In the early 1970s, astronomers wanted more information on Jupiter, Saturn, Uranus, and Neptune. To do this, NASA sent two probes, Voyager 1 and Voyager 2.
Voyager 2 was launched first on August 20, 1977. Voyager 1 launched on September 5, 1977. After they visit Jupiter, Saturn, Uranus, and Neptune, both Voyagers 1 and 2 will continue out of the solar system looking into the unknown.
Voyager 1 made its closest approach to Jupiter on March 5, 1979, and was followed by Voyager 2, which made its closest approach on July 19, 1979. They took over 33,000 pictures of Jupiter, its rings, and its moons.
When the Voyagers started to gather information on Jupiterís four known moons they found interesting facts no one had known before. They also discovered three new moons and gathered information on them, too.
New Moons: Two new moons, Adrastea and Metis, orbit just outside the new ring. The third new moon, Thebe, was discovered between Amalthea and Io.
Europa: Astronomers think Europa may have an ocean underneath its crust up to 30 miles deep.
Ganymede: Ganymede turned out to be the largest moon in our solar system. Before the Voyagers gathered information on it, astronomers thought Saturnís moon, Titan, was the largest moon in our solar system.
Callisto: Callisto has an ancient, heavily cratered crust with enormous cracks. The largest craters were filled with ice. Astronomers hope they may have microscopic organisms in the craters.
Amalthea: Amalthea is about 10 times bigger than Marís largest moon, Phobos, and has 1,000 times the volume.
The Voyagers discovered a ring around Jupiter that had not been seen by telescopes. The ringís outer edge is 80,000 miles from the center of Jupiter. The ring is 20 miles thick and 4,000 miles wide. It is Jupiterís only ring.
The Voyagers made their approaches to Saturn nine months apart, Voyager 1 in November 1980 and Voyager 2 in August 1981.
Probably the biggest surprise was that Saturnís rings were different than astronomers originally thought because they had gaps in between the rings. It was a big surprise!
Before the Voyagersí visit, astronomers believed Saturn had 11 moons. After their visit, they knew Saturn had at least 17 moons and 3 more possible moons were discovered from Earth after Voyagers 1 and 2 left. The ones discovered by the Voyagers are Atlas, Prometheus, Pandora, Epimetheus, Janus, Helene, Tethys, Telesto, and Calypso.
Voyager 2 flew close by Uranus. (Voyager 1 began its trip out of the solar system looking for anything unknown after its encounter with Saturn). NASA was depending on the spacecraft to get lots of information because back then Uranus was a mystery to most people.
Voyager 2 took pictures of Uranusí five known moons: Miranda, Ariel, Umbriel, Titania, and Oberon. It also discovered 10 new moons.
Voyager 2 also took pictures of Uranusí nine known rings. It also discovered two more rings. Astronomers also now know the distance from the rings to the center of Uranus is 13,000 miles to the first ring and 24,000 miles to the second ring.
In the summer of 1989, Voyager 2 became the first spacecraft to visit Neptune. Voyager 2 made its first approach on August 25, 1989.
Voyager 2 left Earth only knowing two of Neptuneís moons, Triton and Nereid. But when it got to Neptune, it discovered six new moons. Voyager 2 gathered lots of information on the six new moons: Proteus, Larissa, Despina, Galatea, Thalassa, and Naiad.
When Voyager 2 started gathering information on Neptuneís rings, astronomers noticed from the pictures Voyager 2 sent back that the rings did not appear to go all the way around Neptune. Like Saturnís rings, there was a gap in the rings. The rings looked like an arc. So astronomers called them ring arcs. After astronomers had the computer view the picture more closely, they found that the rings do go all the way around Neptune, they just appear not to. They also observed that there was a dark object where there appeared to be a gap. Astronomers think it may be a moon that caused the rings to appear in an arc shape.