Pluto's Moon Charon
A newly discovered mountain range lies near the southwestern margin of Pluto's heart-shaped Tombaugh Regio (Tombaugh Region), situated between bright, icy plains and dark, heavily-cratered terrain. Image Credit & Copyright: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
The planet Uranus has 27 known moons, most of which were not discovered until the space age. The largest five are Oberon, Titania, Miranda, Ariel and Umbriel.
A global map of Pluto's largest moon image, obtained Jan. 22, 1986. Image Credit & Copyright: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
The Discovery of Charon
Charon was discovered in 1978 when sharp-eyed astronomer James Christy noticed images of Pluto were strangely elongated. The blob seemed to move around Pluto. The direction of elongation cycled back and forth over 6.39 days - Pluto's rotation period. Searching through their archives of Pluto images taken years before, Christy found more cases where Pluto appeared elongated. Additional images confirmed he had discovered the first known moon of Pluto.
Charon is more neutral grey than Pluto (which has a red tinge), indicating that they have different surface compositions and structure.
Charon's Profile:
Age: About 4.5 billion years old.
Distance from Pluto: Charon is 19,640 km (12,200 miles) away from Pluto. Orbital period is 6.39 Earth days.
Size: Charon is the largest of Pluto's moons. It is 1207 km (750 mi) in diameter, almost half the size of Pluto. They are so close in size that they are sometimes referred to as a double dwarf planet system.
Pluto's largest moon Charon are revealed in this image from New Horizons' Long Range Reconnaissance Imager, taken late on July 13, 2015. Image Credit & Copyright: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute