The heroic death of the Cassini probe helped planetary scientists to accurately weigh the rings of Saturn and find out that they appeared relatively recently, no more than 100 million years ago. Their findings were presented in the journal Science.
The Saturnian rings were discovered by Galileo Galilei in 1610, who considered them to be three major moons. In the middle of the 17th century, Christian Huygens found out that Galileo's "satellites" are actually rings, consisting of the smallest particles of dust and ice.
Scientists still argue about the nature of these rings. Some planetary scientists believe that they arose from fragments of an ancient protoplanet at the dawn of the youth of the solar system, while others consider them a product of recent cataclysms.
Controversy is also added by the fact that the Cassini probe discovered that Saturn "sucks" water from its rings at a very high speed. As NASA recently found out, the rings closest to the planet will disappear in the very near future by cosmic standards, and their entire system will be eaten by Saturn in about 300 million years.
Such discoveries have strengthened the position of supporters of the theory of the "young rings" and made planetary scientists wonder when they appeared. The exact answer to this question, as Militzer explains, can be obtained by knowing only two parameters - the mass of dust and ice particles inside them and how well the rings reflect the light of the Sun.
The fact is that the rings of Saturn and other giant planets should gradually fade due to the fact that miniature dust particles and organic matter should be deposited on the surface of their ice grains, gradually darkening as a result of its "bombardment" by the ultraviolet rays of the Sun.
Accordingly, the lighter the rings, the lower their age, and vice versa. The rate of tarnishing, in turn, depends on their mass, thickness and composition - the more matter is hidden inside them, the slower these structures will “blacken”.
Cassini measured the brightness of Saturn's rings during the first years of its work in its orbit. On the other hand, their exact mass remained inaccessible to him until the very end of his life, for the reason that the probe did not come close enough to them to separate their gravitational influence from the planet's attraction.
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The first such opportunity came from Cassini in 2017, when the probe began to "dive" through the rings, preparing for a heroic death in the atmosphere of Saturn. These flights helped Militzer and his colleagues measure the structure of the planet's gravitational field and begin measuring the mass of the rings.
“When I first saw this data, I couldn’t believe my eyes, as they completely contradicted our models. It took a long time before we recognized that there was something else that was changing the gravitational fields in an unpredictable way. It turned out that in the atmosphere of Saturn gigantic currents of air are raging, penetrating 9000 kilometers into the planet, continues the planetary scientist.
When scientists took this anomaly into account, they found that the mass of the rings was unexpectedly small - it was about 15 million billion tons. This is about half the mass of Mimas, one of Saturn's smallest "death star" moons, and comparable to the weight of small asteroids.
This, in turn, means that Saturn became the "Lord of the Rings" very recently, about 100 million years ago. Its progenitor could be both a small moon and a large comet, which goes well with the fact that Cassini discovered a mass of organic matter inside the rings in the last seconds of its life.
