Earthquakes on Saturn shake its rings and reveal its interior

Two astrophysicists confirm the relevance of an idea developed during the 1990s and which should be able to be put into practice by studying Saturn’s rings. Movements inside the giant, similar to earthquakes on Earth or inside the Sun, change the planet’s gravitational field at the level of its rings, causing them to vibrate. It can then be used as a seismograph to probe the interior of Saturn.

an article published in a famous newspaper nature astronomy, rendering the functions of two astronomers About the legendary Caltech that was based on data from the Cassini probe rings of saturnwould undoubtedly have attracted the attention of German-American astronomer Rupert Wilde (1905–1976). It is to him that we give the first model of the interior giant planet, models proposed and developed by him during the 1940s and 1950s.

According to him the interior of the planets Jupiter And Saturn was probably composed of a tiny rocky core covered by a thick layer of several ice sheets (it’s not just water), all covered in a giant atmosphere fluid, mainly composed ofhydrogen and helium. This also applies to models Uranus And Neptune, except we think we know that these giants must have a Coat Huge ice around a rocky core. The temperature of Jupiter will be brought to a temperature of the order of 20,000 K (on Earth it is estimated that the temperature should reach 6,000 K), of course Pressure It is very difficult to reproduce in laboratories on Earth.

In recent decades, the Giants model has been refined, whether usinghigh pressure lab experiments, From numerical simulation By analyzing data collected by scientists or quite simply missions juno and Cassini. liquid of hydrogen and helium from Jupiter and Saturn, liquid will be solid at great depth, even with Hydrogen which will also acquire metallic properties, Even that superconductors. methane andof ammonia The material can also lead to the formation of diamonds inside Neptune.

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Today we see a new example of this refinement in the case of Saturn, as explained in the article available on arXiv Of Jim Fuller, assistant professor ofastrophysics Theoretician at Caltech, and his post-doctoral fellow Christopher Mankovic. The two men concluded that Saturn’s heart covers more than 60% of the planet’s interior, which is much larger than the latest estimates put forward by planetary scientists. Above all, this heart will be big enough Spilled With differences in rocks, ice, and conductive metallic fluids far less clear than imagined at the time, it is more appropriate to speak of mixing as a matter of course. shield As we sink into the demon’s heart, no more Strategies Homogeneous clearly chemically differentiated. Remarkably, in the case of Jupiter a similar conclusion was already drawn from the analysis of data collected by the Juno probe.

An animation showing that Saturn’s innermost C-ring contains spiral density waves that correspond to the Lindblad waves of spiral galaxies excited by changes in the gravitational field during interactions between galaxies. These waves in the C ring are therefore like a seismograph that deceives the motion of matter inside Saturn and makes it possible to do seismology similar to Earth’s. © Caltech

A New Example of Asteroids

In the case of Saturn, both astronomy also argue that its core is 55 times as massive as Earth, 17 . with public The land of ice and rock and the rest is a fluid of hydrogen and helium. How did the two people draw all these conclusions from Cassini’s data?

He took a brilliant idea several steps forward which dates back to the 1990s and for which we are indebted. mark marley And Carolyn Pig. late colleague Andre BrahicCarolyn Porco has made a name for herself by being a member of the Cassini and Voyager missions to lead the team responsible for the Cassini probe’s images.

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In 2013, Marley and Porco’s colleagues Matt Heidman and PD Nicholson showed their idea to be relevant in practice by analyzing Cassini’s observations.

What observations from Cassini? Quite simply showing the formation and propagation of “spiral” waves in Saturn’s ring. It begins at a distance of 74,658 km from the center of Saturn and extends for 92,000 km, which is included between Ring D, the innermost and from which it is separated by the Guerin division, and Ring B, greater outer and is separated by the division of the lyte.

These waves are excited by a change in the field time Gravity In and around Saturn, as Mark Marley and Carolyn Porco understood, some changes in the gravitational field are unrelated for the movement of the moons of Saturn But for specific variations of the giant planet’s area.

The Cassini probe took images of Saturn’s two small moons whose gravitational fields oscillate the distribution of particles in Saturn’s F ring. Simulations show animations that clearly highlight the ripples generated in the F ring, the outermost part of Saturn’s rings. © NASA

These distinctive variations are caused by changes in the distribution of matter within Saturn, for example, for the spread ofseismic waves as can be found inside soleil And that’s what astrophysicists use to do helioseismology. These changes can also be due to oscillations and deformities of the heart of Saturn which are related to movements from the surface of the water in a moderately shaken glass. Let’s talk about Anglo-Saxon” sloshing To describe the movements of the free surface of a liquid under these conditions, and in French this phenomenon is known as “sloshing.” Spiral waves and sloshing can be seen in the artist’s vision in the first video above .

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Mark Marley and Carolyn Porco logically concluded that the waves in Saturn’s rings were therefore a direct translation of what we might say Earthquake inside Saturn, and we were in front of a Window with as on Earth to allow observations related to the science of asteroids seismology, to explore the composition and structure of Saturn’s interior.

Analysis presented today in the article nature astronomy We now think that the heart of Saturn is the equivalent of a ball of clay made up of a mixture of rocks, ice, and the fluids of hydrogen and helium that seem to make it up. In the end, this mixture is one of a kind fossil From the birth of Saturn.

The cosmology of Jupiter and Saturn involves the early formation of a large nucleus of rocks and ice, on which gas According to the current dominant theory. But there is another model where the process actually begins a Collapse Large and spontaneous region in the protosolar gas and dust disk. Do we have to go back a little in the direction of this model?

For years, Jim Fuller and his colleagues have been exploring the idea of ​​a seismology by studying Saturn’s rings. Here is a technical presentation. To get a fairly accurate French translation, click on the white rectangle at the bottom right. The English subtitle should then appear. Then click on the nut on the right side of the rectangle, then on “Subtitles” and finally on “Translate automatically”. Select “French”. © Cider Dynamic Earth

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