土卫八新运动理论的比较研究

A COMPARATIVE STUDY OF THE NEW THEORIES OF THE MOTION OF IAPETUS

通过归算土卫八轨道根数200年的变化将一个最新的高精度土卫运动理论TASS与经典理论作比较，并用20年现代照相观测资料作理论预报精度的归算．归算表明，在一定时期内TASS与经典理论有较好的一致，但其根数长期变化的差很快变大．由此指出，TASS的合理性和进入实用还有待对更长时期大量高精度观测作实算．

Vienne and Duriez (1991) have built a new theory of TASS of motion for all the eight major satellites of Saturn. They claimed that the theory has an internal precision of a few kilometers, which is compatible with space observations. We compared the theory of inchon of lapetus in TASS with the theory of lapetus given by Harper and Taylor (1993). The epochs and frames of reference adopted in the two theories are quite different and their elements are not directly comparable. So it is necessary to transform the two sets of elements into one and the same frame. We have accomplished these conversions with aid of the spherical triangular geometry and Lieske's formulae, which were used for the conversion from J2000.0 reference system to B1950. Then we calculated the TASS--H&T differences in 200 years of secular and long--period perturbations for each of the elements for lapetus and plotted the variations of the differences with bine in years. Finally, in order to verify. the calculations the authors computed the rms (O-C) residuals obtained with the two theories with some major sets of observational data. TIs study shows that the two theories have a better consistency of residuals in a limited bine span covered by the available data, but in a longer duration the secular variations for the two sets of osculating elements are significantly different. So the authors proposed that for TASS the validity, superiority and applicability to practice remain to be verified by fitting it to more observations over a longer period.