Saturn's Gravity Field and Interior Structure

Details Saturn's Gravity Field and Interior Structure Saturn's Gravity Field and Interior Structure

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.0203a&link_type=abstract

American Astronomical Society, DPS meeting #38, #02.03; Bulletin of the American Astronomical Society, Vol. 38, p.483

Physics

Geophysics

Scientific paper

The orbiting Cassini spacecraft can be used as a probe of Saturn's gravity field. The analysis of Pioneer and Voyager tracking data (Campbell and Anderson, Astron. Jour. 97 1485, 1989) provide the best Saturn gravity field for interior studies prior to Cassini, with a Saturn GM of 37931272 ± 200 km3/s2, and zonal harmonic coefficients J2 = 16298 ± 10, J4 = -915 ± 40, and J6 = 103 ± 50, all in units of 10-6, and for a reference radius RS = 60,330 km. Cassini navigation data provide an improved gravity field (Jacobson et al., Astron. Jour. Submitted July 12, 2006), with GM = 37931207.7 ± 1.1 km3/s2, and harmonic coefficients in units of 10-6 of J2 = 16290.71 ± 0.27, J4 = -935.8 ± 2.8, and J6 = 86.1 ± 9.6. By extrapolating from these measured harmonics to the undetectable J8 and J10, we carry at least some of the interior calculations to fifth order in Saturn's normalized rotation rate. The rotation period is taken from Cassini magnetic-field data (Giampieri et al., Nature 441 62, 2006) at 10h 47m 6s ± 40 s, and is slower than pre-Cassini estimates by about 8 minutes. We use this improved gravity field and rotation rate, along with the Zharkov-Trubitsyn theory of figures, to infer properties of Saturn's interior. Unlike Jupiter, with its regular dipole magnetic field and with little or no core, Saturn has a complex magnetic field. Furthermore, a core of approximately 3.2 Earth masses is required in order to fit the new Cassini gravity data, especially J4. This core mass is at the low end of previous estimates. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. G.S. acknowledges support by grants from NASA through the Planetary Geology and Geophysics Program.

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