An American spacecraft is just about to fly past the planet Neptune (August 1989). No other object from Earth has ever made such a trip. The unmanned spacecraft is called Voyager-2. It will fly past Neptune at four hours, Greenwich Mean Time, Friday (August 25, 1989).
Voyager-2 weighs just one ton. It is moving 27 kilometers a second. As it flies past Neptune, it will get within 5000 kilometers of the planet's north pole. For the first time, scientists will get a close look at a planet that is more than 4000-million kilometers away from Earth.
We know very little about Neptune. From Earth, even through powerful telescopes, the planet looks just like a fuzzy blue-green ball. We have learned some things, however. For example, Neptune is about four times bigger than Earth. It is mostly gas with only a small solid center. It has several moons. And like the other distant planets in our solar system, it has rings. The amount of sunlight reaching Neptune is about 1000 times less than the amount reaching Earth. So we know it is cold, about 212 degrees below zero Celsius.
Voyager-2 will tell us much more about Neptune. It is sending detailed pictures and thousands of pieces of information back to Earth during its flight. Thirty-eight listening centers on four continents are receiving the information. Scientists expect to spend many years attempting to understand the meaning of all this new information.
The trip to Neptune has been a long one. Voyager-2 and another spacecraft, Voyager-1, were launched 12 years ago. The goal was to explore the planets, Jupiter and Saturn. When that work was done, scientists redirected Voyager-2 to the planet Uranus. And three years ago, they used the gravity of Uranus to direct the spacecraft to Neptune