1 Imaging the natural satellites J.E. Arlot IMCCE/CNRS/observatoire de Paris Astro/photo/phemu meeting October 14-18, 2015

2 Natural satellites observations Astrometric observations of the natural satellites are extensively made for dynamical and planetological studies Natural satellites are not punctual targets and the center of mass is not well defined Albedo variations, phase defect and reflexion/diffusion of light law are not well known Mutual events have shown these photometric problems

 field 2°x2° 3

 field 15’ x 15’ 4

The first difficulty: the distance to the planet 5

The second difficulty: the phase defect  cos d = C s sin (i/2) sin Q   = C s sin (i/2) cos Q  the right ascension and declination i is the phase angle C is a coefficient depending on the law of diffusion, 0.75 for Lambert law s is the apparent radius of the body in radians. Q is the position angle of the equator of intensity 6

The third difficulty: the surface albedo variation Ganymede map 7

8 The satellites of Mars

9 Satellites of Mars: Observations:USNO Pascu (photographic plates) IMCCE Pic du Midi Colas (CCD, C-MOS) Russian data (photographic plates, CCD) Faint bodies close to Mars => difficult to observe

Satellites of Mars at USNO (photographic plates) 10

Satellites of Mars at Pic du Midi (CCD) 11

The inner satellites of Jupiter 12

13 The inner satellites of Jupiter Observations:Pascu et al. (Flagstaff: CCD, HST) Colas, Vachier (Pic du Midi: CCD) Vieira-Martins (Itajuba, Brazil: CCD) Ledovskaya (Pik Terskol: CCD)

The inner satellites of Jupiter 14 Thebe © Pic du Midi  Thebe © IRTF

Large and complex objects: « icy satellites » 15 The Galilean satellites of Jupiter

16 The Galilean Satellites of Jupiter: Observations:Photographic plates: old series (Carte du Ciel), USNO Pascu CCD: Pulkovo, OHP Transit circle: Flagstaff Photometric observations: Eclipses by Jupiter Mutual events: PHEMU campaigns Problem: to increase the accuracy of the observations new observational techniques new reduction of the observations

The Galilean satellites of Jupiter The Jovian system: very bright objects: few stars on photographic plates 17

Photographic plates 18

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20 Outer satellites of Jupiter: two families The irregular outer satellites of Jupiter

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22 Irregular outer satellites of Jupiter Observations: OHP for J-6 to J-13, J-17 Brazilian obs. for J-6 to J-13, J-17 Mauna Kea, Paranal for the fainter J-17, … Bodies far from Jupiter easy to observe Slow bodies far from Jupiter => need of observations on a long period of time

The inner satellites of Jupiter 23

24 The inner satellites of Jupiter

25 Cassini images The inner satellites of Jupiter

26 Inner and Lagrangian Satellites of Saturn: Fast and faint bodies close to Saturn  difficult to extrapolate the ephemerides need of numerous observations problem of the bright ring Observations:Poulet and Sicardy (CCD ESO, HST) Veiga et al. (photo and CCD, Itajuba) Nicholson et al. (CCD Palomar) Oberti et al. (photo, ESO) The inner satellites of Jupiter

27 Main Satellites of Saturn S-1 to S-8: Observations: Pascu (photographic plates, USNO) Poulet and Sicardy (CCD ESO, HST) Veiga et al. (photo and CCD, Itajuba) Nicholson et al. (CCD Palomar) Oberti et al. (photo, ESO) PHEMU network similar to the Galilean satellites but much more observed! The main satellites of Saturn

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The large satellites: the Eight main satellites of Saturn Not enough stars due to the short exposure because of the brightness of the satellites and the ring Image made at Observatoire de Haute Provence with the 1.2m telescope The main satellites of Saturn

Cassini Camera ISS Field 0°.35 Dione (1120 km) and Enceladus (512 km) Stars from UCAC2 (magnitude 9) 60 mas (UCAC2) = 3 km 1 mas (GAIA) = 50 m  star star 

31 Observations: for Phoebe for PhoebeOHP Table Mountain FlagstaffItajuba for the fainter: Mauna Kea Paranal Slow bodies far from Saturn as the outer satellites of Jupiter The irregular outer satellites of Saturn

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33 No space probe observing Main satellites: Observations: Inner:Pascu (HST) ESO- VLT (data mining) Main:Veiga et al. (photo and CCD, Itajuba) transit circle in Flagstaff transit circle in Bordeaux Owen (CCD, Table Mountain) Outer (all retrograde):ESO Mauna Kea Calar Alto Palomar Th satellites of Uranus

34  The Uranian system (Itajuba)

 The Uranian system (VLT-ESO) 35

Caliban  CFHT 36

37 The Uranian system NTT (above) VLT ‘below)

38 Main and Inner satellites (Triton, Nereide, N-3 to N-8): Observations: Main and inner: Colas (Pic du Midi) Veiga et al. (photo and CCD, Itajuba) Stone (transit circle, Flagstaff) Owen (CCD, Table Mountain) OHP (CCD) Outer: ESO Mauna Kea CFHT Cerro Tololo Las Campanas The satellites of Neptune

Proteus at ESO 39

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Itajuba (above) HST (below) 41

Pluto/Charon The discovery of Charon on photographic plates 42

Discovering P2, P3 et P4 43 The Pluto system

Pluto is in the Milky Way (cliché ESO, NACO) 44 The Pluton system

45 Conclusions - satellites are more difficult to observe than the asteroids - some satellites are difficult to observe because they are too bright - plan the observational campaigns depending on the need of obervations more than on the ease of observing: databases contains ~ observations of the Galileans and ~ observations of the Saturnians…