The Improvement of Planetary Theories over 6000 Years
Jean Chapront
Observatoire de Paris, France
The JPL numerical integration DE406 covers a long range (6000 years), and
represents the best fit to the observations on the contemporary period. The
planetary theory VSOP87 (Bretagnon et al., 1988) has been fitted to the JPL
numerical integration DE200. For most planets, the solutions are valid over
1 or 2 milliners, and deteriorate rapidly beyond few milliners, particularly
in the case of the major planets. Taking advantage of the semi-analytical
form of VSOP developed in Poisson series, we have made the differences VSOP
minus DE406 and corrected the coefficients of the developments with an
appropriate least-square method. This adjustment improves the integration
constants, the reference frame and frequencies in VSOP as well as Poisson's
terms in the series (terms increasing with the time). A new solution having
the same form as VSOP is then proposed. Globally the gain compared to VSOP
is important. For example, over 2000 years, in the case of the planetary
mean longitudes, the factor goes from 50 to 5000 and is greater beyond.
Finally, in most cases, our new solution is an approximation of DE406 with
an error of a few milliarcseconds.