A moon of Saturn destroyed 160 million years ago could not only explain the majestic rings of the gas giant, but also help answer several other mysteries about the ringed planet. That’s the opinion of a US research team that has carried out extensive simulations of Saturn’s history based on new data. As they now explain, such a moon could explain similarities between Saturn and Neptune that have not yet been conclusively explained. Also, that would answer why the rings are so young. Their models are based on data collected by the Saturn probe Cassini shortly before its end in that “Grand Finale” after it crashed into Saturn.
A vanished moon named Chrysalis
Like the research group at Jack Wisdom from the Massachusetts Institute of Technology now explains, astronomers have long assumed that Saturn’s tilt is due to gravitational interactions with Neptune. This so-called precession is almost identical for both. When the Saturn probe Cassini discovered that Titan was moving away from it faster than expected, it indicated that Saturn’s largest moon was keeping it in resonance with Neptune. In order to confirm this, however, one had to know the exact moment of inertia of Saturn, because depending on whether the mass is concentrated in the center or not, the imbalance can be assessed differently.
Thanks to the data Cassini collected just before its demise, the team writes that the distribution of masses can now be studied much better and a model that fits them can be created. Surprisingly, however, the result was that Saturn and Neptune once orbited the sun synchronously, but no longer. Another moon that once existed but no longer orbited Saturn was able to resolve this discrepancy. Based on the simulations, they were even able to determine its properties. The moon, which they dubbed Chrysalis, was about the size of Iapetus – Saturn’s third-largest moon – which it approached several times during a chaotic phase less than 200 million years ago. The Titan also experienced such approaches, they write.
Eventually Chrysalis came so close to Saturn that its gravity tore it apart. The majority of its components then fell into the gas giant, a small remainder formed the iconic rings. “It’s a really nice story, but like any other result, it needs to be verified by others now,” Wisdom said. After all, it would explain the late formation of the rings and the precession of Saturn. They have been considered a comparatively temporary phenomenon for a while. In 2018 it was determined that they could have disappeared again in 100 million years. The new study by Wisdom and his team has now been published published in the scientific journal Science.
(Image: NASA/JPL-Caltech/Space Science Institute)