May 1, 1930. On this date, 11-year-old Venetia Burney in Oxford, England received £5 for her clever suggestion of the name Pluto for then the solar system’s outermost and newest planet.
Clyde W. Tombaugh – an assistant at the Lowell Observatory in Flagstaff, Arizona – had discovered Pluto earlier that year, on February 18, 1930.
But it was the American astronomer Percival Lowell who initiated the search for a planet beyond Neptune. Lowell had believed that something large was gravitationally pulling on Neptune and the next planet inward, Uranus, affecting the shape of their orbits. He had searched from 1905 until his death in 1916. But he never found his long-sought Planet X.
Thirteen years later, in 1929, Lowell’s observatory in Flagstaff resumed the search for Planet X. The new administrators at Lowell built and dedicated a 13-inch telescope for this sole purpose, and hired 23-year-old Clyde W. Tombaugh to take systematic, painstaking photographs generally along the ecliptic, or pathway of planets in our solar system. After a year of nightly labor, Tombaugh found an object whose orbit showed it was more distant than Neptune, but vastly closer to us than the stars.
It was the object now known as Pluto. From its discovery in 1930 until 2006 – for over seven decades – Pluto was considered the 9th planet of our solar system.
That changed when the International Astronomical Union (IAU) – the organization that currently names and categorizes most space objects – made a controversial decision in 2006 to demote Pluto to dwarf planet status.
Two years after that, in 2008, in a nod to Pluto’s past, Pluto became the first and largest example of a new class of objects called plutoids, defined as space objects which maintain a near-spherical shape and have orbits that may intersect with others beyond the orbit of Neptune. You don’t often hear anyone mention plutoids, though.
In 1930, it wasn’t the IAU but the Lowell Observatory – where both Lowell and Tombaugh had conducted the search for an unseen, outermost planet – that had the right to name the new object.
The observatory received 1,000 suggestions worldwide, according to the Library of Congress. Venetia Burney suggested the name Pluto in part because it kept the nomenclature for planets in the realm of classical mythology, where Pluto was a god of the underworld.
Cleverly, the name also honors Percival Lowell, as the first two letters of the name Pluto are Percival Lowell’s initials.
Bottom line: Pluto officially received its name on May 1, 1930. A girl in Oxford, England – 11-year-old Venetia Burney – suggested Pluto, a classical mythological god of the underworld and in honor of honor Percival Lowell, whose early efforts led to Pluto’s discovery.