In Search Of Subsurface Oceans Within The Uranian Moons

(top row) Parameter space used to forward model the various complex response functions associated with Miranda, Ariel, and Umbriel; the size of the dot indicates the ocean thickness (smallest dot represents thinnest ocean) and the color code represents ocean conductivity. (middle row) The amplitude of the complex response function for the moons of Miranda, Ariel, and Umbriel, each model colored based on the parameter space above it. Note that the complex response amplitude is normalized to the body surface, so the amplitude can be greater than 1 for highly conducting ionospheres. (bottom row) Phase delay corresponding to each amplitude above. Ionosphere-only models (e.g. no ocean conduction) are colored magenta, and are identifiable by their high amplitude at the shortest period and phase response that always asymptotes to 90°. Vertical lines represent the periods associated with the dominant magnetic waves modeled in this work. The key synodic and orbital periods are colored red and cyan, respectively. As illustrated, there are 7 periods modeled for Umbriel, 6 periods for Ariel, and 14 periods for Miranda (some are not shown, as they are too finely spaced to be viewed at this scale).

The Galileo mission to Jupiter discovered magnetic signatures associated with hidden sub-surface 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 sub-surface oceans. Future missions to the ice giants may therefore be capable of discovering sub-surface oceans, thereby adding to the family of known ocean worlds in our solar system.

Here, we assess magnetic induction as a technique for investigating sub-surface 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.

C. J. Cochrane, S. D. Vance, T. A. Nordheim, M. Styczinski, A. Masters, L. H. Regoli
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph); Space Physics (physics.space-ph)
Cite as: arXiv:2105.06087 [astro-ph.EP] (or arXiv:2105.06087v1 [astro-ph.EP] for this version)
Submission history
From: Corey Cochrane
[v1] Thu, 13 May 2021 05:25:04 UTC (12,879 KB)
https://arxiv.org/abs/2105.06087

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