Like the mountains, oceans and continents on Earth, the rings of Saturn would be ephemeral and should disappear within 300 million years. The icy particles that compose them fall indeed on the giant under the effect of its gravity and its magnetic field.
Galileo was the first to observe Saturn with a telescope. He discovered that it had a strange form whose nature was only understood in 1655 by the mathematician, astronomer and physicist, Huygens: the giant was surrounded by a ring, and several even, as Giovanni Domenico Cassini shows a few years later. In 1859, the physicist James Clerk Maxwell, to whom we owe the theory of the
electromagnetic field, shatters the theory proposed by Laplace in 1787, according to which the rings of Saturn are solid. Based ingeniously on the laws of mechanics, Maxwell deduces that they are probably made of a set of small bodies in orbit. It will then be necessary to wait for the work of the Russian mathematician, Sofia Kovalevskaya (1850-1891) to have the proof that the rings of Saturn can not be liquid. It was finally in 1895 that the observations of the American astronomer, James Edward Keeler, definitively confirm the version of Maxwell.
Astrophysicists and mathematicians interested in cosmogony will then try to explain the formation of these rings. Some explained that they would come from the destruction of a small celestial body that would have come too close to Saturn. In doing so, it would have fallen below the limit defined by the mathematician and astronomer Edouard Roche, that is to say the minimum distance below which a small body, approaching a big one, is destroyed by the forces tide. But if so, when did this event occur? Billions of years? At the very beginning of the birth of the solar system or more recently?
The development of space exploration with the Voyager and Cassini probes, and of course the ground instruments, provided us with information that Galileo and Laplace could not have dreamed of. This research allows us to feed theoretical models and numerical computer simulations that can answer all these questions. A group of Anglo-Saxon planetologists has just published in the famous newspaper Icarus an article leading to an astonishing conclusion: the rings of Saturn are ephemeral, they would have formed 100 million years ago, at most, and in 300 million years, they will disappear.
Everything is evolving in the Universe and nothing, except perhaps some basic laws of physics, remains from all eternity. It suffices to refer to the discovery of plate tectonics or the Big Bang theory. It is in the framework of this other representation of the World, this new paradigm of which the Terrians became aware for more than 50 years, that is inscribed the stupendous conclusion of the researchers. They relied on several works and, in particular, observations made in the infrared with the Keck instruments in Hawaii.
A shower of icy and charged particles on Saturn
These observations, dating from the early 2010s, specified the characteristics of the presence of many trihydrogen cations in the ionosphere of Saturn. That it can be found is not surprising since it is H3 +, the most abundant ion in the interstellar medium, where it remains stable, given the very low temperature and the extreme tenuity of this environment. The simplest triatomic molecule, in which three protons share two electrons, had already been detected in giant atmospheres for some time (1989, with Jupiter).But what proved to be instructive, this time around, is that H3 + ions are particularly present in bands in the northern and southern hemispheres where we know that dip and emerge lines of fields from the magnetosphere of Saturn. These bands are particularly bright but, on the contrary, they appeared dark on images taken by the Voyager 1 and 2 probes when they visited Saturn in the early 1980s.
Already in 1986, the planetologist John EP Connerney, better known as Jack Connerney, had interpreted these bands as the result of the influx of charged ice particles leading to "disperse" a fog present in these regions. the ionosphere; these bands becoming less brilliant, less contrasting and therefore darker.
Jack Connerney is back on the subject today, in the article by Icarus, written under the direction of his colleague NASA James O'Donoghue, which allows to fit the pieces of a puzzle.
It now appears that trihydrogen ions, in the bands under consideration, are the final product of chemical reactions from charged ice particles that have vaporized in the ionosphere. These particles come from the rings of Saturn where they acquired their charges, either under the effect of the ultraviolet ionizing radiation coming from the Sun, or in contact with the plasma produced by the collisions between the micrometeorites and the ice particles of these rings. By becoming charged, these particles then become sensitive to the magnetic fields of Saturn which guide them under the influence of the gravity of the planet along the lines of fields which will lead them in the dark bands of Voyager.
The amount of icy particles that can be removed from the rings can be evaluated over time. This is how we end up with the figure of 300 million years for the time that should remain to live to these rings. The phenomenon also constrains estimates of the age of the rings which should not exceed 100 million years, a figure whose order of magnitude is consistent with another estimate already advanced but, on another basis, there are some years.
James O'Donoghue explains: "We are fortunate enough to be there to see the ring system of Saturn, which seems to be in the middle of his life. But if the rings are temporary then we may have missed those of Jupiter, Uranus and Neptune when they were giants.
