The clear view of the clock of Saturn is clouded by solar winds. Picture: P. Zarka
The solar wind changes in a regular rhythm the radio radiation emitted by Saturn, which astronomers use as a clock for the rotational speed of the planet. This has been observed by scientists from France and Austria in the evaluation of measurement data from three years. Accordingly, the fluctuations in the speed of the solar wind at a rate of twenty to thirty days lead to a change in the radio signals by about one percent. The Saturn is like the earth surrounded by a magnetic field. This magnetic field creates radio waves registered by spacecraft such as Voyager and Cassini. The radio signals modulate in a rhythm of ten hours, 39 minutes and 24 seconds, which astronomers therefore regard as the duration of a complete revolution of the planet and thus as a saturday day. Since Saturn, like Jupiter, Neptune and Uranus, does not have a solid surface as a gas planet, such measurements are the only way to determine the rotation speed of these celestial bodies.

But in Saturn, strange fluctuations in this radio signal cause headaches to researchers: measurements have shown that the duration of such a cycle can vary by about one percent within twenty to thirty days. How these fluctuations come about has been a mystery to researchers so far. They could only rule out that the planet actually changes its rotation speed in such a short time. Also in the conversation was an influence of Saturn's moon Enceladus, which threw large amounts of matter into space and could thus adjust the "clock radio" of his mother planet.

The researchers around Philippe Zarka from the Observatoire de Paris in Meudon now believe that they have found in the solar wind the true cause of the supposed changes in the daylength: Since the sun turns around its equator about every 25 days once around, that also varies Speed ​​of this stream of particles, which runs through the whole solar system, in this rhythm. The interactions of the solar wind with the magnetic field of Saturn could lead to the fluctuations of the radio signals, explain the scientists.

Philippe Zarka (Observatoire de Paris, Meudon) et al .: Nature, Vol. 450, p. 265 ddp / Ulrich Dewald ad


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