Io's tidal response precludes a shallow magma ocean

R S Park; R A Jacobson; L Gomez Casajus; F Nimmo; A I Ermakov; J T Keane; W B McKinnon; D J Stevenson; R Akiba; B Idini; D R Buccino; A Magnanini; M Parisi; P Tortora; M Zannoni; A Mura; D Durante; L Iess; J E P Connerney; S M Levin; S J Bolton

doi:10.1038/s41586-024-08442-5

Io's tidal response precludes a shallow magma ocean

Nature. 2024 Dec 12. doi: 10.1038/s41586-024-08442-5. Online ahead of print.

Authors

R S Park¹, R A Jacobson², L Gomez Casajus³, F Nimmo⁴, A I Ermakov⁵, J T Keane², W B McKinnon⁶, D J Stevenson⁷, R Akiba⁴, B Idini⁴, D R Buccino², A Magnanini⁸, M Parisi², P Tortora⁸, M Zannoni⁸, A Mura⁹, D Durante¹⁰, L Iess¹⁰, J E P Connerney¹¹, S M Levin², S J Bolton¹²

Affiliations

¹ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA. [email protected].
² Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA.
³ Centro Interdipartimentale di Ricerca Industriale Aerospaziale, Alma Mater Studiorum - Università di Bologna, Forli, Italy.
⁴ Department of Earth and Planetary Sciences, University of California, Santa Cruz, California, USA.
⁵ Department of Aeronautics and Astronautics, Stanford University, Stanford, California, USA.
⁶ Department of Earth, Environmental, and Planetary Sciences, Washington University, St. Louis, Missouri, USA.
⁷ California Institute of Technology, Pasadena, California, USA.
⁸ Dipartimento di Ingegneria Industriale, Alma Mater Studiorum, Università di Bologna, Forlì, Italy.
⁹ Institute for Space Astrophysics and Planetology, National Institute for Astrophysics, Rome, Italy.
¹⁰ Sapienza Università di Roma, Rome, Italy.
¹¹ NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.
¹² Southwest Research Institute, San Antonio, Texas, USA.

PMID: 39667409
DOI: 10.1038/s41586-024-08442-5

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 Juno^3,4 and Galileo^5-7 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 eruption^8,9, 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.