Saturn is a rather strange place, full of secrets that seem to multiply the more we examine it. One of the biggest is literally one of the biggest things Saturn has: its rings. Surprisingly, while they are the most obvious and iconic feature of the planet, we do not know the answer to two basic questions: how old are they and how did they educate themselves?
But now we use data from the Cassini probe and its application to subtle models of the planet scientists have found an important fact about the rings: they are young. Very young, much younger than the planet. While Saturn was formed about 4.5 billion years ago, the rings are probably no older than 100 million years.
Although the rings look durable and timeless, they are almost certainly a transient feature. They are only there for a tiny fraction of the Saturn age ̵
And how did the scientists do that? find out?
It has to do with the mass of the rings, how much stuff is in it. In short, if the rings are solid, they are old and if they have a lower mass, they are younger. This usually has to do with erosion. The room is not really empty. Dust and other small particles are whirring around. Not much, but enough that they can work for long periods of time. As these micrometeoroids scrape into Saturn's rings, they erode the water ice particles that make up the rings. Over time, the rings wear out, with the smaller particles being drawn into Saturn by various forces (gravity and magnetism). If they have enough time, they will disappear completely.
We have a pretty good idea of how much sandblasting material is in space, so we know how quickly the rings are eroded. If we can determine the mass of the rings, we can work backwards to get an age estimate for them.
It turns out that the ring mass is hard to come by. But not impossible.
One way to get the mass of an object is to fly a spacecraft past it. The spacecraft's path and speed are affected by the gravity of the object, which depends on its mass. If one can measure this speed with sufficient accuracy, one can determine the mass of the object.
Cassini orbited Saturn for 13 years, and his speed could be measured with incredible accuracy, a fraction of a millimeter per second. However, until the end of the mission, the orbit was always outside the main rings, and this made it impossible to separate the mass of rings from the planet (what you get is the mass of the rings plus the planet and by no means) to separate them ).
But then the endgame approached the mission. The engineers sat Cassini on a series of 22 deep dives over the clouds of Saturn, far below the rings. This allowed the measurement of the ring mass …
But not easy. You had to understand the gravity of Saturn well enough to remove it from the calculations (for example, noise canceling headphones that remove background noise in a bar so you hear someone speak in your vicinity). That turns out to be pretty hard! If you are really far away from an object, the gravitational field is smooth and the total mass is easy to find.
However, if you are near this object, gravity will depend on the distribution of mass in that object. Imagine it this way: When you are standing in a plane on the ground, gravity is different than when you are standing near a mountain. This extra mass to the side will attract you and change the power.
Saturn has a lot of things that affect his gravity field. Most are easy enough to correct (like the fact that Saturn is not spherical, its fast spin makes it noticeably wider across the equator than through the poles). But it also affects the interior, and that's harder to understand. When a gas layer rotates faster around Saturn than one above or below it, the mass distribution changes, which in turn changes the shape of the gravitational field.
What the scientists found out when studying the Cassini data is that there is such a layer, deep in the atmosphere of Saturn. Up to a depth of about 9,000 kilometers, a massive layer of gas extends, which does not flow around like the mass of the surrounding atmosphere. By making relatively simple assumptions about the behavior of this gas, they can better match the observed Cassini data.
This allowed them to explain the gravity of Saturn and so could determine the gravity of Saturn gravity from the rings and thus their mass.
They note that the mass of Saturn rings is 1.54 ± 0.49 x 1019 kg – about 1.5 quadrillion tons. That's about 40% of the mass of the Saturn Moon mime with a diameter of about 400 km.
That's pretty small for such a great thing as the rings, which are 300,000. They have such a small mass that they have to be young. Given the erosion rate, the scientists find that they are between 10 and 100 million years old.
That's shocking. Various observations of the rings of Cassini show that the rings have only about 100 million years at the current loss rate before they disappear. In other words, we are fortunate that we can see Saturn with rings throughout the lifetime of the solar system! If the Jurassic Dinosaurs had telescopes, they would have seen Saturn completely naked. The rings did not exist yet!
Now that we know that they have not formed with the planet, it is curious to think about what created them. The fact that it is almost just water ice is a great hint. Perhaps Saturn has conquered a stray icy object from the outer solar system, a giant comet or a centaur, which was then torn apart by the immense gravity of Saturn. It is also possible that they were formed by the collision of two moons, which were crushed on impact and then spread to the rings.
The ring-forming mechanism is a very interesting question that we can now better narrow down. know the ring mass. Sometimes secrets deepen as you look deeper, but sometimes you get an answer that helps you understand the next secret. In that case, we literally had to look deeper. But our understanding is deeper now.
Saturn is a popular target for anyone looking through the eyepiece of a telescope. It is one of the main reasons why I am an astronomer at all. These rings look so perfect even by a small "goal", so beautiful and so timeless.
But they are not like that. This knowledge makes me a bit sad, but I also know that the universe is the way it is, and permanence is a vanishingly rare commodity. I am far from reducing my reaction to the rings, and I appreciate them all the more.