Word: pluto
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Dates: during 2000-2009
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...Pluto Farewell...
...object massive enough for gravity to squeeze into a spherical shape is a planet--unless the object orbits a bigger planet, of course. Otherwise, dozens of moons would have to be reclassified as planets. "Defining planets by size is purely arbitrary," agrees Marsden, who likes Stern's idea. "The Pluto-crats want to cut things off there, but it's absurd to say that an object 2,000 km across is a planet and one 1,999 km across...
...rule would add lots of planets to the solar system in one fell swoop: not just Sedna, Quaoar and 2003 UB313 but also two more icy worlds spotted by Brown and Trujillo--2004 DW, a little bigger than Quaoar, and 2003 EL61, probably about seven-tenths the size of Pluto. The latter made headlines when it was formally announced to the world by Spanish astronomers who, according to Brown, knew where to look because they had used the Internet to tap into his telescope logs (the Spaniards deny the charge). At least five or six asteroids would also qualify, says...
...Trujillo have even more discoveries waiting in the pipeline (they've put their logs behind a firewall to keep prying competitors away) and they're not done yet. Just about all the new worlds have been found by looking even farther outside the plane of the solar system than Pluto's orbit. "Nobody really expected to see anything way up there," says Brown. "But based on what we've found so far, we expect to find at least two or three more of these...
Tyson, ever the iconoclast, thinks the word planet should be retired entirely, not just stripped from Pluto. "You tell me something's a planet," he says, "then I have to ask you 20 more questions to figure out what it actually is." As an educator as well as a scientist, though, he is thrilled that the question of planethood has been opened for freewheeling public discussion. "The point," says Tyson, who is working on a book about the Pluto debacle, "is that the solar system is a lot more interesting than just a list of nine planets." And thanks...