Three years ago, in Prague, astronomers had perhaps the most contentious gathering in modern astronomical history. Usually the International Astronomical Union meeting is nothing but a once-every-three year's chance for astronomers to advertise their latest discovery or newest idea while spending some time in a nice international destination, having dinners with old friends and catching up on their celestial gossip. On the final day of each meeting, in a session attended by almost no one, resolutions are passed, usually all but unanimously, on such pressing topics as the precise definition, to the millisecond, of Barycentric Dynamical Time (I have no idea what this actually even means, but, presumably, it matters critically to someone).

The meeting three years ago was different. The usually placid astronomers had spent their time in Prague arguing and bickering day and night about Pluto and about planets and about how to reconcile the two. While several of the typically unintelligible resolutions were indeed to be voted on this last day, the final two resolutions would be all about Pluto. The usually sparsely attended final session was full of surly astronomers itching for a fight.

Everyone by now knows the outcome. In an overwhelming vote, astronomers agreed to tighten the definition of the word “planet” to mean, essentially, the large dominant things in the solar system. Which Pluto is not. That was the end of Pluto as a planet. That was the end, too, of Eris (the slightly-larger-than-Pluto iceball that I discovered that had precipitated the mess) as a planet.

The solar system makes more sense now, and, in three years most people have come to terms with the new solar system. But not everyone (as an example, read the inevitable comments soon to follow this post….).

Three years ago, when the vote put Pluto into its proper place, some vowed to carry the fight forward. “Onward to Rio!” they cried.

It’s three years later, and it is time, once again, for the Internation Astronomical Union meeting, this time in Rio de Janeiro The meeting. It starts tomorrow and I am currently staring out across Copacabana beach watching the winter waves pound the shore (Winter? Only sort of. The beach is packed and the clothes are skimpy) waiting for the real fireworks to begin.

But will there be any? There is an entire weeklong program called “Icy Bodies in the Solar System” with talks about the Kuiper belt, comets, icy satellites, dwarf planets, and even one talk about Pluto. But nowhere is there slated to be any official discussion about Pluto. Will it happen anyway? Will the partisan defenders of Pluto try to storm the meeting in protest to finally have their day in court?

It would be the right forum, for sure. Because of the special program, many of the astronomers who think deeply about planets and the outer solar system are here. Why not ask?

I predict that by the end of the week, the topic of Pluto and planets will come up, at best, only outside of the actual meeting over a few glasses of caipirhina. I suspect no one will press the fight about Pluto because even the partisans are reluctantly admitting to themselves that the fight is over and planets have won.

After the vote three years ago the Pluto partisans tried every trick and argument they could come up with to convince people that the IAU vote had been ill conceived or procedurally wrong, or poorly attended or anything else. All of that could have been fixed by now and a new vote could be taken. Except that Pluto would lose again. And new excuses would be needed (how about: the moon was full and astronomers became lunatics!).

Will they actually give up? I suspect not. It’s easy enough to keep the controversy alive in the media long after most serious scientists have moved on to better things. But I think the fighting will all be guerilla style these days.

But don’t give up hope! Perhaps something will unexpectedly spill into the open and Rio can turn into a place as fun as Prague. Stay tuned….

For entertainment, and should anyone care, I am (sigh) tweeting the IAU meeting. You can follow me at, appropriately enough, http://twitter.com/plutokiller