1. 1 Phenomena in the Solar System: need of network of observation J.E. Arlot, M. Stavinschi IMCCE/CNRS/observatoire de Paris Institut astronomique de l’académie roumaine Antalya, March 2006

2. 2Summary The observations of the natural planetary satellites The phenomena The occurrences of the phenomena What is a mutual event The difficulties of the observations The infrared observations The network of observers The Uranian satellites The scientific goals

3. 3 For dynamical studies flux time (hours) The mutual events (occurring each 6 years) Two kinds of observation Astrometric observations Photometric observations

4. 4 The accuracy depending on the kind of observation Example: the Galilean satellites Kind of observationAccuracy in masAccuracy in km Eclipses by Jupiter150450 Old photographic plates100300 Transit circle60180 Plates newly reduced50150 CCD observations40120 Mutual events1545 Interest of observing the mutual events

5. 5 The accuracy depending on the kind of observation Kind of observationAccuracy in masAccuracy in km CCD observations40400 Mutual events660 The case of the Uranian satellites

6. 6 The most common events The most common events are the eclipses by the planet The atmosphere on the planet leads to a poor astrometric accuracy

7. 7 Rare events The Mutual events (Galilean satellites of Jupiter)

8. 8 Opportunities for mutual events Mutual events occur when the planetocentric declination of the Earth and the Sun is zero: for example for the Galilean satellites, it happens in 2003 and in 2009 This occurrence should be at the opposition of the planet

9. 9 Rare events Occurrence of mutual events: Uranus: 2007-2008 (every 42 years) Jupiter: 2009 (every 6 years) Saturn: 2010 (every 15 years)

10. 10 What is an observation of a mutual event? The direct astrometric measurement is replaced by a photometric measurement against time

11. 11 What is an observation of a mutual event? It is a light curve which includes physical properties of the surface of the body and dynamical parameters of the motion of both satellites. The light curve must be referred to UTC within 0.1 second of time.

12. 12 What happens during a mutual event

13. 13 Observation of a mutual event An occultation of a satellite by another The satellites are slightly out of focus to improve the photometric accuracy and avoid saturation of the receptor

14. 14 Examples of lightcurves Non-symetrical lightcurve Deep event near total Faint event grazing

15. 15 Sky and meteorological problems

16. 16 Infrared observations An example of infrared observation: the measurement of the thermal emission of a satellite The case of Io

17. 17 Infrared observations Occultation of Io by Europa The first ground-based detections of the volcanoes of Io were made through occultations of Io

18. 18 Observing sites

19. 19 Past observations Galilean Satellites of Jupiter The last campaigns of observations provided numerous data 1985199119972003 Number of sites of observations 28364234 Number of observations made 166401255271 Number of events observed 64115122104

20. 20 The Uranian satellites These satellites are difficult to observe, more easily observable in infrared: Ariel: magnitude 14.4 Umbriel: magnitude 14.8 Titania: magnitude 13.8 Oberon: magnitude 14.2 Miranda: magnitude 16.5 Puck: magnitude 20

21. 21 Example: events observable from Turkey Year Mth Day Hr mn sec Event 2006 5 18 1 7 48. 5 O 1 2006 7 15 0 8 12. 5 O 1 2007 8 1 2 9 7. 1 E 5 2007 8 15 23 58 52. 5 E 3 2007 8 17 1 13 56. 5 O 2 2007 8 26 1 51 48. 2 E 5 2007 8 29 2 20 47. 1 O 5 2007 9 22 18 26 19. 1 O 5 2007 9 30 17 39 10. 1 E 5 2007 10 19 19 22 53. 5 E 4 2007 11 17 17 8 2. 1 E 5 2007 12 6 16 39 59. 5 E 1 2007 12 18 18 4 41. 5 E 1 2008 2 2 15 53 10. 5 E 1 2008 7 14 22 24 31. 5 E 1 2008 9 10 22 26 41. 5 E 1 Event: 5 O 1 means that satellite 5 occults satellite 1 2 E 5 means that satellite 2 eclipses satellite 5

22. 22 The scientific goals Study of dynamics of systems of natural satellites They are small solar systems allowing to understand formation and evolution of such systems Making models including all gravitational effects and dissipation of energy Need of a high astrometric accuracy to quantify all physical and dynamical parameters and measure accelerations

23. 23 A question to be solved with accurate astrometry Tides from satellite to planet Tides from planet to satellite Tidal effects in the jovian system planet satellite a, e satellite planet Satellite escapes Satellite falls

24. 24 First estimations of the acceleration of the Galilean satellites Galilean Satellites of Jupiter: Purpose of the increasing astrometric accuracy: - measure of the tidal effects n’ 1 /n 1 n’ 2 /n 2 n’ 3 /n 3 De Sitter, 1928+33 (+/- 5)+27 (+/- 7)-15 (+/- 6) Greenberg, 1986+32 (+/- 8)-16 (+/- 4.5) Goldstein, 1996+70 (+/- 75)+56 (+/- 57)+28 (+/- 20) Vasundhara, Arlot, 1996 +22.7 (+/- 7.9)-6.1 (+/- 9.3)+10.6 (+/- 10.6) Aksnes, Franklin, 2001 +54.7 (+/- 16.9)+27.4 (+/- 8.4)-27.4 (+/- 8.4)

25. 25Conclusion Rare events are coming soon We need a network of observers Please join us for these observations ! Web site: http://www.imcce.fr/pheura07www.imcce.fr/pheura07 e-mail: arlot@imcce.frarlot@imcce.fr Workshop to be held in Paris on November 16-18, 2006 Web site: http://paris2006.imcce.fr