Venetia Phair, who was 11 years old when she suggested Pluto as the name of the newly discovered planet, has died in England. She was 90.
She died at home in Epsom, south of London, on April 30, her family said. The cause of death was not disclosed.
Phair suggested the name to her grandfather at breakfast in 1930.
"My grandfather, as usual, opened the paper, The Times, and in it he read that a new planet had been discovered. He wondered what it should be called. We all wondered," she recalled in a short film, "Naming Pluto," released earlier this year.
"And then I said, 'Why not call it Pluto?' And the whole thing stemmed from that."
Her grandfather was Falconer Madan, the retired librarian of the Bodleian Library at Oxford University. He relayed the suggestion to his friend Herbert Hall Turner, professor of astronomy at Oxford, who on that day was at a meeting of the Royal Astronomical Society, where possible names for the planet were being discussed.
Turner then passed on the suggestion to Clyde W. Tombaugh, who made the discovery at the Lowell Observatory in Arizona.
When the name was publicly announced May 1, 1930, Phair said her grandfather rewarded her with a five-pound note.
(The same purchasing power today would be about 230 pounds, or $350.)
"This was unheard of then. As a grandfather, he liked to have an excuse for generosity," she told the BBC in 2006.
She was fascinated by astronomy, and recalled playing a game at school using clay lumps to mark out the relative positions of the planets. She was also a keen student of mythology and knew about Pluto, the Roman name for the Greek god of the underworld, Hades.
"There were practically no names left from classical mythology. Whether I thought about the dark and gloomy Hades, I'm not sure," she told the BBC.
She tartly rejected any suggestion that the planet was named for the Disney dog.
"It has now been satisfactorily proven that the dog was named after the planet, rather than the other way round. So, one is vindicated," she said.
The International Astronomical Union downgraded Pluto in 2006 to a dwarf planet -- based on the observation that Pluto was a large chunk in the Kuiper Belt of solar debris.
Phair said she was indifferent about Pluto's change of status, "though I suppose I would prefer it to remain a planet."
Born Venetia Burney on July 11, 1918, she studied mathematics at Cambridge University, and taught economics and math until retiring in the 1980s.
An asteroid discovered in 1987 was named in her honor: 6235 Burney.
Her husband, Maxwell Phair, died in 2006.
She is survived by their son, Patrick.