How many moons must a real planet have?

The title of this post is a play on the words to Bob Dylan's "Blowin' in the Wind":

How many roads must a man walk down
Before you call him a man?
Yes, ’n’ how many seas must a white dove sail
Before she sleeps in the sand?
Yes, ’n’ how many times must the cannonballs fly
Before they’re forever banned?
The answer, my friend, is blowin’ in the wind
The answer is blowin’ in the wind

In the Dylan song, he is talking about people. In my title, I'm talking about planets - or what have recently been reclassified as Dwarf Planets. And specifically, I'm talking about Pluto. As you may remember, the International Astronomy Union (IAU), in 2006, decided by vote that Pluto no longer met the requirements for its newly created definition of a planet. The vote wasn't unanimous with 237 votes for Pluto being declassified a planet and 157 voting against it (with 17 abstentions). Since when is good science done by voting? Pluto actually meets two of the three criteria of a planet (it orbits the Sun and it is massive enough to have formed a sphere due to its own gravitational force). The only one it doesn't meet is the criteria that it must have cleared out the neighborhood around its orbit (sweeping up other rock around it to make them part of itself). But since we know so little about this area, who is to say that it has or has not met this criteria?

This brings me to the recent news that a fifth moon has been discovered circling Pluto. I didn't even know about their discovering a fourth moon (July 20, 2011)! These last two moons are so new they haven't even been given names yet. In the picture, they are labeled as P4 and P5 (with the new, fifth moon circled). How can something that has five moons not be classified as a planet? Why not amend the arbitrary (in my opinion) third criteria for being a planet to say, "...or have at least five moons"? The IAU is making up the rules as they go along. Since its founding in 1919, it took them 87 years (one year longer than the Red Sox had to wait between World Series victories) to come up with the definition of a planet. Why can they not be a little open to "tweaking" the rule?

Well, in about three years, the New Horizons probe will be near Pluto and it should tell a lot more about this planetary body then. My hope is that it will convince the IAU to change the classification. But whether they do or not, the fact that we could send a machine that far away for that long a time (the probe was launched in 2006) is amazing to me. And the fact that we might find more information about the distant, mysterious object is exciting. But it will probably raise more questions than it answers. That's the nature of things.

[Update: Here is my version of Mr. Dylan's song for the astronomy community: ]

How big and round must a real planet be
Before it's a planet for sure?

Yes 'n' how many moons must a real planet have
Before it's demoted no more?

Yes 'n' how much debris from around it must go
Before it's a planet once more?

The answer my friend is in the solar wind
The answer is in the solar wind.