An international team of scientists have successfully solved a longstanding riddle by discovering that planetary rings, such as those found in orbit around the planet Saturn, have universally similar particle distributions, and are in a steady state independent of their history.
The findings, which were published in the journal Proceedings of the National Academy of Sciences (PNAS), set out to determine if the icy rings around Saturn were unique in terms of their particle size distribution, or if the observed distribution was generic for all planetary rings.
They concluded that a power-law size distribution with large-size cutoff, as observed in the rings surrounding the gas giant was universal for systems where there was a sustained balance between aggregation and disruptive collisions. As a result, the same basic size distribution is expected for any ring system where collisions are involved, such as those around Uranus or Chiron.
“This was a fortunate collaboration of leading experts from different areas with astrophysicists,” lead author Professor Nikolai Brilliantov of the University of Leicester, told redOrbit. “The team was comprised of top-level specialists in kinetic theory, statistical physics, differential equations and numerical analysis who collaborated with leading scientists in the field of Saturn rings.”
Law of inverse cubes help explain universal nature of rings
As Professor Brilliantov, a member of the university’s Department of Mathematics explained in a statement, previous research on Saturn’s rings revealed that they are comprised of ice particles ranging in size from several centimeters to nearly 10 meters. Since these particles are most likely debris left over from a past catastrophic event, the varying sizes is not surprising.
What is surprising, however, is the that the relative abundance of different sized particles follows with a high degree of accuracy the mathematical law of inverse cubes, he said. In other words, the abundances of two meter particles is roughly eight times less that of one meter particles, the abundance of three meter particles is 27 times smaller, and so on.
Brilliantov said that this stays true up to the size of about 10 meters, at which point there is a sudden drop in abundance. The explanation as to why the rings follow the law of inverse cubes, and the reason for such a drastic drop at the 10 meter size range, had long remained a mystery, but the authors of the new study have come up with a solution by solving “an enormous number of differential equations” on incredibly fast computers, he told redOrbit via email.
“If particles comprising rings merge, colliding with very small velocities and break into small pieces, colliding with very large velocities, the distribution of particles’ sizes will have a universal form, provided the rings are in a steady state,” the professor said. “Hence, if one observes that a size distribution in rings deviates from the universal law, one can conclude that either the rings are not yet formed, or some catastrophic event has happened recently.”
“On the other hand, if the rings obey the universal size distribution, the parameters of the distribution provide a comprehensive information about the rings’ particles,” Brilliantov said, noting that he and his colleagues believe that these types of rings also exist beyond our Solar System.
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Feature Image: In this simulated image of Saturn’s rings, color is used to present information about ring particle sizes in different regions based on the measured attenuations of three radio signals. (Credit: NASA)
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