Has the mystery of the formation of Saturn's rings been solved?

A team of researchers presented a new model as to the origin of Saturn's rings based on the results of computer simulations. The results of the simulations also cover the rings of other giant planets and explain the differences between the shape of the rings of Saturn and Uranus-Uranus.

A team of researchers presented a new model as to the origin of Saturn's rings based on the results of computer simulations. The results of the simulations also cover the rings of other giant planets and explain the differences between the shape of the rings of Saturn and Uranus-Uranus. The findings were published on October 6 in the online version of "Icarus".

The lead author of the paper is Yudo Ryuki of Kobe University in Japan, and his colleagues Stébon Charnoz of the University of Paris Diderot, Prof. Otsuki Keiji of Kobe University and Prof. Ganda Hidenori of the Tokyo Institute of Technology.

The giant planets in our solar system have very diverse ring systems. Observations show that Saturn's rings are composed of more than 95% icy particles, while the rings of Uranus and Neptune are dark, and may be composed of heavier rock. Since Saturn's rings were first observed in the 17th century, the study of the rings has been expanded using ground-based telescopes, and spacecraft that have orbited Saturn, the last of which so far is Cassini. However, the origin of the rings was still unclear and the mechanisms that led to the creation of the diverse ring systems were still unknown.

The current study focused on a period known as the Late Heavy Bombardment, which is estimated to have occurred about 4 billion years ago in our solar system, when the giant planets underwent orbital migration. The study estimates that several thousand bodies the size of Pluto (one-fifth the size of Earth) orbit the Kuiper belt in the outer solar system beyond Neptune. First, the researchers calculated the odds that these large objects passed close enough to the giant planets and were destroyed by their tidal forces during the late heavy bombardment. The results of the study showed that Saturn, Uranus and Neptune experienced close encounters with these large celestial objects several times.

Members of the research team used computer simulations to study the disturbance caused to these Kuiper belt objects by tidal forces as they passed near the giant planet. The results of the simulations vary according to the initial conditions, such as the trajectory of these objects and their minimum approach distance to the planet. However, they found that many fractions that make up 0.1-10% of the initial mass of these objects were captured in orbits around the planets. The combined mass of these captured fragments was found to be sufficient to account for the mass of the current rings surrounding Saturn and Uranus. In other words, these planetary rings were formed when large enough objects passed very close to the giants and broke up.

The researchers also simulated the long-term evolution of the fragments captured using computers at the National Astronomical Observatory of Japan. These simulations revealed that fragments with an initial size of several kilometers were expected to undergo high-speed collisions and break up into smaller and smaller pieces. The collisions between the fragments are also expected to round their course and lead to the formation of the rings we see today.

This model can also explain the density difference between the rings of Saturn and Uranus. Compared to Saturn, Uranus (and Neptune) has a higher density (the average density of Uranus is 1.27 grams per cubic meter and that of Neptune is 1.64 grams per cubic meter, compared to the density of Saturn - 0.69 grams per cubic meter). This means that in the cases of Uranus and Neptune, the objects can pass close to the planet where they experience very strong tidal forces. Saturn, on the other hand, has a lower density and therefore the rings have a relatively large diameter because objects that pass closer will collide with the planet. As a result, if objects in the Kuiper belt that have layered structures such as a rocky core and an icy shell pass near Uranus or Neptune, in addition to the icy shell, the rocky core will also be destroyed, joining the rings and causing the vehicle to be rocky. However, if they pass by Saturn, only the icy mantle will be destroyed, and the composition of the rings will be ice. This explains the differences between the rings.

These findings illustrate that the rings of the giant planets are natural byproducts of the planet formation process in our solar system. This means that giant planets discovered around other stars must also have rings formed by a similar process. The discovery of a ring system around a planet was recently reported, further discoveries of rings and moons around planets outside the solar system will advance our understanding of their origin.

Comments

(1) The Late Big Bang: a period of orbital instability that occurred in our solar system about 4 billion years ago. It is estimated that during this period there were many small bodies that did not form into planets in orbit beyond Neptune. As a result of the gravitational interactions with the giant planets, the orbits of these small bodies became unstable, and many of them entered the solar system and collided with the already formed planets. It is estimated that most of the lunar craters were formed during this period.
(2) Kuiper belt objects: a large number of small bodies made of ice and rocks that exist beyond the orbit of Neptune.

for the scientific article
to the notice of the researchers