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Saturn

Jupiter and Saturn Size ComparisonSummary

1. At an average distance of just under 10 AU, Saturn takes over 29 years to orbit the Sun

2. Saturn is only slightly smaller than Jupiter (9.5x the Earth) but much less massive (95x Earth).

This means it has the lowest density of any planet in the solar system

3. Saturn rotates rapidly like Jupiter in just over 10 hours

4. Saturn receives roughly 1/100th of the radiation the Earth receives so its outer layers are very

cold – only 93 K

Saturn has belts and zones like

Jupiter, but they are fainter and less

distinct

It also has white oval storm features, but no great red spot!

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Cassini Image of 5000 km diameter Hurricane surrounding Saturn’s South Pole

350 mph winds!

Saturn rotates slower than Jupiter!

Expect: a smaller equatorial bulge

Find: a larger (10%) bulge!

How can this be?

Saturn has a much lower density so is much easier to deform!

Chemical Composition of Outer Atmosphere

Similar to Jupiter – mostly hydrogen and helium

Difference – less helium!

‘Helium Deficient’

Internal Heat

Saturn is smaller and cooled faster!

Expect: less internal heat!

Find: more internal heat!

Why?

Helium condenses out as droplets (rain) in side the planet. As this fall inward it heats the interior by

friction!

Also explains helium deficiency!

Because of its weaker gravity, Saturn’s atmosphere is much more spread out!

Because of Saturn’s weaker gravity, its liquid metallic hydrogen (LMH) layer is thinner and deeper than

Jupiter’s

Overall Saturn is mostly made of gas

Smaller amounts of LMH means its magnetic field is only 1/20th of Jupiter’s but

still 1000x stronger than the Earth’s!

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Saturn’s Aurora Saturn from Earth

Three main rings and a gap (Cassini Division)

As Saturn orbits the Sun we see different views of the rings!

When the rings are seen edge-on, they essentially disappear!

This means they must be very thin:

Width 200,000 kmThickness < 2 km

Saturn with rings edge-on in 2009

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The rings are made of chunks of highly reflective water ice! Origins of the Rings

1. Debris left over from the formation of Saturn

2. More recent breakup of a icy moon spiraling into the planet

Evidence:

Since the rings are so bright, it suggests that they are very young, perhaps only 50 million years

old or so!

They therefore cannot be formation debris!

Objects can spiral into a planet when they are captured into a retrograde orbit where they revolve around the planet in the opposite direction to

planetary rotation

Tidal Forces

Tidal Distortion

As a moon spirals in it eventually breaks apart at the Roche Limit where tidal forces > gravity

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Voyager Flybys

New Rings and Gaps

The rings are made up of

thousands of ringlets

Saturn’s Radial Spokes

What keeps the rings together?

How are the gaps cleared out?

Debris around a planet naturally disperses into a spherical cloud

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The Inner Moons of Saturn The “Braided” F-ring

Shepherd moons keep it together

Mimas

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Cassini Mission to Saturn

A 4 year mission to study the planet and its moons

Cassini Orbiter – Jan 2007

Close-up views of rings!

Two new moons just beyond F-ring

New faint ring between A- and F-rings

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Giant dust ring discovered in IR by Spitzer Space Telescope in 2009

Mimas (2010)

Herschel Crater

Jupiter’s Ring was discovered by Voyager 1

Very thin and faint!

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Saturn has 62 known moons!

Titan is the only moon with an atmosphere!At 1.6 atm it is even thicker than the Earth’s!

Composition: 90% N2 + traces of hydrocarbons

Under conditions on the surface of the Earth water exists as a liquid

Phase Diagram

Under surface conditions on Titan (atmospheric pressure 1.6 atm, temperature 94 K) hydrocarbons

can exist as liquids

Liquid hydrocarbon oceans on surface?

Cassini Orbiter deploying Huygens Lander Designed to land on the surface of Titan

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Infrared image of Titan’s surface Channels carved by liquids?

Ontario Lacus: Hydrocarbon lake on Titan! Cassini image of sunlight reflecting off of a hydrocarbon lake!

Hydrocarbon Fog!

Must have an active hydrological cycle!

Jan 14th 2005 – The Surface of Titan

Slushy mixture of solid water ice and liquid hydrocarbons

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Ice appears to be rounded like river rocks by erosion from liquids

Enceladus

Small inner moon of Saturn

Highly reflective surface

Surface shows geological activity

Interior is tidally heated and may be liquid

Plumes of water recently discovered being ejected from the surface

Cassini Flyby 2009

May have a subsurface ocean like Europa which is suitable for life!

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Other Moons

Tethys

Odysseus crater

Hyperion

Low density and porous like sponger

Pheobe

Retrograde high inclination orbitCaptured Kuiper Belt object?

Iapetus

One hemisphere bright one dark – thermal segregation?Equatorial Ridge