This is according to new research related to the creation of the Glorious Rings with the outward migration of Titan and a resonance between the rotation of Saturn and the orbit of Neptune.
A debate has raged for decades as to the age of Saturn’s rings. Some planetary scientists thought the rings might be as old as the planet itself, but in the early 1980s Peter Goldreich of Caltech and Scott Tremaine of the Massachusetts Institute of Technology (MIT) considers a relatively young age of 100 million years according to the speed of ice particles in the rings and how often they bump and wear.
Related: Saturn’s strange moon Titan looks a bit like Earth, and scientists might finally find out why
The end of the Mission Cassini at Saturn in 2017 brought more evidence for a young age. The spacecraft’s cosmic dust analyzer measured interplanetary dust falling on the rings, then, based on Cassini’s measurement of the rings’ mass, found that only 1% of the rings were dust , which means that the rings could only have been 100 million years old.
Although Cassini’s discoveries were mostly well received, some planetary scientists have urged cautionpointing out that some of the dust could be it’s raining rings and on Saturn itself, thus keeping the rings clean and making them look younger than they really are.
Now, new research, led by MIT’s Jack Wisdom, has found a physical mechanism that not only explains the tilt of Saturn’s axis of rotation and the eccentricity of its largest moon Titan’s orbit, but also states that the age of the rings should be close to 100 million years (opens in a new tab).
“Our scenario is the first explanation that predicts the age of the rings,” Wisdom told Space.com.
It is a curious story of resonances, couples, obliquities and precession. The obliquity of Saturn, that is to say the inclination of the planet with respect to the orbital plane of the solar system, is 26.7 degrees. In 2021, scientists led by Melaine Saillenfest from the Paris Observatory showed that relatively migration out of Titan’s orbit (opens in a new tab) could have tipped Saturn by that amount.
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Saturn also wobbles on its axis in a phenomenon called precession. It is the same effect that makes the axis of rotation of a spinning top turn in a circle. It is not unusual for a planet’s axis of rotation to precede – Earth’s axis of rotation also precedes by thousands of years. Today, the North Pole of the Earth points more or less towards the North Star, Polarisbut in a few thousand years, precession will mean that the north pole will be rather points to the star Vega.
In the case of Saturn, precession is primarily driven by Titan as the sun’s gravity pulls on the moon, resulting in torque on Saturn. A torque is a twisting force, and in the case of Saturn, the torque acts on Saturn’s axis of rotation, causing it to precess.
At one point, as the frequency of Saturn’s precession increased, it resonated with the precession of the node of Neptune’s orbit, that is, where Neptune’s orbit intersects the plane of the ecliptic. A resonance is an amplifying effect, like the classic example of pushing a child on a swing. Push at the right time and the swing range can increase. Resonances in the solar system are gravitational and are tied to specific frequencies of occurrence, in this case the rate of Saturn’s precession and the precession of the node of Neptune’s orbit.
However, today the frequency of Saturn’s precession and the precession of Neptune’s orbit are not in resonance, but are just outside, their frequencies not quite matching.
Is it possible that something happened to pull Saturn and Neptune out of resonance? “We propose that there was an additional satellite that was lost due to chaotic orbital instability, and which encountered Saturn and formed the rings,” said Wisdom, who names the hypothetical moon “Chrysalis.”
In their hypothesis, the Wisdom team proposes that Chrysalis also contributed torque on Saturn, putting the ringed planet in resonance with Neptune. However, their computer simulations show that between 100 and 200 million years ago, Chrysalis itself would also have entered into orbital resonance with Titan – for every three orbits of Saturn that Titan made, Chrysalis would make one. This resonance would have pushed Chrysalis, like the child on a seesaw, and destabilized its orbit, eventually seeing it too close to Saturn where the gravitational tides tore it apart to form the famous rings. Without the Chrysalis couple, Saturn’s precessional frequency would have decreased, moving it just out of resonance with Neptune.
Scott Tremaine, who first hypothesized at young age, describes the new work as “remarkable”, adding that, “Of course, we will never know for sure if an additional satellite was once present in the Saturn system, but explaining four riddles [Saturn’s obliquity, the existence of the rings, the age of the rings, and Titan’s eccentric orbit] with an assumption is a pretty good return on investment.”
The research was published online Thursday, September 15 in the journal Science (opens in a new tab).