Pluto and Charon

After the discovery of Neptune, there was a flurry of astronomical activity to discover another planet. It only seemed logical that there should be more planets after Neptune. By the late ninteenth century astronomers had charted slight anomolies in the revolutions of Uranus and Neptune, which were traceable to the gravitational effect of another body further out in the solar system. Around the turn of the century a man called Percival Lowell embarked on a systematic approach of the heavens, probing for what he called 'Planet X'. When Lowell died in 1916, William Pickering continued the search for Planet X, which he called 'Planet O'. In 1915 and 1919, Pluto was photographed but not recognised because it was much fainter than it had been predicted to be. In 1929 the Lowell Observatory at Flagstaff, Arizona, resumed the search using a 13-inch telescope and a wide-feild survey camera. On 18 February 1930 a young astronomer called Clyde Tombaugh identified a new planet in some photographs he had taken the previous month. He had found Pluto. Pluto's size is estimated to be between 3456 kilometers and 2200 kilometers, making it smaller than seven planetary moons. Pluto's temperature rarely creeps above -175 degrees C, and it's rocky surface is known to contain methane. Pluto is thought to have a rocky core and might have a tenuous methane vapour atmosphere. Pluto makes a complete revolution of the Sun every 248 Earth years, and its rotational period is estimated at 6.3 times that of Earth's. Pluto's moon Charon was discovered in 1978. James Christy was atempting to measure Pluto's size, and he thought he'd noticed that Pluto was not spherical. Further investigation led him to the conclusion that there was a satellite very close to Pluto. Further calculations suggested that Charon might be only 16,900 kilometers from Pluto.