1. Chapter 11 Jovian Planet Systems

2. 11.1 A Different Kind of Planet
Our goals for learning:
Are jovian planets all alike?
What are jovian planets like on the inside?
What is the weather like on jovian planets?
Do jovian planets have magnetospheres like Earth’s?

3. Are jovian planets all alike?

4. Jovian Planet 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

5. Density Differences
Uranus and Neptune are denser than Saturn because they have less H/He, proportionately

6. Density Differences
But that explanation doesn’t work for Jupiter….

7. Jupiter Jupiter’s appearance and physical properties
Jupiter is the largest planet both in diameter and mass more than10x Earth’s diameter and 300x the mass
Dense, richly colored parallel cloud bands cloak the planet
Atmosphere is mainly H, He, CH4, NH3, and H2O
Clouds appear to be particles of water, ice, and ammonia compounds
Bright colors of clouds may come from complex organic molecules with composition still unknown
Jupiter rotates once about every 10 hours with this fast rotation leading to a significant equatorial bulge
Figure 9.1

8. Jupiter Jupiter’s interior
Jupiter’s average density is 1.3 g/cm3 – indicates an interior composed mainly of very light elements
Using average density, Jupiter’s shape, and its gravitational attraction on its moons and passing spacecraft, Jupiter’s interior can be calculated
Interior becomes increasingly more dense as center is approached with its gaseous upper layers turning to liquid hydrogen about 10,000 km below the surface
Deeper still, liquid hydrogen compresses into liquid metallic hydrogen, a material scientists only recently created in tiny high-pressure chambers
An iron rocky core, a few times bigger than the Earth, probably resides at the center
Figure 9.2

9. Jupiter Jupiter’s interior (continued) Jupiter’s atmosphere
Jupiter, with a core temperature of about 30,000 K, emits more energy than it receives
Possibly due to heat left over from its creation
Planet may still be shrinking in size converting gravitational energy into heat
Jupiter’s atmosphere
General convection pattern:
Heat within Jupiter carries gas to the top of the atmosphere
High altitude gas radiates into space, cools and sinks
Coriolis effect turns rising and sinking gases into powerful jet streams (about 300 km/hr) that are seen as cloud belts
Adjacent belts, with different relative speeds, create vortices of various colors, the largest being the Great Red Spot, which has persisted for over 300 years
Figure 9.3, Figure 9.4

10. Jupiter Jupiter’s atmosphere (continued)
Convection in the deep metallic liquid hydrogen layer coupled with Jupiter’s rapid rotation creates a powerful magnetic field
20,000x stronger than the Earth’s field, it is the largest planetary magnetic field
Jupiter’s auroral activity and intense radio emissions are indicative of its magnetic field
Magnetic field also traps charged particles into far above the planet in regions resembling the Earth’s Van Allen radiation belts
Lightning in clouds has been observed
Figure 9.5

11. Jupiter Jupiter’s ring
Jupiter has a thin ring made of tiny particles of rock dust and held in orbit by Jupiter’s gravity
Solar radiation and collisions with charged particles trapped in Jupiter’s magnetic field exert a friction on the ring dust that will eventually cause the dust the drift into the atmosphere
To maintain the ring, new dust must be provided – possibly from collision fragments ejected from the Jovian moons
Figure 9.6

12. Saturn Saturn’s Appearance and Physical Properties
Saturn is the second largest planet with a diameter and mass more than10x Earth’s diameter and 95x the mass
Its average density of 0.7 g/cm3 is less than than of water
Low density, like Jupiter, suggests a composition mostly of hydrogen an its compounds
Internal structures similar to Jupiter
Saturn radiates more energy than it receives, but unlike Jupiter, this energy probably comes from the conversion of gravitational energy from falling helium droplets as they condense in Saturn’s interior
Saturn’s atmosphere looks different than Jupiter’s because Saturn is cold enough for ammonia gas to freeze into cloud particles that veil its atmosphere’s deeper layers
Figure 9.10, Figure 9.11

13. Saturn Saturn’s Rings Rings are wide but thin
Main band extends from about 30,000 km above its atmosphere to about twice Saturn’s radius (136,000 km)
Faint rings can be seen closer to Saturn as well as farther away
Thickness of rings: a few hundred meters
Rings not solid, but made of a swarm of individual bodies
Sizes range from centimeters to meters
Composition mainly water, ice, and carbon compounds and is not uniform across rings
Rings structures into ringlets and gaps
Large gaps probably due to resonances with Saturn’s moons located beyond the rings
Narrow gaps due to complex interaction between ring particles and tiny moons in the rings
Figure 9.12, Figure 9.13

14. Saturn Origin of Planetary Rings The Roche Limit
Rings once thought to be left over remains from a planet’s formation
However, ring lifetime is short since, as pointed out for Jupiter, they are subject to frictional forces that spiral particles into the planet’s atmosphere
For rings to persist they must be replenished
The Roche Limit
Any object held together solely by gravity will break apart by tidal forces if it gets too close to the planet.
Distance of breakup is called the Roche limit and is 2.44 planetary radii if object and planet have the same density
All planetary rings lie near their planet’s Roche limit
Existence of side-by-side ringlets of different compositions indicates rings supplied by varied comets and asteroids
Objects bonded together chemically will survive Roche limit
Figure 9.14
Animation: Roche breakup of a moon

15. Uranus Introduction Uranus’s Atmosphere
Unknown to the ancients, even though visible to the naked eye, Uranus was not discovered until 1781 by Sir William Herschel
While small relative to Jupiter/Saturn, Uranus is 4x larger in diameter than Earth and has 15x the mass
At 19 AU, Uranus is difficult to study from Earth, but even close up images from Voyager reveal a rather featureless object
Uranus’s Atmosphere
Atmosphere is rich in hydrogen and methane
Methane gas and ice are responsible for the blue color of Uranus’s atmosphere
Figure 9.17, Figure 9.18

16. Uranus Uranus’s Interior
With a density of 1.2 g/cm3 and smaller size, Uranus must contain proportionally fewer light elements than Jupiter/Saturn
However, its density is too low for it to contain much rock or iron
Consequently, Uranus’s interior probably contains water, methane, and ammonia, which would also help explain the spectrum of Uranus
Size of equatorial bulge supports the idea that the interior is mostly water and other hydrogen-rich molecules and that it may have a rock/iron core
It is currently not known if the core formed first and attracted lighter gases that condensed on it, or the core formed by differentiation after the planet formed.
Figure 9.19

17. Uranus Uranus’s Rings and Moons Rings Moons
Neptune is encircled by a set of narrow rings composed meter-sized objects
These objects are very dark, implying they are rich in carbon particles or organic-like materials
The extremely narrow rings may be held in place by shepherding satellites
Moons
Uranus has 5 large moons and several small ones that form a regular system
Moons probably composed of ice and rock and many show heavy cratering
Miranda is very unique in that it appears to have been torn apart and reassembled
Figure 9.20, Figure 9.21

18. Uranus Uranus’s Odd Tilt
Uranus’s spin axis is tipped so that it nearly lies in its orbital plane
The orbits of Uranus’s moons are similarly tilted
This odd tilt suggests that Uranus was struck during its formation and splashed out material to form the moons
The large tilt together with Uranus’s fast spin rate gives an odd night/day pattern over the course of a Uranian year
The uneven heating pattern may be the reason Uranus does not have cloud bands
Figure 9.22

19. Neptune Introduction Neptune’s Structure
Neptune is the outermost of the Jovian giants and similar in size to Uranus
A deep blue world with cloud bands and vortex structures – the Great “Dark” Spot being, at one time, the most prominent feature
Neptune was discovered from predictions made by John C. Adams and Urbain Leverrie, who calculated its orbit based on disturbances in Uranus’s orbit
Neptune’s Structure
Neptune’s interior is probably similar to Uranus’s – mostly ordinary water surrounded by a thin atmosphere rich in hydrogen and its compounds and probably has a rock/iron core
Figure 9.23

20. Neptune Neptune’s Atmosphere
Neptune’s blue, like Uranus, comes from methane in its atmosphere
Unlike Uranus, Neptune has cloud belts
Like Jupiter/Saturn, Neptune radiates more energy than it gains from the Sun
The deep interior heat source drives convective currents which then lead, via the Coriolis effect, to the visible atmospheric belts
Neptune’s winds are extremely fast reaching speeds of 2200 km/hr and creating visible vortex structures
Figure 9.24

21. Neptune Neptune’s Rings and Moons Rings
Neptune, like the other giant planets, has rings
They are probably the debris from small satellites or comets that have collided and broken up
They contain more dust than the Saturn/Uranus rings
The rings are not distributed uniformly around the ring indicating they are relatively new
Figure 9.25

22. Neptune Neptune’s Rings and Moons (continued) Moons
Neptune has six small moons orbiting close to the planet and two moons farther out
One of the two is Triton
Triton’s orbit is “backwards” and is highly tilted with respect to Neptune’s equator – Triton is perhaps a captured planetesimal from the Kuiper belt
Triton is large enough and far enough from the some to retain an atmosphere
Triton has some craters with dark steaks extending from them – at least one of which originates from a geyser caught in eruption by the passing Voyager II
The material in the geyser is thought to be a mixture of nitrogen, ice and carbon compounds heated beneath the surface by sunlight until it expands and bursts to the surface
Figure 9.26

23. Pluto
Survey
Discovered by Clyde Tombaugh in 1930 by scanning millions of star images over the course of a year
Pluto’s large distance and very small size makes it difficult to study, even in the largest telescopes
In 1978, James Christy discovered Charon, Pluto’s moon
The orbiting combination of Pluto and Charon allows an accurate measurement of their masses – Pluto is the least massive planet
Charon’s steeply tilted orbit implies that Pluto is highly tilted as well
Charon takes 6.4 days to orbit Pluto once
Pluto rotates with the same period of 6.4 days
Figure 9.27

24. Pluto Survey (continued)
The recent eclipses of Pluto with Charon has allowed the radii of both objects to be determined
Pluto is 1/5 the diameter of Earth
Charon is relatively large being about ½ Pluto’s diameter
From these masses and diameters, Pluto’s density is 2.1 g/cm3 suggesting an object of water, ice, and rock
Very little is known of Pluto’s surface, but computer analysis of eclipse images suggest a bright south pole, perhaps a frozen methane cap
Pluto also has a tenuous atmosphere of N2, CO and traces of CH4
Pluto was once thought to be a moon of Neptune that escaped; now it is thought Neptune captured Pluto, a remnant planetesimal
Figure 9.28

25. Sizes of Jovian Planets
Greater compression is why Jupiter is not much larger than Saturn even though it is three times more massive
Jovian planets with even more mass can be smaller than Jupiter

26. Rotation and Shape
Jovian planets are not quite spherical because of their rapid rotation

27. What are jovian planets like on the inside?

28. Interiors of Jovian Planets
No solid surface.
Layers under high pressure and temperatures.
Cores (~10 Earth masses) made of hydrogen compounds, metals & rock
The layers are different for the different planets. WHY?

29. Inside Jupiter
High pressures inside Jupiter cause phase of hydrogen to change with depth
Hydrogen acts like a metal at great depths because its electrons move freely

30. Inside Jupiter
Core is thought to be made of rock, metals, and hydrogen compounds
Core is about same size as Earth but 10 times as massive

31. Comparing Jovian Interiors
Models suggest cores of jovian planets have similar composition
Lower pressures inside Uranus and Neptune mean no metallic hydrogen

32. Jupiter’s Internal Heat
Jupiter radiates twice as much energy it receives from Sun (it’s radiation would kill an unprotected astronaut in minutes)
Energy probably comes from slow contraction of interior (releasing potential energy)

33. Internal Heat of Other Planets
Saturn also radiates twice as much energy it receives from Sun
Energy probably comes from differentiation (helium rain)
Neptune emits nearly twice as much energy as it receives, but the source of that energy remains mysterious
As Jupiter and Saturn cool, the interior of the planets will approach temperatures where hydrogen and helium no longer mix. This process, which is likely to have already occurred in Saturn, could lead to the formation of helium droplets that would "rain down" towards the center of the planet and provide an additional source of heat.

34. What is the weather like on jovian planets?

35. Jupiter’s Atmosphere Hydrogen compounds in Jupiter form clouds
Different cloud layers correspond to freezing points of different hydrogen compounds
NH3
NH4SH
H2O

36. Jovian Planet Atmospheres
Other jovian planets have cloud layers similar to Jupiter’s
Different compounds make clouds of different colors

37. Jupiter’s colors Ammonium sulfide clouds (NH4SH) reflect red/brown.
Ammonia, the highest, coldest layer, reflects white.

38. Saturn’s colors
Saturn’s layers are similar, but deeper in and farther from the Sun --- more subdued.

39. Methane on Uranus and Neptune
Methane gas of Neptune and Uranus absorb red light but transmit blue light
Blue light reflects off methane clouds, making those planes look blue

40. Jupiter’s Bands White ammonia clouds form where air rises
Coriolis effect changes N-S flow to E-W winds
Between white clouds we see deeper reddish clouds of NH4SH
Warmer red bands are brighter in IR

41. Jupiter’s Great Red Spot
A storm twice as wide as Earth
Has existed for at least 3 centuries

42. Weather on Jovian Planets
All the jovian planets have strong winds and storms

43. Do jovian planets have magnetospheres like Earth’s?

44. Jupiter’s Magnetosphere
Jupiter’s strong magnetic field gives it an enormous magnetosphere (14 times stronger than Earth’s)
Gases escaping Io feed the donut-shaped Io torus

45. Other Magnetospheres
All the jovian planets have substantial magnetospheres, but Jupiter’s is largest by far

46. Thought Question
Jupiter does not have a large metal core like the Earth. How can it have a magnetic field?
a) The magnetic field is left over from when Jupiter accreted
b) Its magnetic field comes from the Sun
c) It has metallic hydrogen inside, which circulates and makes a magnetic field
d) That’s why its magnetic field is weak

47. What have we learned? Are jovian planets all alike?
Jupiter and Saturn are mostly H and He gas
Uranus and Nepture are mostly H compounds
What are jovian planets like on the inside?
Layered interiors with very high pressure and cores made of rock, metals, and hydrogen compounds
Very high pressure in Jupiter and Saturn can produce metallic hydrogen

48. What have we learned? What is the weather like on jovian planets?
Multiple cloud layers determine colors of jovian planets
All have strong storms and winds
Do jovian planets have magnetospheres like Earth’s?
All have substantial magnetospheres
Jupiter’s is largest by far

49. 11.2 A Wealth of Worlds: Satellites of Ice and Rock
Our goals for learning:
What kinds of moons orbit jovian planets?
Why are Jupiter’s Galilean moons so geologically active?
What is remarkable about Titan and other major moons of the outer solar system?
Why are small icy moons more geologically active than small rocky planets?

50. Planetary Fact Sheet - Metric

51. What kinds of moons orbit the jovian planets?

52. Sizes of Moons 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

53. Medium & Large Moons Enough self-gravity to be spherical
Have substantial amounts of ice.
Formed in orbit around jovian planets.
Circular orbits in same direction as planet rotation.

54. Small Moons Far more numerous than the medium and large moons.
Not enough gravity to be spherical: “potato-shaped”

55. Small Moons
Captured asteroids or comets, so orbits do not follow usual patterns.

56. How are Jupiter’s Galilean moons so geologically active?

57. Io’s Volcanic Activity
Io is the most volcanically active body in the solar system, but how?

58. Io’s Volcanoes
Volcanic eruptions continue to change Io’s surface

59. Tidal Heating Io is squished and stretched as it orbits Jupiter
But why is its orbit so elliptical?

60. The tugs add up over time, making all 3 orbits elliptical.
Orbital Resonances
Every 7 days, these 3 moons line up.

61. Europa’s Ocean: Waterworld?

62. Tidal stresses crack Europa’s surface ice.

63. Europa’s interior also warmed by tidal heating
Based on Galileo spacecraft measurements of the strength of gravity over different positions of Europa and theoretical modeling of the interior.

64. Ganymede Largest moon in the solar system
Clear evidence of geological activity
Tidal heating plus heat from radio-active decay?
Largest moon
Figure might work better if there were one with out the callouts.

65. Callisto “Classic” cratered iceball.
No tidal heating, no orbital resonances.
But it has magnetic field !?

66. Thought Question How does Io get heated by Jupiter? a) Auroras
b) Infrared Light
c) Jupiter pulls harder on one side than the other
d) Volcanoes

67. What is remarkable about Titan a major moon of Saturn?

68. Titan’s Atmosphere
Titan is the only moon in the solar system to have a thick atmosphere
It consists mostly of nitrogen with some argon, methane, and ethane

69. Titan’s Surface
Huygens probe provided first look at Titan’s surface in early 2005
Liquid methane, “rocks” made of ice

70. Medium Moons of Saturn
Almost all show evidence of past volcanism and/or tectonics

71. Medium Moons of Uranus Varying amounts of geological activity
Moon Miranda has large tectonic features and few craters (episode of tidal heating in past?)

72. Neptune’s Moon Triton Similar to Pluto, but larger
Evidence for past geological activity

73. Why are small icy moons more geologically active than small rocky planets?

74. Rocky Planets vs. Icy Moons
Rock melts at higher temperatures
Only large rocky planets have enough heat for activity
Ice melts at lower temperatures
Tidal heating can melt internal ice, driving activity

75. 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

76. What have we learned?
What is special about Titan and other major moons of the solar system?
Titan is only moon with thick atmosphere
Many other major moons show signs of geological activity
Why are small icy moons more geologically active than small rocky planets?
Ice melts and deforms at lower temperatures enabling tidal heating to drive activity

77. 11.3 Jovian Planet Rings Our goals for learning:
What are Saturn’s rings like?
How do other jovian ring systems compare to Saturn’s?
Why do the jovian planets have rings?

78. What are Saturn’s rings like?

79. What are Saturn’s rings like?
They are made up of numerous, tiny individual particles
They orbit over Saturn’s equator
They are very thin

80. Earth-based view

81. Spacecraft view of ring gaps
Voyager

82. Artist’s conception of close-up

83. Gap Moons
Some small moons create gaps within rings

84. Shepherd Moons
Pair of small moons can force particles into a narrow ring

85. Resonance Gaps
Orbital resonance with a larger moon can also produce a gap
Ie 4:3

86. How do other jovian ring systems compare to Saturn’s?

87. Jovian Ring Systems All four jovian planets have ring systems
Others have smaller, darker ring particles than Saturn

88. Why do the jovian planets have rings?

89. Why do the jovian planets have rings?
They formed from dust created in impacts on moons orbiting those planets
How do we know that?

90. How do we know?
Rings aren’t leftover from planet formation because the particles are too small to have survived this long.
There must be a continuous replacement of tiny particles.
The most likely source is impacts with the jovian moons.

91. Ring Formation
Jovian planets all have rings because they possess many small moons close-in
Impacts on these moons are random
Saturn’s incredible rings may be an “accident” of our time

92. What have we learned? What are Saturn’s rings like?
Made up of countless individual ice particles
Extremely thin with many gaps
How do other jovian ring systems compare to Saturn’s?
Much fainter ring systems with smaller, darker, less numerous particles
Why do the jovian planets have rings?
Ring particles are probably debris from moons

93. How the Universe Works Videos
How the Universe Works: Jupiter
How the Universe Works: Saturn