After the discovery of Neptune in 1846, scientists suggested that there might still be a ninth planet, and they set out to discover it. Finding the ninth planet was going to be difficult because it was very far away from Earth. Since the planet was so far away, it would be very dim in the sky, and they would need special equipment to locate it.
Percival Lowell was an astronomer who began looking for the ninth planet he called Planet X. He built a private observatory in Flagstaff, Arizona, hoping to find this planet. He had to prove it existed, and he was positive he could. Lowell tried many searches to find Planet X in his observatory, but had no success. His first search ended in 1909, but he started a second search in 1913. He and many other people searched for Planet X from 1913 to 1915. In 1915 Lowell published the results of his search. Unknown to him, that very same year, two small pictures of Planet X were recorded at his observatory. No one would discover those pictures for another 15 years. Along with the two small pictures of Planet X, Lowell also discovered 515 asteroids and 700 different stars no one had ever seen before. Even though he found all this, Lowell was still very disappointed that he didn't find Planet X. He died the next year, not knowing that he actually discovered the new planet.
Tombaugh's Good Luck
No one searched for Planet X for another twelve years. The next search began in April 1927. In December 1929, an amateur astronomer named Clyde Tombaugh was hired to search for Planet X. Tombaugh took photographs of the solar system every one or two weeks and looked for anything that shifted against the background of stars. This method was very successful and this 24-year-old lab assistant from Kansas discovered Planet X on Feb. 18, 1930. Lowell had missed Planet X because he never expected it to be so small. Tombaugh was lucky to have discovered Pluto by accident because Pluto is very far away from the sun and moves very slowly. It takes about 248 years to complete its orbit around the Sun. He is the only American to discover a planet.
Naming Planet X
Since Tombaugh discovered the new planet, he now needed to name it. Many ideas were given for naming Planet X including Lowell, Apollo, Minerva, and Constance. Finally Tombaugh chose a name an eleven-year-old English schoolgirl named Venetia Burney had chosen for Planet X. She named Planet X Pluto, after the Greek God of the underworld. Another reason Planet X was named Pluto is that it's so far away from the Sun that it is always in darkness. So naming it after the Greek God of the underworld.
Discovery of Pluto's Moon
Pluto has one moon named Charon. Jim Christy discovered it in 1978. Before that, it was thought that Pluto was much bigger because in the pictures of Pluto, Charon was blurred together with it, so it looked much bigger. Charon is only slightly smaller than Pluto.
Pluto has not been visited by any spacecraft from Earth and remains one of the most mysterious planets. Since it is very far from the sun it reaches temperatures of -400°F. It took so long to find Pluto because it was not easy to see through a telescope of poor quality, which the early astronomers used. Pluto is smaller then 7 of the solar system's moons, including the Earth's moon. Some scientists think that Pluto really is a moon that escaped Neptune's gravitational pull. However it is still going to remain the ninth planet of our solar system.
Unless otherwise noted, all images courtesy of NASA. Permission for use at http://www.nasa.gov/gallery/photo/guideline.html.
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