Reading about stackexchange Q&A about tidal locking and libration, I wondered about libration and tidal locking emergence.

It seems to me that tidal locking process starts when orbiting body's rotation about its own axis changes direction for the first time, initiating some sort of pendulum state, achieving at first close to 360° swings, then slowly dampening until it looks like our today's own moon's libration, eventually vanishing until full lock, assuming "perfect" circular orbit.

Now considering eccentric orbits and children swings.

Could there be some orbital configuration, where orbiting bodies, their respective masses, mass concentration in smaller body, eccentricity, radii and everything else involved, reach a state of resonance that transforms what should ultimately end up in a tidal locking situation, into some self-balanced rocking or swinging stability, using the same principles used by children on a swing, moving their legs to offset center of mass?

If children legs are replaced by eccentricity, could it lead to some "long term stable" weird motion, allowing for instance "years" where, seen from the orbiting body, the sun rocks between rise and set six times in a row during the same "day", then goes for 2 prograde full revolutions, rocks again for some time, goes for one retrograde revolution, and so on for millions of years?

I agree this looks rather chaotic, but if this weird part is unrealistic for obvious reasons I don't understand, could it at least allow stable long term lasting extreme classical librations? Let's say +/- 175°?

enter image description here

(dark blue part of small body is mass concentration, frame of reference is centered on small body)

EDIT: I think the illustration I made wrongly assumes mass concentration is always at a constant longitude in the small body. Which may not be the case for bodies in hystrostatic equilibrium, or soft bodies where mass could constantly migrate towards orbited large body. Maybe this illustration is only valid for small bodies with no internal mass displacement, such as a rocks or something small. (?)

  • $\begingroup$ You're essentially describing Io. Resonances with Europa and Ganymede keep it in an eccentric orbit, so it "rocks" with respect to Jupiter and the tidal deformations change both in direction and intensity. The resulting tidal heating is what makes it a little ball of volcanism. (en.wikipedia.org/wiki/Io_(moon)#Tidal_heating) $\endgroup$ – Christopher James Huff Jul 15 '20 at 14:45
  • $\begingroup$ @ChristopherJamesHuff I don't see anything there or in the main article about Io doing anything besides rotating at a constant rate. The "rocking motion" discussed in this question refers to the rotation of the object around its own axis, repeatedly turing faster and slower or even stopping and rotating in the other direction for a while. $\endgroup$ – uhoh Jul 16 '20 at 10:08
  • $\begingroup$ I don't believe a rapid change of rotation speed and direction is possible for a small moon. The moon would disintegrate. $\endgroup$ – Uwe Jul 16 '20 at 10:57
  • $\begingroup$ @uhoh That's because the rotation rate of Io is almost constant. That is in fact why it "rocks". $\endgroup$ – Christopher James Huff Jul 16 '20 at 12:14

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