**DPS Pasadena Meeting 2000, 23-27 October 2000**

*Session 29. Io*

Oral, Chairs: W. Smythe, D. Simonelli, Wednesday, 2000/10/25, 10:30am-12:10pm, C106
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## [29.01] Io's Gravity Field and Interior Structure

*G. Schubert, W.B. Moore (UCLA), J.D. Anderson, R.A. Jacobson, E.L. Lau (JPL)*

Radio Doppler data generated by the Deep Space Network (DSN)
from four encounters of the Galileo spacecraft with Io,
Jupiter's innermost Galilean satellite, can be used to infer
Io's gravitational quadrupole moments. By combining the four
flybys into a single solution for the gravity field, both
tidal and rotational components are separately determined,
thereby establishing that Io is in global hydrostatic
equilibrium. Consequently, viable interior models must
satisfy constraints imposed by the mean radius
R~=~1821.6~±~0.5~km, the mean density
\rho~=~3527.8~±~2.9~kg/m^{3}, and the normalized axial
moment of inertia C/MR^{2}~=~0.37685~±~0.00035. With
equilibrium now established for Io, the gravity data and the
mean radius determine Io's principal axes (c~<~b~<~a) as
a~=~1830.0~±~0.5~km, b~=~1819.2~±~0.5~km,
c~=~1815.6~±~0.5~km. Io almost certainly has a metallic
core with a radius between 550 and 900~km for an Fe-FeS core
or between 350 and 650~km for an Fe core. Io is also likely
to have a crust and a partially molten asthenosphere, but
their thicknesses cannot be separately or uniquely
determined from the above constraints.

Supported by NASA through the Galileo Project at JPL and the
Planetary Geology and Geophysics Program.

The author(s) of this abstract have provided an email address
for comments about the abstract:
schubert@ucla.edu

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