Generations of astronomers and amateur stargazers have known Saturn as the only one of the solar system's nine planets that is encircled by rings. Now Saturn has lost that distinction. A team of Cornell University astronomers reported last week that they have discovered rings around remote Uranus, the seventh planet from the sun.
The Cornell team, headed by Astronomer James Elliot, made its observation last month while flying in a specially equipped C-141 "airborne observatory" through the night sky southwest of Australia. The astronomers had aimed the aircraft's 90-cm. (36-in.) telescope at Uranus, which was passing in front of a distant star in the constellation Libra. By recording variations in light from the star just before and after it was eclipsed by Uranus, they hoped to measure the diameter and study the atmosphere of the planet —which at a distance of 2.8 billion km. (1.7 billion miles) from the sun can barely be seen with the naked eye on a clear night.
Snow and Ice. What they observed was entirely unexpected. During nine minutes before Uranus completely blocked out the light from the star, the light disappeared—for seconds at a time —on five different occasions. After the star re-emerged from the other side of Uranus, its light was again obstructed five times at intervals that corresponded to the first set of blackouts. From these observations the astronomers concluded that the star had passed behind at least five rings encircling Uranus. The rings —which are vertical to earth's equatorial plane and cannot be seen by terrestrial telescopes—lie in a 7,000-km.-wide (4,400-mile) belt. Four of the flattened rings are about 10 km. (6 miles) across, while the outermost one is 100 km. (60 miles) wide. What the rings consist of is uncertain. Says Elliot: "One theory about Saturn's rings is that they are made out of snowballs, so one good guess about Uranus' rings would be that they are also some type of ice."