Discuss as:

Pluto postmortem

— Protest petitions are still circulating, protest songs are still being written, and kids are still standing up for the littlest planet. But based on the postmortems on Pluto's "demotion," the icy world seems destined to remain a second-class solar system citizen.

When the International Astronomical Union approved a definition of planethood that put Pluto and other mini-worlds into a category known as dwarf planets, apart from the eight "classical" planets, the outcry wasn't long in coming: Not just one, but two petitions demanding reconsideration of Pluto's fate circulated online, drawing hundreds of signatures each.

The reaction from the general public was decidedly pro-Pluto as well - as reflected in our unscientific Live Vote, our message board and many other forums around the Internet. Many voiced precisely the kind of sentiment expressed musically by the Canadian band SubPlot A: "I don't care what the experts say, you'll always be my Number 9."

Now, however, the pendulum is swinging the other way. Astronomers have moved to give Pluto a number on the long roster of asteroids, a.k.a. minor planets. The IAU's newly elected president, Catherine Cesarsky, stuck to her guns this week and said the organization succeeded in getting "as large a fraction of the community as possible [to] agree with the decision."

In this week's issue of The Space Review, science writer Daniel Fischer recaps the IAU proceedings in Prague and says opponents of the decision lacked "any real arguments" for keeping Pluto on the list. He also pooh-poohs the idea of petitioning for a reversal:

"The tumultuous events of August 2006 are as much a lesson in sociology as in astronomy. Discussing what happened with the general public, you notice that the more they learn about the arguments behind the decision, the more they understand and accept it. This adds to the argument that a vote by a fraction of the world's astronomers after a week of intense arguments might be a better way to determine where to go than aggressively promoted e-mail campaigns. ..."

That's not to say that the case is yet completely closed. Even Cesarsky acknowledges that the IAU's views on planethood will have to be fine-tuned over the next three years or so to account for the wide diversity of celestial objects - ranging from brown dwarfs to the weird theoretical possibilities for extrasolar planets. The requirement that a planet has to be something that has "cleared  the neighborhood around its orbit" might have to be rephrased more precisely.

However, no matter what happens, Pluto will never be returned to the place it held a few years ago, as a solid member of a nine-planet club. Astronomers pretty much knocked Pluto down a notch when a bigger "10th planet," currently known as Xena, was found last year. And there could be scores of other roundish mini-worlds still waiting to be discovered.

It will take years for the Pluto paradigm shift to percolate through new editions of science textbooks, but in reality, most science teachers have been aware for some time that the planetary menagerie is too diverse to be covered by an eight- or nine-word mnemonic. Science teacher Randy Pelton even suggests coming up with a new phrase that includes the solar system's three zones of cosmic leftovers: the asteroid belt, the Kuiper Belt and the Oort Cloud.

So how's this sound? "My Very Eager Marksman Almost Joyfully Shot Up Nasty Killer Owls." Surely you can do better than that, right?