Why is the Pluto and Charon system called a unique pair?

Pluto and Charon face each other by the same hemispheres, the periods of their rotation around their axes and the orbital period of Charon coincide, they are equal to 6.4 days.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.