Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p53c..01s&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P53C-01
Other
[5704] Planetary Sciences: Fluid Planets / Atmospheres, [5724] Planetary Sciences: Fluid Planets / Interiors, [5734] Planetary Sciences: Fluid Planets / Magnetic Fields And Magnetism, [5744] Planetary Sciences: Fluid Planets / Orbital And Rotational Dynamics
Scientific paper
It has been generally believed that a rotation period could be assigned to each of the giant planets. Accepted values of these periods, till now, are 9h 55m 29s, 10h 39m 22s, 17h 14m 24s, and 16h 06m 36s for Jupiter, Saturn, Uranus, and Neptune, respectively. The rotation period of Jupiter is based on the periodic variations in the planet’s kilometric radiation and magnetic field, periodicities that have been unchanged since the Voyager flybys. The association of these periodicities with Jupiter’s internal rotation period is based on the idea that the radio and magnetic phenomena are tied to the planet’s magnetic field lines anchored deep within Jupiter. The periodic variations of the Saturnian Kilometric Radiation (SKR), unlike those of Jupiter, have not been rock solid, however; the periodicity has changed from 10h 39m 22s at the time of Voyager to 10h 45m 45s at the time of Cassini. Clearly, the SKR period does not represent the internal rotation period of Saturn, and it raises the possibility that the rotation periods of the other giant planets are uncertain. In fact, we must seriously reconsider whether the interiors of the giant planets are in solid body rotation with a single period. Even for Jupiter, the 9h 55m 29s rotation period might represent only the rotation of the region in which the magnetic field is generated. The dynamo region could extend from some unknown inner radius out to about 0.9 Jovian radius. The deeper Jovian interior could be rotating with a different period. A recent attempt to model the interior of Jupiter with new equation of state data concluded that the gravitational coefficients of Jupiter could not be fit unless Jupiter’s internal rotation rate was constant on cylinders parallel to the rotation axis (Militzer, B., W.B. Hubbard, J. Vorberger, I. Tamblyn, and S.A. Bonev, A massive core in Jupiter predicted from first-principles simulations, 2008, ApJ, 688, L45-L48 [doi: 10.1086/594364]). For Saturn, two studies of the atmospheric motions (Anderson, J.D. and G. Schubert, 2007, Saturn’s gravitational field, internal rotation, and interior structure, Science, 317, 1384-1387 [doi: 10.1126/science.1144835]; Read, P.L., T.E. Dowling, and G. Schubert, Saturn’s rotation period from its atmospheric planetary-wave configuration, 2009, Nature, 460, 608-610 [doi:10.1038/nature08194 Letter]) have inferred planetary rotation periods significantly shorter than the Voyager period, implying Jovian-like atmospheric winds. The inferred shapes (oblateness) of Uranus and Neptune are inconsistent with heretofore accepted planetary rotation rates. Either the shapes or the rotation periods of the icy giants are not well determined. If the magnetic fields of Uranus and Neptune are generated in relatively thin shells (Stanley, S., and J. Bloxham, Convective-region geometry as the cause of Uranus’ and Neptune’s unusual magnetic fields, Nature, 428, 151-153 [doi:10.1038/nature02376] Letter), then the periodicities of the fields might not reflect the rotation of the bulk of the planets.
Anderson John D.
Helled Ravit
Schubert Gerald
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