Astronomers think they know why Uranus’ strange axial shift

(ORDO NEWS) — Uranus marches to the beat of his own strange little drum.

Despite the fact that it has much in common with another ice giant in our solar system, Neptune, it has a number of features that are unique to it.

One of them is impossible not to notice: its axis of rotation is displaced so much that it can just as well lie down. This is a whopping 98 degree tilt from the plane of the orbit.

And, to top it all off, it rotates clockwise, that is, in the opposite direction to the direction of most other planets in the solar system.

A new study has found a plausible explanation for this strange behavior: The moon is migrating away from the planet, causing Uranus to flip onto its side.

And it doesn’t even have to be a big moon. This could happen with a mass equal to half of our moon, although a larger moon would be a more likely rival.

The reasoning is presented in a paper led by astronomer Melaine Silenfest of the National Research Center. Scientific research in France.

This paper, which has not yet been peer-reviewed, has been accepted by the journal Astronomy & Astrophysics and is available on the arXiv preprint resource.

Scientists have come up with models to explain this strange phenomenon. behavior such as a massive object colliding with Uranus and literally kicking it in the side, but a group of smaller objects is a more preferred explanation.

However, this hypothesis raises questions that are even harder to explain: namely, this annoying resemblance to Neptune.

These two planets have very similar masses, radii, rotational speeds, atmospheric dynamics and composition, and wacky magnetic fields.

These similarities suggest that the two planets could have been born together, and it becomes much more difficult to reconcile them when planet-tipping blows are added to them.

This prompted scientists to look for other explanations, such as a wobble that could have been caused by a giant ring system or a giant moon early in the solar system’s history (albeit with a different mechanism).

But then, a few years ago, Silenfest and his colleagues discovered something interesting about Jupiter.

Thanks to its moons, the inclination of the gas giant could increase from its current negligible 3 percent to about 37 percent in a few billion years due to outward migration of its moons.

Then they looked at Saturn. and found that its current tilt of 26.7 degrees could be the result of a rapid migration of its largest moon, Titan. They found that this could happen with almost no effect on the planet’s rotational speed.

Obviously, this raised questions about the most tilted planet in the solar system. So the team ran simulations of a hypothetical Uranian system to determine if a similar mechanism could explain its features.

Satellite migration is not unusual. Our own Moon is currently receding from Earth at a rate of about 4 centimeters (1.6 inches) per year.

Bodies rotating around a common center of gravity act on each other with a tidal force, which gradually slows down their rotation. In turn, this loosens the grip of gravity, so that the distance between two bodies increases.

Returning to Uranus, the team ran simulations with a number of parameters, including the mass of a hypothetical moon.

And they found that a moon with a minimum mass about half the size of Earth’s moon could tilt Uranus 90 degrees if it migrated more than 10 times the radius of Uranus at a rate of more than 6 centimeters per year.

However, a larger moon comparable to Ganymede was more likely in simulations to cause the tilt and rotation we see on Uranus today.

However, the minimum mass – about half of the Earth’s moon – is about four times the combined mass of the currently known satellites of Uranus.

The work also explains this. At a tilt of about 80 degrees, the Moon destabilized, causing a chaotic phase for the spin axis, which ended when the Moon eventually collided with the planet, effectively “petrifying” Uranus’ axial tilt and rotation.

“This new picture of the tilt of Uranus seems very promising to us,” the researchers write.

“To the best of our knowledge, this is the first time that a single mechanism has been able to both tilt Uranus and petrify it. The axis of rotation in its final state without causing a giant impact or other external phenomena.

Most of our successful launches peak at the location of Uranus, which is a natural result of the dynamics,” they continue.

“This picture also seems attractive as a general phenomenon: Jupiter is about to enter a tilt phase today, Saturn may be halfway there, and Uranus would complete the last stage with the destruction of its moon.”

This is true. it is not clear whether Uranus could have had a moon large enough and with a high enough migration rate to create this scenario, and the researchers say this would be difficult to show through observations.

However, a better understanding of the current rate of migration of Uranus’ moons will help resolve these issues. questions.

If they migrate at a high rate, it could mean that they formed from the debris of the ancient moon after its destruction many millennia ago.


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