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

Cassini image, October 6, 2002

Saturn Facts

Average orbital distance 9.54 A.U.Orbital period 29.42 yrDiameter 120,536 km (Earth =12,756)Rotation period 0.44 daysMass 568e24 kgAverage Density 0.687 g/cc (water = 1.0)Obliquity 26.73 degrees

Surface None – we see cloud topsComposition 89.7% H, 9.9% He, 0.8% H2O by volume

With some methane and ammoniaAnd traces of acetylene, ethylene, etc

Satellites 18 Inner, >33 total

NASA Exploration Pioneer 11, launched 1973Voyager 1, Voyager 2, launched 1977Cassini/Huygens, launched 1997

Rhea

Enceladus

Dione Tethys

Mimas

Titan

NameSemimajor Axis

(km)Period (days)

EccentricityInclination

(deg)Mean Radius (km) Mass (10^20 kg)

Pan 133,583 0.5750 ~ 0 ~ 0 10

Atlas 137,640 0.6019 ~ 0 ~ 0 16

Prometheus 139,350 0.612986 0.0024 0.0 50 0.0014

Pandora 141,700 0.628804 0.0042 0.0 42 0.0013

Epimetheus 151,422 0.694590 0.009 0.34 59 0.0055

Janus 151,472 0.694590 0.007 0.14 89 0.0198

Mimas 185,520 0.9424218 0.0202 1.53 199 0.385

Enceladus 238,020 1.370218 0.0045 0.02 249 0.73

Tethys 294,660 1.887802 0.0000 1.09 530 6.22

Telesto 294,660 1.887802 ~ 0 ~ 0 11

Calypso 294,660 1.887802 ~ 0 ~ 0 10

Dione 377,400 2.736915 0.0022 0.02 560 10.52

Helene 377,400 2.736915 0.005 0.2 16

Rhea 527,040 4.517500 0.0010 0.35 764 23.1

Titan 1,221,850 15.945421 0.0292 0.33 2575 1345.5

Hyperion 1,481,100 21.276609 0.1042 0.43 143

Iapetus 3,561,300 79.330183 0.0283 7.52 718 15.9

Phoebe 12,952,000 550.48 0.163 175.3 110

Notes on satellite dynamics

Moons are 1:1 spin-orbit coupled (and so have leading, trailing sides)Mimas:Tethys 2:1 resonanceEnceladus:Dione 2:1Titan:Hyperion 4:3Dione has leading Trojan: HeleneTethys has Trojans Telesto and CalypsoJanus and Epimethus 1:1 horseshoe resonance

“Cassini division” is a Mimas resonanceA-ring structures caused by Pandora, Prometheus, and JanusPan causes Encke gap in A ring

Feature Boundaries (km) Optical Depth Notes

Inner Outer

D Ring 66,900 74,658 10^-5 Contains narrow ringlets at 67,580 and 71,710 km.

C Ring 74,658 91,975 0.05 to 0.35 Isolated "plateaus" among a surrounding, fainter ring.

Titan Ringlet 77,871 77,896 A narrow, eccentric ringlet inside a gap in the C Ring.

Maxwell Ringlet 87,491 87,555 A narrow, eccentric ringlet inside a gap in the C Ring.

1.470 Rs Ringlet 88,716 88,732 A narrow, eccentric ringlet inside a gap in the C Ring.

1.495 Rs Ringlet 90,171 90,232 A narrow, eccentric ringlet inside a gap in the C Ring.

B Ring 91,975 117,507 0.4 to 2.5Contains fine structure on all scales. The most opaque of Saturn's rings.

Cassini Division 117,507 122,340 0 to 0.1The prominent gap between the A and B Rings. It contains several features of low optical depth.

Huygens Ringlet 117,825 118,185A narrow, eccentric ringlet near the inner edge of the Cassini Division.

A Ring 122,340 136,780 0.4 to 1.0A fairly uniform ring with many density and bending waves near its outer edge.

Encke Gap 133,410 133,740 0A gap in the A Ring "shepherded" open by the embedded moon Pan. One or more faint ringlets are also present.

Keeler Gap 136,510 136,550 0 An empty gap near the outer edge of the A Ring.

F Ring (core) 140,219 0.1 to 1An eccentric ringlet containing clumps and kinks. Based on its eccentricity, its radial limits are 140,194 to 140,244 km.

G Ring 166,000 173,200 10^-6 A very faint, isolated dust ring.

E Ring 180,000 480,000 10^-6A 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 ParticleSize Distribution

F-ring, Pandora, Prometheus (Voyager 2)

Voyager 2: discovery image of satellite Pan

Cassini, Huygens probe, andLaunch vehicle adapter

Cassini/Huygens key dates

June 11, 2004 – Flyby of PhoebeJuly 1, 2004 – Crossing of ring plane during Saturn-orbit insertion sequenceDec 25, 2004 – Huygens probe separatesJan 14, 2005 – Huygens begins its descent into Titan’s atmosphere

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

Christiaan HuygensDiscovered 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