One of the cornerstones of physics is that two objects, no matter how different they are, exert a force on each other. In most cases, size makes a big difference as the larger objects exert a much greater force on the smaller ones.
However, much smaller objects can also affect the larger object in the pair over long periods of time. Recently, a team of researchers from CNRS, the Sorbonne, and the University of Pisa found an example of the smaller object, or in this case a group of objects, that has an oversized impact on the larger. They discovered that Saturn’s moons actually caused its famous tilt.
Saturn, the second largest planet in the solar system, has a total of 82 discovered moons. Although there are many moons, over 96% of the mass in orbit around the planet exists especially on one moon: Titan. The other six “ellipsoidal” moons make up almost another 4% of the mass. However, Saturn itself has all of its moons together over 4000 times.
A top-down image of the orbits of some of Saturn’s larger moons with Titan in red. The moons outside of its orbit are (from outside to inside) Iapetus and Hyperion; those inside are Rhea, Dione, Tethys, Enceladus and Mimas.
Photo credit: Von! Original: rubble, vector: Mysid. – Own work based on: Titans orbit.jpg., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4819125
Recently, scientists have begun to take a closer look at Saturn’s moons, partly because of their potential as harbors of life and as the target of some upcoming missions. Upon taking a closer look, they found that the moons were moving away from their mother planet much faster than previously thought. When they recalculated some models at this increased speed, they found that Saturn’s tilt can be explained almost entirely by the gravitational effects of its moons.
About a billion years ago, the ring planet’s moons forced it into a state of resonance with itself that continues to this day. This resonance, along with a slight perturbation by Neptune as it moved through the early solar system, resulted in the 27 ° tilt we can see on the planet today.
Saturn with its noticeable axial tilt and its largest moon, Titan.
Credit: Credit: NASA / JPL-Caltech / Space Science Institute
It seems even more interesting that this axial tilt will continue for some time. According to the authors’ calculations, it could more than double in the next billion years.
Saturn isn’t the only gas giant in the solar system to get the same boost from its moons. Jupiter is currently being overturned from its moons, with the help of Uranus on the way. Five billion years from now, the largest planet in the solar system is expected to have an axial tilt of 10 times (3 °), making it even more angled than Saturn is currently.
Unfortunately, no one will be alive today to testify to this. But the fact that models can tell us this is going to happen is always impressive. This sustains a small force for a long time.
Learn more:
CNRS: Saturn’s tilt is caused by its moons
ZME Science: Saturn has tilted. The fault lies with its moons
Tech Explorist: Saturn’s tilt – caused by its moon – will increase over the next billion years
Mission statement:
Artistic impression of Saturn’s inclination and Titan’s migration.
Photo credit: Coline Saillenfest / IMCCE
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