DETECTING METEOR IMPACTS ON SATURN'S RINGS.

• Position: Brief Article

Movies like "Deep Impact" and "Armageddon" have popularized the notion that the solar system contains huge chunks of material that represent a potential hazard to life on Earth, but how many of these objects actually lurk in the darkness of space? Mark Showalter's research may help answer that question. The research associate at Stanford (Calif.) University's Space, Telecommunications and Radioscience Laboratory (STARLab), who works out of the NASA Ames Research Center, has discovered the first direct and unambiguous detection of basketball-sized meteoroids striking one of Saturn's rings.

Using images taken by the two Voyager spacecraft that flew by the ringed planet in 1980 and 1981, Showalter identified objects that he calls "burst events" on the F Ring, a faint and narrow ring that orbits about 3,000 kilometers (1,860 miles) beyond the outer edge of Saturn's main ring system. By tracking these bursts long enough to determine that they have a lifetime of about two weeks, he discovered that they are clumps of dust kicked out of the ring when it is hit by small meteoroids ranging from three-quarters of an inch to 16 inches in size.

The F Ring has the best conditions for allowing observation of these dust clouds, Showalter points out. It is dim enough so that the clumps show up and thin enough so that they do not rapidly collapse back into the ring. That allowed him to follow the evolution of three of these clumps in some detail. Their spreading rates were consistent with that expected if the ring were hit by...