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* * * CHAPTER 6 Asteroids, Comets, and Meteoroids 730. An asteroid is (a) a small star; (b) a minor planet; (c) a large gas cloud; (d) a small satellite of a planet. 731. What is an asteroid? Where are most of the asteroids? 732. The usual distinction between a planet and an asteroid is based on (a) orbital period; (b) mean density; (c) size; (d) date of discovery. 733. About how many asteroids have been identified and cataloged? 734. Describe the orbit of an average asteroid. 735. The median semimajor axis of the orbits of asteroids is 2.7 AU. Hence, the sidereal period of revolution of the median asteroid is about (a) 4.4; (b) 20; (c) 2.7; (d) 7.3 years. 736. If in fifteen weeks the line segment from the Sun to an asteroid sweeps out 0.1 of the total area enclosed by its orbit , about what is the period of revolution of the asteroid? (a) 29 years; (b) 2.9 years; (c) not calculable from the data given; (d) 4.3 years. 96 Asteroids, Comets, and Meteoroids / 97 737. How can an asteroid be distinguished from a star with a simple optical telescope? 738. Which one of the following objects is an asteroid? (a) Europa; (b) Triton; (c) Juno; (d) Callisto. 739. Ceres is (a) an asteroid; (b) a satellite of Jupiter; (c) a satellite of Uranus; (d) a bright star in Cassiopeia. 740. Which one of the following is not an asteroid? (a) Hidalgo; (b) Europa; (c) Geographos; (d) Icarus. 741. Calculate the escape speed from the surface of a spherical asteroid whose mean density is 2.3 g cm-3 and whose radius is 5 km. 742. Would you expect an asteroid to have an atmosphere? Why or why not? 743. If you weigh 150 pounds on the Earth what would you weigh on the surface of an asteroid that has a mass 1/300,000th that of the Earth and a radius 1/50th that of the Earth? 744. The total energy emitted in the infrared by a particular asteroid is four times as great as the amount of sunlight it reflects. What is its optical albedo? 745. The Trojans are (a) satellites of Saturn; (b) a family of periodic comets; (c) a particular type of meteorite; (d) a special class of asteroids. 746. The Trojan asteroids (a) are in Keplerian orbits about Jupiter; (b) move in retrograde orbits between the orbits of Mars and Jupiter; (c) illustrate a special solution of the three-body gravitational problem; (d) have orbits that cross the orbit of the Earth. 98 / Asteroids, Comets, and Meteoroids 747. The Trojan asteroids (a) are in Keplerian orbits about Jupiter; (b) are near the Lagrangian points L4 and L5 relative to the Sun and Jupiter; (c) are slowly escaping from the solar system; (d) have perihelion distances less than 1 AU, such that they cross the orbit of the Earth. 748. By what observational technique can the rotational period of an asteroid be determined? 749. The rotational periods of many asteroids have been determined by (a) observing cyclic departures from Keplerian orbits; (b) observing cyclic variations in their brightness; (c) supposing that they are tidally locked to the Sun as they revolve in their orbits; (d) observing the perturbations oftheir orbits by Jupiter's gravitational field. 750. About 65,000,000 years ago, dinosaurs and many other species of animal and plant life suddenly became extinct. Describe a current hypothesis for this effect. 751. What is the essential physical distinction between an asteroid and a comet? 752. According to Oort's theory, comets come from a cloud of icy bodies in Keplerian orbits about the Sun at a distance of the order of 50,000 AU. If such a body is perturbed from its orbit by a passing star so as to fall inwards toward the Sun, how long will it take to do so? 753. A comet that is perturbed from the Oort comet belt at 50,000 AU into an orbit with perihelion at 1 AU spends about (a) 11.2 X 106; (b) 2.0 X 106; (c) 5.6 X 106; (d) 4.0 X 106 years on its inbound flight to perihelion. Asteroids, Comets, and Meteoroids / 99 754. Concerning comets: (a) It is reasonably certain that most comets come from outside the solar system. (b) Kepler's laws are found to be useless in describing the motion of comets. (c) The orbit of a comet...


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