DDA 33rd Meeting, Mt. Hood, OR, April 2002
Session 7. Posters
Monday, April 22, 2002, 7:00pm

## [7.02] The Orientation of the Pole of Jupiter

R. A. Jacobson (JPL/Caltech)

George Null (1976 {\em AJ}\, 81, 1153) determined the orientation of the Jovian pole from a combination of Pioneer 10 and 11 tracking data. The IAU adopted his pole (Davies {\em et al.} 1980 {\em Celest. Mech.} 22, 205) together with rates derived from the motion of the Jovian equator in Lieske's Galilean satellite theory (Lieske 1980 {\em A&A} 82, 340). Campbell and Synnott (1985 {\em AJ} 90, 364) added the Voyager tracking data to the Pioneer data and redetermined the pole, changing it little from Null's value. The IAU pole direction was precessed to the J2000 system in 1983 (Davies {\em et al.} 1983 {\em Celest. Mech.} 29, 309).

We have been using the data from the Pioneer, Voyager, Ulysses, Galileo, and Cassini spacecraft together with Earth based observations in an effort to determine the gravity field of Jupiter and its Galilean satellites and to improve the ephemerides of those bodies. In our analysis we found that we were unable to adequately process the data when we used the IAU pole model which ignores the significant 30 year periodic perturbation induced by Europa. Our current model obtains the pole orientation by numerically integrating Jupiter's rotational equations of motion with torques due to the Galilean satellites, Saturn, and the Sun. The ICRF right ascension and declination of the pole at epoch J2000 that we have determined from the fit to the data are 268.\!\!^\circ0573±.\!\!^\circ0008 and 64.\!\!^\circ4958±.\!\!^\circ0005. The numerically integrated pole may be approximated to an accuracy of 0.\!\!^\circ0001 by:\\[-4ex] \begin{eqnarray*} \alpha&=& 268.\!\!^\circ05815 - 0.\!\!^\circ00496 T - 0.\!\!^\circ00012\sin\Omega1 + 0.\!\!^\circ00095\sin\Omega2 \\ & & + 0.\!\!^\circ00129\sin\Omega3 \\ \delta&=& \hphantom{0}64.\!\!^\circ49585 + 0.\!\!^\circ00195 T - 0.\!\!^\circ00005\cos\Omega1 + 0.\!\!^\circ00041\cos\Omega2 \\ & & + 0.\!\!^\circ00056\cos\Omega3 \\ where\quad\Omega1&=& 278.\!\!^\circ121802 + 4842.\!\!^\circ80 T \qquad\Omega2 = 176.\!\!^\circ060293 + 1191.\!\!^\circ64 T \\ \Omega3&=& 304.\!\!^\circ517402 + 271.\!\!^\circ98 T \\ and\quad T&=& Julian centuries from epoch J2000\\ \end{eqnarray*}

Bulletin of the American Astronomical Society, 34, #3
© 2002. The American Astronomical Society.