Saturn has not always had its rings | Science

Saturn has not always had its rings | Science



Before burning against Saturn's atmosphere in September 2017, the probe Cassini He gave a final gift to science: to reveal when the rings that surround the gas giant formed. Using a sophisticated stratagem, Italian scientists have been able to determine the mass of the planet's belt and, with it, its age. The rings were formed less than 100 million years ago, long after the star they surround.

In the last phase of its operational life, the Cassini He snuck 22 times between Saturn and his rings in what the mission leaders called Grand Finale. In the last of those orbits he got caught by the attraction of the planet in a deliberate movement so that it does not contaminate the surface of Enceladus or Titan, in which it is believed there are conditions for life.

A group of scientists took six of these steps to study the mass and, especially, the gravity of the rings. Until then, it had been impossible to distinguish it from that exercised by the planet. For this, they recorded the variations in the speed of the ship with an accuracy of a few hundredths of a millimeter per second as it entered the space between rings and planet and escaped again. The measurements could be made thanks to a radio connection between the probe and three terrestrial antennas of the deep space network (one in the vicinity of Madrid).

"In essence, Cassini It acted as a mass that fell freely in the combined gravity field of Saturn and the rings, "explains the researcher at the Sapienza University in Rome and the study's lead author, Luciano Iess, in an email." Measure the speed at which Cassini It was falling in Saturn's gravity field and the rings were the key to determining the mass of the rings, "he adds.

The scientists took advantage of the steps of the 'Cassini' probe between Saturn and its rings to determine its mass and gravity

The result, published in the magazine Science, is that the series of rings that surround Saturn has a mass of about 1.54 × 1019 kilograms. That's 40% of the mass of Mimas, one of its medium satellites. But how does the dough help to know when the rings were formed?

"The relationship between the mass and the age of the rings is subtle," says Iess. Data obtained by other instruments on board Cassini they had shown that the rings are made up of 99% ice and a remaining 1% composed of microscopic silica particles. The probe had also determined the flow of particles around Saturn, proving that orbital motions scattered this matter over the ice at a constant ratio. "Measuring the mass of the rings has allowed us to estimate the total amount of impurities deposited and, therefore, calculate the time necessary for them to accumulate: between 10 and 100 million years," adds the Italian space engineer.

It seems an eternity, but Saturn was formed about 4.5 billion years ago. So the rings are newcomers. What this study has not been able to settle is how they were formed. The rings could have arisen from the disintegration of some of the 61 moons of the planet after the impact of a comet or the collision between them.

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