31-07-2005 10:23									#31
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How about to be considered a planet it must lie on the ecliptic and have formed from the initial solar cloud, and have the sun as it's orbital center? Gets rid of everything in the Kuiper belt, eliminates Pluto and any moons, and can be practically applied to any solar system.

	31-07-2005 10:51									#32
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quote: Originally posted by shawnmmcc How about to be considered a planet it must lie on the ecliptic and have formed from the initial solar cloud, and have the sun as it's orbital center? Gets rid of everything in the Kuiper belt, eliminates Pluto and any moons, and can be practically applied to any solar system.

Sounds like my definition earlier in the thread.

	31-07-2005 11:53									#33
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quote: How about to be considered a planet it must lie on the ecliptic and have formed from the initial solar cloud, and have the sun as it's orbital center? Gets rid of everything in the Kuiper belt, eliminates Pluto and any moons, and can be practically applied to any solar system.

Yes, of course it does. Many definitions do. I just like describining space objects in the way they are physically, not their past. They might be an additional definition, which is their relation to something ( i.e. Planet Europa which is a moon of Jupiter )

	31-07-2005 11:56									#34
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Sorry Vince - misunderstood your "orbital plane", didn't realize you meant the same thing as my ecliptic. I really should be asleep.

	31-07-2005 12:06									#35
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quote: Originally posted by shawnmmcc Sorry Vince - misunderstood your "orbital plane", didn't realize you meant the same thing as my ecliptic. I really should be asleep.

Now that I look at it again we do differ on one point: You excluded Pluto and I didn't. Some may see it as a K-belt object but AFAIK it is not in the belt (it even goes inside Neptune's orbit on occasion). Its inclined orbit may be a problem but that could have been caused by a close encounter with Neptune or another object.

	31-07-2005 12:15									#36
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quote: Originally posted by shawnmmcc How about to be considered a planet it must lie on the ecliptic and have formed from the initial solar cloud, and have the sun as it's orbital center? Gets rid of everything in the Kuiper belt, eliminates Pluto and any moons, and can be practically applied to any solar system.

No.

There's no reason why a planet must exclusively orbit the sun/solar center to still be termed 'planet'. You're thinking only in terms of our solar system. Were Pluto and Charon to have been formed further in-system, but otherwise as such, one or both would be considered a planet.

Imagine taking the earth, and ramming it with a really big asteroid, one big enough to split the earth. (Bigger than the one that may have formed the moon. ) It is possible that the earth could then coalesce into two seperate bodies. Those two bodies would have something of an orbit around the former center of mass - which is still roughly the center of mass for the two-body system of 'earth' and 'earth2' - while that center of mass would still orbit the sun in the old orbit (minus or plus any change caused by the addition of the asteroid's mass and velocity). Although I'm not a Pluto scholar, I'd be surprised if this wasn't how Pluto was formed.

Furthermore, why does it need to have been formed from the initial solar cloud? Were we to be capable of taking a few million asteroids and crammed them together somehow to form a body the size of Venus, say, and then let that orbit the Sun - would that not be a planet? (Of course, the asteroids formed from the initial solar cloud. As probably did comets and other non-planetary bodies. Heck, what exactly DIDN'T form from SOME solar cloud? Or would Jupiter-orbitting-Betelgeus not be a planet?)

--

Nasa defines a Planet to be "A planet is a large, round heavenly body that orbits a star and shines with light reflected from the star. " (worldbook@nasa.gov) That's a pretty inspecific definition - but perhaps what is necessary. The word "planet" is quite simply an inspecific word; the fact that there are so many kinds and shapes of bodies in the solar system that "Planet" being defined compared to smaller bodies is unlikely ever to have a meaningful, textbook definition.

Many have tried - and to a decent extent succeeded - in differentiating between planets and *larger* objects; usually Fusion is the seperation (here is a good place to start on THAT debate) - a reasonable definition being "A planet is an object never capable of fusion that orbits an object capable of fusion" (paraphrased from above). Brown dwarves, solo bodies, and other objects are classified this way as non-planets - brown dwarves are capable of fusion, albeit a limited form - but this definition is of no use to clarifying the issue of "planet" from "asteroid" or other small object.

Reasonably, I'd say that a definition of planet includes:
a) the above fusion vs nonfusion
b) must orbit solar (fusion) (as above)
c) must not orbit a larger body that is nonfusion (a moon)
d) must lie in ecliptic
e) must be above a certain mass

I believe many astronomers would agree with the 'formed from solar cloud' part, but I think that's too limiting (although it's presumably trying to keep out gravitated bodies from the outside, Kuiper-type objects... but is there any reason to believe the Kuiper belt objects shouldn't be considered planets??). Certainly a man-made planet of adequate size should be considered a planet itself ...

	31-07-2005 12:19									#37
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quote: Originally posted by Vince278 Now that I look at it again we do differ on one point: You excluded Pluto and I didn't. Some may see it as a K-belt object but AFAIK it is not in the belt (it even goes inside Neptune's orbit on occasion). Its inclined orbit may be a problem but that could have been caused by a close encounter with Neptune or another object.

Isn't it considered fairly likely that the eliptical orbit was caused by whatever object caused the Charon-Pluto binary planet arrangement (possibly Charon and/or Pluto itself)? It's unlikely that Pluto would have formed near to Neptune itself, given the way planets formed (being massive enough to accrete all nearby mass to themselves, generally precluding the possibility of two planets forming close by)? (Of course, there's still the question of why exactly Pluto *continues* on this erratic orbit, which may be as a result of Neptune's interference indeed ...)

	31-07-2005 19:51									#38
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quote: Originally posted by Whoha can we name this one planet X?

Only if you want it to sound like a sex shop franchise, or an Ed Wood film.

	31-07-2005 21:59									#39
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My definition of Planet

A planet is a bright Star that "Wanders" against the background of fixed stars.

This is how the Anchients defined a planet, the word MEANS wanderer it never had anything to do with the density of the ort cloud or the radius of a body it was a purely naked eye observation. Thus their are only 5 planets. Mercury, Venus, Mars, Jupiter and Saturn. No new planets can ever be discovered. All other objects in the Universe are either Stars (objects that sustain Duterium-Duterium Fusion), Planitoids (Objects whose gravity makes them Spherical) or Planitesimals (Objects too small to be spherical).

Thus Uranus, Neptune and Pluto and all these so called extra-solar Planets are de-throned. Only Stars, Planitoids and Planitesimals can be discovered.


As for Plutos formation, it likly formed closer in on a low excentricity orbit but as Neptunes expanded outward Pluto was pushed into a 3:2 Resonence orbit with Neptune (thus why it never crashes into Neptune). Their are likly many smaller objects doing the same thing.

	31-07-2005 22:23									#40
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I read this the other day. What I don't get is this talk of this being the first new planet since Pluto in the 1930s? That was what they said about Sedna too... Anyone willing to enlighten me?

	31-07-2005 23:59									#41
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First off, this weekend there were actually two seperate announcements. One was for a Sedna-sized (or slighly bigger, but still smaller than Pluto) object. The second one is likely larger than Pluto. Many people confused the two initially and believed the smaller diameter announcement was correcting an error in calculating the size of the large one.

Regarding to what to do as there is a quandry is upon us if the larger one is larger than Pluto. There are 4 realistic options:

1. Demote Pluto. Obviously unpopular since Pluto has been called a planet for so long. But Scientifically I believe this to be correct IF you discount all Kuiper Belt Objects (KBO's) from being called planets (which Pluto is just one of many, apparently) due to ellptical orbits/small size, etc.

2. Call the new object a planet. Would keep Pluto's status intact but this may not "feel right" to many people. Additionally are we going to call all KBO's larger than Pluto planets. Now we are subclassifying a general group of objects based on an arbitrary size, the size of Pluto. Could be avoided if we decide to call all non-moons which circle the sun and have enough mass to become speroid in natute. Of course than makes Ceres, Quouar, and Sedna Planets too.

3. Make a special exception for Pluto, but just call new Objects KBO's only. Now we are making a classification of on object based on someting non-scientific in nature, the public sentiment regarding Pluto. I dont know if we want the IUPAC going down this path.

4. Make Pluto "publically" a planet but "technically" a KBO. The IUPAC has no policy to allow this, and the public would still consider is as demoting Pluto.

End Result: I think Pluto must be demoted. But create a "Planetiod" category to account for all objects which are not planets or moons and speroid in nature.

	01-08-2005 03:06									#42
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Is there a picture of this new kid with its projected orbit around the sun? I just want to get a visual on this things orbit and distance.

	01-08-2005 03:25									#43
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No problem Donegeal.

(Image not entirely true to scale). Orbit kind of circular.

Attachment: sun-earth-cover02.jpg
This has been downloaded 33 time(s).

	01-08-2005 03:31									#44
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Thanks for the labels. I would have never guessed...

	01-08-2005 03:48									#45
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Winston

	01-08-2005 04:01									#46
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quote: Originally posted by CiverDan I think Pluto must be demoted. But create a "Planetiod" category to account for all objects which are not planets or moons and speroid in nature.

I second the motion!

	01-08-2005 22:00									#47
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quote: Originally posted by CiverDan 3. Make a special exception for Pluto, but just call new Objects KBO's only. Now we are making a classification of on object based on someting non-scientific in nature, the public sentiment regarding Pluto. I dont know if we want the IUPAC going down this path.

The IUPAC did this already in 1999 - demoting Pluto, and then un-demoting it as a direct result of public pressure. I doubt Pluto is going to go anywhere... and (3) is pretty likely in the scheme of things. But ...

quote: originally posted by CiverDan End Result: I think Pluto must be demoted. But create a "Planetiod" category to account for all objects which are not planets or moons and speroid in nature.

My preferred option - keep Pluto as planet or move to planetoid, not a big difference, and then indeed have a third category. "Planetoid", or even "Kuiper Planets" as essentially a third category of "inner system" (mercury-mars) and "outer system" (Jupiter-Pluto) ...