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R. A. Jacobson (JPL)
We have used Saturnian satellite astrometric observations together with the data acquired during the spacecraft flybys of Saturn (Pioneer~11, Voyager~1, and Voyager~2) to develop new satellite and spacecraft ephemerides and a revised gravity field for the Saturnian system. The astrometric data are from the time period 1966 to 2003. The spacecraft data are more extensive than those Campbell and Anderson (1989 {\em AJ} 97, 1485) used in their determination of the gravity field. We also included a~priori information on Saturn's zonal harmonics from the ringlet constraint devised by Nicholson and Porco (1988 {\em JGR} 93, 10209). The gravity parameters found in our analysis are: \begin{center} \begin{array}{l@{\extracolsep{-1ex}}l l@{\extracolsep{+1ex}}l} \hline\hline \noalign{\smallskip} \multicolumn{1}{l}{Parameter\dag} & \multicolumn{1}{c}{Value} & \multicolumn{1}{l}{Parameter\dag} & \multicolumn{1}{c}{Value} \\ \noalign{\smallskip} \hline \noalign{\smallskip} \begin{array}{l} GM\rm system \end{array} &\hspace{0.5ex} \begin{array}{l@{±l} 37940683. & 58. \end{array} & \begin{array}{l} GM\rm Phoebe \end{array} &\hspace{2.3ex} \begin{array}{r@{±l} 0.48&0.23\ddag \end{array} \\ \begin{array}{l} GM\rm Mimas\\ GM\rm Enceladus\\ GM\rm Tethys\\ GM\rm Dione\\ \end{array} &\hspace{5ex} \begin{array}{r@{±l} 2.56&0.05 \\ 5.76&1.30 \\ 41.21&0.05 \\ 73.13&0.02 \\ \end{array} & .\begin{array}{l} J2 \\ J4 \\ J6 \\ J8 \\ \end{array}}\times106 & \begin{array}{r@{±l} 16294.& 6. \\ -921.&27. \\ 99.&28. \\ \multicolumn{1}{r}{-10.\ddag\hphantom{0}} \end{array} \\ \begin{array}{l} GM\rm Rhea\\ GM\rm Titan\\ GM\rm Hyperion\\ GM\rm Iapetus\\ \end{array} &\hspace{3ex} \begin{array}{r@{±l} 154.53&3.78 \\ 8978.09&0.88 \\ 0.72&0.35\ddag\\ 131.73&15.08 \\ \end{array} & \begin{array}{l} \alpha\rm p \\ \delta\rm p \\ \dot{\alpha}\rm p \\ \dot{\delta}\rm p \\ \end{array} & \begin{array}{r@{±l} 40.59550 &0.00360\ddag \\ 83.53812 &0.00018\ddag \\ \multicolumn{1}{r}{-0.04229\ddag}& \\ \multicolumn{1}{r}{-0.00444\ddag}& \\ \end{array}\\ \noalign{\smallskip} \hline\hline \noalign{\smallskip} \multicolumn{4}{l}{\dagunits:\;\;GM(km^{3}sec^{-2}),\;\; \alpha\rm p,\delta\rm p(deg),\;\; \dot{\alpha}\rm p,\dot{\delta}\rm p(deg century^{-1})}\\ \multicolumn{4}{l}{\ddagnot estimated}\\ \end{array} \end{center}The GMs of Hyperion and Phoebe are based on assumed densities of 1.1±.5 and 1.3±.5 gm/cm3, respectively. The Saturn pole right ascension \alpha\rm p and declination \delta\rm p are from French {\em et al.} (1993 {\em Icarus}, 103, 163) and their rates are computed from the precession rate of Nicholson {\em et al.} (1999 {\em BAAS} 31, 1140).
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.