Chapter 11: Jovian Planet Systems

Chapter 11: Chapter 11:

JovianJovianPlanet SystemsPlanet Systems

Jovian Planet PropertiesJovian Planet Properties

Jovian Planet PropertiesJovian Planet Properties

Compared to the terrestrial planets, the Compared to the terrestrial planets, the Jovians:Jovians:• are much larger & more massiveare much larger & more massive• are composed mostly of Hydrogen, are composed mostly of Hydrogen,

Helium, & Hydrogen compoundsHelium, & Hydrogen compounds• have no solid surfaceshave no solid surfaces• rotate more quicklyrotate more quickly• have slightly have slightly ““squashedsquashed”” shapes shapes• have many moonshave many moons• have ring systemshave ring systems

Why are the Jovian Planets so Different?Why are the Jovian Planets so Different?

• They formed beyond the frost line to form large, icy They formed beyond the frost line to form large, icy planetesimals which were massive enough to… planetesimals which were massive enough to…

• Capture H/He far from Sun to form gaseous planets.Capture H/He far from Sun to form gaseous planets.• Each Jovian planet formed its own Each Jovian planet formed its own ““miniatureminiature”” solar solar

nebula.nebula.• Moons formed out of these disks.Moons formed out of these disks.

Inside JupiterInside Jupiter

Moving from the surface Moving from the surface to the core:to the core:• temperature increasestemperature increases• pressure & density pressure & density

increasesincreases

The core of Jupiter is The core of Jupiter is slightly larger than slightly larger than Earth.Earth.

But it is 5 times as dense!But it is 5 times as dense!• thank to tremendous thank to tremendous

weight from aboveweight from above

So Jupiter's core has 10 So Jupiter's core has 10 times the mass of Earth.times the mass of Earth.

Although Jupiter has no solid surface and consists mostly of H & He,it does have distinct interior layers, defined by phase.

Inside JupiterInside Jupiter• Jupiter emits almost twice as much energy as it absorbs from Jupiter emits almost twice as much energy as it absorbs from

the Sun.the Sun.• accretion, differentiation, radioactivity can not account for itaccretion, differentiation, radioactivity can not account for it• Jupiter must still be contractingJupiter must still be contracting

• Jupiter has 3 x more mass than Saturn, but is not much larger!Jupiter has 3 x more mass than Saturn, but is not much larger!• the added weight of H & He compresses the core to a higher densitythe added weight of H & He compresses the core to a higher density• just like stacking pillowsjust like stacking pillows • Add even more mass,

and Jupiter would get smaller.

• Jupiter is about as large as a planet can get.

• Uranus & Neptune have less mass than Saturn, yet• they have higher

densities• they must be made

of denser material

Inside the Jovian PlanetsInside the Jovian PlanetsAll Jovian cores appear to be similar.All Jovian cores appear to be similar.

• made of rock, metal, and Hydrogen compoundsmade of rock, metal, and Hydrogen compounds• 10 x the mass of Earth10 x the mass of Earth

Uranus & Neptune captured less gas from the Solar nebula.Uranus & Neptune captured less gas from the Solar nebula.• accretion of planetesimals took longeraccretion of planetesimals took longer• not much time for gas capture before nebula was cleared out by not much time for gas capture before nebula was cleared out by

Solar windSolar wind

Only Jupiter and Saturn have high enough pressure for H & He to Only Jupiter and Saturn have high enough pressure for H & He to exist in liquid and metallic states.exist in liquid and metallic states.

JupiterJupiter’’s Atmospheres Atmosphere

In 1995, the Galileo space probe In 1995, the Galileo space probe plunged into the planet Jupiter!plunged into the planet Jupiter!

It measured the atmospheric It measured the atmospheric structure of Jupiterstructure of Jupiter• thermosphere thermosphere {absorbs Solar X-{absorbs Solar X-

rays}rays}• stratosphere stratosphere {absorbs Solar UV}{absorbs Solar UV}• troposphere troposphere {greenhouse gases {greenhouse gases

trap heat from both Jupiter and trap heat from both Jupiter and the Sun}the Sun}

Sound Familiar?

These are the same structures found in Earth’s atmosphere.

Atmospheres are governed by interactions between sunlight and gases.

JupiterJupiter’’s Cloud Layerss Cloud Layers

Convection in the troposphere Convection in the troposphere causes Jovian weather.causes Jovian weather.

Warm gas rises to cooler Warm gas rises to cooler altitudes, where it altitudes, where it condenses to form clouds.condenses to form clouds.

Three gases condense in the Three gases condense in the Jovian atmosphere:Jovian atmosphere:• ammonia (NHammonia (NH33))

• ammonium hydrosulfide ammonium hydrosulfide (NH(NH44SH)SH)

• water (Hwater (H22O)O)

They condense at different They condense at different temperatures, so their temperatures, so their clouds form at different clouds form at different altitudes.altitudes.

Like Earth, Jupiter has Like Earth, Jupiter has circulation cells in circulation cells in its atmosphere.its atmosphere.

Jupiter is much larger Jupiter is much larger & rotates much & rotates much faster.faster.• Coriolis effect is Coriolis effect is

much stronger on much stronger on JupiterJupiter

• circulation cells circulation cells are split into many are split into many bands of rising and bands of rising and falling airfalling air

• these are the these are the colored colored ““stripesstripes”” which we seewhich we see

The so-called:The so-called:• zoneszones (rising air) (rising air)• beltsbelts (falling air) (falling air)

JupiterJupiter’’s Cloud Layerss Cloud Layers

Jovian StormsJovian StormsWe also see high pressure storms We also see high pressure storms

• analogous to hurricanes, but they rotate in the opposite directionanalogous to hurricanes, but they rotate in the opposite direction

JupiterJupiter• the Great Red Spotthe Great Red Spot• we are not sure whywe are not sure why

it is redit is red

NeptuneNeptune• the Great Dark Spotthe Great Dark Spot

The Jovian AtmospheresThe Jovian Atmospheres

The temperature profile of The temperature profile of each planet determines each planet determines the color of its the color of its appearance.appearance.

Cloud layers form where a Cloud layers form where a particular gas condenses.particular gas condenses.

Saturn has the same cloud Saturn has the same cloud layers as Jupiter.layers as Jupiter.• they form deeper since they form deeper since

Saturn is colder overallSaturn is colder overall• they are spread farther they are spread farther

apart since Saturn has lower apart since Saturn has lower gravitygravity

Uranus & NeptuneUranus & Neptune• cold enough to form cold enough to form

methane cloudsmethane clouds

Why Uranus & Neptune are BlueWhy Uranus & Neptune are BlueThey have a higher fraction of They have a higher fraction of

methane gas.methane gas.• Methane absorbs red sunlight.Methane absorbs red sunlight.• Only blue light is reflected Only blue light is reflected

back into space by the clouds.back into space by the clouds.

Uranus is Uranus is ““tippedtipped”” on its side. on its side.

It should experience the most It should experience the most extreme seasonal changes.extreme seasonal changes.• no clouds or banded structure no clouds or banded structure

seen in 1986 when N pole seen in 1986 when N pole facing Sunfacing Sun

• no weather, no internal heat?no weather, no internal heat?• HST saw storms in 1998, HST saw storms in 1998,

perhaps b/c the S hemisphere perhaps b/c the S hemisphere is warming nowis warming now

• long seasons cause more haze long seasons cause more haze so that Uranus is a paler blue so that Uranus is a paler blue than Neptunethan Neptune1986 - Visual 1998 - IR

JupiterJupiter’’s Magnetospheres Magnetosphere

• Its general properties are very similar to EarthIts general properties are very similar to Earth’’s, s, exceptexcept• it is about 20,000 times strongerit is about 20,000 times stronger• it extends 3,000,000 km beyond Jupiterit extends 3,000,000 km beyond Jupiter

• Charged particles from the Solar wind (& Io) cause Charged particles from the Solar wind (& Io) cause auroras.auroras.

The Io TorusThe Io TorusThe moon Io loses volcanic gases into space.The moon Io loses volcanic gases into space.

• gases are ions on Sulfur, Oxygen, Sodiumgases are ions on Sulfur, Oxygen, Sodium• they form a donut-shaped belt of charged particles, called the they form a donut-shaped belt of charged particles, called the Io Io

torustorus• they follow Iothey follow Io’’s orbit & are a source of charged particles for the s orbit & are a source of charged particles for the

aurorasauroras• they alter the surfaces of other moons & form bombardment they alter the surfaces of other moons & form bombardment

atmospheresatmospheres

Jovian MagnetospheresJovian Magnetospheres

Saturn, Uranus, & Neptune have smaller & weaker magnetospheres.Saturn, Uranus, & Neptune have smaller & weaker magnetospheres.• fraction of electrically conducting material in interiors is smallerfraction of electrically conducting material in interiors is smaller• Solar wind is weaker farther out, or else their magnetospheres would Solar wind is weaker farther out, or else their magnetospheres would

be even smallerbe even smaller• we can not explain the magnetic field tilts of Uranus & Neptune.we can not explain the magnetic field tilts of Uranus & Neptune.

Jovian Planets have Numerous MoonsJovian Planets have Numerous Moons

medium moonsmedium moons• 300 to 1,500 km in diameter300 to 1,500 km in diameter

large moonslarge moons• greater than 1,500 km in greater than 1,500 km in

diameterdiameter

both groups formed like planets both groups formed like planets out of the out of the ““mini-Solar nebulaemini-Solar nebulae”” surrounding the Jovian planets surrounding the Jovian planets

small moonssmall moons• less than 300 km acrossless than 300 km across• they are not sphericalthey are not spherical• probably captured probably captured

asteroidsasteroids

We can divide them into three groups:

You might think these moons are too You might think these moons are too small for active geology to occur.small for active geology to occur.

You would be wrong!You would be wrong!terrestrial planets are made mostly of rockterrestrial planets are made mostly of rock

Jovian moons are made mostly of iceJovian moons are made mostly of ice

Ices melt at lower temperatures than rock.Ices melt at lower temperatures than rock.less heating is required to have molten coresless heating is required to have molten cores

volcanism and tectonics can occur volcanism and tectonics can occur

There is another heat source.There is another heat source.tidal heating plays a more important roletidal heating plays a more important role

There is very little erosion due to lack of substantial There is very little erosion due to lack of substantial atmospheres atmospheres with the exception of Titanwith the exception of Titan. .

The Large Jovian MoonsThe Large Jovian Moons

JupiterJupiter• Io - Io - sulfur volcanoes• Europa - Europa - world of water ice (and liquid?)• Ganymede - Ganymede - active ice world• Callisto - Callisto - dead & dirty ice world

SaturnSaturn• Titan - Titan - has a thick atmosphere (N2 & CH4)

NeptuneNeptuneTriton - Triton - nitrogen volcanoes, retrograde orbit

The Jovian MoonsThe Jovian MoonsThe moons of Jupiter become less dense The moons of Jupiter become less dense

as you get farther from Jupiteras you get farther from Jupiter• ““mini Solar Systemmini Solar System””

Gravitational tidal heating keeps the Gravitational tidal heating keeps the interiors of the inner moons hot.interiors of the inner moons hot.

IoIoJupiterJupiter’’s tidal forces flex Io s tidal forces flex Io

like a ball of silly putty.like a ball of silly putty.• friction generates heatfriction generates heat• interior of Io is molteninterior of Io is molten

Volcanoes erupt frequently.Volcanoes erupt frequently.• sulfur in the lava accounts sulfur in the lava accounts

for yellow colorfor yellow color• surface ice vaporizes and surface ice vaporizes and

jets awayjets away

Evidence of tectonics & Evidence of tectonics & impact cratering is impact cratering is covered.covered.

EuropaEuropaMetallic core, rocky mantle, Metallic core, rocky mantle,

and a crust made of Hand a crust made of H22O iceO ice

Its fractured surface tells a tale Its fractured surface tells a tale of tectonics.of tectonics.• few impact craters seenfew impact craters seen• double-ridged cracks double-ridged cracks • jumbled icebergsjumbled icebergs

These provide photographic These provide photographic evidence of a subsurface evidence of a subsurface ocean.ocean.

Europa has a magnetic field.Europa has a magnetic field.• implies liquid salt water implies liquid salt water

beneath the icy crustbeneath the icy crust

Where liquid water exists, Where liquid water exists, there could be life!there could be life!

GanymedeGanymede

Largest moon in the Solar SystemLargest moon in the Solar System

Its surface has 2 types of terrain:Its surface has 2 types of terrain:• heavily cratered, implies oldheavily cratered, implies old• long grooves, few craters, long grooves, few craters,

implies young like Europaimplies young like Europa

It also has a magnetic field.It also has a magnetic field.

Could it have subsurface ocean?Could it have subsurface ocean?• case not as strong as Europacase not as strong as Europa’’ss• tidal heating would be weakertidal heating would be weaker• would need additional heating would need additional heating

from radioactive decayfrom radioactive decay

CallistoCallisto

It has an old surface.It has an old surface.• heavily cratered, dirty iceheavily cratered, dirty ice• cratering reveals clean, cratering reveals clean,

white icewhite ice• no evidence of tectonicsno evidence of tectonics

Its interior did not Its interior did not differentiate.differentiate.• rock mixed with icerock mixed with ice

It does not experience tidal It does not experience tidal heating.heating.

Yet it has a magnetic field.Yet it has a magnetic field.

Could it have a subsurface Could it have a subsurface ocean anyway?ocean anyway?

TitanTitan

Largest of SaturnLargest of Saturn’’s moonss moons

It has a thick atmosphere.It has a thick atmosphere.• Nitrogen (90%), Argon, Nitrogen (90%), Argon,

methane, ethanemethane, ethane• N comes from dissociated N comes from dissociated

NHNH33

• methane, ethane are methane, ethane are greenhouse gases: surface greenhouse gases: surface is warmer than it should beis warmer than it should be

• ethane may condense to ethane may condense to form clouds and rainform clouds and rain

The atmosphere blocks our The atmosphere blocks our view of Titanview of Titan’’s surface.s surface.• it may have oceans of it may have oceans of

ethaneethane• erosion may be importanterosion may be important

TritonTriton

• It orbits in the opposite direction of Neptune's rotation in a highly It orbits in the opposite direction of Neptune's rotation in a highly inclined orbit.inclined orbit.• this implies that it was probably captured by Neptunethis implies that it was probably captured by Neptune

• It has a thin Nitrogen atmosphere, sublimed from the surface.It has a thin Nitrogen atmosphere, sublimed from the surface.• Some sort if volcanic activity occurs.Some sort if volcanic activity occurs.

The Rings of SaturnThe Rings of Saturn

From Earth, they look solid.From Earth, they look solid.• concentric rings separated by concentric rings separated by

the the Cassini divisionCassini division

From spacecraft flybys, we see From spacecraft flybys, we see thousands of individual rings.thousands of individual rings.• separated by narrow gapsseparated by narrow gaps• they differ in brightness & they differ in brightness &

transparencytransparency

From within the rings, we would From within the rings, we would see many individual particlessee many individual particles• size ranges from boulders to size ranges from boulders to

dustdust

• made of reflective Hmade of reflective H22O ice O ice (snowballs)(snowballs)

• many collisions keep ring thinmany collisions keep ring thin

Rings, Ripples, and SpokesRings, Ripples, and SpokesGravitational interaction with Gravitational interaction with

moons inside the rings push moons inside the rings push particles into specific orbits.particles into specific orbits.• clear gapsclear gaps

Interaction with larger, distant Interaction with larger, distant moons can clear gaps and moons can clear gaps and form ripples.form ripples.

Dark patches called Dark patches called spokesspokes appear and disappear.appear and disappear.

They are still a mystery.They are still a mystery.

Perhaps they might be particles Perhaps they might be particles of dust drawn out by Saturnof dust drawn out by Saturn’’s s magnetic field.magnetic field.

Comparing Jovian Ring SystemsComparing Jovian Ring Systems

Compared to Saturn, the Compared to Saturn, the other ring systems:other ring systems:• have fewer particleshave fewer particles• are smaller in extentare smaller in extent• have darker particleshave darker particles

Why this is so, we are Why this is so, we are not sure.not sure.

Other unsolved Other unsolved mysteries:mysteries:• UranusUranus’’ rings are rings are

eccentric and slightly eccentric and slightly tilted from its tilted from its equatorial plane.equatorial plane.

• Neptune has partial Neptune has partial rings.rings.

Origin of Planetary RingsOrigin of Planetary Rings

• Within 2 or 3 planetary radii of a planet, its tidal forces Within 2 or 3 planetary radii of a planet, its tidal forces will be greater than the gravity holding a moon will be greater than the gravity holding a moon together.together.• a moon which wanders too close will be torn aparta moon which wanders too close will be torn apart• matter from the mini-nebula at this distance will not form moonmatter from the mini-nebula at this distance will not form moon

• Rings can not last the age of the Solar System.Rings can not last the age of the Solar System.• particles will be ground to dust by micrometeorite collisionsparticles will be ground to dust by micrometeorite collisions• atmospheric drag will cause ring particles to fall into planetatmospheric drag will cause ring particles to fall into planet

There must be a source to replenish ring particles.There must be a source to replenish ring particles.• the gradual dismantling of small moons, which formed from the the gradual dismantling of small moons, which formed from the

mini-nebula, by collisions, tidal forces, etc.mini-nebula, by collisions, tidal forces, etc.

The appearance of ring systems must change The appearance of ring systems must change dramatically over millions or billions of years. dramatically over millions or billions of years.