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Chapter 8 Moons, Rings, and Plutoids Copyright © 2010 Pearson Education, Inc. Copyright © 2010 Pearson Education, Inc. Chapter 8 Moons, Rings, and Plutoids Copyright © 2010 Pearson Education, Inc. 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 Plutoids and the Kuiper Belt Copyright © 2010 Pearson Education, Inc. Question 1 As their distance from Jupiter increases, the four Galilean satellites show a consistent Copyright © 2010 Pearson Education, Inc. a) increase in density. b) increase in size. c) decrease in cratering. d) decrease in density. e) amount of cratering. Question 1 As their distance from Jupiter increases, the four Galilean satellites show a consistent a) increase in density. b) increase in size. c) decrease in cratering. d) decrease in density. e) amount of cratering. Like a miniature version of our solar system, Jupiter’s four large moons show a decrease in density as distance increases. Io is most dense of the four; Callisto is least dense. Copyright © 2010 Pearson Education, Inc. 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 Galileo: Io, Europa, Ganymede, and Callisto. Copyright © 2010 Pearson Education, Inc. The Galilean Moons of Jupiter This image shows Jupiter with two of its Galilean moons. Galilean Moons Copyright © 2010 Pearson Education, Inc. The Galilean Moons of Jupiter The Galilean moons and their orbits Copyright © 2010 Pearson Education, Inc. The Galilean Moons of Jupiter Their interiors Copyright © 2010 Pearson Education, Inc. 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. Copyright © 2010 Pearson Education, Inc. Question 3 What is thought to cause Io’s volcanism? Copyright © 2010 Pearson Education, Inc. a) Jupiter’s magnetosphere b) Jupiter’s rapid rotation c) tidal stress from Jupiter and Europa d) radioactive decay from its core e) Io’s large mass and tectonic activity Question 3 What is thought to cause Io’s volcanism? a) Jupiter’s magnetosphere b) Jupiter’s rapid rotation c) tidal stress from Jupiter and Europa d) radioactive decay from its core e) Io’s large mass and tectonic activity Io is constantly “squeezed” by its huge neighbor as well as by companion moons, heating its interior. Copyright © 2010 Pearson Education, Inc. The Galilean Moons of Jupiter Io Cutaway Io is very close to Jupiter, and also experiences gravitational forces from Europa. The tidal forces are huge, and provide the energy for the volcanoes. Copyright © 2010 Pearson Education, Inc. Question 2 The surface of which jovian moon most resembles the pack ice of the Arctic Ocean? Copyright © 2010 Pearson Education, Inc. a) Europa b) Io c) Amalthea d) Ganymede e) Callisto Question 2 The surface of which jovian moon most resembles the pack ice of the Arctic Ocean? a) Europa b) Io c) Amalthea d) Ganymede e) Callisto Ice-filled surface cracks indicate an ocean may lie below. Copyright © 2010 Pearson Education, Inc. 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. Galileo’s View Copyright © 2010 Pearson Education, Inc. 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. Galileo’s View Copyright © 2010 Pearson Education, Inc. The Galilean Moons of Jupiter Callisto is similar to Ganymede; no evidence of plate activity. Copyright © 2010 Pearson Education, Inc. 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. Makes surface impossible to see; the picture at right was taken from only 4000 km away. Saturn Moon Copyright © 2010 Pearson Education, Inc. The Large Moons of Saturn and Neptune Infrared image of Titan, showing detail, and possible icy volcano Few craters, consistent with active surface Complex chemical interactions in atmosphere Copyright © 2010 Pearson Education, Inc. The Large Moons of Saturn and Neptune The Huygens lander took these images of the surface of Titan. Huygens Probe Copyright © 2010 Pearson Education, Inc. The Large Moons of Saturn and Neptune Trace chemicals in Titan’s atmosphere make it chemically complex. Copyright © 2010 Pearson Education, Inc. 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. Copyright © 2010 Pearson Education, Inc. The Medium-Sized Jovian Moons Densities of these moons suggest that they are rock and water ice. Copyright © 2010 Pearson Education, Inc. The Medium-Sized Jovian Moons Moons of Saturn, in natural color Note the similarities, as well as the large crater on Mimas. Copyright © 2010 Pearson Education, Inc. The Medium-Sized Jovian Moons Moons of Uranus and Neptune Copyright © 2010 Pearson Education, Inc. The Medium-Sized Jovian Moons Miranda shows evidence of a violent past, although the origin of the surface features is unknown. Copyright © 2010 Pearson Education, Inc. Question 8 Which moon in the solar system shows a dense atmosphere? Copyright © 2010 Pearson Education, Inc. a) our Moon b) Phobos c) Europa d) Titan e) Triton Question 8 Which moon in the solar system shows a dense atmosphere? a) our Moon b) Phobos c) Europa d) Titan e) Triton The Huygens probe, deployed by the Cassini spacecraft in 2005, showed that Titan’s atmosphere has a complex organic chemistry. Copyright © 2010 Pearson Education, Inc. Planetary Rings The ring system of Saturn is large and complex, and easily seen from Earth. The other Jovian planets have ring systems as well. Copyright © 2010 Pearson Education, Inc. Question 13 Which of these moons are most exciting to exobiologists? Copyright © 2010 Pearson Education, Inc. a) Io and Enceladus b) Titan and Europa c) Titan and Triton d) Europa and Miranda e) Phobos and Deimos Question 13 Which of these moons are most exciting to exobiologists? a) Io and Enceladus b) Titan and Europa c) Titan and Triton d) Europa and Miranda e) Phobos and Deimos Titan shows evidence of channels under its dense atmosphere. Europa has indications of liquid water beneath the ice. Copyright © 2010 Pearson Education, Inc. Planetary Rings The rings are not solid; they are composed of small rocky and icy particles. Copyright © 2010 Pearson Education, Inc. Planetary Rings Our view of Saturn’s rings changes as the planets move in their orbits. Copyright © 2010 Pearson Education, Inc. Question 7 Why are the rings of Saturn so bright? Copyright © 2010 Pearson Education, Inc. a) They are made of frozen metallic hydrogen. b) They contain glassy beads expelled by volcanoes on Enceladus. c) They contain shiny bits of iron. d) Titan and other moons reflect additional glow onto the rings. e) They are made of relatively new ice. Question 7 Why are the rings of Saturn so bright? a) They are made of frozen metallic hydrogen. b) They contain glassy beads expelled by volcanoes on Enceladus. c) They contain shiny bits of iron. d) Titan and other moons reflect an additional glow onto the rings. e) They are made of relatively new ice. Saturn’s rings are perhaps only 50 million years old, the result of a small moon coming within the planet’s Roche limit. Copyright © 2010 Pearson Education, Inc. 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. Copyright © 2010 Pearson Education, Inc. Question 5 The Roche limit is defined as the critical Copyright © 2010 Pearson Education, Inc. a) distance from a planet, inside of which a moon can be tidally destroyed. b) density that a moon can have and be solid. c) distance from a planet that a moon can experience synchronous rotation. d) mass a moon can have and still be classified as a moon. Question 5 The Roche limit is defined as the critical a) distance from a planet, inside of which a moon can be tidally destroyed. b) density that a moon can have and be solid. c) distance from a planet that a moon can experience synchronous rotation. d) mass a moon can have and still be classified as a moon. Saturn’s rings, as well as those of the other jovian planets, lie within its planet’s Roche limit. Copyright © 2010 Pearson Education, Inc. Planetary Rings All observed ring systems are within this limit. Copyright © 2010 Pearson Education, Inc. Planetary Rings Voyager probes showed Saturn’s rings to be much more complex than originally thought. Ring Crossing Copyright © 2010 Pearson Education, Inc. Earth is shown on the same scale as the rings. Planetary Rings “Shepherd” moons define the edges of some of the rings. Copyright © 2010 Pearson Education, Inc. Cassini Spacecraft Copyright © 2010 Pearson Education, Inc. Question 6 Shepherd satellites are defined as Copyright © 2010 Pearson Education, Inc. a) satellites in the coma of a comet. b) moons that confine a narrow ring. c) a type of moon that orbits another moon. d) moons that share an orbit of another, larger moon. e) moons that orbit inside a system of rings. Question 6 Shepherd satellites are defined as Copyright © 2010 Pearson Education, Inc. a) satellites in the coma of a comet. b) moons that confine a narrow ring. c) a type of moon that orbits another moon. d) moons that share an orbit of another, larger moon. e) moons that orbit inside a system of rings. Planetary Rings Jupiter has been found to have a small, thin ring. Copyright © 2010 Pearson Education, Inc. Question 4 How was the ring of Jupiter discovered? Copyright © 2010 Pearson Education, Inc. a) by optical telescopic observers from Earth b) by Voyager I as it passed Jupiter c) by an occultation of a star d) by radar imaging using the Arecibo dish e) with the Hubble Space Telescope’s superior resolution Question 4 How was the ring of Jupiter discovered? a) by optical telescopic observers from Earth b) by Voyager I as it passed Jupiter c) by an occultation of a star d) by radar imaging using the Arecibo dish e) with the Hubble Space Telescope’s superior resolution Jupiter’s ring is composed of dark, dusty particles that were first seen when Voyager was past the planet, looking back toward the Sun. Copyright © 2010 Pearson Education, Inc. Planetary Rings The rings of Uranus are more complex. Copyright © 2010 Pearson Education, Inc. Planetary Rings Two shepherd moons keep the epsilon ring from diffusing. Copyright © 2010 Pearson Education, Inc. Planetary Rings Neptune has five rings, three narrow and two wide. Copyright © 2010 Pearson Education, Inc. Question 10 The rings of Neptune Copyright © 2010 Pearson Education, Inc. a) were confirmed by Voyager 2 in 1989. b) appear both narrow and diffuse. c) all lie within Neptune’s Roche limit. d) often appear as clumpy ring arcs, rather than complete and symmetrical rings. e) All of these are correct. Question 10 The rings of Neptune Copyright © 2010 Pearson Education, Inc. a) were confirmed by Voyager 2 in 1989. b) appear both narrow and diffuse. c) all lie within Neptune’s Roche limit. d) often appear as clumpy ring arcs, rather than complete and symmetrical rings. e) All of these are correct. Beyond Neptune Pluto was discovered in 1930. 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. Copyright © 2010 Pearson Education, Inc. 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 two smaller moons, Nix and Hydra, discovered in 2005. Copyright © 2010 Pearson Education, Inc. Question 12 Many astronomers believe Pluto is perhaps best classified as Copyright © 2010 Pearson Education, Inc. a) a cold terrestrial planet. b) a small jovian planet. c) a large Kuiper belt object. d) a wandering moon. e) a captured comet. Question 12 Many astronomers believe Pluto is perhaps best classified as a) a cold terrestrial planet. b) a small jovian planet. c) a large Kuiper belt object. d) a wandering moon. e) a captured comet. Several other large Kuiper belt objects have been discovered, including the largest known, called Eris. Copyright © 2010 Pearson Education, Inc. Beyond Neptune Charon’s orbit is at a large angle to the plane of Pluto’s orbit. Copyright © 2010 Pearson Education, Inc. Astronomy for $100 What is a celestial body that (a) is in orbit around the Sun (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape (c) has cleared the neighborhood around its orbit Copyright © 2010 Pearson Education, Inc. What is a planet? Copyright © 2010 Pearson Education, Inc. Plutoids and the Kuiper Belt The first Kuiper belt objects were observed in the 1990s, and more than 700 are now known. Some of them are comparable in size to Pluto. These images show Eris and its moon Dysnomia. Copyright © 2010 Pearson Education, Inc. Plutoids and the Kuiper Belt This figure shows several of the largest known trans-Neptunian objects, now collectively called plutoids. Copyright © 2010 Pearson Education, Inc.