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Une vue d'artiste de Saturne et de son intérieur selon le modèle proposé dans une publication récente. © Caltech/R. Hurt (IPAC)

Earthquakes shake Saturn’s rings and reveal its interior

Two astrophysicists emphasized the importance of the idea introduced during the 1990s that it should be applicable by studying Saturn’s rings. Movements within the giant, similar to earthquakes on Earth or inside the Sun, by changing the planet’s gravitational field at the level of its rings cause it to vibrate. It can then be used as a seismograph to examine the interior of Saturn.

Article published in the famous newspaper natural astronomy, show two works Astronomy scientists From the legendary Caltech that was based on data from the Cassini probe regarding Saturn’s ringsIt will draw the attention of the German-American astronomer Robert Weldt (1905-1976). To him we owe the first models of the interior giant planets, models proposed and developed during the forties and fifties.

According to him, the interior of the planets Jupiter It is likely that Saturn consisted of a small rocky core covered by a thick layer of several layers of ice (not just water), all surrounded by a vast Atmosphere liquid, mainly consists ofhydrogen and helium. These models also apply to Uranus And Neptune, except that we think we know these giants must have Coat Much larger ice surrounds a rocky core. Jupiter’s temperature will be raised to nearly 20,000 K (it is estimated on Earth that the temperature should reach 6000 K), of course pressure Giant difficult to breed in laboratories on Earth.

In recent decades, giants’ models have been improved, both usingHigh pressure lab experiments, From numerical simulation Scientists or simply by analyzing data collected by expeditions Juno and Cassini. liquid hydrogen and helium from Jupiter and Saturn, liquid In the great depth, it will also become solid with Hydrogen that may even acquire metallic properties, even in superconductors. methane andammonia The contents could also lead to the formation of diamonds within Neptune.

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Today we see a new example of this refinement in the case of Saturn, as described in the article available at arXiv From Jim Fuller, Assistant ProfessorAstrophysics theory at Caltech, and postdoctoral colleague Christopher Mankovitch. The two men concluded that Saturn’s core probably extends over about 60% of the planet’s interior, which is much larger than the most recent estimates provided by planetary scientists. Above all, this heart will be much more diffuse With the distinction between rock, ice, and conductive mineral fluids less clear than one had imagined hitherto, it is more appropriate to speak of a mixture that changes according to regression While we plunge into the heart of the giant, no strings Clearly homogeneous chemically differentiated. Remarkably, a similar conclusion has already emerged from analyzes of data collected by Juno on the case of Jupiter.

Animation showing that Saturn’s innermost C ring contains dense spiral waves that are similar to Lindblad waves from spiral galaxies that are excited by changes in the gravitational field during intergalactic interaction. Thus these waves in the C ring are like a seismograph that betrays the motions of matter within Saturn and makes it possible to do the same as in the case of Earth with seismology. © caltech

A new example of seismology

In the case of Saturn, both astrophysicists He also argues that the Earth’s core is 55 times the mass of Earth, with 17 masses The land of ice and rocks and the rest is a liquid of hydrogen and helium. How did the two men draw all these conclusions from Cassini’s data?

They took a few more degrees, a great idea from the ’90s and we owe it Mark Marley And Caroline Big. late colleague Andre BraichCaroline Porco has made a name for herself by being a member of the Cassini and Voyager missions to the point of leading the team responsible for Cassini images.

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In 2013, Marley and Porco co-stars Matt Hedman and B.

What are the notes from Cassini? Quite simply the ones that show the formation and propagation of “spiral” waves in the C ring of Saturn. It starts at 74,658 km from the center of Saturn and extends up to 92,000 km, as it is included between the D ring, the innermost and separated by the Guérin division, and the B ring, more external and separated by the Lyot division.

These waves excited by time changes in the field of gravity About Saturn As Mark Marley and Caroline Porco understand, part of the differences in the gravitational field are unrelated motions of Saturn’s moons But for specific differences to the giant planet’s field.

The Cassini probe has captured images of two small moons of Saturn whose gravitational fields oscillate in the particle distribution in Saturn’s F ring. The simulations show animations that clearly display the waves generated in the F ring, which is farthest from Saturn’s rings. © NASA

These specific differences are created by changes in the distributions of matter within Saturn in response, for example, to diffusionseismic waves Like the ones that can be found inside Soleil which are used by astrophysicists to do the science of the sun. These changes could also be due to the associated oscillations and distortion in the core of Saturn movements From the surface of the water in a moderately stirred glass. The Anglo-Saxons speak of ” flow To describe the free surface motions of a liquid under these conditions, this phenomenon is referred to in French as “sag.” Spiral waves and diffraction can be seen in the artist’s view of the first video above.

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Mark Marley and Caroline Porco reasonably concluded that the waves in Saturn’s rings were thus a direct translation of what one might call earthquakes Inside Saturn, that we were in front of a Window Observation related to the science of Mercury allowing, as on Earth with seismology, to explore the structure and composition of the interior of Saturn.

The analyzes presented today in an article written by natural astronomy Now make us think that Saturn’s core is a bit equivalent to a ball of clay with the mixture of rock, ice, liquids hydrogen and helium that seems to form it. Finally, this combination is a kind of fossil The birth of Saturn.

The cosmogony of Jupiter and Saturn includes the initial formation of a large core of rock and ice on it Gas According to the current prevailing theory. But there is another form where the process actually starts with a Collapse Large and spontaneous area in the initial gas and dust disk. Will we have to go back a bit in the direction of this model?

For years now, Jim Fuller and his colleagues have been exploring the idea of ​​seismology for Saturn by studying its rings. Here is a technical demo For a fairly accurate French translation, click on the white rectangle at the bottom right. The English translation should then appear. Then click on the nut to the right of the rectangle, then click on “Subtitles” and finally on “Translate automatically”. Choose “French”. © CIDER Dynamic Earth

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