The theory of an inner satellite ripped apart by the gravity of a gas giant 100-200 million years ago also explains the rings’ relative youth.
According to scientists, Saturn’s famous rings could result from a moon ripped apart by the planet’s gravity.
Based on data from the last stage of NASA’s Cassini mission, the study suggests that Saturn may have been ring less for nearly all of its 4.5 billion-year existence. However, about 160 million years ago, an inner moon got too close to the gas giant, causing it to be ripped apart and leave a trail of shattered icy fragments in its wake.
Chrysalis is the name given to the hypothetical lost moon.
“Like a butterfly’s chrysalis, this satellite was extended dormant and unexpectedly became active, and the rings emerged,” said Jack Wisdom, a planetary science professor at Massachusetts Institute of Technology and the study’s lead author.
Prof Scott Tremaine of Princeton’s Institute for Advanced Study, who was not involved in the research, called the findings “remarkable” because they have the potential to solve several different Saturn puzzles with “one bold but plausible hypothesis.”
Wisdom’s team explained why Saturn’s axis tilted about 27 degrees. According to theoretical models, the tilt was predicted to be caused by Saturn being trapped in a gravitational resonance with Neptune. However, these models are frequently sensitive to small changes in various variables.
The original explanation crumbled as the Cassini mission, orbited Saturn from 2004 to 2017, filled in details on everything from Saturn’s inner composition to the dynamics of the planet’s 83 moons. These new details suggested that Saturn had slipped past Neptune’s grasp at some point in the past.
This prompted the scientists to look for potentially disruptive events that could have resulted in this. The data fit unexpectedly well with the lost moon scenario. “We set out to try to explain Saturn’s tilt,” Wisdom explained. “However, we discovered that we needed to propose an additional satellite and then get rid of the satellite again.”
Wisdom and his colleagues used computer simulations to figure out the characteristics of a hypothetical moon. These indicated that Chrysalis entered a chaotic orbital zone between 100m and 200m years ago and had several close encounters with Saturn’s moons Iapetus and Titan. It eventually got too close to Saturn, and the collision ripped the moon apart, leaving a debris-strewn ring in its wake.
The absence of Chrysalis would explain Saturn’s current tilt and rings. It would also be consistent with measurements of the rings’ chemical properties, which date them to around 100 million years old but were dismissed by some because it was unclear how the rings could have formed so late in the planet’s history. “I think we make a pretty compelling case,” Wisdom said.
“We’ll never know for sure if an extra satellite was ever present in the Saturn system,” Tremaine said, “but explaining [several] puzzles with one hypothesis is a pretty good return on investment.”
Saturn’s rings weigh approximately 15 million trillion kilograms and are almost entirely composed of ice, 95% of which is pure water, and the remainder is ice.