New Moon Over Saturn

Phoebe, Saturn's ninth moon, was discovered in 1898, and astronomers have been vainly looking for others ever since. Their long quest has finally been rewarded. French Astronomer Audouin Dollfus reported last week that he had found another friend for Phoebe--a tenth moon orbiting close to the outer edge of Saturn's rings.

The determined search for the new moon had actually been hindered by the spectacular rings, which reflect sunlight brilliantly, obscuring other objects in the vicinity of the planet. But though the rings are wide, they are also incredibly thin--perhaps even less than a foot thick. Thus every 14 years or so, when the earth passes through Saturn's equatorial plane and astronomers can get an edge-on view of the rings, their glow practically disappears. In place of their familiar, disklike shape, the rings appear as a faint, straight line, much like the side view of a phonograph record held flat at eye level.

In mid-December, when one of the infrequent edge-on views occurred, Dollfus photographed Saturn through a telescope at the Paris Observatory's Meudon station. When the plates were developed, he detected on several of them a tiny spot of light only about 52,000 miles from the planet's surface. Reasonably confident that he had found a tenth Saturnian moon, he promptly telegraphed news of his discovery to the Smithsonian Astrophysical Observatory, the world's clearing house for celestial discoveries.

Alerted by the Smithsonian's announcement last week, Astronomer Richard Walker of the Naval Observatory's Flagstaff station examined Saturn photographs that he had taken on the night of December 18. On four of his plates he found what looked like a tiny droplet superimposed on the edge-on rings. The confirmation of the discovery will entitle Dollfus to name the new moon. If he abides by tradition established in identifying Saturn's moons, he will pick the name of a mythological character associated with Saturn, a Roman god of agriculture.

Astronomers estimate that the new moon orbits Saturn once every 18 hours and is between 100 and 200 miles in diameter. It is thus slightly larger than Saturn's smallest moon (Phoebe) but dwarfed by the largest (Titan), which is 2,900 miles in diameter--nearly as large as the planet Mercury. Despite the diminutive size of the new satellite, its gravity is probably strong enough to cause significant perturbations in the orbits of the countless tiny particles that constitute the nearby Saturnian rings. Thus, in conjunction with the gravitational pull of some of the other inner Saturnian moons, it may well be responsible for a mysterious characteristic of the rings--the dark gaps or divisions that separate them.

This file is automatically generated by a robot program, so reader's discretion is required.