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Why does Charon always show the same side to Pluto?
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Pluto
Pluto as observed by the New Horizons spacecraft, July 13, 2015.
Charon always shows the same side to Pluto because it is in a state of synchronous rotation, meaning its rotation period is identical to its orbital period.12
This phenomenon occurs because of gravitational (tidal) interactions between the two bodies. These same forces have also synchronized Pluto’s rotation period with Charon’s orbital period, which is why Charon remains fixed above the same location on Pluto’s surface and is visible from only one of Pluto's hemispheres.12