True-color image of the dwarf planet Pluto, taken by the New Horizons spacecraft, 2015
27 March 2023
The trans-Neptunian object Pluto was discovered in 1930 by Clyde Tombaugh, a twenty-four-year-old researcher at the Lowell Observatory in Flagstaff, Arizona. The observatory’s founder, Percival Lowell, had predicted the existence of a “Planet X” in 1916, and Tombaugh had been hired in 1929 to conduct a systematic search for the predicted planet. Tombaugh discovered the object on 18 February 1930. The observatory announced the discovery on 13 March 1930, the seventy-fifth anniversary of Percival Lowell’s birth.
It is now widely recognized that Lowell’s prediction of a Planet X was wrong, and that Tombaugh’s discovery was happenstance. (There may possibly be a large planet beyond Neptune, but if so, it does not accord with Lowell’s mathematical prediction.) And Pluto’s size (about one-fifth the mass of the Earth’s moon) and eccentric orbit does not fit with the other planets. Pluto is now known to be just one of many such trans-Neptunian objects in the Kuiper Belt.
Yet at the time, the discovery of what was hailed as the ninth planet produced a flurry of suggested names. The name Pluto, the Roman god of the underworld, was suggested by an English schoolgirl, Venetia Burney. Her grandfather, a retired librarian who had worked at the Bodleian Library passed the suggestion on in a letter to a friend, an Oxford professor of astronomy, who happened to be attending a meeting of the Royal Astronomy Society in London at the time. The suggestion was immediately telegraphed from the meeting to the Lowell Observatory. Others may have independently thought of the name, but Burney’s suggestion is likely to have been the first to reach Flagstaff.
The first mention of the name Pluto in print that I have found is in a 23 March 1930 article in the Boston Globe that includes it in a list of potential names for the body being suggested by the US Naval Observatory:
According to Capt. Freeman, Minerva appears to be the only major deity of the Graeco-Roman mythology not employed as a name of an important celestial body. Among the other names suggested for the planet and received at the Naval Observatory are Leda, Atlas, Cronos, Pluto, Lowell, and Percival, the last two names [sic] those of Prof Lowell.
On 25 March 1930, the Associated Press reported that Italian astronomers were also suggesting the name Pluto. This story was printed in newspapers across North America the following day:
“Pluto” is the provisional name that Italian astronomers have given the new trans-Neptune planet discovered on March 13 at Lowell Observatory, in Flagstaff, Arizona.
Whether the Naval Observatory and the Italian astronomers were aware of Burney’s suggestion or if they chose the name independently is unknown, but it’s reasonable to assume that multiple people thought of it as Pluto was an obvious choice for several reasons: Pluto was the only major Greco-Roman god not to have an astronomical body named for him; he was the god of the underworld, an appropriate moniker for an object in the far reaches of the solar system; and the name began with PL, the initials of Percival Lowell.
The Lowell Observatory decided on the name Pluto that May, with an announcement on either 24 or 26 May. The date of the official announcement is uncertain because there was evidently a leak in advance of the official announcement. The Associated Press reported the announcement on 24 May 1930, but this may have been the result of the leak in advance of the official announcement. A longer Associated Press article that includes a transcript of the official announcement and details about the naming deliberations appears on 26 May:
Pluto has been selected by scientists of the Lowell observatory here as the name for the recently discovered transneptunian body which they believe is the long-sought Planet X. The name is symbolic of the comparatively dark and distant regions thru which the celestial body rides in its orbit about the sun.
The announcement was made by Roger Lowell Putnam, trustee of the observatory and nephew of the late Dr. Percival Lowell, founder of the observatory, who predicted the existence of Planet X 16 years ago.
Mr. Putnam, who came here from Springfield, Mass., to take part in the official naming of Planet X, revealed that Pluto was selected after the host of suggested names had been narrowed down to three—Minerva, Pluto and Cronus.
“We felt,” said Mr. Putnam, “that the line of Roman gods for whom other planets are named should not be broken and we believed that Dr. Lowell would have felt the same way.
“The discovery of this planet is so preeminently a triumph of reasoning that Minerva, the goddess of wisdom, would have been our choice if her name had not for so many years been borne by an asteroid.
“Cronus, the son of Uranus and the father of Neptune, would have been appropriate, but so is Pluto, the god of the regions of darkness where Planet X holds sway. Jupiter and Neptune already are in the heavens and it seems particularly appropriate that the third brother should have a place.”
Mr. Putnam added that Pluto lent itself easily to the monogram “P.L.,” the initials of Percival Lowell, and “would be a fitting memorial to him.”
“We therefore felt,” Mr. Putnam concluded, “that Pluto is the proper name for the planet and are so suggesting to the American Astronomical society and the Royal Astronomical society.”
The announcement of the naming was due to a premature report that leaked from a printing office.
In 2006 the International Astronomical Union officially demoted Pluto from planetary status, labeling it as a dwarf planet.
Sources:
Associated Press. “Name is Chosen for New Planet” (25 March 1930). Globe (Toronto), 26 March 1930, 12. ProQuest Historical Newspapers.
———. “Name Pluto Given to Body Believed to Be Planet X” (24 May 1930), New York Times, 25 May 1930, 1. ProQuest Historical Newspapers.
———. “Pluto Picked as Name for New Planet.” Asbury Park Evening Press, 26 May 1930, 3. ProQuest Historical Newspapers.
Grimes, William. “Venetia Phair Dies at 90; as a Girl, She Named Pluto” (online 10 May 2009). New York Times, 11 May 2009, A21.
Hoyt, William Graves. “W.H. Pickering’s Planetary Predictions and the Discovery of Pluto.” Isis, 67.4, December 1976, 551–64 at 557. JSTOR.
Oxford English Dictionary, third edition, September 2006, s.v. Pluto, n.1.
“Planet ‘Minerva,’ Navy’s Suggestion” (22 March 1930). Boston Globe, 23 March 1930, A19. ProQuest Historical Newspapers.
“Pluto, in Astronomy.” Columbia Electronic Encyclopedia, 6th edition, 2021.