Book chapter
The Mysterious Periodicities of Saturn Clues to the Rotation Rate of the Planet
Saturn in the 21st Century, pp.97-125
Cambridge Planetary Science Series, Cambridge Univ Press
01/01/2019
DOI: 10.1017/9781316227220.005
Abstract
The rotation rate of a planet is a fundamental parameter, no less than its mass or composition, and planetary investigators require this rate to assess various other phenomena such as planetary wind speeds, internal and atmospheric models, ring dynamics and so forth. Saturn presents a conundrum, however, because none of its various planetary periods indicates the "true" rotation of the planet. Thus, although the planet displays an abundance of periodicities near 10.7 hours, the exact rotation period of Saturn is unknown. In the magnetosphere, "planetary-period oscillations" (PPOs) appear in charged particles, magnetic fields, energetic neutral atoms, radio emissions and motions of the plasma sheet and magnetopause. In Saturn's rings, the spoke phenomenon can exhibit periodicities near 10.7 hours, and ring phenomena themselves may be related to the interior rotation of the planet. In the highlatitude ionosphere, modulations near this period appear in auroral motions and intensities. In the upper atmosphere, some cloud features rotate near this period, although wind speeds are generally faster, and the well-known polar hexagon rotates with a period close to 10.7 hours. Some of the magnetospheric/ionospheric oscillations differ in the northern and southern hemispheres and their periods do not remain constant, sometimes varying on long time scales of a year or longer and sometimes on much shorter time scales. These variations in the period argue against a cause related to changes interior to Saturn, and because the magnetic and spin axes of Saturn are reported to be axisymmetric (unlike those of any other known planet), Saturn's periodicities cannot be explained as "wobble" caused by a geometric tilt or by a nondipolar magnetic anomaly. Several models have been proposed to account for the observed periodicities, including rotating atmospheric vortices, periodic plasma releases and a flapping magnetodisk, but none can satisfactorily explain all of Saturn's periodicities nor their common origin, and none can determine the exact rotation rate of the planet. This chapter reviews Saturn's periodicities, theories thereof, and how they might be used to determine the elusive rotation rate of the planet.
Details
- Title: Subtitle
- The Mysterious Periodicities of Saturn Clues to the Rotation Rate of the Planet
- Creators
- James F. Carbary - Johns Hopkins UniversityMatthew M. Hedman - University of IdahoThomas W. Hill - Rice UniversityXianzhe Jia - University of Michigan–Ann ArborWilliam Kurth - University of IowaLaurent Lamy - Univ PSL, LESIA, Observ Paris, CNRS, Paris, FranceGabrielle Provan - University of Leicester
- Contributors
- K H Baines (Editor)F M Flasar (Editor)N Krupp (Editor)T Stallard (Editor)
- Resource Type
- Book chapter
- Publication Details
- Saturn in the 21st Century, pp.97-125
- Publisher
- Cambridge Univ Press; CAMBRIDGE
- Series
- Cambridge Planetary Science Series
- DOI
- 10.1017/9781316227220.005
- Number of pages
- 29
- Grant note
- NAS5-97271; 003 / NASA Office of Space Science; National Aeronautics & Space Administration (NASA) 1405851 / NASA JPL contract 1415150 / NASA; National Aeronautics & Space Administration (NASA) Southwest Research Institute Jet Propulsion Laboratory
- Language
- English
- Date published
- 01/01/2019
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984455543302771
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