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