Pluto – Is it a Planet?


A Planet Lurking in the Darkness?

In the mid-1800s, astronomers began wondering if there was something out there besides Neptune – perhaps another planet – that accounted for the discrepancy in Uranus’ orbit. Astronomers were keenly interested in discovering what lurked in the darkness. And they began coming up with names for the unknown planet, including ‘Hyperion’, ‘Planet X’, and  ‘Planet O’.

Teams of astronomers spent years searching for the unknown plant. Finally, in 1930, Planet X was found by Clyde Tombaugh, who was working for the Lowell Observatory at the time. Tombaugh’s story is unusual. He was an itinerant hobbyist – he had no background in astronomy, was self-educated, and built his own telescopes.

Clyde Tombaugh

Clyde Tombaugh with His Homemade Telescope (1928)

In 1928, Clyde Tombaugh built a telescope (the one pictured above) from the crankshaft of a 1910 Buick and parts from a cream separator. He also ground his own mirrors for the reflector. He used this telescope to observe Jupiter and Mars, making drawings of what he saw. He sent his drawings to the Lowell Observatory hoping to get some professional feedback. Instead, he got a job.

Clyde Tombaugh died in 1997. He later had a rather special reward for his work. In 2006, his ashes were carried to Pluto by the NASA New Horizons mission, a space probe sent to study the planet he had discovered.

From Planet X to Pluto

Having finally found Planet X, the next question was, “What should this new-found planet be called?” A worldwide competition to name ‘Planet X’ was held in 1930, and was won by Venetia Burney, an 11-year-old English girl, who proposed the name Pluto after the Greek god of the underworld, who was able to make himself invisible. Burney was rewarded with £5 (5 pounds, UK currency).

Venetia Burney (1918-2009) was an English woman. As the winner of the planet-naming competition, Clyde Tombaugh credited Burney with first suggesting the name Pluto for the planet he discovered in 1930. At the time, she was 11 years old and lived in Oxford, England. As an adult she worked as an accountant and a teacher.

Venetia Burney -age 11-1929
Venetia Burney, age 11

Pluto Becomes a Dwarf Planet

Pluto’s reign as a planet was relatively short-lived.  In 2006, the International Astronomical Union (IAU) agreed on a formal definition for a ‘planet’ for the first time, and in the process, Pluto lost its planet status.

The IAU decreed three key requirements which must be met in order for a celestial body to be designated as a planet – Pluto passed the first two criteria, but failed on the third, that of dominating the area around its orbit, since Pluto’s orbit is cluttered with asteroids and other debris. In addition, one of Pluto’s moons, Charon, is about 1/2 the size of Pluto, which violates another standard expected of a planet.

So, having lost its status as a full-fledged planet, Pluto has become a dwarf planet, designated 134340 Pluto – now it’s just one of many large objects in the Kuiper belt. Other dwarf (minor) planets include Ceres in the asteroid belt and Eris, which lies beyond Pluto’s orbit.

How the World Works: Astronomy: From Plotting the Stars to Pulsars and Black Holes
How the World Works: Astronomy: From Plotting the Stars to Pulsars and Black Holes
Anne Rooney



Ann Rooney
Anne Rooney

. Anne Rooney website
. Royal Literary Fund (RLF)
. Scholastic Magazine

Before turning to full-time writing, Anne completed a PhD at Trinity College, Cambridge, and taught medieval English and French literature at the universities of Cambridge and York. She teaches creative writing as part of the Pembroke-King’s summer program in Cambridge. She is an RLF (Royal Literary Fund) Fellow at Newnham College, Cambridge. She lives in Cambridge and has two daughters.

Anne Rooney has written extensively on modern science, technology and contemporary issues for young people. She has worked in the computer industry for about 20 years, as well as advising educational bodies on various technological matters.

Anne Rooney writes books on science, technology, engineering and the history of science for children and adults. She has published around 200 books on a variety of subjects. Before writing books full-time, she worked in the computer industry and wrote and edited educational materials, often on aspects of science and computer technology.

Books written by Anne Rooney include:

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