Expert: Jesse Martinez - 9/13/2009

Question
I was taught in school in Mexico that Pluto was the ninth planet in the solar system. That was over ten years ago. Now I am hearing that it is not a planet. In fact here in the United States, I recently saw a poster in the mall that had all the planets and it did not include Pluto. Is it just that Mexico considers it such and the United States does not?

Answer
Three years ago, Pluto was downgraded to "dwarf planet" by general international agreement. It has nothing to do with the differences between Spanish and other languages. It only means that in the scientific community for now, it is not considered to be in the same category of solar system objects as the other eight planets. I personally would still classify it as a planet even though there is a larger "dwarf planet" out there, Eris, which I would not classify a planet. See links below.

In short, I believe the reclassification happened only because some persons needed recognition in the scientific world. Fueling such debates does gain recognition for some people. This is what Scientists do: hypothesize, theorize, postulate, publish, etcetera. For the time being, it is NOT a planet officially. Here are some of my personal pro/con thoughts.

My main reason for planet status: It has a large moon along with at least two others. The larger one draws comparison to Earth's moon in terms of relative size compared to the main object. My main reason against: It is small and is composed of a large amount of ice.

One could also argue that the eccentricity of the orbit of the object sort of breaks the concept of what most think an orbit is for a planet. Eccentricity is a measure of how elliptical an orbit is. Pluto orbits around the sun about every 248 years. during this time it will be closer to the sun than the 8th planet Neptune for 15 to 20 years. The last such occurrence happened late last century. It also doesn't line up well with the other eight orbits in other ways. I hope I am not being overly simple in my response. This is actually my first question since I was accepted by AllExperts. Feedback would be appreciated.

Here are two sites that you can see and read for more information and decide for yourself. http://en.wikipedia.org/wiki/Pluto states that there is no clear definition of what a planet is while this one http://www.newscientist.com/article/mg20327181.600-is-pluto-a-planet-after-all.h... says there is. I personally think there is  a case for reclassifying Pluto as a planet. It has a fairly large orbiting satellite like Earth. For now just call it 134340 Pluto or just plain Pluto. A name is only a name. Designations like planet and dwarf planet are meant to help us understand "what" an object is. But until scientists agree on the definition, there will be confusion in this area. Thank you for your question.