Transcript Chapter 8 Jovian Planet Systems

Chapter 8 Jovian Planet Systems
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Formation
Internal Structure
Appearance
Weather---the Great Red Spot and bands of Jupiter
Satellites---the Galilean Moons of Jupiter
Rings
Overview: Similarities and Differences
The jovian planets can be roughly divided into two groups:
• Jupiter and Saturn are similar in size (large, ~ 10 Rearth),
with similar reddish and brownish color.
• Uranus and Neptune are smaller in size (~ 4 Rearth), with
similar bluish color.
Physical Parameters of The Jovian
Planets
Planets
Hydrogen
& Helium
[by mass]
Others
Materials
[by mass]
Mass
[Mearth]
Size
[Rearth]
Density
[g/cm3]
Distance to
Sun [AU]
Jupiter:
~97%
~3%
318
11.2
1.33
5.2
Saturn
~90%
~10%
95
9.5
0.71
9.5
Uranus
~30%
~70%
14
4.0
1.24
19.2
Neptune
~30%
~70%
17
3.8
1.67
30.1
General Trend…
• The distance of the planets (w.r.t Sun) roughly determines their final
mass and size.
• The closer to the Sun, the more materials to accrete to form larger
planet.
• Planets that are closer to the Sun probably grew the fastest.
• Planet formation process ends at the same time for all the planets,
when solar wind started and cleared the planetary nebula.
Formation of the Jovian Planets
At location far from the Sun, beyond the frost line, there are
plenty of ice-rich planetesimals.
• The Jovian planets are thought to form from ice-rich
planetesimals of about the same mass---roughly 10
times the mass of the Earth.
• The high mass and their strong gravity allow them to
draw in large amount of hydrogen and helium gas,
and keep them (remember that light gases are more
difficult to keep on planet surface).
• The icy component makes up a larger fraction of the
mass for planets farther away from the Sun.
The density of the Jovian planets should
increases the farther away the planet is from the
Sun. But this is not the case for Jupiter!
Physical Parameters of The Jovian
Planets
Planets
Hydrogen
& Helium
[by mass]
Others
Materials
[by mass]
Mass
[Mearth]
Size
[Rearth]
Density
[g/cm3]
Distance to
Sun [AU]
Jupiter:
~97%
~3%
318
11.2
1.33
5.2
Saturn
~90%
~10%
95
9.5
0.71
9.5
Uranus
~30%
~70%
14
4.0
1.24
19.2
Neptune
~30%
~70%
17
3.8
1.67
30.1
The density of Saturn, Uranus, and Neptune
indeed increase as we expected, but that of
Jupiter is too high…
Gravitational Compression of Gases
To understand how the interior of the Jovian planets are layered, we need to
understand how gas behave when they are compressed by gravitational
force…
– Under gravitational pressure, the density of the bottom layer increases
– The temperature increases as well
– Eventually, adding more materials onTherefore,
the top does
not increase
theofsize of
although
the mass
the planets
Jupiter is almost 3 times higher than
that of Saturn, its size is only about
10% larger…and therefore, its density
is much higher
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Formation
Internal Structure
Appearance
Weather---the Giant Red Spot and
bands of Jupiter
• Satellites
• Rings
Internal Structure of Jupiter
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The interior of Jupiter is not uniform in
density and temperature
The temperature and density of Jupiter
increases rapidly as the depth increases.
The composition of Jupiter at different
depth is about the same, mostly hydrogen
and helium, except in the core where it is
mostly rock, metals and hydrogen
compounds.
From the top to the core, the interior of
Jupiter can be divided into different
layers:
– Gaseous hydrogen: Temperature ~ 125K 2,000K
– Liquid hydrogen: T ~ 2,000K – 5,000K
– Metallic hydrogen: T~ 5,000-20,000
– Core: rock, metals, hydrogen compounds
– the heavier materials, T > 20,000K.
Internal Structure of the Jovian Planets
• Computer models showed that all four jovian planets have core of
rock, metal, and hydrogen compounds, with a total mass of about
10 Mearth.
• Jupiter and Neptune captured large amount of hydrogen gas, while
Uranus and Neptune, being further away from the Sun where the
density of the solar nebula is smaller, captured smaller amount of
gas before solar wind cleared the gas supply for planet formation
(Repeating myself!).
M = 318 Mearth
M = 95.2 Mearth
M = 14.5 Mearth
M = 17.1 Mearth
The Magnetosphere of the Jovian
Planets
• The rapid rotation (~ 10 hours for Jupiter and Saturn, ~ 17 hours for Uranus
and Neptune), and the presence of a metallic hydrogen layer in the core
generate strong magnetic field for all the jovian planets.
• Just like on Earth, the strong magnetic field of Jupiter traps and funnels the
high energy charged particles of solar wind into its north and south poles.
These high energy charged particles interact with Jupiter’s atmosphere and
produce aurora on its north and south poles.
http://www.nasa.gov/vision/universe/solarsystem/new_year_aurora.html
Aurora Australis taken by NASA’s IMAGE
Satellite.
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Formation
Internal Structure
Appearance
Weather---the Giant Red Spot and
bands of Jupiter
• Satellites
• Rings
The Colors of Earth
• Green and Brown: Land
• White: Clouds
– Clouds are tiny liquid water droplets suspended in air
– Clouds reflect all the visible light…therefore they looks white.
• Blue: Atmosphere and ocean
– Earth’s atmosphere scatters blue light more strongly than red
light…
– Water absorbs red light more strongly than blue light
The combined
effects make the
ocean (without
clouds) looks
blue
Blue Sky and
Red Sunset
Air molecules scatters blue
light more strongly than
red light…
• When we look at sky far
away from the Sun during
the day, we see mostly
blue light scattered by the
atmosphere…blue sky
• When we look toward the
Sun around sunset, most
of the blue light are
scattered into other
direction, but red light is
transmitted through…red
sunset
How about a Blue sunset?
The Colors of Jupiter and Saturn
Jupiter
Different color stripes on Jupiter and Saturn are due to clouds formed at
different level in the atmosphere.
• WHITE – Ammonia clouds condense at the ‘top’ of Jupiter’s atmosphere.
• BROWN and RED – Ammonium hydrosulfide condense at -50 km below
(we in fact don’t know why it is red).
• WHITE – Water vapor condenses at 100 km below.
Saturn
• Saturn is much (almost 2 times) further from the Sun than Jupiter is. It is
also less massive than Jupiter. The surface of Saturn is much colder than
Jupiter. Thus, the clouds are formed much deeper (where the
temperature is high enough) in Saturn, resulting in the more subdued
colors.
The Color of Uranus and Neptune
The blue color of Uranus and Neptune comes from methane gas
and clouds.
• Uranus and Neptune are so cold (so far away from the Sun, and
small) that the ammonia and water clouds can only be formed very
deep in the atmosphere that it is not possible to see.
• Methane gas absorbs red light, transmitting blue light…
• Methane clouds reflect blue light back into space…
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Formation
Internal Structure
Appearance
Weather
– the Giant Red Spot and bands of
Jupiter
• Satellites
• Rings
Origin of Wind
On the surface of Earth, winds are driven by
• Pressure gradient force:
– Air flows from high-pressure region to low
pressure region.
– Local air pressure are strongly influenced by
differences in external heating.
– Jupiter emits more energy than it receives
from the Sun, indicative of internal heating.
• Coriolis Effect:
Coriolis Effect
The coriolis effect is an apparent deflection of motion observed by an
observer on a rotation coordinate system (e.g., on the Earth)
• Motion on the northern hemisphere appears to be deflected to the right
• Motion on the southern hemisphere appears to be deflected to the left
• The coriolis effect causes the hurricanes on the northern (southern)
hemisphere to rotate counterclockwise (clockwise)
• Coriolis effect is proportional to the angular speed (e.g., how many
rotations per hour).
L
Southern Hemisphere
L
Northern Hemisphere
Demonstration of Coriolis
Effect
Link to the video above:
http://video.google.com/videoplay?docid=9028457827554708337&q=coriolis+effect&hl=en
Another interesting video demonstration of the coriolis effect from the
perspective of an observer not rotating with the system can be found at
http://video.google.com/videoplay?docid=6756977880077693108&q=corioli
s+effect&hl=en
It is at the end of the video….
Weather on Jupiter
• The white bands are where rising air forms white ammonia clouds.
• Strong east-west winds caused by strong coriolis (due to its high
rotation rate of 10 hours) effect carry the clouds around the globe to
form the stripes.
• Snow from ammonia cloud depletes the atmosphere of ammonia
cloud, allowing us to see deeper into the brown ammonium
hydrosulfide clouds
• In these old Paloma Observatory images, the infrared
image on the left clearly shows the temperature of the
stripes – white bands are cold, and brown-reddish bands
are hot (false color image).
Great Red Spot
• The great red spot has been around for several hundred
years…
• It is a high pressure storm system, because it rotate
counterclockwise (see movie in previous slide) in the southern
hemisphere.
All the Jovian planets have stripes
and dots, indicative of wind and
storms activities (refer to the image
in the first slide).
Voyager I image
Click on images to start animations
Weather on Jovian Planets
• All the Jovian planets
have bands, indicative
of weather system…
Uranus in the
Infrared
showing band
structures and
rings
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Formation
Internal Structure
Appearance
Weather
– the Giant Red Spot and bands of
Jupiter
• Satellites
– The Galilean Moons: Io, Europa,
Ganymede, Callisto.
• Rings
The Moons of the Jovian Planets
All the Jovian planets have large number of moons…
• Most of the large- and medium-sized moons are
probably formed in the accretion disks of the
planets. They are all spherical. They rotate and
revolve in the respective ‘ecliptic plane’ of each
planet in the same direction of the planet’s
rotations.
• They are composed of rocky materials and large
amount of water (no hydrogen or helium, why?)
• The small moons have irregular shapes, and do
not have any orbital pattern. They are probably
captured moons.
The Galilean Moons of Jupiter
• The four largest moons of Jupiter was first discovered by
Galileo
– Io: active volcanism
– Europa: under surface water, ice or liquid?
– Ganymede: under surface water, ice or liquid?
– Callisto: under surface water, ice or liquid?
Io, The Most Volcanically Active Object
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One of the great surprise Voyager spacecraft
reached Jupiter in the late 1970s was the
discovery of active volcanism on Io. The picture
on the right shows plum ejected by active volcano.
Io (1,821 km) is about the same size as Earth’s
Moon (1,738 km). But the Moon is geologically
dead…
Why is Io so active?
Tidal heating is responsible for the strong volcanic
activities on Io…
Prometheus Plum
Pele
The energy sources in celestial bodies
1. Nuclear Fusion,
2. Gravitational collapse and
compression,
3. Radioactive material heating,
4. Tidal Heating.
Tidal Heating
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Just like the tidal effect of the of the Earth on the Moon, Io is gravitationally
locked to Jupiter – the same side of Io always face Jupiter…
We know that Io’s orbit around Jupiter is slightly eccentric (e = 0.041).
Depending on its orbital position, the amount of the stretching is different.
Constant changes in its shape cause heating.
How does it get its elliptical orbit?
 Orbital Resonance.
Orbital Resonance
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Orbital period of O2 is integral multiple of the orbital period of O1
The stronger gravitation pull on O1 in configuration 1 causes it to move into an elliptical
orbit.
O2
Configuration 1
O1
O1
Configuration 2
O2
Configuration 3
O1 has completed
one rotation, but
O2 has just finished
half of its rotation
Resonance of Io, Europa, and
Ganymede
The orbits of Io, Europa, and Ganymede are
in resonance…
• Io’s orbital period is half that of Europa.
• Europa’s orbital period is half that of
Ganymede.
• Callisto is NOT in orbital resonance with
Ganymede.
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The ratio of the periods (from Io to
Europa to Ganymede) is 1:2:4
The ratio of the distance (from Io to
Eurpoa to Ganymede) is 1:1.58:2.52
Resonance of Io, Europa, and
Ganymede
How did this happen?
• Tidal friction cause Io to slowly
move away from Jupiter, until it
reaches the orbit where the orbital
frequency is two times that of
Europa (Kepler’s Third Law).
• Io and Europa than move into the
2:1 resonant orbit of Ganymede.
• When O1 moves too fast, the
gravitational pull of O2 will slow it
down
Too fast
• When O1 moves too slow, the
gravitational pull of O2 will speed
it up. …(recall negative feedback)
O2
O1
O2
O1
Too slow
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Formation
Internal Structure
Appearance
Weather
– the Giant Red Spot and bands of
Jupiter
• Satellites
• Rings
The Rings Of The Jovian Planets
All the Jovian planets have a ring system, but Saturn’s rings is the
most prominent, visible even with small telescopes.
The Rings Of Saturn
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Composition: highly reflective water ice particles.
Location: within two to three radii of Saturn (Roche Tidal Zone).
Origin: (1) Strong tidal force in the Roche tidal zone prevents particles from
accreting into a large object. (2) wondering moon strayed too close to the
planet and was torn apart by the tidal force.
Motions:
All the particles in the
Cassini Division
Rings orbit the planet
According to Kepler’s
Laws.
Structure
rings, caps, and spokes
Detailed View
The Formation Of The Rings and Gaps
We still don’t have a complete understanding of how the rings and gaps are formed!
Gap moons
The stronger gravity of the small moons located inside the rings can change the orbits of the
smaller particles in nearby regions, clearing a gap as it orbits the planet.
Shepherd Moons
Two gap moons close by can push the particles between their orbits to form a sharp narrow
ring.
Orbital Resonance
1. Ring particles revolving in a orbit that is in resonance
with a larger moon will be moved away from its
Shepherd Moons
original orbits, making a gap.
2. The Mimas 2:1 resonance is responsible for the large
Cassini division.
The bright rings of Saturn most likely is also a transit
phenomenon. The rings of Jupiter, Uranus, and Neptune
may be as brilliant as the rings of Saturn long time ago.
1. The particles of the rings are constantly colliding with
each other, chipping away the particles.
2. Collision with the small moons may create more
particles to replenish the rings.
Why Is The Rings of Saturn So Much More
Prominent?
The rings most likely is also a transit phenomenon. The rings of
Jupiter, Uranus, and Neptune may be as brilliant as the rings of
Saturn long time ago.
1. The particles of the rings are constantly colliding with each other,
chipping away the particles.
2. Collision with the small moons may create more particles to
replenish the rings.
The Cassini-Huygens Mission to Saturn
• Four NASA spacecraft have been sent to explore
Saturn. Pioneer 11 was first to fly past Saturn in 1979.
Voyager 1 flew past a year later, followed by its twin,
Voyager 2, in 1981.
• The Cassini spacecraft is the first to explore the Saturn
system of rings and moons from orbit. Cassini entered
orbit on Jun. 30, 2004 and immediately began sending
back intriguing images and data. The European Space
Agency's Huygens Probe dove into Titan's thick
atmosphere in January 2005. The sophisticated
instruments on both spacecraft are providing scientists
with vital data and the best views ever of this
mysterious, vast region of our solar system.
http://saturn.jpl.nasa.gov/home/index.cfm