If the astronomers at Lowell Observatory suspected they had something not-quite-planetlike on their hands in 1930, they had ample reason to keep their suspicions to themselves.  The long-delayed search for Planet X had finally resumed in early 1929.  Thousands of dollars of new facilities and equipment had been brought in.  Expectations were high.  By February 1930, Clyde Tombaugh had been examining high-resolution photographic images for ten months.  And Lowell Observatory had its reputation to rescue. 

In 2006, Mike Brown finally called their bluff.  His blog is here.  And here’s his thoughtful, funny (scientists are usually funny, except when they’re really not funny at all) piece on the reasoning behind Pluto’s demotion.

“I would have been happy if we’d tried to come up with some new words to describe the eight large objects that orbit the sun, but the word “planet” is cultural, so we’re not touching it. But the IAU felt the pressure to come up with a scientific definition. As scientific definitions go, I think saying there are only eight planets works better, but it’s an aesthetic choice. It’s a religious choice. There’s no science there…

So Pluto is not a planet now, it’s a dwarf planet. A dwarf planet, for those of you who were wondering, is something that looks like a planet because it’s round, but is not a planet. We currently know of about 35 objects that fit the bill of dwarf planet, but we’ll find hundreds.”

Other planet killers include The Lexx, The Foreshadow, The Eye of Ra, The Krenim Temporal Inclusion Ship, Red Matter, The Death Star (I and II), Arkon Bombs, and Ice-Nine.