some comments on characterizing Pluto as a planet
To all:
The issue of whether Pluto constitutes a planet or not, actually, reveals a lot about the process of what is termed "science", these days. More a back-and-forth than anything else, the source of the dispute lies more with the fact that it is based on an, at best, nebulous concepts, and geared toward "legitimizing" pre-determined "facts", rather than deriving whatever the actual truth is. Rather than start from - or, at least, try to derive - some accepted idea of what a "planet" is, instead, ideas and challenges, undefined proclivities and prejudices, hit, head-to-head, and, basically, whoever gets the most support - in whatever manner! - "wins"! Devotees of older conceptualizations and space art have one idea. Those determined to push the idea of the Kuiper Belt, and, likely, finance expensive searches, apparently, "adopt" a separate concept! Whoever manages to get the most influential individuals behind them, usually by dangling the prospect of big money line-item appropriations before them, generally, seems to be the one the media "crowns the victor", by assigning their assertions to print!
But that is not the way true science is supposed to work! Indeed, terming Pluto a planet or not does rest on affirming what the word "planet" generally and universally can be represented as meaning. And, there, it seems there has been little work done. But defining what "planet" means should be based on ideas intrinsic to what the general concept of a planet is, not whatever term will facilitate cadging big money in grants and appropriations.
By and large, the invoking of a Kuiper Belt of icy-rocky bodies beyond Neptune has been used to "jusify" large-scale proposals for deep space telescope assays, in the hopes of finding as many large bodies as possible. "Defining" Pluto as, not a planet, but just one of these bodies, has added media exposure and controversy as a driving force for these ambuitious - and expensive! - surveys! Establishing that Pluto constitutes a planet, and not a "Kuiper Belt Object" could threaten to take this glitz and panache away.
But the truth doesn't necessarily work on the basis of who can get what from where. And a decent approach would be based more on the idea of establishing what "planet" really means, than on trying to set up a grant proposal.
Since, unfortunately, a genuine look at what calls itself "science" today will see a system dominated by money, with the search for truth a little, out-of-the-way consideration, it turns out that those not affiliated with cash-hungry institutions or organizations can, perhaps, be more trusted to act legitimately. And don't think that someone without a dozen letters after their name can't make a genuine, even universal, contribution! Isaasc Newton is credited with establishing the basis for modern physics, but he didn't have an MIT degree! You can't allow their insistences that you're just a dummy, who doesn't deserve to be heard, convince you of that!
Defining what a planet is rather resembles the Sorites Paradox, the question of when a "collection of sand particles" starts to constitute "a heap". In fact, there is a certain degree of understanding as to what a "heap" should look like. If you put just one particle of sand in front of you, you, likely, would not term it a "heap". Two bits of sand, likewise, would not be automatically considered a "heap". But, add particle after particle, and eventually, you will term what you see a "heap". Where does the change come about, between a "collection", the paradox asks, and a "heap"? In the same way, it might be questioned, when does something cease to be just "an orbiting body", and become "a planet"?
In fact, though, there are criteria that come into play in considering a "heap", as well as those that can be invoked in considering the nature of a "planet".
Sheer number does not, for example, constitute a "heap". If you had a billion sand particles in a 125 foot by 125 foot square, it would only be "a sandy surface". Being on top of each other doesn't, either, since a two-layer collection of sand, 80 feet square would still appear like just a flat surface. A "heap" requires a collection in some central point, consisting of much more than stretches out to the sides. If, in fact, the height is comparable to, or greater than the width at the base, it can be considered a heap. Closer to how a heap behaves, you can say that if it exceeds the angle of repose, so that parts on the sides fall down at the slightest provocation, or it is close to the size of the person judging it, it can be called a heap. In any event, there are fairly well understood characteristics which can be invoked to consider it a heap or not.
In the same way, there can be definite, and all but non-arbitrary, qualities that can be invoked to determine if a body is a planet or not.
In point of fact, anything orbiting the sun can be called a “planet”. In the same way, anything orbiting it can be called an “orbiting body”. Those advocating terming Pluto a “Kuiper Belt Object”, continually bring up the image of “rubble” left over from the beginning of the solar system, lumps of material that did not collide and coalesce into larger bodies. They are represented as idle pieces of ice and dust, orbiting perpetually, after the formation of the official planets had finished.
One significant problem with this is that the coalescing of the solar system is not yet done! The impact of Comet Schumacher-Levy on Jupiter, Stuart’s Event on the moon, and, likely, the Tunguska Explosion indicate that bodies in the solar system are still sweeping up material. If you argue that Pluto cannot be a planet because it is “rubble” that has yet to combine to form a planet, you have to remember the theory that the moon was formed by the earth, when it was only about 80% the size it is today, being hit by an object about the size of Mars, vaporizing and shooting off a huge pocket of material that formed the moon. Both objects were bodies involved in the still incomplete formation of the solar system, yet were both larger than Pluto. Bodies of their size would be considered planets today, even though they were “rubble” from which larger bodies were composed!
In terms of appointing the term “planet”, though, it is crucial to bring up those qualities that we would expect of something termed a planet, yet which we can expect to be absent in something constituting a simple “orbiting body”.
The, generally inert conceptualization associated with a simple “orbiting body”, at least at present, would then suggest that part of what would comprise a “planet” would be a vital nature, a definite active or changeable character. This would include such things as a spherical shape, due to a gravity strong enough to cause it; an atmosphere; tectonic activity; radial differentiation of material, due to gravity; significant differences in topography, across the face of the body; a magnetic field; a sizable satellite. Pluto is spherical and has a relatively large moon. It also seems to have an atmosphere, perhaps about 1/1,000,000 earth’s, but with temperature differences across it, it is suggested. Changes in albedo of subsurface material are also suggested to cause localized absorption of sunlight, producing geysers of sorts. It is suggested that its makeup consists of a relatively large rocky core, covered by a thick layer of water ice, with variegated “surface ices” in a thin region above that. Its gravity is probably also strong enough to cause some internal heating.
Perhaps another quality to be looked for is the simple fact that, when on the surface of a planet, you don’t know you’re on a planet. On the earth, looking outward, your range of vision covers two almost exactly equal sized sections, the ground and the sky. For a smaller body, the horizon would curve more, and take up less of the vision. It would be more obvious that you were on the surface of something. The most of your vision that any planet should take up is 50%. If it took up only 25%, that could be considered too little. It would be just too obvious you were on the surface of a body if only one quarter of your entire view was that body, and the rest sky. We can, then, split the difference and suggest that, if a person, standing on the surface of a body, has at least 37.5% of their view taken up by the body, then it qualifies as a planet.
These are reasonable, and, more important, not agenda driven considerations, for defining a planet. No matter how much you may want to suggest that Pluto is composed very largely of ice and is close in size to bodies orbiting further out, in the Kuiper Belt, these conditions still qualify Pluto as a “planet”! There are those who may suggest that Pluto formed by accretion of icy/rocky bodies, but all the officially accepted planets did! Such things as that Pluto is inclined significantly to the ecliptic, and it has the largest eccentricity of any major body are invoked to suggest that it is not a planet. But these are characteristics of its orbit, not the body itself! Many interactions can cause a more traditionally planet-like body to have so unusual an orbit. Too, it can be suggested that, so far out in the solar system, away from the bulk of activity, and with fragments moving so slowly in orbit, Pluto could have formed with less impulse to force it to follow the exact same lockstep as the inner worlds. Indeed, it is almost too close to the orbits of the other planets for something so far out in the solar system! Too, how many of the officially designated “Kuiper Belt Objects” have high eccentricities to their orbits, or highly inclined orbits? A number, in fact, have inclinations in orbit much less than Pluto’s!. It is commented that Pluto is smaller than seven moons in the solar system, but it’s larger than dozens more! Its axis of rotation is, supposedly, tipped at more than 90 degrees to the ecliptic, but so is Uranus’! There are even suggestions that Pluto’s moon, Charon, formed by a portion of Pluto being ripped off in a massive collision with another body, such as is suggested for earth!
Just because Pluto formed near the Kuiper Belt, out of Kuiper Belt objects, doesn’t mean it, too, must be considered a Kuiper Belt object. The general theory is that all the official planets formed from Kuiper Belt objects, and since the Kuiper Belt is theorized to be many times the size of the solar system, in extent, every planet can be said to have be en formed “near the Kuiper Belt”!
In fact, the decision to downgrade Pluto seems to be motivated by the initiative to emphasize the idea of the Kuiper Belt, and, likely, to give Dave Jewitt, proclaimed an expert of the Kuiper Belt, and the man who proposed downgrading Pluto, publicity. But machinations aren’t supposed to be the basis for constructing scientific definitions, but, rather, the application to reality, to make discoveries or determinations.
Julian Penrod