I can’t believe I wrote this!!!
I came back to Recom.org to see if there’s anything new, and there’s the usual news on Pluto’s new title. Looking back at what I had posted, I was quite shocked at what I had wrote more than 2 years ago. It’s nothing controversial, but it gives an idea on how much time I had last time. 
For those of you who wondered at what makes a planet a planet, this would a great help. Yep, it’s outdated, but the considerations are still relevant to the issue even today. Maybe if I have the free time, I might just do a ‘2 years later, the follow-up’ post. 
Here’s the post, with some minor touch-ups.
Posted: Wed Jun 02, 2004 9:52 pm Post subject:
Hie everyone, just to contribute some additional info to the planet status classification.
As far as I know, the IAU arbitrarily assigns the planet status according to their choosing, since there are no clearly defined set of criterions for a celestial object to be classified as a planet. If you have noticed in your search for a conclusive answer, the IAU and many other sources on astronomy do not have an official definition of the term ‘planet’. This is largely because the general population instinctively knows what is meant when you use the term planet.
Consequently, as the IAU tries to define what constitutes a planet, the major thorny issue they have to sort through this is the problem of Pluto. Most mainstream astronomers today agrees that it shouldn’t be called a planet in the first place, but the public had gradually grown attached to Pluto as the ninth planet! It is generally accepted among the astronomical community today that Pluto is in fact a Trans-Neptunian Object orbiting the Sun alongside thousands of other asteroids in the Kupier Belt.
Now, the key points in defining a planet are as follows: it’s mass, possession of celestial bodies and its type of orbit. All these parameters and others are currently being hotly debated in the quest to settle this problem for once and for all.
It is argued that a planet must be of sufficient mass so that the object has sufficient gravity to have a spherical shape, which will distinguish them from asteroids. The problem is on deciding the bottom limit of the object to be classified as a planet and its upper limit to distinguish it from brown dwarfs. This would be to Pluto’s advantage, since it does have sufficient mass to hold itself together, even though some moons in the Solar System are larger than it! As for the upper limit, it must also not be too massive or else it will be taken into consideration as a brown dwarf. But thankfully these burn deuterium, or else Jupiter’s status is also threatened.
Another one is that it must possess a moon, but this is debatable as Pluto has Charon, but the innermost 2 planets have none! Furthermore, some asteroids also have its own companion, which added to the problem of using this as a criterion.
Pluto and Sedna both have the most erractic orbits among all the planets in the Solar System. So astronomers argue that both of them should not be classified as planets since their orbits are not as regular as the other planets. Furthermore Sedna could possibly be part of the Oort Cloud as it is currently 86 AU from the Sun, compared to Pluto’s average distance of 39.5 AU! Pluto’s orbit is also inclined with respect to the Solar System’s plane, which is one of the reasons some say it shouldn’t be called a planet.
So, with all this problems, the issue is not likely to be settled quickly, and the discovery of these additional objects is definitely going to complicate matters. For now, Sedna would still be called a planetoid and Pluto-which is roughly twice its size-a planet.
Note: Xena, or 2003 UB313 by official designation is actually larger than Pluto. If IAU wants to keep Pluto, it would also have to admit Xena AND Ceres. In short, given the choice to kick Pluto out or admit another 3 into its fold (Ceres, Sedna, 2003 UB313), the IAU chose to kick one out. They did that by adding in a novel criteria, which I might delve into in the future. If you’re a Pluto lover and say this sucks, an appeal by the Pluto supporters is underway. It might not go far, but it’s hard to say at the moment.
