how to define planets

SpeedFreek · Aug 16, 2006

To brandbll: The reason Charon may be included is because it seems like it may not actually orbit Pluto. Recent measurements indicate that it (I don't know the technical terms here) is kind of "riding alongside" Pluto. It seems they are both individually orbiting the sun but very close to each other and thus gravitiationally bound to each other. Charon may not actually orbit around Pluto, but just move around a bit, close to it! <div class="Discussion_UserSignature"> _______________________________________________ SpeedFreek </div>

brandbll · Aug 16, 2006

Oh yeah, forgot about good ole 'Xena.' Re: Speed freak Well, that also poses another debacle. If New Horizon's discovers taht they are indeed orbiting eachother, then we have to change it again. <div class="Discussion_UserSignature"> You wanna talk some jive? I'll talk some jive. I'll talk some jive like you've never heard! </div>

MeteorWayne · Aug 16, 2006

Again, the reason is Charon does not orbit around Pluto. Both Pluto and Charon revolve around a point in the space between the two "whatever they are's". So they are a binary planet, or a binary pluton, or a binary KBO, or a binary "Rocks in Space" I'm sure we will discover more such pairs (or triplets) of objects that revolve around a barycenter not within the surface of one of the objects. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

MeteorWayne · Aug 16, 2006

Again, we have already discovered that they orbit about a point between the two objects. New Horizons will discover more about what they are, but that fact will not change. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

ittiz · Aug 16, 2006

I have to agree with cuddlyrocket on this one. What if we went to another solar system and found an earth mass object in a belt like the asteroid belt? By you're definition it wouldn't be a planet. Including characteristics like orbit don't make sense because then how would you define the huge gas giants that have elliptical orbits around other stars. They are way to big to be anything but a planet. I think this definition is good because it makes it easy to define what a planet is. Making the naming scheme not apply outside the solar system would over complicate things. With how many planets there are outside the solar system what weird system could we use to define them except the simple one the IAU came up with?

masterregal · Aug 16, 2006

I like the IAU proposal, and as people say, it is simple. I agree all aspects of the definition and the fact is, it is one of the only definition that hold true for ALL solar systems. Sure, in 10 years we may have 100 planets, but that should not matter. Who said the children should know all the planets. I think they should know the Classical 8 or 9 planets, and if they want to be an Astronomy major they will learn the rest there.

thebigcat · Aug 16, 2006

The definiton under proposal: "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet." One way to clear up a lot of garbage would be to add one word. "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in an unique orbit around a star, and is neither a star nor a satellite of a planet." Okay, that's two words, but is some languages it's only one. Besides, are articles really words? What is your definition of a word? <img src="/images/icons/wink.gif" /> Anyway... Now this still leaves room for all the follecular bisectionists out there but basically allows for Pluto to remain a planet, Charon to remain a moon, Ceres to remain an asteriod (or Associated Planetoid, ie. a planetoid orbitally associated with a group of other objects), 2003 UB213 (is there a UB40 out there somewhere in the Kuiper Belt?) to become a planet because it's orbit isn't associated with the Kuiper Belt due to it's extreme orbital angle, and all of the KBOs with hydrostatic-equilibrium overcoming masses to be classified as Associated Planetoids. As for how we shall carry this definition to extra-solar systems, we are sure to encounter objects which shall force us to rethink our definitions no matter what we do know, so bother it. And as for those 5th graders, we had better not anger them or sadden them or confuse them. Not of you want there to BE any astronomy scientists tomorrow. You heartless so-and-so. <div class="Discussion_UserSignature"> </div>

thebigcat · Aug 16, 2006

Ittiz said:
What if we went to another solar system and found an earth mass object in a belt like the asteroid belt? <hr /> An earth-mass object in an asteriod belt similar to ours would be a young planet, and not one we would be interested in visiting due to the constant bombardment as it sweeps it's orbit clear of those pesky asteroids. <img src="/images/icons/rolleyes.gif" /> What morons were teaching theories like "We think the asteroid belt is the remnants of an unformed planet."? This even after it was calculated that the total mass of the objects in the belt is significantly less than Mars. The fact is that the belt is a region that is too far from Jupiter or Mars to be affected on any scale by their respective gravitation and Ceres, Vesta and the other large asteroids (or associated planetoids) are too small to effectively sweep the area clear of loose debris. <div class="Discussion_UserSignature"> </div>

mythrz · Aug 17, 2006

Unfortunately, the term planet has a significant meaning for the 20% of humans who care about what's up there at all. You can't just BAM away centuries of human history. No one is going to accept the term IOO! Precisely. Which is also why a % will not accept the terms appointed by the IAU. Like said years ago and for the coming years, "This will be a heated debate long after it has been decided". Why? Because so many are not going to accept it. Oh..... and "BAM"!

acevonwildfire · Aug 17, 2006

<blockquote>In reply to:<hr />What morons were teaching theories like "We think the asteroid belt is the remnants of an unformed planet."? This even after it was calculated that the total mass of the objects in the belt is significantly less than Mars.<hr /></blockquote> You forget... even so far from Jupiter and Mars... Jupiter has enough influance to move the astroids. That theory is possible simply because it is likely that Jupiter drew the ones with an eccentric enough orbit out of the belt and either flung it into the outskirts of space or caused the astroid to be swallowed by Jupiter itself. It's also possible that some of Jupiter's moons are originally from the astroid belt. Jupiter's gravity is still strong enough to do so should any astroid move beyond, even slightly, the astroid belt. So much for your idea that the 'fifth rocky planet from the sun' never existed. Ace Von Wildfire

cuddlyrocket · Aug 17, 2006

"is in an unique orbit around a star" Which would mean that Charon would be a planet by your definition, as it is in a unique orbit around a star. It's not in the same orbit as Pluto. "Ceres to remain an asteriod.." Ceres meets all the criteria for a planet by your definition. "...is there a UB40 out there..." As 2003 UB213 is the 213rd 'unclassified body' found in 2003, there is likely at least one UB40! <img src="/images/icons/smile.gif" />

alokmohan · Aug 17, 2006

We are likely to add to our stock of KBOs.Some of them may be larger than pluto,Again IAU has to meet.

edawg · Aug 17, 2006

i think we need to have planet classes like star trek does( like class H for habitible P for pluton and so on..) whats gonna happen when then next-gen of telescopes comes on-line and we can see all these exo-planets??

harmonicaman · Aug 17, 2006

Edawg - "I think we need to have planet classes like star trek does( like class H for habitably P for pluton and so on..)" I couldn't agree more; science is supposed to be all about putting groups of like objects together in little categories so things are less ambiguous. For example; asteroids are asteroids, KBOs are KBOs, Jovian planets are Jovian planets, etc. This decision really muddles everything; now we'll basically just call everything a "Planet". Science is supposed to be about making the universe more understandable by putting everything in its proper place; not less so by lumping everything together in one big pile... <img src="/images/icons/rolleyes.gif" />

Philotas · Aug 17, 2006

"This decision really muddles everything; now we'll basically just call everything a "Planet". Science is supposed to be about making the universe more understandable by putting everything in its proper place; not less so by lumping everything together in one big pile..." Oh yeah. So correct to put a big object like Ceres, which might harbor an atmosphere, in the same class as big rocks. <img src="/images/icons/rolleyes.gif" /> <div class="Discussion_UserSignature"> </div>

harmonicaman · Aug 17, 2006

Size shouldn't be the only criterion for planetary classification. It's location and the company it keeps should also be a factor. It just seems logical to me that we keep all the asteroids in there own little category, regardless of size -- just like a moon is a moon, regardless of size. This proposal demonstrates a lack of common sense and adds an unnecessary layer of obfuscation to the Solar System; which is something science usually tries to avoid.

JonClarke · Aug 17, 2006

I am generally very happy with this decision. It recognises the fundamental difference between small irregular bodies and large r bodies have have attained hydrostatic equilibrium, and all that implies for internal differentiation. The only thing I am not happy about is the word "pluton". It already has a very distinct anhd long established meaning in geology (large intrusive bodies), and could end generate confusionn in the future when people describe water-ammonia plutons on pluton planets. Pluton is also the word for Pluto in French, and again causes confusion when the word is used in that language - is what is meant the planet or the class? Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

mikeemmert · Aug 17, 2006

I think this is the best idea I've heard so far. Are you a trekkie? I don't have a TV! Please find whatever information is available from the 'web about Star Trek's classsification system and share. We do after all have class O,B,A,F,G,K,M,N,S, and L for stars. Further clarification comes from a designation as a dwarf, subgiant, giant, and supergiant star. Planets cannot use any of the above letters, for obvious reasons. The letters H and P are available. That might be good for the size, too, and use different words such as micro, mini, meso, macro, whatever. Wait; those size designations are wrong; they all use the initial M. Oh, well, Edawg, this is your idea! Sure rolls off the tougue better, "OK, folks, off to the right we have the class MH planet Earth, 78% water, medium mountains, and a top predator using nuclear, ballistic, and propaganda weapons..." Why didn't astronomers think of this? Probably because they don't rot their minds with TV!

ittiz · Aug 17, 2006

Although bombardment of such a planet would probably be high it doesn't matter because under that definition it still wouldn't be a planet. This brings a lot of ambiguity because how "clear" does space have to be before you can consider bodies in it planets. The new definition makes deciding what is or isn't a planet a lot easier and faster. From what I heard the asteroid belt has about the same mass as the moon. Definitely big enough to be a planet even by our old standard.

Philotas · Aug 18, 2006

"It just seems logical to me that we keep all the asteroids in there own little category, regardless of size -- just like a moon is a moon, regardless of size. This proposal demonstrates a lack of common sense and adds an unnecessary layer of obfuscation to the Solar System; which is something science usually tries to avoid. " The term 'moon' is really wrong. The term moon should only be used on "planets" orbiting a bigger planet(barycenter below the host planets surface). Anything smaller should just be called satelites as well as asteroids. Asteroids should just be rocky irregulary shaped objects, while icy irregulary shaped objects should be classsified as comets. That way the definition would tell alot more about the object than today's definitons. Planets may also have undergone internal differention, as JonClarke mentioned. Another thing is the way we classify stars. Star clusters consists of stars, don't they? The class below, the brown dwarfs, one might say are about the same as asteroids/comets are to planets. Because, why can't Earth and Ceres belong in the same class, when Mercury and Neptune can? That makes no sense. Ceres is as much a terrestrial planet as Earth is. <div class="Discussion_UserSignature"> </div>

edawg · Aug 18, 2006

thanks but no im not a trekkie, here is what i dug up tho http://en.wikipedia.org/wiki/Star_Trek_planet_classifications

SethCohen · Aug 18, 2006

Ceres should be called a planet. If that idea is too upsetting to people, then at the very least they need to come up with some way of distinguishing it from the regular asteroids which are quite different in several ways. As for the plutons, perhaps a better name could be chosen, but I agree with the classification.

mikeemmert · Aug 18, 2006

Thanks for the link. I think Roddenberry's classification is much better than the one being put forth by the IAU. This tells you with a letter just what the planet is like. It's ironic that Roddenberry was able to do this with the astronomical knowlege base of the 1960's! Time marches on and discoveries are made. One flaw of this system is uncovered by examining real worlds that we know about; some planets are described by two letters, i.e. Venus: Class N or Class Y, Mars: Class C or Class H or Class K, and Jupiter: Class I or Class J. I think we can do better than Roddenberry did at the very dawn of the Space Age. So let me throw a skeleton of a classification scheme out. First, instead of one letter, a number/letter/number sequence is used. Just as stars use a letter/number system to classify and subclassify a star, so does this give a better description. A star would be, for example, a G 0 dwarf (our sun). The first number, a Roman numeral, describes the state of civilization/life of a planet. 0 (not a Roman numeral) depicts planets in which this quantity is unknown. It would be in contact with an interstellar community (if any). II has a civilization with a global educational system and communication through space and time. This describes Earth at present, back to about 1492 A.D. or so. (This might be variable. 1455, invention of printing, 700-800 BC, or agriculture ~2500 BC-4000 BC, or spaceflight, July 20, 1969, which get my vote). III would be a land plant and animal ecosystem, on Earth dating to roughly the Devonian period, and IV would be aquatic life such as in the Precambrian. V would be prebiotic chemistry, and VI would be extinct lifeforms; I think Mars is a VI. VII is uninhabitable. Most of what we know is 0. As time goes on, this may change. The letter could describe a lot of things; cold, lukewarm, or hot; micro-, mini-, meso-,large-, either diameter or mass; composition; orbital

jroswald2001 · Aug 21, 2006

If classifying Ceres as a planet is to increase interest in the place so that we decide to send probes there ahead of probes to Europa, Enceladus or Titan, then what is the point of such a classification? It most certainly would not be in th interests of good science. Defining objects as planets and satellites is obsolete in this age of contradictions. We need another word that encompasses both objects, and other unforeseen orbital exotics. Ages ago people used to call whales fish, simply because they swum in the sea. This is just about where we stand today in this debate.

jroswald2001 · Aug 21, 2006

"This decision is exactly the same as classifying animals by their size alone" Or indeed where they live, whether it be on land (orbiting a planet) or in the sea (orbiting a star).

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