Dynamical Reference Frames in the Planetary and Earth-Moon Systems
We summarize our previous estimates of the accuracies of the ephemerides. Such accuracies determine how well one can establish the dynamical reference frame of the ephemerides. Ranging observations are the dominant data for the inner four planets and the Moon: radar-ranging for Mercury and Venus; Mariner 9 and Viking spacecraft-ranging for the Earth and Mars; lunar laser-ranging for the Moon. Optical data are significant for only the five outermost planets. Inertial mean motions for the Earth and Mars are determined to the level of 0.″003/cty during the time of the Viking mission; for Mars, this will deteriorate to 0.″01/cty or more after a decade or so; similarly, the inclination of the martian orbit upon the ecliptic was determined by Viking to the level of 0.″001. Corresponding uncertainties for Mercury and Venus are nearly two orders of magnitude larger. For the lunar mean motion with respect to inertial space, the present uncertainty is about 0.″04/cty; at times away from the present, the uncertainty of 1″/cty2 in the acceleration of longitude dominates. The mutual orientations of the equator, ecliptic and lunar orbit are known to 0.″002. The inner four planets and the Moon can now be aligned with respect to the dynamical equinox at a level of about 0.″005.
KeywordsOuter Planet Jovian Planet Inertial Space Celestial Reference Frame Ephemeris Error
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- Morrison, L.V., Helmer, L., Fabricius, C., Einicke, O., Quijano, L., Muinos, J.L., Argyle, R.W.: 1990, “Optical Reference Frame Defined by Carlsberg Meridian Catalogues for the Years 1984–1987”, these proceedings.Google Scholar
- Seidelmann, P.K., Santoro, E.J. and Pulkkinen, K.F.: 1985, Systematic Differences between Planetary Observations and Ephemerides”, in Dynamical Astronomy, V. Szebehely and B. Balazs, Eds., University of Texas Press, Austin, 55–65.Google Scholar
- Standish, E.M.: 1988, “Celestial Reference Frames: Definitions and Accuracies”, in The Impact of VLBI on Astrophysics and Geophysics (M.J. Reid and J.M. Moran, Eds.), D. Reidel, publ., 309–315.Google Scholar
- Standish, E.M.: 1989, “An approximation to the outer planet ephemeris errors in JPL’s DE200“, Astron. Astrophys, in press.Google Scholar