1. Department of Physics, University of Oxford, Oxford OX1 3PU, UK
2. Department of Physics & Astronomy, University of Louisville, Louisville, Kentucky 40292, USA
3. Department of Earth & Space Sciences, University of California, Los Angeles, California 90095-1567, USA

Correspondence to: P. L. Read¹ Correspondence and requests for materials should be addressed to P.L.R. (Email: p.read1@physics.ox.ac.uk).

Abstract

The rotation period of a gas giant's magnetic field (called the System III reference frame) is commonly used to infer its bulk rotation¹. Saturn's dipole magnetic field is not tilted relative to its rotation axis (unlike Jupiter, Uranus and Neptune), so the surrogate measure of its long-wavelength (kilometric) radiation is currently used to fix the System III rotation period². The period as measured now by the Cassini spacecraft is up to 7 min longer³ than the value of 10 h 39 min 24 s measured 28 years ago by Voyager². Here we report a determination of Saturn's rotation period based on an analysis of potential vorticity. The resulting reference frame (which we call System IIIw) rotates with a period of 10 h 34 min 13  20 s. This shifted reference frame is consistent with a pattern of alternating jets on Saturn that is more symmetrical between eastward and westward flow. This suggests that Saturn's winds are much more like those of Jupiter than hitherto believed⁴.

1. Department of Physics, University of Oxford, Oxford OX1 3PU, UK
2. Department of Physics & Astronomy, University of Louisville, Louisville, Kentucky 40292, USA
3. Department of Earth & Space Sciences, University of California, Los Angeles, California 90095-1567, USA

Correspondence to: P. L. Read¹ Correspondence and requests for materials should be addressed to P.L.R. (Email: p.read1@physics.ox.ac.uk).

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