Download Gas Giant Planets

Spacecraft to the Outer Solar System
Flybys: Pioneer 10, 11
Voyager 1, 2
Orbiters/ : Galileo, Cassini
Landers (Jupiter) (Saturn)
Voyager 2 is the only
spacecraft to visit all
four outer planets.
Gas Giant Planets
• Our goals for learning
• What are jovian planets like?
• What are the clouds like? (Jupiter as a type
example)
• Why are there rings systems? (Saturn as a
type example)
What are Jovian planets Like?
Similarities: Ring Systems
• All four jovian planets have ring systems, Saturn
merely the most obvious.
• Others have smaller, darker ring particles than Saturn
Similarities: Interiors
•
•
•
•
No solid surface.
Layers under high pressure and temperatures.
Strong magnetic fields => conducting materials
Cores (~10 Earth masses) made of hydrogen
compounds, metals & rock
• The layers are different for the different planets
due to differences in composition and pressure.
Inside Jupiter
(the best understood)
• Inside Jupiter, high
pressures cause
hydrogen to change
phase with depth.
• Hydrogen acts like a
metal at great depths
because the hydrogen
is squeezed until
electrons move freely
Inside Jupiter
• Core is thought to
be made of rock,
with some metals,
and hydrogen
compounds
• Core is about
same size as
Earth but 10 times
as massive
Subdividing the Gas Giants
Differences: Composition
• Jupiter and Saturn
– Mostly H and He gas
• Uranus and Neptune
– Mostly hydrogen compounds: water (H2O),
methane (CH4), ammonia (NH3)
– Some H, He, and rock
Differences: Interiors
• Models suggest cores of jovian planets have
similar composition
• Lower pressures inside Uranus and Neptune
mean no metallic hydrogen
What are the Clouds Like?
Colors of The Gas Giants
•Colors are temperature controlled
•Decreasing temp. : increasing methane clouds
•methane clouds reflect blue light
high thin haze
• Jupiter - high brown
and white clouds
high haze
• Saturn- bands deeper
thicker smog haze
thicker clouds .
thick heavy clouds
• Uranus -light blue
• Neptune dark blue
Jupiter
Jupiter’s
vertical
atmospheric
structure
Different materials form
stable ice clouds at
different temperatures
& pressures
=> different clouds form
at different heights
Jupiter
convection
Convection cells
create a pattern
of white high
clouds & brown
low clouds
Saturn
Uranus
Early Voyager
images, taken
at southern
summer,
showed no
cloud bands
Uranus
This Hubble image
shows the Uranus,
system, with its
ten rings and eight
of its moons.
In this false color
image, taken in
infrared light, the
moving bands of
cloud show up
well.
Neptune
Surprising discovery or fraud? - Saturn's core
is pockmarked with impact craters and dotted
with volcanoes erupting basaltic lava.
A. Plausible. Saturn's moons also show impact
craters and volcanoes.
B. Plausible. Saturn's atmosphere originated from
the volatiles in impactors that were released via
volcanic activity.
C. Implausible. No impactors would survive the
immense pressures at the depth of Saturn's core.
D. Implausible. Saturn's high rotation would prevent
an impactor from reaching its core.
© 2014 Pearson Education, Inc.
Since there are a lot of flammable gases on
Gas Giants, such as methane and propane,
if you lit a match, would Jupiter burn?
A. yes
B. no
© 2014 Pearson Education, Inc.
What Are The Rings Like?
Saturn’s Rings: Type Example
Rings made of
thousands of small
rings of ice particles
like fluffy snowballs
The B ring is sandy
colored, while the
outer A ring is white
from ice.
Ring Location in Gas Giants
• Rings occur within 2-3 radii away (inside the
Roche Limit)
–
Region where gravity of a planet is so strong
that materials can’t hold together to form a
moon.
• Planet’s gravity pulls in material, moons’
gravities push and pull in opposite direction.
• Tug-o-war holds rings in place (for a while)
Keeping Rings in Place 1:
Shepherd Moons
Some rings are
held in place by
the gravity of tiny
moons.
-They are called
'Shepherd Moons'
F ring has three
shepherds.
close-up of the F ring and two shepherds. It is held
between the gravity of these two moons.
Prometheus
(moves inside the ring)
Pandora
(moves outside the ring)
Keeping Rings in Place 2:
Resonances
Orbital resonance
with the gravity of
a larger moon can
push the particles,
producing a ring or
a gap
Ring Formation in Gas Giants
• Rings aren’t leftover from planet formation
because the particles are too small to
survive this long in a strong gravity field.
• There must be a continuous replacement of
tiny particles.
• The most likely source is impacts with the
gas giants’ moons.
Ring Formation in Gas Giants
• Impacts continually occur on the many small moons,
chipping off fine material
• Fine material spreads out in orbit around the gas giant
• The gravity effects from the moons then hold the bits
in place as rings.
What have we learned?
• What are the clouds like?
– The gas giant planets have different color
clouds at different heights due to temperature
differences
– They are striped because different clouds are
visible due to convection plus rapid rotation
causing a strong coriolis effect.
What have we learned?
• What are the rings like?
– The rings are tiny pieces of fluffy snow balls held
in orbit 2-3 radii away from a gas giant world.
– They occur because gas giants have lots of
moons:
• Impacts chip off material that becomes rings.
• Material is nudged into resonance orbits by the gravity
of the moons, forming rings
• Some rings are held by the gravity of tiny shepherd
moons.
Why don't ring particles form a moon?
A. They collide too violently to accrete into a moon.
B. Tidal forces from moons prevent them from
accreting.
C. Tidal forces from the planet prevent them from
accreting.
D. Their masses are too small for them to accrete.
© 2014 Pearson Education, Inc.
A Wealth of Worlds: Moons of Ice and Rock
• Our goals for learning
• What kinds of moons orbit Gas Giant
planets?
• Why are Jupiter’s Galilean moons so
geologically active?
• What is special about Titan and other
major moons of the solar system?
What kinds of moons orbit
Gas Giant planets?
• Small moons (< 300 km)
– No geological activity
• Medium-sized moons (300-1,500 km)
– Geological activity in past
• Large moons (> 1,500 km)
– Ongoing geological activity
Medium and Large Icy Worlds
•
•
•
•
Enough self-gravity to be spherical.
Metal/rock core, ice mantle and crust.
Some geological activity
Two main locations:
– Larger Icy moons orbiting gas giant planets
– Largest objects in Kuiper belt in the outermost
solar system (Pluto, Sedna, Quoaor and
others)
Medium &
Large Moons
• Formed in orbit around
gas giant planets.
• Circular orbits in same
direction as planet
rotation.
Why are Jupiter’s Galilean
moons so geologically active?
Io
12th
largest
world
Active
sulfur
volcanism
Io’s Volcanic Activity
• Io is the most volcanically active body in
the solar system, but why?
Tidal Heating
Io is squished and
stretched as it orbits
Jupiter
But what is
causing it to
stretch?
Every 7 days,
these 3 moons
line up.
Orbital Resonances
The tugs add up over
time, making all 3
orbits elliptical, which
pulls on the worlds.
Europa -13th largest world
Tidal stresses crack surface ice
No surface volcanos, but millions of faults all over the
surface. A few small craters are seen.
Europa’s Ocean: Waterworld?
•Chaos regions: where warm ice wells up, breaks and
spreads the surface.
Inside Europa
• Secondary magnetic field (requires liquid)
• Broken disrupted surfaces from flowing ice
• Surface covered in faults -some areas
spread apart.
• Conclusion:
• Liquid interior layer -a global ocean
Europa’s interior also warmed by tidal heating
Ganymede -8th largest world
• Largest moon
in the solar
system
• Surface has
long fault
regions, but
also heavily
cratered
plains.
Ganymede
• Clear evidence of
geological activity
• Tidal heating plus
heat from radioactive decay?
• Has a magnetic
Field that varies.
Callisto
• cratered iceball.
• No tidal heating, no
orbital resonances.
Orbital
Resonances
Every 7 days,
these 3 moons
line up.
The tugs add up over
time, making all 3
orbits elliptical.
What have we learned?
• What kinds of moons orbit jovian planets?
– Moons of many sizes
– Level of geological activity depends on size
• Why are Jupiter’s Galilean moons so
geologically active?
– Tidal heating drives activity, leading to Io’s
volcanoes and ice geology on other moons
Saturn’s Moons
What is special about Titan?
Titan’s Atmosphere
• Titan is the only
moon in the solar
system to have a
thick atmosphere
• It consists mostly
of nitrogen with
‘smog’ clouds that
obscure the
surface
Mosaic of Hygens Images
• ~5 miles high
shows dark
curving lines with
branching
tributaries (lower
left).
• pattern is identical
to desert rivers
on Earth and the
dry-river beds of
Mars.
• conclude that
Titan has flowing
liquids eroding out
channels.
Fish-eye Mosaic of Hygens Images
• mountains and a shoreline to some kind of
dark-colored lake.
• However, at -290 °F at
the surface, water is
frozen as hard as rock.
• The lake must be made
of organic liquids,
probably a methaneethane mix.
channels
mountains
lake
Giant North Pole Lakes
• The biggest lake so far is 39,000 square miles, it is larger
than lake Superior and about the size of the Black Sea
Active Methane Cycle :(
• There is a tiny amount of
methane rainfall
• The lakes do not appear
to grow and shrink in size
• There is probably not a
permanent methane
recycling system like
Earth's water cycle
Saturn has 6 medium-sized moons.
Mimas
They are big enough
to be round, but vary
in their amount of
geological activity.
Rhea
Dione
Enceladus
Tethys
Iapetus
• The south pole
of Enceladus is
covered in
recent faults!
• This suggests
some unknown,
but complex,
internal activity
is occurring.
This is a false color image taken during Cassini’s approach to this moon.
•
•
Enceladus has live volcanic ice eruptions!
– The water freezes into ice particles and
rises in a plume over 300 miles high.
Only 3 other worlds have observed active
volcanism: Earth, Io and Triton.
Water eruption plume
This colorized image shows the
enormous extent of the faint plume.
Enceladus and E Ring
The volcanism on Enceladus is a major source for the
particles for Saturn's outer rings.
Here Enceladus emits water in the middle of the E ring .
E
Enceladus
Volcanic plume
Neptune’s
Moon
Triton
Neptune’s Moon Triton
• Similar to Pluto,
but larger
• Evidence for past
geological activity
Icy
Volcanism
on Triton
Spouts of nitrogen
geysering above
the surface
What have we learned?
• What is special about Titan and other major
moons of the solar system?
– Titan has strong active processes like Galileans
– Titan is the only moon with a thick atmosphere
– Titan is the only moon with liquid rivers and lakes.
– Many other major moons show signs of geological
activity.
– 3 of gas giants have an actively volcanic moon.
Small Worlds
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•
•
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Our goals for learning
What are asteroids like?
Why is there an asteroid belt?
Where do comets come from?
• Small Worlds are:
– Not round,
– Covered in craters,
– Have no atmosphere,
– Main surface process is mass wasting
• Asteroids are made of metals and rock
• Comets and KBOs are made of rock and
volatiles
Asteroids
Asteroid Orbits
• Most asteroids orbit in
a belt between Mars
and Jupiter
• Trojan asteroids
follow Jupiter’s orbit
• Orbits of near-Earth
asteroids cross
Earth’s orbit
Origin of Asteroid Belt
• Rocky planetesimals
between Mars and
Jupiter did not accrete
into a planet.
• Jupiter’s gravity, through
influence of orbital
resonances, stirred up
asteroid orbits and
prevented their accretion
into a planet.
Kuiper Belt Objects -Dirty snowballs
Two regions for small
icy worlds:
• Kuiper belt, KBOs
have orderly orbits
from 30-100 AU in
disk of solar system
• Oort Cloud, worlds
have random orbits
out to >50,000 AU
Sources for comets.
Growth of Tail
What have we learned?
• What are comets like?
– Comets are like dirty snowballs
– Most are far from Sun and do not have tails
– Tails grow when comet nears Sun and nucleus
heats up
• Where do comets come from?
– Comets in plane of solar system come from
Kuiper Belt
– Comets on random orbits come from Oort cloud