Chapter 8 - Astronomy: A Beginner's Guide to the Universe, 7th Edition

Astronomy: A Beginner's Guide to the Universe, 7e (Chaisson/McMillan) Chapter 8 Moons, Rings, and Plutoids: Small Worlds Among Giants 1) Two of the Galilean moons of Jupiter are the size of Mercury, and the two others are about as big as our own Moon. Answer: TRUE Diff: 1 Section Ref.: 8.1 2) Besides Mars, exobiologists find Europa also a good candidate for life. Answer: TRUE Diff: 1 Section Ref.: 8.1 3) The surface of Io looks most like the pack ice of the Arctic Ocean of Earth. Answer: FALSE Diff: 1 Section Ref.: 8.1 4) Io's internal heat is due to tidal interactions with Jupiter and Europa. Answer: TRUE Diff: 1 Section Ref.: 8.1 5) Like our Moon and most others, all four large Jovian satellites have one side constantly fixed toward Jupiter as they revolve and rotate. Answer: FALSE Diff: 1 Section Ref.: 8.1 6) Like Jupiter's other icy moons, Europa is covered with craters. Answer: FALSE Diff: 1 Section Ref.: 8.1 7) The Cassini probe Huygens made a soft landing on Titan. Answer: TRUE Diff: 1 Section Ref.: 8.1 8) All four of Jupiter's big moons, like most moons in the solar system, revolve clockwise (retrograde) around their planet's equator. Answer: FALSE Diff: 2 Section Ref.: 8.1 9) While Ganymede and Callisto are about the same size, the surface of Callisto is much younger, with considerable tectonic reformation. Answer: FALSE Diff: 2 Section Ref.: 8.1 10) Of all the Galilean satellites, the surface of Europa is the youngest in age. Answer: FALSE Diff: 2 Section Ref.: 8.1 11) Io's surface volcanism is driven by phase changes of sulfur and its compounds. Answer: FALSE Diff: 2 Section Ref.: 8.1 12) Due to tidal stresses, it is likely most of Io is molten, with a relatively thin solid crust. Answer: TRUE Diff: 2 Section Ref.: 8.1 13) The weak magnetic field of Europa may originate from a rapidly rotating liquid iron core. Answer: FALSE Diff: 2 Section Ref.: 8.1 14) Ganymede is the largest satellite in the solar system. Answer: TRUE Diff: 2 Section Ref.: 8.1 15) The processes which produced Ganymede's groove terrain are on-going, according to the latest Galileo images. Answer: FALSE Diff: 2 Section Ref.: 8.1 16) The large, dark mare on Ganymede were created by water that erupted from within the moon. Answer: TRUE Diff: 2 Section Ref.: 8.1 17) Alone of all the Galilean moons, Callisto shows no sign of plate tectonics. Answer: FALSE Diff: 2 Section Ref.: 8.1 18) It appears that while they are similar in size, Ganymede is much more differentiated than Callisto. Answer: TRUE Diff: 2 Section Ref.: 8.1 19) In terms of composition and density, the atmosphere of Titan is closer to our own than any other place we have found in the solar system. Answer: TRUE Diff: 1 Section Ref.: 8.2 20) Triton and Pluto both probably originated in the Kuiper Belt. Answer: TRUE Diff: 1 Section Ref.: 8.2 21) Because the probe came so close, Voyager 1 sent back high resolution photos of detail on the surface of Titan in 1980. Answer: FALSE Diff: 2 Section Ref.: 8.2 22) Titan's surface has been mapped using Earth based visual telescopes. Answer: FALSE Diff: 2 Section Ref.: 8.2 23) Methane drives the weather of Titan, for there it can be liquid, solid, or gas. Answer: TRUE Diff: 2 Section Ref.: 8.2 24) Like Titan, Triton has a nitrogen atmosphere. Answer: TRUE Diff: 2 Section Ref.: 8.2 25) The tectonic surface features we see on Triton are similar to the grooves of Ganymede. Answer: TRUE Diff: 2 Section Ref.: 8.2 26) Alone among all the large moons, Triton orbits Neptune retrograde, and also at a 20 degree inclination to Neptune's equator. Answer: TRUE Diff: 2 Section Ref.: 8.2 27) Spacecraft have imaged erupting volcanoes on Io and Triton. Answer: TRUE Diff: 2 Section Ref.: 8.2 28) The retrograde orbit of Triton dooms it to spiral inward toward Neptune, perhaps someday to make a ring system. Answer: TRUE Diff: 2 Section Ref.: 8.2 29) Cassini's probe Huygens returned images of what may have been a shoreline on Saturn. Answer: FALSE Diff: 2 Section Ref.: 8.3 30) The haphazard terrain of Miranda suggests it was broken up by impact after it had differentiated, then fell back together as a jumbled maze. Answer: TRUE Diff: 2 Section Ref.: 8.3 31) The surface of Saturn's moon Enceladus is the most reflective of any in the solar system, suggesting very fresh ice is exposed. Answer: TRUE Diff: 2 Section Ref.: 8.3 32) The rings of Uranus were discovered when it passed in front of a star, and the dark rings occulted the star several times for brief intervals. Answer: TRUE Diff: 1 Section Ref.: 8.4 33) Saturn's rings appear to be brighter and younger than the dirty, dark rings around Uranus and Neptune. Answer: TRUE Diff: 1 Section Ref.: 8.4 34) All four ring systems orbit the equators of Jovian planets outside their Roche limits. Answer: FALSE Diff: 2 Section Ref.: 8.4 35) Saturn's rings are thick, perhaps a few thousand kilometers. Answer: FALSE Diff: 2 Section Ref.: 8.4 36) At its equinoxes, Saturn's rings are most open and double the planet's brightness. Answer: FALSE Diff: 2 Section Ref.: 8.4 37) The F-ring is held in place around Saturn by two shepherd moons. Answer: TRUE Diff: 2 Section Ref.: 8.4 38) A resonance with Mimas clears out the ring particles from Cassini's Division. Answer: TRUE Diff: 2 Section Ref.: 8.4 39) Two sets of rings around Jovian planets were found by Earth-based observers, while two others were first imaged by the Voyagers. Answer: TRUE Diff: 2 Section Ref.: 8.4 40) Probably the next satellite to get turned into ring debris will be Neptune's backward moon, Triton. Answer: TRUE Diff: 2 Section Ref.: 8.4 41) Saturn's rings are extremely old, possibly older than four billion years. Answer: FALSE Diff: 2 Section Ref.: 8.4 42) The particles in Saturn's E ring probably come from volcanic eruptions on Enceladus. Answer: TRUE Diff: 3 Section Ref.: 8.4 43) Neptune has a single, broad ring that is extremely thin. Answer: FALSE Diff: 3 Section Ref.: 8.4 44) Like Saturn's more famous ring system, Jupiter's ring is also made of ice, just older and dirtier than the bright fresh material at Saturn. Answer: FALSE Diff: 3 Section Ref.: 8.4 45) Pluto is smaller than many moons in the solar system. Answer: TRUE Diff: 1 Section Ref.: 8.5 46) The initial prediction by Percival Lowell of Pluto's position was close to the place it was, in fact, found by Clyde Tombaugh in 1930. Answer: TRUE Diff: 2 Section Ref.: 8.5 47) Both Pluto and Charon are tidally locked to always keep the same faces toward each other, rotating and revolving around their common center of mass every 14.2 hours. Answer: FALSE Diff: 2 Section Ref.: 8.5 48) Pluto is probably one of the largest of the Kuiper Belt bodies beyond Neptune. Answer: TRUE Diff: 2 Section Ref.: 8.5 49) Based on our current knowledge of the motions of Uranus and Neptune, it is obvious that Pluto's discovery was a triumph of physics, on par with Adams and Leverrier's work in finding Neptune. Answer: FALSE Diff: 3 Section Ref.: 8.5 50) Pluto is visible to the naked eye on extremely dark nights. Answer: FALSE Diff: 2 Section Ref.: 8.5 51) Pluto is no longer classified as a planet. Answer: TRUE Diff: 1 Section Ref.: 8.5 52) Pluto has only a single moon, Charon. Answer: FALSE Diff: 1 Section Ref.: 8.5 53) Which element is critical to the formation of the volcanic surface of Io? A) iron B) silicon C) sulfur D) phosphorus E) carbon Answer: C Diff: 1 Section Ref.: 8.1 54) What is thought to be the cause of Io's volcanoes? A) Jupiter's magnetosphere and its charged particles B) energy emitted by Jupiter C) gravitational tidal stresses from both Jupiter and Europa D) solar radiation focused by Jupiter's gravity E) radioactive decay in Io's interior Answer: C Diff: 1 Section Ref.: 8.1 55) Which of the Galilean moons is densest and most geologically active? A) Io B) Europa C) Ganymede D) Callisto E) Titan Answer: A Diff: 1 Section Ref.: 8.1 56) Which are the four Galilean moons of Jupiter? A) Europa, Titan, Ganymede, and Callisto B) Io, Ganymede, Callisto, and Titan C) Europa, Ganymede, Io, and Triton D) Io, Europa, Ganymede, and Callisto E) Io, Titan, Triton, and Charon Answer: D Diff: 2 Section Ref.: 8.1 57) The surface of Europa is most like the Earth's A) tundra. B) deserts. C) Arctic Ocean. D) Himalayan peaks. E) South Pole. Answer: C Diff: 2 Section Ref.: 8.1 58) The weak magnetic fields around Europa and Ganymede were found during flybys of A) Voyager 1. B) Pioneer 10. C) Cassini. D) Galileo. E) Stardust. Answer: D Diff: 2 Section Ref.: 8.1 59) In size and density, both Io and Europa resemble A) Mercury. B) our Moon. C) Mars. D) Pluto. E) Charon. Answer: B Diff: 2 Section Ref.: 8.1 60) The mare on Ganymede were formed by A) basalt erupting onto the surface. B) plate tectonics. C) gravitational interactions with Callisto and Europa. D) water erupting and spreading over the surface. E) sulfur spewed from volcanoes. Answer: D Diff: 2 Section Ref.: 8.1 61) In terms of dark, smoother mare and cratered highlands, which Jovian moon most resembles the near side of our own? A) Io B) Europa C) Ganymede D) Triton E) Titan Answer: C Diff: 2 Section Ref.: 8.1 62) Of the Jovian satellites, which shows the oldest, most cratered surface? A) Enceladus B) Callisto C) Triton D) Ganymede E) Miranda Answer: B Diff: 2 Section Ref.: 8.1 63) The largest moon in the solar system, bigger but not as massive as Mercury, is A) Europa. B) Ganymede. C) Callisto. D) Titan. E) Triton. Answer: B Diff: 2 Section Ref.: 8.1 64) A moon with a smooth, uncratered surface would imply A) meteorites have never struck the moon. B) a strong magnetic field surrounds the moon. C) the surface is very young. D) the moon lies within the planet's Roche Limit. E) the surface is completely liquid. Answer: C Diff: 3 Section Ref.: 8.1 65) Which of these moons has the densest atmosphere? A) Io B) Europa C) Callisto D) Titan E) Triton Answer: D Diff: 1 Section Ref.: 8.2 66) Which of these moons are most interesting to exobiologists? A) Io and Enceladus B) Europa and Titan C) Titan and Triton D) Europa and Miranda E) Triton and Charon Answer: B Diff: 2 Section Ref.: 8.2 67) At Titan, the lakes are made mostly of liquid A) water. B) carbon dioxide. C) ethane. D) metallic hydrogen. E) nitrogen. Answer: C Diff: 2 Section Ref.: 8.2 68) The Huygens probe of the ESA made a successful landing on A) Mars. B) Europa. C) Saturn. D) Titan. E) Triton. Answer: D Diff: 2 Section Ref.: 8.2 69) The atmosphere of Titan is composed mostly of A) oxygen. B) methane. C) carbon dioxide. D) hydrogen. E) nitrogen. Answer: E Diff: 2 Section Ref.: 8.2 70) The grooves and ridges on Ganymede are thought to A) be due to crustal tectonics motion (plate tectonics) B) have formed within the last thousand years. C) have grown considerably larger since the Voyager spacecraft discovered them. D) be part of an ongoing volcanic process. E) be due to the moon's rapid rotation. Answer: A Diff: 3 Section Ref.: 8.2 71) What is true of Titan's atmosphere? A) It is similar to Earth's in composition and density. B) It is primarily hydrogen. C) It is oxygen rich. D) It was discovered by the Voyager 1 spacecraft. E) It has produced a runaway greenhouse effect. Answer: A Diff: 3 Section Ref.: 8.2 72) The erupting geysers of nitrogen gas on Triton A) can be viewed by the Hubble Space Telescope. B) are caused by a not yet determined internal energy source. C) produced the large liquid oceans. D) are increasing the moon's rotation rate. E) produced the frozen nitrogen surface. Answer: B Diff: 3 Section Ref.: 8.2 73) Voyager 1 was unable to image Titan's surface because A) of "smog" in Titan's atmosphere. B) of Titan's high reflectivity. C) the moon was in shadow during the mission. D) the cameras were damaged by Saturn's magnetic field. E) volcanic activity spewed sulfur clouds, obscuring the surface. Answer: A Diff: 3 Section Ref.: 8.2 74) The brightest and probably youngest surface of any moon of Saturn belongs to A) Titan. B) Tethys. C) Mimas. D) Enceladus. E) Iapetus. Answer: D Diff: 2 Section Ref.: 8.3 75) Which Jovian moon shows the most diverse terrain, suggesting a violent impact broke it into many pieces, some of which reformed it as a jumbled puzzle? A) Io B) Ganymede C) Enceladus D) Miranda E) Triton Answer: D Diff: 2 Section Ref.: 8.3 76) What statistic below has changed the most in the last decade? A) the masses of the Galilean moons B) the compositions of moons of Uranus C) the rotational period of the Jovian moons D) the densities of the larger moons E) the number of known Jovian moons Answer: E Diff: 2 Section Ref.: 8.3 77) Which moon of Saturn shows the largest impact crater, relative to its size? A) Titan B) Callisto C) Mimas D) Miranda E) Enceladus Answer: C Diff: 2 Section Ref.: 8.3 78) For a moon the same density as its planet, the Roche limit lies at ________ times the radius of its planet. A) 1.4 B) 2.5 C) 3.6 D) 5.2 E) 7 Answer: B Diff: 2 Section Ref.: 8.4 79) Why are the rings of Saturn so bright? A) They are made of frozen metallic hydrogen. B) They are made of glassy beads expelled by the volcanoes of Enceladus. C) They are made of metallic iron, never rusted by exposure to oxygen. D) Light reflected off of gigantic Titan reinforces the sunlight. E) They are made of young, fresh water ice. Answer: E Diff: 2 Section Ref.: 8.4 80) Which statement about Jupiter's rings is true? A) They are larger than Saturn's, but darker. B) They lie inside Jupiter's Roche Limit. C) They are made, in part, of material ejected by Europa's volcanoes. D) They are dark because their ices are dirtier than Saturn's. E) They were discovered by Galileo at the same time he discovered the moons. Answer: B Diff: 2 Section Ref.: 8.4 81) When Saturn is at Equinox, its rings will A) double the planet's brightness. B) lie in the plane of the ecliptic. C) contract closer to the planet's surface. D) appear face-on to the earth. E) lie perpendicular to the plane of the ecliptic. Answer: B Diff: 2 Section Ref.: 8.4 82) What best explains the darkness of the rings beyond Saturn's? A) The sunlight is much fainter out there. B) old, sooty debris and radiation darkening C) Water ice reflects light poorly at the low temperatures beyond Saturn. D) Rocky debris doesn't reflect as well as water ice. E) They are pieces of captured comets. Answer: B Diff: 2 Section Ref.: 8.4 83) The Cassini Division is a gap in Saturn's rings caused by A) Saturn's excess heat. B) two shepherding moons. C) Saturn's magnetic field. D) gravitational interaction with Mimas. E) the icy ring particles melting. Answer: D Diff: 2 Section Ref.: 8.4 84) Inside the Roche Limit A) large moons are torn apart. B) is where large moons form. C) ring systems cannot exist. D) there is a gap in a planet's magnetic field. E) hydrogen can only exist in its liquid metallic form. Answer: A Diff: 2 Section Ref.: 8.4 85) If Saturn takes about 30 years to orbit the Sun, and its rings were seen edge-on in 1995, when did they next appear most open at solstice? A) 1998 B) 2002 C) 2005 D) 2007 E) 2010 Answer: B Diff: 3 Section Ref.: 8.4 86) If Uranus takes 84 years to orbit the Sun, and Voyager 2 found its rings wide open at solstice in 1989, when will or did they next appear edge on, as seen from Earth? A) 1995 B) 2003 C) 2010 D) 2025 E) They can never appear edge on, due to Uranus' 98 degree axial tilt. Answer: C Diff: 3 Section Ref.: 8.4 87) Which was not a Voyager discovery about the rings of Saturn? A) They have dark spokes that defy gravity. B) They are made of tens of thousands of narrow ringlets. C) There are hundreds of smaller moons imbedded in them, creating the gaps. D) The F ring particles are herded by two shepherd moons. E) The E ring may have been made by volcanic eruptions from Enceladus. Answer: C Diff: 3 Section Ref.: 8.4 88) Which of the following rings of Saturn lies closest to the planet? A) the A ring B) the B ring C) the C ring D) the E ring E) the F ring Answer: C Diff: 3 Section Ref.: 8.4 89) Which moon orbits a body only twice as big as it is? A) Triton B) our Moon C) Charon D) Miranda E) Mimas Answer: C Diff: 2 Section Ref.: 8.5 90) Pluto's density is most similar to A) the terrestrial planets. B) the jovian planets. C) the moons of the jovian planets. D) Mercury, but not Venus, Earth, or Mars. E) Saturn, but not Jupiter, Uranus, or Neptune. Answer: C Diff: 2 Section Ref.: 8.5 91) Pluto was discovered in A) ancient times. B) 1789. C) 1859. D) 1930. E) 1992. Answer: D Diff: 2 Section Ref.: 8.5 92) The two names most associated with the discovery of Pluto are A) Adams and Leverrier. B) Herschel and Bode. C) Kuiper and Whipple. D) Lowell and Tombaugh. E) Shoemaker and Levy. Answer: D Diff: 2 Section Ref.: 8.5 93) Charon's orbit A) lies exactly in Pluto's orbital plane. B) is highly inclined to Pluto's orbital plane. C) is perpendicular to Pluto's equator. D) is retrograde. E) has not been determined yet. Answer: B Diff: 3 Section Ref.: 8.5 94) Pluto is most similar to A) Europa. B) Miranda. C) Triton. D) our Moon. E) Mercury. Answer: C Diff: 2 Section Ref.: 8.5 95) What is so unusual about Pluto's orbit? A) It lies exactly on the ecliptic. B) It has the lowest eccentricity of any planet's orbit. C) It is more inclined to the ecliptic than any of the eight planets. D) It has an unexpectedly short orbital period. E) Its orbital period is exactly twice that of Neptune's. Answer: C Diff: 2 Section Ref.: 8.5 96) Ganymede and Callisto have densities suggesting they are made of rocky cores and mantles of ________. Answer: water and/or ice Diff: 1 Section Ref.: 8.1 97) In general, the less cratered a moon's surface, the ________ it is. Answer: younger Diff: 1 Section Ref.: 8.1 98) To explain its magnetic field, Europa must have an ocean of ________. Answer: (salty) liquid water Diff: 2 Section Ref.: 8.1 99) As we go outward from Io to Ganymede, the density of the moons ________. Answer: decreases Diff: 2 Section Ref.: 8.1 100) The Galilean moon of most interest to exobiologists is ________. Answer: Europa Diff: 2 Section Ref.: 8.1 101) The element erupting from the volcanoes of Io is ________. Answer: sulfur Diff: 2 Section Ref.: 8.1 102) Europa is covered with an ocean of ________. Answer: liquid water (under ice). Diff: 2 Section Ref.: 8.1 103) A moon whose surface is smooth, with no craters, is probably ________. Answer: active. Diff: 2 Section Ref.: 8.1 104) Compared to the size of Mercury, Ganymede is ________. Answer: larger. Diff: 2 Section Ref.: 8.1 105) The tidal stresses that create Io's volcanism come from Jupiter and ________. Answer: Europa Diff: 3 Section Ref.: 8.1 106) The atmosphere of Titan is chiefly ________. Answer: nitrogen Diff: 1 Section Ref.: 8.2 107) The atmospheres of both Titan and Triton are mainly ________. Answer: nitrogen Diff: 1 Section Ref.: 8.2 108) The orbit of Triton is ________, very different from all other major moons. Answer: retrograde (or clockwise) Diff: 1 Section Ref.: 8.2 109) The lakes of Titan consist of liquid ________. Answer: ethane, methane, or just hydrocarbons Diff: 2 Section Ref.: 8.2 110) On Neptune's moon ________, geysers of liquid nitrogen rise 10 km high. Answer: Triton Diff: 2 Section Ref.: 8.2 111) The only Jovian moon to orbit its planet retrograde and out of the equatorial plane is ________. Answer: Triton Diff: 2 Section Ref.: 8.2 112) The Saturnian moon of most interest to exobiologists is ________. Answer: Titan Diff: 2 Section Ref.: 8.2 113) The next moon likely to be broken up into a ring is ________. Answer: Triton Diff: 3 Section Ref.: 8.2 114) The cantaloupe skin terrain of Triton is thought to be due to ________. Answer: faulting and deformation, or tectonic activity. Diff: 3 Section Ref.: 8.2 115) One hemisphere of Enceladus may have the youngest surface of any of the jovian moons, with volcanoes spewing "ash" and "lava flows" of ________. Answer: Water Diff: 2 Section Ref.: 8.3 116) The moon ________ may have erupted to create the E rings around Saturn. Answer: Enceladus Diff: 3 Section Ref.: 8.3 117) All four ring systems lie around their planet's ________. Answer: equators Diff: 1 Section Ref.: 8.4 118) All four rings systems lie within their planet's ________. Answer: Roche Limit Diff: 2 Section Ref.: 8.4 119) The striking gap between Saturn's A and B rings is called the ________. Answer: Cassini Division Diff: 2 Section Ref.: 8.4 120) The planet with the least obvious ring system is ________. Answer: Neptune Diff: 2 Section Ref.: 8.4 121) The dusty ring around Jupiter was discovered in 1979 by ________. Answer: Voyager 1 Diff: 2 Section Ref.: 8.4 122) The F Ring around Saturn is maintained by ________. Answer: two shepherd moons Diff: 3 Section Ref.: 8.4 123) Pluto was named after the Roman god of the dark underworld, and also for ________. Answer: Percival Lowell Diff: 2 Section Ref.: 8.5 124) Pluto was discovered in 1930 by ________. Answer: Clyde Tombaugh Diff: 2 Section Ref.: 8.5 125) It is likely that both Pluto and Triton were originally ________. Answer: Kuiper Belt Objects or KBOs Diff: 2 Section Ref.: 8.5 126) It takes the Pluto-Charon system ________ to rotate around its common center of mass. Answer: 6.4 days Diff: 3 Section Ref.: 8.5 127) Discovered in the 1990s, the ________ is a vaster, darker version of the more famed asteroid belt between Mars and Jupiter. Answer: Kuiper Belt Diff: 1 Section Ref.: 8.5 128) Most astronomers now regard Pluto as the largest ________, and not a planet. Answer: Kuiper Belt Object, or KBO Diff: 2 Section Ref.: 8.5 129) How are the large amounts of heating at Io generated? Answer: Io's elliptical orbit causes variations in the gravitation pull of Jupiter and Europe. The changing force of gravity causes tidal stressing on Io's interior by Jupiter and Europa, heating the moon. Diff: 2 Section Ref.: 8.1 130) Contrast the volcanism of Io and Triton. Answer: Both are driven by tidal flexing, but at Io, it is sulfur erupting, while Triton is much colder, with liquid nitrogen geysers. Diff: 2 Section Ref.: 8.2 131) In what two ways is the orbit of Triton unusual? Answer: It is 20 degrees off the equator of Neptune, and revolves clockwise or in retrograde motion, the only big moon to behave this way. Diff: 3 Section Ref.: 8.2 132) What is the smallest of the Galilean moons? Why is it then the brightest? Answer: Europa has a very young, bright ice crust that reflects light well. Diff: 3 Section Ref.: 8.2 133) What is the likely origin of Triton? Why do we believe this? Answer: It is probably a captured KBO. It orbits Neptune backwards (or retrograde), and well off from the planet's equator. Diff: 3 Section Ref.: 8.2 134) What is the future of Triton? Answer: In retrograde orbit, it will spiral inside Neptune's Roche Limit, to be broken up into a new, spectacular ring around the blue world. Diff: 3 Section Ref.: 8.2 135) Describe the Cassini mission to Saturn in 2004-5. Answer: The orbiter went into orbit about Saturn, to keep track of the weather on Saturn and survey the moons with higher resolution than the Voyagers could. It did the same kind of survey that Galileo did at Jupiter. But the Huygens lander touched down on the moon Titan, instead of going to Saturn itself. Diff: 3 Section Ref.: 8.2 136) In what way could the Huygens probe be considered a first? Answer: It made the first successful soft landing on a moon other than Earth's. Diff: 3 Section Ref.: 8.2 137) The lakes on Titan have not been observed to have any waves. What does this suggest? Answer: This suggests the presence of viscous, tar-like hydrocarbons. Diff: 3 Section Ref.: 8.2 138) Which moon of Saturn has the surface with the widest range of ages? Why? Answer: Enceladus has one ancient hemisphere, very cratered, but the other has been reworked with tectonic ridges and possibly volcanism as well. As with the mare on our own Moon, tidal forces act differentially on the two hemispheres. Diff: 2 Section Ref.: 8.3 139) What makes the surface of Mimas so striking? Answer: The huge crater Herschel is a third as large as the moon. Diff: 3 Section Ref.: 8.3 140) Which four moons are believed to have large bodies of liquid water? Answer: Titan, Europa, Ganymede, and Enceladus. Diff: 3 Section Ref.: 8.2, 8.3 141) How were the rings of Uranus discovered? Answer: In 1977, they passed in front of a star, and the star blinked off as its light was occulted by the dark rings. Diff: 2 Section Ref.: 8.4 142) What do all four ring systems have in common? Answer: They are made of small debris orbiting in the equatorial place of Jovian planets, and within their Roche Limit. Diff: 2 Section Ref.: 8.4 143) What is the relationship between Mimas and Saturn's rings? Answer: The tidal resonance of Mimas causes ice to be cleared out from the Cassini Division. Diff: 2 Section Ref.: 8.4 144) Define shepherd moons and give an example of them at work. Answer: The two small moons on each side of Saturn's F ring herd the particles into this narrow, twisted ring. Diff: 2 Section Ref.: 8.4 145) Define the Roche Limit. Answer: It is a region where the tidal stresses of a planet's gravity would break apart any major moon that tried to orbit that close; it lies about 2.5 planetary radii out. Diff: 2 Section Ref.: 8.4 146) The volcanic activity of Enceladus has what effect outside the moon itself? Answer: It is believed to have created the E ring of Saturn, which shares the same orbit as this moon. Diff: 3 Section Ref.: 8.4 147) What would happen to a large moon inside the Roche Limit? Answer: Tidal forces would pull and tug the moon out of shape until it was torn apart. The pieces would eventually form a ring around the planet. Diff: 3 Section Ref.: 8.4 148) Describe the odd rotations of Pluto and Charon. Answer: They are tidally fixed to keep the same faces toward each other during their 6.4-day periods of rotation. Diff: 2 Section Ref.: 8.5 149) What is the closest thing to a binary planet we find in the solar system? Why? Answer: Pluto's moon Charon is half as big as Pluto, and both objects are tidally fixed to always face each other during their 6.4 day rotations. Diff: 2 Section Ref.: 8.5 150) What role did Percival Lowell play that led to the discovery and naming of Pluto? Answer: He predicted the existence of "Planet X" and its position, and began the search for it at his observatory before his death. When Clyde Tombaugh found it while continuing the search at Lowell Observatory, Pluto was close to the position Lowell had expected, but this turned out to be just luck. Diff: 3 Section Ref.: 8.5 151) Contrast the densities and compositions of the four Galilean moons. Answer: Closer to Jupiter and dried out by its tides and radiation, Io and Europa are about as dense as our own Moon and made chiefly of rock. But larger Ganymede and Callisto are less stressed, less dense, and have extensive mantles of water and ice above their rock cores. Diff: 2 Section Ref.: 8.1 152) How does counting craters help us estimate the age of a moon's surface? Answer: Surface bombardment was much heavier early in the solar system's history. A surface with few craters implies many, or all, of the early craters were covered up by lava flows or other activity. The fewer the craters and the smoother the surface, the younger we assume it to be. The smoothest surfaces are the youngest. Diff: 3 Section Ref.: 8.1, 8.3 153) Why does the surface of Triton appear so young? Answer: When this KBO was trapped into orbit around Neptune recently, the tidal stresses of the retrograde capture orbit heated the interior, leading to the tectonic cantaloupe skin terrain and the liquid nitrogen geysers that covered almost all the craters. Diff: 2 Section Ref.: 8.2 154) Why did Saturn's rings appear very different in 1995 and 2003? Answer: At equinox in 1995, the thin rings almost disappeared as seen from Earth. By solstice in 2003, the rings were tilted 27 degrees toward the Sun and more than doubled the planet's brightness. Diff: 2 Section Ref.: 8.4 155) Name three ways that Saturn's ring system is unique. Answer: It contains a lot more debris than all the other systems, it is made of young, bright shiny ice, it shows spoke patterns driven by the magnetic fields, and at solstice it is so bright it doubles the brightness of the planet. Diff: 2 Section Ref.: 8.4 156) Using Jupiter's axial tilt, explain why its rings are harder to observe from Earth than even the dark rings of Uranus. Answer: Like Saturn, the rings of Uranus can appear at a variety of tilts. But Jupiter has only a 5 degree axial tilt, so its rings are seen almost edge-on all the time. Diff: 3 Section Ref.: 8.4 157) How would most planetary scientists classify Pluto? Why was this not done when it was found in 1930, misleading generations of elementary school children? Answer: It is the largest of the Kuiper Belt Objects, certainly neither a Jovian nor a terrestrial planet. It is comparable to Neptune's moon Triton, which is also a captured KBO as well. We did not know about the Kuiper Belt until its discovery in 1992. Other similar Kuiper Belt Objects are now known as Plutoids. Diff: 2 Section Ref.: 8.5 158) Why were the mass and density of Pluto unknown until Charon was found? Answer: Pluto is so distant that its disk was not resolved well, and it had no discernable gravitational influence on Uranus and Neptune (Lowell's prediction was just luck). But Charon's orbit let us find the mass of both objects, and the series of eclipses allowed us to calculate the sizes of both bodies with great accuracy. Diff: 3 Section Ref.: 8.5 159) How did discovering the KBOs demote Pluto's planetary status? Answer: If Pluto were to be considered a major planet, then many Kuiper Belt Objects are almost as big as Pluto, also orbit the Sun, some of them have moons also, and most are in more circular orbits closer to the ecliptic, behaving more like planets than Pluto does. Should they not also have been counted as planets as well? Diff: 2 Section Ref.: 8.5 160) Based on its orbit, give two reasons to revoke Pluto's planetary status. Answer: It does not orbit in the ecliptic, but off by 17 degrees. It also has a more eccentric orbit than even Mercury or Mars, and cut inside of the orbit of Neptune between 1979 and 1999 at perihelion. Diff: 1 Section Ref.: 8.5 1 Copyright © 2013 Education, Inc.