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Pluto rises again

The top scientist behind NASA's mission to Pluto, Alan Stern, says the icy world is making a comeback among astronomers: The debate over Pluto's planethood is resurging at scientific meetings, and even the International Astronomical Union hasn't yet delivered the final word on its planet definition. When all is said and done, it may be the IAU – or, as Stern terms it, the "Irrelevant Astronomical Union" – that ends up getting Plutoed, he says.

You can probably tell already that Stern isn't a dispassionate observer when it comes to Pluto: He's the principal investigator for the New Horizons probe, which was launched a little more than a year ago to study the solar system's edge. The spacecraft is due to zoom by Jupiter next month, on its way to a 2015 rendezvous with Pluto and its icy neighbors.

The IAU decision seemed to dis the $700 million mission even before it really hit its stride. But Stern says his disagreement rests on a deeper principle - that scientific classifications shouldn't be legislated in and out of existence.

"Science does not work the way the legal system works," Stern, a planetary scientist at the Southwest Research Institute, told me today. "We didn't vote on relativity or quantum mechanics. We don't vote on any scientific discovery, because it just doesn't work that way. ... The IAU can vote that the sky is green, but that doesn't mean people will follow, because it's not."

Stern said recent developments have borne out his view. He pointed to the agenda for the European Geosciences Union's annual meeting in Vienna this April, which headlines a forum titled "What Is a Planet?"

"Astronomy is not the only discipline that deals with planets, and the criteria defined by astronomers might not be shared by planetary scientists, for example," the agenda abstract reads.

Stern said the fact that the Europeans were revisiting the issue was just one indication of a turning tide. "The American Geophysical Union has been discussing something similar," he said. "The real planetologists aren't happy."

Even the IAU is still working through the fuzzier parts of its definition - such as the idea that an honest-to-goodness planet has to have cleared out its celestial neighborhood. Many of Pluto's proponents have claimed that provision could disqualify the whole solar system, depending on how it's applied.

But Stern says trying to patch up the IAU's definition of planethood just won't work. Instead, the status of Pluto (and other junior-partner planets, ranging from the asteroid Ceres to the iceball Eris) will likely be worked out step by step, as scientists learn more about the diversity of worlds in our own solar system and beyond.

Stern is still hoping to organize a conference on planethood later this year, although he's had to delay his original schedule due to his work on New Horizons as well as some organizational glitches. "We will have this conference, and it will highlight all points of view, but there won't be any voting, I can tell you that," he said.

The issue is sure to be revisited at scientific conferences for years to come, including the IAU's next general assembly, in 2009 in Rio de Janeiro.

Stern said he's not banking on a quick reversal of Pluto's fortunes.

"In 20 years, this will be just a memory," he said of the spat. "But I can't tell you whether it will come to the kind of culmination that's obvious in two years or four years. ... It's like the middle of an episode of 'CSI,' and we don't know how it's going to turn out."

He is confident, however, that Pluto will eventually be back in the solar system's good graces: "I pity all the poor people who have removed Pluto from their posters of the solar system, because they're going to have to make them again," he said.

For more on the current state of the controversy, check out Deborah Byrd's posting at Earth & Sky's blog.

Maybe it'll all be settled by the time the New Horizons probe zooms by Pluto, on July 14, 2015. That day may seem far off, but Stern is already planning for the party. This week, he said he'd invite some guests who can't even walk by themselves yet, let alone dance to the strains of "I Miss Pluto."

Stern and his colleagues are setting up a "New Horizons Kids" program to select about a half-dozen children who were born on the day the spacecraft was launched - Jan. 19, 2006. The program would also seek out another half-dozen kids who turned 10 on launch day - that is, with a birthdate of Jan. 19, 1996.

"We'll follow those 10 or 12 kids as they grow to be 10 and 20 years old, respectively, while our dream machine New Horizons soars across the solar system," Stern said on the New Horizons Web site. "From time to time, we'll check in on our kids, and by the time the newborns from launch reach fourth grade and the 10-year-olds from launch reach the middle of college, we'll be at Pluto."

Stern told me the kids would be treated as VIPs - "Very Important Pluto Personalities" - and would probably be in line for some perks when the mission hits prime time in 2015. So if you know someone who fits the chronological qualifications, send your nomination to plutokids@jhuapl.edu. Stern said the nomination should include the child's name, birthdate, a recent picture and the parents' names and e-mail contacts.

Roughly 12,000 kids are born every day in the United States alone, so there should be plenty to choose from. The New Horizons team will announce the roster of Pluto Kids after next month's Jupiter flyby.