Identification of Jupiter’s magnetic equator through H3+ ionospheric emission

Abstract

Our understanding of Jupiter’s magnetic field has been developed through a combination of spacecraft measurements at distances >1.8RJ and images of the aurora1,2,3,4,5,6,7. These models all agree on the strength and direction of the Jovian dipole magnetic moments, but because higher-order magnetic moments decay more strongly with distance from the planet, past spacecraft measurements could not easily resolve them. In the past 2 years, the Juno mission has measured very close to the planet (>1.05RJ), observing a strongly enhanced localized magnetic field in some orbits8,9, and resulting in models that identify strong hemispheric asymmetries at mid-to-high latitudes10,11. These features could be better resolved by identifying changes in the ionospheric density caused by interactions with the magnetic field, but past observations have been unable to spatially resolve such features12,13,14. In this study, we identify a dark sinusoidal ribbon of weakened H3+ emission near the jovigraphic equator, which we show to be an ionospheric signature of Jupiter’s magnetic equator. We also observe complex structures in Jupiter’s mid-latitude ionosphere, including one dark spot that is coincident with a localized enhancement in Jupiter’s radial magnetic field observed recently by Juno10. These features reveal evidence of complex localized interactions between Jupiter’s ionosphere and its magnetic field. Our results provide ground-truth for Juno spacecraft observations and future ionospheric and magnetic field models.

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Fig. 1: H3+ ionospheric emission at wavelengths of 3.42–3.46 and 3.53 μm.
Fig. 2: Equatorial magnetic field mapping.

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Acknowledgements

This work was supported by the UK STFC Consolidated Grant ST/N000749/1 (to H.M. and T.S.S.) and a PhD studentship (to R.E.J.). A.G.B. was supported by NERC grant NE/K011766/1 and the start-up funds provided to R. Stoneback by the University of Texas at Dallas. L.N.F. was supported by a Royal Society Research Fellowship at the University of Leicester. L.M. was supported by NASA under grant NNX17AF14G issued through the SSO Planetary Astronomy Program. J.E.P.C. and T.S. were visiting astronomers at the NASA Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement NNX-08AE38A with the National Aeronautics and Space Administration Science Mission Directorate Planetary Astronomy Program.

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T.S.S. led the project, performed data reduction and data analysis, produced the figures, and wrote the paper. A.G.B. performed equatorial modelling for Earth comparison, took part in detailed discussions and co-wrote the section on magnetic field interactions. H.M. performed data analysis, including image processing and limb fitting. L.N.F. performed data analysis on tropospheric emission and discussed the troposphere. S.M. discussed the data analysis techniques. L.M. took part in detailed discussions of Jupiter’s ionosphere and co-wrote the section on the ionosphere. J.O. discussed ionospheric darkening and comparisons with Saturn. J.E.P.C. was project leader for the original observations, performed data reduction, and discussed in detail the magnetic field modelling. T.S. was an observer, took part in detailed discussion of the instrumental errors, and led the discussion on testing of the image-processing technique. R.E.J. discussed the data analysis techniques. All authors reviewed and edited the manuscript.

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Correspondence to Tom S. Stallard.

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Supplementary Figures 1–9, Supplementary text, Supplementary reference

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Stallard, T.S., Burrell, A.G., Melin, H. et al. Identification of Jupiter’s magnetic equator through H3+ ionospheric emission. Nat Astron 2, 773–777 (2018). https://doi.org/10.1038/s41550-018-0523-z

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