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| Introduction |
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The twin Voyager spacecraft, over the course of a dozen years, drew back the curtain on nearly half of the solar system. From launch in 1977 through the spectacular parting shots in 1989 of Neptune at the outer reaches of the solar system, this pair of gangly, instrument-laden spacecraft explored four planets -- Jupiter, Saturn, Uranus and Neptune -- as well as tens of moons, and the rings and magnetic environments of those planetary systems.
The Voyagers were designed to take advantage of a rare geometric arrangement of the outer planets that occurs only once every 176 years. This configuration allows a spacecraft to swing from one planet to the next without the need for large onboard propulsion systems; the flyby of each planet both accelerates the spacecraft and bends its flight path. Without this gravity assist, the flight time to Neptune would be 30 years.
Voyager 2 was launched first, on August 20, 1977, followed by Voyager 1, which was put on a faster, shorter trajectory to Jupiter on September 5, 1977. Both launches took place at the Cape Canaveral Air Force Station in Florida. Eighteen months after launch, Voyager 1 reached Jupiter, 650 million kilometers (400 million miles) away. The spacecraft made its closest approach on March 5, 1979, while Voyager 2 followed on July 9 of the same year. Images streaming back from the pair of spacecraft began to show the complicated, swirling turbulence of Jupiter's atmosphere in exquisite detail. A giant storm three times the size of Earth was raging in Jupiter's upper atmosphere, surrounded by rippling currents that rotated around it. Voyager 1 made a startling discovery; it found nine active volcanoes erupting on Io, the innermost of Jupiter's four major moons. Four months later, Voyager 2 found that eight of the nine volcanoes were still erupting. Much to everyone's surprise, a thin, dusty ring was also discovered around Jupiter, forcing scientists to revise their thinking on the origins and mechanics of planetary ring systems.
At Saturn, with its majestic rings, the Voyagers took high-resolution pictures to help scientists determine what the rings were made of and what kept them in orbit. Theories to explain planetary rings were being rewritten as fast as the images came down in November 1980 and August 1981, when Voyager 1 and 2, respectively, paid their visits to the gaseous giant.
Saturn was the last planetary encounter for Voyager 1. Project controllers sent Voyager 1 on a trajectory that took it very close to Saturn's large moon Titan. That trajectory bent the spacecraft's path inexorably northward out of the ecliptic plane -- the plane in which most of the planets orbit the Sun. However, JPL scientists and engineers were confident enough in Voyager 2 to send the aging probe on to Uranus and Neptune.
At Uranus, the spacecraft photographed a world oddly tipped on its side, perhaps the result of a colossal primordial collision. Ten new moons were discovered in the Uranus system and the planet's magnetic field turned out to be nearly parallel to Uranus's axis of rotation.
In August 1989, two and a half million kilometers (1.24 million miles) beyond Uranus, Voyager 2 sailed past Neptune, showing off the planet's surprisingly active atmosphere for the first time. Because the planet receives so little sunlight, scientists had expected to see a placid, featureless planet; instead, Voyager showed them a dynamic atmosphere with winds blowing westward, opposite the direction of rotation, at speeds faster than the winds of any other planet. Neptune revealed its Great Dark Spot for the first time, a storm system that resembled Jupiter's Great Red Spot, and a smaller, eastwardly moving cloud, called a "scooter," which was circling the planet about every 16 hours. The blue planet was encircled in diffuse, dusty rings and six new moons were discovered orbiting along with the two that were already known, Nereid and Triton.
As Voyager 2 passed Neptune and began its journey to the edge of the solar system, its camera was rotated to look back at the planets and take one last parting shot of the solar system. Voyager 2's "family portrait" illustrates the vastness of the solar system and the huge expanses of emptiness that lie between the outer planets. Both Voyagers are now headed for the outer boundary of the solar system, where the Sun no longer influences interplanetary space. That edge is thought to be somewhere between 8 billion and 23 billion kilometers (5 billion and 14 billion miles) beyond the Sun. Engineers are optimistic that the Voyagers will still be transmitting data when that boundary is encountered sometime in the first quarter of the 21st century.
| Voyager Images |
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Voyager
Twin Voyager spacecraft, depicted here in a full-scale model, are now
traveling out of the solar system. In this view, the
science boom, containing cameras and other instruments requiring
maneuverability, is seen at right. The long boom at left carries two
magnetic-field detectors and stretches 13 meters (43 feet) out from the
spacecraft. The dominant feature at center, the 3.7-meter (12-foot)
diameter high-gain antenna, provides communication between the
spacecraft and controllers on Earth. Just below is a shiny gold disk, a
record called "Sounds of Earth," bearing messages and pictures from our
planet.
(Courtesy NASA/JPL)
Launch of Voyager 2
Voyager 2 was launched August 20, 1977, onboard a Titan III/ Centaur
rocket. Although Voyager 2 was launched 16 days before Voyager 1, it
arrived at Jupiter four months later than its sister craft. The initial
mission plan for Voyager 2 specified visits only to Jupiter and
Saturn. The plan was augmented in 1981 to include a visit to Uranus,
and again in 1985 to include a visit to Neptune. Voyager 2 completed
both of those missions and is currently performing scientific
experiments in interstellar space.
(Courtesy NASA/JPL)
The Sounds of Earth
On the chance that someone is out there, NASA approved the placement of
a phonograph record on each of the Voyager spacecraft. The recording,
called "Sounds of Earth" fits on a 12-inch, copper disc
containing greetings from Earth people in 60 languages, samples of music
from different cultures and eras, and natural sounds of surf, wind and
thunder, and birds, whales and other animals.
The record also contains electronic information that an advanced
technological civilization could convert into diagrams, pictures
and printed words, including a message from President Carter.
Space History
The Voyager Planetary Mission
Copyright © 1997 by Calvin J. Hamilton. All rights reserved.