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What places on Pluto and Charon are facing each other? Are Pluto and Charon perfectly tidally locked, or is there a slow rotation over time? And how long after formation should they have become tidally locked? Before or after the late heavy bombardment?

EDIT to add the image series of Pluto below, found at University Today

enter image description here

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  • $\begingroup$ Here's a related question on the Moon with math worked out. astronomy.stackexchange.com/questions/1859/… There are problems with accuracy as they depend highly on how close Pluto and Charon were at the time of formation. $\endgroup$
    – userLTK
    Oct 7, 2015 at 13:00

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As New Horizons past through the Pluto system, it travelled so that the spacecraft was on the far side of Pluto, as seen from Charon. It did this so both Pluto and Charon were roughly in the same direction, so the space craft would not have to rotate 180 degrees between imaging Pluto to imaging Charon.

It means that in images of Charon, the face that you can see is roughly the face that faces Pluto, However the it is the far side of Pluto (the side with the "whale" and the "dots" that faces Charon.

Tidal locking is pretty stable. See our own moon: it is locked, and has been for a long time. There is likely to be some wobble, just like the libations of the moon, but no overall rotation of either Pluto or Charon.

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    $\begingroup$ As I understand it, libations are largely a factor of orbital eccentricity more than anything else, as a planet's or moon's rotation isn't going to speed up or slow down in relation to it's orbital arc. Charon, having a very nearly circular orbit should have minimal libations. en.wikipedia.org/wiki/Charon_%28moon%29 $\endgroup$
    – userLTK
    Oct 7, 2015 at 4:42

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