New observations of the Natural Planetary satellites through the Natural Satellites USNO Plates Archive

International audienceThe U.S. Naval Observatory in Washington DC owns the largest collection of photographic plates of the natural planetary satellites. The USNO Plates Archive, made by D. Pascu from 1967 to 1998 proposes observations of the Martian satellites, the Galilean satellites and the main satellites of Saturn. Most of these plates have been reduced at a time where star catalogues were not enough accurate and dense to ensure a good astrometric reduction. The arrival of new accurate catalogues such as the UCAC2 and, in the future, the GAIA catalogue, make valuable the scanning of selected plates from which the positions of the satellites will be used for the improvement of the dynamical models of motions. More, it will be possible to extract from these plates the positions of the planets themselves for periods of time where observations are needed. We will be able to make the precovery of the planets' positions. The satellites of Mars have been observed from 1967 to 1997 during 88 nights leading to 1788 exposures. Observations were made even during the non favourable periods, when no one were observing and allow to complete the observational sample with unique observations and make possible the determination of the short periodic terms in the motion of the satellites due to the fast rotating nature of these objects. The Galilean satellites were observed from 1967 to 1998 during 264 nights providing 2791 exposures. The main satellites of Saturn were observed from 1974 to 1998 during 175 nights making available 1828 exposures. Databases including the USNO Plates Archive will bring new scientific information for the dynamical exploration of these systems. This work has been made possible thanks to CNRS and the Scientific Council of Paris Observatory