Mr. Smith Earth Space Blizzard Bag Number Two. Accompanying notes and lesson plan included.

Transcription

1 Mr. Smith Earth Space Blizzard Bag Number Two. Accompanying notes and lesson plan included.

2 Academic/Career & Technical Related/Demonstration Lesson Plan Name: Stephen Smith Title: Blizzard Bag Number Two Earth Space Scope/Sequence: Second of Three covering unit on the outer planets State Indicator/Competency: History of the Universe Comparative Planetology Solar Systems and Their Origins Instructional Objective(s): At the end of this lesson the student will be able to list the four main chemical constituents found in the Jupiter-Like planets atmospheres with 100% accuracy At the end of this lesson the student will be able to state the number of moons Jupiter has with 100% accuracy At the end of this lesson the student will be able to name the four Galilean moons with 100% accuracy At the end of this lesson the student will be able to state the internal heating mechanism of Io with 100% accuracy At the end of this lesson the student will be able to state the significance of Europa with 100% accuracy At the end of this lesson the student will be able to name the largest moon in the solar system with 100% accuracy At the end of this lesson the student will be able to name the most heavily cratered moon in solar system with 100% accuracy At the end of this lesson the student will be able to composition of Saturn s rings with 100% accuracy At the end of this lesson the student will be able to state the mass, distance from sun, density of Saturn, albedo with 100% accuracy At the end of this lesson the student will be able to list the named moons of Saturn with 100% accuracy At the end of this lesson the student will be able to state the total number of moons of Saturn with 100% accuracy At the end of this lesson the student will be able to state the significance of the moon Titan with 100% accuracy At the end of this lesson the student will be able to state the significance of the moon Enceladus with 100% accuracy Materials: Blizzard Bag One Handout Vocabulary and Notes Handout Method of Instruction: Homework Activities: Students will complete worksheet at home including vocabulary, guided notes, and guided reading. Assessment: This assignment is worth 10 pts.

3 Name: Points: /10 Earth Space Science Blizzard Bag Assignment 2 Chapter 10 The Jupiter Like Planets Lesson Three and Four Jupiter s Moons and Saturn Date Due: Lesson Objectives state the number of moons Jupiter has name the four Galilean moons state the internal heating mechanism of Io state the significance of Europa name the largest moon in the solar system name the most heavily cratered moon in solar system composition of Saturn s rings state the mass, distance from sun, density of Saturn, albedo list the named moons of Saturn state the total number of moons of Saturn state the significance of the moon Titan state the significance of the moon Enceladus Vocabulary: use glossary gossamer rings - forward scattering - Guided Notes: Jupiter s Moons Io

4 Europa Ganymede Callisto Saturn Fast Facts:

5 Planetology of Saturn Differentiated Interior Rings of Saturn Saturn s Moons Associated Text: Jupiter's Family of Satellites Jupiter has well over a dozen moons, but most are small, only a few tens of kilometers in diameter, and some of these have retrograde (backward) orbits. This evidence suggests that many of Jupiter's smaller moons are captured asteroids. In contrast, the four largest moons are called Galilean moons (Figure 18-7) after their discoverer, Galileo. These four moons are clearly related to each other and probably formed with Jupiter. We know these worlds surprisingly well because the two Voyager spacecraft and the Galileo spacecraft have studied them in detail. The outermost Galilean moon, Callisto, is half again as big as Earth's moon, but it has a low density of only 1.79 g/cm3. This means it must consist roughly of 50:50 rock and ice. Observations of its gravitational field by the Galileo spacecraft reveal that it does have a dense core and a lower-density exterior, so it presumably differentiated. Also, it interacts with Jupiter's magnetic field in such a way that astronomers suspect it has a mineral-rich ocean of liquid water 100 km below its icy crust. Photos of its surface, however, show thousands of impact craters with little sign of geological activity (Figure 18-8). Next inward from Callisto is Ganymede, with a density of 1.9 g/cm3, suggestive of a mix of rock and ice. The Galileo spacecraft has detected a weak magnetic field, which suggests a differentiated metallic core. The icy crust is marked by old, cratered, dark areas, and younger, brighter regions of grooved terrain believed to be

6 systems of faults in the brittle crust (Figure 18-9a). Sets of groves overlap other sets of grooves, and that suggests extended episodes of geological activity (Figure 18-9b). The density of the next moon inward, Europa, is 3,03 g/cm 3, high enough to suggest the moon is mostly rock with a thin icy crust. The visible surface is very clean ice, contains very few craters, and has long scars suggestive of cracks in the icy crust (Figure 18-10). Evidently the icy crust we see overlays an ocean of liquid water or watery slush. The surface is estimated to be only about 10 million years old-very young for a geological surface. Thus Europa is apparently still an active world. lo, the innermost of the four moons, is also the most active. Its density of 3.55 g/cm3, combined with gravity measurements by the Galileo spacecraft, shows that it has a large metallic core and a rocky, sulfur-rich crust. Spectra show no trace of water. Spacecraft photos reveal active volcanoes venting gases and sulfur rich ash high above the surface (Figure 18-11). A new crater on lo would be buried under the sulfur ash at the rate of a few millimeters per year. That burying explains why photos show no impact craters on lo. The activity we see in the Galilean moons must be driven by energy flowing outward. The violently active volcanism of lo is apparently caused by tidal heating. lo is too small to have remained hot from its formation, but its orbit is slightly elliptical; and as it moves closer to and then farther from Jupiter, the planetary gravitational field flexes the moon with tides, and friction heats its interior. That heat flowing outward causes the volcanism. Europa is not as active as lo, but it too must have a heat source, presumably tidal heating. Ganymede is no longer active, but when it was younger, it had internal heat that broke the crust to produce the grooved terrain. Callisto, the most distant of the four moons, appears never to have been geologically active. Tidal heating has probably affected the Galilean moons, but we must also suspect they formed together in a disk-shaped nebula around the proto-jupiter. Heat from Jupiter would have heated the inner part of that disk, and the outer parts would have remained colder. Thus, we can understand the densities and compositions of the four Galilean moons by the condensation sequence (Chapter 16) acting in a miniature solar nebula around Jupiter. Jupiter's Family of Satellites Jupiter has well over a dozen moons, but most are small, only a few tens of kilometers in diameter, and some of these have retrograde (backward) orbits. This evidence suggests that many of Jupiter's smaller moons are captured asteroids. In contrast, the four largest moons are called Galilean moons (Figure 18-7) after their discoverer, Galileo. These four moons are clearly related to each other and probably formed with Jupiter. We know these worlds surprisingly well because the two Voyager spacecraft and the Galileo spacecraft have studied them in detail. The outermost Galilean moon, Callisto, is half again as big as Earth's moon, but it has a low density of only 1.79 g/cm3. This means it must consist roughly of 50:50 rock and ice. Observations of its gravitational field by the Galileo spacecraft reveal that it does have a dense core and a lower-density exterior, so it presumably differentiated. Also, it interacts with Jupiter's magnetic field in such a way that astronomers suspect it has a mineral-rich ocean of liquid water 100 km below its icy crust. Photos of its surface, however, show thousands of impact craters with little sign of geological activity (Figure 18-8). Next inward from Callisto is Ganymede, with a density of 1.9 g/cm3, suggestive of a mix of rock and ice. The Galileo spacecraft has detected a weak magnetic field, which suggests a differentiated metallic core. The icy crust is marked by old, cratered, dark areas, and younger, brighter regions of grooved terrain believed to be systems of faults in the brittle crust (Figure 18-9a). Sets of groves overlap other sets of grooves, and that suggests extended episodes of geological activity (Figure 18-9b). The density of the next moon inward, Europa, is 3,03 g/cm3, high enough to suggest the moon is mostly rock with a thin icy crust. The visible surface is very clean ice, contains very few craters, and has long scars suggestive of cracks in the icy crust (Figure 18-10). Evidently the icy crust we see overlays an ocean of liquid water or watery slush. The surface is estimated to be only about 10 million years old-very young for a geological surface. Thus Europa is apparently still an active world.

7 lo, the innermost of the four moons, is also the most active. Its density of 3.55 g/cm3, combined with gravity measurements by the Galileo spacecraft, shows that it has a large metallic core and a rocky, sulfur-rich crust. Spectra show no trace of water. Spacecraft photos reveal active volcanoes venting gases and sulfur rich ash high above the surface (Figure 18-11). A new crater on lo would be buried under the sulfur ash at the rate of a few millimeters per year. That burying explains why photos show no impact craters on lo. The activity we see in the Galilean moons must be driven by energy flowing outward. The violently active volcanism of lo is apparently caused by tidal heating. lo is too small to have remained hot from its formation, but its orbit is slightly elliptical; and as it moves closer to and then farther from Jupiter, the planetary gravitational field flexes the moon with tides, and friction heats its interior. That heat flowing outward causes the volcanism. Europa is not as active as lo, but it too must have a heat source, presumably tidal heating. Ganymede is no longer active, but when it was younger, it had internal heat that broke the crust to produce the grooved terrain. Callisto, the most distant of the four moons, appears never to have been geologically active. Tidal heating has probably affected the Galilean moons, but we must also suspect they formed together in a disk-shaped nebula around the proto-jupiter. Heat from Jupiter would have heated the inner part of that disk, and the outer parts would have remained colder. Thus, we can understand the densities and compositions of the four Galilean moons by the condensation sequence (Chapter 16) acting in a miniature solar nebula around Jupiter. A History of Jupiter Can we put all of the evidence together and tell the story of Jupiter? Creating such a logical argument of evidence and hypotheses is the ultimate goal of planetary astronomy. Jupiter formed far enough from the sun to incorporate large numbers of icy planetesimals, and it must have grown rapidly. Once it was a dozen times more massive than Earth, it could grow by gravitational collapse (Chapter 16), the capture of gas directly from the solar nebula. Thus, it grew rich in hydrogen and helium from the solar nebula. Its present composition is quite sunlike and resembles the composition of the solar nebula. The location of Jupiter's point in Figure shows that its gravity is strong enough to hold on to all of its gases. The large family of moons may be mostly captured asteroids, and Jupiter may still encounter a wandering asteroid or comet now and then. Some of these are deflected, some captured into orbit, and some, like the comet that struck Jupiter in 1994, actually fall into the planet. Dust blasted off of the inner moons by micrometeorites settles into the equatorial plane to form Jupiter's rings. The four Galilean moons seem to have formed in a disk of gas and dust around the forming planet. They have different compositions much like planets in our solar system, but they have also been affected to different degrees by tidal heating. REVIEW Critical Inquiry Why is Jupiter so big? We can analyze this question by constructing a logical argument that relates the formation of Jupiter to the solar nebula theory. Jupiter is rich in hydrogen and helium, but Earth is relatively poor in these elements. While the solar nebula existed, Earth grew by the accretion of solid, rocky planetesimals, but it never became massive enough to capture gas directly from the solar nebula. That is, it never grew by gravitational collapse. Jupiter, however, grew so rapidly from icy planetesimals in the outer solar nebula that it was eventually able to grow by gravitational collapse. By the time the solar nebula cleared away and ended planet building, Jupiter had captured large amounts of hydrogen and helium and was quite massive. Often the present nature of a world can be traced back to the way it formed. Can you create a logical argument to explain the nature of the Galilean moons? We have studied Jupiter in detail because it is the basis of comparison for the other Jovian worlds. Now we can turn our attention to the most beautiful Jovian world, Saturn.

8 18-2 Saturn Saturn has played second fiddle to its own rings since Galileo first viewed it through a telescope in The rings are dramatic, strikingly beautiful, and easily seen through even a small telescope; but Saturn itself, only slightly smaller than Jupiter (Data File Eight), is a fascinating planet. Although Saturn lies roughly 10 AU from the sun, we know a surprising amount about it. The beautiful rings are easily visible through the telescopes of modern amateur astronomers, and large Earth-based telescopes have explored the planet's atmosphere, rings, and moons. The two Voyager spacecraft flew past Saturn in 1979, transmitting back to Earth detailed measurements and images, and the Cassini spacecraft now on its way to Saturn will arrive in 2004 (Window on Science 18-2). That mission will tell us even more about the Saturn system. Saturn the Planet Seen from Earth, Saturn shows only faint evidence of belt-zone circulation, but Voyager and Hubble Space Telescope photos show that belts and zones are present and that the associated winds blow up to three times faster than on Jupiter. The belts and zones on Saturn are less visible because they occur deeper in the cold atmosphere below a layer of methane haze. Saturn is less dense than water (it would float), and that suggests that it is, like Jupiter, rich in hydrogen and helium. In fact, its density is so low that it must have a relatively small core of heavy elements. The shape of a Jovian planet can tell us about the interior. All of the Jovian planets, being mostly liquid and rotating rapidly, are slightly flattened. A planet's oblateness is the fraction by which its equatorial diameter exceeds its polar diameter. As photographs show, Saturn is the most oblate of the planets, and that evidence tells us that it is mostly liquid. A world with a large rocky core and mantle would not be flattened much by rotation, but an all-liquid planet would flatten significantly. Thus the oblateness of a Jovian planet, combined with its average density, can help astronomers model the interior. Models of Saturn predict that it must have a small core of heavy elements and less liquid metallic hydrogen than Jupiter because Saturn's internal pressure is lower. Perhaps this is why Saturn's magnetic field is 20 times weaker than Jupiter's. Like Jupiter, Saturn has a hot interior and radiates more energy than it receives from the sun (Figure 18-13). Saturn may look a bit bland, but it makes up for that in the splendor of its rings. The Rings of Saturn Saturn's rings contain billions of icy particles ranging from specks of dust to rare chunks the size of houses. These particles are confined in a thin layer perhaps only meters thick in the equatorial plane of the planet. A few gaps, such as Cassini's division, are visible from Earth (Figure 18-13), but the true complexity of the rings was not evident until the Voyager 1 spacecraft flew past Saturn in The Voyager images showed that the rings were made up of over a thousand narrow ringlets, some as narrow as 2 km. There were even ringlets in Cassini's division. From Earth, astronomers had identified three main rings, A, B, and C, and had hints of a few other ring features. The Voyager images revealed a dusty E ring extending far from the planet and a threadlike F ring lying just outside the bright A ring (Figure 1814). This F ring is confined in a narrow strand by two small moons that orbit just inside and just outside the ring. As a particle drifts away from the F ring, the moons shepherd it back into the ring, and thus the moons are known as shepherd satellites. A similar G ring and the sharp outer edge of the A ring are believed to be confined by shepherd satellites. Some gaps in the rings seem to be caused by resonances with satellites. A particle in Cassini's division, for example, orbits Saturn twice in the time the moon Mimas takes to orbit once. Thus, on every other orbit, the ring particle overtakes Mimas at the same place in the particle's orbit, and the gravitational tugs of Mimas gradually pull the particle into a slightly elliptical orbit. Such an orbit is dangerous because the particle crosses

9 the paths of millions of other particles. Our unfortunate particle is almost certain to suffer a collision and have its orbit altered dramatically. Thus, particles cannot remain in orbit at a resonance with a moon, and gaps in the rings mark such spots. But not all gaps are caused by resonances. Encke's division in the A ring is caused by a small satellite that keeps the gap clear of particles, and the hundreds of other ringlets cannot all be produced by resonances. Small moons in the rings and waves, such as spiral density waves, moving through the rings are believed to explain many of the gaps. Saturn's icy rings can't be debris left over from the formation of the planet. The planet would have formed hot and would have vaporized ices and driven away the gas. Also, micrometeorites would tend to darken the icy particles over periods of 100 million years. These facts suggest that the material in Saturn's rings is debris from collisions between the heads of cornets and icy moons. Such collisions must occur every few tens of millions of years and occasionally supply the rings with fresh ice. Saturn's moons certainly show signs of impacts. The Moons of Saturn Saturn has almost two dozen moons, many of which are small and all of which contain mixtures of ice and rock. We know these moons because the Voyager spacecraft flew past Saturn; another spacecraft, Cassini, will orbit Saturn in 2004 and study the moons as well as the planet and its rings. The largest of Saturn's moons, Titan (Figure 1815), is a few percent larger than the planet Mercury. Its density suggests that it must contain a rocky core under a thick mantle of ice, but its surface is not visible through its cloudy atmosphere. We might not expect such a small world to have an atmosphere, but Titan is so cold its gas molecules do not travel fast enough to escape (see Figure 17-20). The gas is about 90 percent nitrogen with nearly 10 percent argon and a small amount of methane. Sunlight acting on the methane and nitrogen produces the thick orange smog of organic molecules. Organic molecules are common in living things on Earth but do not have to be derived from living things. One chemist defines an organic molecule as "any molecule with a carbon backbone." The organic smog particles produced in Titan's atmosphere drift down and collect in an organic goo on the moon's surface. Organic goo on the surface of Titan sounds exciting because it could harbor primitive life, but the surface of Titan is very cold at -179 C (-290 F). Also, models of the atmosphere suggest that the surface may be partly covered by oceans of liquid methane and ethane. Oddly, Titan is cooled by an inverse greenhouse effect as the organic haze blocks much of the incoming sunlight but allows infrared radiation to escape to space. Clearly, Titan is a peculiar world. In 2004, the Cassini spacecraft will drop an instrumented probe into the atmosphere of Titan before the spacecraft goes into orbit around Saturn. Cassini's cameras are sensitive at a number of different wavelengths and will be able to image the surface of Titan through the smog. We will soon know much more about this mysterious world. The remaining moons of Saturn are small, icy, have no atmospheres, and are heavily cratered. Most have ancient surfaces. Tethys, for example, is less than a third the diameter of Earth's moon, and its heavily cratered crust seems quite old (Figure 18-16a). A valley 3 km deep trails three-fourths of the way around the satellite. Such cracks are found on a few other satellites and appear to have formed long ago, when the interiors of the icy moons froze and expanded. The moon Enceladus, a bit smaller than Tethys, nevertheless shows signs of recent activity (Figure 1816c). Some parts of its surface contain 1000 times fewer craters than other regions, showing that these lightly cratered regions must be younger. At some point in its history, this moon had internal heat that produced geological activity and resurfaced some areas of its crust. The energy source is unknown, but tidal heating is likely. Like nearly all moons in the solar system, Saturn's moons are tidally locked to their planet, rotating to keep

10 the same side facing the planet. The leading side of these moons, the side facing forward in the orbit, is sometimes modified by debris. Iapetus, for example, has a cratered trailing side about as dark as dingy snow, but its leading side is as dark as fresh asphalt (Figure 18-16b). One hypothesis is that the dark material is carbon-rich dust from meteorite impacts on the next moon out, Phoebe. The History of Saturn Can we put all of the evidence and hypotheses together and describe the history of Saturn? Doing so is a real test of our understanding. Saturn formed in the outer solar nebula, where ice particles were stable and may have contained more trapped gases. The protoplanet grew rapidly and became massive enough to attract hydrogen and helium by gravitational collapse. The heavier elements sank to the middle to form a small core, and the hydrogen formed a liquid mantle containing liquid metallic hydrogen. The outward flow of heat from the interior is believed to drive convection inside the planet that produces its magnetic field. Because Saturn is smaller than Jupiter, the internal pressure is less, the planet contains less liquid metallic hydrogen, and its magnetic field is weaker. The rings can't be primordial. That is, they can't be material left over from the formation of the planet. Such ices would have been vaporized and driven away by the heat of the protoplanet. Rather, we can suppose that the ring material is debris from occasional collisions between comets and Saturn's icy moons. Such giant impacts are not unheard of in the solar system. Jupiter was hit by a comet in Some of Saturn's moons are probably captured asteroids that wandered too close, but some of the moons probably formed with Saturn. Many have ancient surfaces. The giant moon Titan may have formed with Saturn, or it may be a very large icy planetesimal captured into orbit around Saturn. We will see more evidence for this capture hypothesis when we explore farther from the sun. Guided Reading Questions: Jupiter s Family of Satellites 1. How many moons does Jupiter have? 2. What evidence suggests some of Jupiter s smaller moons are actually captured asteroids? 3. When did the Galilean moons probably form? 4. (10 pts.) Galilean moon data table Name Position Density Size (km) Evidence of water/ice Magnetic Field Surface Features 5. What is tidal heating? A History of Jupiter 6. Give a brief summary of why Jupiter is so big. (6 pts)

11 18.2 Saturn 7. Compared to the Earth, how far is Saturn away from the Sun? 8. How long is a year on Saturn? 9. What is Saturn s average density? Would Saturn float in water? 10. What is Saturn s albedo? How does that compare to Earth s? 11. What is a planet s oblateness? How does this help scientists to determine the likely composition of a planet? The Rings of Saturn 12. What are the rings of Saturn made of? 13. What is a shepherd satellite? 14. What explanation does the text give for the hypothesis that Saturn s rings are not left over material from the formation of Saturn. The Moons of Saturn 15. About how many moons does Saturn have? 16. Which is the largest of Saturn s moons? 17. What does Saturn s largest moon s density suggest? 18. What is the basic chemical makeup of Titan s atmosphere? 19. How can such a small body as Titan hold a substantial atmosphere? 20. What is an organic molecule? Are organic molecules always produced by living things? 21. What is the surface temperature of Titan? 22. What are the two other moons of Saturn named in the text?

12 Earth Space Science Blizzard Bag Notes Day Two Jupiter s Moons Jupiter has over 60 moons four largest moons are called the Galilean satellites named after Italian astronomer Galileo Galilei in 1610 Io innermost rocky interior tidal heating active sulfur volcanoes most active body in solar system slightly larger than Earth s moon Europa outer layers of water ice tidal heating interior may be liquid thin atmosphere slightly smaller than Earth s moon Ganymede 50% larger than Earth s Moon largest moon in solar system 3 layers iron core rocky mantle rock/ice crust Callisto most heavily cratered object in solar system large 38% larger than Earth s moon geologically dead mostly ice Saturn Fast Facts: Distance from Sun : 9.5 AU Diameter: 9.4 Ed Mass: 95 Em Surface Gravity: 1.16 Eg Albedo:.61 Length of Day: 10 h 40 m Length of Year: 29.4 y Density:.69 g/cm 3 6 th planet from sun most oblate* planet

13 Planetology Differentiated Interior small rocky core relatively small metallic hydrogen layer low overall density relatively weak magnetic field 20x weaker than Jupiter s Rings of Saturn made of billions of particles of water ice size varies from small as dust to large as a house 1 km thick extend 175,000 miles above equator broken up moons or asteroids Saturn s Moons 62 total Titan is the largest Enceladus has active volcanoes and lots of water ice