Tidal locking and rotation

In summary: 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
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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!
 
  • #3
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?
 
  • #4
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.
 
  • #5
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.
 
  • #6
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?
 
  • #7
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.
 

1. What is tidal locking?

Tidal locking is a phenomenon in which an object, such as a moon or planet, has a rotation period that is equal to its orbital period. This means that the same side of the object always faces its parent body, resulting in one side always being in daylight and the other always being in darkness.

2. What causes tidal locking?

Tidal locking is caused by the gravitational forces between the two objects. As the smaller object orbits around the larger one, the gravitational pull of the larger object creates a bulge on the smaller object. This bulge creates a torque that slows down the rotation of the smaller object until it becomes tidally locked.

3. Which celestial bodies are tidally locked?

Several moons in our solar system are tidally locked to their parent planets, including our moon, Mercury, and Pluto's moon Charon. In addition, many exoplanets have been discovered to be tidally locked to their host stars.

4. Can tidal locking occur in both directions?

Yes, tidal locking can occur in both directions. This means that the smaller object can either become tidally locked to its parent body, or the larger object can become tidally locked to the smaller one. An example of the latter is the Pluto-Charon system, where both objects are tidally locked to each other.

5. What are the effects of tidal locking?

The most noticeable effect of tidal locking is that one side of the object always faces its parent body, resulting in extreme temperature differences and weather patterns. Other effects include the slowing down of the object's rotation, changes in its orbit, and the formation of tidal bulges and ocean tides.

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