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Why the Word 'Planet' Will Never Be Defined
eldavojohn writes "What makes a planet a planet? Slashdot covered the great debate about whether or not Pluto qualified and Space.com now has up an article explaining why we'll never have the term 'planet' defined to a point that everyone can agree on. Divisions in the scientific community currently stand over whether or not it has to be in orbit around a star, the dynamics of the body in question and apparently the country you come from plays a part in it too. Some feel the United States is the dominant deciding factor on the definition but the IAU has not turned to democratizing the definition yet." From the article: "In the broadest terms, a planet could be thought of as anything from an 800-kilometer-wide (500-mile-wide) round rock orbiting a dead star to a colossal gas ball floating alone in space."
Floating mass of sh*t bigger than the moon that isn't on fire, but that is orbiting some floating mass of sh*t that is, in fact, on fire.
Luck favors the prepared, darling.
Some feel the United States is the dominant deciding factor on the definition but the IAU has not turned to democratizing the definition yet."
Lets see now.. democratically deciding a definition? hmm...
At any rate, the USA being the dominant deciding factor might make some sense seeing how they also invest a lot into the actual science part of this, but if the IAU did turn to democratize the decision, then the USA can't be the deciding factor seeing how they are a mere 4% of the world population....
actually called an "Air Biscut"....never heard it described as a planet before, but, I suppose if it really were that colassal....
A goal is a dream with a deadline
'A series of gaming sites ran by counter strike kiddies who think that half life 2 is going to be better than far cry.'. Not sure I quite get that 100%, but you can't argue with the wisdom of the internet.
Don't see what's so hard about that ...
I hear there's rumors on the Slashdots
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Layne
From Wikipedia:
In ancient times, Grecian astronomers noted how certain lights moved across the sky in relation to the other stars. These objects were believed to orbit the Earth, which was considered to be stationary. The "wandering" lights were called planets, a Greek term meaning "wanderer".
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Why not just stick to this original definition? If it "wanders" among the stationary celestial lights and casts light visible to the naked eye, it's a planet.
Everything else can be labeled SAO "speculative astronomical object."
Read any good sonnets lately?
Anything equal to or greater than the size of Marvin's brain.
I don't get the problem? First, start off with the idea that a planet must be orbiting a star... similar to how moons are defined as orbiting a planet. Even if they are orbiting a pulsar (dead star) they are still planets, but not if they are orbiting a failed star (brown dwarf). If you find a brown dwarf with satellites call that something else. Then the article mentions the possibility of having planet sized objects orbiting each other the same way binary stars orbit one another. OK, make that a seperate category. After that just define the mass need to be called a planet and be done with it. I'm sure there are plenty of other scenarios out there that need to be defined, but the basic rules don't seem difficult to set up.
Unfortunately, as we do not have the minimum 9 planets required to qualify as a class A solar system, we will have to wait for a trial date with a municipal court first.
Have gnu, will travel.
"Anything which is roughly spherical under its own gravity, in a more-or-less circular orbit around the sun, and its orbital path isn't shared with an object larger than itself."
How about "It is a planet if Galactus would consume it" ?
The real question is, why do we need a precise, "official" definition of "planet"? Astronomers and other scientists aren't going to make scientific decisions based on it -- it's not like it matters whether Pluto is officially a planet according to the IAU when an astronomer decides to study Pluto. "Oh, the IAU says it's not a planet, therefore it's not interesting enough to study."
In general, the whole point of category words like "planet" is so that I can point at an object and say, "That's a planet," and you immediately have some basic information about it, because we agree on what "planet" means. But if we're scientists, studying it (or deciding whether to study it), then we need a whole lot more info. Gas giant? Small, terrestrial rock? Iceball? Distance from star? Eccentricity of orbit? Etc. "Planet" doesn't tell you any of that.
Ultimately, the main reason to specify an "official" definition of "planet" is for the sake of deciding whether and how we want to encourage space travel, exploration, astronomy, and related sciences. To give an extreme example, if the definition of "planet" included any solid body primarily orbiting a star, there'd be millions of planets in every star system, and saying that NASA's going to go explore a planet would be meaningless. The public wouldn't care and wouldn't go out of its way to support it.
At the other extreme, limiting the planets to rocky or gaseous bodies at least the size of Mercury, orbiting a star, and having a very low orbital eccentricity, means that when you discover a body that only misses ONE of those criteria, the definition seems arbitrary and people will just ignore it. Imagine if we find a trans-Neptunian object that's the size of Mars, and is a rocky, terrestrial body like Mars, but merely has an eccentric orbit? Very few laypeople would accept that that's not a planet, mostly because laypeople's perception of a stellar body is based on its physical characteristics, not its orbital ones. If Earth was somehow flung out into space, orbiting nothing, it'd stop being a planet? (Well, we'd all be dead, but that's another issue.)
"Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
... so why not the IAU. Simply break planets down into different subclasses. Everyone knows that Earth is a Class M planet.
There's already a helpful classification guide to help them get started.
It's a problem with any discipline -- language is not exact.
What qualifies as meat? Does seafood count as meat? Not for Catholics.
What qualifies as a person? What about in utero? Maybe for manslaughter, but why not count that time for age restrictions?
What qualifies as blue? Is cyan blue enough? It depends on what you're using the category for.
Anyone who's tried to work on standardize terminology (eg, specialized thesauri, or even just a controlled vocabulary) will know that it is a long, exhasting process that takes years in some cases, and even then, is likely to change.
Planets are not a classical category, and will be subject to prototype effects.
Build it, and they will come^Hplain.
There can't be one definition because there are three classes of planets. Gas giants, rocky planets and icy planets. The big argument is whether to include icy planets but icy planets are closer to earth than gas giants so how do you include one but not the other? The sensible definition to come up with three classes and require them to orbit the sun to exclude moons and to have sufficent gravity for a roughly round shape, the Earth isn't perfectly round. What it would leave us with is four rocky planets, four gas giants and a similar number of icy planets. The Oort cloud gets tougher. Since they still orbit the sun it might be wise to come up with a fourth definition of outer planets for any Oort Cloud objects. One excuse for eliminating Pluto was it's eliptical orbit but most planets have eliptical orbits so that factor gets arbitary. Splitting the definition avoids demoting any planets and allows for new objects including some that may not fit well with the current definition.
Richard Feynman had something to say about this debate, though somewhat obliquely. The parentheticals below are my own.
"You can know the name of a bird (or a planet) in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird (or planet)... So let's look at the bird ( or planet) and see what it's doing -- that's what counts. I learned very early the difference between knowing the name of something and knowing something."
The point here is that scientific knowledge (whether it be social, biological, or physical) is about explaining how things work (understanding processes) or why they are the way they are (understanding variation). Debate over essentialist categories like "planet," "species," "nation-state," etc. are, as one other person in this discussion has already mentioned, problems of language.
Interestingly, Wittgenstein might have a thing or two regarding this topic as well, especially in later work.
The first principle is that you must not fool yourself - and you are the easiest person to fool. -Richard Feynman
A better way to do it would be to set a minimum atmosphere, size, density for Planet/Dwarf Planet/Asteroid/Gas Giant classification...A nomenclature similar to Chemistry is needed.
Quite right. They're all planets but of different classes. We could list up all the types of planets we know about and assign alphabetic class numbers to them. An Earth-type planet could be, "Class M". I know, wild, original idea...
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