Greetings from scenic Xena

OUR SOLAR SYSTEM turns out to be a whole lot messier than we once thought.

For generations, schoolchildren were taught that the sun had precisely nine planets revolving around it. Anyone who could memorize the phrase ``My Very Educated Mother Just Showed Us Nine Planets " could (maybe) remember their names.

But reality is more complex. And this week, a committee of the International Astronomical Union defined ``planet" in a way that would take in three more heavenly bodies. Earthlings, meet Ceres, Charon, and Xena.

According to the panel, a planet is any spherical object that orbits the sun and has a diameter of roughly 250 to 500 miles or larger. If the astronomical union adopts that proposal, it's bound to cause a stir in the general public. Being told that there are 12 planets in the solar system rather than nine is like finding out that your own home has a few more rooms that you'd somehow overlooked. Once you get past the cognitive dissonance, it's interesting to contemplate what you might do with all the extra space.

Granted, two of the three would-be planets in question have been common knowledge for some time. Ceres was previously designated as an asteroid; Charon, as a moon of Pluto.

But in the last several years, astronomers have discovered plenty of new real estate in the outskirts of the solar system. One such object is Xena, first observed in 2003 and named unofficially for the television character played by Lucy Lawless. (Let's hope that the name sticks.) Under the committee's new definition, it supplants Pluto as the most distant planet in the solar system.

None of this would have happened had Pluto lived up to its billing. Discovered in 1930, it was once believed to be larger than Mercury -- but now appears to be smaller than Xena. Previous efforts to downgrade it into a mere ``transneptunian object" raised howls of protest.

So in a triumph of rebranding, the committee has lumped Pluto, Charon, Xena, and any similar as-yet undiscovered objects into a subcategory called ``plutons." Plutons would be considered planets, and would overlap with a separate category called ``plutinos." These categories might sow confusion among astronomers, just as the drugs Celebrex, Cerebyx, and Celexa have among pharmacists, but the new nomenclature might just placate Pluto buffs the world over.

Astronomers may revolt if, as some predict, the new definition ends up making planets out of dozens more objects. But for now, it's comforting to learn that the solar system has more planets than most of us realized. The universe is cold and vast, but there are still plenty of wonders waiting to be discovered so close to home.