Geodesy of Amalthea and the Galilean Satellites of Jupiter

Details Geodesy of Amalthea and the Galilean Satellites of Jupiter Geodesy of Amalthea and the Galilean Satellites of Jupiter

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.g42c..01s&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #G42C-01

Physics

1227 Planetary Geodesy And Gravity (5420, 5714, 6019), 5417 Gravitational Fields (1227), 5430 Interiors (8147), 6218 Jovian Satellites

Scientific paper

An important scientific legacy of the Galileo mission is the determination of the masses and quadrupole components of the gravitational fields of the Galilean satellites. A final report of the mission results is given including values of GM (G is the universal gravitational constant, M is satellite mass), the gravitational coefficients J2 and C22, and the correlation coefficient μ between J2 and C22. The values of J2 and C22 are deduced using the a priori assumption J2 = (10/3)C22. The least squares method for fitting the Doppler residuals does not fix this ratio, but allows J2 and C22 to vary independently and determines the correlation between them. The a priori assumption is consistent with the hydrostatic equilibrium of a satellite, but it does not require hydrostaticity. Values of μ show that J2 and C22 are independently determined only for Io; the ratio of J2 and C22 is consistent with a hydrostatic Io. J2 and C22 are not independently determined for Ganymede even though there are both equatorial and polar flybys of the satellite. A quadrupole field is insufficient to fit the Ganymede data to the noise level. The additional signal is interpreted in terms of mascon anomalies at the surface of Ganymede. The gravitational coefficients, together with the assumption that the degree~2 gravitational fields of the satellites derive from their hydrostatic distortions to rotation and the Jovian tidal force, are used to infer the moments of inertia of the satellites and their internal structures. The mass and closest approach distance for Amalthea can be determined from Doppler data from the Galileo encounter of 5~November 2002. The final results indicate a density that is significantly smaller than the approximate 1000~kg\ m-3 density of water ice. The quadrupole components of Amalthea's gravitational field are undetectable in the encounter Doppler data.

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