Cosmology Views

Tidal Locked Moons

Nearly all moons in the solar system are in an orbit called a tidal lock or in synchronous rotation. Either means the moon maintains one side facing the primary while moving in its elliptical orbit around that primary.

None of the planets exhibit this behavior in their orbit around the Sun except Mercury, which has a resonance as noted in Wikipedia:

Mercury rotates in a way that is unique in the Solar System. It is tidally locked with the Sun in a 3:2 spin–orbit resonance, meaning that relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun.

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definition from Wikipedia:

idal locking (also called gravitational locking, captured rotation and spin–orbit locking), in the best-known case, occurs when an orbiting astronomical body always has the same face toward the object it is orbiting. This is known as synchronous rotation: the tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner. For example, the same side of the Moon always faces the Earth, although there is some variability because the Moon's orbit is not perfectly circular. Usually, only the satellite is tidally locked to the larger body. However, if both the difference in mass between the two bodies and the distance between them are relatively small, each may be tidally locked to the other; this is the case for Pluto and Charon.

The effect arises between two bodies when their gravitational interaction slows a body's rotation until it becomes tidally locked. Over many millions of years, the interaction forces changes to their orbits and rotation rates as a result of energy exchange and heat dissipation. When one of the bodies reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit, it is said to be tidally locked.The object tends to stay in this state when leaving it would require adding energy back into the system. The object's orbit may migrate over time so as to undo the tidal lock, for example, if a giant planet perturbs the object.

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My comment:

The explanation says 'may migrate over time.'

When looking at the solar system now (which is after some time), which moons are NOT in synchronous rotation?

The answer is a very short list:

around Saturn:
Hyperion rotates 13d for 21.3d orbit

Ymir rotates 12h for 3.6y orbit

'Ymir is the largest retrograde irregular moon of Saturn' at about 18 km or 11 mi.

from Wikipedia:
 The outer irregular satellites follow moderately to highly eccentric orbits, and none are expected to rotate synchronously as all the inner moons of Saturn do (except for Hyperion).

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my comment:

I suspect they are too distant to detect any rotation.

around Neptune:

Nereid - rotates 12h for 360d orbit

around Pluto:

Styx  - rotates 3.24d  for 20.16d orbit
Nix - non-spherical  rotates 44h for 24.9d orbit

My comment after all of the above:

Cosmologists have an interesting caveat about a tidal lock changing over time.

When looking now, there are only 5 candidates. The current count of moons is either 175 or over 200 depending on the reference.

I began this post expecting to find more than 5 and one of those is explicitly not a sphere so it could be excused. Perhaps I missed others.

After reading the description of this behavior, apparently the number should be more but is not. At only 2.5% this behavior is more stable than I expected.

I expect Hyperion had to be explained and the statement  excused others to be found later.

The most striking statement, regardless of the % value:

"for example, if a giant planet perturbs the object."

Cosmologists explicitly accept Jupiter and Saturn  roamed the solar system. Their excursion is placed in the Late Heavy Bombardment Period.

I find references to that accepted excursion in conflict with the consistent rejection of Velikovsky.