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How Would You Define a Planet?

Cliff posted more than 9 years ago | from the heavenly-body-...-or-not dept.

Space 410

It doesn't come easy asks: "The argument over the definition of a planet continues. So far, two definitions are favored but without much consensus so far: base the definition of a planet simply on an object's size. Pluto would be near the lower limit and the newly discovered Kuiper Belt objects could also qualify, giving us 10 or 11 planets so far; or define the single dominant body in its immediate neighborhood as the only qualifying object for planetary status. If no one body dominated (such as the millions of individual asteroids in the asteroid belt) then none would qualify for planetary status. In this case Pluto would be disqualified (Neptune would be the dominant body in Pluto's region of space), and the newly discovered Kuiper Belt objects would also fail to qualify. The International Astronomical Union (IAU) working group charged with pinning down the definition of a planet may vote on the proposals within the next two weeks (or they may decide to start all over again with something new). Maybe Slashdot readers can give them some help. How would you define a planet?"

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anything with a roman god name (3, Funny)

DarkProphet (114727) | more than 9 years ago | (#13635281)

sounds good enough for me ;-)

Re:anything with a roman god name (2, Funny)

kfg (145172) | more than 9 years ago | (#13635326)

Ah, well, looks like Earth is shit outta luck.


Re:anything with a roman god name (1)

Haydn Fenton (752330) | more than 9 years ago | (#13635351)

"Earth"s real name is Terra - the personified Roman goddess of the earth. She is also a fertility goddess, known as Bona Dea.

Re:anything with a roman god name (4, Informative)

kfg (145172) | more than 9 years ago | (#13635519)

Terra Mater (Mother Earth)is not commonly held to be the same as the Goddess Bona Dea (Fauna). They would typically have seperate shrines, often in the same area, built by the same people. One is a personification of Earth itself, the other of living things. Of course here and there the lines might well blur.

I am fauna, but not terra. The child, but not the mother. I come from, but do not share identity.

In any case, the current official name of the earth is Earth, which is Germanic. s/earth.html []


this is simple (1)

Baric (681935) | more than 9 years ago | (#13635425)

A gravitationally round body (Ceres or larger) that is the dominant mass within its orbital space. Pluto has a highly elliptical orbit, so it shares an orbital space with many other large KBO's. None of the first eight planets have this problem.

Planet criteria... (0, Troll)

drewcaster (517860) | more than 9 years ago | (#13635282)

Pluto-sized or bigger. Next problem?

Re:Planet criteria... (0)

Anonymous Coward | more than 9 years ago | (#13635301)

What is your favorite colour?

Re:Planet criteria... (0)

Anonymous Coward | more than 9 years ago | (#13635358)

What is your quest?

Re:Planet criteria... (0, Offtopic)

Rakshasa Taisab (244699) | more than 9 years ago | (#13635496)

Please define what life is, I've always pondered that one.

Dude... (1, Funny)

Anonymous Coward | more than 9 years ago | (#13635287)

A planet is, like, one of those rocky things that goes around the sun... oh wait Jupiter is gas. Ok, it has to be like big and shit. It can't be a star though. Ok lets say 1,000km diameter minimum. If it's 1000km diameter or more, and it orbits a star, but it's not a star itself, it's a planet.

There. I just settled what thousands of "smart" astronomers with their "Ph. D's" can't figure out.

Pass the bong man...

Dave's not here... (-1, Flamebait)

Anonymous Coward | more than 9 years ago | (#13635389)

Basically, this type of trip is what we have to expect when the quality of stories here are just so fucking low. I guess between lining up Slashvertisments, the Slashdot "staff" is left with no time to find actual stories to "edit". Go back to fucking your sister on you parents' hardwood floor, Zonk. When you're done, you can blow the other "editors" befor loading up the next "story".

Re:Dude... (0)

Anonymous Coward | more than 9 years ago | (#13635487)

You assume you are correct. However other people might not agree with you. Hence the problem.

Re:Dude... (4, Funny)

Tatarize (682683) | more than 9 years ago | (#13635507)

I think we should just drop the name. It can still exist, but not in a scientific context. We just go with MVEMJSUNP as "planets" and make up words with given definitions before we start trying to apply them them to things.

BOOS: Big Objects Orbiting Star.
BOOBOOS: Big Objects Orbiting Big Objects Orbiting Star.
LOOS: Little Objects Orbiting Star.
FOSC: Floating Outer Space Crap.
Planet: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

Oh, and since I know you'll ask the difference between a BOOS and a LOOS is that a BOOS is large enough that it's own gravity keeps it roughly spherical.

Shape and orbit (5, Insightful)

Belseth (835595) | more than 9 years ago | (#13635289)

The obvious conditions are round shape and orbits the sun. Size is somewhat subjective although to have a round shape it would have to be above a certain mass.

Re:Shape and orbit (4, Insightful)

rm999 (775449) | more than 9 years ago | (#13635423)

Thats an observational definition (all the planets are round, so that makes a good definition) but like all definitions of planets that have been so far this produces problems. A couple I can think of:

1. We will have to define round. This is a gray scale, and picking what "round" is will create controversy too. For example, how rough can the surface be? How oval can it be (even the earth isn't a sphere).
2. What about a baseball orbiting the sun? You need some sort of size requirement. The more liquidy a substance, the more easily it will become round at smaller sizes.

I don't mean to put down your definition - I actually like it - just pointing out that nothing is obvious in this debate.

Re:Shape and orbit (3, Insightful)

Belseth (835595) | more than 9 years ago | (#13635528)

A baseball isn't a naturally occuring object. There obviously would have to be some limitations set as to what defines a round body since perfectly round is impossible. The round shape more defines a given mass. Low mass objects can be fairly large and still not be round but above a certain mass the gravity tends to form round shapes. It has to be a definition of mass and orbit since even composition brings up issues. Half the planets in our system aren't rocky and everyone seems to agree gas giants are planets. Are large gas clouds planets? There needs to be a mass range given as a ceiling for gas giants as you enter brown dwarf territory at a certain point. Exact definitions are subjective but general ones should be easy enough. After mass and orbits are definated simply live with the result. scientifically splitting hairs is pointless. Condensed objects vary from asteroids and comets to suns and everything in between. Size, shape, composition and orbit are the defining factors but there will always be close but no cigar objects. The line between will always be arbitary. Say it's .25 earth mass but a new object is found that is .2499999999 earth mass, is it a planet? No based on the definition. The line between a large object orbiting the sun and a planet will always be arbitary.

Re:Shape and orbit (2, Interesting)

slavemowgli (585321) | more than 9 years ago | (#13635431)

Round shape pretty much depends on size only, yes; the bigger an object is, the smoother it'll always be (which is why the highest mountain on Earth is less than 9 km above sea level, while on Mars, which is smaller than Earth, it's more than 27 km). However, pretty much everything that's bigger than an asteroid will have a more or less round shape overall, so that's a non-criterion.

A better idea that I've heard being discussed would be to abandon the term "planet" altogether and instead label objects according to their characteristics - so Mercury, Venus, Earth and Mars would be "earth-likes", Jupitur, Saturn, Neptun and Uranus would be "gas giants", and Pluto, Sedna etc. would be - for example - "ice dwarves". "Large Kuiper belt objects" (LKBOs?) would also be a good term, of course, but "ice dwarves" could probably be applied to objects in other solar systems more easily, as it doesn't rely on the existence of a Kuiper belt to define the objects being talked about.

Re:Shape and orbit (2, Insightful)

tool462 (677306) | more than 9 years ago | (#13635452)

This is what always made the most sense to me as well. Not massive enough to be roughly spherical? Then it's an asteroid or comet. Planets orbit a star. Satelites/moons orbit a planet. I suppose it could get trickier if you have planetoids orbiting each other with their center of mass orbiting a star (which one is the moon and which the planet? Are they both planets? Both moons?), but I imagine a suitable name could be created to describe this seemingly rare condition.

Does it have life? (0)

Anonymous Coward | more than 9 years ago | (#13635291)

If not, it's just a rock.

Planets should be bigger than Pluto (0)

Anonymous Coward | more than 9 years ago | (#13635296)

But Pluto gets grandfathered in. Unless a huge planet is discovered, we're stuck at 9.

Re:Planets should be bigger than Pluto (2, Insightful)

sycomonkey (666153) | more than 9 years ago | (#13635366)

No, Xena (one of the new trans-neptunian objects) is quite a bit larger than Pluto, so that would be 10 now.

Re:Planets should be bigger than Pluto (1)

utnow (808790) | more than 9 years ago | (#13635544)

exactly... without pluto all of our school children would come home spouting off phrases like "My very extroverted mom just sold us nine" and other such rediculousness. WE NEED THE 'PIZZAS'!

Quick definition (4, Funny)

brassman (112558) | more than 9 years ago | (#13635304)

Something more than 1000 miles in diameter that's named after a Greek deity.

Oataox or whatever the hell? The guy who came up with that needs to be kicked out of the Astronomy club.

I'm partial to... (1)

dpbsmith (263124) | more than 9 years ago | (#13635307)

1. A nonluminous celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves. In the solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. 2. One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to revolve in the heavens about a fixed Earth and among fixed stars. 3. One of the seven revolving astrological celestial bodies that in conjunction with the stars are believed to influence human affairs and personalities.


  a : any of the seven celestial bodies sun, moon, Venus, Jupiter, Mars, Mercury, and Saturn that in ancient belief have motions of their own among the fixed stars b (1) : any of the large bodies that revolve around the sun in the solar system (2) : a similar body associated with another star c : EARTH -- usually used with the
2 : a celestial body held to influence the fate of human beings
3 : a person or thing of great importance : LUMINARY

is good, too.

Re:I'm partial to... (0)

Anonymous Coward | more than 9 years ago | (#13635386)

The Earth does not only reflect the suns radiation but also creates its own energy. It is much smaller than what it reflects from the sun but it is definitely not zero.

The problem with the definition of planet is that you will have to fit it to earth-like planets and the Jovian type planets. The latter are more failed stars IMHO.
For the definition for Earth type planets i would give a rock crusted object who's size is so that it is self rounding and who's major source of illumination are stars with which it forms a system

By mass & composition (3, Insightful)

EngrBohn (5364) | more than 9 years ago | (#13635311)

Personally, I think a good definition of a major planet is one that is massive enough that, given its composition, it assumes a sphere-like shape.

Re:By mass & composition (0)

Anonymous Coward | more than 9 years ago | (#13635374)

By your definition, the sun is a planet. :-)

Re:By mass & composition (5, Funny)

iggy_mon (737886) | more than 9 years ago | (#13635458)

by your definition my ex-wife is a planet!

Re:By mass & composition (1)

Courageous (228506) | more than 9 years ago | (#13635466)

Setting aside the sun is a planet guy, I saw the question, thought up my answer, did a search, and yours is the first one I came to. So while I have no mod points at the moment, I say "+1, you're a genius" on the grounds you said the thing I would have. If gravity forces the mineraloid into a sphere, it's a planet.


Re:By mass & composition (1)

Belseth (835595) | more than 9 years ago | (#13635560)

Got to consider orbit as well or several of Jupiter's moons would probably qualify.

Simplest is best (3, Insightful)

Greg Hullender (621024) | more than 9 years ago | (#13635313)

Use Pluto as the yardstick. Require a "planet" have at least the mass of Pluto and be in solar orbit -- any solar orbit, regardless of eccentricity or orientation.

The public will be happy to learn of more planets -- it feels like progress. It'll be hard to convince the public we lost a planet somehow. That sounds like an unimportant consideration, but I don't want us giving the Creationists more ammo for their arguments that Science is fickle. "They used to think there were nine planets, but then they found they were WRONG!"

It's not like any serious science rests on this definition anyway.


Re:Simplest is best (1)

BewireNomali (618969) | more than 9 years ago | (#13635348)

This is a good argument. Sound and simple.

The only issue, I can imagine, is the eccentric orbit that Pluto has. but everything else holds water.

Re:Simplest is best (1)

YoDave (184176) | more than 9 years ago | (#13635471)

Current estimates of the number of objects in the Solar system larger than Pluto are in the thousands. It seems to me that planets would be fairly limited in number in any given system. If the definition of a planet allows for thousands of them in a single system, it isn't much of a definition.

Thank God fior the Uncyclopedia (4, Funny)

iceborer (684929) | more than 9 years ago | (#13635315)

A nonluminous celestial body larger than an asstroid or cumbucket, illuminated by light from a star, such as Michael Jackson, around which it revolts.

Uncyclopedia: Planet []

How about... (1)

pwnage (856708) | more than 9 years ago | (#13635316)

Kirstie Alley?

She's on a diet.... (1)

Karma_fucker_sucker (898393) | more than 9 years ago | (#13635456)

and starting to look good again! At least on the latest Jenny Craig commercials ;-)

Heh (3, Funny)

B3ryllium (571199) | more than 9 years ago | (#13635317)

If it's the size of Marvin's brain, or bigger, it's a Planet.

If it's smaller ... well, it's just depressing.

Wretched, isn't it?

+1, DNA Reference (0)

Anonymous Coward | more than 9 years ago | (#13635429)


My definition of a Gas Giant (1)

Karma_fucker_sucker (898393) | more than 9 years ago | (#13635319)

Me after I eat: a Granny Smith Apple, yogurt, onions, and a Guiness or three...

Late 90's Obligatory Game Site Prefix (1)

msjacoby (528263) | more than 9 years ago | (#13635322)

e.g. and eight billion others from that brief time period

Planet Criteria - Size (1)

repruhsent (672799) | more than 9 years ago | (#13635327)

Most astronomers agree that an object can be classified as a planet or not a planet by its size. I think a good rule of thumb is to compare it to Kathleen Malda. If it's as big as or bigger than she is, it's a planet. Otherwise, it's just a piece of rock.

But.. (0)

Anonymous Coward | more than 9 years ago | (#13635329)

"Planet" derives from "Plane"?

The Bigger Question... (1)

balthan (130165) | more than 9 years ago | (#13635333)

How to Measure a Planet?

Re:The Bigger Question... (0)

Anonymous Coward | more than 9 years ago | (#13635413)

By far The Gathering's finest work.

I salute you.

I'll know it ... (1)

dynoman7 (188589) | more than 9 years ago | (#13635335)

... when I see it.

Why bother? (3, Insightful)

Ardeaem (625311) | more than 9 years ago | (#13635337)

Words like "planet" are meant to "carve nature at its joints". Problems arise when historically there appeared to be joints (planets moved differently than stars in the sky) but, we are learning now that there are no useful joints here. Why bother defining the word planet at all? Is it really that useful to astronomers? And why, say, want Mercury (a small rocky body with no atmospere) to be grouped in a category with Jupiter (a large, mostly gaseous body with an atmosphere) instead of with asteroids (small, rocky bodies with no atmospere)?

A rose by any other name... (1)

maximthemagnificent (847709) | more than 9 years ago | (#13635341)

I would say that the definition of what consitutes a planet would depend entirely on what such a definition is to be used for. I can't think of any decision that would hinge on a body's designation as a planet, so any system is as good as any other.

Gravity (1, Insightful)

Sergeant Beavis (558225) | more than 9 years ago | (#13635342)

Gravity is a constant that should be used to define a planet. Any body that has enough mass to generate enough gravity to maintain a spherical shape should be a planet. Yes, even Ceres would be a planet by this definition.

By that definition, (3, Insightful)

Sturm (914) | more than 9 years ago | (#13635377)

wouldn't stars be "planets" as well?

Re:By that definition, (1, Funny)

Anonymous Coward | more than 9 years ago | (#13635522)

No, duh! Stars are pointy, not round!

Re:By that definition, (0)

Anonymous Coward | more than 9 years ago | (#13635527)

Easy fix: In order to be a planet, a body must not at present be totally exploding all over the place.

A consistant solar system centric orbit. (1)

NeuroManson (214835) | more than 9 years ago | (#13635346)

While asteroid belts will vary widely by interfering gravitational effects, planets manage a consistant orbit.

Who Cares? (1, Insightful)

Otto (17870) | more than 9 years ago | (#13635350)

The definition is largely meaningless anyway. No science hinges on what a planet is. It's a waste of time even to argue about it.

Tell those bitches to stop with the silly arguments and get back to the telescopes. When they have a valid scientific reason to differentiate a planet from a hunk of rock that just happens to orbit the sun, then we can start arguing about definitions with some kind of actual reason for it.

they're thinking too hard (1)

scooviduvoctagon (801935) | more than 9 years ago | (#13635352)

A planet has to be round, and it has to be in an orbit, in outer-space.

Multiple classes? (1)

kalyptein (313110) | more than 9 years ago | (#13635353)

Maybe split the difference between the proposals? Anything orbiting the sun with enough mass to assume a spherical shape (but not enough for fusion) is a planetoid, but only the dominant body in the region gets to be a planet. That way we can avoid busting Pluto all the way down to "piece of rock", but avoid a situation in 30 years when we end up with 74 "planets" in the solar system after they map the Kuiper Belt some more.

I'm enough of a sentimentalist that I'd like to see Pluto keep some status. It deserves a bit of historic recognition just for being the first KBO to be discovered, and so much earlier than the others.

Re:Multiple classes? (-1, Offtopic)

Anonymous Coward | more than 9 years ago | (#13635480)

Your sig: "Entropy gets everyone."

True but, unfortunately, the converse is not.

Doesn't matter to me (1)

Torgo's Pizza (547926) | more than 9 years ago | (#13635354)

As long as the official definition contains the phrase "It's bigger than a breadbox", then I'm happy.

I suggested... (4, Funny)

grub (11606) | more than 9 years ago | (#13635355)

I suggested this on [] a few weeks ago. In Pluto's case have astrologers draw up two parallel charts. One with Pluto as a planet, the other without. After a few weeks we can compare what happened in the world to the astrology charts and that'll settle it.

"The planets don't lie" as I said there. ;)

magnetic field (1)

helioquake (841463) | more than 9 years ago | (#13635356)

If a rock is massive enough to have a molten core and sustain any magnetic field (and not orbiting a more massive counterpart), I'd call it a planet.

If it has a sustained atmosphere, then that's a plus, too (c.f., Mercury doesn't have one, however).

Re:magnetic field (0)

Anonymous Coward | more than 9 years ago | (#13635476)

So then we need to construct that death star, shoot the superlaser at every planet-candidate and see if it has a molten core.

The problem is, after qualifying for a planet, it immediately fails to be a planet anymore. The inhabitants could be a bit upset.

Maybe we could calibrate the superlaser to destroy only half the planet. The inhabitants must be required to move at the other half (avoid to confuse the "left side" with "the other left side" when shooting). Instruct them to not go and take a look down at the borders of the planet after the test. If they are primitive enough, some stories about a flat world and ships falling at the borders could help.

I think it's time to have some sleep.

Re:magnetic field (2, Informative)

phageman (627693) | more than 9 years ago | (#13635539)

Ignoring for the moment the fact that the gas giants aren't rocky or have molten cores, even Mars wouldn't qualify. Its core cooled and solidified several million years ago, killing its geodynamo (which BTW, may be the reason it lost its water and most of its atmoshpere).

Too many people (1)

QuietLagoon (813062) | more than 9 years ago | (#13635360)

with too much time on their hands....

well i blame the usa... (1)

La Fourmi Nihiliste (906448) | more than 9 years ago | (#13635364)

... its fun to have the americans to blame for everything in this world: it makes every problem so easy to understand! Pluto has been, to what i can understand, qualified as a planet just so the americans could boast to have discovered a planet in the solar system... the planet definition loophole that this created is still going on today... its clearly the usa's fault!

Like this (4, Informative)

christurkel (520220) | more than 9 years ago | (#13635365)

I would define it thus: An object is a planet if it has enough gravity to form into a sphere but not large enough to ever had fusion start in its interior and has cleared its orbit of debris left over from its formation. This would allow Pluto to remain a planet, as well as "promote" Sedna to planet stus but rule out Ceres.

Disqualifying Pluto (3, Interesting)

calibanDNS (32250) | more than 9 years ago | (#13635372)

The problem with disqualifying Pluto because of Neptune being the more dominant body falls apart when you consider the eccentric orbit of Pluto and just how far that takes it from Neptune's "region of space".

What exactly is the definition of a region of space?

How much larger must an object be than its neighbors in order to be considered the dominant object of its neighbors? Twice as large? Four times?

Define More Than Simple 'Planets' (1)

FlipmodePlaya (719010) | more than 9 years ago | (#13635384)

Emily Lakdawalla wrote a good summary of this debate for her blog [] the other day. She echoes the suggestion that we should define more than just 'planets', but rather specific types of planets. Things like Jupiter and Saturn would be defnined as 'Gas Giant Planets' while planets like Earth and Venus would be 'Terrestrial Planets', Plutos would be 'Minor Planets', etc. Seeing as gas giants and terrestrial planets really are completely different things that aren't fit to be grouped together as 'planets', I support this plan. Of course, there will innevitably be arguments about the intricacies of these sub-definitions...

Re:Define More Than Simple 'Planets' (1)

YoDave (184176) | more than 9 years ago | (#13635531)

Having categories of planets wouldn't simplify the definition. It would make it complicate the definition. If there is one type of planet the definition can be fairly simple. If it's massive enough that gravity causes it to have a sphere like shape but isn't massive enough to cause fusion, it's a planet. If there are more then one type of planet then there must be a definition for each. When would an object be considered a terrestrial planet instead of a minor planet? How large of an atmosphere would a terrestrial planet need before it was considered a gas giant?

What exactly is this going to affect? (1)

Flumph (58891) | more than 9 years ago | (#13635387)

Will NASA get a stipend for each planet? Is there an astronomy-textbook lobby that's pushing for more chapters?

Creating arbitrary categories so we can think we know about stuff is no substitute for knowing about stuff. The map is not the territory.

Deciding "what's a planet" is a game for people who don't care about astronomy, and just want to argue over beers at the pub.


What would actually be useful (1)

fred fleenblat (463628) | more than 9 years ago | (#13635388)

Is a definition that would make sense in other solar systems, too.

How about, big enough that its gravity could retain an atmosphere?

The Kirk Test (4, Funny)

MattC413 (248620) | more than 9 years ago | (#13635390)

If you can land on it and score with an alien chick, it's a planet.

You know it's a Friday Night on /. ... (1)

Karma_fucker_sucker (898393) | more than 9 years ago | (#13635409)

When my girlfriend is deflated and on the rag. And I find the parent fucking hilarious!

Re:The Kirk Test (1)

wombert (858309) | more than 9 years ago | (#13635562)

Unless, of course, it's hollow and you can touch the sky. Then it's a spaceship.

Something noticable that orbits a star (1)

Nelson (1275) | more than 9 years ago | (#13635411)

Asteroids should be grouped together. If there is only one or 2 entities in an orbital slot, it doens't create its own heat. It's visibly noticable from other "planets" in the system then it's planet.

If there are cluster of entities in the same slot, asteroids.

Anything with a Sailor Senshi named after it (1, Insightful)

Anonymous Coward | more than 9 years ago | (#13635416)

I personally think that the anime Sailor Moon has solved this problem for us already. There are:
  1. Sailor Mercury
  2. Sailor Venus
  3. Sailor Moon (okay, Earth-Moon is almost a double planet, so let it slide)
  4. Sailor Mars
  5. Sailor Jupiter
  6. Sailor Saturn
  7. Sailor Uranus
  8. Sailor Neptune
  9. Sailor Pluto

See? Pluto's a planet. Nothing else is. Now move on about your daily life, citizen.

Ask Bush! (0)

Anonymous Coward | more than 9 years ago | (#13635424)

We blindly follow him on every other issue. Oops, did I say that out-loud!

Atmosphere (0)

Anonymous Coward | more than 9 years ago | (#13635436)

Something that's large enough to hold an atmosphere, any atmosphere.

Viewing method (1)

Achra (846023) | more than 9 years ago | (#13635443)

I still think that the definition of a planet should hinge on how easily it can be viewed from Earth. Personally, I don't think that any Kuiper belt object is a planet. Pluto is not a planet. Mercury, Venus, Mars, Jupiter, and Saturn can all be easily observed with the naked eye. Uranus usually requires binoculars to be seen, and Neptune some kind of telescope (however amateur)... Pluto, and the rest of the Kuiper belt, are a very difficult thing to view. If you're an amateur astronomer, you're going to be able to discern a speck of faint light from a "medium" sized telescope.. That is, 6" reflector or so. I would love to see the definition involve being able to view the celestial object as a disc from earth's surface. Hell, even the HST barely discerns much more than a grayish disc. releases/1996/09/ []

Re:Viewing method (1)

wombert (858309) | more than 9 years ago | (#13635545)

I still think that the definition of a planet should hinge on how easily it can be viewed from Earth.

So you can definitively state that there are no planets outside our solar system?

Brown is right. (1)

bcrowell (177657) | more than 9 years ago | (#13635446)

Brown (the leader of the team that discovered Xena [] ) is right: "planet" is no longer a scientific term, it's a cultural term.

Flash back to 1915: that Einstein has published his theory of relativity, should we reconsider our definition of the term "luminiferous aether?" No, the term needs to go away completely, because it's become clear that it serves no useful scientific purpose.

a planet is defined as... (1)

null-sRc (593143) | more than 9 years ago | (#13635449)

when does a man become bald?

when do grains of sand become a pile?

no need to bicker... just keep it simple--planet: a wanderer of the heavens...

Why is this so hard? (2, Insightful)

coaxial (28297) | more than 9 years ago | (#13635462)

Orbits a star or stars.
Enough mass so that its gravity forces it into a spherical or an ellipsoid shape.

This defintion does make large astroids like Ceres a planet. Personally, I don't necessarily have a problem with this, but I don't really care. If you want to remove these you can add:

Must be a "free standing" object (i.e. not in a belt)

If you're dead set against Pluto, you can add:

Orbital inclination must be close to the orbital plane.

I not be an astronomer or an astrophysicist, but I really don't see what's so hard about defining a planet. Whatever the Powers That Be(tm) decide, it should be based on physics and not legislation. (e.g. "mass in excess of x metric tons")

Easy (1)

cy_a253 (713262) | more than 9 years ago | (#13635467)

A planet is an object massive enough to become spherical under its own weight who orbits a star.

Solar Orbit Won't Work... Size Only (1)

Seraphnote (655201) | more than 9 years ago | (#13635469)

Solar Orbit Won't Work... Size Only

With all those other stars out there, probably some other stellar-planetary systems have been disrupted and the planets freed from their orbits around their star...

...what do we call them then if we're basing their "planet" status based on their orbits around a star...
..."the big round thing formerly known as a planet"??

Lets think a little beyond the here and now, so we don't have to have this discussion AGAIN in a 100 years...

Geez keep it simple.
Either add some new planets to our system, or give Pluto "honorary planet" status to keep our count above 8.

If there's a Sailor Senshi... (1)

DavidBrown (177261) | more than 9 years ago | (#13635474)

...then it's a planet. Planets have Sailor Senshi. Everyone knows this. Pluto? Sailor Pluto proves Pluto is a planet.

And don't go talking to me about Sailor Moon. The Moon isn't a planet, because Sailor Moon is really Princess Serenity.


A conquered one! (0)

Anonymous Coward | more than 9 years ago | (#13635485)

As I sit here, on my throne atop Mount Bitterness on the Warworld of Angst I look out upon the inky darkness of space and I know all of its planets belong to ME! If I find a planet to be worthy of my leadership I SIEZE IT AT ONCE and add it to my vast, vast Empire. If I do not find a planet fit to RULE OVER it is not a planet for long and I ELIMINATE IT so that it may not be used AGAINST ME!

          Pathetic Earthlings. Undeserving of my rule. You will soon discover you do not have a planet, indeed you will soon have NO PLANET AT ALL!

          Oh, but I do enjoy the villany of CAPITAL LETTERS! HA HA HA! * sigh *.


Has anyone asked... (3, Funny)

Brad1138 (590148) | more than 9 years ago | (#13635494)

...the mice?

Obligatory Wikipedia Link (1, Informative)

Anonymous Coward | more than 9 years ago | (#13635495)

The definition of a planet is disputed. Please see [[Definition of planet [] ]] for more information.

Although planets are the principal component of the solar system other than the sun, a precise definition of the term is surprisingly elusive. This article details the questions that may arise when trying to formulate a strict definition of the word.

For most astronomers the issue will be decided by the International Astronomical Union [] (IAU). According to a published report from Nature magazine [] (corresponding entry at BugMeNot [] ), the discovery of 2003 UB313 [] (which is a Kuiper Belt object bigger than Pluto) has forced the issue. An IAU committee which had already been working on a definition is now expected to promulgate one soon.

Let's decide the Battlestar Galactica way (1)

Ziggurat Dan (876294) | more than 9 years ago | (#13635499)

It's a planet if:

A) If you could travel from it to the system's star in less than a centar, traveling at no more than 100 hectars per centon, and;

B) It is at least 10 to the 10th power laxons in mass, and;

C) Free from intergalactic casinos run by Ovions

A mass equal or greater than Reza Lockwood (0)

Anonymous Coward | more than 9 years ago | (#13635508)

I don't know an easier way to do it than to supply a lower bound for the mass. Using Reza Lockwood as an example, we can still consider Pluto a planet, but we would dismiss most (although not all) of the trans-Neptunian objects, since Lockwood has more mass.

One thing is certain: A hard and fast definition needs to be standardized upon. This whole "Well, X is a planet because we've always considered it to be one" is unscientific, and we (as a scientific community) can do better.

...bigger than a baby's arm? (1)

Karl Cocknozzle (514413) | more than 9 years ago | (#13635510)

Smaller than a star, bigger than its own natural sattellites? Composed of some kind of matter?

Gravity? Christmas trees?

Why at all? (1)

EnsilZah (575600) | more than 9 years ago | (#13635511)

Why not just abolish the whole idea of a planet?
If it's so vague you can't find a definition for it, why have one at all?

Why not just classify objects by their mass, radius, orbit, maybe temperature and other significant information too?
-For example, you have an object of a certain mass classified as M# where # is its location on an exponential mass scale.
-Then you add R# for its size.
-Then have O# for degree of orbit, where # = 1 + (O# of the object it orbits), having something like the galactic center as the O# = 0.

Then you could use any of the characteristics as needed.
Or maybe my brain is just in parsing mode right now.

Who cares... (1)

Eric Smith (4379) | more than 9 years ago | (#13635515)

as long as we can get to Planet Ten real soon!

(There are monkeyboys in the facility.)

Ecliptic (1)

Ironweaver (894947) | more than 9 years ago | (#13635538)

I think that at least one qualification that something needs to have to be considered a planet is that it orbits within a certain number of degrees from the ecliptic plane. This new thing out there is orbiting with an orbital tilt of something like 45 degrees! Personally I'd be in favour of narrowing the slice down to the point where we exclude pluto as well.

Round = Planet, Not Round = Not Planet. (0)

Anonymous Coward | more than 9 years ago | (#13635540)

My suggestion

Roundish thing orbiting a start = planet.
Not round thing orbiting anything = asteroid.
Has a moon(s) = planet.

Grandfather in Pluto (1)

GIL_Dude (850471) | more than 9 years ago | (#13635550)

So, Pluto has been a planet "forever" (all of many of our lives). It should just STAY a planet. Now, if they want to re-define the term planet to mean "something a bit larger than Pluto", or even "most dominant thingy in its orbit" - that's all cool as long as Pluto gets grandfathered in and remains a planet.

anything smaller than cowboy neals mom (1, Funny)

Anonymous Coward | more than 9 years ago | (#13635557)

thats right and yo moma too

Simple (0)

Anonymous Coward | more than 9 years ago | (#13635563)

When you have at least two bloggers syndicated to one point and the post interval is at least one post per day, then you have a planet.

Planet Definition? My thoughts. (1)

Kranfer (620510) | more than 9 years ago | (#13635565)

Personally, I have never given this much thought. Defining a planet on its size cannot be it. If that were true, I am sure in some star systems you might see a planet the size of Pluto in a orbit patter much like a comet. Is that a planet? No. Its a a LARGE comet.

Obviously a planet should be based on size. However orbital verlocity and orbital path should also factor in. The other planets in this star System would then be considered apart of the planet definition. Astmophere... Possibly might be something to consider in the definition of "planet" vs "planetoid"

But I think orbital mechanics, size and maybe some other small details should play in myself.
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