Why isn't pluto a planet? (Part I)

Pluto, what a non-planet!! Am I right?? In one word, Yes. Lets make this as basic as possible. On August 24, 2006 Pluto was taken off the list of ‘planets’ in our solar system. Well, its not that easy, you see it was on August 24, 2006 that science finally defined what a planet is, and Pluto, didn’t fit the bill. For a long time there was no definition because there was no debate as to what bodies should be included on our list of planets. But, the more people investigated Pluto the more they began to question whether it was or was not a planet. Some of the things that caused scientists to wonder about plutos viability as a planet included:

It’s path around the sun is not like the rest of our solar system, it’s more elongated. So much so that for 20 years of its nearly 250 year orbital adventure, it is closer to the Sun than Neptune.

Its orbit takes Pluto well above and below the disk shape orbit that all the other planets and even the asteroid belt are attune to. Taking Pluto well outside the boundaries of the Zodiac constellation that all other planets stay well within.

It’s size, its smaller than Mercury. Originally we thought Pluto was much larger than it turned out to be.

Its make up was identical to the many large icy bodies that can be found in a far region of the Solar System called the Kuiper Belt. Scientists have also discovered that Pluto isn’t even the largest Kuiper Belt object. Pluto was just the first one and largest one found up until recently.

The outer planets are “gas giants” (Jupiter and Saturn) or slushy “ice giants” (Uranus and Neptune). Pluto is the only tiny, icy world that isn’t remotely similar to any of the outer planets. And certainly nothing like those closer to the sun (like us).

These things and more prompted scientists to debate Plutos standing as a planet. When a much larger Kuiper Belt object was discovered in 2002 the jig was up. Since then many other Kuiper Belt objects have come into view (Nix, Hydra, Xena, Eris, Quaoar and Sedna are a only a few). All of these objects have the same makeup as Pluto, some larger some smaller. They all orbit the sun in the same elongated path, but since it takes these objects 250-550 years to orbit the sun, many of these them haven’t been close enough for us to see until recently.

None of this means that Pluto and the other Kuiper Belt Objects aren’t just as important as the 8 planets in our solar system, in fact they may be even more important because they teach us more about the orbital make up of our galaxy and have obviously allowed us to define what makes up a planet, at least in this solar system.


Above, is an illustration of the orbital patterns of the Kuiper Belt objects, you can see how it is different from the orbital path of the plaents in our solar system