A team of scientists from NASA's Voyager Project have determined the rotation period of Saturn -- the length of Saturn day -- using bursts of radio signals from the planet recorded by the two Voyager spacecraft.
The new Saturn day is 10 hours, 39 minutes, 24 seconds long. The determination was made by Michael Kaiser and Michael Desch of NASA's Goddard Space Flight Center in Greenbelt, Maryland, and James Warwick and Jeffrey Pearce of Radiophysics Inc. in Boulder, Colorado. They are members of the Voyager Planetary Radio Astronomy Team headed by Warwick.
Warwick's team recorded radio signals from variety of sources in the sky during January and February 1980, when Voyager 1 was more than 380 million kilometers (236 million miles) from Saturn, and Voyager 2 was more than 554 million kilometers (344 million miles) from the planet.
By gradually eliminating signals coming from the Sun, Jupiter and other sources, they determined that the signals they were receiving every 10 hours, 39.9 minutes originated at the north pole of Saturn, and were precisely controlled by the planet's rotating magnetic field.
Radio astronomers were able to pin down the rotation rate of Jupiter using this method several years ago. Scientists feel it is the most accurate method of determining rotation. Although the Earth, Jupiter and Saturn are all emitters of radio signals, scientists do not as yet understand how the signals are generated.
Astronomers using Earth-based observations of the ringed planet had calculated the length of day at about 10 hours, 15 minutes, but admitted their measurements lacked great accuracy.
Their problem was that the planet does not have solid surface, observers can see only the tops of Saturn's clouds, and the clouds lack sharply defined features to allow accurate determination of the planet's rotation.
Voyager 1 is scheduled to make its closest approach to Saturn Nov. 12, 1980. Voyager 2 will pass the planet Aug. 26, 1981.
The Voyager Project is managed for NASA's Office of Space Science by the Jet Propulsion Laboratory, California Institute of Technology.