Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Eight Worlds wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Sample-return mission wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Definition of planet wikipedia , lookup
Planets in astrology wikipedia , lookup
Exploration of Io wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Name CHAPTER 28 Class Date Minor Bodies of the Solar System SECTION 3 Satellites of Other Planets KEY IDEAS As you read this section, keep these questions in mind: • How are the two moons of Mars similar, and how are they different? • How did scientists discover volcanoes on Io? • What is one special characteristic of each of the Galilean moons? • How do the rings of Saturn differ from the rings of the other outer planets? What Are the Characteristics of Mars’s Moons? Mars has two tiny moons named Phobos and Deimos. They revolve around Mars relatively quickly. Unlike most other moons, Phobos and Deimos are not spherical. Instead, they are chunks of rock with irregular shapes. Scientists think these moons are actually asteroids that were captured by Mars’s gravitational pull. At its longest, Phobos is about 27 km across. Deimos is about 15 km across. Both Phobos and Deimos are dark, like the maria on the surface of Earth’s moon. Phobos and Deimos both have many craters. These craters indicate that many asteroids and comets have hit the moons. Scientists think the large number of craters means the moons are quite old. What Are the Characteristics of Jupiter’s Moons? In 1610, Galileo Galilei discovered four moons orbiting Jupiter. Since then, scientists have discovered that Jupiter has many more than 60 moons. Most of Jupiter’s moons are relatively small. The largest of the moons are those that Galileo discovered. These four moons are called the Galilean moons. They are • • • • READING TOOLBOX Summarize Before you read this section, create a two-column table with six rows. In the first column, list the names of the six main objects described in this section (Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto). In the second column, describe the moons and other characteristics of each object. READING CHECK 1. Explain Why do scientists think Phobos and Deimos are very old? READING CHECK 2. Identify What are the four Galilean moons? Io Europa Ganymede Callisto Copyright © Holt McDougal. All rights reserved. Holt McDougal Earth Science 445 Minor Bodies of the Solar System Name SECTION 3 Class Date Satellites of Other Planets continued IO READING CHECK 3. Describe How was Io’s volcanism discovered? Io orbits closest to Jupiter. It is the first body other than Earth on which scientists saw evidence of active volcanoes. An engineer discovered the volcanoes while studying images of Io that were taken by the Voyager spacecraft. Volcanoes on Io eject thousands of metric tons of material each second. The lava that erupts on Io is even hotter than lava on Earth. Parts of Io’s surface are yellow-red. This color is evidence that volcanic material on Io is mostly sulfur and sulfur dioxide. Data collected by the Galileo spacecraft show that Io has a giant iron core and may have its own magnetic field. Io is one of the most volcanically active bodies in our solar system. Critical Thinking 4. Compare Describe two differences between Io and Europa. EUROPA Europa is the second closest Galilean moon to Jupiter. Europa is about the same size as Earth’s moon. Astronomers think Europa has a rocky core that is covered with ice up to 100 km deep. Spacecraft have made observations of Europa. From the observations, scientists have concluded that liquid water may exist under the ice. If liquid water exists, it is possible that life might also exist on Europa. GANYMEDE Ganymede is the third Galilean moon from Jupiter. It is also the largest moon in the solar system. However, the mass of Ganymede is relatively small because the moon is made up mainly of ice mixed with rock. Images of Ganymede show that it has dark, crater-filled areas. It also has light areas that scientists think are long ridges and valleys. Ganymede is the only moon in our solar system that has its own magnetic field. Copyright © Holt McDougal. All rights reserved. Holt McDougal Earth Science 446 Minor Bodies of the Solar System Name SECTION 3 Class Date Satellites of Other Planets continued CALLISTO Of the Galilean moons, Callisto is the farthest from Jupiter. Callisto is similar to Ganymede in size, density, and composition. However, the surface of Callisto is much rougher than the surface of Ganymede. Its surface has a very large number of craters. Callisto has more craters per square kilometer than most other moons in the solar system. LOOKING CLOSER 5. Infer How did Callisto’s craters form? What Are the Characteristics of Saturn’s Moons? Saturn has dozens of moons. Many of them are small, icy bodies that have many craters. However, five of Saturn’s moons are quite large. Saturn’s largest moon, Titan, has a diameter of 5,000 km. TITAN Unlike other moons in our solar system, Titan has a thick atmosphere. Its atmosphere contains so many hydrocarbons that smog hides most of Titan’s surface. In 2005, the Huygens probe gathered data about Titan’s atmosphere. Scientists are using the data to find clues about how Titan and its atmosphere formed. The probe sent back images of Titan’s surface as well. The images show signs of a flowing liquid, which scientists think is liquid methane. READING CHECK 6. Identify What is the main difference between Titan and other moons in our solar system? SATURN’S OTHER MOONS Saturn’s icy moons resemble Jupiter’s icy Galilean moons. Enceladus has erupting geysers, so scientists think this moon may have underground water near the surface. The presence of water could mean Enceladus might have conditions needed for life. Saturn’s other smaller moons have irregular shapes. Copyright © Holt McDougal. All rights reserved. Holt McDougal Earth Science 447 Minor Bodies of the Solar System Name SECTION 3 Class Date Satellites of Other Planets continued LOOKING CLOSER 7. Identify Name three of Saturn’s moons other than Enceladus and Titan. Telesto Calypso Helene Enceladus Phoebe Hyperion Tethys Dione Rhea Titan Iapetus Saturn This image shows some of Saturn’s largest moons. Distances are not to scale. What Are the Characteristics of the Moons of Uranus and Neptune? READING CHECK 8. Explain How did scientists discover most of Uranus’s smaller moons? Talk About It Model With a partner, create a model to represent the motions of Pluto and Charon. Together, talk about how to use your model to figure out whether you could see Charon from all points on Pluto’s surface, or whether Charon would be visible only from certain places. By the mid-1800s, scientists had discovered Uranus’s four largest moons: Oberon, Titania, Umbriel, and Ariel. A fifth moon, Miranda, was discovered in 1948. Scientists have recently discovered many smaller moons using spacecraft and observatories such as the Hubble Space Telescope. Scientists now know that Uranus has at least 24 small moons. Neptune has at least 13 moons. Triton, which is a large icy moon, is unusual. It revolves around Neptune in a backward, or retrograde, orbit. Some scientists think Triton formed somewhere else in the solar system and was captured later by Neptune’s gravity. Triton’s diameter is 2,705 km, and its atmosphere is thin. What Are the Characteristics of Pluto’s Moons? Scientists no longer consider Pluto a planet. However, Pluto has at least three moons. Pluto’s largest moon, Charon, is almost half the size of Pluto. Because Charon and Pluto are so close in mass, both bodies orbit a common balance point called a barycenter that is located between both bodies. Charon orbits Pluto in 6.4 days, which is the same length of time as one day on Pluto. Thus, Charon stays in the same place in Pluto’s sky. In the same way that one side of Earth’s moon always faces Earth, one side of Pluto always faces Charon. Pluto’s other two moons, Nix and Hydra, are much smaller. Nix and Hydra also orbit the barycenter between Pluto and Charon. Copyright © Holt McDougal. All rights reserved. Holt McDougal Earth Science 448 Minor Bodies of the Solar System Name SECTION 3 Class Date Satellites of Other Planets continued Critical Thinking Pluto Charon Nix Hydra 9. Infer Why do you think scientists had to use very strong telescopes to discover Nix and Hydra? Scientists discovered Nix and Hydra in 2005 using the Hubble Space Telescope. What Are the Characteristics of the Rings of the Gas Giants? Each of Saturn’s rings is divided into hundreds of smaller rings, or ringlets. The ringlets are made up of billions of pieces of rock and ice. The pieces range in size from particles the size of dust to chunks as big as a house. Each piece follows its own orbit around Saturn. Scientists once thought that the material in Saturn’s rings was as old as Saturn itself. Evidence now shows that the rings are much younger. Scientists think the particles came from a large cometlike body that entered Saturn’s orbit and broke apart. The other gas giants also have rings. These rings are relatively narrow, and thus harder to detect. For instance, Saturn’s rings were discovered more than 300 years ago, but Jupiter’s ring was not discovered until 1979. The table below describes the rings of the gas giants. Characteristics of the Rings of Gas Giants READING CHECK 10. Identify What are Saturn’s rings made of? LOOKING CLOSER Planet Description of Rings Saturn • hundreds of small ringlets forming larger rings • very thin ring system Jupiter • single thin ring • made up of particles that may have come from Io or another one of Jupiter’s moons Uranus • 12 thin rings Neptune • a relatively small number of rings • clumpy rather than thin and uniform 11. Compare How are Neptune’s rings different from the rings of the other gas giants? Copyright © Holt McDougal. All rights reserved. Holt McDougal Earth Science 449 Minor Bodies of the Solar System Name Class Date Section 3 Review SECTION VOCABULARY Galilean moon any one of the four largest satellites of Jupiter—Io, Europa, Ganymede, and Callisto—that were discovered by Galileo in 1610 1. Describe Complete the table below to describe the special characteristics of the Galilean moons. Moon Special Characteristics Io covered with a thick layer of ice; may have liquid water under the ice largest moon in the solar system; has its own magnetic field Callisto 2. Compare How are Io’s volcanoes different from volcanoes on Earth? 3. Describe Give one similarity and one difference between Phobos and Deimos. 4. Compare What is the main difference between Saturn’s rings and the rings of other planets? 5. Identify How is Triton different from most other planets in the solar system? 6. Describe How do scientists think Saturn’s rings formed? 7. Infer Scientists did not discover Jupiter’s ring until 1979. What is the most likely reason it took scientists so long to discover Jupiter’s ring? Copyright © Holt McDougal. All rights reserved. Holt McDougal Earth Science 450 Minor Bodies of the Solar System