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Is {pluto|sedna} A Planet?
Dr. Zowie writes "NASA's announcement last week of Sedna's discovery reignited the debate
over whether Pluto is a planet. Dr. Alan Stern a noted planetary scientist and leader of the New Horizons mission to Pluto, pours on some gasoline with this
article in which he skewers the various arguments against Pluto-as-planet. Choice quotes include 'You wouldn't deny a chihauhau a place among dogs because it is too small,' and 'if your brain was so completely full of names of people that it just couldn't take any more, would anyone new who you met after that, therefore not be a person?'"
Although you have to admit that we NEED a planet named after the god of the dead. Perhaps we can put some trash out there and christen it.
What we call folk wisdom is often no more than a kind of expedient stupidity.-Edward Abbey
Err, by 'FP', I am of course refering to 'Final Planet'.
Of course. What did you think I meant?
Huxley
Does that mean every comet/asteroid that orbits the sun is technically a planet? If you throw out the size requirement, what other criteria remain for designating something a planet?
The Doormat
If you're not outraged, then you're not paying attention.
The two-legged things in my office have names?! Not just email addresses?
".. pours on some gasoline with this article..."
You haven't seen squat until you've seen astronomers argue.
Chihuahuas everywhere growl in unison.
Planet or not, it's out there and it's circling the sun. It's large enough to attract space dust and rocks in its vicinity. It will eventually grow larger and then there will be no doubt that it is a planet.
But really, who cares? Is this a big deal?
I have been pwned because my
How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not. Pluto, BTW, Sedna, and many of the largest moons can all do this.
I also think, for the record, that if something as large as Luna, or Titan, or Europa were out floating in space orbiting the sun and not another planet, they would be considered planets too.
A problem with this is that there really is no clear-cut differentiation between "planet" and "planetoid". There's no qualifying size-- it's more subjective than anything. Almost like different species: we all differ genetically, yet a species is a generally-recognized "set".
One agreed-upon qualification is being formed round by its own gravity. I'm not sure if that applies to Sedna.
---
Never criticize religion on Slashdot. You will be modded down for "Troll" no matter how factual it is.
...a pluto. And Sedna a sedna. The solar system would have 8 planets, a pluto and a sedna, then. :)
{(Pluto AND NOT Sedna) | (Pluto AND Sedna)}
Seeing that if Pluto is NOT a planet, then Sedna certainly is not either.
If the above pseudo expression is true, Pluto is a planet, and Sedna may or may not be.
This SHOULD be what we are asking.
The Atlantic Monthly had an article about the Pluto situation years ago. The problem, though, is that "kids love Pluto." Scientists have tried to change names before (such as the dinosaur example). It'll be interesting to see what the public says about Pluto's demotion (if it occurs).
Does this guy have a PHD in faulty reasoning?
If it's a sphere, it's a planet. If it's irregular shaped, it's not.
And just what makes me an authority on this? I've taken more Astronomy classes in University than the average bear.
So here is my reasoning from an old assinment of mine:
A) Is Pluto a planet? Many measurable criteria signify that Pluto is a planet, but it is not a major planet. It is too small to be a major planet, so it is a minor planet or a giant comet. The only reason some astronomers still accept Pluto as one of the major planets, is because an American astronomer discovered Pluto in 1930, and they feel that changing its status to "minor" will minimize Pluto's significance in the solar system. Obviously books will need to be changed to reflect its new status, and many feel it would just be simpler to let it continue to be seen as a major planet, despite the facts saying otherwise.
It might make sense to consider placing Pluto into different categories, such as minor planet and comet. "Dual status already exists for some comets and minor planets, which are given formal numbers and names in both kinds of catalogues." [Green] The various categories we have for collections of matter in our solar system are many. The main categories are star, giant gaseous planets, smaller rocky planets orbiting the sun inside the "asteroid belt", satellites orbiting both major and minor planets, trojans, comets, trans-Neptunian objects (TNOs) and Kuiper belt objects. Meteoroids, and bits of dust, gas, and sub-atomic particles round out the other matter in our solar system.
A large asteroid named Ceres was first discovered in 1801, and was first presumed to be a comet. Then it was classified as a planet. That means astronomers, hypothesized that Ceres was a planet, they tested their hypothesis, and upon inspection of the available data years later they concluded that Ceres part of a new family of minor planets that was just being discovered. We now know of other TNOs, and Pluto doesn't look all too different from them, so we could adjust our view to place it as one of those other 100+ objects.
We can teach school children valuable lessons about science and astronomy if we teach them the history of the classification of Pluto, but stop calling it the ninth major planet. Pluto would not be called a major planet if it were discovered today, so it is a bad lesson in science to ignore data in favour of political concerns. People who say Pluto should remain a planet because for 70 years we have called it so, do not know the history of astronomy. They either don't know or don't care that many celestial bodies have been reclassified as new scientific data is gathered. Outdated models are thrown away in favour of newer, and more accurate models. Pluto no longer fits the major planet model that we use for the 8 major planets, so with our new data we should find Pluto a new category.
B)
Pluto was classified as a planet, when the data available to astronomers indicated it was one. Now the technology has allowed us to gather more accurate data about Pluto's characteristics, we should re-evaluate it's current categorization. People have had to re-evaluate "scientific facts" for millennia. Classifying the Earth as the center of the universe made sense several hundred years ago, but now we know more data that shows it cannot be the center.
From what we know about the physical characteristics about Pluto, I say it is a special minor planet. It seems odd to classify it as a kind of a comet, since I've seen no evidence that it leaves a trail of debris, and we don't know if the core is rocky, or ice like.
Saskboy's blog is good. 9 out of 10 dentists agree.
They won't answer you anyway.
Huh... Post subject would literally translate to "Is pluto or sedna a planet?" implying a choice between the two, an either/or scenario. However, I believe the poster ment "Are {Pluto|Sedna} planets?" which sounds strange, but parses better, to "Are pluto or sedna planets?"
Since when has this country used intellectual elite as a pejorative term?
0
Nope. Guess not.
I don't know what to think about this...I mean, Pluto IS rather small, and so maybe we should just consider it part of a ring of minor planets on the edge of the solar system, along with Sedna and Quaoar. There's a ring of minor planets in between Mars and Jupiter, somewhere around the asteroid belt, too, so it wouldn't be totally out of the ordinary. (Which raises the question on the diference between an asteroid and a planet...) However, I also think that maybe we should consider Pluto a planet, if for no other reason then we have always considered it a planet, and wouldn't want to avoid confusion. But that's hardly scientific, is it?
Either way...I just think the scientific community needs to make up it's mind already.
"You wouldn't deny a chihauhau a place among dogs because it is too small."
Dog? I always that chihauhaus were large rats.
Alan Stern said, "wouldn't deny a chihauhau a place among dogs because it is too small"
yeah, no kidding. But if the definition of a dog included, "must not weigh less than 30lbs" then yes, a chihauhau would most certainly not be dog.
I know there is no such definitive critereon for planets, but jeeze...a simple webster's definition includes the phrase "...large heavenly bodies..." (emph mine). Any reasonable defintion of large would probably exclude pluto, just as any reasonable definition of "large dog" would most certainly exclude the lowly chihauhau
Honestly, the question is almost worthless. Does pluto change because I say it is/isn't a planet? Does it get bigger? It it worth more?
Pluto is pluto. whether it is a planet or not is mere bookkeeping, not even worth discussion.
Laws are horrible moral guides, moral guides make even worse laws.
Comment removed based on user account deletion
My charts are going to have to all be recalculated if Sedna is a planet. What a PITA if there ends up being 900 planets! How will I ever be able to calculate this week's horoscope before the week is up?
We should have stuck to the original five. Mercury, Mars, Venus, Jupiter and Saturn. Earth doesn't count, since all these revolve around it.
Let's not mess with our destinies. Don't upset the natural systems any more.
So what do we settle upon for criteria? Size is actually rather an arbitrary and vague boundary at both ends.
The fact that it orbits the Sun, specifically? The Sun's nothing special, we've found plenty of other stars that have planets. And if the Sun snuffed it tomorrow, would the Earth cease to be a planet? Would Ganymede be a planet if it were let loose for a stroll on its own away from Jupiter?
What about moons? Venus and Mercury don't have them, and those two rocks around Mars don't count.
It can't be geological activity, because Mercury is dormant and Io, a moon, beats everything we've yet seen for volcanic eruptions.
I think that having a discernable stata and a core of different composition than the crust sounds like a good rule of thumb, because then you're not just talking about a lump of rock that happens to be round, like Ceres. Now we just need to see what Pluto, Quaoar, Sedna have got in that department.
Harvard has a nice page with lots of links an references for people looking to dig deeper into the Minor Planet definition under which asteroids like Ceres and Sedna fall under.
Saskboy's blog is good. 9 out of 10 dentists agree.
Okay, both are spheroids. Both have atmospheres. Both orbit our sun. Both even have satellites of their own. The only reasons one COULD say that they're not are that they're small, and they're way far out there. Both of those 'arguments' are pretty pathetic, IMO.
In short, there are more reasons for them to BE classes as planets than for them NOT to be.
On a related note, 'Sedna' is a really good name for an HMO, but a really _horrible_ name for a planet! *booo* Hell, even 'Planet 10' is a better name than Sedna!
I think there needs to be the addition of an atmosphere to be considered a planet. Really it's just a round rock without one. It pretty much classifies moons as planets without that qualifier.
Not since Marie-Antoinette played milkmaid has looking simple and honest been so fake and complicated.
Or however it was spelled? Didn't this whole debate come up a relatively short while back when this planetoid was discovered? It seems a little odd that no mention is made of this other recent Kuiper Belt planetoid discovery, in all of these stories on Sedna. Does the media have a ridiculously short memory these days or what?
---
http://thewired.blogs.com/teotwawki
The techno-mediated cultural conspiracy
Lucky for us we didn't discover a 'planet' with a completely liquid surface yet, to limit the 'round' criterion even more. This way astronauts making water bubbles on ISS can claim they're planet-makers ;-)
(hint: surface tension also makes things round)
When i was in grade school (2nd or 3rd grade) we made up a stupid sentence to remember the planets...
M y
V ideo
E ye
M ay
J ust
S how
U s
N ine
P lanets
Damn you people for robbing me of my childhood!
Oh, ok, I suppose it's in space, and space is usually a pretty good vacuum, so doesn't smell. Unless you're in a space suit. In which case it wouldn't necessarily smell sweet. Might smell as sweat; but that's the smellor not the smellee asteroid. Hmm. Right.
But my point remains I think. Glad to have made it I think. Worth saying. Right. Good. Yes.
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"Six months after Kirk stranded us here, Ceti Alpha 6 blew up, and according to GRAVITY RULES the 720 fractured pieces large enough to collapse into roughly spherical shapes count as planets, even though they aren't spherical yet and won't be even in my eugenically extended life time.
So the shockwave that blasted our planet outside their orbit means THIS is Ceti Alpha 726. Gravity Rules. MINE is the superior intellect!
Recycle PCs and build a wireless community network www.hillsborough.org.nz
Ignoring the size issue would mean there are literally millions of "planets" orbiting our sun. Obviously there must be some threshold, just as Saturn doesn't have a ring of moons, and there isn't a Planet Belt just past Mars. But ignoring the absolute idiocy of that arguement, many astronomers don't consider Pluto to be a planet because it's orbit is in an entirely different plane than the rest of the planets. While the other eight all line up nicely, Pluto and Sedna have their orbits tilted at an angle. The orbits themselves are also much more elliptical. All this is in line with the definition of an asteroid, not a planet.
But yes purely excluding on size seems stupid. What he says makes a lot of sense. So what if it upsets some people who like a nice clean solar system. Simply saying But one thing I miss is what seperates moons from planets. Is the moon also a planet? Or did he forget to include that a planet has to orbit a star directly? (the moon orbits the sun indirectly).
MMO Quests are like orgasms:
You may solo them, I prefer them in a group.
He wants a Boolean criterion (yes/no) for planethood, but then criticizes a 'minimum mass' limit as being arbitrary. It is not possible to impose a Boolean criterion onto parameters that vary continuously without there being an arbitrary boundary somewhere.
Other than that, a pretty good discussion. His suggestion will still require an arbitrary boundary (how round is round?) but it is not totally arbitrary.
His rule has a problem that it turns into planets objects that we had previously decided were not planets. It has the advantage of being less arbitrary than the alternatives. Whether the advantage outweighs the disadvantage is a matter of taste.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
I think part of the problem is the fact that memorizing the 9 planets are all most people really know about our solar system, and so they tend to be fairly sentimental about it. I think a much more accurate and interesting approach to teaching kids would be to start of by brainstorming all the different types of objects in space - galaxies, solar systems, stars, moons, astroids, comets, nebulas. Then instead of memorizing just the planets memorize all the different regions of our solar system and what makes them special. Start with the sun, then you get to the inner planets, then astroid belt made mostly of rock, then giant gass planets, then the Kupier Belt full of icy objects and finally the Oort cloud. Then lastly you describe the interesting features of each area, including the planets and what makes them unique.
This journey approach would be far more interesting to the kids and by the time you got to the point of describing pluto and charon, they would have an understanding of how diverse (for lack of non PC word) matter in space is and would be less concerned about sticking a specific catagory on it, and just be excited that it was yet another unique and interesting thing.
It's the difference between decribing the cool terrain, people and features in country as opposed to just memorizing the state capitals. The former is far more interesting, and informative, and kids will eat it up.
Deimos and Phobos are the moons of Mars and they are not round.
Ceres doesn't even have its own orbit (it shares it with other asteroids).
I don't think in the grand scheme of things, that it makes a bit of difference. WHO CARES!
I'd be more concerned if another idiot with a cause would fly a plane into a building.
Will someone, once and for all, tell me what difference it makes whether something is called a planet or not?
Classifications can be such a pain. You'll always have someone arguing about those members at the border between classes. What are important are an object's characteristics not its name. Just saying the word "planet" wouldn't tell me anything, I'd still need to know its vital statistics. So why not call it a planet or a belt object or an invisible pink unicorn, for all the good it does, and then file all the USEFUL information we can about it.
It's like the koan about what to call a short staff. If you call it a short staff, you deny the truth that it is also a piece of firewood, a lever, a weapon, a paperweight, or any number of other things. If you don't call it a short staff, you ignore the fact that it IS a short staff.
Don't blame me, I voted for Durga.
Tomato is, and always has been, a fruit.
The supreme court rulled that it was a vegitibale so schools could meet nutrienal guide lines.
Rule of thumb:
Does it have seeds? then its a fruit.
The Kruger Dunning explains most post on
I think I've seen this criteria somewhere, but not in the aforementioned article:
if it orbits the sun and it is round, then it's a planet.
Planetoid could be something approximately spherical/ellipsoid, like Vesta.
Everything that orbits the Sun is a planet. Everything. Whether it deserves a name is another matter.
So let's arbitrarily set a threshold of 500 miles as the minimum diameter for something to get a name. What about objects that are 499 miles wide? Oh, well.
(Yo quiro Taco Bell...)
They say the first thing to go is your penis. Well, it's either that or your brain. I forget which...
chihauhaus are clearly rodents, not dogs. Therefor, Sedna is not a planet, but a rodent.
One future, two choices. Oppose them or let them destroy us.
planot
What usefulness is the "planet" designation anyway? To me, it's just an arbitrary classification that doesn't mean anything in the end. If you describe the body in question--its orbit, its size, its composition, atmosphere, etc.--then you've told me everything I need to know about it to make my own judgements. Calling it a planet or not is just for warm fuzzies.
People argue over whether to call Pluto, Sedna, and Quaoar "planets" or "trans-Neptunian objects," but even once they finally decide, they won't have actually told me anything new that I didn't already know.
How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not.
:)
:) But clearly a planet-sized object orbiting another planet is a moon. Again, this definition makes perfect sense.
:)
I like this definition a lot. While it does leave some wiggle room as to what exactly constitutes "spherical", it is still based on a physical property of the object related to its mass. This makes it better than any arbitrary size/mass requirement (e.g. "Anything as big or bigger than Pluto").
Pluto, BTW, Sedna, and many of the largest moons can all do this.
I'm going to be extremely unhappy with any definition that demotes Pluto. Also, anything that makes Pluto not a planet is going to be close to making Mercury not a planet, and that's just not acceptable.
I also think, for the record, that if something as large as Luna, or Titan, or Europa were out floating in space orbiting the sun and not another planet, they would be considered planets too.
Titan is bigger than Mercury, so a Sun-orbiting Titan not being considered a planet is unacceptable.
I'm not an astronomer (but I play one on occasional weekends), but of all the definitions I've heard, "big enough to be spherical and orbiting a star" is the simplest and most logical.
And for the record -- if there was some comet out in the Ort cloud with an incredibly eccentric orbit around the sun that was the size of Titan, that'd be a planet too. IMHO.
The enemies of Democracy are
Only major planets have moons.
Does Pluto have a moon? [checking] Yes.
Therefore, Pluto is a major planet.
M any
V ery
E gocentric
M en
J ust
S aid
U ntrue
N ine
P lanets
S urpassed
It is no longer uncommon to be uncommon.
Pluto has a moon. Find me a minor planet that has a moon.
Any object the orbits a star that has enough mass, and therefore gravity, to become spherical. The moons of Mars for instance, are very much like asteroids caught in Mars' gravity. They do not, however have enough mass to become round. Most of the objects past Pluto probably are very small. Sedna's planet status should governed by it's shape.
Anyone think to ask Disney?
One thing to keep in mind in the planet/not a planet debate is the fact that the first eight planets have relatively circular orbits, while Pluto and Sedna have highly, highly elliptical orbits, more similar to comets than the other planets. Also, the first eight planets all orbit fairly close to the same plane (think "plate like"), while Pluto is inclined around 30 degrees, if my memory serves me correctly. This obviously won't end the argument, but it is something to think about.
Pluto doesn't care what you call it, it's f*cking rock.
Speaking for myself, I'd say the first criteria for planet status would be having an orbit in the plane (within reason) of the rest of the planets and not crossing the orbits of any of the others.
I wouldn't say that was sufficient, but I would say it is required.
Man! And here I thought that Taco Bell was being weird with a talking, undersized, somewhat twitchy rat!
Chas - The one, the only.
THANK GOD!!!
It's pretty clear from the planes that each planet makes around the sun that every planet except for Pluto came from the original gas formation or whatever that created the solar system. Pluto is the only one that has a messed up orbit, so it's obvious it's some type of captured mass that got too close to the solar system.
But who cares? Let's just call it a planet for the sake of history. Jeeze, I mean we have the Pacific, Indian, and Atlantic Oceans even though they are clearly the same body of water. The difference between the Indian and Pacific Ocean is even more nebulous.
Why not call Pluto a captured planet, and keep it as it is, ie. a planet within the solar system, and everything else, just forget it. We don't need any new members... the people who are trying to induct anything new just want their names in the history books.
My Very Eager Mother Just Served Us Nine Pickle Sandwiches?
There's an interesting discussion of this and some facts at kuro5hin.
How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not.
This is exactly what is proposed in the article. I don't think moons should be included, though, since their primary orbit is a planet, rather than a star.
The objects out there don't care what you call them. Astronomy doesn't magically change because we call something a "planet" or not, the bodies still have the same properties that they had whether or not you classify them, reclassify them, or unclassify them. The map is not the territory. Those shouting the loudest for reclassification of Pluto as a non-planet, etc., are those who aren't even professional astronomers. That shouldn't tell you a great deal about how important this issue is to the astronomical community.
We already know what a comet or an asteroid is. So why not define a "moon" as an object that circles a planet, and a "planet" as an object that circles the sun? Man made objects are satellites, of course.
I suppose there will always be those who will argue that size matters.
Perhaps he didn't mention it because all objects meeting his "gravity rules" requirement happen to have stable orbits.
SNIFF
A truly lovely bit of poetic art.
grub
Damn my short-term memory loss. A week or so ago I read an article where an astronomer said that Pluto is not a planet because of it's interaction with the rest of the solar system. Pluto's orbit doesn't lie in the ecliptic and intersects Neptune's at two points (2D projection). Also, Pluto's orbit is slightly less circular than the rest of the planets.
This doesn't really disprove Pluto's status as a planet, but it does raise the question of Pluto being a planet in our solar system.
I also agree that there should be a Little Prince standard to classifying planets. Of course that is just placing our arbitrary viewpoint on science. Of course the whole argument is moot as long as we have to sit on our planet to explore the universe.
You gotta love that term. It's crazy to hear and read what astronomers are coming up with these days.
... .
If it revolves around the sun, spins around its own axle, and it is spherical, it's a planet. And so is Quaoar.
Case closed, move on
How about instead of an atmosphere (which would rule out Mercury), we say that planets are anything large enough to have gravitational rounding and orbits around the sun, rather than another body? That would fix moons as moons.
-T
Is Pluto a planet?
Is Sedna a planet?
That's what the regexp ment. You don't convert it to english and the interpret the result, you read it in the language it was written (i.e., a bastardized regexp/english combination).
Just for reference if I were to do:
ls -1 | grep 'j[a|b]c'
in a suitable directory I would get:
jac
jbc
i.e., I would get all matching facts. So assuming we had a directory with all the questions about space, the regexp in the topic would enumerate the two questions I stated above. Of course, I'm assuming the semantics of {word|otherword} is the same as [a|b] but with words instead of letters, but I believe that was the intent.
How we know is more important than what we know.
It isn't Sedna, get it right, it's Rupport. They practice astrology, and we really do need some sort of planetary shielding right about now!
Dogs, coyotes, and wolves can interbreed and make perfectly fertile offspring -- that's a real problem for the preservation of wolves and coyotes. There's a quite a bit of tradition involved in deciding what is a species and what isn't. Greeks and Romans saw wolves as something other than wild dogs, and thus we do too. And of course, the vast majority of organisms on Earth are asexual, making the whole issue of "fertile offspring" moot. Logically, all decisions should simply be based on percent identity of DNA, but then the question becomes what percent should be the cutoff.
Ok, maybe I just don't get it, but why is there such an argument over whether to classify pluto or sedna as planets?
Does having the name "planet" attatched to a celestial body raise it's intrinsic value? The word planet is just a word, like any other word, and exists merely as a way to denote a thing or group of things more easily.
Since the general population doesnt really care, and the astronimers will know what object is being refferred to regardles of the word used to describe it, why don't we just toss a coin/roll a dice/whatever and pick something
I'm not trying to troll here, I'm genuinly curious as to if there is a reason or not for the big argument.
Famous Last Words: "hmm...wikipedia says it's edible"
ok
There may be another Earth-sized planet that was ejected by Neptune and that in turn shifted the orbit of Sedna. Why don't we see that planet? Because it may be in the aphelion, perhaps light week away. Not only it is far away from us, but it's also in the darkness, being far away from the Sun.
Or maybe the Sun approached another star in the past, which changed the orbits of the outermost Kuiper Belt Objects. Finally, maybe it was our Sun that snatched Sedna from another star.
Astronomer: "oh oh oh, yeah, well, you have your head up Uranus"
"There is no teacher but the enemy."-Mazer Rackham
Why? because I said so ..
**bong** AT&T, how may I help you?
Yes, I'd like the dialing instructions for Pluto, please. You know, the planet.
Sir, I have no listing for a "Pluto, Planet of"
It's gotta be there -- it's right past Neptune
I'm sorry sir, I have no listing.
OK, thanks for your help
Well, I guess that settles it. If the phone company says it's not a planet, then it's not a planet, no matter what those astronomers say.
Chip H.
This is exactly the same as the continent-versus-island debate in geography. Why isn't the United Kingdom considered a continent by anyone except the Brits? Why is one single monolithic land mass with a dotted line down the middle considered two continents, Europe and Asia? How is Australia not a continent?
How hard can it be, just set a limit. Here is my proposal:
Any planetary body orbiting the sun in a regular orbit and has a size >= Pluto is a planet. All planetary bodies with a size Pluto is a Planetoid, Planetlet, Asteroid, Comet whatever...
How hard can it be for the astronomical community to decide on something like that???
By your definition any satellite we put at one of Lagrange points is a planet. The point of classifications is to supposed to simplify discussions not complicate them. The problem is mostly due to trying to use a single criterion for determining what is a planet. There's been some good suggestions, and there should be several criteria.
Orbits the sun is pass/fail. Mass above a certain value then makes it a planet, else check further. Some possibilities are eccentricity of the orbit, how spherical the planet/planetoid is, size (as opposed to mass), escape velocity from the gravity well, atmosphere, etc....
Some of the above are better choices than others. For example, eccentricity of the orbit is a poor choice. A captured object should be just as likely to be called a planet as one formed with the original planets. Also, these criteria could be evaluated on a scale and total score applied, rather than pass fail on any chosen.. Just my $.012 after taxes.
Our founding fathers removed the guys in charge. Be American. Vote incumbents out.
There are a few senisible rules that we need to consider when asking whether something is a planet. First and formost, is it spherical? If something has enough mass to cause it to take a spherical shape then it has passed the first test. Second, does it fuse anything? If it doesn't fuse anything, then it passes the second test.If it fuses anything, then it is a star. Although if it is deuterium that the object fuses, then it is a brown dwarf star. Third, does it orbit a star? If it orbits something other than a star, then it is considered a moon. If it orbits a star, then it has passed the third test. By these tests, both Sedna, Pluto, and Quaoar are planets. However, so is Ceres (the largest astroid in the inner belt). So, the real question is do we want to make a distinction between really small planets and big planets. Mecury only has a diameter of 4879.4 km. That is about twice the size of pluto, but it is still smaller than Titan and Ganymede which are both moons. So should we strike Mecury from the list of planets, I think not. An arbitrary size is not good enough. If we don't follow the guidelines laid out above, I hope there is a damn good reason.
Yes, that would be why he stated that GRAVITY would be making the object round, not some other force. So, no, by that definition water bubbles would not be planets.
common sense: noun
What those who are ignorant of the subject matter think; usually wrong.
Offtopic: could the editors please pay a tiny bit of attention to spelling and so forth? "Is {pluto|sedna} A Planet?" is just insane. Capitalize your proper nouns, people (especially if you're going to cap "a" in a title, which is generally considered silly).
Everything you said was right,
Though the earths "moon" should be considered a second plant in our bi-planetary system. It is large enough that the center of gravity for our orbit is well off from the center of the earth.
(just another pet peeve of mine when it comes to astronomy)
I live in a giant bucket.
People, please Read The Article. The definition the author proposes is: a body in space that
1. is large enough that its own gravity forces it into a sphereoidal shape
2. isn't large enough to initiate fusion.
This covers objects larger than some hundreds of kilometers and upto about 75 Jovan masses.
The author points out we have no truble further qualifying stars, for example, dwarf, giant, super-giant, etc., so we can surely further qualify planets.
And to the four usual categories of asteroids (stony, metallic, stony-metallic, carboniferious) I'd add icy. So the trans-neptunian objects are either icy asteroids or ice planets, assuming that what we think we know about their origin is correct.
And, yes, a planet that's in orbit around a larger planet is a moon. So Luna is both a moon and a planet.
Now, where do we draw the line between minor and major planets? Atmosphere?
Second, the object must be round. This criteria excludes most asteroids.
Third, the body must be large enough that its own gravitational forces can account for it shape. This criteria excludes any objects which might happen to be round but can't really be called planets, such as small round rocks or asteroids.
Fourth, there must not be any similarly sized objects in the same orbit unless the gravity of one significantly affects the orbit of the others. This requirement excludes comets and all remaining asteroids.
Fifth, the object cannot be in orbit around another object that otherwise qualifies as a planet. Objects which orbit eachother may qualify as a double planet if all other criteria are met.
File under 'M' for 'Manic ranting'
...kinda threw me for a loop. Look, chihuahuas are classified as dogs due to their genetic composition. They're sorted down to a certain genus and species and are most certainly close enough (in their genetic makeup) to other animals we call dogs to be considered one. Size does not matter.
:P
If we classifed planets using the closest possible method, say material composition ("This rock is 70% nickel, 30% iron... whatever, you get what I mean?"), it would be too damn hard to classify an object as a planet properly. Compare Jupiter's chemical composition to Earth's. Doesn't work. So instead, I believe planets should be classified by relative size, orbital pattern, and possibly the rate at which they orbit.
It's easy to say that in order to be a planet, the object must be determined to be orbiting a solar system's sun. You could also possibly define a certain speed of orbit to further clarify things, though it would be harder to settle on. The first (relative size) isn't as easy to define as the others though, for example say a rock out there orbiting the sun is, oh, 5km in diameter. We decide to call it a planet. It's fairly big, it's orbiting the major heavenly body (sun) in the solar system in question. Then suddenly from around the planet comes another rock with a slightly larger orbit and different orbital trajectory. It's big too, but only 4.9km in diameter. Or 4km. Or 3km. Size is hard to include in the definition of a planet. But it does matter.
But no matter what you decide, with the knowledge we have of the universe today, it's going to be hard to settle these little conflicts over what's a planet, and what's just an asteroid, and what's just a little rock that happens to be orbiting the sun. Maybe a committee should come up with a set of standards for defining and classifying heavenly bodies?
I dunno. I just kinda jumped on the chihuahua thing and wanted to contest that argument.
Is Ceres the fifth planet from the sun, then? It is shaped into a (rough?) sphere by gravity.
Ewige Blumenkraft.
You wouldn't deny a chihauhau a place among dogs because it is too small,' and 'if your brain was so completely full of names of people that it just couldn't take any more, would anyone new who you met after that, therefore not be a person?'"
Mmmmmm... Somebody who likes the sound of his own voice way too much.
As far as planet vs planetoid goes, I'd think the difference relies on how much influence is imparted on what body of mass. For instance, the majority of influence imparted on asteroids comes from the planets and stars they revolve around, whereas the planets principle influence is the sun.
So which influnces these celetial bodies more? The sun or other planets around it? Does the body influence other celetial bodies a great deal? Does it have it's own bodies trapped in orbit around it? If this body careened through the solar system close to a planet (say, earth), how much influence would it impart on us??
I'm leaning more toward planet, especially in the case of Pluto. Sedna, I'm not so sure about given the lack of hard data, but I'm pretty sure a near pass from Pluto would seriously screw things up here. Besides, all this crap is relative anyway. I'm sure if you had a huge enough planet, Earth could be considered a moon or something.
You need a FREE iPod Nano
The definition that makes Pluto not a planet is not based completely on arbitary size and so would probably not demote Mercury as well. The most prevalent definition of a planet (which was not stated in the article as far as I could tell, at least not completely) is any gravitationaly round object that is more massive than the rest of the mass in a similar orbit COMBINED. Mercury would be safe with this definition, while Pluto would be quickly tossed out. I actually like this better as the term "planetoid" now means something different than either "planet", "asteroid" or "satelite." (it would become a synonym of one of these otherwise) I propose the following definitions:
Planetoid: Any object that becomes round by its own gravity but does not sustain fussion.
Moon: Any planetoid that orbits another planetoid (let's face it, it's a generic term and nothing will ever change that). BTW: This would demote a lot of "moons" to mere satelites.
Planet: Any planetoid that is more massive than the the rest of the matter in its orbit combined.
common sense: noun
What those who are ignorant of the subject matter think; usually wrong.
"Potatoes... who the fuck cares about a potato is."
I bet the Irsh do you insensitive clod.
Actually, potatoes are the most important dicot (non-grass) food crop in the world, and forth most important overall after corn, wheat, and rice.
Don't knock spuds. Oh, and a potato fruit looks very similar to a "cherry" tomato.
Ceres is round. Vesta is nearly so. Do they get promoted to planet status?
"One doesn't deny a Chihuahua a place among dogs because it is too small."
First: The designation 'planet' should mean something. Sure we can group small dogs under the category of dogs but that doesn't mean we can go around calling pomeranians' greyhounds. The same with planets. We can group pluto and sedna under the category of masses but we shouldn't call them planets. Planets should be its own category of the junk floating around in the universe, just as asteroids and comets are categories. When someone says this object is a planet we should thus be able to make some assumptions about that object. Otherwise we have to break that category up even more. If we have to have sedna added and a couple hundred other, the category of planets becomes so vague that it becomes meaningless. Thus we will have to break the category of planets up into sub categories in order to get any meaning out of it: gas gaints, rocky planets, etc.. Think of it like the dogs again. If we call every dog a pomeranian then the label 'pomeranian' loses its meaning.
Now the problems with his gravity rules. The first problem is moons. No one wants to call luna a planet. If we go around saying a planet in the solar system (Jupiter) has 32 other planets orbiting it, things will get very confusing awfully quick. So we would want to declare that for it to be a planet it has to orbit the sun. But then their is the problem of 'planets' that orbit each other. For example, we see this in some asteroids - two asteroids that orbit each other while traveling in a circular path around the sun - similiar to binary star systems where two stars orbit each other and tavel in a circular path around the galaxy. They can't both be moons. They can't both be planets. And what about rogue planets that no longer orbit a star but have been orphaned and are currently floating in interstellar space.
The second problem is comet-like bodies. What if you have a planet that as it orbits its sun sheds its atmosphere and mass to the point that it loses the gravity necessary to keep it circular. Likewise, what if you run into an asteroid that through a series of collisions gains enough mass to become a planet. This is fine but what happens when you have a whole belt of such objects. When you classify something, its best it stays in that classification for awhile or else the act of classification becomes somewhat meaningless. For example, you don't classify water by its mass in a rain storm cause that mass is constantly changing. Rather you state the rate of that change. If you didn't, you'd be forced to constantly reclassify it every observation.
So simply stating that gravity rule as the only criteria doesn't work. We'd have to make it more complex. Moons aren't planets (assuming you still want the word moon and planet to mean anything - and yes I know some moons could have their own moons). Belts like the asteroid belt and the kuiper belt where objects could conceivably change in every observation from planet to non planet and back would create a nightmare for astronomers using such a system. And remember these are only problems we face with a small data set like our solar system. Add in problems like the Super jupiters, some of which are undoubtfully brown stars or close to becoming them, and other as of yet unknowns and one could only imagine even more problems would arise in the gravity rule system. Now if these means adding addition requirements or not, or perhaps just abandoning the whole system is anybodies guess. He's write in stating you can't just use the old size requirement - but that was and is why we called pluto a planet and ceres an asteroid. Becuase someone said theres a size difference - there is really no other reason. Some asteroids have atmospheres. Some have moons. Some planets don't have moons. Some planets have moons larger than other planets. Perhaps the best bet is to just throw all the labels out and start over.
There's a growing sense that even if The Future comes,
most of us won't be able to afford it.
-- Lemmy
I bet the folks who live on Jupiter think our solar system only has 4 planets. After all, Earth and Venus aren't so much bigger or different than Pluto or Sedna. Certainly, Earth is closer in size to Pluto than to Jupiter.
People argue so much over where to draw the line between Planet and non-Planet, but everyone seems to take for granted that Earth is a member of the former class.
Bigots.
Paranoid
Bwaahahahahaa.
If an object is large enough for gravity to round its shape, then it is no longer just a structure ruled by mechanical strength, like a rock, a building, or a mountain - instead, it is a wholly different kind of structure that we call a planet. I like to call this criterion, "Gravity Rules."
Does that make the moon a planet? How about Tyne Daly?
Pluto by 2 Skinnee J's
With depravity I break laws of gravity
Blast past the atmosphere to the last frontier
I go boldly through space and time
The skies the limit but they're limiting the sky
I break orbit by habit, ignite satellites and leave rings round the planet
A flying ace like that beagle
Nevertheless this alien remains illegal
'cause their discovery don't cover me
the immigrant's been left in the cold to grow old and disintegrate
discriminate against the distant and disclaim this
cause small minds can't see past Uranus
But I shun their rays, 'cause stuns just a phase
And my odyssey runs in two thousand and one ways
And I can see clearly now like Hubble,
Shoved off the shuttle, here's my rebuttal
It's a planet
Who you represent? I represent the smallest planet
Attorney in this tourney versus those who've tried to ban it
If you don't agree go see Interplanet Janet
Cause sun is star, like Pluto is planet
Lend me all your ears and let me state my case
About all the types of satellites you must embrace
Cause like my parents, great grandparents
This planet was an immigrant
To deport it makes no sense
It's an upstanding member of the solar system
Apply the laws of earth and make it a victim
Of Proposition 187
When Pluto spawns a moon it will apply to the heavens
I will damn thee like Judas of Iscariot
If you demote this mote remote to affiliate
It's like taking ET's custody from Elliot
Support your Lilliput, cause simply put
Pluto is a planet
Do it for the children
Lyrics - MP3
-prator
To my mind, the questions are similar. No, Puerto Rico is not a state because it hasn't been admitted to the US. What makes Pluto a planet is that we say it's a planet. Same goes for Sedna. Size does not matter (in this case).
Good definition here.
A planetoid is a gravity-rounded body.
A planet is a planetoid more massive than everything else, taken together, in a similar orbit.
By these definitions, Pluto and Sedna are not planets, just planetoids.
I've never seen why we'd want to call Pluto a planet. The rocky inner planets we can build on and walk around on, the gas giants might well be tapped for fusion fuel and populated with many orbiting colonies, but Pluto, Sedna, and similar large asteroids and comets are only interesting as collections of raw materials.
I like this planetary definition. As you may have guessed, my private definition is, "Place big enough to consider living on, not orbiting a planet itself." but this one seems good enough to me.
Ida and Dactl
If we call Jupiter a gas giant, can we call Pluto a ice midgit?
When looking at the vast differences in other planets, is there yet a significant scientific reason to classify Pluto as something different.
(That is the question.)
I won't join Slashcott. OTOH, If Beta goes live, I just won't be back until it's fixed. Sorry Dice.
Planets were originally named "planets" because they wandered around the sun. We should define a planet, then, by the movements it makes in the sky. If it moves around in a funny way and makes loop-de-loops, it's a planet. And since we can't classify every speck of dust that goes around the sun a planet, we'll have to restrict ourselves to what's visible. That's right, the only planets in existance are Mercury, Venus, Mars, Jupiter, and Saturn.
There was a good presentation at today's blackboard lunch at the Institute for Theoretical Physics in Santa Barbara today. The first 15 minutes or so are a great summary of why Sedna is important for our understanding of the solar system.
Unless you want to say that a vegtable is any sort of large plant product that doesn't classify as a fruit, I'd say that the Tomatoe can reasonably classify as both.
Free Software: Like love, it grows best when given away.
exist to illustrate similarrities and differences. It is less useful to argue whether this definition of a planet or that definition of a planet should rule but rather we should be discussing what is a useful classification system.
Pluto has more in common with a whole class of objects which spend most of their time out past the orbit of Neptune. Sedna is another such large object but there are hundreds more identified.
That Neptune and Pluto's orbits cross is, I think, a major blot on our current classification.
I have discovered a truly marvelous sig, unfortunately the sig limit is too small to contain i
sedna, its a planet if we can run linux on it
how about a beowulf cluster of these
1. make pluto a planetoid
2.make sedna a planetoid
3.???
4. uh, profit?
link to goaste.?x
oh yea rtfa
did i miss anything, (nerds... *shakes head*...)
Shouldn't that be (pluto|sedna), if you were thinking of regexps, or {pluto,sedna} if you were thinking of shell expansions?
Liberty in your lifetime
Does anyone have a good site for explaining how all these new objects fit into the old scheme? I am still confused about the KBOs and "potential planets" 10 (Varuna) and 11 (I forget the name), and now we've got this and it's being referred to as potential planet 10...
Isn't this just another KBO? Isn't Pluto just another KBO? Why would we call this planet 10 and ingore Varuna?
Is {pluto|sedna} a Planet?
Speaking of planets, what kind of crazy regular-expression planet do you come from?
Your alternatives don't require grouping (if they did use parentheses not curly braces) and you have to quote the special character "?", as such:
Is Pluto|Sedna a planet\?
All obscure regular expression trolls are required to be modded as funny or insightful as per the Slashdot moderation guidelines.
Michael.
Linux : Mac
What about an object in a ternary system where the graivtation pull of the other two objects is so strong that the first object becomes oblong instead of spherical?
Pendantry strikes again.
Of course I want Pluto to still be called a planet. I think that changing its status at this point would annoy a lot of people.
Of course, the right thing to do would be to call it the thing that scientifically makes the most sense. But if the answer were to stop calling it a planet, that would be heart-breaking.
This excludes stars and any gas giants so massive that they could become stars at some point in their existence.
Ummmm... given that the only difference between a gas giant and a star is their mass, does this statement make any sense at all? If a planet has "enough mass to become a star at some point" then it will immediately ignite. If it doesn't, it won't.
It's not like planets get a choice in the matter. It's not like Jupiter might get ambitious one day and decide to get lit.
Clear, Dark Skies
Holy cow! What a leading line!
But no, I wouldn't touch it with a ten foot Lithuanian.
Is it fascism yet?
What about asteroid belts with planets stuck in them? What if we run into two planets in the same orbit but orbiting at such a speed that they don't collide? What about gas gainst orbitted by super dense asteroids?
There's a growing sense that even if The Future comes,
most of us won't be able to afford it.
-- Lemmy
simply put:
:= stellar object := planetary object :=
black hole = so big that no light can escape
star = big enough to make fire
planet = revolves around star or larger, big enough to hold atmosphere
planetoid = revolves around star. NOT big enough to hold atmosphere but big enough to be round.
moon = revolves around planet or planetoid. large enough to be round (and possibly hold atmosphere).
moonlet = revolves around planet or planetoid. not large enough to be round. does not occur in groups.
asteroid = revolves around star. Occurs in groups. Not large enough for atosphere or to be round.
comet = revolves around star. Does not occur in groups. Not large enough for atmosphere or to be round
planetary ring = groups of particles not large enough to be round. Oribt planets.
You can classify them according their orbits:
planetary-orbital object
Each of these three things are definable with physics based on the object's gravity... that is, if we make an assumption that stellar objects do not revolve around each other (but instead that their path through the universe in not a dependant but instead a codependant function of gravity in relation to other stellar objects (which is arguably the case since if 2 objects are large enough to initiate fission and are in a codependant orbital pattern, then the orbit is in fact outside of the mass of either body and is in some point between the two.
I could explain this point with math, but I just don't have the fonts.
Well, since we are throwing out just about every possible way to classify a planet, or in this case, a way to keep Pluto and exclude Sedna, why not use the old method that led to the discovery of Neptune and Pluto?
If the body in question exerts a measurable gravitational force on another planet, then it's a planet. As I understand, Sedna is much too distant to exert any kind of force on the orbit of Pluto. This also can discount Ceres and other large planetoid objects in the asteroid belt, since most of their gravitational exertion can only really be measured on other objects in the belt.
If we keep promoting solar objects with a mass greater than a Volkswagon to planetary status, then I guess all those numbers in Drake's equation just skyrocketed...
"Luck is what others call skill when they have none." --Phelan Kell
Let's be honest. The New Horizons mission is being launched for completeness. Once it completes its flyby, all of the nine planets will have been explored by a visiting spacecraft.
Classifying Sedna and Quaoar and all that other stuff out there as planets will require more missions. Demoting Pluto would elimiate the need for New Horizons. So lets make sure New Horizons hits space before doing anything else.
The first asteroid, Ceres, was predicted before it was discovered. According to the Titus-Bode series, there is a gap between Mars and Jupiter where there must be a planet. So, astronomers looked and surprise surprise, there's Ceres. But it didn't take too long to discover Vesta and Juno and Pallas and all of Ceres' other friends. Its those friends, immediately discovered, which caused Ceres to be demoted.
Pluto was predicted to explain otherwise unexplained perturbations in the orbits of Neptune and Uranus. So, astronomers looked and looked and looked and eventually found Pluto in the predicted position. Then they stopped looking. If they had kept it up, they would have discovered the rest of the Kuiper belt, and Pluto would have suffered the same fate as Ceres.
The proposed Gravity Rule would cause the answer to the question "How many planets are there in the solar system?" to change from "9" to "we don't know." We can be reasonably confident based on the tracks of the Pioneers and Voyagers that there aren't any other large masses out in the outer solar system. We will never be sure we have discovered all the round things out there.
Besides, there are objects which should be round, but aren't, like Hyperion, and things which have no business being round, but are, like Comet Wild/2. How would the Gravity Rule treat those?
Lots of technical and environmental problems are solved by the application of vast amounts of nuclear power
planet = revolves around star or larger, big enough to hold atmosphere
planetoid = revolves around star. NOT big enough to hold atmosphere
Eh. First of all, what do you mean by "atmosphere"? Exactly how much more dense than the immediately surrounding stellar medium?
Second, what if we find some planet - excuse me, I mean "thing" - way out there that would be be big enough to "hold atmosphere", but doesn't actually have an atmosphere?
This whole argument that's tied in with many people's need to divide things into discrete groups, even if such groups don't exist, strikes me as more than a bit childish. We already know what it is, who cares how it's categorised? Let's just get on with learning more about it.
Richard Feynman had some great things to say about this on a BBC Horizon documentary some time ago. You can attach names to things as much as you like, but having a name for it doesn't compare with actually understanding it.
Correct.
Which fits in perfectly with my dictum that should Ralph Kramden some day make good on his threats to send Alice to the moon, but somehow she misses the moon and enters solar orbit, then as far as I'm concerned, Alice becomes a planet at that point.
Is it fascism yet?
So if we accept that a planet is anything that has been rounded by its own gravity, we have to make assumptions about the density of the matter that it's made of. Stars that went through a supernova and no longer have enough mass to undergo fusion may be round and of comparable size to known planets, but many times denser. They clearly are not in fact planets but the author's criterion would have it that way. Of course we can say, "They aren't planets because they used to be stars" but he threw out the entire argument-from-origins criterion as being too difficult to establish.
Conveniently, he did not make a biological analogy for the argument-from-origins -- that is because biologically, it is the most sensible argument.
What he really did was shift the question from "how big do you have to be to be a planet" to "how dense do you have to be to be a planet." Now we have to establish an upper limit to planetary density, which is hard since it's hard to see small, dense objects.
Worst. Planetary Classification Debate. Ever.
boogabooh
The article has an elegant rule - the boundary is when the object's gravity can overcome the mechanical forces that hold an object in a specific shape. This usually produces a sphere (except, of course, in your pedantic case) but the actual shape is irrelevant.
Anyway. The more phenomena we discover, and the faster we discover them, the less interesting each individual one becomes. The more diverse they are, the less likely it is that the 'labels' invented 3000 years ago will still make sense. We're lucky that the simple categorization 'planet/comet/asteroid' has held up as long as it has. We've patched it up with TNOs and KPOs and so on, but at some point it'll be a continuum. A sparsely sampled continuum, but a continuum nonetheless.
We've been debating this here: vote totals so far:
Sedna is:
tenth planet 17 votes - 29 %
the eleventh planet 14 votes - 24 %
the 42nd planet 9 votes - 15 %
not a planet! 17 votes - 29 %
Energy: time to change the picture.
Speaking of dog's, too bad the poster of this article can't spell "chihuahua". Fortunately, the author of the article spelled it correctly, inferring bad trasposition on the part of the "quoter". Chuhauhau = Chi-ha-ha?
+ G to tha Izzo, A to tha Tizee, Talking Giz-oat, Ya'll Bettah Feel Me... +
I like to think that the 2 Skinnee Js have decided this issue once and for all as evidenced by the lyrics for their song Pluto off the $uperMercado album. They might even have mp3s on their site still.
Asteroids are also called planetoids, which just flips the above comparison on its head -- they're like planets, but they're not exactly like planets. The really amusing thing about this double terminology is the way it confuses Star Trek writers.
Then there's the word planet, from a Greek word that translates literally as "wanderer". All the objects in the sky that move with respect to the stars were originally considered planets. Not including the asteroids, because you can't see an asteroid without a telescope which hadn't been invented yet. But what about the Sun and Moon? These were considered planets too. But not the Earth, because everybody knew that the Earth didn't move. Hey, motion is define in reference to the Earth, how could the Earth move? What is that Copernicus dude taking, anyway?
Incidentally, that's why there are seven days to the week. Each planet that you can see without a telescope (and thus that is actually considered to exist) is dominated by a deity, and each deity has their own special day: Saturn Day, Sun Day, Moon Day, Mars Day, Mercury Day, Jupiter Day, and Venus Day. Most of the names we use in English come from Norse gods that medieval scholars thought were cognate with familiar Roman gods; their logic was a little stretched, but nobody cared, since the Norse religion was already dead, and hadn't involved planet worship anyway.
But I digress. The important point it that all these names are historical relics -- there's no way to be really precise with them. The cover issues we no longer care about, and don't cover issues we do. If you want to be more precise than anybody is in real life, you refer to rocky body, gaseous bodies, and Kuiper objects. But in real life you use familiar terms, because they're, well, familiar. If there are confusions and ambiguities, you take a moment to clear them up ("for the purposes of this discussion, any large body that orbits the sun is a planet; also Greenland is an island, not a continent"), and then you move on to stuff that really matters.
How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not. Pluto, BTW, Sedna, and many of the largest moons can all do this.
Doesn't that tend to favor gas planets like Jupiter?
May we never see th
Cool - another point to debate. What is the transition point from 'planet-moon' to 'bi-planetary' ?
Basing it on the center of gravity seems like a good idea, but 'well off from the center' is a little bit fuzzy. We could pick a number - say, 50% of the larger planet's radius - in which case the Earth-Moon system meets the criterion, since the center point is about 75% of the Earth's radius away from the Earth's center (some references).
But now we've done the same thing the original article was complaining about - we picked an arbitrary value, just, well, because.
It's seems like a physical point would work a bit better - say, the surface of the larger planet. Then the definition becomes a bit easier: if the center of gravity is in space, it is a dual-planet system. Otherwise, it's a planet-moon.
How you categorize a center of gravity within an atmosphere is left as an exercise ...
What about asteroid belts with planets stuck in them? What if we run into two planets in the same orbit but orbiting at such a speed that they don't collide?
I do love how, in your scenarios, you automatically assumed my definition doesn't work through the use of the word "planet." Explain how, through my proposed definition, there can ever be planetS in a given orbit? You would either have one planet and one (or more) planetoid(s), or two (or more) planetoids. I fail to see the point of your third, as volume doesn't play into this at all, only mass.
common sense: noun
What those who are ignorant of the subject matter think; usually wrong.
The first response was correct. I should have said "can become round through its own gravity." Of course though, round != spherical, it includes the approximation of being spherical/cylindrical. So even a squashed ball would count as being "round" (heck, the Earth is squashed slightly just from its rotation).
common sense: noun
What those who are ignorant of the subject matter think; usually wrong.
So... Mercury is now a planetoid? Mars is a planetoid also, as it isn't holding its sparse atmosphere well. Even Earth will eventually be a planetoid, we've been steadily loosing our atmosphere for billions of years.
Why moonlet? Why not just satellite?
What do we call rocks, of any size or composition, just moving through the void between stars? They can't be asteroids as asteroids must revolve around stars, right?
common sense: noun
What those who are ignorant of the subject matter think; usually wrong.
The IAU's current concern is to distinguish between extrasolar planets and dark stars. It takes about 13x the mass of Jupiter before an object generates the gravitational pressure needed to ignite the D-D reaction. So the IAU says that if it's smaller than 13x Jupiter, it's a planet. Bigger than that, it's a "brown dwarf" if not shining.
This site has an interesting definition of "planet".
any body in the solar system that is more massive than the total mass of all of the other bodies in a similar orbit.
This would, however, demote Pluto...
"Ignorance more frequently begets confidence than does knowledge"
- Charles Darwin
how about anything smaller than mercury is not a planet... because mercury itself is somewhat dubious... i mean, our own moon is pretty big.... i think saturn has a moon (titan?) which is bigger than mercury... in fact, all of the gas giants have moon systems which rival the solar system itself in terms of variety and interesting attributes (atmospheres, volcanic activity, water), as well as size
as long as the gas giant's moons can't be called planets, than anything smaller than mercury should be a planetesimal... either than, or elevate the gas giant's moons to be called something like "secondary planetary systems"/ "secondary planets" or something like that, because europa, titan, io, titania, triton, ganymede, etc... they are all way more interesting than pluto and charon, which itself is more interesting than sedna
clearly, just being a rock in orbit around the sun does not a planet make
you need to characterize things
size is one option, but another is qualities like: atmosphere
perhaps you could call the gas giants one thing
i think anything with an appreciable atmosphere another: "true planets" perhaps
and then anything moon like or smaller that is at least spherical: subplanets maybe mercury would be one such subplanet, ceres too (isn't it a sphere?), sedna too
additionally, things like titan, a moon of a gas giant, would and should be called a planet- it's huge, with an atmosphere, it really, really is more important than a barren rock orbitting the sun, even a big one like mercury
and of course, you have comets, asteroids, loose pieces of rock and oort cloud objects... these are just orbitting trash, not planets at all- no appreciable atmosphere, nothing of interest except ice and rock, not even round
these things are not planets
so:
gas giant - brown dwarf, failed stars: tier one planets or "superplanets" until a more interesting word appears
large, spherical objects with appreciable atmospheres- tier two planets, "true" planets, just because they are like earth, our home... things like titan, venus
spherical objects without appreciable atmospheres or oceans or magnetic or core activity (volcanic/ earth quakes)... these are just big dumb crater scarred rocks... subplanets, tier three planets, like ceres, sedna, mercury
nonspherical objects, of any size (usually small, as gravity would make them spherical up to a certain point)... planetesimals, tier 4 planets, including comets, asteroids, etc.
the arguments about chihuahuas and forgetting anyone past your list of known people are dubious arguments, as the size of the dog does matter in terms of classificaiton, and yes, when you start knowing too many people, it is natural for human beings to start classifying their friends into groups, not just one big giant group called "friends", you now have "college friends" and "work friends", etc.
so, since our list of planets is increasing, it is time to break down what we call planets into subgroups, based on size, roundness, and interesting characterisitcs like oceans/ vulcanism, atmosphere, etc...
additionally, moons should be elevated to the status of planets- who care sif they rotate a gas giant, if they are big round and interesting with an atmosphere, i am sorry, something like titan really should be considered a planet, perhaps call them "secondary system planets"
they are no moons, they deserve to be called planets if we are even considering a little piece of spittle such as sedna to be planet, compared to the vastness of titan? please
the word "moon" should be thrown out all together
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
Tomatoes are planets.
Know your pads. One time pad: good for cryptography. Two timing pad: where to take your mistress.
When we see a white dwarf star orbiting around a red giant we don't quibble about whether the dwarf is a planet or star or star-oid or whatever. We classify it according to its intrinsic properties.
It would be useful to classify smaller bodies in the same way, regardless of their orbital situation:
1) Gas giants.
2) Bodies made of heavier elements large enough to have vulcanism and tectonic activity.
3) Smaller solid bodies large enough to be rounded by gravity.
4) Even smaller solid bodies, sub-classified into rocky and iron.
5)Dirty snowballs.
Of course there will not be an exact boundary between these classes. For example, vulcanisn in "planets" is fueled by long-lived radioactives but in Jupiter's "moons" by tidal energy.
Possibly there could be intermediate objects between 1) and 2) or between 1) and 5) or 3) and 5). Concievably there could be bodies made of water or solid methane or blue cheese but these would be unlikely to form naturally.
How similar is similar when it comes to orbits? As you get further away, the planets get further apart. So might it not be possible to accidentally discard Earth with this criterion, since we are relatively close to Mars and Venus, especially compared to the distance between Neptune and Pluto?
I think the straight-forward approach is fine. A planetoid is an object that becomes round by its own gravity but does not sustain fusion. That's fine. A planet is a planetoid that orbits a sun, whereas a moon is a planetoid that orbits a planet (or a moon I suppose. I'm sure it must be possible for a planetary system to have a moon orbiting a moon!)
That would simplify the school situation because then maybe kids would learn why things are called what they are called, instead of rote-learning a list of names, which seems to be the hallmark of almost every subject right up to the end of tertiary schooling.
If you want to get the pedantry flowing, try bringing up the subject of glass being liquid. Then you'll really get some people fired up.
Karma: It's all a bunch of tree-huggin' hippy crap!
The tomato was declared to be legally a vegatable by the supreme court of the State of New York so that they would be subject to import tarriffs during the 1930s.
What makes a tomato a fruit, is that is the ripened ovary of a flower. Anyone who has grown their own food would tell you that a tomato is more similar to an apple than it does a carrot.
Common sense is simply a set of popular misconceptions. If you always adhere to common sense, you'll most often be wrong, but you'll never be alone.
This is not a case for "common sense" or tradition to determine. Geography and trade law are not scientific disciplines, and thus have little bearing on the question of planets and what constitutes one. You claim that planets and planetoids behave similarly, yet the author has provided a definition that makes the distincion between the two clear, and it is based on observable phenomenon. There's no reason to fall back on "common sense" in this case, as physics has provided the criteria for us.
Read, L
Sedna is really much more interesting as an object than the planet-definition argument addresses.
It's important to note in this regard that the fact it is named Sedna at all reflects its importance as a new object. Plutinos--planetoids having orbits like Pluto--are to be named after things related to the underworld (thus Pluto, Charon, Ixion, etc.). Classical EKOs--non-Plutino trans-Neptunian objects--are supposed to be named after creation myths (thus Quaoar, Varuna). Sedna, being outside the E-K belt, is from artic mythology. The discoverers are proposing that objects in this region--tentatively the inner Oort clound--be named after artic mythology.
So the fact that it has the name it does is reflective of its unique status. It is so new and unique, so to speak, that it deserves its own naming convention.
If there's any astronomical taxonomy discussion that should be going on, that's it.
i like the cut of your jib, AC.
Every true Geek knows that Pluto is actually a moon of the 8th planet of this system, which was knocked out of orbit around that planet and left to wander around the Sun in a highly elipitical orbit by the impact at a good fraction of light speed by a stasis field encased slave of a Slaver, about a billion years ago, give or take.
"It's the height of ridiculousness to say for those 9 lines you get hundreds of millions."
if you look at the planets (except pluto), they all follow relatively circular orbits and are close to the same orbital plane, as well as orbit the sun in the same direction.
Maybe this can be an added test for planets, since these are most likely the result of creation from the same material as the sun, rather some captured object.
D6 63 0D 70 89 81 BB 8E 7B 7C 5F 5D 54 EA AB 73
Pluto is a dog. Sedna is a plane. What's all this talk about planets?
Eurohacker European paranoia, gun rights, and h
A possible criterion? If its got an atmosphere it's a planet.
Is {pluto|sedna} A Planet? It's just a matter of definition. It's not a question concerning the nature of these bodies, but a question of how we view them. Therefore, it doesn't really matter.
IMHO, orbit does matter, because it points to the object's origin. Circular and in the ecliptic? Planetary disk -> planet. Highly inclined and/or eccentric? Oort cloud or Kuiper Belt object, i.e. comet. That leaves the asteroids (unless they are captured comets...but are we all captured comets? Let's not go there right now...;-), but you can bring in sphericity, possibly differentiation, or Crowscape's definitions to take care of them.
Not enough astronomers come right out and say it or even consciously realize it, but they are looking more at the orbit than the size. There is more of a size difference between Earth and Jupiter than Sedna, Pluto, Mercury, or probably even Mars. But the acknowledged planets all have fairly circular orbits in the ecliptic. Also, newly discovered things tend to be the brightest/biggest/exceptional examples of relatively small and common things. Sheer size can be misleading.
If we were ants living on a Rubik's cube, differential geometry would be a little more confusing.
Well, you have written {Pluto|Sedna}, which
is read as "Pluto given Sedna" in Mathematics.
It doesn't really make any sense.
To avoid the confusion, simply Pluto and Sedna is much better..
To answer the question, it's doubtful that they are planets, but it's a matter of taste and definition.
Martin.
+5 insightful.
"Now the technology has allowed us to gather more accurate data about Pluto's characteristics"
What about current going from + to - ?
Now the technology has allowed us to gather more accurate data about electrons & current characteristics, therefore, current goes
from - to + except that every book on Earth
says otherwise from + to -, with new books mentionning hey don't forget it now goes from
- to +, but hey don't worry about it...
Tomato is a vegetable for the same reasons,
because people more often used it as a
"vegetable" then as a "fruit", whatever that means biologically. If Joe Nowhere or Homer Simpson thinks Pluto is a planet, so be it.
Samething for Tomato soup, Tomato Pasta, Tomato in sandwich, etc. Everyone does electronics
thinking hey current goes from + to -, even while designing circuits, because in the ends in doesn't matter.
Words in the dictionary is about common sense
most of the time, sometime based on actual facts,
sometimes not.
Hey shall we say that Atoms are not Atoms,
because Aristotle was somewhat wrong ?
People like to makes thinks complicated for nothing, oh well.
At least if we're gonna change Pluto as a Platenoid, Plutoid or Plutonium (imho).
Let's change all the wrong things in the dictionary too, including current!
Would a "The Cheat" rank up there in
Actually stars aren't that clear. What kind of fusion? Brown darf's are the muddy end of the stellar side, they have enough mass to fuse lithium and deuterium, but not enough for hydrogen fusion, so they don't shine at all.
l ookup.cgi ?title=Brown_dwarf
Similar to planets, the deliniation is fuzzy because the most visible stars are all way way bigger than this, and is not until relatively recently that we have been able to see brown dwarfs.
Food for thought: graviatationally, Jupiter is the sun's binary partner.
page on brown dwarfs:
http://www.wordiq.com/cgi-bin/knowledge/
Would a "The Cheat" rank up there in the list of planets?
(Pressed Enter in the wrong edit box)
Er... not a comment on the categories but fusion isn't self sustaining. Pressure from gravity sustains the fusion. If fusion overcomes gravity the star is blown apart (supernova).
Size has absolutely no reason being in this conversation. It all depends on what we call a planet. Is a planet something that came toghethor due to a conglomerating of a large number of rocks and the such due to gravitational pulls in a protoplanatary disk? If that is what a planet is (by definition) then this is or isn't a planet...depending on how it was formed. This is stupid to have a system which is based upon judgement and not simple facts. Why is pluto a planet? Because we deemed X-size a plenet? I don't know... Anyone know?
Mad, adj : Affected with a high degree of intellectual independence. Ambrose Bierce - The Deveil's Dictionsary
I "deny a chihauhau a place among dogs" not because they are too small, but because they're really fucking annoying, something that True Dogs never are.
Dude, you need to get out of your email client and spend more time on IRC.
Hasn't anyone played computer games here? If its large enough to land colonists on, its a planet!
Moon: Any planetoid that orbits another planetoid (let's face it, it's a generic term and nothing will ever change that). BTW: This would demote a lot of "moons" to mere satelites.
Planet: Any planetoid that is more massive than the the rest of the matter in its orbit combined.
All moons are planets?
If it's much more than a hundred kilometers across, we don't care how it got round. It would have gotten round under it's own gravity regardless
To be painfully anal about this (as is the style it seems), the strength of a body's gravity is due to it's mass, not it's size. Size usually relates to mass nicely, but that's not always the case. It's entirely possible to have a very small planetoid (perhaps only 15km radius) that just happens to be incredibly dense to the point where it would have the gravity to pull itself into a sphere.
Likewise, a large planetoid could be mostly porous, made of extremely light material, or even partly hollow, then it's possible that it might not have enough mass to sustain a spherical shape (which it might have obtained due to unknown influence).
-"One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man." -EH
It is indeed a simple criteria, but not very suited to human understanding. How would it feel to walk on a planet that is just big enough to pull itself into a spherical shape?
How about just define a planet as an object you can walk on comfortably without launching into the air and flipping over your head or worse going into orbit? Luna might qualify, but asteroids will not.
No, it is the 6th, because the moon is shaped into a sphere by gravity, and thus is a planet also.
Unless you add in the "orbits a star" limitation of course, heh. Otherwise for 14 days in 28 Earth will be the 4th planet from the sun, and the 3rd for the other 14 days.
Of course, the Earth is a master planet in our bi-planetary system. Jupiter is the master planet in its quite large planetary system.
mmmmmmmmmmmmmmmmmmmmmmm.
PIE!!
...and he grinned, like a fox eating shit out of a wire brush.
It is pretty arbritary. You can easily get species (gulls, for example) where population A can breed with popuulation B, and B can breed with C, but A can't breed with C. Are gulls a single species or not?
Then you get the problem of animals that only mate (with viable offspring) with human intervention - zoos and painting the animals. Are these single species or multiple species?
And what about organisms that reproduce asexually? These would each be in their own species (or outwith the definition).
And then you get micro-organisms...
Generally it doesn't matter because when it is used in a technial sense the odd cases don't matter.
Haven't read the article, but regarding these two quotes... it seems like he wants to see all the KBO's and the asteroids as planets as well, after all they aren't any less planets simply because they're too small. Right? I mean we have planets and asteroids and kuiper objects, would it be wrong to at least try to classify them differently, even though the lines between are blurred?
And what about the analogy with people? I can't see how that is applicable here.
Well now we have just drawn a new arbitrary line in the sand.
Instead of arbitrary radius and mass, we have to set some arbitrary spherical aberation.
How can we objectively tell how spherical an object is unless we take some sum of its spherical harmonics?
A Usenet Troll Triumphs on Slashdot
If a human being can take a running jump and achieve orbit and/or escape velocity, it's an asteroid. If it has sufficient gravity to be a planet, but it orbits around another planet instead of the sun, it is a moon.
--- Generation X: The first generation to have SIG lines inferior to their parents... ---
Slightly inaccurate. Ceres isn't spherical, so wouldn't fit the description. No-one (that I've read) suggested removing the 'orbits a star' requirement. Mars has two moons, both spherical as far as I know, so counting moons would make Ceres 8th (except for being disqualified by shape).
In any case, Ceres fitting the definition of a planet is fairly good case for saying the definition isn't good enough.
Why is anything anything?
They're really, really big (bigger than trees), they could eat people with one bite (if there were any at the time) and they really existed.
What's there not to be fascinated about dinosaurs?
The way I see this maybe NASA/other space agencies should come up with a set of standards that outlines what are the attributes that make up a planet. With a clear standard they're would be no arguments. Simple huh? Anyway that's my 2 cents.
"Moon: Any planetoid that orbits another planetoid"
this becomes a slightly strange definition, when you consider Newtonian physics showed that two objects, attracted by each other's gravity, actually orbit a common center of gravity. Hence, you could have two identically sized planetoids orbiting each other, than who's the moon?
Or in a less extreme, but more common, example, the moon doesn't exactly (stricly) revolve around the Earth, it would be more safe to say both the Earth and the Moon orbit around their common gravitational center, which, admittedly, I believe, lies within the Earth's surface.
But still, who's orbiting who isn't so cut and dry an issue as we're lead to believe.
Oh, and don't try any of the "Newton's old and busted, Einstein's new hotness" crap. If you want to go by Einstein, it only gets harder to say who's orbiting who, since gravitational attractions aren't even certain to be gravitational attractions. Sabe?
For example "Deviates from a sphere with at most 1%". I think that'll do it for me.
That would rule out Earth as a planet (and several others, including all of the gas planets). Technically, Earth is an "oblate spheroid." Nowhere near a perfect sphere. You can blame the fact that we're spinning, and thus, bulging at the equator.
Like woodworking? Build your own picture frames.
Is Pluto a planet, or not?
Is tomato a fruit, or veg?
The fact that they are arbitrary classifications made by the same people (us) who decided what is and what is not a Planet seems irrelevant. It seems that the classification systems are the problem here, not the fact that Pluto is a celestial body orbiting the same Sun as Earth, with one natural satellite.
So, we decide that Pluto is not, in fact, a planet. What difference does it make? Maybe the indigenous population, a small race who live entirely of methane by-products, will get angry and attack the Earth, resulting in the destruction of mankind? Or maybe nobody will care.
Mars' moons aren't spherical, they are captured asteroids. Very unimpressive things, lumpen.
Whereas Ceres appears to be spherical from all reports I've read about it. No good pictures seem to exist of it though. It is nearly 1000km in diameter though, so big enough to sphericalise itself under self-gravity.
Has Atmosphere = Planet
Does not = Not a planet.
May the Force be with you
ROFLMAO
I know this is completely offtopic, but after reading all the comments to this post, I have come to the conclusion that you all are crazy. Only on slashdot could a story about about the classification of a piece of rock in outer space devolve into an argument about whether a tomato is a fruit or a vegetable (it's both!).
I love it.
So, let's just call Sedna a "planetoid" and be fucking done with it. I have to go eat my fruit salad (sans tomato).
+1 Insightful, -1 Troll. What can I say, I'm an Insightful Troll.
Can we promote her to planet status?
I like that definition of dual-planet, though astronomers just might have a fit over calling Charon a planet. Still, the barycenter of that system is definitely in space rather than within one body or another.
Pluto and Charon are also far closer together - both in absolute terms and scaled by size - than Earth and Luna. But it's the mutual center of rotation that I think is more important.
The odds of having a center of gravity within a planet's atmosphere are, on solid worlds, pretty darn slim. But when gas giants are included, that elevates the problem to new levels of complexity. How do you define "within the atmosphere"? A planet's atmosphere doesn't have a very firm boundary; it just gets increasingly vacuous.
If an astronomer out there knows how the boundary of an atmosphere is designed, I think that would be the better outer limit for dual-planet vs planet-moon: if the barycenter is not within the average diameter of either body, atmospheres included, it's a multiple-planet system.
Having a naturally-occurring, balanced system with more than two such bodies would seem highly unlikely, but, hell, life is highly unlikely. Given enough trials, though, one will eventually succeed. Anyway, the definition of "planet" might need to be amended so as to include the possibility of orbiting with another body such that the barycenter is in space, and declaring that those two, if they otherwise meet the definitions, are still planets. (If the smaller one couldn't pull itself into a spheroid, it's not a planet, so the whole argument here is moot.)
NB: YMMV. IANAL. Take the above with a grain of salt.
In many respects, people think in categories. Apparently, short-term memory can only manage a certain number of objects at a time, making it necessary to chunk concepts into mentally digestible pieces--hence taxonomies, and categories containing fewer than 10 objects.
Also, our pattern recognition capabilities are fine-tuned for determining whether things fit in a particular category or not. Pattern-recognition is the only way the human brain can make predictions about things it has never seen (or heard, tasted, smelled, or touched) before. The neural networks in our brains will almost automatically assign certain properties to various unknown objects and events if they match enough criteria to fit into a certain archetypal category.
And because of how integral categories are to how the brain works, reclassifications of things have profound effects on our societal weltanschauung.
For example, Einstein's work on the photoelectric effect once and for all exploded the idea that categories such as waves and particles even exist. They are both, and this forever changed the way that the West has looked at the world. It has definitively changed the way we try and predict unknowns.
On the social side of things, the move from an empirically based biological taxonomy to one based on genetic-relatedness has destroyed the Victorian idea of a great chain of being. We find that, instead of being, evolutionarily-speaking, superior to monkeys (in the sense that we are "higher," "more evolved" organisms), we are in fact merely branches off the same tree.
The recognition of the importance of genetic-relatedness has allowed us to perform useful experiments on rats and monkeys that are completely applicable to humans. Without this kind of reclassification, it is doubtful that we would have made the genetic and pharmaceutical advances that we have.
And the destruction of the great chain of being has also led us to a more egalitarian society. Now that the idea of genetic-relatedness is in the fore, it becomes harder to justify racial segregation on the basis of supposed evolutionary superiority. Genetics has shown us that, truly, humanity is one race, descended from the same mother, regardless of our skin color.
In many ways, classification schemes is at the heart of thinking like a human.
Maybe the problem isn't how we define planet's, but rather how we define asteroids and KBOs. All asteroids are considered 'Minor Planets' a name I think would better suit objects like Pluto, Sedna, Quauor and the "asteroid" Ceres. Consider these minor planets, Mercury through Mars are already classfied as terrestial planets (by size and composition), and of course you have gas giants. And there you have it. With so many minor planets, we could still rank Pluto among the 9 planets as the largest representative of it's class. The only problem with that is that it now seems likely that there are other KBOs larger than Pluto that we haven't detected, possibly even vast numbers of them.
Charon actually doesn't orbit Pluto; it and Pluto orbit a center of gravity between them (this is true of all orbital relationships, except that in most the two bodies are too disproportionate in size for the center of gravity to not be contained within the space occupied by one of them)...perhaps Pluto-Charon should be considered one planet, with each part being a moon (lol), just like "we" consider Sol-Mercury-Venus-Earth & Co.-Mars & Co.-Asteroid Belt-Jupiter & Co.-Saturn & Co.-Uranus & Co.-Neptune & Co.-Pluto-Charon-and (perhaps) more asteroids and various comets to be "The Solar System". On second thought, how about just calling them orbital objects? PLEASE!!!!!!
'You wouldn't deny a chihauhau a place among dogs because it is too small,'
I would, because chihauhaus don't exist; chihuahuas do.
The best way to predict the future is to invent it
Unfortunately, that won't work either. The local path of the center of gravity can also vary. Consider a large planet with 4 moons.
....x[ ] .[x] . .
At some point, the moons will all be on the same side of the planet and the center of gravity will be outside the planet.
The whole system has a center of gravity (the one that describes the system's solar orbit), but that center wobbles from the point of view of any of the planets or moons involved.
Sorry about that. See my r0x0r ascii below, where the planet is [] and the moons are . and the center of gravity is x.
.
"It's seems like a physical point would work a bit better - say, the surface of the larger planet. Then the definition becomes a bit easier: if the center of gravity is in space, it is a dual-planet system. Otherwise, it's a planet-moon. "
So if we put a satellite at the Sun/Earth lagrange point could it be said that the Sun and Earth are moons of the satellite?
Probably not - I'm guessing that my understanding of terms is probably a bit off (no doubt someone can enlighten me) but perhaps you see the potential for abuse your definition leaves? Any two items may have a center of gravity.
Exercises for the reader:
1) Is a lagrange point for a system a center of gravity? Explain the difference in the two terms
2) Propose a potentially amusing example of "abuse" as mentioned above.
Ceres, Vega, etc. A number of asteroids are spherical.
The Moon is not a planet because it doesn't dominate it's orbital slot around the sun, although sometimes the Earth/Moon system is called a "double planet" because the moon has a profound effect on the earth (they both in fact orbit around a point about 2000 miles below the earth's surface - halfway from the crust to the core, approximately). However, larger moons around the gas giants don't evenget that much distinction because they have negligble effect on their parent planet, which outsizes them hundrds of times over.
This guy attacks lots of layman's arguments against Pluto as a planet, but he COMPLETELY igores THE KEY argument among SCIENTISTS (the people who actually get to say wether it's a planet or not) against both Pluto and Sedna as planets: They DO NOT have planetary orbits. They both have cometary orbits. Plus, Pluto and its moon Charon are known to be composed of the same material as comets, and Sedna is strongly believed to be. They're freaking big comets, but they're still comets.
But all the combined moons of, say, Jupiter or Satrn won't displace the center of gravity a fraction of the planet's radius, and they can be accurately modeled over fairly long-term projections by assuming the moons have 0 gravity/mass. However, if you put a second moon around the earth with, say, 1/3 lunar gravity (about 1/18g, if I remember my high school earth science right), it would have a considerable effect. You already can't model the Earth/Moon system with any accuracy without taking lunar gravity into effect. Add in another object with significant gravity, and you wouldn't have a planet with two moons, you'd have the infamous Three Body System. It's incredibly unlikely the three objects would even settle into a stable orbit. It would probably fall apart in short order when two or more of the objects collide, or one of them is ejected from the system. (For that matter, Astronomy magazine had an article a few years back that the solar system itself would eventually decay in the same manner, although with the much larger scale involved, a collision is pretty unlikely - odds are the four terrestrial planets would be ejected from repeated interactions with Jupiter.
The "gravity rules" criterion does make the most logical sense of the highest planetary classification criterion. A body whose self-gravity is sufficient to shape it into a spherical body is classified as a planet. This suggests further sub-classifications such as gas giant, terrestrial/rocky, ice/rocky and ice planets. Or using a logarithmic scale we have giant, terrestrial, and minor. With this classification scheme we will add several planets to our system. They would appear to be rocky/ice and ice minor planets. The classification of a moon is a body that is in orbit of a second body that is not a star. Remember there are some asteroids that do not meet the above classification of planet that have moons. With the above definition, then if our on moon Luna were in its own orbit it would also classify as a planet. So perhaps we should have the following sub-classification of moons: Planet-moons, and asteroid (non-planet) moons. With this classification then our system has about a dozen planet-moons. Lorenz H. Menke, Jr.
ROFL
Of course, I've never considered him to not have a place among humanity.
--
"Outlook not so good." That magic 8-ball knows everything! I'll ask about Exchange Server next.
I also think, for the record, that if something as large as Luna, or Titan, or Europa were out floating in space orbiting the sun and not another planet, they would be considered planets too.
Do you realize just *how many* Sedna-size (and larger) objects we are bound to find out in the Kuiper belt? Trans-Neptunian space is truly vast, and very ill-lit - we have not even begun to scratch the surface of what's lurking there. Calling the thousands or millions of sizeable Kuiper belt objects we will discover over time all "planets" serves *no* purpose but deprives us of a term to denote the 4 major rocky bodies orbiting the sun inside the asteroid belt, and the 4 gas giants orbiting the sun between the asteroid and Kuiper belts, without the ludicrous verbiage to which I'm going here.
As we discover more about the denizens of the Kuiper belt, we are likely to require more new terms to denote sub-populations - all the more reason to stay away from the already overburdened "planet" category. Pluto is a captured Kuiper belt object, and should be labeled as such. Finally, as someone else has pointed out, there are real differences between Kuiper belt objects (including Pluto) and true planets as to their orbital parameters.
Be faithful to your obsessions. Identify them and be faithful to them, let them guide you like a sleepwalker. JG Ballard
You're of course free to continue calling cetaceans fish and believing in brontosauri that never existed (they were a shoddy/fraudulent paleontologist's chimera), but just because you think you shouldn't ever have to learn anything new after grade school doesn't give you the right to criticize others for showing more intellectual flexibility.
Be faithful to your obsessions. Identify them and be faithful to them, let them guide you like a sleepwalker. JG Ballard
I'm giving him some points though. Considering as by your definition a gas giant can in certain circumstances not be called a planet. It's basically what the writer of the article said, to arbitrary. And it also requires more grueling research work, no mass is much easier thank you.
Quickshot
I believe the word "planet" has origins in Greek, and means "wanderer". Hence, the "planets" were called such because they appeared as wandering stars by human eyes on earth. Certainly anything in orbit around our Sun, out to about a light year, will have enough "wandering" associated with it (by parallax due to Earth's revolution about the Sun) to fit this classification. Unfortunately, that simply isn't a very useful way to classify things since we already have some sort of common notion about what "planet" means, even though it still a little vague.
Orbital inclination might be a good start to finding a not-so arbitrary way to classify things as "planets" or maybe at least as "primary planets". Maybe everything with an orbit inclined less than 10 degrees from the ecliptic can be a planet. Other than the specific degree-cuttoff, this criteria is not arbitrary, since the ecliptic plane exists due to the rotation of the Sun. Things orbiting far off of the ecliptic are more likely to be things which were thrown out of the system at the onset of fusion, so maybe they shouldn't be called "planets", or maybe they can be "secondary planets". (Pluto's orbit is inclined *17 degrees*, the next most inclined is Mercury at *7 degrees*)
Perhaps we can add a mass criterion based on the size of the Earth, which is admittedly totally arbitrary, but when coupled with orbital inclination, it's much less so. Maybe nothing with less than 1% the mass of the Earth should be classified as a planet. That excludes asteroids from accidentally being "planets" under the orbital inclination criterion, but we can still have Mercury, which has about 5.5% the mass of the Earth. (Pluto has about 0.2% the mass of the Earth)
Finally, to account for moons, we could add that for multiple bodies orbiting one another, and together orbiting the Sun, in the case that both are more than 1% Earth-mass, the one containing the center of mass is the planet and the other(s) the moon(s). If the center of mass is outside both or all (if there are many), then it's a double- or triple- planet system.
How does that sound?
-=[You cannot consistently judge this statement to be true.]=-
Originally, orbit was all that mattered. There is even an equation that says how far each successive planet would be from the sun, since things too far from those "slots" would tend to have unstable orbits and would be deflected into elliptical paths. Mercury through Mars fit these slots exactly, the asteroid belt occupies the fourth, but failed to form a planet due to gravitational interactions between the Sun and Jupiter. Jupiter and Saturn fit the next two exactly. When they were discovered, Uranus and Neptune were believed to be slightly off, although it's been determined that Neptune's orbit wasn't as irregular as had been thought (somebody forgot that Uranus effects Neptune as well, and only determined Neptune's effect on Uranus). Pluto is not only about half a billion miles off from it's slot, it's also tilted 30 degrees off - most of the planets have negligible orbital tilt, none of them over about 3 degrees. Sedna has a wildly elliptical and highly tilted orbit. Both of them have classical long-period cometary orbits, are of classical cometary composition. Somewhere along the line, after they realized Pluto didn't fit the planetary bill, they discovered Charon, which has been Pluto's only clinging thread to planethood ever since. However, that was then. Now, we know of multiple asteroids with their own moons, and I remember some evidence that the larger moons around Jupiter and Saturn appeared to have their own tiny satellites. Anyway, the planetary requirements, as I learned them in college: 1. A relatively circular orbit (Pluto and Sedna fail miserably). 2. A relatively "flat" orbit (failed again) 3. The dominant object in their orbit (Pluto looses, as Charon has a major effect on it. The Earth stretches this one, too, and sometimes both get the term "Double planet" attached to them. The large moons around the gas giants are far smaller than their parent planets, so the planets dominate). 4. Fitting an orbital slot (This breaks down the farther you get from the gas giants, though, so it would likely be excused for far-flung planets). Size doesn't matter (a small object may not count, but a large one doesn't count on size alone).
Oh, someone suggested common airwaves should stick to common standards of decency? Poor baby, it must be difficult for you.
But you are missing the fact that many asteroids have powerful enough gravity to pull themselves into spherical shapes. There are several asteroids that are hundreds of miles in diameter. Vesta, the fourth largest, has even had lava flows.
If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.
I suggest we enter every object in the Solar System greater than one metre in diameter into a battle to the death. The last nine survivors will be named the planets.
qntm.org
http://www.onthejohnnews.com/2004/004/sedna.htm
Sedna: "size doesn't matter, it's the elliptical motion in the astronomical ocean"
I'll take any opportunity to insert a quote from Eddie Izzard.
For those that would die defending it, Freedom
has a sweet taste that the protected will never know.
It's a SPACE STATION!
For those that would die defending it, Freedom
has a sweet taste that the protected will never know.
Bronto-Burgers or Bust!
For those that would die defending it, Freedom
has a sweet taste that the protected will never know.
Did you read the parent and grandparent posts? Of course they can be accurately modeled; the center of gravity of the planet and its moons are considered. The parent post was giving its parent a reason why his particular definition of planet wouldn't work.
...Astronomy...article...collision unlikely...
Who would model the earth/moon without lunar gravity? That was never suggested. Infamous three body system? That was never suggested either. With the [earth/moon]'s center of gravity barely falling within the earth's crust, the parent suggests that a system with another similar moon would put the center of gravity outside of the solid planet.
Are we on the same topic here?
You have obviously never dealt in inter-stellar real estate.
Would you rather want to buy a 9 planet solar system, or an 8 planet solar system?
"I don't know, we were looking at a system in NGC 876 that had a bigger sun, and that 9th planet is a bit small.... you sure that's a planet?"
(I know, "informative" would have been more appropriate, but this is /. after all.)
Freedom to fear. Freedom from thought. Freedom to kill.
I guess the War on Terror really is about freedom!