The Galaxies Newest Member

by Savannah Beckham

The Discovery of Pluto

It was American astronomer Percival Lowell who first questioned the idea of there being another planet somewhere near Neptune and Uranus. Lowell had noticed that the gravitational pull of something large was affecting the orbits of those two planets. However, even after observing what he called "Planet X" from 1905 until his death in 1916, Lowell never found it.


Thirteen years later, the Lowell Observatory decided to recommence Lowell's search for Planet X. They had a specially made powerful, 13-inch telescope built for this sole purpose. The Observatory then hired 23-year-old Clyde W. Tombaugh to use Lowell's predictions and the new telescope to search the vast skies for a new planet.

It took a year of long tedious work, but Tombaugh did find Planet X. The discovery occurred on February 18, 1930 while Tombaugh was carefully examining a set of photographic plates created by the telescope.

Despite Planet X being discovered on February 18, 1930, the Lowell Observatory wasn't ready to announce this huge discovery until they could dig a little deeper into their research.

After a few weeks, it was confirmed that Tombaugh's discovery was infact a new planet. On what would have been Percival Lowell's 75th birthday, March 13, 1930, the Observatory publicly announced to the world the astonishing news that a new planet had been discovered.

Once discovered, Planet X needed a name. Everyone had an idea that they thought was better than others. However, the name Pluto was chosen by 11-year-old Venetia Burney in Oxford, England on March 24, 1930 after she suggested the name "Pluto." The name signifies both the rough surface conditions (as Pluto was the Roman god of the underworld) and also honors Percival Lowell, as Lowell's initials make up the first two letters of the planet's name.

Pluto was considered to be the ninth planet in the solar system. Pluto was also the smallest planet, being less than half the size of Mercury and two-thirds the size of earth's moon.

Pluto is also the planet farthest from the sun. This great distance from the sun makes Pluto very inhospitable; it's surface is expected to be made up of mostly ice and rock and it takes Pluto 248 years just to make one orbit around the sun.

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In the archives of Lowell Observatory, under the guidance of archivist Antoinette Beiser, someone came across this typewritten memo – in its original, a few pages long. While it’s not clear who composed this note, someone has penciled “VM?” in the upper margin. Many believe VM stands for Vesto M. Slipher, director of the Observatory. In this memo, Slipher (we assume) is acknowledging that there was some delay in the announcement of the discovery of Planet X (Pluto). Clyde Tombaugh found the retrograding trans-Neptunian object on February 18, 1930. Lowell Observatory didn’t announce their findings until March 13. This happened to be Percival Lowell’s birthday as well as the date on which Uranus was first discovered.