Pale Blue Dot ( PDFDrive.com ) (1)

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.
JUST BEFORE VOYAGER 2 was to encounter the Uranus system, the mission design had specified a final
maneuver, a brief firing of the on-board propulsion system to position the spacecraft correctly so it
could thread its way on a preset path among the hurtling moons. But the course correction proved
unnecessary. The spacecraft was already within 200 kilometers of its designed trajectory-after a
journey along an arcing path 5 billion kilometers long. This is roughly the equivalent of throwing a
pin through the eye of a needle 50 kilometers away, or firing your rifle in Washington and hitting the
bull's-eye in Dallas.
Mother lodes of planetary treasure were radioed back to Earth. But Earth is so far away that by the
time the signal frog Neptune was gathered in by radio telescopes on our planet, the received power
was only 10 -16 watts (fifteen zeros between the decimal point and the one). This weak signal bears
the same pro, portion to the power emitted by an ordinary reading lamp as the diameter of an atom
bears to the distance from the Earth to the Moon. It's like hearing an amoeba's footstep.
The mission was conceived during the late 1960s. It was first funded in 1972. But it was not