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Imaging the natural satellitesImaging the natural satellites

J.E. ArlotJ.E. ArlotIMCCE/CNRS/observatoire de ParisIMCCE/CNRS/observatoire de Paris

Astro/photo/phemu meetingAstro/photo/phemu meetingOctober 14-18, 2015October 14-18, 2015

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Natural satellites observationsNatural 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°

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field 15’ x 15’

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The first difficulty: the distance to the planet

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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 angleC is a coefficient depending on the law of diffusion , 0.75 for Lambert laws is the apparent radius of the body in radians.Q is the position angle of the equator of intensity

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The third difficulty: the surface albedo variationThe third difficulty: the surface albedo variation

Ganymede map

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The satellites of MarsThe satellites of Mars

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The satellites of MarsThe satellites of Mars

Satellites of Mars:Satellites of Mars:

Observations:Observations: USNO Pascu (photographic plates)USNO Pascu (photographic plates)IMCCE Pic du Midi Colas (CCD, C-MOS)IMCCE Pic du Midi Colas (CCD, C-MOS)Russian data (photographic plates, Russian data (photographic plates,

CCD)CCD)

Faint bodies close to Mars => difficult to observeFaint bodies close to Mars => difficult to observe

• Satellites of Mars at USNO (photographic plates)

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• Satellites of Mars at Pic du Midi (CCD)

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The inner satellites of JupiterThe inner satellites of Jupiter

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The inner satellites of JupiterThe inner satellites of Jupiter

Observations:Observations: Pascu et al. (Flagstaff: CCD, HST)Pascu et al. (Flagstaff: CCD, HST)Colas, Vachier (Pic du Midi: CCD)Colas, Vachier (Pic du Midi: CCD)Vieira-Martins (Itajuba, Brazil: Vieira-Martins (Itajuba, Brazil:

CCD)CCD)Ledovskaya (Pik Terskol: CCD)Ledovskaya (Pik Terskol: CCD)

The inner satellites of JupiterThe inner satellites of Jupiter

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Thebe © Thebe © Pic du MidiPic du Midi

Thebe © IRTFThebe © IRTF

Large and complex objects: « icy satellites »15

The Galilean satellites of JupiterThe Galilean satellites of Jupiter

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The Galilean Satellites of Jupiter:The Galilean Satellites of Jupiter:

Observations:Observations: Photographic plates:Photographic plates: old series (Carte du Ciel), old series (Carte du Ciel), USNO PascuUSNO PascuCCD: CCD: Pulkovo, OHPPulkovo, OHP

Transit circle: FlagstaffTransit circle: FlagstaffPhotometric observations:Photometric observations:

Eclipses by JupiterEclipses by JupiterMutual events: PHEMU campaignsMutual events: PHEMU campaigns

Problem: to increase the accuracy of the observationsProblem: to increase the accuracy of the observationsnew observational techniquesnew observational techniquesnew reduction of the observationsnew reduction of the observations

The Galilean satellites of JupiterThe Galilean satellites of Jupiter

• The Jovian system: very bright objects: few stars on photographic plates

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Photographic platesPhotographic plates

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20 Outer satellites of Jupiter: two familiesOuter satellites of Jupiter: two families

The irregular outer satellites of JupiterThe irregular outer satellites of Jupiter

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Irregular outer satellites of JupiterIrregular outer satellites of Jupiter

Observations: Observations: OHP for J-6 to J-13, J-17OHP for J-6 to J-13, J-17Brazilian obs. for J-6 to J-13, J-17Brazilian obs. for J-6 to J-13, J-17Mauna Kea, Paranal for the fainter J-17, …Mauna Kea, Paranal for the fainter J-17, …

Bodies far from Jupiter easy to observeBodies far from Jupiter easy to observeSlow bodies far from Jupiter => need of observations on a Slow bodies far from Jupiter => need of observations on a long period of timelong period of time

The inner satellites of JupiterThe inner satellites of Jupiter

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The inner satellites of JupiterThe inner satellites of Jupiter

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Cassini imagesCassini images

The inner satellites of JupiterThe inner satellites of Jupiter

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Inner and Lagrangian Satellites of Saturn:Inner and Lagrangian Satellites of Saturn:

Fast and faint bodies close to Saturn Fast and faint bodies close to Saturn difficult to extrapolate the ephemeridesdifficult to extrapolate the ephemerides

need of numerous observationsneed of numerous observationsproblem of the bright ringproblem of the bright ring

Observations:Observations: Poulet and Sicardy (CCD ESO, HST)Poulet and Sicardy (CCD ESO, HST)Veiga et al. (photo and CCD, Itajuba)Veiga et al. (photo and CCD, Itajuba)Nicholson et al. (CCD Palomar)Nicholson et al. (CCD Palomar)Oberti et al. (photo, ESO)Oberti et al. (photo, ESO)

The inner satellites of JupiterThe inner satellites of Jupiter

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Main Satellites of Saturn S-1 to S-8:Main Satellites of Saturn S-1 to S-8:

Observations:Observations:Pascu (photographic plates, USNO)Pascu (photographic plates, USNO)Poulet and Sicardy (CCD ESO, HST)Poulet and Sicardy (CCD ESO, HST)Veiga et al. (photo and CCD, Itajuba)Veiga et al. (photo and CCD, Itajuba)Nicholson et al. (CCD Palomar)Nicholson et al. (CCD Palomar)Oberti et al. (photo, ESO)Oberti et al. (photo, ESO)PHEMU networkPHEMU network

similar to the Galilean satellites but much more observed!similar to the Galilean satellites but much more observed!

The main satellites of SaturnThe main satellites of Saturn

The main satellites of SaturnThe main satellites of Saturn

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The large satellites: the Eight main satellites of SaturnThe large satellites: the Eight main satellites of Saturn

Not enough stars due to the short exposure Not enough stars due to the short exposure because of the because of the brightnessbrightness of the satellites and the ring of the satellites and the ring

Image made at Observatoire de Haute Provence with the 1.2m telescopeImage made at Observatoire de Haute Provence with the 1.2m telescope

The main satellites of SaturnThe main satellites of Saturn

Cassini Camera ISSCassini Camera ISSField 0°.35 Dione (1120 km) and Enceladus (512 km) Field 0°.35 Dione (1120 km) and Enceladus (512 km) Stars from UCAC2 (magnitude 9)Stars from UCAC2 (magnitude 9)

60 mas (UCAC2) = 3 km60 mas (UCAC2) = 3 km1 mas (GAIA) = 50 m1 mas (GAIA) = 50 m

starstar

starstar

starstar

starstar

star star

star star

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Observations:Observations: for Phoebefor Phoebe

OHP OHP Table MountainTable MountainFlagstaffFlagstaffItajubaItajuba

for the fainter:for the fainter:Mauna KeaMauna KeaParanalParanal

Slow bodies far from Saturn as the outer satellites of Slow bodies far from Saturn as the outer satellites of JupiterJupiter

The irregular outer satellites of SaturnThe irregular outer satellites of Saturn

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No space probe observingNo space probe observing

Main satellites:Main satellites:

Observations:Observations:

Inner:Inner: Pascu (HST)Pascu (HST)ESO- VLT (data mining)ESO- VLT (data mining)

Main:Main: Veiga et al. (photo and CCD, Itajuba)Veiga et al. (photo and CCD, Itajuba)transit circle in Flagstafftransit circle in Flagstafftransit circle in Bordeauxtransit circle in BordeauxOwen (CCD, Table Mountain)Owen (CCD, Table Mountain)

Outer (all retrograde):Outer (all retrograde): ESOESOMauna KeaMauna KeaCalar AltoCalar AltoPalomarPalomar

Th satellites of UranusTh satellites of Uranus

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The Uranian system (Itajuba)The Uranian system (Itajuba)

The Uranian system (VLT-ESO)

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Caliban CFHT

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The Uranian systemThe Uranian system

NTT (above)

VLT ‘below)

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Main and Inner satellites (Triton, Nereide, N-3 to N-8):Main and Inner satellites (Triton, Nereide, N-3 to N-8):

Observations:Observations:

Main and inner:Main and inner:Colas (Pic du Midi)Colas (Pic du Midi)Veiga et al. (photo and CCD, Itajuba)Veiga et al. (photo and CCD, Itajuba)Stone (transit circle, Flagstaff)Stone (transit circle, Flagstaff)Owen (CCD, Table Mountain)Owen (CCD, Table Mountain)OHP (CCD)OHP (CCD)

Outer: Outer: ESOESOMauna Kea CFHTMauna Kea CFHTCerro TololoCerro TololoLas CampanasLas Campanas

The satellites of NeptuneThe satellites of Neptune

Proteus at ESO

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Itajuba (above)HST (below)

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Pluto/CharonPluto/Charon

• The discovery of Charon on photographic plates

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• Discovering P2, P3 et P443

The Pluto systemThe Pluto system

• Pluto is in the Milky Way (cliché ESO, NACO)44

The Pluton systemThe Pluton system

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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 ~10 000 observations of the Galileans and ~ 50 000 observations of the Saturnians…