Neptune Uranus Size comparison of the Outer Planets Earth

Early telescopic observations of Saturn a. Galileo, 1610; b. Huygens 1655; c. Cassini 1676

Spacecraft that have visited Saturn Pioneer 11 flew within 21,000 km of Saturn on 1 September 1979, discovered two new moons and an additional ring, charted Saturn's magnetosphere and magnetic field and found its planet-size moon Titan, to be too cold for life. The Voyager 1 and 2 Saturn encounters occurred nine months apart, in November 1980 and August Discovers larger of internal to external heat: 2-to-1 compared to 1-to-1 for Jupiter. Cassini orbital insertion on July 1, Took first image of a moon (Phoebe) on June 11, Still working in April 2006: Cassini dropped the Huygens probe into atmosphere of Titan on January 14, 2005.

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Cassini spacecraft; launched on Oct. 15, 1997 from KSC 7 Year cruise on Venus-Venus-Earth-Jupiter Gravity Assist Trajectory

The Cassini Spacecraft

Interior Structure of Saturn

Like on Jupiter, there are latitudinal bands of clouds and storms

Ribbon clouds in atmosphere – high-speed turbulence

Wind speeds at top of Saturn’s Atmosphere 1700 km/hr Opposite direction

Multiple Rings!CC AA BB Encke Gap F Cassini Division E Ring extends to 7.5 Saturn radii from cloud top DD

Structure: Non-symmetric on each side of Saturn

Braided F-Ring of Saturn due to co-orbiting “shepherd” moons

Two shepherd satellites confine Saturn’s narrow F ring. The outer shepherd gravitationally deflects ring particles inward, and the inner shepherd deflects ring particles outward.

Prometheus = 47 km, Density = 0.42

= 41 km, Density = 0.54 Pandora

Ring Spokes – Dust above the ring plane

The Smaller Moons of Saturn Atlas Prometheus Pandora Janus Epimetheus Telesto Calypso Helene

= 90 km, Density = 0.61 Janus

Epimetheus = 58 km, Density = 0.64

Mimas, 392 km in diameter Herschel Crater is 130 km wide and 10 km deep!

Enceladus – 500 km in diameter Diverse surface, with some tectonics

Enceladus

Tethys – 1,060 km in diameter. Heavily cratered, with some lineaments

Dione – 1,120 km in diameter. Bright surface swirls, many craters

Rhea – 1,530 km in diameter. Very heavily cratered

Pioneer 11 Voyager 1 Cassini visible light image Various spacecraft views of Titan – 5,150 km in diameter Cassini near- IR image

What do we know about Titan? It is the biggest of Saturn’s moons. Titan’s diameter of 5,150 km makes it larger than the planet Mercury with a diameter of 4,880 km and Pluto (2,350 km). Only Jupiter's moon Ganymede is larger. Three-and-a-quarter Earth Moons could fit inside Titan. Titan is the only moon known to have a large atmosphere – maybe thicker than Earth’s (>1,000 mb)! Its atmosphere is mostly nitrogen, just like the atmosphere surrounding Earth, but thicker. Its atmosphere contains methane and tiny amounts of oxygen.

Comparison of Titan’s atmosphere with Earth’s Important gases in Titan’s atmosphere

1.Ethane-methane lakes 2. Moist convection in methane clouds 3. Sedimentation of aerosols 4. Elevated terrain washed by rain

January 14, 2005 – Huygens Probe sent to Titan’s surface

Huygens scientific instruments Aerosol Collector and Pyrolyzer: collects Titan's aerosols for chemical composition analysis; Descent Imager/Spectral Radiometer: makes spectral measurements and takes pictures of Titan's surface and atmospheric hazes; Doppler Wind Experiment: uses radio signals to deduce wind speeds on Titan; Gas Chromatograph/Mass Spectrometer: identifies and quantifies various atmospheric constituents on Titan; Surface Science Package: determines the physical properties of Titan's surface.

Radar Image of Titan’s surface – valley systems

Few impact craters seen on Titan – implies young surface

Horizon at 66 m 15 cm diameter 30 cm diameter Range 85 cm Range 240 cm Surface image from Huygens probe

Iapetus – 1,460 km in diameter. Striking albedo differences

Cassini Views of Iapetus Iapetus is 1,460 km diameter Orbits 59.1 Saturn radii from planet 100 km

What’s Interesting about Phoebe? Phoebe is roughly spherical and is ~220 km in diameter. Phoebe rotates on its axis every 9 hours and orbits Saturn in ~18 months. Its irregular, elliptical orbit is inclined ~30 degrees toward Saturn’s equator. Phoebe’s orbit is retrograde. Phoebe’s average distance from Saturn is 13 million km, which is ~4 times farther away from Saturn than its nearest neighbor, the moon Iapetus. Phoebe and Iapetus are the only major moons in the Saturn region that do not orbit close to the plane of Saturn’s equator. Unlike most major moons orbiting Saturn, Phoebe is very dark and reflects only 6 percent of the sunlight it receives.

Saturn’s moon Phoebe

Identification of surface materials on Phoebe

Saturn Summary