In 1930, when a former farm boy - Clyde Tombaugh discovered the ninth planet, which he named Pluto, after the Roman god of the Underworld. The first two letters of the name also served to posthumously honor his patron, astronomer Percival Lowell. According to an article published in the 7 January 2000 issue of Science magazine, researchers from the California Institute of Technology and the University of Nevada-Reno, claim to have discovered crystalline water and ammonia ice on the surface of Pluto's moon, Charon. Prior to this data collected by Voyager, surveys have revealed that this ice is a part of similar sized moons in the outer solar system. Until the 1970s' the world did not even know of Charon. Pluto has a diameter of 1,413 miles, while Charon's is 728 miles. As far as relative planet-to-satellite size ratios go, this system stands out as the largest body compared to parent planet in the Solar System. The Earth and its moon however, come close. But unlike the Earth/Moon system, their rotations are both exactly the same (6.387 days), this means that they always show the same face to each other. Charon is 19,640 km (12,177 miles) from Pluto. This is real close as compared to the Earth's moon, which is 230,600 miles from the Earth.
The discovery of Charon was a very fortuitous event in 1978, when astronomer Jim Christy, noticed a previously unseen bump on images of Pluto recorded at the U.S. Naval Observatory in Arizona. He crosschecked with numerous other images that were taken in the past decade. After noting that the feature appeared in different spots on the surface in different images, he realized that it had the same day as the planet. Christy wanted to name it in honor of his wife, Charlene, but the established international naming rules for astronomical objects prevented this. He found a way around the problem when he found that the name of the ferryman who piloted dead souls across the River Styx and into Pluto's realm, was named Charon. It consists of slightly different materials than Pluto, and is suspected to have a very tenuous atmosphere. It may even share an atmosphere with the planet, since they orbit so closely together. Recently the Hubble Space Telescope has been able to produce sharp images that show them both as distinct bodies.
Charon's discovery has led to the unearthing of some answers that were previously unknown to astronomers. It gives clues to Pluto's pronounced axial tilt. One of the accepted theories is that something huge hit the planet. This was in accordance with the times when it was common for large-sized celestial objects to crash into planets. This was because these objects had not decided upon their orbits, Uranus, Venus, and Earth, were all hit and their axial tilts changed. Charon must have hit Pluto. As a double world, they orbit a common center of mass. Moons and their planets always share a common center of mass, but it usually lies deep inside the parent planet. This is not the case here: the center of mass lies between the two worlds, and it is this center of mass that orbits the sun.
While Pluto is thought to be made up of a mixture of rock and ice, Charon is thought to be almost completely composed of various ices. Moons such as this, that are very cold, could still be harboring live geology. The reasons for these could range from gravitational factors to the orbital patterns. Uranus's moons - Ariel and Umbriel - both of which demonstrate clear evidence of geological activity at some point in their life histories, are similar in size to it.