Is Pluto a Planet Again?
Is Pluto a planet again? Yes and no. While the International Astronomical Union does not consider Pluto a planet, it's counterintuitive to think of it as just a giant asteroid. The IAU considers Pluto a "dwarf planet", which is sort of like being on the junior varsity team: you're still on the team, but you don't get cheerleaders or your name in the local paper.
Back in the day, there were two types of planets: rocky worlds (like Earth and Mars) and gassy giants (like Saturn and Jupiter). But what if Pluto isn't a non-planet, but a third type of planet? As we see more and more of the universe around us, we're forced to rethink the concept of the planet. For example, what about a potential ocean-world like GJ 1214b (I prefer "Planet Zarkon", but hey)? "It's a planet, Jim, but not as we know it..."
Pluto has not changed; only our perception has changed. I bet it's only a matter of time before Pluto gets to ditch its numerical moniker and rejoin its celestial brethren. "Dwarf planet", indeed! Surely a planet of small stature is still a planet.
Pluto isn’t the ninth of nine; it’s the first of many. Thanks to the discoveries of the past couple of decades, we’ve gained a whole new tribe of worlds to watch in the Kuiper Belt, and the vast, diffuse Oort Cloud represents an even farther frontier we haven’t yet begun to explore.
Incidentally, the State of Illinois is keeping the faith, and still considers Pluto a planet.
MEanwhile, NASA is organizing a surprise inspection:
NASA's New Horizons spacecraft, launched in 2005, will arrive at Pluto in 2015.
Look busy, Pluto.