An unknown Moon is the cause of the tilt of the axis of rotation of Uranus
Even if Uranus has many points in common with Neptune, it has some peculiarities of its own. One of them is still difficult to explain. It is about its axis of rotation which knows a huge 98 degree inclination to its orbital plane. Other than that, it spins clockwise, counterclockwise to most other planets in the solar system.
In this regard, astronomer Melaine Saillenfest, of the national center for scientific research in France, exposed a new theory in an article, which his colleagues have not yet analyzed. The article was still accepted in the journal Astronomy & Astrophysics and is available on the preprint resource arXiv.
According to this new study, a moon moving away from the planet would cause the tilt. Possibly half the mass of Earth, it would have tipped the giant planet on its side.
Astronomers have turned to new explanations
Neptune and Uranus have similar masses, radii, rotation rates, dynamics, atmospheric compositions, and magnetic fields. These similarities suggest that they are born together. The hypothesis that a massive object, or a collection of smaller objects, struck Uranus and crushed it sideways, presents inconsistencies.
The scientists then thought of a swing that a giant ring system or a giant moon would have introduced early in the history of the solar system. However, Saillenfest and his colleagues found that through outward migration of Jupiter’s moonsthe percentage of its inclination would go from 3% to about 37% in a few billion years.
Then, looking at Saturn, they discovered that its current tilt of 26.7 degrees is probably the result of Titan’s rapid outward migration, its largest moon. They noticed that this phenomenon did not change the rotation rate of the planet. So what about the most tilted planet in the solar system?
Simulations of a hypothetical Uranian system
The simulations revealed that a moon with a minimum mass of about half that of Earth’s Moon could tilt Uranus to 90 degrees. This mass is about four times the combined mass of currently known Uranian moons. However, for this to be possible, it would have to move more than 10 times the radius of Uranus at a rate greater than 6 centimeters per year.
A larger moon, the size of Ganymede, could cause tilt and rotation observed today on Uranus. But there is no evidence to suggest that Uranus hosted a large enough moon, at a high enough rate of migration to produce this scenario. In addition, the researchers claim that it would be difficult to demonstrate by observations.
Nevertheless, understanding the current rate of migration of the moons of Uranus would answer these questions. If they are migrating at a high rate, it could mean thatthey were formed from the debris of the old moon after its destructionmany eons ago.