Discovery and Demotion of PlutoPluto travels around the sun in an elliptical (oval-shaped) orbit. At some point in its orbit, it comes closer to the sun than Neptune, the outermost planet. It stays inside Neptune's orbit for about 20 Earth years. This event occurs every 248 Earth years, which is about the same number of Earth years it takes Pluto to travel once around the sun. Pluto entered Neptune's orbit on Jan. 23, 1979, and remained there until Feb. 11, 1999. As it orbits the sun, Pluto spins on its axis, an imaginary line through its center. It spins around once in about six Earth days.
In 1905, Percival Lowell, an American astronomer and a young Kansas farmer, found that the force of gravity of some unknown object seemed to be affecting the orbits of Neptune and Uranus.
In 1929, Clyde W. Tombaugh, an assistant at the Lowell Observatory, used predictions made by Lowell and other astronomers and photographed the sky with a more powerful, wide-angle telescope. In 1930, Tombaugh found Pluto's image on three photographs. The planet was named after the Roman god of the dead. The name also honors Percival Lowell, whose initials are the first two letters of Pluto.
In 1978, astronomers at the U.S. Naval Observatory substation in Flagstaff detected a satellite of Pluto. They named it Charon. This satellite has a diameter of about 750 miles (1,210 kilometers). This moon has a density roughly one-third that of Earth. Thjsi reflects Charon’s rocky-icy composition.
In 1987, Jet Propulsion Laboratory, reported observations that showed Pluto has a substantial atmosphere. In 1996, the images, taken by the Hubble Space Telescope, show about 12 large bright or dark areas. The bright regions, which include polar caps, are probably frozen nitrogen. The dark areas may be methane frost that has been broken down chemically by ultraviolet radiation from the sun.
However, in 2006, the International Astronomical Union, for the first time, created a scientific definition for the word planet and thereby demoted the former major planet Pluto to the lesser status of dwarf planet. Pluto is now considered the largest member of a distinct region called the Kuiper belt. Michael brown, who discovered Eris, a new “planet” past Pluto prompted other astronomers to redefine the definition of planet. He presented his discovery at 25th annual Bunyan Lecture at Kresge Auditorium on Oct.25th 2006. His talk titled "Pluto, Eris and the Dwarf Planets of the Solar System”.Discovery and Demotion of Pluto
