Reading 52

The following passage is adapted from an article entitled “Voyage to Saturn” (© 2006 by Bill Douthitt).

1. The rain comes just once every
2. thousand years, in torrents of
3. liquid methane. The noxious
4. air dims sunshine to an eternal
5. orange twilight. The cold—290
6. degrees below zero Fahrenheit
7. —is a lethal assault. Yet here
8. on Saturn’s outsize moon Titan
9. is a world eerily like our own.
10. “Titan is a Peter Pan world,”
11. says Tobias Owen of the
12. University of Hawaii. “It was
13. formed around the same time
14. as the Earth, it’ got all the
15. materials and elements to
16. develop into a planet like
17. Earth, but it never had the
18. chance to grow up.”
19. Owen and his fellow planetary
20. scientists are used to picturing
21. Titan in their imaginations.
22. Now they’ve visited, if only by
23. remote control: a space probe
24. called Cassini gazes down on
25. the giant planet. Soon after
26. arriving, Cassini even launched
27. a smaller probe called Huygens,
28. which touched down on Titan’s
29. surface. The Titan encounter
30. was a high point in what has
31. amounted to a voyage back in
32. time. From the metallic
33. hydrogen in its interior to the
34. fine rubble of its rings, Saturn
35. carries clues to how the solar
36. system took shape and gave
37. rise to life.
38. Saturn has been slow to give
39. up its secrets. In 1610 Galileo
40. discovered what turned out to
41. be its most amazing feature,
42. the rings, but through his
43. primitive telescope, he
44. mistook them for two smaller
45. bodies flanking Saturn. Only
46. in 1656 did Dutch astronomer
47. Christiaan Huygens recognize
48. what they were. Huygens
49. also discerned a faint spark
50. outside the rings—a moon
51. later named Titan. Since then,
52. astronomers have picked out
53. 56 smaller moons. In the
54. 1940s, they discerned a haze
55. around Titan, the first sign
56. that it had a dense
57. atmosphere. Finally, the first
58. space probes flew past Saturn
59. —Pioneer 11 in 1979 and
60. Voyagers 1 and 2 in 1980 and
61. 1981. They snapped close-ups
62. and gleaned the first hints
63. that Titan is a time capsule of
64. conditions similar to those
65. found on the early Earth.
66. Now, after centuries of
67. curiosity and anticipation,
68. scientists are taking a long,
69. close look at Saturn. A metal
70. cylinder 22 feet tall, bristling
71. with scientific instruments
72. and topped by a white
73. saucerlike antenna,
74. Cassini-Huygens was built by
75. NASA, the European Space
76. Agency, and the Italian Space
77. Agency. It rocketed toward
78. Saturn in 1997 and arrived in
79. 2004, to begin at least four
80. years of exploration.
81. As it neared the end of its
82. 2.2-billion-mile journey,
83. Cassini shed speed so that
84. Saturn’s gravity could capture
85. it. The spacecraft dropped to
86. within 13,000 miles of the
87. planet’s clouds, making a
88. daring passage between the
89. outer rings. The rings look
90. manicured, but they are
91. actually swarms of debris:
92. billions of particles from
93. mite- to mansion-size.
94. Saturn could hold more than
95. 700 Earths, yet the planet,
96. made almost entirely of
97. hydrogen, is lighter than
98. water. It spins so fast that
99. it bulges to a diameter 7,300
100. miles greater at the equator
101. than at the poles, so fast that
102. a Saturn day lasts less than
103. 11 hours. Because Saturn is
104. mostly gas, it has no fixed
105. landmarks to reveal its exact
106. rotation rate. But its dense
107. interior generates a powerful
108. magnetic field that spins
109. with the planet. Over the past
110. two years, Cassini has clocked
111. the field’s rotation at 10 hours,
112. 47 minutes, and 6 seconds,
113. although no one is sure the
114. planet itself spins at exactly
115. the same rate. But the field
116. also opens a window into the
117. heart of Saturn.
118. Saturn began in the disk-shaped
119. cloud of dust and gas that
120. swirled around the newborn
121. sun 4.6 billion years ago. Bit
122. by bit, particles stuck together
123. until gravity could take over,
124. drawing material into lumps
125. of iron and rock. One of them
126. was the seed that grew into
127. Saturn. Over time, the gravity
128. of this rocky core attracted
129. clouds of hydrogen gas. The
130. gas settled around the core,
131. and the planet’s mass rapidly
132. grew. Pressures mounted,
133. squeezing the innermost layer
134. of hydrogen so hard that
135. scientists believe it turned
136. into a liquid metal—a superb
137. electrical conductor. Currents
138. surging through the metallic
139. hydrogen generate Saturn’s
140. immense magnetic field.
141. More than four billion years
142. later the core still retains heat
143. from its formation, which
144. stirs massive updrafts in the
145. planet’s atmosphere. They
146. whip up supersonic winds
147. and drive vast weather
148. systems. In images from
149. Cassini’s camera, the heat
150. rising from deep in the
151. atmosphere sets the planet
152. aglow. “We can watch the
153. weather day and night” Owen
154. says. “It’s a revelation.”