Slashdot Mirror
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.
Don't see what's so hard about that ...
I hear there's rumors on the Slashdots
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.
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.