1. Curtis Peebles, Asteroids: A History . Washington, DC: Smithsonian Institution, 2000, p. 1.
2. Quoted in Carl Sagan and Ann Druyan, Comet. 1985. Reprint: New York: Random House, 1997, p. 19.
3. William Shakespeare, Julius Caesar , act 2, scene 2, lines 30–31.
4. Plutarch, Life of Caesar , in Fall of the Roman Republic: Six Lives by Plutarch , trans. Rex Warner. New York: Penguin Books, 1972, p. 309.
5. Seneca, Natural Questions , trans. John Clark. London: Macmillan, 1910, pp. 275–77.
6. Quoted in Gerrit L. Verschuur, Impact: The Threat of Comets and Asteroids. New York: Oxford University Press, 1996, p. 55.
7. Quoted in William S. Weed, "Chasing a Comet," Astronomy , September 2001, p. 35.
8. Quoted in Sagan and Druyan, Comet , p. 29.
9. Sagan and Druyan, Comet , pp. 31–32.
10. Quoted in Paul R. Weissman, "Cometary Reservoirs," in J. Kelly Beatty et al., The New Solar System. Cambridge, England: Cambridge University Press, 1999, pp. 59–60.
11. Quoted in Eugene MacPike, ed., Correspondence and Papers of Edmund Halley. Oxford, England: Clarendon Press, 1932, p. 67.
12. Quoted in Peebles, Asteroids , p. 5.
13. Quoted in Peebles, Asteroids , p. 7.
14. Quoted in Peebles, Asteroids , pp. 9–10.
15. Quoted in Peebles, Asteroids , p. 28.
16. John K. Davies, Beyond Pluto: Exploring the Outer Limits of the Solar System. Cambridge, England: Cambridge University Press, 2001, p. 11.
17. Peebles, Asteroids , pp. 40–41.
18. Clark R. Chapman, "Asteroids," in Beatty et al., New Solar System , pp. 339–40.
19. John A. Wood, "Origin of the Solar System," in Beatty et al., New Solar System , p. 19.
20. Davies, Beyond Pluto , pp. 13–14.
21. David H. Levy, Comets: Creators and Destroyers. New York: Simon and Schuster, 1998, p. 25.
22. Weissman, "Cometary Reservoirs," p. 62.
23. Levy, Comets , p. 19.
24. William K. Hartmann, Moons and Planets. Pacific Grove, CA: Brooks Cole, 1998, p. 201.
25. Peebles, Asteroids , p. 38.
26. Chapman, "Asteroids," p. 347.
27. Quoted in Weed, "Chasing a Comet," p. 34.
28. Quoted in Weed, "Chasing a Comet," p. 35.
29. John C. Brandt, "Comets," in Beatty et al., New Solar System , pp. 329–30.
30. Davies, Beyond Pluto , p. 19.
31. Quoted in Maggie Mckee, "Comets Split Far from Sun," Astronomy , December 2002, p. 30.
32. Brandt, "Comets," p. 335.
33. Peebles, Asteroids , p. 100.
34. Peebles, Asteroids , p. 109.
35. Quoted in Peebles, Asteroids , p. 114.
36. Quoted in Robert Zimmerman, "NEAR-Shoemaker Scores a Touchdown," Astronomy , May 2001, p. 20.
37. Daniel D. Durda, "Stepping Stones to Mars," Astronomy , August 2001, p. 48.
38. Weed, "Chasing a Comet," p. 34.
39. Brandt, "Comets," p. 324.
40. Quoted in Richard Talcott, "Comet Borrelly's Dark Nature," Astronomy , April 2002, p. 44.
41. John S. Lewis, Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. Cambridge, MA: Perseus, 1997, p. 186.
42. Lewis, Mining the Sky , p. 194.
43. Hartmann, Moons and Planets , p. 211.
44. Minor Planet Center, Smithsonian Astrophysical Observatory, "Asteroids Near Earth: Retrieval for Materials Utilization," June 2003, p. 2. www.permanent.com.
45. Durda, "Stepping Stones to Mars," p. 46.
46. Minor Planet Center, "Asteroids Near Earth," p. 3.
47. Minor Planet Center, "Asteroids Near Earth," p. 16.
48. Durda, "Stepping Stones to Mars," p. 47.
49. Minor Planet Center, "Asteroids Near Earth," p. 3.
50. Verschuur, Impact , p. 6.
51. Alan E. Rubin, Disturbing the Solar System: Impacts, Close Encounters, and Coming Attractions , Princeton, NJ: Princeton University Press, 2002, pp. 156–57.
52. Verschuur, Impact , pp. 7–8.
53. Quoted in Hartmann, Moons and Planets , p. 215.
54. John S. Lewis, Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment. Reading, MA: Addison-Wesley, 1996, p. 151.
55. David L. Chandler, "Asteroid for the Millennium," Astronomy , December 2002, p. 46.
56. Levy, Comets , p. 157.
57. Levy, Comets , pp. 155–56.
58. Verschuur, Impact , p. 221.
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