Ring World

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Mass

Earth Saturn

1 95.2

(x 1024 kg) 5.97 568

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Size

Earth Saturn

Radius 1 9.45

Equatorial 6378 60,268

Polar 6357 54,364

Oblateness 0.3% 9.8%

Look for the flattening in the next photo.

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Earth Our Moon

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Density

Earth Saturn

100% 12.5

kg/m3 5515 687

Saturn has the lowest density of all the planets and moons.

Saturn would float in water!

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Large Magnetosphere

• Saturn’s magnetosphere is about 1/5th as large as Jupiter’s.– This is expected because Saturn has a

thinner conducting mantle of metallic H than Jupiter has.

• It’s 20x weaker than Jupiter’s field.– It’s actually only 68% as strong as Earth’s!

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Magnetosphere

• Jupiter’s magnetosphere is tipped slightly to its rotation, and is complex in structure

• Saturn’s magnetosphere is aligned almost perfectly with its rotation (axisymmetric), and its structure is very simple.

• Interesting feature: a ring current.

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Evidence for Saturn’s Magnetic Field! 11

Equatorial Ring Current

• Saturn’s moons Enceladus, Dione, and Tethys are enclosed in a torus of ions (like Jupiter’s Io).

• This torus is outside the major rings (but inside the thin, tenuous E ring).

• A current of about 10 million amps flows through this outer ring.

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Chemical Composition

• 96.3% H 3.25% He (by volume)

• Traces of methane (CH4), ammonia (NH3), water, ammonium hydrosulfide (NH4SH)

• Like Jupiter, there is a mantle of metallic H under a gaseous H envelope.

• Rocky / metallic core

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Saturn’s Orbit

• Average distance from the sun:

1.43 billion km (9.6 A.U.)

• Perihelion: 1.35 billion km

• Aphelion: 1.51 billion km

• Orbit Eccentricity: 0.056 (slightly more eccentric than Jupiter’s orbit)

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Orbit (2)

• Orbital Period: 29.5 years– Orbital Velocity: 9.7 km/s

• Inclination of orbit to ecliptic: 2.5o

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Saturn’s Rotation

• Rotational Period: 10.66 hours (10h 40m)

• Saturn has zonal winds, like Jupiter, but the colors are more muted.

• The rotational axis is tilted 26.7o to the ecliptic. This makes for a periodic tilt in the rings as viewed from the earth.

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Notice the rotational storm.

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A red oval similar to Jupiter’s GRS.22

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apod.nasa.gov/apod/ap090111.html24

The Rings !

• 2 (3) rings visible to the naked eye.

– separated by visible gaps.

• 3 more rings visible telescopically

• A new ring appears to be forming!

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Pan orbits within the Encke Division27

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Movie

Dustyring“spokes”

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Rings are Dynamic, not Static

• Dusty spokes indicate that the rings may be able to change on a short time frame.

• There are also periodic “ripples” in part of the rings…evidence of a collision between the rings & a comet or asteroid.

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BraidedF ring

The ringisn’t reallybraided,but hasspiralsaround it.

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Here’s a site with more info about the spiralaround the F ring.

http://www.aim.ufr-physique.univ-paris7.fr/CHARNOZ/homepage/SPIRAL/spiral_uk.htm

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Shepherd Moons

• Collisions between ring particles should remove kinetic energy from some particles, transfer kinetic energy to others.

– Slower particles should fall into Saturn.– Faster particles should leave the ring.

– Net: the rings should spread out and dissipate.

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The gravityof theshepherdmoonsfocuses therings.

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Barelydiscerniblenew ring(with 2 newtiny moons)

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The Larger Moons

• They’re all ice balls, but they’re not all the same.

• Mimas Enceladus Tethys• Dione Rhea Titan• Iapetus

• All of these moons are in synchronous rotation (leading vs. trailing hemisphere differences)

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MimaswithHerschelCrater

Mimas isabout thesize ofOhio

1150 kg/m3

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Enceladus

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Bluish “tiger stripes”

South Pole

Geysers of water & water vapor erupt fromEnceladus’ south pole region.

Hot spots have been discovered here by Cassini.44

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Tethys hasa giganticcanyonwhich nearlycircles themoon.

Ithaca Chasma

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Dione, leading hemisphereat left, trailing at right.

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Dione

Direction ofmovementthrough space.

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Rhea

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Rhea also hasthose strangelighter stripeson its trailinghemisphere.

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Titan 5150 km diameter 1880 kg/m3

Ganymede 5262 km dia. 1940 kg/m3

How can Titan have a thick atmosphere, when Ganymede doesn’t?

Atmosphere of N2

heavily laden withhydrocarbons:methane ethane

Very smoggy

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Titan hasa complexlayeredatmosphere

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Titan’s atmosphere is 95% N2, 10X denser thanEarth’s, and extends 600 km above the surface.

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Some liquidflows ontitan’ssurface.

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The shoreline of an ethane lake.

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The darker areas are lakesof liquid methane and ethane.

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At Titan’s surface, theTemperature is about95K (-290oF)

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Iapetussooty leading hemispherebright trailing hemisphere

equatorial ridge

What’s thesource ofthe soot?

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Hyperion – a captured comet?apod.nasa.gov/apod/ap090118.html 61

Missions to Saturn

• Pioneer 11– Launched 1973, flyby 1979.– Transmitted low-resolution photos of Saturn,

rings, moons.

• Voyager 1– Launched 1977, flyby 1980– Transmitted 900+ photos of the moons.– Discovered complexity of rings & nature of

Titan’s atmosphere.62

Missions to Saturn (2)

• Voyager 2– Launched 1977, flyby 1981– 1150 photographs of the moons

• Cassini Orbiter with Huygens probe to Titan’s surface.– Launched 1997, arrived in orbit July 1, 2004.

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Cassini’s Mission• Cassini is designed to photograph and

map Saturn & its moons in visible, infrared, and ultraviolet wavelengths.

• It has a magnetometer, magnetic imager, and plasma imager to closely study Saturn’s magnetic field.

• Huygens probe landed on Titan on January 14, 2005.

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