The math genius behind Pluto’s discovery

Dated photo of woman standing outside large facility (© Lowell Observatory Archives)
Elizabeth Williams’ work as a “human computer” at Lowell Observatory paved the way for the discovery of Pluto in 1930. (© Lowell Observatory Archives)

Astronomers’ discovery of Pluto in 1930 wouldn’t have happened without Elizabeth Williams, whose razor-sharp math skills left the world with a more complete picture of our solar system.

Her name is far from familiar, though, and her face is barely visible in a surviving photo.

Astronomer Percival Lowell hired Williams in 1905 as a “human computer” to help guide his search for Planet X, which he suspected orbited somewhere beyond Uranus and Neptune. Williams had graduated from the Massachusetts Institute of Technology with a degree in physics in 1903, one of the first women to graduate the elite university with honors.

Planet against black backdrop (NASA/JHUAPL/SwRI)
The dwarf planet Pluto, discovered in 1930. (NASA/JHUAPL/SwRI)

According to the American Astronomical Society, Williams’ calculations were “critical” to guiding Lowell’s search for the planet, which became known as Pluto. After Lowell’s death, Clyde Tombaugh discovered Pluto on February 18, 1930, while searching where Lowell — guided by Williams’ calculations — had predicted.

“In carrying out the complex calculations necessary for the Planet X search, the talented Williams reportedly wrote in cursive with her right hand and printed with her left,” the society says in a report issued in January.

Williams’ brilliance provided an early glimpse of the role that women mathematicians would play in support of NASA’s critical early missions. The contributions of three African-American women — Katherine Johnson, Dorothy Vaughan and Mary Jackson — are chronicled in the book and December 2016 movie Hidden Figures.

Williams married astronomer George Hamilton in 1922, which prompted Lowell Observatory to fire the couple, according to the observatory’s archives. The pair then worked at the Harvard College Observatory in Jamaica. After her husband’s death, Williams joined her sister in Lebanon, New Hampshire, where they ran a summer retreat home, the Lowell Observatory Archives say. Williams died in 1981 at the age of 101.