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Home , Aegaeon (moon), Anthe (moon), Atlas (moon), Calypso (moon), Daphnis (moon), Dione (moon)

Cassini Small Bodies Observations

Ymir

Tilmann Denk Freie Universität Berlin, Germany

10th Small Bodies Assessment Group Meeting (SBAG) Washington, DC – Thu 09 Jan 2014 2:20 p.m. EST (8:20 p.m. CET)

T.D. gratefully acknowledges the support of this research by the Deutsches Zentrum für Luft- und Raumfahrt (DLR) in Bonn (Germany) (grant no.: 50 OH 1102). Cassini Orbiter Remote Sensing (ORS)

• Imaging (ISS NAC, WAC) • Vis./near-IR spectrometer (VIMS) • IR spectrometer (CIRS) • UV spectrometer (UVIS)

ORS FOVs:

= 3.5° = 0.35°

Denk -- Cassini Small Bodies Observations – page 2 Small Bodies or "Rocks" of

"Alkyonides" 3 38 "Irregulars"

"Ring rocks", 9 • , , • , Siarnaq, Albiorix, "Sheperds", Paaliaq, , , "Co-orbitals" between • Tarvos, , Erriapus, and Skathi, Hyrrokkin, Suttungr, • , , Atlas , Mundilfari, Thrymr, Narvi, • Discovered by Cassini etc. , Bestla, , Tarqeq, • Beyond 11 million km (> 180 R ) • Inside Mimas ; 4 "Lagrange " S

partly inside A ring or "Trojans" • 9 prograde, 29 retrograde

• Cassini: disk-resolved • , • Discovered from & spectra ,

• Cassini: only disk-integrated L4 & L5 moons of • (except Phoebe) , Denk -- Cassini Small Bodies Observations – page 3 "Ring rocks" Pan, Daphnis

Denk -- Cassini Small Bodies Observations – page 4 "Ring rocks" Pan Daphnis Atlas 34 x 21 km 9 x 6 km 41 x 19 km

Denk -- Cassini Small Bodies Observations – page 5 "F-ring Sheperds" Prometheus, Pandora 136 x 59 km 104 x 64 km

Denk -- Cassini Small Bodies Observations – page 6 "F-ring Sheperds" Prometheus, Pandora 136 x 59 km 104 x 64 km

Denk -- Cassini Small Bodies Observations – page 7 "Co-orbitals" "Problem": Δai < ΣRi

Janus, Epimetheus [ The difference of objects' semi-major axes is smaller than Horse-shoe orbits the sum of the objects' radii ]

aJA = 151,460 km aEP = 151,410 km rJA = 100 km rEP = 65 km

=> Exchange of orbits every 4 years

Rotating coordinate system January Cartoon is not to scale 2014 Denk -- Cassini Small Bodies Observations – page 8 "Co-orbitals" Janus 203 x 153 km

Epimetheus 130 x 106 km

Denk -- Cassini Small Bodies Observations – page 9 Aegaeon Produces the G ring

Semi-major axis: 167,500 km Orbit & : 19.4 h Object size: 1.5 x 0.5 km

Denk -- Cassini Small Bodies Observations – page 10 "Alkyonides" Methone, Anthe, Pallene orbit between Mimas and Enceladus; P ~ 24...28 h

øMethone ~ 3.2 km øPallene ~ 5.0 km

Denk -- Cassini Small Bodies Observations – page 11 "Lagrange Moons" or "Trojans"

Tethys or Dione

Saturn

Denk -- Cassini Small Bodies Observations – page 12 "Lagrange Moons" Polydeuces (Dione L5)

Helene 3 x 2 km (Dione L4) 43 x 26 km

Telesto Calypso (Tethys L4) (Tethys L5)

33 x 20 km 30 x 14 km

Denk -- Cassini Small Bodies Observations – page 13 Irregular Moons 38 objects are known at Saturn 9 progrades, 29 retrogrades Range ~ 8...33 million km Sizes: 213 km (Phoebe); <40 km (all others)

Phoebe Ymir

Denk -- Cassini Small Bodies Observations – page 14 Irregular-Satellite Observations with Cassini: Motivation

• Gain information on basic properties of these objects (like rotation period, size, shape, pole-axis orientation, color, ...; search for binaries)

Denk -- Cassini Small Bodies Observations – page 15 Irregular-Satellite Observations with Cassini: Motivation

• Gain information on basic properties of these objects (like rotation period, size, shape, pole-axis orientation, color, ...; search for binaries)

• So far (2013): 17...20 periods, 2 shape models • Expected (2017): up to 32 periods, up to 13 shape models

Paaliaq, 102° phase Ymir

0 days 1 2 days

Denk -- Cassini Small Bodies Observations – page 16 Irregular-Satellite Observations with Cassini: Motivation

• Gain information on basic properties of these objects (like rotation period, size, shape, pole-axis orientation, color, ...; search for binaries)

• Periods, pole-axes orientations: Purely random, or shaped by a physical process?

• Compare to each other and to other solar-system objects

• Understand their role related to the dichotomy of and the reddish color of

• Understand the impact history of the Saturnian system (origin of the irregular moons)

Denk -- Cassini Small Bodies Observations – page 17 Cassini Future Opportunities

• Irregular moons until EOM

• Small inner moons in Cassini Solstice Mission (example of rev 227)

• Small inner moons in F-ring orbits

Denk -- Cassini Small Bodies Observations – page 18 Irregular-moons accessible to the NAC 2014 to 2017 (EOM)

• Synodic rotation - 01/14: Tarqeq • Pole/ shape/ - 03/14: Fornjot sidereal rotation - 09/14: Thrymr* - 12/14: - 12/13: Siarnaq - 12/14: S/2004 S7 - 04/14: Kiviuq • Color - 07/14: Ijiraq - 04/15: Aegir - 08/14: Tarvos - 06/15: Bergelmir* - 12/13: Siarnaq - 06/15: Greip - 04/14: Kiviuq - 05/15: Paaliaq - 10/15: Narvi* - 07/14: Ijiraq - 07/15: Hyrrokkin - 10/15: - 01/16: * - 01/15: Albiorix - 11/15: Bestla - 03/16: Surtur - 04/15: Ymir - 11/15: Narvi

- 01/17: S/2004 S12 - 04/17: Paaliaq - 05/16: Albiorix - 04/17: S/2006 S1 - 08/17: Tarvos - 08/16: Erriapus - 06/17: S/2004 S13 - 12/16: Tarqeq - 09/17: S/2007 S2

Denk -- Cassini Small Bodies Observations – page 19 Cassini Future Opportunities: rev 227 Epimetheus 2,680 km / 16 m/pxl

Atlas 20,640 km / ~130 m/pxl

Prometheus 20,860 km / ~130 m/pxl View from north. Movements of objects: CCW. direction: up.

Denk -- Cassini Small Bodies Observations – page 20 Cassini F-ring and Proximal Orbits

T125 T126

F-ring orbs.: 29 Nov 2016; rev 250 out Prox. orbs.: 22 Apr 2017; rev 270 out EOM: 15 Sep 2017; rev 293 peri

Denk -- Cassini Small Bodies Observations – page 21 Cassini F-ring Orbits "Rocks" Opportunities <25,000 km Orbit Object Altitude Spatial. res.* Moon size*

253 Pandora 18,000 km 110 m/pxl 961x591 pxl

257 Daphnis 18,300 km 110 m/pxl 78x58 pxl Atlas 24,200 km 150 m/pxl 281x129 pxl

258 Pandora 24,100 km 150 m/pxl 720x443 pxl

259 Epimetheus 4,500 km 30 m/pxl 4760x3900 pxl

262 Epimetheus 9,600 km 60 m/pxl 2250x1840 km

264 Pan 23,500 km 140 m/pxl 244x147 pxl

269 Janus 7,900 km 50 m/pxl 4310x3240 pxl Atlas 11,100 km 70 m/pxl 612x282 pxl Aegaeon 22,800 km 140 m/pxl 10x4 pxl *...ISS NAC; phase angle ignored Denk -- Cassini Small Bodies Observations – page 22 Cassini F-ring Orbits Pan – rev 023, and rev 264 simulation

Pan rev 264 244 x 147 pxl

Denk -- Cassini Small Bodies Observations – page 23 Cassini F-ring Orbits Atlas – rev 009, 046, and rev 269 simulation

Atlas rev 269 612 x 282 pxl

Denk -- Cassini Small Bodies Observations – page 24