From the Journal of Improbable Research:
With the loss of Pluto, the number of major planets in our solar system has dropped to eight. If the current trend continues, then come April 13, 3703 the solar system will no longer have any major planets. My analysis suggests several possible causes, for the loss of major planets….
The moto of the Improbably Research Journal is: First it makes you laugh, then it makes you think.
The “makes you think” part here is realizing there was nothing sacred about the number 9 when it came to planets. The number of planets has gone up and down in the past many times as we’ve learned more about our solar system. This was well put by Darren Bennett’s Census of the Solar System last year in 365 Days of Astronomy.
I’m still more of a fan of the “enough gravity to make it round” view of planets, which give us dozens (possibly hundreds) of new planets, including turning the major moons of the gas giants into planets. We’d need one hell of a mnemonic to keep track of them all, but I think even the current definition of planets is going to become problematic when we get more data on extra solar planets. For those wondering, that number is currently 453 and growing.