The most distant planet known to the ancients is NASA’s latest target for exploration.

Cassini image, October 6, 2002

Saturn Facts Average orbital distance9.54 A.U. Orbital period29.42 yr Diameter120,536 km(Earth =12,756) Rotation period0.44 days Mass568e24 kg Average Density0.687 g/cc(water = 1.0) Obliquity26.73 degrees SurfaceNone – we see cloud tops Composition89.7% H, 9.9% He, 0.8% H 2 O by volume With some methane and ammonia And traces of acetylene, ethylene, etc Satellites18 Inner, >33 total NASA ExplorationPioneer 11, launched 1973 Voyager 1, Voyager 2, launched 1977 Cassini/Huygens, launched 1997

Rhea Enceladus Dione Tethys Mimas Titan

Name Semimajor Axis (km) Period (days) Eccentricity Inclination (deg) Mean Radius (km)Mass (10^20 kg) Pan133, ~ 0 10 Atlas137, ~ 0 16 Prometheus139, Pandora141, Epimetheus151, Janus151, Mimas185, Enceladus238, Tethys294, Telesto294, ~ 0 11 Calypso294, ~ 0 10 Dione377, Helene377, Rhea527, Titan1,221, Hyperion1,481, Iapetus3,561, Phoebe12,952,

Notes on satellite dynamics Moons are 1:1 spin-orbit coupled (and so have leading, trailing sides) Mimas:Tethys 2:1 resonance Enceladus:Dione 2:1 Titan:Hyperion 4:3 Dione has leading Trojan: Helene Tethys has Trojans Telesto and Calypso Janus and Epimethus 1:1 horseshoe resonance “Cassini division” is a Mimas resonance A-ring structures caused by Pandora, Prometheus, and Janus Pan causes Encke gap in A ring

Rings of Saturn FeatureBoundaries (km)Optical DepthNotes InnerOuter D Ring66,90074,65810^-5Contains narrow ringlets at 67,580 and 71,710 km. C Ring74,65891, to 0.35Isolated "plateaus" among a surrounding, fainter ring. Titan Ringlet77,87177,896A narrow, eccentric ringlet inside a gap in the C Ring. Maxwell Ringlet87,49187,555A narrow, eccentric ringlet inside a gap in the C Ring Rs Ringlet88,71688,732A narrow, eccentric ringlet inside a gap in the C Ring Rs Ringlet90,17190,232A narrow, eccentric ringlet inside a gap in the C Ring. B Ring91,975117, to 2.5 Contains fine structure on all scales. The most opaque of Saturn's rings. Cassini Division117,507122,3400 to 0.1 The prominent gap between the A and B Rings. It contains several features of low optical depth. Huygens Ringlet117,825118,185 A narrow, eccentric ringlet near the inner edge of the Cassini Division. A Ring122,340136, to 1.0 A fairly uniform ring with many density and bending waves near its outer edge. Encke Gap133,410133,7400 A gap in the A Ring "shepherded" open by the embedded moon Pan. One or more faint ringlets are also present. Keeler Gap136,510136,5500An empty gap near the outer edge of the A Ring. F Ring (core)140, to 1 An eccentric ringlet containing clumps and kinks. Based on its eccentricity, its radial limits are 140,194 to 140,244 km. G Ring166,000173,20010^-6A very faint, isolated dust ring. E Ring180,000480,00010^-6 A broad, faint dust ring encompassing the orbits of Mimas through Dione. Densest near the orbit of Enceladus. Up to ~ 30,000 km thick.

Inferred Ring Particle Size Distribution

F-ring, Pandora, Prometheus (Voyager 2)

Voyager 2: discovery image of satellite Pan

Cassini, Huygens probe, and Launch vehicle adapter

Cassini/Huygens key dates June 11, 2004 – Flyby of Phoebe July 1, 2004 – Crossing of ring plane during Saturn-orbit insertion sequence Dec 25, 2004 – Huygens probe separates Jan 14, 2005 – Huygens begins its descent into Titan’s atmosphere

Jean Dominique Cassini Saw “Cassini Division”, and satellites Iapetus, Rhea, Tethys, and Dione

Christiaan Huygens Discovered Titan Proposed flat ring system

Pandora, F-ring, Prometheus, Cassini orbiter

Enceladus: Ice geysers supply material for E ring?

Izanagi and Izanami craters on Rhea