Cassini: Rings of Saturn used as a seismograph for looking inside

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Two US researchers used the rings of Saturn as seismographs and drew conclusions about the interior of the gas planet from the waves that run through them. Its core is therefore not solid, as previously assumed, but rather a kind of “diffuse soup made of ice, rocks and liquid metals”, they explain. In addition, the core of Saturn extends over 60 percent of the diameter and is therefore considerably larger than expected. Now in the trade magazine Nature Astronomy The presented analysis is based on data from the Saturn probe Cassini, which fell into the gas giant in 2017.

In order to investigate the conditions inside giant gas planets like Saturn, it was primarily their gravitational fields that had to be measured, explain Christopher Mankovich and Jim Fuller from the California Institute of Technology. The theory that Saturn makes its rings vibrate and that they can therefore be used as a seismograph was proposed 30 years ago. It was not until 2013, thanks to Cassini, that it was possible to directly demonstrate this phenomenon. The so-called C-ring therefore contains characteristic patterns that go back to fluctuations in the gravitational field of Saturn. This is exactly what the two of them have now analyzed and based on that they have developed a new model of the interior of Saturn.

Mankovich explains that the surface of Saturn is constantly moving slightly and behaving like a gently rippling lake. It rises and falls about three feet an hour. Like a seismograph, the rings record the slight disturbances caused by them in the gravitational field and the particles that make up the rings wobble accordingly. From these movements they could have inferred the composition of the interior. The interior must therefore be stable, in such a way that the proportion of ice and rock gradually increases the deeper you go. Overall, the core is said to be diffuse and not as firm as assumed. Among other things, this makes it more difficult to explain Saturn’s magnetic field.

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Saturn’s atmosphere and the rings
(Bild: NASA/JPL-Caltech/Space Science Institute)

The result the analysis matches a similar find of the Jupiter probe Juno, the researchers explain. The largest planet in the solar system could also have a similarly thinned core. Both results are also a challenge for the current models for the formation of the gas giants, they still admit. These are based on the assumption that solid rock cores first form, which then attract the gas and collect around them. If the findings are now confirmed, the gas would probably have been involved in the process earlier. At the same time, the discovery of Saturn joins a recently presented analysis of Mars, which has also shown that our knowledge of the interior of other planets in the solar system is still very limited.

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