Science: Bonanza from a Ringed Planet

• Share

Pioneer reports an eleventh moon, more rings and a frigid Titan

Battered and pitted from its encounter with the rings of Saturn, the Pioneer 11 spacecraft headed into deep space last week, its mission accomplished. In its sweep past Saturn, it had provided the best look yet at the solar system's second largest planet, discovered what is probably an eleventh Saturnian moon and two more rings. It also confirmed the existence of another ring and a magnetic field, and dimmed hopes that Titan, Saturn's largest moon, might harbor some form of life.

The computer-enhanced Saturn pho tos taken by Pioneer were far better than any pictures of the planet shot through earthbound telescopes. More details of the famous rings were evident, and for the first time the bands formed by the yellow-and orange-hued clouds enveloping Sat urn could be clearly seen. Still, compared with the spectacular shots of Jupiter and its moons transmitted earlier this year by the twin Voyager spacecraft, the Pioneer pictures were disappointing. The difference is that Pioneer is equipped with a relatively crude camera-like instrument called an imaging photopolarimeter; the Voyagers have far more sophisticated TV-camera systems. But NASA will have an opportunity to try again late next year and in 1981 when Voyagers 1 and 2, respectively, reach Saturn with their superior cameras.

If Pioneer lacked a sharp eye, it made up for that deficiency with its other sensors. Last week, as scientists at NASA'S Ames Research Center near San Francisco skimmed data transmitted during the spacecraft's flyby of Saturn, they made an exciting discovery. While Pioneer was close to Saturn's rings, a detector recording a bombardment by charged particles fell practically silent for twelve seconds, then began registering particles again. Analysis indicated that Pioneer had been briefly shielded from the rain of particles as it flew under a massive object.

Based on these readings and others that showed changes in the surrounding magnetic field, scientists concluded that the spacecraft had passed within about 2,500 km (1,560 miles) of what appears to be a previously undiscovered moon* with a diameter as large as 600 km (370 miles). "The object was very close," says Physicist John Simpson of the University of Chicago. "It could be rocky or composed largely of ice. Either material will effectively block high energy particles." The moonlet, in orbit about 90,000 km (56,000 miles) above Saturn's cloud tops, was nicknamed "Pioneer rock" by the scientists, and it is being officially designated as 1979 S-l (for the first new moon of Saturn discovered this year).