Mystery solved behind birth of Saturn’s rings
A team of researchers has presented a new model for the origin of Saturn's rings based on results of computer simulations. The results of the simulations are also applicable to rings of other giant planets and explain the compositional differences between the rings of Saturn and Uranus.
|Image of Saturn's rings taken by the Cassini spacecraft [Credit: NASA/JPL/STScI]|
The present study focused on the period called the Late Heavy Bombardment that is believed to have occurred 4 billion years ago in our solar system, when the giant planets underwent orbital migration. It is thought that several thousand Pluto-sized (one fifth of Earth's size) objects from the Kuiper belt existed in the outer solar system beyond Neptune. First the researchers calculated the probability that these large objects passed close enough to the giant planets to be destroyed by their tidal force during the Late Heavy Bombardment. Results showed that Saturn, Uranus and Neptune experienced close encounters with these large celestial objects multiple times.
|Image of Uranus' rings taken by the Hubble Space Telescope [Credit: NASA/JPL/STScI]|
The researchers also simulated the long-term evolution of the captured fragments using supercomputers at the National Astronomical Observatory of Japan. From these simulations they found that captured fragments with an initial size of several kilometers are expected to undergo high-speed collisions repeatedly and are gradually shattered into small pieces. Such collisions between fragments are also expected to circularize their orbits and lead to the formation of the rings observed today.
These findings illustrate that the rings of giant planets are natural by-products of the formation process of the planets in our solar system. This implies that giant planets discovered around other stars likely have rings formed by a similar process. Discovery of a ring system around an exoplanet has been recently reported, and further discoveries of rings and satellites around exoplanets will advance our understanding of their origin.
(1) Late Heavy Bombardment: a period of orbital instability that occurred in our solar system approximately 4 billion years ago. It is thought that during this period there were many small bodies that did not ultimately become planets that existed in orbit beyond Neptune. As a result of 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 planets that had already formed. It is thought that most of the craters on the surface of the moon were formed during this period.
(2) Kuiper belt objects: A large number of small bodies made of ice and rock that exist beyond the orbit of Neptune.
The findings were published in Icarus.
Source: Kobe University [October 31, 2016]