Reaction to Pluto's new status as a dwarf planet has been mixed among scientists and on the internet.
Astronomers decided on Thursday on a new definition to describe a planet, and Pluto no longer qualifies.
The discoverer of 2003 UB313, a dwarf planet slightly larger than Pluto, was philosophical about the new designations.
"Eight is enough," said Michael Brown of the California Institute of Technology, referring to the number of planets now recognized in the solar system.
"I may go down in history as the guy who killed Pluto," he added.
Brown's discovery three years ago of the dwarf planet he nicknamed Xena sealed the fate of little Pluto.
Astronomers had to either accept Xena and other objects like it as planets, or change the definition to exclude Pluto.
In the end, the International Astronomical Union decided on the latter Thursday at a conference in Prague. Some 2,500 astronomers from 75countries attended the conference, but only about 300 showed up for the vote on the new definition.
'It's bad science'
The head of NASA's New Horizons mission to Pluto said the dwarf planet's status wouldn't affect the project, but predicted that the IAU wouldn't end the debate.
"It's a sloppy definition. It's bad science," said Alan Stern. "It ain't over."
The Baltimore Sun ran an editorial response ostensibly from the former planet itself. "What did I do to deserve this?" Pluto moans. "I, Pluto, am taking a stand. I'm here. I'm a sphere. Get used to it."
The Wall Street Journal ran a story on its front page on the effect of the IAU's decision on astrologers, suggesting that Scorpios could be in trouble because the sign is closely associated with Pluto.
Many bloggers expressed disappointment that the smallest and most distant planet is a planet no more.
Jason Kottke of the blog kottke.org held a contest for a new mnemonic device to protest Pluto's new status. The winner: "My! Very educated morons just screwed up numerous planetariums."