Slashdot Mirror
Defining "Planet"
beardoc writes "The Sydney Morning Herald is running a story today about a controversial proposal to define what size a planet might be - depending on what the final definition of how big a planet is, we could end up losing Pluto (at 2300 kilometres) to the status of "asteroid" or gaining three more planets - Quaoar, Varuna and Ceres."
... agreed to be "Marlon Brando"
If someone bothered to name a Roman god after it, it's a planet. Pluto, Mars, Jupiter--all friendly planets.
Alpha Centauri? Bah--probably a reflection off that Hubble thingy.
We recently had heard in the office over one of the Yellow Machine that's made by Anthology Solutions.
Maybe my neighbour can be defined as the "first living planet"?
Wouldn't it make sense to take into account whether the planet could feasibly sustain life too? I mean could a 700km round body in space support an atmosphere?
(stolen from DaBum) I am dyslexia of borg - your ass will be laminated.
The fellows at www.lunarembassy.com have announced(on the Conan O'Brian show, no less) their interest in selling the entire planet of Pluto for about $250k. If Pluto gets downgraded to a mere asteroid or Oort-object or what not, will that lower it's real-estate value?
Planet: n. Any object orbiting a star, not orbiting a planet, and having a radius greater than the radius of Pluto minus one millimeter.
How do you pronounce Quaoar?
And the l33t shall inherit the 34r7h.
I went to an astronomy talk at the University of Toronto a few years ago. The presenter defined a planet as any celestial body that doesn't radiate light. That explicitly includes asteroids and moons. Why is it necessary to make the distinction between planet and asteroid?
The whole point of the article is to arbitrarily define the distinction which just proves how stupid it is.
Jason
ProfQuotes
they say bodies larger than 700km go from being potatoe shaped to round. why not set a defined width above this 'minimum', and anything larger be called a planet? twice the minimum sounds plausible, and that means Pluto would still be defined as planet.
Feed the need: Digitaladdiction.net
Because the traditional designation of what made up a planet was anything that we could find that orbits the sun. We didn't include comets because they looked different from planets and we didn't include asteroids because we couldn't resolve them. Now that we continue to find many large objects that are really little different from Pluto it has suddenly become important to have a real definition of which are planets and which are just big asteroids.
Also, as we find bodies orbiting other stars, the traditional designations for planets is obviously useless.
We hope your rules and wisdom choke you / Now we are one in everlasting peace
Because the traditional designations are spotty at best, and certainly not definitive enough.
Currently, a planet is defined to be a body larger than an asteroid and orbiting a star. There's no distinction between planet and asteroid, except "oh that looks big enough.. i guess it's a planet."
If we use a pure size-based measure of whether a lump of matter is a planet, then will the moon Titan be reclassified as a planet?
Maybe we need to define a planet as something relatively big, not orbiting something bigger than itself, and almost alone. e.g. Pluto is a planet because it's pretty much by itself and bigger than anything around it. Ceres is not a planet because it's got a lot of other stuff around it.
Even this exception would need an exception to handle things like Earth's moon and Pluto's moon.
Oh what a tangled web we weave...
Why do they always need to complicate things. I thought size doesnt matter.
I've left to find myself. If you happen to see me, please, keep me there until I return.
a) this is science, not tradition, scientific terms need an absolute definition.
b) traditionally, you only had the naked-eye planets: Mercury, venus, Mars, Jupiter, Saturn. What do you call the other gas giants? Not to mention, Mercury was thought to be two planets by some (the morning and evening star).
c) my opinion, just set it so that Pluto-size is the cut-off. Anything smaller isn't one. However, in a few centuries when we can detect "planets" in other solar systems this would seem a bit heliocentric, so I can see the Basri's point (in the FA: "Basri's definition, a planet must orbit a star, not another planet, and it must be round. That means it must be 700 kilometres in diameter, when gravity moulds it into a sphere, or bigger.").
Seeing as our moon is 1/3 the size of the earth itself, and since they revolve around each other (hence the moon eclipsing the earth and vice versa), shouldn't we call earth/moon a two-planet system? Just some random musings...
it seems silly to go about redefining something like what constitutes a planet. what possible scientific value could this have? why can't we be content to keep the traditional designations of what make up a planet?
that's exactly the problem; there_are_no universal definitions for "planet." the most common definition is "any celestial body that orbits a star". I think we can all see the problem with that definition; we would have to classify even the least massive meteors (probably numbering in the millions in our solar system alone) as planets.
According to Professor Basri's definition, a planet must orbit a star, not another planet, and it must be round. That means it must be 700 kilometres in diameter, when gravity moulds it into a sphere, or bigger. Smaller objects are potato-shaped.
That seems like as good a measure as any. For something like this it's nice to have some sort of event like the forming of a sphere (or whatever you consider a sphere) to give a line in the sand rather than picking a nice sounding number.
On the other hand it didn't cover reason the other astronomers wanted to drop Pluto, is it missing some characteristics that the other 8 planets are? He also has a nice upper limit where a planet becomes a sun.
Still being the nitpicker I am one would have to wonder if they found a object as big as Pluto pulling a figure-8 around Jupiter and the sun would it be a planet or not?
I stole this Sig
The point, to me anyway, is not really to redefine the planets in our solar system--some people will argue it, but it will remain the same. Just like Columbus didn't "discover" America, but we're always taught that anyway.
Making a definition of what constitutes a planet will aid scientists more as they continue to find new planets. In the forseeable future, astronomy technology will allow us to see disant solar systems with great clarity, and then will be the need to differentiate between a planet/astreoid/etc.
[este]
Ceres is not that spherical hence it can't qualify to be a planet.
People keep trying to wage a debate about this, but no matter what technical hand-waving is going on in the press, the International Astronomical Union is committed to the traditional status of all nine planets, and isn't likely to change that opinion.
--brian
"gaining three more planets - Quaoar, Varuna and Ceres."
There are those that claim that Luna (the moon) actually qualifies as a planet.
I understand that we want to define planets as orbiting stars, but I think there will need to be exceptions. For example, what if a planet is pulled out of a star's orbit (due to a galaxy-wide catastrophe, maybe)? Would the planet be called a "former planet" ? Or "rogue planet" ? In either case, it still has the word planet in its name...
Very popular slashdot journal for adul
Would not relevance of neighbouring objects come into effect. I mean, there's nothing out there with pluto, but there are lots of stuff hanging around the asteroid belt, of which ceres happens to be the largest...
It's not absolute size but importance in the neighbourhood, I would have thought....
OS/2 - because choice is a terrible thing to waste.
As a representative one of the nine planets, I find this proposal deeply troubling, especially since there are not any other representatives from the other eight. Once a planet is classified as an "asteroid" or "floating piece of shit with gravity", it not only loses its prestige, but also, it cannot apply for federal grants, and hence, usually suffers a major economic blow. Laugh you may, but I've seen planets go from a heavenly body to a drunk spinning horizontal and finally distingrate into an asteroid belt in no time. We must support our planets because if we don't, then who will?
okay, well a planet should fall under these circumstances:
1.) in a regular orbit around a star
2.) a generally round shape
3.) has regular rotation around a axis whist it orbits around its star
so basically that should do it, a planet does not need to have a atmosphere, but it should also be large enough for it's own gravity to make it a spherical shape. #3 is another thing that is overlooked often, and it also will keep asteroids and comets from being defined as planets.
Is there a corresponding Sailor Senshi? If so, it's a planet. Ironically, this means that the Earth is not a planet, but the Moon is. Go figure.
-- This and all my posts are in the public domain. I am a lawyer. I am not your lawyer, and this is not legal advice.
The moon is actually very large, especially in comparison to the size of the Earth (Earth = 6371, Moon ~1750, in comparison Pluto ~ 1130). Current thought is that the Moon formed by impact by an approximately Mars sized body early in planetary formation.
While the proposed definition says that a Planet must "orbit the sun and not another planet", I think that if this definition is accepted, we should be considered a "binary planet system" or something similar.
Anyway, just my 2 cents.
If I had no sense of humor, I would long ago have committed suicide. -Ghandi
With the discovery over the past few decades of the Oort Cloud and Kupier Belt, it seems obvious that there are tens, if not hundreds/thousands of Pluto-sized objects out there. Obviously, we're not going to name all 10,000 of these rocks "planets." But then again, Pluto has a special place in history as the last "great" planet discovery on the level of Uranus and Neptune, so purists wouldn't want to ruin that by demoting it.
:-) Therefore, I say we define a planet however they want, but keep Pluto for historical significance. I knew med school would start paying off soon :-)
My solution? Define "Planet" as something bigger than Pluto, maybe with Mercury as the smallest, or whatever. But keep Pluto as a planet (as an exception ot the rule) for historical purposes. But, you may be thinking, "that's so stupid! Why give something a name if that name is now invalid?" The answer? We do it all the time. Here's an example...
Take a look at ANY diet softdrink/diet product with Nutrasweet. It warns you that this product contains "Phenylalanine" and should not be taken by "Pheylketonurics." Take a look at that word. It's called "Phenyl-keton-uria" (PKU) because years ago, people with this disease were diagnosed when "Phenylketones" were detected in their Urine. However, no one diagnoses PKU via a urine test anymore, they use another method. So should we change the name of the disease? Of course not. But due to historical significance, we keep it. Unlike the Indian/Native American designation, "Planet Pluto" should not offend anyone
For my money, the smartest thing said in the article came at the end:
It strikes me that planets have traditionally been considered as geographical features of our solar system. But now that the Hubble telescope and other detectors are beginning to extend our knowledge of planets beyond our solar system, if we want to define a natural category planet it makes sense that the definition this category should have a basis in a well founded theory of planets, not arbitrary size and shape limits. So it makes sense to hold off on a definition of planet until we learn more about planets outside our own solar system.
This is just like taxonomy... some scientists like to lump similar creatures into one family or genus, while others like to split them up into different categories based on minor differences.
Looks like astronomers do it too.
Different discipline, same problem.
Even if a man chops off your hand with a sword, you still have two nice, sharp bones to stick in his eyes.
You know, this could bring about some astronomy-related "Yo Mama" jokes.
Yo mama's diameter is so large that gravity pulls her into a spherical shape, making her the thirteenth planet! On second thought, scratch that.
where the comment ends and sig begins
Is this going to be submitted to the ISO org to be classified under a certain standard?
Indian astrology studies planets as those heavenly bodies that affect life-forms on the Earth in a 'major' way. Thus the Sun and the Moon are also planets as per the Indian definition. Two planets (Raagu & Kethu) are also defined - these do not denote physical planets, rather, the clock-wise and the anti-clockwise 'spin' of the Earth.
The system also defines 27 stars (the nearest ones from the Earth) and a 60-year cycle.
Under this system:
It is possible to accurately determine 'events' such as eclipses, birth & death, progeny, well-being, etc.
There is no need for 'leap-year' correction, since a year can be 'born' at mid-day, mid-night or anytime in between.
If you keep throwing chairs, one day you'll break windows....
Well we can always just end the debate and give everything new names. 'big-round-objects' and 'Shiny-thing-projecting-light' makes a lot more sense.
Hmm, why don't we just say any object orbiting a star is a planet? That way, we can classify the Oort cloud as a billion planets and see how kids decide to build it into their solar system models. ;)
0- Eamonman Proud member of DNRC
I'm no astromer (and my asbestos jocks are at the drycleaner, so hold your flame if I'm wrong here) but pretty much all the currently accepted "planets" in our solar system boast either some sort of atmosphere, or they're gas giants (ie: Jupiter) or frozen liquid (Neptune?)
I think Mercury has an atmosphere; Mars has a very thin one, doesn't it?
Also, if it fits the criteria above and has a satellite(s) orbitting it, it's certainly a planet in the accepted sense, wouldn't you say?
Pluto has me puzzled though... I don't recall hearing of it having any atmosphere, and it does have a very eccentric orbit - almost like an asteroid...
"You might think it's a long way to the chemist, but that's just peanuts compared to space!" - Douglas Adams
Look!
A planet is a planet and an asteroid is an asteroid. How hard is that to remember? Get with the program! Gesh.
http://saveie6.com/
This superficial naming convention makes absolutely no difference at all. It has no effect on anything.
It would be like if you changed the biological classification system so that bears were no longer Mammals. What difference does this make to the bears? None. What difference does this make in how we relate to bears? None.
It is simply an arbitrary naming convention. As are all naming conventions.
It reminds me of an old Zen saying that I am likely paraphrasing miserably:
"Before Zen, a mountain is a mountain. While one is practicing Zen, a mountain is no longer a mountain. After Zen, a mountain is once again a mountain."
Justin Dubs
From the article:
People like to classify things. We live on a planet; it would be nice to know what that was.
And as if making up an arbitrary differentiation between an asteroid based on it's diametre or mass is gonna make us any wiser.
I inderstand that "gray areas" are unwelcome, but in most cases I don't quite agree with people's tendency to overcategorize things. It's sometimes more constructive to see the common nominators, that's what science usually is about, i.e. to understand that asteroids and planets have shitloads in common, but perhaps one day we know more about them to tell them apart better, say, based on how they were formed or wether they're on chaotic orbits around their sun or some other ideas.
Besides the quote in the end of the article puts it well: "It's way too early to define a planet," he said. "Even though we have now found over 100 of them, these are still early days in planet hunting."
1 Earth is warming, 2 It's us, 3 it's royally bad, 4 we need to take action NOW
Alone in it's orbit, it's moons orbits it
isn't too far out
Sorry about the writing. Robot fingers, you know? Cliff Steele in DOOM PATROL #23
Why is there so much mention of radius and size and such. It's just so petty. I would think in this enlightened age we'd all know:
It's not the size that matters, it's how you orbit!
*Dodging tomatoes should be a sport*
Hogwash. Scientific terms need a definition in terms of a scientific theory. So an "absolute" definition like "anything spherical with a radius smaller than the sun and bigger than the moon" or something like that, although suitably absolute (notwithstanding changes in the radii of the sun and moon), obviously has no connection to a scientific theory of planets. But there's a bigger point here too: absolute definitions make for crappy science. We can't legislate the way the world is via definition; good science should seek to describe the world. Imagine, for a moment, we were having this discussion not about planets but about marmots. We wouldn't want to specify maximum and minimum sizes in some definition of marmots because it would be silly to disqualify something as a marmot purely on the basis of its size, regardless of other factors (say, its marmot parents). And analogously, it would be silly to disqualify something that otherwise fit into our theory of planets perfectly on the basis of its size. Or to be forced to include something as a planet on the basis of its size, despite the fact that it has no other place in a scientific model of planets.
<RightBrain>A planet is something we can go send probes to without having them bounce off! We can land on a planet and walk around without needing magnets and ropes to keep us from going into orbit! Too small, and you fly off. Too big, and it burns you up! Of course planets always orbit stars, not other planets, so the Moon doesn't count.</RightBrain>
-Ansel.
p.s. I do realize that the Moon and Earth orbit each other and the sun, but the Earth is so much bigger...
G=C800:5
"Size matters not. Judge me by my size, do you?"
Sorry, my willpower is weaker than my taste for an perfectly timed movie quote. As for my opinion, I think what they are wanting here is a guideline for future exploration and habitation, or possibly to try and narrow down what would constitute studying under "planetary" effects like rotation, atmosphere, etc. and debris effects, like asteroids and comets. Still though, it seems kinda silly, but I can understand them wanting a more explicit point of reference. Still, it does sound kinda silly, after all, its a big universe, and remember, we're still learning it's rules, it doesn't play by ours. I'm sure theres a rock the size of a winnebago with its own atmosphere out there.....
Mod Points: Helping you keep your opinion to yourself.
The number will be rather small, so I can claim ownership of the two planets in my pants.
1. Should revovle around the star & should not have 20% more eccentric orbit(to a circle)
2. Should be 5% bigger than the parent star
3. Should have volcanic activity.
If EITHER one is not satisfied..it is a big space-rock
When I think of a planet, I think of a fluid (hot non-plasma gas, liquid metal) held together by self-gravity. Contrast with an asteroid, which is a rigid object (i.e., a rock). Furthermore, a planet must orbit around the sun, and not another body; if it does, it should be called a moon.
...
My $0.02
Pluto currenly has an atmosphere, oneof the reasons for the Pluto Express/Kuiper Belt mission is to examine the atmosphere bfore it condenses as its eccentric orbit takes it past the point where the temp drops and the atmosphere condenses.
The Singularity is closer than you think
Quant
Just use the Star Trek planet classifications... Come on, it's time to make use of sci fi in astronomy for once. :-) Hmm, btw, I wonder what the heck the copyright at the top of the page is about? Courtesy JPL? Errr...
Beware: In C++, your friends can see your privates!
Please define "is".
Why was this put up?
When you calculate the objects properties, the math is still the same.
This site is (or used to be) about the 'math' not the 'management bs'.
Mercury was thought to be two planets by some (the morning and evening star).
In my part of the world, Venus is the morning and evening star. Thats probably how it is over at your place to.
I fully support Quaoar's candidacy in the planet club. Quaoar isn't a Roman god? No problem; we'll make him one. "Quaoar, god of burlap"
Works for me.
Yes. Which is not contradictory with what I wrote.
And analogously, it would be silly to disqualify something that otherwise fit into our theory of planets perfectly on the basis of its size.
"Analogously" doesn't prove anything, it's just a way of illustrating what you believe.
And anyway, "size" WASN'T the determinant offered by the astronomer, but being large enough to be spherical due to gravity, which turns out to be about 700 km diameter.
"...we could end up losing Pluto (at 2300 kilometres) to the status of "asteroid" or gaining three more planets - Quaoar, Varuna and Ceres."
:)
If Ceres is a planet, then Paverotti could be one too
Fuzzy Knights: New RPG Strips Tuesday and Friday!:
http://www.fuzzyknights.com
What happened to the tenth planet? It was claimed to be bigger than Jupiter and had made big news back then (2000?). Where the hell did it disintegrate off to?
> In my part of the world, Venus is the morning and evening star. Thats probably how it is over at your place to.
"A" instead of "the".
(See Mercury is often visible near the rising or setting Sun as the morning or evening star) But I don't think Venus was ever thought to be two planets, but IIRC, Mercury was.
Any Definition for "planet" will be arbitrary. Is a little ball of snow and ice on a highly elongated orbit a planet? No. It's a comet. Is a gas giant that generates more heat internally than it receives from the star it orbits a planet? Maybe, maybe not. OK, perhaps that's not arbitrary. If the thing gives more heat then it gets, then perhaps you could classify it as a brown dwarf, but what if the star it orbits flares up? Then does it suddenly become a planet because it starts receiving more heat?
I think the only thing we can conclude is that the definitions for "planet", "moon", "ring material", "asteroid", "comet" and "brown dwarf" are all arbitrary. It's all a matter of perspective.
So, here are my definitions:
Planet -- orbits a star, is big enough so that gravitational pull forces it to appear round or smoothly eliptical to the naked eye.
Asteroid -- orbits a star, If it's not round due to gravity, it's definitely an asteroid. Problem--this makes Ceres a planet.
Moon -- orbits a planet, unless it's not round then it's just a "captured asteroid". Problem--this makes Deimos and Phobos non-moons.
Ring material -- If the human eye perceives the planet as having rings, then any ojbect within the region containing the perceived rings is "ring material" regardless of how big it is or how it's shaped.
Comet -- any item that forms a tail when passing close to the star.
Brown dwarf -- Gives off more heat then it gets.
Really, when you get right down to it, all of these things are just "stuff that's not space". Choosing to call them "planet" or "comet" makes as much sense as choosing to call one city Cincinnati and another Buffalo. Somebody's gotta name the thing. Now, people have been living in Buffalo a long time, and they've been calling Pluto a planet a long time too. Whaddya say we make a deal? Get Buffalo to change its name to Cincinnati, and we can stop calling Pluto a planet. Now, what do I call a single hydrogen atom on a hyperbolic trajectory with Jupiter?
For all intensive purposes, "whom" is no longer a word. That begs the question, "who cares"?
uhm no....
we use "naming conventions" or "Categories" to group related thing togeather.
thus maing them easier to reference.
naming conventions should show that all these objects have one or more properties. so that we can easily say
Mammal:
and you know it is warm blooded
I say Planet:
and you know
-It orbits a star
-it doesn't radiate light
-it is of size > X
if you include random shit in it (like a bear). it becomes hugely more complicated to talk about something that has all the above properties...that may have more properties in common...
Biotch.
--meh--
Just as you spell it.
There are two rules for success:
1. Never tell everything you know.
But doesn't it [Ceres] have a satellite? -- and -- What would we qualifty that as, because a satellite must orbit a planet.
It doesn't appear that Ceres has any satellites. But, there are 31 asteroids that do! That doesn't make them planets though...they're just small asteroids with really small moons.
Can anyone remind me what that sequence of numbers is called that vaguely predicts the distances of planets from the Sun?
Yep, its the Titius-Bode Law. Ceres does fit into this. But the reason we don't have a planet in between Mars and Jupiter is because "many astronomers think the asteroid belt is where a planet tried to form, but was pulled apart before it could solidify, caught between the strong opposing tugs of Jupiter and the sun's gravity." Quote taken from here.
Why does a planet _have_ to be a shpere...How perfect a sphere?
Well.... Ceres's shape is too distorted. Its shape is not spherical enough to be like regular planets. And, to get really technical, no planet is really a sphere. Due to rotation, all planets have a slightly distorted shape.
planet n.
1.) An object orbiting a star that is smaller than Cowboyneal's ego but larger than his mother. 2.) Cowboyneal's mother. 3.) Any large piece of rock, such as a fundie's brain.
Repeal the DMCA!
Following up myself ("Mercury was thought to be two planets"):
Mercury was believed by the Greeks to be two different stars. Mercury's appearance in the morning was called Apollo, and its evening appearance was referred to as Hermes.
Questions pertaining to the planets are a favourite in many kinds of different quizes, and the popularity of e.g., tv-quizes show that these are important to real people. Changing the definition of planet can change the lives of many.
The last question in do you want to be a millionaire: What is name of the smallest plantet?
Ouch!
IANAA (duh).
How big does a planet have to be to hold an atmosphere? Would that do to define a planet? Whether or not it has one doesn't matter.. as long as it would retain one if the gas were present.
I'm sure the committee will do what the committee that decided what the definition of a tall building did: offer half-a-dozen definitions without really making one of them definitive. Depending on which definition you use, the tallest building in the world is Petronas Twin Towers in Kuala Lumpur, the Sears Tower in Chicago, the CN Tower in Toronto, or a few others. (Hey, the CN Tower is a small building with a really big "architectural spire"! ;-)
I think the World Trade Center also might have been the tallest by one of the definitions. It seems odd that the replacement building is going to stop 40 feet short from definitively grabbing the title from the CN Tower.
Committee, n.: A group of people that, when given the task of deciding whether to start array indices from either 0 or 1, compromises to declare that they are to start from 0.5.
Badly?
It is possible to accurately determine 'events' such as...birth & death, progeny...
It would be very useful to have a way of predicting things like that. What evidence is there that the system of astrology you describe actually has these abilities?
TTFN
If the crew of Enterprise would use the teleporter to reach the SURFACE of it, then it's a planet, if they are teleporting to a chamber inside it, it's most likely an asteroid or something.
"Your superior intellect is no match for our puny weapons!"
Why don't they just create a new intermediate classification like companies do when they realize their engineering managers can't manage. They give them a title like "Lead Architect" (no offense intended to all of the Lead Architects out there). I propose that all obects orbiting a sun, less than 700KM in diameter be call "Planetoids". Not quite a planet, but not as low as a lowly asteroid. Planetoids are valuable contributors to the solar system!
How about this: A mass with an self-sustained atmosphere of measurable magnitude.
I swear, the reason we're not in flying cars powered by cold fusion is because the world's best and brightest are too busy arguing over stupid things like the definition of a planet. Maybe I need to rethink my concepts of "best" and "brightest."
scientific terms need an absolute definition
A rigorous definition may be necessary but not sufficient for the "usefulness" of a scientific term. In this case, it doesn't seem like the proposed definitions are useful.
If we determined (for example) that bodies above a certain mass had some other properties of interest, or that stellar systems with a certain number of bodies above a certain mass had some interesting properties, then it would be useful to define "planets" as being bodies of at least that mass. The class of such bodies would be a regular subject of analysis, and it's easier to say "planets" than to say "non-stellar gravitationally stellar-bound bodies of Werkeltroff-Schmeltergruber-Minayevich mass or greater."
See, in the ordinary course of developing a scientific lexicon, we discover scientifically useful concepts, and then define terms for those concepts in order to provide economy of expression.
In this case, however, it seems that we have a term that already exists in the popular lexicon, but no related scientific concept with a compelling need for the term.
So why bother? Why not just allow the term to continue its peaceful existence in the popular lexicon, without attaching an arbitrary definition to it? Are we trying to serve some purpose other than allowing slashdot geeks another way to point out where the popular press gets something wrong? If we can identify a purpose for a definition, I the definition will probably follow naturually from the identified purpose; if not, then the whole discussion is silly, at best.
There is also the problem of suns that orbit other suns. If your "planet" is a light source, then I'm sorry, it ain't no planet in my book.
Congratulations! Now we are the Evil Empire
How do we solve that? We say what we mean in a particular context and then use the word as a shorthand. "In this paper, we will use the term 'planet' to refer to extrasolar bodies with diameters over 700km and masses less than 13 times the mass of Jupiter." "In this paper, we will be talking about the traditional nine planets of the solar system, Mercury, Venus, ..." Etc.
Terms like "planet" would actually be less useful if they did have a precise definition, because than each of those papers would have to use a much more awkward circumlocution when referring to bodies that don't meet the definition precisely.
Quaoar - http://www.gps.caltech.edu/~chad/quaoar/ Varuna - http://www.ifa.hawaii.edu/faculty/jewitt/varuna.ht ml
Ceres - http://www.mallorcaweb.net/masm/Ceres1.htm
cat
Problem: There are likely many Pluto-sized objects
in the Kuiper Belt. How about making the
threshold dependent on radius / solar-distance?
Pluto lucks out by being close enough to get
counted first.
-I like my women like I like my tea: green-
But it's proximity to other objects. That's why Pluto should remain a planet. There isn't really anything else around it, so it should be a planet. Ceres on the other hand, is in the middle of a large belt of other similarly sized objects, so it should stay as what it is, an asteroid.
Back when I was a whipper snapper a planet was nothing more than a wandering star.
Well, it does appear to be a definition. It doesn't actually *have* to do anything. (Though that would certainly be nice.)
OK, so we'll debate whether Pluto's a planet or not. But we know that Pluto is Mickey's dog. My question is, what is Goofy? A wolf? A dog? Certainly not a planet!
I like Basri's definition; it makes the most sense so far. But I wonder if one should take into account the shape of the orbit of the object. A highly irregular orbit (as in, "not moving in (or close enough to) the same orbital plane as the majority of objects orbiting the star") might make an object an asteroid. But this definition might not make sense anywhere else but the solar system; also, it might throw out Pluto (but just because we call it "Planet" now doesn't mean we have to make sure the definition fits it).
So for now the characteristics used to define a planet include (1) directly orbiting a star, and (2) having a size large enough to allow gravity to shape it spherical. Maybe there will be (3) its orbit has a certain nature, or (4) its distance from the star is not larger than x, or (5) its density is between x and y (because maybe there might be non-round objects more than 700 km in diameter which are simply not dense enough); (5) might be avoided by defining (2) as above through the shape and not a diameter number.
I haven't seen many posts here trying to define characteristics -- I'd like to see some ideas here, even if it might mean that Pluto isn't a planet anymore, or we suddenly have twelve planets in our system.
If Pluto was discovered today, it'd just be considered an asteroid or Kuipier belt object
The fact that its called a planet is just due to when it was discovered.
Not that it really matters...
The International Astronomical Union released a statement (a little dated) that they would not consider changing the status of Pluto. It can be found here.
The IAU is the body that would make such an official decision and it seems they don't want to change it.
Because new objects have been and will be discovered in our solar system, and others, that some might think of as "planets", and so the question of where actually to draw the line has arisen (actually many years ago, this is just the latest proposal).
Anyway, I won't continue this thread. Feel free to make more condescending comments for your fans.
Aah, yes of course! doh! I think I'm posting messages too early in the monday morning...
Beware: In C++, your friends can see your privates!
from dictionary.com, of course.
"Note: The term planet was first used to distinguish those stars which have an apparent motion through the constellations from the fixed stars, which retain their relative places unchanged."
and
"Middle English, from Old French planete, from Late Latin planta, from Greek plants, variant of plans, plant-, from plansthai, to wander"
The most useful definition of "star" appears to be "Any of the celestial bodies visible at night from Earth as relatively stationary, usually twinkling points of light."
So our original definition of planet depends on our own perception. As our ability to perceive objects improves, we either need to accept the classification of new objects under the old naming scheme, or come up with a new naming scheme, which will have to be based on something that is not variable, for example mass, or size. The obvious problem here is that we are trying to come up with a new naming scheme but using the old names; that, surely, is what is ridiculous, not whether or not Pluto is a planet.
So called because it looks like a pair of boobies, and that's the first thing the boobonomers, er, sorry, astronomers said when they saw it?
it's a space station!
It's pretty unlikely that such a proposal will be met with much acceptance or exuberance in the astronomical community. There's no objective definition of planet (or any other of the classifications of celestial bodies) for a reason: because, quite frankly, it doesn't really matter. If you're an astronomer studying Pluto, you can study it whether or not it's called a planet. The celestial bodies don't care what they're called; the classification system we use is a man-made one. There's no reason to think it has value outside our own internal thought processes; the Universe isn't compelled to match our expectations.
That is, a planet is what the IAU says one is: nothing more, nothing less. Changing this won't have any useful effect on astronomy.
a more in-depth article on planet definitions including a grainy photograph of ceres can be found at:
o ns /tnl/59/planetdefine.html
http://www.astrosociety.org/education/publicati
... YO MOMMAS ASS!
Hehe.
Dammit, I had to.
We need more planets, because of my network hostnames, I already used quaoar for an old 486, ceres for another 486 and charon for the 320H.
sysadmins who name their servers after planets.
Fine for your first 2 or 3 servers, but...
> a planet must orbit a star, not another planet
Imagine two planets orbiting "themselves". A double-planet minisystem which, as a whole, orbits a star. Much like earth and moon, except that moon is too small to have athmosphere and life. If that prehistiorian impact that allegdly separated earth and moon had hit in a different way, maybe earth and moon were now of same size, and both had atmosphere? Would they then disqualify as planets?
It boils down to - what is orbiting, exactly?
Yell & scream & rant & rave... it's no use... you need a shaaaave ~ Bugs Bunny
Now if we could just lose the rest of Disney, our freedom might be safe.
-Miko
Miko O'Sullivan
Man, I gotta drink me some of that Ganges water...
Pluto, if stripped of its rank as it should, shouldn't be called an asteroid, but a comet. It is made of the same composition as one but it just cannot get close enough to the center of the Sol system to have a tail. Instead of the smallest planet it could be known as the largest comet, but who knows what that Oort cloud is composed of...
- Danny
As one who tends to think functionally (as demonstrated by my membership in ten-step programs for living with addiction to obscure programming languages...) I am sympathetic to the refining of the term "planet". I really never liked all those pictures of the solar system with Pluto flying wild and off he plane of the other planets anyway.
But size doesn't do the trick either, as well cited. Reflecting light...bah. Tradition...puhleez! this is what future kids are going to be learning as one of the uber-sciences.
No, I think we need to admit that good ol' Sol doesn't have a handful of one thing (which we want to call "planet"), but an inventory along the lines of (from inside out):
- 4 rocky round thing (one of which is probably best seen as a double-rocky thing)
- a boatload of little rocky things (asteroids)
- 4 gas giants
- another boatload of little rocky things (comets/Kuiper belt object)
I'm sure that looking closer will yield more detail in a nice fractal manner, as it does in most any taxonomic endeavor, but whaddeva.
Just think about how much clearer reports of "planets" in other systems would be if the headline distinguished "gas giant found" from "rocky round thing found" - I certainly am looking for the latter as I scan!
While I wouldn't go so far as to call it "the dark side" of science, stuff like this makes it clear that there are the usual pecking-order rivalries and power games going on in science just as anywhere else.
Obviously there's very little no scientific importance to the definition of "a planet." It's a little self-aggrandizing, for example, to suggest that the Earth is somehow in the same category as Jupiter.
It's all about which scientists get to have _their_ definition of planet get into the textbooks (and control what projects can get "planetary studies" funding, etc.)
"How to Do Nothing," kids activities, back in print!
'Quaoar'?
That sounds like the noise a geek makes when a good looking female walks past the window...
"Planet" is a huge, vague term that isn't really of practical use. Sure, you can use it for anything that doesn't produce its own light, and you can narrow that down by saying stuff about what it orbits or doesn't orbit, and then you can try to cull the comets and asteroids from that list using size (or whatever) as a criterion... The definition doesn't DO much, practically, to help us understand the big woolly universe out there.
Example: Pluto's the small end, great, but what about the current methods for searching for extrasolar "planets"? Because of our methods, we're mostly limited to seeing massive, super-Jupiters in incredibly close orbits around their stars. ('Till last year, anyway.) I guess those are "planets," but they sure don't look or act like anything familiar to us, and calling them a "planet" doesn't help us understand them much.
If we settle this debate, elementary school kids everywhere will know the names to memorize for the solar system. And that's about it.
"Fundamentalism" isn't about divine morality. It's about human authority.
Well, looks like "My Very Excited Mother Just Sat Upon Nine Porcupines" will no longer work.
Something more, um, "topical" may be chosen, now that we'll have the opportunity --- like "Osama Bin Laden Just Sat Upon Nine Porcupines and Must Die, Die, Die".
Or not.
Redundancy is good; triple redundancy is twice as good! - Me.
The englishman who landed on an asteroid and took off a planet.
Duct tape + WD40 => DevOps
If you take Earths moon. Place it in its orbit possition right between Earth and Sol. This point Sol will have more g's pulling pull then the Earth does.( How it stays in orbit is other topic). No other (the Moon)does this. Each moons own planet has much more g's pulling vrs the sun. The Moon realy is in orbit aruond Sol. Does the moon become a planetiod? Concept from artical writen bye Issac Azmov (RIP)
we find a moon that happens to also sustain life? Suddenly we're going to be like 'dude, you only live on a moon, but we live on a planet' and they're going to be like 'yeah, well take this' and suddenly there goes the Earth, just because someone had to open their big mouth.
And I swear this conversation didn't just take place in my office. (The problem of working with other geeks)
I will shred my adversaries. Pull their eyes out just enough to turn them towards their mewing, mutilated faces. Illyria
"You're a cinch for World's Fattest Man!"
--
"Outlook not so good." That magic 8-ball knows everything! I'll ask about Exchange Server next.
It seems to me that one of the reasons this issue is so controversial is because it would mean we have to update our conception of reality, be it dropping Pluto or adding Ceres, and people just hate that.
I remember back in the 70s when telling people that Neptune was farther out (at that time) than Pluto, they would get very upset and push aside the SciAm diagram explaining the intersecting orbits. These are people who would otherwise be found a kid talking about the stars and trips to the moon quite endearing.
I think the problem with asteroids is that we want an "orbit" to contain a single concentration of mass. Mars and Jupiter seem to be planets, but a bunch of rocks wandering approximately in the space between planets doesn't seem like what a planet "should be".
Probably if we had a habitable gas torus around our sun we'd have a different definition of significant astronomical bodies...
We'll need a definition more precise than "outside Pluto's orbit" unless we are satisfied with having Neptune sometimes not be a planet.
Still haven't seen a post here siding with Gibor Basri's proposal. As strange as it feels to have 12 planets, I think gravity-induced roundness + solar orbit within the plane of the solar system seems like a logical standard for planet status. How much else does Mercury have in common with Jupiter that it doesn't have in common with Ceres?
The (current) arbitrary 2300 kilometer size limit seems a bit elitist.
What if we had to include Ceres but downgrade Pluto (because of its orbit)? Man is that weird.
The earth and moon are a double-planetary system. If you calculate the gravitational pull of the earth on the moon vs the pull of the sun on the moon, the sun's pull is always grearter. That means that the moon's orbit is always concave toward the sun. The earth does a lot to perturb the moon's orbit, but it's not strong enough that the moon can be said to orbit the earth as the earth orbits the sun.
The moons of jupiter and saturn, for example, move in paths that are always concave toward their respective planets. Earth's artificial satellites and so forrth can be sait to orbit the earth, but the moon does not.
Liberty uber alles.
Is it possible that extraterrestrials, putting around the solar system in their flying saucers, might even now be consulting their "Solar System on $5 Credits A Day" (or, "Earth through the Back Door") and reading about the "binary planets Earth/Luna"?
Naaaaah!
No one ever had to evacuate a city because the solar panels broke!
See previous posts on this point.
no, it makes sence becasue look at how a solar system is formed. a gas cloud condenses with a large mass of gass at the center. the rest of it is a disk in the same plane or orbit. then planets form from the gas as well as rouge bodies...the rouge bodies are smaller than the planets adn have highly irregular orbits about the star.
I am the Alpha and the Omega-3
it all depends on how you define "hilarious"
Keep your packets off my GNU/Girlfriend!
The lunar atmosphere is also only 1/100,000,000,000,000 that of Earth, and in fact is often called the exosphere. For planets, the exosphere is the tenuous part of the atmosphere beyond the ionosphere that blends into space, says Galvin. "The Earth's exosphere starts at 480 kilometers up. For the moon, you have the surface of the moon and -- bang! -- the exosphere right next to it."
scripsit lu3hr:
What I find interesting is that the Romans called the morning appearance of Mercury ``Lucifer'' -- the light-bringer. AFAIK that came before the use of ``Lucifer'' to refer to the fallen angel. Does anyone know if there was a connection between Satan and the planet Mercury in any Hebrew tradition?
In principio creauit Linus Linucem.
That news came out when I was in highschool, like four years ago. And it doesn't even really matter; by the classic scientific definition, all the asteroids are planets, and no one gets all panicky when they find that out.
/. ...
'Oh gosh!' we'd all say, 'we've got to memorize the order of fifty million planets!'
Heh... My Very Educated Mother isn't going to cut it anymore, it's going to take a mnemonic the length of the Encyclopedia Britainica.
~SL
Yeah I'm crotchety... it's 8:00 in the friggin' morning and I'm up early to post to
Well obviously, this is political gerrymandering at its worst. First, the Plutonians lose their precious "planet" status. Next we'll see toxic chemical plants relocating from Beaumont, Texas and East St. Louis to Pluto. pretty soon, it's a prison-industrial wasteland.
must... stay... awake...
Planet is from the greek for 'wanderer'. The stars seen from Earth appear to move as the earth rotates and also as the earth revolves around the sun, giving a different night sky for the winter than in the summer. And though moving, these stars all keep the same relationship between themselves. Planets, however, are objects seen in the sky which move in relation to the other objects in the sky. They wander about and have no fixed position. Thus, planets are objects which wander about in the night sky -- which means they are indeed objects which orbit the sun.
And what, exactly, is wrong with this definition? Why is it important to us that we have only a few large 'planets'? Are we afraid it would necessitate learning the names of each and every object orbiting the sun?
I do not have a good response to this question myself, but something does seem wrong with it -- we want relatively few planets because we view them as somehow important. When we identify what makes these objects important to us (and it may well just be their size), then we can come to a suitable scientific definition of what makes a planet, and have it be one that does not contradict our intuitive assessment of the same.
I actually grew up near Ceres and I can say with some authority that it's a very strange planet indeed. Whether or not it has life is open to debate.
This is one of those cases that makes it obvious just how arbitrary any particular boundary is.
.. pretty much. And leaves it open to find more distant planets.)
I propose the following definition: All those bodies that orbit the sun in orbits approximately the same as those specified by Bode's law. (A totally silly definition, that just happens to work for all the current planets
Alternatively, we could say "The nine largest bodies in orbit around the sun.", but that would risk earth eventually being declared not a planet. (Who knows what's in orbit out beyond Pluto? We've got guesses and theories, but we could easily be wrong. And then Earth wouldn't be a planet any more.)
Probably the simplest way is just to enumerate them, and say "These are the ones I mean. Them and no others!"
Currently any of these choices would work. And they are all essentially arbitrary.
How about this:
The term planet is stricken from the official terminology and is replaced by the term "classical planets" which refers to an explicit list of planets (the current planets). The new term replacing is is worlds, and it refers to any body in orbit around the sun. I.e., if at no point of your orbit do you move backwards against the direction of your orbit around the sun, you count as a world. Otherwise you are a moon.
OTOH, in biology I tend to be a cladist, even if that would class a trout as being more related a cow than to a shark.
I think we've pushed this "anyone can grow up to be president" thing too far.
Someone will have to go back and re-code the stage names in Gyruss if the planetary scheme changes!
According to the Catholic Encyclopedia, "Lucifer" was Venus, and was Satan's name before his fall.
Or maybe better to say that the moon is the freaking moon, and those things around Jupiter are something else?
If the Moon is the Moon, and you go and call something flying around Jupiter a Moon too, but later find out that it really isn't much like The Moon at all, seems like the appropriate course of action is to realize your mistake and stop calling all those other things moons, not rename the moon to cover your error.
paintball
the moon and earth, could they be considered a binary system? Maybe the moon is not just a moon of the earth but a planet.
photosMy Photostream
Yes, many people think Earth/Moon should be considered a binary planet. The Moon is much larger than Pluto, and is large enough that the Earth obviously rotates around the center of gravity of the two bodies. Perhaps a definition could require that a planet's center of gravity between it and the next larger object be outside the larger object -- that would require the Moon to be somewhat larger for it to draw the center of gravity above the Earth's surface.
...Offtopic?!? Jeez, did you even *listen* to the thing?
In Soviet Russia, Chuck Norris will still kick your ass.
scripsit 1u3hr:
Doh! Yes, of course. s/Mercury/Venus/ in my previous comment. I repeated the earlier poster's conflation of Mercury and Venus without error-checking.
Thanks for the added info. I'm still not clear, though, on whether Helel refers to the Morning Star (i.e., Venus when occidental) or just to the Adversary. That is, was the association between the planet and the fallen angel made prior to the Septaugint's use of Heosphoros (``Dawn-bringer,'' equiv. to Lucifer) to refer to the angel as well as the Morning Star?
I guess the larger question, in my mind, is whether the pre-Rabbinic Jews associated luminaries with angels, or if that association came when Christians fused Classical astrology with the Hebraic tradition.
In principio creauit Linus Linucem.
-Shylock0
Statistically speaking, there's a 99.998% chance that my IQ is higher than yours. Get over it.
Downgrading Pluto to the largest known Kuiper belt object would seem to be the best course of action. The reason Ceres wasn't given the status of a planet when it was found was that it was just the largest of a number of similar object, the asteroid belt. When Pluto was discovered in the 1930's the Kuiper belt was unknown and so it got planet status.
However in recent years it has become clear that there are many similar objects to Pluto forming a belt outside the orbit of Neptune. In fact the the Kuiper belt is thought to be over 100 times larger, in terms of total mass and number of objects, than the asteroid belt between Mars and Jupiter. Given that they are much further away and only a very small fraction of them have been found it is possible that Pluto is not even the largest member of the Kuiper belt.
The definition of a planet should probably include the proviso that the object not be part of a collection of objects in similar orbits. This would rule of all asteroids and Kuiper belt objects (KBOs) which includes Pluto. A part of the traditional understanding of what a planet is, is that it is, with the possible exception of its moons, a solitary body.
A planet is anything so large that its destruction requires the use of the Shadow "Planet Killer", or a space station large enough to be mistaken for a moon.
The REAL jabber has the user id: 13196
What you do today will cost you a day of your life
The poster should have pointed you guys to this Berkeleyan article where the whole debate is fleshed-out...
... Planemos, KPOs, 'super-Plutos' [berkeley.edu]
An orb by any other name
Lets crash a bunch of asteroids into Pluto to make it big enough that nobody questions its status anymore, and be done with it.
Either that, blow it up into fine dust.
Who was that king in the Bible who threatened to rip a baby in half because two women claimed it was theirs? Name the result after him.
Table-ized A.I.
I know this far-fetched, but...
Instead of all the trash that the parent wants to send why not just send the 3 pesky planets that are causing such a fuss to Jupiter.
We'll have to leave Pluto though just to spite that NY planetarium since that damned NY Times always wants us to register.
Life moves pretty fast; if you don't stop and look around once in a while, you could miss it. -FB
I believe that is the definition. For a two body system to be a "double body" instead of a planet and a moon, the mutual center of gravity must be outside both. Since the point that the earth revolves around the moon is actually just below the earth's surface, it doesn't count as a double body.
Pluto/Charon, however, I believe is a double planet in that sense.
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
> There's no distinction between planet and asteroid
Is the gravity heavy enough such that a male mounting a female in the missionary position could penetrate her without any additional force needed?
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
b) traditionally, you only had the naked-eye planets: Mercury, venus, Mars, Jupiter, Saturn. What do you call the other gas giants? Not to mention, Mercury was thought to be two planets by some (the morning and evening star).
Nope, it was Venus that were traditionally thought of as Hesperos and Phosphoros, the main evening and morning star. If you've ever seen Venus, you know why: bright sucker.
The Ptolemaic planets were (in order of "spheres") Earth (Gaia), Moon (Selene), Venus (Aphrodite), Mercury (Hermes), Sun (Helios), Mars (Ares), Jupiter (Zeus), Saturn (Kronos), sphere of the fixed stars (all the stars). The division of Venus into Hesperos and Phosphoros goes a few hundred years further back than Ptolemy. It is also worth noting that Ptolemy, whose cosmology held sway in the west until Galileo proved in the Siderius Nuntius that Copernicus had been right, was later than Aristarchus, who believed that the Sun was the center of the solar system, suspected that the stars were other suns, and that the universe was effectively infinite.
To the Greeks, by the way, Ouranos was the basic word for "heaven" and could be thought of as their word for "space." The god Ouranos was the father of Kronos (the Roman analogs being Uranus and Saturn). Poseidon is the name of the god of the sea; the Greeks would have thought it quite odd to name a planet that (the Roman analog to Poseidon is Neptune), as Poseidon's realm was the ocean and the seas around them. And Hades (Roman analog would be Pluto) would have been right out, as he was the god of the underground and underworld.
> and makes Lucifer the name of the principal
> fallen angel who must lament the loss of his
> original glory bright as the morning star
Laments? Can you imagine all the ass he's gotten since then?
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
Moon: A large mass following a main body. Sometimes in the light, sometimes "where the sun don't shine", it's often pockmarked and always with an enormous trench. Although apparently lifeless, they all possess some "biologically active" areas when searched deeply enough. Some from the outer areas tend to be larger. This is generally esthetically preferred to tiny ones, but not too large as they become gravitationally unstable, unable to support their own weight.
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
That sounds like it's comparing the gravity as if the moon and earth weren't in orbit and one wanted to see which way the moon would "roll" if "let go". Very interesting.
Even though the net effective gravity on either the earth or moon is (roughly) zero, so the orbit is more or less identical to what it would be if the earth were floating in space without the sun.
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
seriously, that term has a different meaning to diffrent people and is steeped in tradition.
Designate them by size,gravity, atmosphere, manmade.
so you could say, its a size X object with an atmosphere of H/no atmosphere/whatever, natural.
The Kruger Dunning explains most post on
Yeeha ... now we can throw a spanner in the works for all of those astrologists. If we suddenly give them three new planets or take one away, all of the astrologists are going to have real problems. Here's our chance to mess with astrologers' minds!
"Aries: The influence of Ceres says that today is not a good day to buy lottery tickets. Quaoar is in the sector of your chart pertaining to money and fortune, so don't back racehorses with funny names this week."
The only thing necessary for the triumph of evil is for good men to do nothing. - Edmund Burke
I may be wrong, but gas giants (like jupiter, saturn, neptune, etc) become brown dwarves at 10-13x Jupiter's mass, and the point at which they become full stars (well, red dwarves) is some unknown mass above that. Really- last I checked, the exact mass wasn't known.
So, to recap. Stars are objects massive enough to maintain nuclear fusion in their cores and are hot enough on their surface to radiate visible light. Brown dwarves are objects not as massive as stars, but massive enough to maintain fusion in their cores but aren't hot enough to radiate visible light. Planets are objects not as massive as brown dwarves, but are.... uhhhh.... hmm....
I read the article too- if I recall correctly, he was stating that because of the fact (I can't verify this atm, maybe tomorrow) that the force exerted on the Moon by the Sun was greater than the force exerted on the Moon by the Earth, it would be more appropriate to say the Moon orbited the Sun, not the Earth, and as such couldn't be called one of Earth's moons.
However, the point of his argument was to put forth an interesting argument. Issac Asimov is an author by trade, not a scientist. (to say nothing of the fact he was very good at it)
The standard practicing definition of a moon is something along the lines of "any hunk of matter which has enough gravity to form itself into a sphere and has a stable, relatively circular orbit around a planet." Issues with the definition as I stated it are A) it doesn't include Phobos and Deimos(sp?). This isn't much of a problem as IMHO they shouldn't be moons anyway, just large asteroids stuck orbiting a planet. B) It assumes you have a working definition of a planet. We're working on that. It's because A) the Moon is so massive compared to the Earth. Several moons of Jupiter and Saturn are more massive than the Moon, and they do not exibit any of the properties stated above. B) the Moon is so far from the Earth. If the Moon was close to the Earth the Earth would exert a much greater force on it, eventually more than that of the Sun. Additionally, if the Moon was even farther away than it is now, the combined center of gravity of the Earth/Moon system would be outside Earth's surface, and what you stated in your post would be true. C) the Earth/Moon are so close to the Sun. Gravity decreases as per the square of the distance, and so the Sun exerts a far, far greater force on the Moon than the more massive moons of Jupiter or Saturn.For the record, I don't think Pluto is a planet. Its physical characteristics are virtually identical to those of other Kuiper belt objects, it just happens to be bright enough to be noticed so long before the Kuiper belt was discovered that astronomers assumed it was a planet. The initial estimates of Pluto's size made it a far larger planet than we know it to be today- at least 3 times larger. Pluto was just initially assumed to be the ninth planet, and it's been that way ever since.
Sorry, but what does the color red have to do with it?
Jesus saves and takes half damage.
I think the point of the original post was not so much about atmosphere (or life) as it was about size. What if the Earth and Moon were the same size and orbited each other as they revolved around the Sun?
Jesus saves and takes half damage.
2 Skinnee Js
HomePage Here have already covered this topic on the first track of $upermercado.
Full link to lyrics - warning, pop-ups - Lyrics
A snippet of the lyrics below:
Who do you represent?
I represent the smallest planet
Attorney in this tourney versus those who tried to ban it
If you don't agree go see interplanet Janet
Cause sun is star like Pluto is planet
So lend me all ears and let me state my case
about all the types of satellites we must embrace
Cause like my parents' great grandparents - this planet is an immigrant,
to deport it's an offense
It's an upstanding member of the solar system
Apply the laws of Earth and make it a victim
Of Proposition 187
If Pluto spawns a moon, it will apply to the heavens.
I'll damn you 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
(If not for yourselves)
Pluto is a planet
I assert that my comment is only my opinion, not that of any employer, past, present or future.
Isaac Asimov figured this one out a long time ago. He pointed out what is clear just from looking at it: that our solar system consists of a star, four planets, and debris.
:-p
I am the Alpha and the Omega-3
Should be 5% bigger than the parent star
Hm. I don't think so. Nothing in our solar system would qualify, and I think the baseline for our definition should include Earth.
Here're my 3 params:
1. Should revolve around a star (exceptions to this rule that fit the other rules may be termed "rogue planets")
2. Should have enough mass that, during it's creation, the heat generated from its accretion would have resulted in the majority of the body becoming molten.
3. It cannot support fusion.
*** *** You're just jealous 'cause the voices talk to me... ***
But our knowledge of the timeline of planet formation is far from complete. So this way classifying may not be feasible for now.
It would be cool though, because then it be similar to the biological classification, where "relatedness" of two species (in terms of similar DNA) is strongly correlated with how early they diverged from one another.
I widely held theory is that material surrounding the star sorts by mass with denser materials being closer to the star. These clouds of material condense into planets. You'd expect that metallic planets would be closest to the star, rocky ones next and icy ones (gas giants) last. At least in our solar system, we have bands of broken up rocky bodies (the asteroid belt between Mars and Jupiter) and icy bodies (the Kuiper belt between Neptune and the Oort cloud).
Large bodies that fall into the correct sorting areas would seem to be planets original to the star. Pluto, as a rocky body way out past the gas giants is probably not an original planet, but could be considered a captured planet for any number of reasons. It has its own, admittedly large, moon. It has a reasonably isolated orbit (which is way I'm reluctant to think of Ceres as a planet anymore than I think of the members of Saturns rings as moons). And yes, tradition.