Ang Kape Ni LaTtEX

It’s official: as of yesterday, you oughta throw out all those encyclopedias and Solar System mobiles, or at least break the last planet off, because Pluto does not fit the new definition of a planet as agreed by the International Astornomical Union, and is demoted to the status “dwarf planet”

The IAU members gathered at the 2006 General Assembly agreed that a “planet” is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
This means that the Solar System consists of eight “planets” Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called “dwarf planets” was also decided. It was agreed that “planets” and “dwarf planets” are two distinct classes of objects. The first members of the “dwarf planet” category are Ceres, Pluto and 2003 UB313 (temporary name). More “dwarf planets” are expected to be announced by the IAU in the coming months and years. Currently a dozen candidate “dwarf planets” are listed on IAU’s “dwarf planet” watchlist, which keeps changing as new objects are found and the physics of the existing candidates becomes better known.[IAU]

In other words, Pluto has been demoted from being a planet because of definition c. Pluto comes closer to the sun than Neptune is for a period alternating between 13 and 20 years, the most recent occurence being February 7, 1979 to February 11, 1999.
What amuses me however, are the reaction of some people regarding this issue, as illustrated here. In more ways than one, the change in the definition of our solar system as having eight planets affects us emotionally.

We learned that Pluto was the farthest planet of the Solar System as children, the time when everything we heard from our parents and teachers was true and infallible. Just like believing that Santa will give us presents every Christmas even if our houses in the Philippines don’t have chimneys.

For me, I accept this new definition with open arms, since it not only lays to rest the Pluto debate, but it also underscores the fact that science is evolutionary. Science is an exercise in making definitions — and Pluto has evaded definition for decades.