Three days before New Horizons’ closest pass by Pluto and we already have the first final image of the mission: this is the last “best” view we will have of Pluto’s Charon-facing side, as the spacecraft will be acquiring its most detailed images of the planet’s opposite side on July 14.
Pluto and its largest moon Charon are locked together gravitationally, a scenario called tidal locking. The face of one is always aimed at the same face of the other, and they orbit around a point in space (the barycenter) that is located between the two (but closer to Pluto.) Thus the image above shows the side of Pluto that Charon always “sees.”*
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