Jupiter and Saturn Guidepost Jupiter and Saturn One reason

1
Jupiter and Saturn

2
Guidepost
As we move to the outer planets, we leave behind
the psychological security of planetary surfaces.
We can imagine standing on the moon, on Venus, or
on Mars, but Jupiter and Saturn have no surfaces.
Thus, we face a new challengeto use comparative
planetology to study worlds so unearthly we
cannot imagine being there.
3
Jupiter and Saturn

• One reason we find the moon and Mars of interest
  is that we might go there someday. Humans may
  become the first Martians. But the outer solar
  system seems much less useful, and that gives us
  a chance to think about the cultural value of
  science.
• This program begins our journey into the outer
  solar system. Next, we will visit worlds out in
  the twilight at the edge of the suns family.

4
Outline
I. Jupiter A. Surveying Jupiter B. Jupiter's
Magnetic Fields C. Jupiter's Atmosphere D.
Jupiter's Ring E. Comet Impact on Jupiter F.
The History of Jupiter II. Jupiter's Family of
Moons A. Callisto The Ancient Face B.
Ganymede A Hidden Past C. Europa A Hidden
Ocean D. Io Bursting Energy E. The History of
the Galilean Moons
5
Outline (continued)
III. Saturn A. Planet Saturn B. Saturn's
Rings C. The History of Saturn IV. Saturn's
Moons A. Titan B. The Smaller Moons C. The
Origin of Saturn's Satellites
6
Jupiter
Largest and most massive planet in the solar
system
Contains almost 3/4 of all planetary matter in
the solar system.
Most striking features visible from Earth
Multi-colored cloud belts
Explored in detail by several space probes
Visual image
Pioneer 10, Pioneer 11, Voyager 1, Voyager 2,
Galileo
Infrared false-color image
7

• Jupiter
• Distance from Sun 5.2028 AU (7.783 X 108 km
• Eccentricity 0.0484
• Aphelion 5.455 AU
• Perihelion 4.951 AU
• Orbit inclination 1o 18 29
• Average Orbital Velocity 13.06 km/sec
• Orbital Period 11.867 y (4334.3 days)
• Period of rotation 9h 55m 30s
• Obliquity 3o 5
• Equatorial Diameter D ? 142,900 km (11.20
  Dearth)
• Mass 1.899 X 1027 kg (318.0 Mearth)
• Average Density 1.34 g/cm3
• Surface Gravity 2.54 gearth
• Escape Velocity 61 km/sec (5.4 Vearth)
• Surface Temperature -120 o C , - 180 oF
• Albedo 0.51
• Oblateness 0.0637

8
The Mass of Jupiter
Mass can be inferred from the orbit of Io, the
innermost of the 4 Galilean Moons
Io
Moon
Jupiter
Earth
Relative sizes, distances, and times to scale
1 s corresponds to 10 hr in real time.
Using Keplers third law ? MJupiter 318 MEarth
9
Jupiters Interior
From radius and mass ? Average density of Jupiter
1.34 g/cm3
gt Jupiter can not be made mostly of rock, like
earthlike planets.
? Jupiter consists mostly of hydrogen and helium.
T 30,000 K
Due to the high pressure, hydrogen is compressed
into a liquid, and even metallic state.
10
The Chemical Composition of Jupiter and Saturn
11
Jupiters Rotation
Jupiter is the most rapidly rotating planet in
the solar system
Rotation period slightly less than 10 hr.
Centrifugal forces stretch Jupiter into a
markedly oblate shape.
12
Jupiters Magnetic Field
Discovered through observations of decimeter
(radio) radiation
Magnetic field at least 10 times stronger than
Earths magnetic field.
Magnetosphere over 100 times larger than Earths.
Extremely intense radiation belts
Very high energy particles can be trapped
radiation doses corresponding to 100 times
lethal doses for humans!
13
Aurorae on Jupiter
Just like on Earth, Jupiters magnetosphere
produces aurorae concentrated in rings around the
magnetic poles.
1000 times more powerful than aurorae on Earth.
14
Explorable Jupiter
(SLIDESHOW MODE ONLY)
15
The Io Plasma Torus
Some of the heavier ions originate from Jupiters
moon Io.
Io flux tube
Io flux tube
Visible
UV
Inclination of Jupiters magnetic field against
rotation axis leads to wobbling field structure
passing over Io ? Acceleration of particles to
high energies.
16
Jupiters Atmosphere
Jupiters liquid hydrogen ocean has no surface
Gradual transition from gaseous to liquid phases
as temperature and pressure combine to exceed the
critical point.
Jupiter shows limb darkening ? hydrogen
atmosphere above cloud layers.
Only very thin atmosphere above cloud layers
transition to liquid hydrogen zone 1000 km
below clouds.
17
Jupiters Atmosphere (2) Clouds
Three layers of clouds
1. Ammonia (NH3) crystals
2. Ammonia hydrosulfide
3. Water crystals
18
Planetary Atmospheres
(SLIDESHOW MODE ONLY)
19
The Cloud Belts on Jupiter
Dark belts and bright zones.
Zones higher and cooler than belts high-pressure
regions of rising gas.
20
The Cloud Belts on Jupiter (2)
Just like on Earth, high-and low-pressure zones
are bounded by high-pressure winds.
Jupiters Cloud belt structure has remained
unchanged since humans began mapping them.
21
The Great Red Spot
Several bright and dark spots mixed in with cloud
structure.
Largest and most prominent The
Great Red Spot.
Has been visible for over 330 years.
Formed by rising gas carrying heat from below the
clouds, creating a vast, rotating storm.
2 DEarth
22
The Great Red Spot (2)
Structure of Great Red Spot may be determined by
circulation patterns in the liquid interior
23
Jupiters Ring
Not only Saturn, but all four gas giants have
rings.
Galileo spacecraft image of Jupiters ring,
illuminated from behind
Jupiters ring dark and reddish only discovered
by Voyager 1 spacecraft.
Composed of microscopic particles of rocky
material
Location Inside Roche limit, where larger bodies
(moons) would be destroyed by tidal forces.
Ring material cant be old because radiation
pressure and Jupiters magnetic field force dust
particles to spiral down into the planet.
Rings must be constantly re-supplied with new
dust.
24
Roche Limit
(SLIDESHOW MODE ONLY)
25
Comet Impact on Jupiter
Impact of 21 fragments of comet SL-9 in 1994
Impacts occurred just behind the horizon as seen
from Earth, but came into view about 15 min.
later.
Impact sites appeared very bright in the infrared.
Impacts released energies equivalent to a few
megatons of TNT (Hiroshima bomb 0.15 megaton)!
Visual Impacts seen for many days as dark spots
26
The History of Jupiter

• Formed from cold gas in the outer solar nebula,
  where ices were able to condense.

• In the interior, hydrogen becomes metallic (very
  good electrical conductor)

• Rapid rotation ? strong magnetic field

• Rapid growth

• Soon able to trap gas directly through gravity

• Rapid rotation and large size ? belt-zone cloud
  pattern

• Heavy materials sink to the center

• Dust from meteorite impacts onto inner moons
  trapped to form ring

27
Jupiters Family of Moons
Over two dozen moons known now new ones are
still being discovered.
Four largest moons already discovered by Galileo
The Galilean moons
Io
Europa
Ganymede
Callisto
Interesting and diverse individual geologies.
28
Callisto The Ancient Face
Tidally locked to Jupiter, like all of Jupiters
moons.
Av. density 1.79 g/cm3
? composition mixture of ice and rocks
Dark surface, heavily pocked with craters.
No metallic core Callisto never differentiated
to form core and mantle.
? No magnetic field.
Layer of liquid water, 10 km thick, 100 km
below surface, probably heated by radioactive
decay.
29
Ganymede A Hidden Past
Largest of the 4 Galilean moons.

• Av. density 1.9 g/cm3

• Rocky core

• Ice-rich mantle

• Crust of ice

1/3 of surface old, dark, cratered
rest bright, young, grooved terrain
Bright terrain probably formed through flooding
when surface broke
30
Jupiters Influence on its Moons
Presence of Jupiter has at least two effects on
geology of its moons
2. Focusing of meteoroids, exposing nearby
satellites to more impacts than those further out.
1. Tidal effects possible source of heat for
interior of Gany-mede
31
Europa A Hidden Ocean
Av. density 3 g/cm3
? composition mostly rock and metal icy surface.
Close to Jupiter ? should be hit by many
meteoroid impacts but few craters visible.
? Active surface impact craters rapidly erased.
32
The Surface of Europa
Cracked surface and high albedo (reflectivity)
provide further evidence for geological activity.
33
The Interior of Europa
Europa is too small to retain its internal heat ?
Heating mostly from tidal interaction with
Jupiter.
Core not molten ? No magnetic field.
Europa has a liquid water ocean 15 km below the
icy surface.
34
Io Bursting Energy
Most active of all Galilean moons no impact
craters visible at all.
Over 100 active volcanoes!
Activity powered by tidal interactions with
Jupiter.
Av. density 3.55 g/cm3 ? Interior is mostly
rock.
35
Interaction with Jupiters Magnetosphere
Ios volcanoes blow out sulfur-rich gasses
? tenuous atmosphere, but gasses can not be
retained by Ios gravity
? gasses escape from Io and form an ion torus in
Jupiters magnetosphere
36
The History of the Galilean Moons

• Minor moons are probably captured asteroids
• Galilean moons probably formed together with
  Jupiter.

• Densities decreasing outward ? Probably formed
  in a disk around Jupiter, similar to planets
  around the sun.

Earliest generation of moons around Jupiter may
have been lost and spiraled into Jupiter
Galilean moons are probably a second generation
of moons.
37
Saturn
Mass 1/3 of mass of Jupiter
Radius 16 smaller than Jupiter
Av. density 0.69 g/cm3 ? Would float in water!
Rotates about as fast as Jupiter, but is twice as
oblate ? No large core of heavy elements.
Mostly hydrogen and helium liquid hydrogen core.
Saturn radiates 1.8 times the energy received
from the sun.
Probably heated by liquid helium droplets falling
towards center.
38

• SATURN
• Distance from Sun 9.5388 AU (14.27 X 108 km)
• Eccentricity 0.0560
• Aphelion 10.07 AU
• Perihelion 9.005 AU
• Orbit inclination 2o 29 17
• Average Orbital Velocity 9.64 km/sec
• Orbital Period 29.461 y ( 10.760 days)
• Period of rotation 10h 39m 25s
• Obliquity 26o 24
• Equatorial Diameter D ? 120,660 km (9.42 Dearth)
• Mass 5.69 X 1026 kg (95.147 Mearth)
• Average Density 0.69 g/cm3
• Surface Gravity 1.16 gearth
• Escape Velocity 35.6 km/sec (3.2 Vearth)
• Surface Temperature -180 o C , - 292 oF
• Albedo 0.61
• Oblateness 0.102

39
Saturns Magnetosphere
Magnetic field 20 times weaker than Jupiters
? weaker radiation belts
Magnetic field not inclined against rotation axis
? Aurorae centered around poles of rotation
40
Saturns Atmosphere
Cloud-belt structure, formed through the same
processes as on Jupiter,
but not as distinct as on Jupiter colder than on
Jupiter.
41
Saturns Atmosphere (2)
Three-layered cloud structure, just like on
Jupiter
Main difference to Jupiter
Fewer wind zones, but much stronger winds than on
Jupiter
Winds up to 500 m/s near the equator!
42
Planetary Atmospheres
(SLIDESHOW MODE ONLY)
43
Saturns Rings
A Ring
Ring consists of 3 main segments A, B, and C Ring
B Ring
C Ring
separated by empty regions divisions
Cassini Division
Rings cant have been formed together with Saturn
because material would have been blown away by
particle stream from hot Saturn at time of
formation.
Rings must be replenished by fragments of passing
comets meteoroids.
44
Composition of Saturns Rings
Rings are composed of ice particles
moving at large velocities around Saturn, but
small relative velocities (all moving in the same
direction).
45
Shepherd Moons
Some moons on orbits close to the rings focus the
ring material, keeping the rings confined.
46
Divisions and Resonances
Moons do not only serve as Shepherds.
Where the orbital period of a moon is a
small-number fractional multiple (e.g., 23) of
the orbital period of material in the disk
(resonance), the material is cleared out
? Divisions
47
Electromagnetic Phenomena in Saturns Rings
Radial spokes in the rings rotate with the
rotation period of Saturn
Magnetized ring particles lifted out of the ring
plane and rotating along with the magnetic-field
structure
48
Titan

• About the size of Jupiters moon Ganymede.
• Rocky core, but also large amount of ice.
• Thick atmosphere, hiding the surface from direct
  view.

49
Titans Atmosphere
Because of the thick, hazy atmosphere, surface
features are only visible in infrared images.
Many of the organic compounds in Titans
atmosphere may have been precursors of life on
Earth.
Surface pressure 50 greater than air pressure
on Earth
Surface temperature 94 K (-290 oF)
? methane and ethane are liquid!
Methane is gradually converted to ethane in the
Atmosphere
? Methane must be constantly replenished,
probably through breakdown of ammonia (NH3).
50
Saturns Smaller Moons
Saturns smaller moons formed of rock and ice
heavily cratered and appear geologically dead.
Tethys Heavily cratered marked by 3 km deep,
1500 km long crack.
Iapetus Leading (upper right) side darker than
rest of surface because of dark deposits.
Enceladus Possibly active regions with fewer
craters, containing parallel grooves, possibly
filled with frozen water.
51
Saturns Smaller Moons (2)
Hyperion Too small to pull itself into spherical
shape.
All other known moons are large enough to attain
a spherical shape.
52
The Origin of Saturns Satellites

• No evidence of common origin, as for Jupiters
  moons.

• Probably captured icy planetesimals.

• Moons interact gravitationally, mutually
  affecting each others orbits.

• Co-orbital moons (orbits separated by only 100
  km) periodically exchange orbits!

• Small moons are also trapped in Lagrange points
  of larger moons Dione and Tethys.

53
Coorbital Moons
(SLIDESHOW MODE ONLY)
54
New Terms
oblateness liquid metallic hydrogen decameter
radiation decimeter radiation current sheet Io
plasma torus Io flux tube critical
point belt zone forward scattering Roche
limit gossamer rings grooved terrain tidal
heating shepherd satellite spoke  
55
Discussion Questions
1. Some astronomers argue that Jupiter and Saturn
are unusual, while other astronomers argue that
all solar systems should contain one or two such
giant planets. What do you think? Support your
argument with evidence. 2. Why dont the
terrestrial planets have rings?
56
Quiz Questions
1. Jupiters mass is approximately 0.001 solar
masses. How is the mass of Jupiter
determined? a. We use Newtons form of Keplers
third law. b. We use the period and semimajor
axis of Jupiters orbit around the Sun. c. We can
use the period and semimajor axis of Callistos
orbit around Jupiter. d. Both a and b above. e.
Both a and c above.
57
Quiz Questions
2. What evidence do we have that Jupiter is
primarily composed of hydrogen and helium rather
than rock? a. Jupiter has hydrogen and helium
lines in its spectrum. b. The density of Jupiter
is 1.3 grams per cubic centimeter. c. Jupiters
equatorial diameter is about 6 larger than its
polar diameter. d. Both a and b above. e. All of
the above
58
Quiz Questions
3. What energy source drives the weather that we
see on Jupiter? a. Thermal energy escaping from
Jupiters interior, still hot from formation. b.
Thermal energy escaping from Jupiters interior,
created by nuclear fusion. c. Sunlight striking
the cloud tops warms Jupiters atmosphere from
above. d. Sunlight heats the surface of Jupiter,
then the surface radiates at infrared
wavelengths, which warms the atmosphere. e.
Thermal energy escaping from Jupiters interior
due to the condensation of helium droplets that
sink beneath the less dense hydrogen.
59
Quiz Questions
4. What evidence do we have that Jupiter has a
very hot interior? a. It reflects 170 of the
visible light than it receives from the Sun. b.
It reflects 170 of the infrared light than it
receives from the Sun. c. It emits 70 more
energy at visible wavelengths than it receives
from the Sun. d. It emits 70 more energy at
infrared wavelengths than it receives from the
Sun. e. Both a and b above.
60
Quiz Questions
5. Which method of heat transfer is responsible
for Jupiters belts zones, and the Great Red
Spot? a. Radiation. b. Convection c.
Conduction. d. All of the above. e. None of the
above.
61
Quiz Questions
6. In the 1950s, radio telescopes first detected
synchrotron radiation from Jupiter. What did
this discovery tell us about Jupiter? a. Jupiter
has three distinct cloud layers in its
atmosphere. b. Jupiter began emitting radio waves
in the 1950s. c. Io orbits around Jupiter once
every 1.8 days. d. Jupiter has a strong magnetic
field. e. Jupiter rotates rapidly.
62
Quiz Questions
7. The two requirements for a strong planetary
magnetic field are rapid rotation, and a
convective interior zone composed of an
electrically conductive material. Jupiters
rotational period is slightly less than 10 hours.
What type of matter fulfills the second
requirement? a. Liquid molecular hydrogen. b.
Molten copper-aluminum. c. Liquid metallic
hydrogen. d. A salty subsurface ocean. e. Molten
iron-nickel.
63
Quiz Questions
8. What is the Roche Limit? a. The maximum
distance from a planet at which planetary rings
can exist. b. The maximum distance that a moon
can travel from its planet. c. The maximum mass
of a blattella germanica. d. The maximum mass of
a Terrestrial planet. e. The minimum mass of a
Jovian planet.
64
Quiz Questions
9. Jupiters ring appears dark in back-scattered
light, yet appears bright in forward-scattered
light. What does this tell us about the particles
that make up Jupiters ring? a. The average
diameter of a particle is a few micrometers. b.
The particles are most likely dust. c. The
particles are most likely ice. d. Both a and b
above. e. Both a and c above.
65
Quiz Questions
10. How does Ganymede differ from Callisto? a.
Ganymede has more impact craters than
Callisto. b. Ganymede is differentiated, and
Callisto is not. c. Ganymede has a lower density
than Callisto. d. Ganymede is smaller than
Callisto. e. All of the above.
66
Quiz Questions
11. The density of Callisto is 1.8 grams per
cubic centimeter, and that of Ganymede is 1.9
grams per cubic centimeter. What does this
suggest about these outer two of Jupiters four
big moons? a. These two moons must be made of
roughly equal volumes of rock and iron. b. These
two moons must be made of roughly equal volumes
of ice and rock. c. Both moons must be larger
than Earths moon. d. Both moons must be smaller
than Earths moon. e. Both b and c above.
67
Quiz Questions
12. What evidence do we have that the surface of
Europa is young and active? a. Europa has very
few impact craters. b. The icy crust of Europa is
highly reflective. c. Europa is the smallest of
Jupiters four large moons. d. Both a and b
above. e. All of the above.
68
Quiz Questions
13. What evidence do we have that Ios crust and
lava is mostly silicate rock rather than sulfur
compounds? a. Some mountains on Io are much
higher than any mountains on Earth. b. Much of
the lava flowing from Ios volcanoes is hotter
than Earth lava. c. The various hues of yellow,
orange, and red cannot be explained by sulfur. d.
Both a and b above. e. All of the above.
69
Quiz Questions
14. Why are Europa, Ganymede, and Callisto
necessary for the continued heating of Io? a.
The tidal forces that these moons exert on Io are
greater than the tidal force on Io due to
Jupiter. b. These moons periodically tug on Io
and keep its orbit elliptical. c. These moons
send incoming comet bodies toward Io. d. These
outer moons disrupt Jupiters magnetic field
lines, causing them to twist back and forth
across Io. e. Io is the smallest of these moons
and subject to their influence.
70
Quiz Questions
15. What evidence supports the model of Jupiters
Galilean satellites forming in a mini accretion
disk around Jupiter? a. The density trend of
these four moons is highest close to Jupiter and
decreases with distance. b. The two inner moons
are much smaller than the two outer moons of this
group. c. Moons closer to a large planet have
more impact craters on their surface. d. Both a
and b above. e. All of the above.
71
Quiz Questions
16. In which way does Saturn differ from
Jupiter? a. Saturn is less oblate. b. Saturn has
more mass. c. Saturn has a stronger magnetic
field. d. Saturn has more distinct belts and
zones e. Saturn has a smaller zone of liquid
metallic hydrogen.
72
Quiz Questions
17. How do Saturns three layers of clouds differ
from Jupiters three layers of clouds? a.
Saturns three cloud layers have a very different
chemical composition than Jupiters. b. Saturns
three cloud layers are at much lower temperatures
than Jupiters. c. Saturns three cloud layers
are located higher up in the atmosphere than
Jupiters. d. All of the above. e. None of the
above.
73
Quiz Questions
18. What gives Saturns rings their beautiful
structure? a. The gravitational interaction
between ring particles. b. The gravitational
influence of Saturns moons on the ring
particles. c. The gravitational interactions
between Saturn and the ring particles. d. Both
and b above. e. All of the above.
74
Quiz Questions
19. How can Titan have a nitrogen-methane
atmosphere with a surface pressure 1.5 times that
of Earths atmosphere, whereas the larger and
more massive Ganymede has no atmosphere at
all? a. Titan does not have the strong
gravitational field of Jupiter nearby to break
apart atmospheric gas molecules. b. Titan has a
stronger surface gravity and can hold onto gas
molecules more easily than Ganymede. c. Titan
does not have to compete for gases with other
large moons that are located nearby. d. Titan has
a sticky surface that holds onto large gas
molecules. e. Titan is farther from the Sun, and
thus colder than Ganymede.
75
Quiz Questions
20. What causes the leading side of Saturns
small moon Iapetus to differ from its trailing
side? a. The leading side is darker, because it
collides with and captures dark dust. b. The
leading side is brighter, since it collides with
and captures fresh ices. c. The leading side is
darker, as ices melt and condense on the trailing
side. d. The leading side is darker, eroded as it
is by impacts with solar wind particles. e. The
leading side is brighter, eroded as it is by
impacts with solar wind particles.