Slashdot Mirror
How Would You Define a Planet?
It doesn't come easy asks: "The argument over the definition of a planet continues. So far, two definitions are favored but without much consensus so far: base the definition of a planet simply on an object's size. Pluto would be near the lower limit and the newly discovered Kuiper Belt objects could also qualify, giving us 10 or 11 planets so far; or define the single dominant body in its immediate neighborhood as the only qualifying object for planetary status. If no one body dominated (such as the millions of individual asteroids in the asteroid belt) then none would qualify for planetary status. In this case Pluto would be disqualified (Neptune would be the dominant body in Pluto's region of space), and the newly discovered Kuiper Belt objects would also fail to qualify. The International Astronomical Union (IAU) working group charged with pinning down the definition of a planet may vote on the proposals within the next two weeks (or they may decide to start all over again with something new). Maybe Slashdot readers can give them some help. How would you define a planet?"
The obvious conditions are round shape and orbits the sun. Size is somewhat subjective although to have a round shape it would have to be above a certain mass.
Personally, I think a good definition of a major planet is one that is massive enough that, given its composition, it assumes a sphere-like shape.
cb
Oooh! What does this button do!?
The public will be happy to learn of more planets -- it feels like progress. It'll be hard to convince the public we lost a planet somehow. That sounds like an unimportant consideration, but I don't want us giving the Creationists more ammo for their arguments that Science is fickle. "They used to think there were nine planets, but then they found they were WRONG!"
It's not like any serious science rests on this definition anyway.
--Greg
Words like "planet" are meant to "carve nature at its joints". Problems arise when historically there appeared to be joints (planets moved differently than stars in the sky) but, we are learning now that there are no useful joints here. Why bother defining the word planet at all? Is it really that useful to astronomers? And why, say, want Mercury (a small rocky body with no atmospere) to be grouped in a category with Jupiter (a large, mostly gaseous body with an atmosphere) instead of with asteroids (small, rocky bodies with no atmospere)?
Gravity is a constant that should be used to define a planet. Any body that has enough mass to generate enough gravity to maintain a spherical shape should be a planet. Yes, even Ceres would be a planet by this definition.
There is nothing inherently safe about liberty. That's why so many people died protecting it.
The definition is largely meaningless anyway. No science hinges on what a planet is. It's a waste of time even to argue about it.
Tell those bitches to stop with the silly arguments and get back to the telescopes. When they have a valid scientific reason to differentiate a planet from a hunk of rock that just happens to orbit the sun, then we can start arguing about definitions with some kind of actual reason for it.
- Give a man a fire and he's warm for a day, but set him on fire and he's warm for the rest of his life.
No, Xena (one of the new trans-neptunian objects) is quite a bit larger than Pluto, so that would be 10 now.
--The universe will not be altered by forum threads, even those which are very wry. --Tycho Brahe (Penny Arcade)
wouldn't stars be "planets" as well?
See? Pluto's a planet. Nothing else is. Now move on about your daily life, citizen.
Orbits a star or stars.
Enough mass so that its gravity forces it into a spherical or an ellipsoid shape.
This defintion does make large astroids like Ceres a planet. Personally, I don't necessarily have a problem with this, but I don't really care. If you want to remove these you can add:
Must be a "free standing" object (i.e. not in a belt)
If you're dead set against Pluto, you can add:
Orbital inclination must be close to the orbital plane.
I not be an astronomer or an astrophysicist, but I really don't see what's so hard about defining a planet. Whatever the Powers That Be(tm) decide, it should be based on physics and not legislation. (e.g. "mass in excess of x metric tons")
I would add the condition that it must orbit a star, (to exclude moons) and not be a star itself (to exclude binary or multiple stars). And not be part of a belt of similar objects (to exclude Ceres, Juno, Pluto/Charon, and Sedna which are all spherical).
The days of the digital watch are numbered.
"planet" is a social term, not a technical one and freeze the list of planets at 9.
This leaves us free to give the things we discover designations that reflect their structure or their position.
I *do* think we will eternally regret wasting so many perfectly good names on moonlets and asteroids.
Clear, Dark Skies
That would further expand the definiton of a planet as there isn't much you can't blow up with the Death Star, the rebel cruisers in Return of the Jedi and the targeted rebel base in A New Hope on the moon of Yavin. It may even be able to destroy a star, since it got from Aldaraan to Yavin in what was at most a few I'm guess it has hyperdrive and can outrun the shockwave created by an exploding/collapsing star.
What about twin planets, say Romulus and Remus? They both appear to be planets, they do support life, which one would be conidered the domanant planetary body in its region of space? As far as Pluto and everything else in the Kuiper belt, we won't be able to agree on it until infinite improbability drive is invented or V'ger 6 is launched to map the area.
F7 doesn't work, ignore spelling and grammar
A botanist, a landscaper and a plumber walk into the forest. The botanist says "that's a wonderful specimen of Acer rubrum!". The landscaper says "Yes, a very nice Red Maple.". The plumber says "Are you guys talking about that tree?"
The different names are useful for different contexts, but they're all correct and proper. A layman is going to use the generic term "tree" because they don't really care about what species it is. A landscaper will use the more common name because they have to be able to distinguish different types of trees. A botanist will use the scientific name, because trees in other parts of the world have different common names, but scientific names are the same.
The naming system for planets needs to work the same way. A layman can call Pluto a snowball, and they're right. A school teacher can call Pluto a planet, and they'd be right. A scientist can call Pluto a Kuiper Belt Object, and they're right.
Pluto is a ball of ice, which describes composition. Pluto is a planet, because it's been so for the last 75 years; it's like trying to say Columbus didn't discover America. Pluto is also a Kuiper Belt Object, but that doesn't describe anything unless you understand the context; most people you ask "what is the Kuiper Belt" would respond "something to hold up Kuiper's pants".
I think the IAU need to take a step back, and look at biology for a minute. Come up with something like a binomial or trinomial nomiclature system for astronomy, and stop dicking around with common terms like "planet" and "star".
The bottom line here is that most professional astronomers don't care about these objective definitions. When astronomers are doing research, none of it hangs precariously on the definition of planet or asteroid or something else. They specify what they mean -- Jupiter, or the major gas giants, or the Earth-crossing asteroids, or transneptunian objects, or plutinos.
These names (planet, asteroid, comet, etc.) are just arbitrary labels invented by people, after all. They have no special significance, and they never have. After all, planet comes from the Greek word for "wanderer," a reference to the fact that planets appeared to be stars in the sky that moved. Asteroid means "star-like," a reference to the fact (as astronomical observations improved) they appeared to be moving objects that didn't have observable disks like the other planets (because they are too small).
The IAU, the international organization responsible for such names, has never given them any objective definitions. Why? Because they don't need any. Sorting out terminology like this is almost completely ancillary to getting actual astronomy and astrophysics done. The very reason that those interested in establishing definitions can't agree on objective definitions underlines the point: because they are totally arbitrary and not very important.
Almost all of the furor about redefining terms, recategorizing objects, demoting planets and promoting asteroids, has come from amateurs and the popular media. Don't you think that if professional astronomers thought that this was such a crucial issue that they wouldn't have taken care of it handily? They haven't because it's not nearly as important as amateurs seem to think. That amateurs and the popular media are seemingly fixated on such trivialities indicates strongly to me that they're missing something: namely that these classifications have no external significance.
The map is not the territory. Give it a rest, already. I know, why doesn't everyone concentrate their energies on doing actual astronomy?
If you can land on it and score with an alien chick, it's a planet.
By that definition, most slashdotters live on a big blue asteroid.
Table-ized A.I.