Pale Blue Dot - Carl Sagan [35]
Voyager 2 took advantage of a rare lining-up of the planets: A close flyby of Jupiter accelerated it on to Saturn, Saturn to Uranus, Uranus to Neptune, and Neptune to the stars. But you can’t do this anytime you like: The previous opportunity for such a game of celestial billiards presented itself during the presidency of Thomas Jefferson. We were then only at the horseback, canoe, and sailing ship stage of exploration. (Steamboats were the transforming new technology just around the corner.)
Since adequate funds were unavailable, NASA’s Jet Propulsion Laboratory (JPL) could afford to build spacecraft that would work reliably only as far as Saturn. Beyond that, all bets were off. However, because of the brilliance of the engineering design—and the fact that the JPL engineers who radioed instructions up to the spacecraft got smarter faster than the spacecraft got stupid—both spacecraft went on to explore Uranus and Neptune. These days they are broadcasting back discoveries from beyond the most distant known planet of the Sun.
We tend to hear much more about the splendors returned than the ships that brought them, or the shipwrights. It has always been that way. Even those history books enamored of the voyages of Christopher Columbus do not tell us much about the builders of the Niña, the Pinta, and the Santa María, or about the principle of the caravel. These spacecraft, their designers, builders, navigators, and controllers are examples of what science and engineering, set free for well-defined peaceful purposes, can accomplish. Those scientists and engineers should be role models for an America seeking excellence and international competitiveness. They should be on our stamps.
At each of the four giant planets—Jupiter, Saturn, Uranus, and Neptune—one or both spacecraft studied the planet itself, its rings, and its moons. At Jupiter, in 1979, they braved a dose of trapped charged particles a thousand times more intense than what it takes to kill a human; enveloped in all that radiation, they discovered the rings of the largest planet, the first active volcanos outside Earth, and a possible underground ocean on an airless world—among a host of surprising discoveries. At Saturn, in 1980 and 1981, they survived a blizzard of ice and found not a few new rings, but thousands. They examined frozen moons mysteriously melted in the comparatively recent past, and a large world with a putative ocean of liquid hydrocarbons surmounted by clouds of organic matter.
On January 25, 1986, Voyager 2 entered the Uranus system and reported a procession of wonders. The encounter lasted only a few hours, but the data faithfully relayed back to Earth have revolutionized our knowledge of the aquamarine planet, its 15 moons, its pitch-black rings, and its belt of trapped high-energy charged particles. On August 25, 1989, Voyager 2 swept through the Neptune system and observed, dimly illuminated by the distant Sun, kaleidoscopic cloud patterns and a bizarre moon on which plumes of fine organic particles were being blown about by the astonishingly thin air. And in 1992, having flown beyond the outermost known planet, both Voyagers picked up radio emission thought to emanate from the still remote heliopause—the place where the wind from the Sun gives way to the wind from the stars.
Because we’re stuck on Earth, we’re forced to peer at distant worlds through an ocean of distorting air. Much of the ultraviolet, infrared, and radio waves they emit do not penetrate our atmosphere. It’s easy to see why our spacecraft have revolutionized the study of the Solar System: We ascend to stark clarity in the vacuum of space, and there approach our objectives, flying past them, as did Voyager, or orbiting them, or landing on their surfaces.
These spacecraft have returned four trillion bits of information to Earth, the equivalent of about 100,000 encyclopedia volumes. I described the Voyagers 1 and 2 encounters with the Jupiter system in Cosmos. In the following pages, I’ll say something about the Saturn, Uranus, and Neptune encounters.