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Published February 6, 2025 | Published
Journal Article Open

Io's tidal response precludes a shallow magma ocean

Park, R. S.1 ORCID icon
Jacobson, R. A.1
Gomez Casajus, L.2 ORCID icon
Nimmo, F.3 ORCID icon
Ermakov, A. I.4
Keane, J. T.1 ORCID icon
McKinnon, W. B.5
Stevenson, David J.6 ORCID icon
Akiba, R.3 ORCID icon
Idini, B.3
Buccino, D. R.1
Magnanini, A.2 ORCID icon
Parisi, M.1 ORCID icon
Tortora, P.2 ORCID icon
Zannoni, M.2 ORCID icon
Mura, A.7
Durante, D.8 ORCID icon
Iess, L.8 ORCID icon
Connerney, J. E. P.9
Levin, S. M.1 ORCID icon
Bolton, S. J.10 ORCID icon
  • 1. ROR icon Jet Propulsion Lab
  • 2. ROR icon University of Bologna
  • 3. ROR icon University of California, Santa Cruz
  • 4. ROR icon Stanford University
  • 5. ROR icon Washington University in St. Louis
  • 6. ROR icon California Institute of Technology
  • 7. ROR icon Institute for Space Astrophysics and Planetology
  • 8. ROR icon Sapienza University of Rome
  • 9. ROR icon Goddard Space Flight Center
  • 10. ROR icon Southwest Research Institute
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Abstract

Io experiences tidal deformation due to its eccentric orbit around Jupiter, which provides a primary energy source for Io's ongoing volcanic activity and infrared emission1. The amount of tidal energy dissipated within Io is enormous and has been hypothesized to support the large-scale melting of Io's interior and the formation of a global subsurface magma ocean. If Io has a shallow global magma ocean, its tidal deformation would be much larger than in the case of a more rigid, mostly solid interior2. Here we report the measurement of Io's tidal deformation, quantified by the gravitational tidal Love number k2, enabled by two recent flybys of the Juno spacecraft. By combining Juno3,4 and Galileo5-7 Doppler data from the Deep Space Network and astrometric observations, we recover Re(k2) of 0.125±0.047 (1σ) and the tidal dissipation parameter Q of 11.4±3.6 (1σ). These measurements confirm that a shallow global magma ocean in Io does not exist and are consistent with Io having a mostly solid mantle2. Our results indicate that tidal forces do not universally create global magma oceans, which may be prevented from forming due to rapid melt ascent, intrusion, and eruption8,9, so even strong tidal heating – like that expected on several known exoplanets and super-Earths10 – may not guarantee the formation of magma oceans on moons or planetary bodies.

Copyright and License

© 2024, The Author(s). This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Acknowledgement

This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. All rights reserved. We thank W. Folkner and A. Konopliv for providing comments and suggestions, as well as guidance throughout this endeavour. We thank the Juno flight team for providing science and engineering data that facilitated the successful gravity science investigation of Io, and the Juno navigation team for the safe and precise flybys of Io. L.G.C., A.M., M.Z., and P.T. are grateful to the Italian Space Agency (ASI) for financial support through Agreement No. 2022-16-HH.0, and its extension 2022-16-HH.1-2024, for NASA’s Juno and ESA’s BepiColombo radio science experiments. L.G.C., A.M., M.Z., and P.T. acknowledge Caltech and the Jet Propulsion Laboratory for granting the University of Bologna a license to an executable version of MONTE Project Edition S/W.

Contributions

R.S.P. led the experiment and supervised the data analysis. R.S.P., R.A.J., L.G.C., A. Magnanini, P.T. and M.Z. contributed to the orbit determination and recovery of the Io gravity parameters. L.G.C., D.R.B. and M.P. contributed to data calibration and conditioning. R.S.P., F.N., A.I.E., J.T.K., W.B.M., D.J.S., R.A., B.I., A. Mura, D.D. and L.I. contributed to interior modelling and interpretation of the Io gravity results. A.I.E., R.A. and F.N. contributed to the statistical analysis of interior modelling. J.E.P.C., S.M.L. and S.J.B. supervised the planning and execution of the gravity experiment. All authors contributed to the discussion of the results and writing of the paper.

Data Availability

The Juno radio science data used in this research are publicly available through NASA’s Planetary Data System at https://atmos.nmsu.edu/PDS/data/jnogrv_1001/. Partial Galileo data are available through the NASA Planetary Data System at https://pds-ppi.igpp.ucla.edu/.

Code Availability

The results presented in this study can be reproduced using the MONTE software. The license for MONTE can be requested through https://montepy.jpl.nasa.gov/. The code that can reproduce our MCMC results is available on Zenodo at https://doi.org/10.5281/zenodo.14029354 (ref. 85).

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