[SunkenCiv]

"To Pluto And Far Beyond" By David H. Levy, Parade, January 15, 2006 -- We don't have a dictionary definition yet that includes all the contingencies. In the wake of the new discovery, however, the International Astronomical Union has set up a group to develop a workable definition of planet. For our part, in consultation with several experienced planetary astronomers, Parade offers this definition: A planet is a body large enough that, when it formed, it condensed under its own gravity to be shaped like a sphere. It orbits a star directly and is not a moon of another planet.

[SunkenCiv]

The discovery of 2003 UB313, the 10th planet
by Michael Brown

Is this object really a planet? Is Pluto a planet? What makes a planet?

Even after all of these years of debate on the subject of whether or not Pluto should be considered a planet, astronomers appear no closer to agreement. I wrote extensively about this at the time of the discovery of Sedna in March 2004. My thoughts have evolved since then, so it might be amusing to see what I said 1 1/2 years ago... The main stumbling block in defining planets in our solar system is that, scientifically, it is quite clear that Pluto should certainly not be put in the same category as the other planets... There is no good scientific way to keep Pluto a planet without doing serious disservice to the remainder of the solar system. Culturally, however, the idea that Pluto is a planet is enshrined in a million different ways, from plastic placemats depicting the solar system that include the nine planets, to official NASA web sites, to mnemonics that all school children learn to keep the nine planets straight, to U.S. postage stamps. Our culture has fully embraced the idea that Pluto is a planet and also fully embraced the idea that things like large asteroids and large Kuiper belt objects are not planets. In my view scientists should not be trying to legislate an entirely new definition of the word "planet." They should be trying to determine what it means. To the vast majority of society, "planet" means those large objects we call Mercury through Pluto. We are then left with two cultural choices. (1) Draw the line at Pluto and say there are no more planets; or (2) Draw the line at Pluto and say only things bigger are planets. Both would be culturally acceptable, but to me only the second makes sense for what I think we mean when we say the word planet... Thus, we declare that the new object, with a size larger than Pluto, is indeed a planet. A cultural planet, a historical planet. I will not argue that it is a scientific planet, because there is no good scientific definition which fits our solar system and our culture, and I have decided to let culture win this one. We scientists will continue our debates, but I hope we are generally ignored.