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In Search of Subsurface Oceans Within the Uranian Moons.

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Title: In Search of Subsurface Oceans Within the Uranian Moons.
Authors: Cochrane, C. J.1 corey.j.cochrane@jpl.nasa.gov, Vance, S. D.1, Nordheim, T. A.1, Styczinski, M. J.2, Masters, A.3, Regoli, L. H.4
Source: Journal of Geophysical Research. Planets. Dec2021, Vol. 126 Issue 12, p1-21. 21p.
Subject Terms: *Ocean, Satellites of Uranus, Jupiter (Planet), Magnetic fields, Callisto (Satellite)
Abstract: The Galileo mission to Jupiter discovered magnetic signatures associated with hidden subsurface oceans at the moons Europa and Callisto using the phenomenon of magnetic induction. These induced magnetic fields originate from electrically conductive layers within the moons and are driven by Jupiter's strong time‐varying magnetic field. The ice giants and their moons are also ideal laboratories for magnetic induction studies. Both Uranus and Neptune have a strongly tilted magnetic axis with respect to their spin axis, creating a dynamic and strongly variable magnetic field environment at the orbits of their major moons. Although Voyager 2 visited the ice giants in the 1980s, it did not pass close enough to any of the moons to detect magnetic induction signatures. However, Voyager 2 revealed that some of these moons exhibit surface features that hint at recent geologically activity, possibly associated with subsurface oceans. Future missions to the ice giants may therefore be capable of discovering subsurface oceans, thereby adding to the family of known "ocean worlds" in our Solar System. Here, we assess magnetic induction as a technique for investigating subsurface oceans within the major moons of Uranus. Furthermore, we establish the ability to distinguish induction responses created by different interior characteristics that tie into the induction response: ocean thickness, conductivity and depth, and ionospheric conductance. The results reported here demonstrate the possibility of single‐pass ocean detection and constrained characterization within the moons of Miranda, Ariel, and Umbriel, and provide guidance for magnetometer selection and trajectory design for future missions to Uranus. Plain Language Summary: The best evidence for the existence of an ocean within Jupiter's moons of Europa and Callisto comes from interpretations of measurements collected from the magnetometer on the Galileo spacecraft. Their salty oceans are able to conduct electrical currents that are driven by Jupiter's strong time‐varying magnetic field, producing a unique secondary magnetic field signature that can be measured externally by as spacecraft passing by. Some of the large moons of the Ice Giant planets of Uranus and Neptune are also thought to possibly contain subsurface oceans. Unfortunately, Voyager 2 did not pass close enough to any of these planetary bodies for its onboard magnetometer to sense magnetic field signatures associated with a subsurface ocean. In this work, we investigate the feasibility of detecting magnetic signatures of subsurface oceans within the moons of Uranus based upon various assumed interior structure profiles, thus providing guidance to required magnetometer performance and trajectory design for possible future missions. Key Points: The major moons of Uranus exhibit surface features which hint at recent geologically activity, possibly associated with subsurface oceansFavorable geometry of the Uranus system facilitates magnetic induction investigation of potential oceans within the primary moonsSubsurface ocean detection and constrained characterization is possible within these moons, even in the presence of an ionosphere [ABSTRACT FROM AUTHOR]
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Abstract:The Galileo mission to Jupiter discovered magnetic signatures associated with hidden subsurface oceans at the moons Europa and Callisto using the phenomenon of magnetic induction. These induced magnetic fields originate from electrically conductive layers within the moons and are driven by Jupiter's strong time‐varying magnetic field. The ice giants and their moons are also ideal laboratories for magnetic induction studies. Both Uranus and Neptune have a strongly tilted magnetic axis with respect to their spin axis, creating a dynamic and strongly variable magnetic field environment at the orbits of their major moons. Although Voyager 2 visited the ice giants in the 1980s, it did not pass close enough to any of the moons to detect magnetic induction signatures. However, Voyager 2 revealed that some of these moons exhibit surface features that hint at recent geologically activity, possibly associated with subsurface oceans. Future missions to the ice giants may therefore be capable of discovering subsurface oceans, thereby adding to the family of known "ocean worlds" in our Solar System. Here, we assess magnetic induction as a technique for investigating subsurface oceans within the major moons of Uranus. Furthermore, we establish the ability to distinguish induction responses created by different interior characteristics that tie into the induction response: ocean thickness, conductivity and depth, and ionospheric conductance. The results reported here demonstrate the possibility of single‐pass ocean detection and constrained characterization within the moons of Miranda, Ariel, and Umbriel, and provide guidance for magnetometer selection and trajectory design for future missions to Uranus. Plain Language Summary: The best evidence for the existence of an ocean within Jupiter's moons of Europa and Callisto comes from interpretations of measurements collected from the magnetometer on the Galileo spacecraft. Their salty oceans are able to conduct electrical currents that are driven by Jupiter's strong time‐varying magnetic field, producing a unique secondary magnetic field signature that can be measured externally by as spacecraft passing by. Some of the large moons of the Ice Giant planets of Uranus and Neptune are also thought to possibly contain subsurface oceans. Unfortunately, Voyager 2 did not pass close enough to any of these planetary bodies for its onboard magnetometer to sense magnetic field signatures associated with a subsurface ocean. In this work, we investigate the feasibility of detecting magnetic signatures of subsurface oceans within the moons of Uranus based upon various assumed interior structure profiles, thus providing guidance to required magnetometer performance and trajectory design for possible future missions. Key Points: The major moons of Uranus exhibit surface features which hint at recent geologically activity, possibly associated with subsurface oceansFavorable geometry of the Uranus system facilitates magnetic induction investigation of potential oceans within the primary moonsSubsurface ocean detection and constrained characterization is possible within these moons, even in the presence of an ionosphere [ABSTRACT FROM AUTHOR]
ISSN:21699097
DOI:10.1029/2021JE006956