The second rings of Saturn

These are particles of water that wriggle out of the rings, drawing the characteristic bands on the planet

Saturn with gas rings NASA
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It owes its majestic appearance to them: the rings are the hallmark of Saturn. Now astronomers have discovered that the rings floating around the planet are reflected in its atmosphere. Reason for this are electrically charged water particles from the ring system. They constantly migrated from the Saturn rings to the planet to react with the upper part of the atmosphere, the so-called ionosphere. This effect is characteristic of the infrared radiation of this layer: Dark bands appear in the pattern of the Saturn rings. The researchers now present the results in the journal "Nature".

The findings of James O'Donoghue's researchers from the University of Leicester are based on infrared images of the Keck telescope in Hawaii. Actually, the ionosphere of Saturn should shine evenly in these pictures. This part of the high atmosphere of a planet is indeed strongly ionized by the high-energy particles of the solar wind, which releases infrared radiation. But unlike the Earth's ionosphere or, for example, Jupiter, there are areas of intense and less intense radiation at Saturn, the researchers report.

As far back as 1980, recordings of the Voyager spacecraft that had passed Saturn had provided clues to the band structures. Already at that time there was a presumption that they are due to an interaction between the rings and the ionosphere of Saturn. Until the current recordings of the Keck telescope, the existence of the tapes could not be confirmed again.

This artistic representation shows the precipitation of the particles from the rings on Saturn. © NASA / JPL-Caltech / Space Science Institute / University of Leicester.

Along the magnetic field lines

O'Donoghue and his colleagues have now succeeded and they also provide the explanation of the phenomenon: It is raining on the atmosphere. Because the Saturn rings consist almost exclusively of water ice, and especially the small ice particles can catch themselves by the influence of the sun and also by collisions with each other electrical charges. As a result, the magnetic field of Saturn begins to tug at them - they are exposed to the so-called Lorenz force, explain the scientists.

They then walk slowly along the magnetic field lines like a string of pearls towards the planet and hit the atmosphere, where they influence the ionization. There they reduce the electron density and thus ultimately reduce the radiation - this is how the dark bands on the infrared images of the Keck telescope are created. They correspond to the gap pattern of the rings, since the magnetic field lines project the particles onto the Saturn in an arc-shaped manner. display

The findings now also provide new information on the development history of the Saturn rings. So far, it is unclear whether the ring system is an ancient relic from the time of Saturn's origin or whether its characteristic halo is a comparatively young phenomenon. The current results make a ripe old age rather unlikely, because the process is a type of erosion that dissolves the ring. How strong the effect is, however, future investigations have yet to unravel, the researchers emphasize. (Nature, 2013; doi: 10.1038 / nature12049)

(Nature, 12.04.2013 - MVI)