1. Astrometry of planets through their satellites J.-E. Arlot IMCCE/CNRS/observatoire de Paris

2. 2 Pseudo positions of planets through their 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 natural planetary satellites 3 Photographic plates on the 26-inch USNO refractor in Washington CCD images on the 1m50 Strand USNO telescope in Flagstaff

4. Advantages:Advantages: –Bright objects –Link to many stars Problems:Problems: –Only one observation each night –Observation at different dates for several objects FlagstaffBordeaux Observing meridian transit of planetary satellites

5. Test of the planetary ephemerides (Jovian system) from photographic plates: mean residuals in  (in mas) DE200DE405DE421INPOP06INPOP08INPOP10 J-1J-4J-1J-4J-1J-4J-1J-4J-1J-4J-1J-4 1967- 1979 -30-422318-3-6 -980702-3 1980- 1989 -86-9014100-5-6-10444061 1990- 1998 -118-120-11-5-9-3-15-101114-51 1967-1979: r.m.s. = 58 mas 1980-1989: r.m.s. = 62 mas 1990-1998: r.m.s. = 62 mas residuals from transit circle observations

6. DE200DE405DE421INPOP06INPOP08INPOP10 J-1J-4J-1J-4J-1J-4J-1J-4J-1J-4J-1J-4 1967- 1979 0841184625382079393114 1980- 1989 -31540233722331849333519 1990- 1998 61322216181022130-102618 1967-1979: r.m.s. = 61 mas 1980-1989: r.m.s. = 66 mas 1990-1998: r.m.s. = 67 mas Test of the planetary ephemerides (Jovian system) from photographic plates: mean residuals in  (in mas) residuals from transit circle observations

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. 8 residuals from transit circle observations TitanHyperion alphadeltaalphadelta FASTT 19990.140.170.180.23 20010.110.120.160.18 Bordeaux 19990.050.100.170.25 20010.040.100.220.34 20030.050.090.260.19 20040.030.120.250.36 20060.08 0.170.28 Test of the planetary ephemerides (Saturnian system) from transit circles: rms of the residuals in arcsec

9. 9

10. 10 The accuracy of the satellite’s observations used is critical but the residuals are similar

11. Residuals for the Saturnian satellites in RA and DEC ObjectsRADEC Residuals(mas) All satellites-13+20 Enceladus-47-33 Tethys+3+27 Dione-55-12 Rhea-7+51 Titan-18+23 Hyperion+15+23 Iapetus+10+12 Dispersion10072 11 Residuals in RA and DEC are calculated using INPOP10 for Saturn and the JPL SAT351 ephemeris for the satellites Results from photographic plates using the UCAC2 catalogue

12. 12 residuals from transit circle observations OberonUranus alphadeltaalphadelta FASTT 19980.150.140.120.15 20010.150.13 0.14 20020.130.110.160.11 20040.110.100.110.14 Bordeaux 19970.160.090.050.08 19980.110.180.09 20010.260.230.060.11 20020.110.310.080.09 20040.130.240.080.14 20050.220.280.080.25 rms of the residuals in arcsec: Uranus’ system

13. 13 Uranus’ (O-C)s (DE 405) From Bordeaux transit circle observations

14. 14 (O-C) residuals in arcsec Observations of Uranus and satellites from 2000 to 2005 with transit circle and CCD images ObjectObservatoryMean residual in alpha (‘’) Mean residual in delta (‘’) UranusFlagstaff-0.01-0.05 TitaniaFlagstaff-0.10-0.11 OberonFlagstaff-0.11-0.12 Uranus Table Mountain -0.02-0.06 UmbrielTable Mountain-0.17-0.11 TitaniaTable Mountain-0.09-0.13 OberonTable Mountain-0.12 UranusBordeaux-0.12-0.16 UmbrielBordeaux-0.10-0.07 TitaniaBordeaux-0.14-0.18 OberonBordeaux-0.13-0.07

15. 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) VSOP82DE200DE421INPOP06INPOP08INPOP10 (O-C)  Bx Ff -131 -204 -125 -202 -55 -54 -62 -64 -120 -124 -84 -80 (O-C)  Bx Ff -149 -130 -148 -130 -84 -53 -62 -34 -156 -123 -138 -100  Bx Ff 255 265 252 264 199 156 201 160 226 192 209 167  Bx Ff 268 184 267 185 241 142 233 135 275 181 268 167 Bx = Bordeaux Ff= Flagstaff (O-C) residuals with transit circle observations in mas

16. (O-C) residuals of transit circle observations (DE 405) 1997-2005  

17. 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

18. 18Conclusion 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