New column from me at The American Prospect Online, "Fear of a Ninth Planet" makes the case against denying Pluto it's rightful status as a planet. I should perhaps note that despite enjoying the "reality-based community" phrase, I actual adhere to a fairly Kuhnian line about the nature and history of science which some folks would regard as unduly relativistic.
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Fear of a Ninth Planet
29 Aug 2006 03:36 pm
Comments (6)
Man, fuck Saturn. No time for that shit.
In your commentary you stated that by the new definition 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 neighborhood around its orbit." During the conference a scientist pointed out that by this definition Neptune would fail as a planet, since Pluto affects its orbit (see part C of definition). This scientist was then refered to a footnote in the committee report where Neptune was EXPLICITLY defined as a planet, that is, "grandfathered in." There is no logical reason they could not have done the same for Pluto. I owe this information to a report from NPR.
You should check out the writings of Gallison re: how science happens.
An unpersuasive argument with some false assertions. For example, Matthew claims that astronomy has done "perfectly well" without a definition of a planet. Well, no, Pluto's status has been in question for a long time—and its status as a "planet" is important because the question is simply whether or not Pluto is essentially like the the other things we call planets. And the real trouble began when it became obvious that it's more like other things we intuitively know we don't want to call "planets" than it is like things we do. This is not "perfectly well".
Matthew's implicit assertion that quibling over arbitrary distinctions for nomenclature purposes isn't anything at all to do with science would indicate a profound ignorance of both the present practice and history of science that I had not previously thought of him. This is more likely a peculiar error than ignorance.
His assertion that how astronomy "really" classifies celestial objects is according to "what they're made of" is simply false. I don't understand this at all: all celestial objects, with so few exceptions that they cannot matter, are made of almost nothing but hydrogen. That being the case, this isn't a useful means to distinguish them. A better definition would be "how they behave".
But more to the point, the very few extra-solar planets that have been discovered are all brown dwarfs which are a type of celestial object which also may not orbit a star. In other words, not planets. Yet the discovery of a brown dwarf which orbits a star is noteworthy precisely because such an object is certainly a planet. Moreover, we become more and more certain each day that these few discoveries imply rocky, not gaseous, planets around extra-solar stars. The discovery of such an object is at hand and this is why pinning down what a "planet" is becomes urgent in a way in which it hasn't been in the past.
So, to sum up, all of the major assertions of Matthew's argument are false. Defining "planet" has been a problem for astronomy since not long after Pluto was discovered. Celestial objects are not sufficiently defined by "what they're made of", but "by how they behave". Planets obviously behave differently than stars and other objects which don't orbit stars, and, furthermore, they behave differently than the majority of objects which do orbit stars. More rigorously defining "planet" has taken on a much greater importance as we only now begin to deal with extra-solar objects which orbit stars.
As to the assertion that there's no distinction between Neptune and Pluto, that's just plain silly. The sense in which it has "failed" to clear its orbit of Pluto is not the same sense in which Pluto has failed to clear its orbit of Neptune. Indeed, I haven't read the report, but I'd guess that "Pluto hasn't cleared its orbit of Neptune" is more a media gloss than it is central to that point of the definition. Because, you see, it's almost certain that Pluto has failed to clear its orbit of a lot of other stuff similar to that which Neptune and the other planets have. But more than that, Neptune is a gas giant and unquestionably more like the other planets than is Pluto. For one thing, its orbit is in the plane of the ecliptic, unlike Pluto.
I suspect NPR got screwed up. Neptune HAS "cleared its orbit" - Pluto remains where it is only because it is locked in a resonance relationship with Neptune. (In the same way, the so-called Trojan asteroids survive in Jupiter's orbit by being at Jupiter's Lagrange points.
Comments closed September 12, 2006.
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Heads in the Sand
"Planet” could just mean “Mercury, Venus, Earth, Mars, Jupiter, Uranus, Neptune, and Pluto.”
And, as the B-52's would most assuredly add, "SATURN!"
Posted by spinozista | August 29, 2006 7:38 PM