CLYDE TOMBAUGH

The scientist who discovered Pluto, once the ninth planet of the Solar System

The existence of a planet beyond Neptune had been predicted by prominent American astrologer Percival Lowell in 1905, but it was never proven in his lifetime. He had aimed a 40-inch reflector at what he believed to be the right section of the sky, but he died in 1916 with his dream of discovering his so-called Planet X sadly unrealised. It was his biggest disappointment, yet it was the catalyst for a continued search. And for amateur astronomer Clyde Tombaugh, Lowell’s hunch would yield great results.

Lowell’s legacy was the observatory that bore his name, which had been built in 1894 for the purpose of studying Mars. It had come to be looked after by his nephew, Roger Lowell Putnam, who in a twist of fate had been approached by Tombaugh in 1929 seeking feedback on his detailed drawings of Jupiter and Mars. Tombaugh was in his early 20s at the time, and he had built his own telescope. With an instant offer of a job, Tombaugh could never have foreseen what his decision to contact astronomers at Lowell Observatory would lead to.

Tombaugh, who was born in Streator, Illinois, and grew up on a farm in Kansas, was tasked with leading the search for Planet X using a device called a blink comparator – a piece of viewing apparatus used to discover the differences between two images of the night sky. By looking for apparent changes in the positions of objects, Tombaugh struck upon something extraordinary after ten months of hard work. He noticed a planet-like body on 18 February 1930, and some three weeks later on 13 March 1930, Pluto’s discovery was announced.

It would prove to be an amazing start to Tombaugh’s astronomy career, but it was not quite a case of him peaking early. Tombaugh continued to work at the Lowell Observatory until 1945, and he took the opportunity from 1932 to 1938 to study for a bachelor’s and master’s degree in astronomy at the University of Kansas. He was making a long-lasting contribution to the understanding and exploration of space, and his discoveries would have ramifications for decades to come.

Certainly, his qualifications stood him in good stead during his time teaching astronomy at

New Mexico State University from 1955 until his retirement in 1973, but it was his other discoveries that provided the icing on the cake. He found hundreds of new variable stars and asteroids. He also discovered two comets and thousands of new star and galaxy clusters. Fittingly, Asteroid 1604 Tombaugh, which he discovered in 1931, was named after him. And some others were named after his family.