Word: planet
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Dates: during 2000-2009
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...thank-you--and flowers wouldn't be a bad idea either. Back in 2000, Tyson, an astrophysicist and the director of the Hayden Planetarium in New York City, triggered an international furor when he decreed that in his prestigious establishment Pluto would no longer be listed as a planet. Henceforth, it would be considered just another ball of ice in the Kuiper Belt, a swarm of debris orbiting the sun out beyond Neptune. He was on firm scientific ground: many professional astronomers have been leaning that way for years. But people evidently had a soft spot for the runt...
...something very much like Pluto, only bigger, and last month he declared that the object known officially as 2003 UB313--and temporarily nicknamed Xena--has its own little moon. Suddenly, the question Tyson had raised to make a provocative educational point became something much larger: if Pluto is a planet, then Brown's new object must be one as well...
...doesn't stop there. What do you call all the other planetlike objects that have lately been discovered orbiting around our sun, tiny worlds with names like Sedna, Quaoar and 2004 DW? Part of the problem is that there is no precise scientific definition of the word planet. The International Astronomical Union (IAU) is trying to hammer one out, but the decision is proving more difficult than anyone thought. An apparent consensus, reached just weeks ago, seems to have fallen apart. "The current state," admits Brian Marsden, director of the IAU's Minor Planet Center at Harvard, "is rather confusing...
Most people don't worry much about such distinctions. With planets, however, it's different--as Tyson discovered. How do you resolve the problem he created? One idea would be to arbitrarily set the lower limit for a planet at about 2,000 km (1,250 miles) in diameter, which would let Pluto remain a planet and make 2003 UB313 one as well, but keep the rest of the riffraff out. "Pluto," says Alan Boss, an astronomer at the Carnegie Institution of Washington and a member of the IAU working group, "has historically been considered a planet...
...another idea, favored by Alan Stern of the Southwest Research Institute in Boulder, Colo., would open the door even wider. By his definition, any 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...