Saturn’s largest moon Titan has an outsized effect on the planet’s tilt, and its outwards migration could knock the planet onto its side and doom Titan itself.
Titan is moving away from Saturn at a rate of about 11 centimetres per year. That isn’t too strange – Earth’s moon is migrating away from our planet too, at a rate of just under 4 centimetres per year – but it is unexpectedly fast. As Titan’s orbit moves further from Saturn, it affects the planet’s spin by making it wobble more quickly on its axis. This wobble is slowly tilting Saturn.
“If Titan goes on migrating as predicted from this observed rate, then the axis tilt of Saturn will probably grow in the next billions of years,” says at the French National Centre for Scientific Research.
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He and at the University of Pisa in Italy conducted a series of simulations of this process. They found that Saturn will eventually reach a tilt of 90 degrees, meaning its spin will be perpendicular to the plane in which it orbits the sun.
A similar mechanism could explain why Uranus is tilted by 98 degrees, a feature that astronomers have largely attributed to major collisions in the planet’s past. That explanation is still under debate, though, so this alternate mechanism could be a solution.
Tilting Saturn isn’t the only effect that Titan’s migration will have. If its orbit continues to widen, it will eventually reach a critical point at which the various gravitational forces on it destabilise its trajectory. The researchers found that this will happen when Titan is about twice as far from Saturn as it is now. At that point, their simulations showed that Titan will likely be either tossed out of Saturn’s system or fall towards the planet.
“The destabilisation of Titan would have strong consequences on the whole satellite system of Saturn, with possibly further ejections or collisions between moons,” says Saillenfest.
The fact that this will take billions to tens of billions of years means that it may not actually happen, though. If it takes long enough, the sun will become a red giant before then, devouring the inner planets and catastrophically reshaping the entire solar system.
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