Saturn's Gravity Field and Interior Structure: First Results From the Cassini Mission

Details Saturn's Gravity Field and Interior Structure: First Results From the Cassini Mission Saturn's Gravity Field and Interior Structure: First Results From the Cassini Mission

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p23d..01a&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P23D-01

Physics

1221 Lunar And Planetary Geodesy And Gravity (5417, 5450, 5714, 5744, 6019, 6250), 5714 Gravitational Fields (1221), 5724 Interiors (8147), 5734 Magnetic Fields And Magnetism

Scientific paper

The orbiting Cassini spacecraft can be used as a probe of Saturn's gravity field. In particular, two close approaches are planned for Cassini Radio Science on 2006 September 9 and 2008 May 17 at distances of 2.94 R_S and 3.26 R_S (R_S = 60,330 km), distances comparable with Voyager flyby distances at 3.04 R_S and 2.63 R_S. However, with Doppler tracking at X-Band (~ 8.4 GHz), rather than the Voyager and Pioneer tracking at S-Band (~ 2.3 GHz), and with slower velocities at closest approach, Cassini can improve on results from Voyager I and II and Pioneer 11. The Pioneer flyby distance is the most favorable of all, 1.27 R_S, but at a separation angle of 8° from the Sun, where the S-Band tracking data are compromised by coronal plasma noise. Remarkably, in the process of navigating the craft, the Cassini Navigation Team has determined an improved gravity field from five Saturn periapsis passages between 6 February 2004 and 10 March 2005, two of which are closer than the Voyager flybys. They report a Saturn GM of 37931123 ± 36 km3/s2, and zonal harmonic coefficients J2 = 16291.4 ± 0.9, J4 = -931 ± 5, and J6 = 91 ± 13, all in units of 10-6, and for a reference radius R_S, the one-bar equatorial radius. With the Gundlach and Merkowitz G of (6.674215 ± 0.000092) × 10-11 m3/kg/s2, the total mass M is (5.683234 ± 0.000078) × 1026 kg. The mean radius R is 58,265,253 m for a mean density of 685.9297 ± 0.0094 kg/m3. We use this improved gravity field, along with the Zharkov-Trubitsyn theory of figures, to infer properties of Saturn's interior, similar to the inferences drawn from the gravity fields of the Galilean satellites during the Galileo mission at Jupiter. We use a solid-body rotation period from magnetic-field data of 10h 39m 23.0s, in close agreement with the IAU value. The associated smallness parameter ω2R3/GM is 0.139883.

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