Radio Occultations Offer Limited Insight into Ice Giant Internal Rotation

This paper investigates the potential of radio occultations to constrain the internal rotation periods of Uranus and Neptune. The authors re-examine the idea that planetary shapes and wind profiles can reveal interior rotation rates, focusing on the ice giants. They find that for Uranus, a narrow range for the 1-bar polar radius is consistent with existing data, even when treating the interior spin as a free parameter. This limitation arises because the isobaric shape is primarily determined by the total rotation of the isobaric surface, which is already well-constrained. However, radio occultations remain valuable for validating assumptions about the influence of winds on planetary shape. The study highlights the potential for detecting a north-south asymmetry in Uranus's winds, which could produce a measurable difference in polar radii. For Neptune, the greater uncertainty in wind profiles leads to larger variations in radii. The authors confirm that magnetic rotation periods yield non-zero mean dynamical heights for the atmospheres of both planets. Accurate radius determination requires incorporating latitude-dependent rotation. Significantly faster interior rotation periods (close to 15 hours) would be needed to minimize dynamical heights. The research underscores the challenges in using radio occultations to directly determine internal rotation periods, while emphasizing their utility in refining atmospheric models and testing assumptions about wind dynamics. Future missions with advanced radio occultation capabilities could provide valuable insights into the atmospheric structure and dynamics of Uranus and Neptune, but alternative methods may be needed to probe their deep interiors.

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