October 1, 2008

Pluto, Plutoids and Exoplutoids

At first I was saddened when Pluto was demoted from planethood. Then I was amused by the new classification called "plutoids". I love playing with words, but plutoid sounded too funny to me. Why not have Jupiteroid, or even Earthoid? And all the debate that ensued about pluto's demotion just prompted me to call Pluto as the Great Hemorrhoid of Astronomy, because it was painful to "lose" such a planet.
However, we are given a consolation by the fact that Pluto is still a planet in some way, eventhough the IAU denies it being so. Yes, it is actually a dwarf planet, and a first in its class called "plutoids".
So let us examine the heirarchy of these 3 terms: Planet, Dwarf Planet, and Plutoid.
A planet is a round object that orbits the sun. Its large enough for its gravity to clear out the rocks and other debris within its orbital path.
A dwarf planet is also a round object that orbits the sun. But it is too small to have anough gravity to clear out debris in its path. Hence there are other objects sharing its orbital path.
A plutoid in turn, is any dwarf planet that orbits farther out than neptune (a trans-neptunian object or TNO).
Ceres is an example of a dwarf planet. It is round and it orbits the sun in the asteroid belt, along with millions of other smaller objects. Pluto and Makemake are also dwarf planets since they also share their orbital path with other objects , but they are also plutoids, as is Eris. They are plutoids because they orbit farther from the sun than the farthest planet, Neptune.
So currently, some established members of the plutoid class are Pluto, Makemake, Haumea, and Eris. But it could well grow to more than 70 in a few years time as more dwarf planets fall into the class of plutoids.
Unlearning is also part of learning. And this is what progress in Science is all about. Painful and controversial as it may have seemed, the IAU's decision to "demote" pluto was necessary to for a better classification of a bewildering array of celestial objects orbiting our sun. To a certain extent, I support the IAU on their decision (even though it still needs a little tweaking). Most often than not, collective intelligence is smarter than emotions, and I believe it will sway one final tweak to simply put dwarf planets as a subset of the broader term "planet" to settle the debate.
Now what does it hold for Exoplanetology? As it will turn out, the term plutoids would actually make it easier to categorize "extrasolar dwarf planets" that fit in place: Exoplutoids! But it will be decades AFTER planet-hunting capabilities resolve to discovering earth-like planets. Then we may actually discover exoplutoids next.