Just days ago, on August 14, the International Astronomical Union (IAU) held its 26^th General Assembly. The IAU is an authority -- the authority, actually -- that classifies objects in outer space. This meeting and this group may not sound like big deals but they actually are. Together they are the reason that there is no longer a planet called Pluto.

See, members of the IAU were recently granted suffrage on matters of science, a right they had lost during the 25^thGeneral Assembly. Newly armed with a political voice, they got right down to business. On the August 2006 agenda was the matter of coming up with a true-blue definition of the word 'planet'. Lo and behold, by the end of the ten day conference, 'planet' was redefined. At the same time, a qualifying term, 'dwarf planet', was created. Then, the former planet Pluto was recatagorized as a dwarf planet, where it was united with a couple of formerly ambiguous celestial bodies, Ceres and 2003 UB₃₁₃.

As anyone can imagine, the fallout was tremendous, and it is hard to know who was the most wounded victim: whether it was the staunchly traditionalist astrologers of Myanmar who will continue calling Pluto a planet as they calculate destinies, or the man with a freshly-tattooed solar system on his belly, or the myriad kindergarten teachers who were forced to edit their lessons to accommodate the eight-some-odd planets. The media quickly fell into a frenzy over the event, which continues even this week.

Now, if everyone were able to just cool their jets for a minute and think through this issue they would understand that there is no reason to get worked up. What is happening amounts to nothing more than some growing pains for the classification system of astronomical objects. It's not as if Pluto is getting booted from the solar system club, or was found to be some sort of phony. In fact, when all of the current consternation pans out, there will be a more orderly solar system than there was before. This sort of thing happens with biological classification all of the time.

To understand why Pluto really is still part of our solar system, and to understand the reasons for this new micromanagement of the sun's satellites, a bit of universe history must be covered. Before there was a Sun, and before there were any planets, there was a big cloud of gas called a solar nebula. As it happened, this cloud was just dense enough to start contracting. Gravity was the acting force here; the rule goes that any two objects with mass attract one another. In some ways, gravity works the way magnets work, but even for the experts it's still more like magic when you get down to it.

Anyway, due to various forces that are easily understood using Newtonian physics, this nebula gradually flattened, grew hot in the middle, and began to rotate more quickly. Some of the gas went on to become the sun. A lot more of it cooled off, solidified, and became the fodder for planets, asteroids, comets and the rest. In short, little bits begin to bump together and stick, and as they get bigger they experience more collisions and grow more rapidly in a process called accretion. These small conglomerations are called 'planetesimals' and become fated to be planets or other objects, depending on how far from the sun they are and what they happen to bump into. To make a long, long story short, anything that formed from the initial solar nebula is part of the current solar system, whether deemed to be a planet or not, including Pluto.

But there are many fates for a planetesimal, and becoming a planet is just one of many unique things that may occur. In early August, Pluto and 2003 UB313 fell into an ambiguous zone where they could be 'planets' for some characteristics but were nothing more than 'trans-Neptunian objects' for other reasons. Truth is, nobody knew quite what these things should be called. If they were deemed planets, there were half-a-dozen more such orbs in the grey zone that could also be named planets for one reason or another. That may not sound like such a big to-do, but imagine ten years from now. There could be twenty or thirty planets in the solar system, or hundreds. Planets galore! Much of this could depend on how well telescope technology progresses. Regardless, given the current hubbub, the thought of more than just nine planets is pretty concerning to many people.

With reason, some of the folks at the IAU decided that the word planet needed to carry a bit more weight than it had in the past. They needed to set a precedent, vaguely analogous to the kind of precedent that is set by a ruling in the Supreme Court which will specify the outcome of future cases. That said, this August, a few new astronomical guidelines were created. A true planet must orbit the sun, be round on account of its own gravity, and clear the neighborhood (a fancy way of saying 'the path of its orbit') of smaller objects. Dwarf planets are planets that have done everything but clear their neighborhoods of smaller objects. This clearing the neighborhood business is important -- it eliminates any big objects that rotate the sun in a shared path from being real planets, so that there remains no more debris in the hypothetical planet's proverbial lane on the proverbial track. There you have it. What sets apart a planet from a dwarf planet is clearing the neighborhood.

In scientific classification, the family tree that organizes the relations among organisms, similarities between species are based on shared ancestry. Thus, an octopus and a flounder are hardly kin, despite their shared habit, while a flounder and an elephant might as well be cousins, since they both have backbones. At one point in time, before Charles Darwin enlightened the field, these classifications would have never held the water that they do today. In astronomy, the absence of such a prophet has led the IAU to step in and set some things straight. Pluto will continue to be a part of the solar system, and its significance shouldn't be overlooked, in classrooms, encyclopedias or anywhere else. Pluto can still hold rank because it comes from the same solar nebula as the other planets, comets and asteroids that rotate the sun. But until it can successfully claim an orbit of its own, free of other planets, rotating spacerocks or whatnot, it will remain apart, an also-ran, far from bearing sacred term that humans have bestowed on their own little globe: planet.

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