Celestial rings are usually associated with gas giants, but even some of the smallest members of the Solar System sport the unusual configuration. Now, Japanese researchers have simulated how asteroids can keep their rings.
Chariklo is a centaur asteroid that orbits between Saturn and Uranus. It is about 250 kilometers (155 miles) across and has two rings. The researchers simulated both rings by modeling millions of real-size particles and, in doing so, discovered that the innermost ring should be unstable, with a lifetime of less than 100 years.
According to the paper, published in the Astrophysical Journal Letters, for the inner ring to survive, either the particles are much smaller than predicted or the asteroid is orbited by a smaller object that keeps it stable.
"Small ring particles is one possibility," co-author Professor Eiichiro Kokubo, from the National Astronomical Observatory of Japan, said in a statement. "If the size of the ring particles is only a few millimeters, the rings can be maintained for 10 million years. Another possibility is the existence of an undiscovered shepherd satellite which slows down the dissolution of the rings."
The researchers used a supercomputer to simulate 345 million particles of about 1 meter (3.3 feet) in size. By modeling how these particles interact with each other, they discovered that the material organizes itself into a striped pattern known as self-gravity wakes. These self-gravity wakes are responsible for the eventual break-up of the ring.
Detail of the simulation with the self-gravity wakes visible. Shugo Michikoshi, Eiichiro Kokubo, Hirotaka Nakayama, 4D2U Project, NAOJ
This analysis is not only important for Chariklo and Chiron, the other minor planet with rings, but also for the gas giants that have similar processes going on, although on a much larger scale.
"The interaction between the rings and a satellite is also an important process in Saturn's rings," lead author Dr Shugo Michikoshi added. "To better understand the effect of a satellite on ring structure, we plan to construct a new model for the formation of Chariklo's rings."
Until now, simulations of ring systems have been incredibly difficult due to the high number of particles and interactions involved. However, supercomputers are finally getting good enough to let researchers make simulations that are closer and closer to reality.