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W. B. Hubbard (U. Arizona)
High-resolution, high-precision maps of surface shape and gravity are available for most of the terrestrial planets, but such data are still lacking for the giant planets because of the difficulty of executing low-periapse orbiter missions. With the approval of the Juno mission to Jupiter, a highly capable geodetic mission to a giant planet is now in prospect, and a Juno-like mission could eventually fly to Neptune. With the capability of measuring near-surface gravity anomalies well below a milligal, it becomes possible to probe the deep dynamics of giant planets. Jupiter's static (zonal) gravitational spectrum will depend on the style of interior convection. Measurements of dynamic (tidal) response and pole precession may provide independent information about the deep interior. Measurements of windspeeds and geodetic data in Saturn and Neptune already provide us with constraints on interior dynamics in those planets: a reported dramatic shift in Saturn's equatorial windspeed should be reflected in its measurable atmospheric shape, and, if deep-seated, its near-surface gravity. Available data and models show that Neptune's pronounced retrograde equatorial wind does not entrain a substantial fraction of the planet's mass.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.