Discovery of Pluto

Astronomer expected that irregularities in Neptune’s motion would lead to the discovery of another remote, unknown planet.

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. He made a long, laborious mathematical analysis of the small ‘left over’ deviations of Uranus not attributed to Neptune.

In 1909 William Pickering argued that both Neptune and a remote Planet O were producing gravitational tugs on 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.

On February 18, 1930, Tombaugh found Pluto's image on three photographs, which were obtained a month earlier in January 23 and 29. 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.

The discovery was announced to the world in March 13, 1930.

In 1976, three astronomers at the University of Hawaii – Dale Cruikshank, Carl Pilcher and David Morrison – discovered hints of how just minuscule Pluto really is.

They found that Pluto’s suffice bears methane ice, which reflect much of the sunlight hitting it.

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. This 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. 

However, in August 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.
Discovery of Pluto