

Harmonic coefficients for the ZWA model using winds projected at 0.95 RJ

Supplementary Dataset 2

Harmonic coefficients for the ZWA model using winds projected at 0.94 RJ

Supplementary Dataset 3

Harmonic coefficients for the ZWA model using winds projected at 0.93 RJ

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Moore, K.M., Cao, H., Bloxham, J. et al. Time variation of Jupiter’s internal magnetic field consistent with zonal wind advection. Nat Astron 3, 730–735 (2019). https://doi.org/10.1038/s41550-019-0772-5

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