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Paper: Pluto and Planets X
Volume: 107, Completing the Inventory of the Solar System
Page: 163
Authors: Standish, E. M.
Abstract: The discovery of Neptune was inevitable; its gravitational force causes residuals in the observations of Uranus which are large and undeniable. The subsequent attempts at repeating that type of discovery, however, have met with a notable lack of success, because they were doomed from the start: the remaining residuals are smaller than many of the known systematic errors which exist in the observations. It is now known that the discovery of Pluto, in contrast, was the result of a systematic search. While the ephemerides of Uranus and Neptune seem to have no unexplained problems, the ephemeris of Pluto does have problems. The observations span only a small portion of the planet's full period and they are prone to systematic zone errors in the catalogues. Furthermore, there is a large bias which can not be removed from the residuals by a mere orbit adjustment; its cause is presently unknown though it probably is the result of inhomogeneous data reductions. Such problems become especially important for navigational concerns with the Pluto Fast Flyby Mission. For that, optical navigation will provide certain relative ephemeris updates, but they will not be able to improve the uncertainties in the radial direction until only a few days before encounter. Improvements to the absolute ephemerides of Pluto will come from re-measurement of older photographic plates using newer measuring equipment, reductions of such measurements with respect to modern star catalogues (Hipparcos/Tycho) and new positional determinations using modern measuring techniques, such as photoelectric, CCD, and, possibly, radio measurements.
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