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2. Chapter 8 Moons, Rings, and Plutoids
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3. Units of Chapter 8 The Galilean Moons of Jupiter
The Large Moons of Saturn and Neptune
The Medium-Sized Jovian Moons
Planetary Rings
Beyond Neptune
Summary of Chapter 8
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4. 8.1 The Galilean Moons of Jupiter
All four Jovian planets have extensive moon systems, and more are continually being discovered.
The Galilean moons of Jupiter are those observed by the astronomer Galileo in 1610: Io, Europa, Ganymede, and Callisto.
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5. 8.1 The Galilean Moons of Jupiter
This image shows Jupiter with two of its Galilean moons.
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6. 8.1 The Galilean Moons of Jupiter
The Galilean moons and their orbits
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7. 8.1 The Galilean Moons of Jupiter
Their interiors
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8. 8.1 The Galilean Moons of Jupiter
Io is the densest of Jupiter’s moons, and the most geologically active object in the solar system.
It has many active volcanoes, some quite large.
Io can change surface features in a few weeks.
Io has no craters; they fill in too fast. Io has the youngest surface of any solar system object.
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9. 8.1 The Galilean Moons of Jupiter
Io is very close to Jupiter and also experiences gravitational forces from Europa. The tidal stretching is huge, and provides the energy for the volcanoes.
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10. 8.1 The Galilean Moons of Jupiter
Europa has no craters; surface is water ice, possibly with liquid water below.
Tidal forces stress and crack ice; water flows, keeping surface relatively flat.
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11. 8.1 The Galilean Moons of Jupiter
Ganymede is the largest moon in the solar system—larger than Pluto and Mercury.
It has a history similar to Earth’s Moon, but with water ice instead of lunar rock.
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12. 8.1 The Galilean Moons of Jupiter
Callisto is similar to Ganymede but with heavy cratering and no evidence of resurfacing activity.
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13. 8.2 The Large Moons of Saturn and Neptune
Titan has been known for many years to have an atmosphere thicker and denser than Earth’s; mostly nitrogen and argon.
Titan’s cloudy atmosphere makes it impossible to see the surface; the picture at right was taken from only 4000 km away.
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14. 8.2 The Large Moons of Saturn and Neptune
Infrared image of Titan, showing detail and possible icy volcano.
There are few craters, consistent with active surface.
Complex chemical interactions occur in atmosphere.
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15. 8.2 The Large Moons of Saturn and Neptune
The Huygens lander took these images of the surface of Titan.
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16. 8.2 The Large Moons of Saturn and Neptune
Trace chemicals in Titan’s atmosphere make it chemically complex.
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17. 8.2 The Large Moons of Saturn and Neptune
Triton is in a retrograde orbit; its surface has few craters, indicating an active surface.
Nitrogen geysers have been observed on Triton, contributing to the surface features.
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18. 8.3 The Medium-Sized Jovian Moons
Densities of these moons suggest that they are rock and water ice.
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19. 8.3 The Medium-Sized Jovian Moons
Moons of Saturn, in natural color
Note the similarities, as well as the large crater on Mimas.
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20. 8.3 The Medium-Sized Jovian Moons
Moons of Uranus and Neptune
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21. 8.3 The Medium-Sized Jovian Moons
Miranda shows evidence of a violent past, although the origin of the surface features is unknown.
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22. 8.4 Planetary Rings
The ring system of Saturn is large and complex and is easily seen from Earth. The other Jovian planets have ring systems as well.
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23. 8.4 Planetary Rings
The rings are not solid; they are composed of small rocky and icy particles.
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24. 8.4 Planetary Rings
Our view of Saturn’s rings changes as the planet moves in its orbit.
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25. 8.4 Planetary Rings
The Roche limit is where the tidal forces of the planet are too strong for a moon to survive; this is where rings are formed.
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26. 8.4 Planetary Rings All observed ring systems are within this limit.
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27. 8.4 Planetary Rings
Voyager probes showed Saturn’s rings to be much more complex than originally thought.
Earth is shown on the same scale as the rings.
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28. 8.4 Planetary Rings
“Shepherd” moons define the edges of some of the rings.
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29. 8.4 Planetary Rings Jupiter has been found to have a small, thin ring.
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30. 8.4 Planetary Rings
Uranus has nine thin rings. The inset (top) shows the Epsilon ring.
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31. 8.4 Planetary Rings
Two shepherd moons keep the Epsilon ring of Uranus from diffusing away.
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32. 8.4 Planetary Rings Neptune has five rings, three narrow and two wide.
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33. 8.5 Beyond Neptune
Pluto was discovered in It was thought to be needed to explain irregularities in the orbits of Uranus and Neptune, but it turned out that there were no such irregularities.
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34. 8.5 Beyond Neptune Pluto’s moon, Charon, was discovered in 1978.
It is orbitally locked to Pluto, and about a sixth as large.
Pluto also has four smaller moons: Nix, Hydra, Styx, and Kerberos.
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35. 8.5 Beyond Neptune
Charon’s orbit is at an angle of 118º to the plane of Pluto’s orbit.
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36. 8.5 Beyond Neptune
The first Kuiper belt objects were observed in the 1990s, and more than 1200 are now known. Some of them are comparable in size to Pluto.
These images show Eris and its moon Dysnomia.
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37. 8.5 Beyond Neptune
This figure shows several of the largest known trans-Neptunian objects, now collectively called plutoids.
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38. Summary of Chapter 8
The outer solar system has 6 large moons, 12 medium ones, and many smaller ones.
Titan has a thick atmosphere and may have flowing rivers of methane.
Triton has a fractured surface and a retrograde orbit.
Medium-sized moons of Saturn and Uranus are mostly rock and water ice.
Saturn’s rings are complex, and some are defined by shepherd moons.
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39. Summary of Chapter 8, cont.
The Roche limit is the closest a moon can survive near a planet; inside this limit, rings form instead.
Jupiter, Uranus, and Neptune all have faint ring systems.
Pluto has five moons: Charon, Nix, Styx, Kerberos, and Hydra.
Dwarf planets beyond Neptune (including Pluto) are now known as plutoids.
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