Can a planet or moon have two axes of rotation and remain tidally locked?

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Discussion Overview

The discussion explores the possibility of a planet or moon having two axes of rotation while remaining tidally locked. It examines theoretical implications, the effects of external forces, and the conditions under which such a scenario might occur.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether Uranus, if moved closer to the sun, would lose its current rotation before becoming tidally locked.
  • It is suggested that the moon's tidal locking could be influenced by its internal structure and distance from Earth, with some arguing that a solid object rotating on two axes would not experience interaction between those rotations.
  • Others propose that the absence of moons or planets rotating on two axes is curious, given the history of collisions during their formation.
  • Some participants discuss the concept of precession, noting that for an object to rotate on two axes, a constant torque must be applied, which is not present in freely rotating bodies.
  • A hypothetical scenario is presented regarding a perfectly round solid body in space rotating on two perpendicular axes, questioning whether it would continue to do so without external forces.
  • One participant asserts that removing the torque would cause one of the rotations to cease, raising further questions about the dynamics involved.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the feasibility of dual-axis rotation in celestial bodies and the conditions necessary for such a phenomenon. The discussion remains unresolved with no consensus reached.

Contextual Notes

The discussion includes assumptions about the nature of solid and non-solid bodies, the effects of external forces, and the implications of tidal locking, which are not fully explored or agreed upon.

Timoothy
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Uranus rotates on its side and its poles always point in the same direction...

http://www.ifa.hawaii.edu/~barnes/ast110_06/quizzes/disc02_fig01.png

...if it was moved close enough to the sun to become tidally locked, would it necessarily lose all of its current rotation by the time it became tidally locked?

Our moon is already tidally locked, so if it was struck by a large body which created a sideways rotation like Uranus has, could it remain tidally locked to Earth without losing its (new) sideways rotation?

Can a planet or moon rotate on two different axes, and if so, would the two rotations tend to slow each other down until it has only one axis of rotation?
 
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It is thought that the rotation of large bodies (planets) is a remnant from the rotational forces present during the formation of the solar system from the primordial cloud.

For the larger planets this rotational energy is dissipated very very slowly. Smaller objects such as the Earth's moon (and the lesser extent Mercury and Venus) for various reasons have become locked so the same side faces what it is orbiting.

It is generally thought that unless acted on by an outside force or body that these objects will keep rotating close to their original state.

All this said the planet Uranus, because it is large and distant from other large objects, would have to have been effected by something in the distant past. Probably an impact. And since Uranus is not reasonably solid like the Earths moon there is little that will act on it to change its present state other then another collision, it would not get locked to the sun.

Tidal locking of more solid objects is thought to be caused by a combination of gravitational and physical effects. The locking of the moon could have been caused by the cooling and partial solidification of its internal structure so that it gradually slowed down and stopped rotating with respect to the Earth., at the present time its heavier side is facing the Earth. This would not have happened as quickly if the moon was lighter or was further away from the Earth.

A solid object that is rotating on 2 axis has nothing that will have an effect between the two rotations. Not sure about a non-solid object!
 
Robot B9 said:
A solid object that is rotating on 2 axis has nothing that will have an effect between the two rotations.

If it's possible for a moon or planet to rotate on two axes, it seems odd that none do, because all moons and planets have surly been "bumped" by large objects while they were forming and since they formed which would have given them more than one axis of rotation, no?
 
One reason may be because of the align of the moons. On Earth we have a wobble due to the center of gravity off the Earth-Moon system called a Barycenter. Uranus with its moons Miranda, Ariel, Umbriel, Titania, Oberon and its rings may have a similar warped center of gravity.
 
Timoothy said:
If it's possible for a moon or planet to rotate on two axes, it seems odd that none do, because all moons and planets have surly been "bumped" by large objects while they were forming and since they formed which would have given them more than one axis of rotation, no?

For an object to rotate on two axes, there has to be a constant torque acting on it. This is called precession. For example, the Earth rotates around its polar axis, but because the pull of the Moon on the equatorial bulges applies a torque which tries to align the Earth's axis with the axis of the Moon's orbit, the Earth's axis also "wobbles".

A freely rotating object with no outside torque acting on it will only rotate on one axis.
 
Janus said:
For an object to rotate on two axes, there has to be a constant torque acting on it. This is called precession. For example, the Earth rotates around its polar axis, but because the pull of the Moon on the equatorial bulges applies a torque which tries to align the Earth's axis with the axis of the Moon's orbit, the Earth's axis also "wobbles".

A freely rotating object with no outside torque acting on it will only rotate on one axis.

Ok that explains why there aren't any moons or planets rotating on two axes in the "real world", but what about this hypothetical situation:

A perfectly round solid body (in outer space) is caused to rotate (equally) on two perpendicular axes, and then all outside forces are instantly withdrawn, will it continue to rotate on both axes without slowing down, eventually just rotate on one axis, or eventually not rotate at all?
 
Timoothy said:
Ok that explains why there aren't any moons or planets rotating on two axes in the "real world", but what about this hypothetical situation:

A perfectly round solid body (in outer space) is caused to rotate (equally) on two perpendicular axes, and then all outside forces are instantly withdrawn, will it continue to rotate on both axes without slowing down, eventually just rotate on one axis, or eventually not rotate at all?

One of those rotations will be in response to a torque applied to the spinning object. Remove the torque and this rotation ceases.
 

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