Journal Entry 1/24

Why is there a debate about whether or not Pluto is a planet?

There is debate about whether or not Pluto is a planet because objects have been discovered beyond it that are much larger and also orbiting the sun. This orbit makes these objects a part of our solar system, and since there are many varied definitions for what a planet actually is, they may all be worthy of the title: "Planet".

How is Pluto similar to the inner planets? How is it different?

Pluto is similar to the inner planets in that it is circular (which means that there is a gravitational force pulling all matter towards the center) and that it orbits the sun. Its orbit is questionable though, because it is the only object that crosses orbits with another (Pluto's "planetary orbit" crosses paths with Neptune). Within the eight inner planets, there are inner and outer planets. The inner planets are: Mercury, Venus, Earth and Mars. The outer planets are: Jupiter, Saturn, Uranus, Neptune. All of the outer planets are larger than the inner ones. Pluto does not fit this mold, for it would be considered an outer planet, but is smaller than the other outers. It is also different in that it does not have the hydrogen and helium atmosphere of the other outer planets.

What is the name of the region in the outer solar system, beyond Pluto, which contains many recently-discovered large objects?

The region beyond Pluto is called the "Kuiper Belt". It contains many recently-discovered large objects.

What do you think of the controversy about whether or not Pluto is a planet? How should we decide who is correct?

In a way it is entertaining that there is such a controversy surrounding Pluto. I think that because this celestial body is so distant and so mysterious, it appeals to the public and there is some kind of instinctual need to protect it. As far as determining whether or not Pluto is a planet, I don't think it should be considered one. Objects that are much larger have been discovered and they have not been classified as planets. The sense of obligation to keep Pluto as a planet is just a product of the human tendency to reject change. Just because Pluto has been considered a planet for 60 years, that does not necessarily mean that it is one. A universal definition of a planet is necessary to decide whether or not Pluto qualifies as one. If this definition is created, the future of planetary science will be a lot more manageable.