`Incredible shrinking planet'

August 21, 2006

When the Hubble Space Telescope snapped the first pictures of the surface of Pluto, it captured the elusive planet's icy veneer and summer shroud, which one scientist likened to the bright snows of Colorado. And although Pluto didn't have the sexiness of Venus or the panache of Mars, the photographs of a decade ago provided scientists with the first detailed views of the faraway planet since its discovery in 1930.

"It's fantastic," gushed astronomer Marc W. Buie back then.

Fast forward to 2006. Pluto is in the news again, but all anyone wants to talk about is its planetary pedigree - or lack thereof. It's dominating a convention of astronomers in Prague, who this week could yank its membership in that exclusive Club of Nine. That doesn't seem quite fair to us. OK, Pluto is awfully small, and it does have that loopy orbit, and bigger objects have been discovered spinning around other stars.

But why pick on Pluto? Because astronomers have discovered that Pluto was neither the farthest thing out there, nor was it alone. A bunch of similar-sized bodies or icy objects raised questions about whether Pluto was uniquely different. The advance of space telescopes also didn't help matters - they allowed astronomers to see more into the depths of space and with greater clarity. As Ray Villard, a spokesman for the Hubble Space Telescope, put it: "Pluto has been the incredible shrinking planet." When it was discovered, astronomers thought it was bigger. They didn't realize what they were seeing was Pluto and its large moon, Charon, blurred together.

So it was a case of mistaken identity. But scientific advancement and knowledge triggered this planetary debate. That's a good thing, really. Within the International Astronomical Union, Pluto does have its supporters. The proposal under debate at the IAU convention would expand the definition of a planet to account for other celestial objects in line for planetary status and, at the same time, designate Pluto-size objects into a new category of planet known as "plutons." That's a reasonable compromise.

After all these years, why relegate Pluto to a has-been?

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