"The 45-minute pulsations are very mysterious," adds Elsner. Theyre not perfectly regular like a signal from E.T. might be; the period drifts back and forth by a few percent. "This is a natural process," he adds, "we just dont know what it is...."While the researchers were using Chandra to observe Jupiter, two NASA spacecraft -- Cassini and Galileo -- were near the giant planet. Galileo was deep inside Jupiters magnetic field, while Cassini was outside sampling the solar wind. Neither craft detected 45-minute variations in their surroundings, such as plasma waves or surges of energetic particles, "although such variations have been detected by Galileo at other times," notes Gladstone. Galileo has also picked up 1 to 200 kHz-frequency radio bursts that come and go with a 45-minute period, as did the Ulysses spacecraft when it flew by Jupiter in 1992.http://science.nasa.gov/headlines/y2002/07mar_jupiterpuzzle.htm?list454505
