Since its discovery in 1930 by an American amateur astronomer named Clyde Tombaugh, Pluto has been classified as the ninth planet of the solar system. Only to be removed from the solar planetary group in 2006. Why? The following are the major criteria at classifying a heavenly body whether it's a planet or not:
- A planet must be in orbit around the sun.
- A planet must be massive to produce gravity strong enough to give it a round shape.
- A planet must dominate its orbit, that is, its path is in relative isolation.
- A planet should be by far larger than the rest of minor bodies in the solar system.
- A planet's orbit must be relatively located in the same plane as the other planets.
Planetary data has it that each planet in the solar system satisfies the above criteria while Pluto meets only the first and the second. It does not satisfies the third and fourth, for numerous other bodies populates its orbital vicinity and some of the members of these host of minor objects now known as the Kuiper belt are as large as Pluto itself - plutinos the astronomers would put it. Comparing to the rest of the planets, Plutos's orbit is relatively tilted away from the common orbital plane. Thus, neither the last is met.
The international community of astronomers convinced, Pluto was formally reclassified as one of the dwarf planets in 2006. The news quickly enkindled debate and controversy among various communities, even among astronomers. I think as far as science is concern there is nothing adverse to this remarkable scientific step. Had Clyde Tombaugh now alive, I believe he would have no opposition either.
Unfortunately, some visual teaching aids about the Solar System for graders here in the Philippines still maintains the nine planets I noticed, an intellectual act which I would certainly deify if I were in the shoes of those elementary school teachers.
