Download The JOVIAN PLANETS

Lecture 25
The JOVIAN PLANETS
They formed beyond the frost line to form large, icy
planetesimals which were massive enough to…
Capture H/He far from Sun to form gaseous planets.
Each Jovian planet formed its own “miniature” solar nebula.
Moons formed out of these disks.
The Jovian planets are principally made of hydrogen &
helium, with composition very similar to the Sun.
•Moving from the surface to the core:
•temperature increases
•pressure & density increases
At low temperatures and pressures
characteristic of the outer layers of
Jovian planets: Hydrogen is a
diatomic gas (H2)
At higher pressures (few thousand
km below the upper cloud deck): H2
becomes dissociated and undergoes
a phase transition from the gaseous
to a liquid state.
At pressures greater than 3 million
atmospheres, H is squeezed so
tightly that the atoms are separated
into freely moving protons and
electrons: liquid metallic hydrogen
(LMH).
LMH is highly conducting (the
electrons are highly mobile)
The combination of a metallic hydrogen
interior and high rotation rates give the
Jovian planets (especially Jupiter)
strong magnetic fields.
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All Jovian cores appear to be similar.
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Uranus & Neptune captured less gas from the Solar nebula.
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made of rock, metal, and Hydrogen compounds
10 x the mass of Earth
accretion of planetesimals took longer
not much time for gas capture before nebula was cleared out by Solar wind
Only Jupiter and Saturn have high enough pressure for H & He to exist in
liquid and metallic states.
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Jupiter emits almost twice as much energy as it absorbs from the
Sun.
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accretion, differentiation, radioactivity can not account for it
Jupiter must still be contracting
Jupiter has 3 x more mass than Saturn, but is not much larger!
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the added weight of H & He compresses the core to a higher
density, just like stacking pillows
Uranus & Neptune have less mass than Saturn, yet
they have higher densities
they must be made of denser material
Jovian Planet Atmospheres
Jupiter’s Atmosphere
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In 1995, the Galileo space probe plunged
into the planet Jupiter!
It measured the atmospheric structure of
Jupiter
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thermosphere {absorbs Solar X-rays}
•
stratosphere {absorbs Solar UV}
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troposphere {greenhouse gases trap heat from
both Jupiter and the Sun}
These are the same structures found in Earth’s
atmosphere.
• Atmospheres are governed by interactions between
sunlight and gases.
Jupiter’s Cloud Layers
 Convection in the troposphere causes
Jovian weather.
 Warm gas rises to cooler altitudes,
where it condenses to form clouds.
 Three gases condense in the Jovian
atmosphere:
 ammonia (NH3)
 ammonium hydrosulfide (NH4SH)
 water (H2O)
 They condense at different
temperatures, so their differently
colored clouds form at different
altitudes.
The Jovian Atmospheres
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The temperature profile of
each planet determines the
color of its appearance.
Cloud layers form where a
particular gas condenses.
Saturn has the same cloud
layers as Jupiter.
they form deeper since
Saturn is colder overall
• they are spread farther
apart since Saturn has
lower gravity
Uranus & Neptune
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cold enough to form
methane clouds
• Convection in the troposphere,
where the clouds form, coupled
with rapid rotation of the Jovian
planets leads to numerous bands
of rising and falling air.
• These are the colored “stripes”
which we see in Jovian cloud
structure.
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We also see high pressure storms
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analogous to hurricanes, but they rotate in the opposite direction
Jupiter
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the Great Red Spot
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we are not sure why it is red
Neptune
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the Great Dark Spot
Saturn’s Atmosphere
Saturn is not as colorful or turbulent as Jupiter.
This may be due to the fact that Saturn is cooler
because it is further away from the Sun.
It does not contain storms as large as those seen
on Jupiter, nor are they permanent.
It also has enough gravity to hold on to all the
gasses and consists of 92.4% hydrogen, 7.4 %
helium, and traces of methane and ammonia.
Atmospheres of Uranus and Neptune
Both planets have similar makeup to Jupiter and
Saturn
Unlike Jupiter and Saturn, ammonia is not
significant in either of these planets.
However, both planets have significant amounts
of methane in their upper atmospheres - makes
them appear blue.
Magnetospheres
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A planet’s magnetic field attracts and
diverts the charged particles of the solar
wind to its magnetic poles.
•
particles spiral along magnetic field
lines and emit light (aurora);
protective “bubble” is called the
magnetosphere
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The Earth is only terrestrial world with a
strong magnetic field
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solar wind particles impact the
exospheres of Venus & Mars
solar wind particles impact the
surfaces of Mercury & Moon
Jovian Planet Rings
The Rings of Saturn
• From Earth, they look solid.
• concentric rings & Cassini division
• From spacecraft flybys, we see
thousands of individual rings.
• separated by narrow gaps
• differ in brightness & transparency
• From within the rings, we would
see many individual particles
• size ranges from boulders to dust
• reflective H2O ice (snowballs)
• many collisions keep ring thin
The other ring systems: fewer particles, smaller
in extent, darker particles
Origin of Planetary Rings
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Within 2 or 3 planetary radii of a planet, tidal forces will be greater
than the gravity holding a moon together.
A moon which wanders too close will be torn apart.
Matter from the mini-nebula at this distance will not form moon.
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Rings can not last the age of the Solar System.
Particles will be ground to dust by micrometeorite collisions.
Atmospheric drag will cause ring particles to fall into planet.
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There must be a source to replenish ring particles.
gradual dismantling of small moons by collisions, tidal forces, etc.
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The appearance of ring systems must change dramatically over
millions or billions of years.
Jovian Planets have Numerous Moons
• small moons (< 300 km across)
• not spherical
• probably captured asteroids
• Medium/large moons
formed like planets out of
the “mini-Solar nebulae”
surrounding the Jovian
planets
Are these moons are too small for active
geology to occur?
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No!
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terrestrial planets made mostly of rock; Jovian moons
mostly ice
Ices melt at lower temperatures than rock.
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less heating is required to have molten cores
• volcanism and tectonics can occur
There is another heat source.
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tidal heating plays a more important role
There is very little erosion due to lack of substantial
atmospheres with the exception of Titan.
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The Jovian Moons
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The moons of Jupiter become less dense as you get
farther from Jupiter
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“mini Solar System”
Gravitational tidal heating keeps the interiors of the
inner moons hot.
The Large Jovian Moons
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Jupiter - Galilean Moons
sulfur volcanoes
world of water ice (and liquid?)
active ice world
dead & dirty ice world
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Io
• Europa
• Ganymede
• Callisto
Saturn
thick atmosphere (N2 & CH4)
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Titan
Neptune
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Triton
nitrogen volcanoes, retrograde orbit
Io
• Jupiter’s tidal forces flex
Io like a ball of silly putty.
• friction generates heat
• interior of Io is molten
• Volcanoes erupt
frequently.
• sulfur in lava accounts for
yellow color
• surface ice vaporizes and
jets away
• Evidence of tectonics &
impact cratering erased.
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Io loses volcanic gases
into space.
ions of Sulfur,
Oxygen, Sodium form
a donut-shaped belt
of charged particles,
called the Io torus
they follow Io’s orbit &
are a source of
charged particles for
the auroras
The Io Torus
Io Torus as imaged by the Galileo Spacecraft
Europa
• metallic core, rocky mantle, &
a crust made of H2O ice
• fractured surface -> tectonics.
• few impact craters seen
• double-ridged cracks
• jumbled icebergs
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(evidence of a subsurface
ocean).
• Europa has a magnetic field.
• implies liquid salt water beneath
the icy crust
• Where liquid water exists,
there could be life!
Ganymede
• largest moon in the Solar System
• Two types of terrain:
• heavily cratered, implies old
• long grooves, few craters, implies
young like Europa
• It also has a magnetic field.
• Could it have subsurface ocean?
• case not as strong as Europa’s
• tidal heating would be weaker
• would need additional heating from
radioactive decay
Callisto
• It has an old surface.
• heavily cratered, dirty ice
• cratering reveals clean, white ice
• no evidence of tectonics
• Its interior did not differentiate.
• rock mixed with ice
• It does not experience tidal
heating.
• Yet it has a magnetic field.
• Could it have a subsurface ocean
anyway?
Titan
• largest of Saturn’s moons
• Huygens landed in January 2005
• has a thick atmosphere.
• Nitrogen (from dissociated NH3; 90%),
Argon, methane, ethane
• methane, ethane are greenhouse gases:
surface is warmer than it should be
• Ethane/methane may condense to form
clouds and rain
• Atmosphere blocks view of surface
• may have oceans of ethane/methane
• erosion may be important
http://saturn.jpl.nasa.gov
Liquid Lakes on Titan:
Some regions on Titan reflect very
little radar. The leading explanation
for this is that these regions are lakes,
possibly composed of liquid methane.
This image is a false-color radar map
of a northern region of Titan taken by
the Cassini spacecraft. On this map,
which spans about 150 kilometers
across, dark regions reflect relatively
little of the broadcast radar signal.
Titan is the only body in the Solar
System, other than the Earth, known
to possess liquids on its surface.
Cold, windy, surface like wet clay, ice “rocks”
Enceladus
Triton
• orbits in the opposite direction of Neptune's rotation in a
highly inclined orbit.
• implies that it was probably captured by Neptune
• Thin Nitrogen atmosphere
• Volcanic activity