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.”