Nope - we have 8 planets in the Solar System

[Fiosh]

I still think it's mean.

"Sorry, Mr macintosh, I know you've been growing on our trees for the past gazillion years, but you're not really one of us Grannysmiths. Go away!"

Poor little Pluto.

t.

Why did it take them 75 years to decide its not a planet???

ted, maybe you can claim it as part of your kingdom and elevate it to "royal territory" status. That'll show 'em!

[nebula]

Ooooooo - someone asked a science question.

To put it simply, understanding the solar system, and what a solar system is, is still a work in progress.

The word "planet" means "wanderer." Basically, those that observed the stars (OK, back then everyone pretty much observed the stars - no light pollution and no indoor electricity, if you catch my drift ) noticed that certain stars "wandered" among the other stars. They noted that these stars were not fixed with relation to the rest or each other; so they called them "wanderers." The main observers, the astrologers, gave them special significance in their readings.

With the development of the telescope, people eventually figured out what these wandering stars (planets) actually were and that "earth" was just like them (technically).

The problem is, no one ever developed a formal definition of what a planet is. In essence, our solar system is still in discovery phase. We truly do not understand all of its mysteries.

Pluto was discovered because it had been determined that the planets in general have a mathematical proportion to their distances from each other. The main asteroid belt, for instance, exists where a planet is supposed to be. Thus, when you see the solar system in a some-what scale drawing, you will see an unusually large gap between Mars and Jupiter. Anyway, either Uranus or Neptune was discovered by an astronomer actually calculating where a planet should be and looked for it. So, another astronomer calculated where a planet beyond Neptune should be . . . and discovered what became known later as Pluto!

Fine and dandy - except that Pluto was not like the other "planets". Besides the fact that it's more or less a giant "dirty iceball", its orbit is on an entirly different plane from the other 8 planets and the eccentricity of its eliptical orbit is much larger than for the other planets (the others are close to being circular; Pluto's is not close to circular by any means).

Back in the '90's, a couple of astronomers found a smaller "dirty iceball" in orbit somewhere along the outskirts of Neptune's orbit. Then some more were discovered. An astronomer named Kuiper had hypothesized a ring of objects - much like the asteroid belt - to exist outside the planet's orbits (or something like that). So, these objects were considered part of this hypothesized Kuiper Belt (thus they were called Kuiper Belt Objects, or KBO's). They were also dubbed Trans-Neptunian Objects, or TNO's.

It is these "dirty iceballs" that have become what we call comets. It is figured that as the Sun moves through the solar system, it travels close enough to other stellar objects that a gravitational pull causes these TNO's to get knocked out of their orbit around the sun, but instead of flying off away from the sun get pulled back in along a different orbit route - thus they travel through the orbits of the other planets. This is why Haley's comet keeps coming back - it happens to be in a smaller orbit that than others.

So, this discovery led some astronomers to question whether or not Pluto was a "planet" like the other 8, or if it was better classified as a TNO.

In more recent years, more TNO's have been discovered with a "round" shape to them. 2003 UB### in fact is larger than Pluto.

So, the International Astronomical Society was forced to decide what they consider to be "planet" and what becomes classified as "TNO" - or something else.

So, this is what they decided. Pluto belongs in a different category than the "Classical planets" (4 terrestrials and 4 gas giants).

Down the road with new discoveries - who knows if or how they may decide to reclassify things.

But that's what makes science so much fun.

[RGR]

I still think it's mean.

"Sorry, Mr macintosh, I know you've been growing on our trees for the past gazillion years, but you're not really one of us Grannysmiths. Go away!"

Poor little Pluto.

t.

Why did it take them 75 years to decide its not a planet???

ted, maybe you can claim it as part of your kingdom and elevate it to "royal territory" status. That'll show 'em!

[LadyGunivere]

nebs you know since the sun has a certain amount of gravity and the distance to Pluto is what is causing the orbit to be off kilter???????

[ted]

Thanks Neb!

But it's still mean.

ted, maybe you can claim it as part of your kingdom and elevate it to "royal territory" status. That'll show 'em!

I had thought of doing that very thing already, but to do so would mean coming out of retirement.

I am, after all, a retired king.

I could, however, simply rename it Planet Ted. That alone would be enough for people to leave it alone and not mess with it.

t.

[nebula]

nebs you know since the sun has a certain amount of gravity and the distance to Pluto is what is causing the orbit to be off kilter???????

OK, I am not following your train of thought on this one.

Pluto's orbit is quite stable. The Sun's gravity is strong enough to keep it in orbit. I've never heard of decreased gravity causing an orbit to be off-kilter.