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Astrometry of planets through their satellites

This article discusses the astrometry of planets using their satellites. It explores the dynamics of the satellites to determine the center of mass of the system and the best dynamical model to use. The article also highlights the advantages and challenges of observing planetary satellites and presents the results of observational tests on the Jovian and Saturnian systems.

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Astrometry of planets through their satellites

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  1. Astrometry of planetsthroughtheir satellites J.-E. Arlot IMCCE/CNRS/observatoire de Paris

  2. Pseudo positions of planetsthroughtheir satellites • Jupiter and Saturn not directly observable (too bright and too large) • Better to observe their satellites and coming back to the center of mass of the system through the dynamics of the satellites • What dynamical model to be used for the satellites? The best (!) made through relative observations. In fact, it is not critical because of the high accuracy of the relative ephemerides. • Maybe we should buid ephemerides especially made for that purpose

  3. Imaging naturalplanetary satellites CCD images on the 1m50 Strand USNO telescope in Flagstaff Photographic plates on the 26-inch USNO refractor in Washington

  4. Observingmeridian transit of planetary satellites • Advantages: • Bright objects • Link to many stars • Problems: • Only one observation each night • Observation at different dates for several objects Flagstaff Bordeaux

  5. Test of the planetary ephemerides (Jovian system) from photographic plates: mean residuals in a (in mas) residualsfromtransit circle observations 1967-1979: r.m.s. = 58 mas 1980-1989: r.m.s. = 62 mas 1990-1998: r.m.s. = 62 mas

  6. residualsfromtransit circle observations Test of the planetaryephemerides (Jovian system) fromphotographic plates: meanresiduals in d (in mas) 1967-1979: r.m.s. = 61 mas 1980-1989: r.m.s. = 66 mas 1990-1998: r.m.s. = 67 mas

  7. Residuals in RA and DEC for each opposition In RA : average near 0 mas for all satellites with a periodic term (12 years=period of Jupiter) In DEC : average near 20 mas from 0 to 50 mas depending on the considered satellite and on the ephemeris used

  8. residualsfromtransit circleobservations Test of the planetaryephemerides (Saturnian system) fromtransit circles: rms of the residuals in arcsec

  9. The accuracy of the satellite’s observations used is critical but the residuals are similar

  10. Residuals for the Saturnian satellites in RA and DEC Resultsfromphotographic platesusing the UCAC2 catalogue Residuals in RA and DEC are calculatedusing INPOP10 for Saturn and the JPL SAT351 ephemeris for the satellites

  11. residualsfromtransit circleobservations rms of the residuals in arcsec: Uranus’ system

  12. Uranus’ (O-C)s (DE 405) From Bordeaux transit circle observations

  13. (O-C) residuals in arcsec Observations of Uranus and satellites from 2000 to 2005 with transit circle and CCD images

  14. (O-C) residualswithtransit circleobservations in mas • Observations made from 1997 to 2005 with transit circles: residuals in mas (positions of the centre of mass of Uranus calculated from satellites through LA06 ephemeris) Bx = Bordeaux Ff= Flagstaff

  15. (O-C) residuals of transit circle observations (DE 405) d 1997-2005 a

  16. More recent data • After analyzing the 1997-2005 transit circle observations (Bordeaux and Flagstaff) what about the 2006-2014 observations? • At the present time, I confirm unexplained starnge biases

  17. Conclusion • Planets are observable through their satellites and we may use: • Positions of space probes around the planets • Positions of natural satellites easily measurable from ground based telescopes • Natural satellites orbiting around the center of mass of the system • Need of a good dynamical model of the planetary satellites

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