Saturn day is now five minutes shorter

New method corrects rotation and wind speeds on the gas planet

Saturn rotates faster than expected © NASA
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The planet Saturn rotates five minutes faster than previously thought. His day is only exactly ten hours, 34 minutes and 13 seconds long. Even the previously calculated wind speeds could thereby be more than 250 kilometers per hour, as scientists now report in "Nature". A new method, no longer based solely on magnetic field measurements, helped them to the more accurate values.

Measuring the rotation of gas planets like Jupiter or Saturn is difficult. Because these planets do not have a solid surface that can be used as a reference. In addition, it is aggravating for Saturn that its magnetic fields are aligned almost exactly along the axis of rotation - the magnetic poles correspond to one percent with the geographical one. Therefore, their fluctuations do not allow a clear inference to the rotation in the deeper areas of the planet.

Gas movements instead of magnetic field as a basis

Now, however, an international team of researchers, led by scientists from the University of Oxford in the United Kingdom and the University of Louisville in the US, has solved this problem with a new method. Instead of using magnetic data as a basis, they focused on differences and similarities in the movement of the various layers of the gas planet.

On the one hand, they evaluated data on the movements of the ammonia clouds in the atmosphere, which had been collected and analyzed by the University of Louisville scientist Timothy Dowling for ten years. On the other hand, they relied on measurements from the Saturn probe Cassini, which has been using infrared spectrometers since 2004 to provide data on the deeper parts of the planet.

"We realized that we could combine information about what was visible on the planet's surface with Cassini's infra-red data about the deep interior of the planet and used it to create a three-dimensional map of Saturn's winds, " explains Professor Peter Read, a physicist at Oxford University. "With this map, in turn, we were able to follow how large waves and whirlpools develop in the atmosphere. This resulted in a new estimate of the underlying rotation of the planet. "Display

Rotation faster and more complicated

The new findings also suggest, according to the researchers, that the rotation of Saturn could be more complicated than that of rocky planets like Earth, because its interior is not solid but fluid. At the same time, they shed new light on the evolution and properties of the other gas planets of the solar system, Jupiter, Uranus and Neptune.

Although shortening the saturday day by five minutes does not sound like much, it does indicate that, for example, our recent estimates of wind speeds may be off by more than 250 kilometers per hour nnten, explains Read. It also means that the weather patterns on Saturn are much more similar to those we see on Jupiter. Despite their differences, these two giant planets seem to have more in common than previously thought

(Oxford University, 31.07.2009 - NPO)