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Littlemews
2003-Nov-27, 02:47 AM
I think Pluto is a satellite the belong to a Planet somewhere around 50 light yrs from pluto....

Compare to Mars's moon...they look the same (to me)...

imported_Jerry
2003-Nov-27, 04:39 AM
?????????????????????????????????????????????????? ??????????????????

I think Pluto is a satellite the belong to a Planet somewhere around 50 light yrs from pluto....

Compare to Mars's moon...they look the same (to me)...

I think you goofed that one up a little bit!
I say Pluto was a rouge moon that had gotten thrown out of orbit from one of the outer gas giant planets; probably from a collision, Pluto has a moon half its mass and are locked in a lunar orbit always facing each as if a bar was connecting them together. And one light year is 5.9 trillion miles.The next closest sun is 4.3 light years away.



PLUTO

Distance from the sun is 3 Billion 666 million miles


Light from the sun takes approximately
5 hrs. & 30 minutes to reach Pluto

If you traveled at 100 mph, 24 hours
per day it would take 4,185 years

Diameter is 1,440 miles

One year is 248.5 earth years

One day is 6 days 9 earth hours

Temperature is around -380f

The smallest planet, our moon is larger

100 pounds would weigh 6.7 pounds

number of moons ( 1 )

Jerry B)
http://doctorlock.net

droherty
2003-Nov-27, 04:57 AM
:o Jerry. Thank you for sharing that information. If you don't mind I would like to add on a little more information as well on Pluto too.
Here you go!

Pluto's Equatorial Diameter is 2,274 kilometers

Mass is 1.3 x 10(22) kilograms

Density is 2.05 grams per cubic centimeter

Atmosperic Composition:
Probably Methane, Nitrogen, and Carbon Monoxide

I hope you are ok with letting me add more information to yours if that is ok. If not, I am truely sorry. :)

imported_Jerry
2003-Nov-27, 06:16 AM
thats wat we are all here for! to share info :D

Littlemews
2003-Nov-27, 06:20 AM
Originally posted by Jerry@Nov 27 2003, 04:39 AM
?????????????????????????????????????????????????? ??????????????????

I think Pluto is a satellite the belong to a Planet somewhere around 50 light yrs from pluto....

Compare to Mars's moon...they look the same (to me)...

I think you goofed that one up a little bit!
I say Pluto was a rouge moon that had gotten thrown out of orbit from one of the outer gas giant planets; probably from a collision, Pluto has a moon half its mass and are locked in a lunar orbit always facing each as if a bar was connecting them together. And one light year is 5.9 trillion miles.The next closest sun is 4.3 light years away.



PLUTO

Distance from the sun is 3 Billion 666 million miles


Light from the sun takes approximately
5 hrs. & 30 minutes to reach Pluto

If you traveled at 100 mph, 24 hours
per day it would take 4,185 years

Diameter is 1,440 miles

One year is 248.5 earth years

One day is 6 days 9 earth hours

Temperature is around -380f

The smallest planet, our moon is larger

100 pounds would weigh 6.7 pounds

number of moons ( 1 )

Jerry B)
http://doctorlock.net
That&#39;s ture, they both orbitting each other >< like a binary star....so I might think that the Pluto is a(n) Asteriod that left its home, the Kuiper belt and was capture by Neptune&#39;s gravity...j/k

imported_Jerry
2003-Nov-27, 06:34 AM
could be&#33;

Denni
2003-Nov-27, 11:05 PM
Since Clyde Tombaugh discovered Pluto in 1930, it has been considered a planet. Now it seems people are eager to rewrite history. Pluto, in my estimation, is a planet. Is it small? Sure, but so is Mercury. Is it in a resonant orbit? Yes, but so are a couple of other planets. Is it rotationally locked? Yes, but, again, so is Mercury. If Pluto can&#39;t be considered a planet for those reasons, then neither can Mercury. I can even go further. Which two planets, do you suppose, have orbits most tilted to the ecliptic? Which two planets have orbits with the greatest degree of eccentricity. Golly, you&#39;re right&#33;

Until we discover otherwise, Pluto is the largest of the Kuiper Belt objects, and is undeniably the closest large Belt object to Earth. If Mercury is a planet, then so is Pluto. I like to think of Pluto as I think of the city where I spent most of my life: small but important. My city&#39;s motto is "Gateway to the North", and it provided (and still provides) both a jumping-off point and supplier to deep Arctic destinations. Pluto, should we ever arrive "in person", may well herald itself proudly as "Gateway to the Kuipers," and act as a base for explorers and prospectors of the solar system&#39;s true "final frontier."

I do not believe Pluto&#39;s status as "planet" is arguable, especially as there is no hard and fast rule sorting planets from non-planets when it comes to issues of size. Besides, with the amazing diverity we have discovered in our solar system, it is a satisfaction to consider the Pluto-Charon system as close a match to an actual binary planet as I anticipate we will ever find this close to home.

withaGee
2003-Nov-28, 01:59 AM
An interesting discussion&#33; I had to find out more about Pluto and I came up with this website in my search:

http://www.geocities.com/CapeCanaveral/Lau.../7460/news.html (http://www.geocities.com/CapeCanaveral/Launchpad/7460/news.html)

Cheers,
G

Josh
2003-Nov-28, 04:13 AM
That is a really good site withaGee. I feel like I&#39;ve just read a Lonely Planet guide to Pluto before a trip. I&#39;m packed got my thermal socks and ready to go. Who wants to light the fuse?

DippyHippy
2003-Nov-29, 01:41 AM
There&#39;s a lot of debate as to whether Pluto deserves it&#39;s status as a planet or whether it should be relegated to Kuiper Belt status...

We know Pluto is about 3 and a half billion miles... so how far away is next nearest Kuiper Belt object? Surely if it was a lot further, that would settle it?

Cheri13
2003-Nov-30, 01:19 AM
I think Pluto is a planet. A very strange planet, but one, nonetheless. The arguments put forth with Mercury as a comparison are really very cogent.
Compared to anything we have managed to discover in the rest of the universe, our whole planetary system is unique and strange. So, Pluto fits right in.

Haglund
2003-Nov-30, 09:18 PM
The IAU have decided that Pluto is a planet, so officially it is to be counted as one. However I think Pluto is at a distance of 39.5 AU and the Kuiper belt from 30-50 (some say 30 to 100) AU. Pluto is probably an icy/dusty/rocky body and probably not too unlike the traditional KBO&#39;s. Officially it&#39;s a planet, but personally I would like to say it&#39;s a KBO. What if we find a KBO larger than Pluto, would it be considered a planet?

Littlemews
2003-Nov-30, 09:51 PM
maybe....I will call it the "Sub-Planet".

Planetwatcher
2003-Dec-01, 01:12 AM
I nomenate Pluto for duo citizenship, as both a planet, and a Kupier Belt object.
Do we have a second on the motion?
If so discussion around the motion... :P

DippyHippy
2003-Dec-01, 02:15 AM
I guess, technically, it&#39;s a KBO then but I think it will always be a planet as far as I&#39;m concerned. Why can&#39;t we just make an exception in this case anyway? Why must we re-classify it at all?

I second your motion, Planetwatcher :)

Haglund
2003-Dec-01, 05:54 AM
The best thing would probably be to try to learn as much about the Kuiper Belt as well as Pluto as possible, and if the differences in both size and composition, for example, are too big, then maybe it&#39;s a planet. Either way the discovery of other KBO&#39;s seem to have sparked the debate on what a planet really is. Where is the upper and lower limit when it comes to size and mass? Does it have to be over a certain size counted in km? Would it have to be massive enough to have at least a roughly spherical shape? I will follow the guidelines of the IAU when I&#39;m involved in discussions about the planets etc, even if I might point out the other things too... and besides I could be wrong about Pluto being more similar to a KBO than a planet.

Planetwatcher
2003-Dec-01, 08:18 AM
We have a motion, and a 2nd. There is discussion around the motion.
Any further dissussion?
If not, all in favor of the motion of Pluto having dual citizenship, say aye.
All opposed, same side, motion passed. But discussion may continue.

Dave Mitsky
2003-Dec-01, 10:09 AM
Originally posted by DippyHippy@Dec 1 2003, 02:15 AM
I guess, technically, it&#39;s a KBO then but I think it will always be a planet as far as I&#39;m concerned. Why can&#39;t we just make an exception in this case anyway? Why must we re-classify it at all?

I second your motion, Planetwatcher :)
Perhaps logic should rule over sentiment in cases like this.

Dave Mitsky

Dave Mitsky
2003-Dec-01, 10:21 AM
Originally posted by dwindrim@Nov 27 2003, 11:05 PM
Since Clyde Tombaugh discovered Pluto in 1930, it has been considered a planet. Now it seems people are eager to rewrite history. Pluto, in my estimation, is a planet. Is it small? Sure, but so is Mercury. Is it in a resonant orbit? Yes, but so are a couple of other planets. Is it rotationally locked? Yes, but, again, so is Mercury. If Pluto can&#39;t be considered a planet for those reasons, then neither can Mercury. I can even go further. Which two planets, do you suppose, have orbits most tilted to the ecliptic? Which two planets have orbits with the greatest degree of eccentricity. Golly, you&#39;re right&#33;

Until we discover otherwise, Pluto is the largest of the Kuiper Belt objects, and is undeniably the closest large Belt object to Earth. If Mercury is a planet, then so is Pluto. I like to think of Pluto as I think of the city where I spent most of my life: small but important. My city&#39;s motto is "Gateway to the North", and it provided (and still provides) both a jumping-off point and supplier to deep Arctic destinations. Pluto, should we ever arrive "in person", may well herald itself proudly as "Gateway to the Kuipers," and act as a base for explorers and prospectors of the solar system&#39;s true "final frontier."

I do not believe Pluto&#39;s status as "planet" is arguable, especially as there is no hard and fast rule sorting planets from non-planets when it comes to issues of size. Besides, with the amazing diverity we have discovered in our solar system, it is a satisfaction to consider the Pluto-Charon system as close a match to an actual binary planet as I anticipate we will ever find this close to home.
It is not an attempt to "rewrite" history (that&#39;s the province of politicians) but is simply the consideration of data that wasn&#39;t available seventy years ago. That&#39;s the way science works.

You neglected to mention that Pluto&#39;s angle to the ecliptic is 2.4 times that of Mercury. This fact is rather significant.

Dave Mitsky

DippyHippy
2003-Dec-02, 01:50 AM
True, but Pluto was discovered before we knew what a KBO was... I mean, if something similar were discovered now, then yeah, it would be classed as a KBO - albeit an exceptional one.

But I say "if it ain&#39;t broke..." - leave it alone LOL

TheThorn
2003-Dec-17, 02:22 AM
I think Parker had it right when he suggested finding out as much as possible about Kuiper Belt Objects and Pluto to see what the similarities and differences are.

This would be a good starting place: http://www.ifa.hawaii.edu/faculty/jewitt/kb.html

From info on that page, you&#39;ll find that there is a whole family of KBOs that have orbits very similar to Pluto&#39;s. In fact, about 1/4 of the KBOs are "Plutinos", and half of the plutions have orbits that are closer to the sun than Pluto.

Also, there are several KBOs (including at least 1 Plutino) that are similar in size to Charon, although Pluto is twice that big in diameter.

Another point, there seem to be a large number of KBOs that have satelites, or are double objects, like Pluto and Charon.

All in all Pluto looks pretty normal for a KBO. The only thing special about it is that it&#39;s the biggest one. Which is why it was discovered decades before the others.

Now, does being the biggest KBO make it a planet? IMHO, no. But getting discovered decades before the other ones does. I know its just an accident of history, but it stands.

The term "Planet" to me, seems to have little scientific significance. The terrestrial planets (Mercury, Venus, Earth, and Mars) are not at all the same type of object as the gas giant planets (Jupiter, Saturn, Uranus and Neptune) - they&#39;re more like asteroids. They should never have been thrown together into the same classification in the first place but the ancients called both the gas giants and the terrestrials "planets" so we&#39;re stuck with that. And when Uranus and Neptune were discovered, we called them planets, but we didn&#39;t call Ceres and Vesta planets, and then we did call Pluto a planet. All pretty arbitrary and meaningless, if you ask me, but there you are.

So, Pluto is a KBO, and a planet. It&#39;s the only KBO that is a planet too. Just like Earth, Venus, Mars, and Mercury are the only ones of tens of thousands of rocky inner solar system objects that are also planets.

That&#39;s not hard to live with once you recognize how meaningless the term "planet" really is.

Dave Mitsky
2003-Dec-17, 07:17 AM
"The terrestrial planets (Mercury, Venus, Earth, and Mars) are not at all the same type of object as the gas giant planets (Jupiter, Saturn, Uranus and Neptune) - they&#39;re more like asteroids. They should never have been thrown together into the same classification in the first place but the ancients called both the gas giants and the terrestrials "planets" so we&#39;re stuck with that."

And just what is your justification for saying that the terrestrial planets are not planets?

Dave Mitsky

Matthew
2003-Dec-17, 11:20 PM
What, do we now want to classify Mercury, Venus, Earth and Mars in a totally different catorgory thatn Jupiter, Saturn, Uranus and Neptune?

Pluto:
Orbits the Sun
Has an atmosphere
Has a moon

Don&#39;t other planets also have these things? Pluto is a bit small, but it would be no small feat to reclassify it to a KBO, many astronomy books would become outdated instntly.

Littlemews
2003-Dec-18, 01:32 AM
astronomy books would become outdated instntly.
LOL that is fate, accepted it please, someday someone might come up with a new theory which can prove this is ture, then all the books has to be change as well...yea someday :P

TheThorn
2003-Dec-18, 05:21 AM
"And just what is your justification for saying that the terrestrial planets are not planets?"

Sorry if I left THAT impression, Dave. (although re-reading what I said, I can&#39;t figure out how you got that out of it.) They&#39;re planets alrighty.

"What, do we now want to classify Mercury, Venus, Earth and Mars in a totally different catorgory thatn Jupiter, Saturn, Uranus and Neptune?"

Sure, Matthew. They ARE totally different, after all, and I&#39;m not the first one to point that out. Consider the following:

Jupiter&#39;s diameter is 142,000 km. Mercury&#39;s is 5,000km. Ceres&#39; diameter is 1,000 km. All orbit the sun. Jupiter has an atmosphere and may not have a solid surface Mercury and Ceres have no atmosphere and rocky surfaces. Jupiter has many moons, Ceres and Mercury have none. Jupiter has rings, Mercury and Ceres don&#39;t. Jupiter has a density slightly higher than water, Ceres and Mercury are over twice as dense. Now which of these things is not like the others?

I&#39;m not saying Ceres is a planet. Ceres is not a planet and Mercury is. I&#39;m just pointing out how arbitrary that designation really is.

(BTW, Ceres is almost twice as big as the next biggest asteroid. Kind of similar to Pluto which is almost twice as big as the next biggest Kuiper Belt Object. Neat, eh?)

Pluto is a planet by accident of history. So are the terrestrial planets. So are the gas giants. They are all completely different types of objects, but we&#39;ve arbitrarily decided to group them all together and call them all planets. We have also arbitrarily decided to leave out all the asteroids and KBOs (other than Pluto) and the Centaurs, which look a lot like KBOs but are inside Neptune&#39;s orbit, and the comets which look a lot like small Centaurs or KBOs and come a lot closer to the sun. That&#39;s just the way it is, and no justification is required. Or possible, given the major differences between the objects we&#39;ve decided to call "planets".

As far as the Astronomy books becoming outdated is concerned, that&#39;s just the nature of science - it advances. Think about what happened to all the Geology textbooks when they finally realized that continental drift was a REAL phenomenon. Or the Physics textbooks when Quantum mechanics was developed.

Other people here were suggesting "dual citizenship" for Pluto - planet and KBO. I was just agreeing in my own wordy way, and stating my reasons.

It&#39;s both, IMHO.

rajasun
2003-Dec-18, 07:16 AM
Whether Pluto is a planet or a KBO or for that matter many of the substellar objects found e.g. the "planetary mass objects" in Orion, Upper Scorpious, Taurus-Aurigae are planets or "sub-brown dwarfs" i.e. sub-BDs and if objects such as GL 229B are truly brown dwarfs (BDs) or supermassive planets depend on one&#39;s whims and fancies.

If one respects the International Astronomical Union (IAU) to be the authority on these things then STRICTLY speaking planets, BDs and sub-BDs are objects satisfying the following conditions:

1) Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.

2) Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located.

3) Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).


Source:
WORKING GROUP ON EXTRASOLAR PLANETS (WGESP) OF THE INTERNATIONAL ASTRONOMICAL UNION

http://www.ciw.edu/boss/IAU/div3/wgesp/def...efinition.shtml (http://www.ciw.edu/boss/IAU/div3/wgesp/definition.shtml)

BTW inclined orbits is NOT a hindrance to a body being defined as a planet as it is evidenced in the 110+ Extrasolar Giant Planets (EGPs) found. MOST of the known EGPs have orbital inclination to the plane of their primary star&#39;s orbit that are FAR FAR GREATER than that of Pluto&#39;s. Don&#39;t belive me, check the following link out >>>
http://www.obspm.fr/encycl/cat1.html
Do pay attention to the 6th column i.e. INCL. (deg) listing the orbital inclination of ALL the known Main Sequence EGPs.


A MORE technical study and possibly MORE thorough CRITERION could be the one porposed by Professor Gibor Basri from Berkely. The FULL text of his well-thought out criterion is reposted as follow:

What is a Planet?
Gibor Basri, Astronomy Dept., UC Berkeley

Abstract

A spate of new discoveries of objects in the mass range 0.5-15 Jupiter masses (jupiters), along with the Pluto controversy, has caused increasing debate over the meaning of the word "planet" (as differentiated from "stellar or substellar" objects). A variety of uses for this word have occurred, each with a somewhat different intent. No formal definition has been officially adopted. I examine the problem in the light of current astrophysical observations and theory. The debate can be framed in terms of three distinct arenas that drive it: characteristics, circumstance, and cosmogony. By "characteristics" I mean the physical properties of an object - primarily its means of support against gravity and its source of luminosity. By "circumstance" I mean the environment in which it is found, most importantly whether it is in orbit, what primary object and other companions are present, and their orbital characteristics. By "cosmogony" I mean the origin or mode of formation of the object. The current lack of consensus derives from differing weights being applied to these three arenas in forming the definition of "planet". Each arena contains dividing lines between "planets" and "stars" which are partly matters of opinion, and end up sorting objects differently. The main purpose of this paper is to bring order to the discussion, so that we may eventually find a broadly accepted consensus definition. I cannot resist, however, offering a possible solution that steers a middle path through the various quandaries that come up in attempting a formal definition.

"When I use a word", Humpty-Dumpty said in a rather scornful tone, "it means just what I choose it to mean neither more nor less".
"The question is", said Alice, "whether you can make words mean so many different things".
"The question is", said Humpty-Dumpty, "which is to be master that&#39;s all."
Lewis Carroll in Alice Through the Looking Glass (1872)


I. Introduction
Until 1991, the only planets we knew were the 9 objects given that appellation, which comprise our Solar System. These all lie in a disk around our Sun, with small rocky objects near it, and larger gaseous objects further out (Pluto is an anomaly). Since then, however, we have discovered many substellar objects in the solar neighborhood, ranging in mass from as perhaps as low as Saturn up to the bottom of the main sequence of stars. Some of these are in orbit about other stars and appear to have masses similar to Jupiter, while others are different in various ways, and some are clearly brown dwarfs. We have begun to determine the numbers of objects found with various characteristics and circumstances. During the same period, our understanding of the star formation process has moved rapidly forward. We now understand through observations and theory that circumstellar disks are a natural and common early part of this process. At the same time, the configuration of the extrasolar planetary systems has challenged pre-discovery theories of planet formation, making us realize that Nature (as always) is more inventive than suggested by a single example (our Solar System). A good recent summary of relevant information can be found in Protostars and Protoplanets IV (Univ. of Arizona Press, 2000).
The original meaning of the English word "planet" is rooted in Greek and means "wanderer" (it would be interesting to include other cultures and languages). This refers to the apparent positions of the objects in the sky from Earth, and so is not much use as an astrophysical definition. After examining a number of definitions from dictionaries and encyclopedias, a fair summary of the "cultural" definition of "planet" seems to be something like "an object resembling the planets in the Solar System, which is orbiting a star". The problem with this definition is that it is not very specific about how closely an object must resemble one of our planets, or in what ways, and it does not take into account the recent discoveries bearing on this question.
There have been a number of announcements of new objects that stretch the use of the word "planet". There are the many announcements of "exoplanets" in orbit about solar-type stars. These, especially considering that their published masses are lower limits, extend up to the mass needed for the onset of deuterium fusion. Whether that is the appropriate upper mass limit for planets depends on the definition of "planets" as well as "brown dwarfs". The big surprise in these systems is the presence of objects with masses up to several jupiters in the "inner" system, sometimes just above the star. Furthermore, they are mostly in reasonably eccentric orbits, counter to the expectation engendered by the Solar System. There have also been several recent announcements of "free-floating planets" (called that because they are inferred to be below the deuterium-burning limit) in young stellar clusters. Papers on brown dwarfs have also sometimes referred to objects below this limit as "planets", without regard to any other properties.
These pronouncements have been accompanied by objections to the terminology employed. It has been retorted that since the free-floating objects are not orbiting stars, they do not conform to the cultural meaning of "planet". It is further suggested they should be given some sort of "stellar" name under the presumption that they formed by themselves in a "star-like" fashion. There has been a suggestion that most of the exoplanets deserve similar treatment, because their eccentric orbits are presumed to suggest that they also didn&#39;t form the way Jupiter did. Recently it was proposed that most exoplanets are really brown dwarfs, because the lower limits from Doppler searches consistently and substantially underestimate their true mass. If this were actually the case (which their mass-limit distribution makes highly unlikely), it would be a sound reason for not calling them "exoplanets".
In this paper, I examine each of the three arenas (characteristics, circumstances, and cosmogony) separately. For each I summarize the state of our current theories and observations. I try to separate what is "known" from what is conjectured, or just a matter of opinion. I try to show how each might be used to construct the definition of "planet", and on what basis one would separate planets from stars in each arena. I begin with a table that organizes all the pieces one might use, and invite the reader to see how your predilections would put them together in defining "planet". I then provide more detailed reasoning about why the table looks as it does, and justifying my proposed definition.
Table I. The Defining Arenas for Planets

I. Characteristics
A. Source of Internal Pressure (inferred from well-accepted models)
1. Coulomb forces (free electron, crystalline, or liquid); ideal gas law
2. Free electron degeneracy
3. Thermal pressure, supplied by fusion, due to gravity
B. Source of Luminosity (inferred from well-accepted models)
1. Internal Heat Capacity (and radioactive decay)
2. Gravitational Contraction
3. Fusion of Deuterium
4. Fusion of Hydrogen
II. Circumstance
A. Object is in Orbit (observed)
1. In circular orbit around a main sequence star
2. In any orbit around an object capable of fusion (fusor)
3. In any orbit around a more massive object
B. Object is in a system (observed or observable)
1. Object is in unique, non-crossing orbit, dynamically cleared
2. Other similar objects are in similar orbits
C. Object is not in orbit (observed)
1. Object was never in orbit (difficult to ascertain)
2. Object used to be in orbit, but was ejected (difficult to ascertain)
III. Cosmogony
A. Formed in a disk around a fusor (depends on developing models)
1. Built up by agglomeration of planetesimals (difficult to ascertain)
2. Gas added by accretion onto rock/ice planetary core (difficult to ascertain)
3. Formed directly by gravitational instability in disk (difficult to ascertain)
B. Formed in a disk as a result of gravitational perturbations
1. Perturbations were due to other companions (ascertainable?)
2. Perturbations were due to passing external bodies (difficult to ascertain)
C. Formed at the center of an isolated disk (observable)


Proposed Definitions:

"A planet is a spherical non-fusor which is born in orbit around a fusor."

"A fusor is an object capable of core fusion at some time during its life."


II. Characteristics

One of the most basic characteristics of astrophysical objects is their mass. It is mass which determines their structure and evolution, and often serves as the basis for classification. Does mass make sense as a basis for defining planets? It certainly plays a role in one of the few points on which there seems to be complete consensus: if an object has core conditions capable of generating nuclear fusion (which depends on its mass), it is not a planet. The proposition that we should therefore define planets as spherical objects incapable of fusion, however, has been made but enjoys no such consensus. The role of mass in the characteristics of objects is important here in two contexts: determining the dominant pressure-support mechanism in the interior, and setting the sources of luminosity (all opaque objects emit thermal radiation). These two ways do not, unfortunately, boil down to the same thing, so a mass-based definition has to combine them somehow. It also probably makes sense to continue to tell young children that planets shine by reflected light while stars make their own.
The structural divisions are fairly straightforward and sensible. Most stars (especially after their pre-main sequence phase) derive their internal support from thermal pressure. The heat may be generated by fusion, or by gravitational collapse. Of course, without support the object will just collapse further and heat up, so one might view core fusion as a strategy for keeping the core relatively cool (I am indebted to John Faulkner for pointing this out to me). As one moves to the lowest mass stars, the core densities become high enough that free electron degeneracy provides increasing pressure. It is the eventual dominance of this source of pressure that relieves the stars from "cooling" themselves by fusion, and causes the substellar realm to begin (at about 75 jupiters, depending on metallicity). Degeneracy support extends below this limit down to about 2 jupiters. At this point the internal density and pressure has decreased again enough (due to the low mass of the object), that ordinary Coulomb forces can begin to support the object. An obvious difference between "degenerate" and "ordinary" objects is that adding mass to the former make them smaller, while adding mass to the latter make them larger. All of the Solar System planets fall into the "ordinary" category.
The luminosity divisions are similar, but not identical. One problem here is that objects change their luminosity sources as they evolve, so it is harder to put an object into one bin. Almost everything is first luminous due to gravitational release of energy (by accretion and contraction). If fusion can occur, it will first occur for deuterium, then hydrogen. Main sequence stars (especially low mass ones) can burn hydrogen for a very long time. Hydrogen burning can occur in objects down to 60 jupiters (well into the substellar regime). Deuterium is much less abundant, and can only burn for a short time in any object. This occurs in objects down to 13 jupiters, early in their lives. All objects in the substellar regime derive most of their time-integrated luminosity from gravitational contraction. When an object is finally neither fusing nor contracting, its emission comes only from trapped heat inside. This happens fairly soon for rock/ice planets. Jupiter and Saturn are still contracting slightly. Although legal definitions would be hard to formulate, astronomers have been comfortable with the following categories. A "star" is an object that burns hydrogen for a "long" time, during which its luminosity is practically stable and derives exclusively from that (i.e. it achieves the main sequence). If hydrogen fusion is never the sole source of luminosity and the object continually fades, it is a (substellar) "brown dwarf". It is still a brown dwarf if it doesn&#39;t burn hydrogen at all, but only deuterium. Most would agree that the lower mass limit of brown dwarfs occurs at the deuterium limit.
At this point, cosmogony is often thrown into the mix. The deuterium boundary was originally thought to be close to the lower limit for isolated star formation as well, but that is no longer clear. Some have recently proposed that degenerate non-fusors are still brown dwarfs (or maybe "grey dwarfs" to differentiate them) if they form the same way as fusing brown dwarfs. Others would like to call such objects sub-substellar (with various names proposed), and still others would like to call them planets (without regard to cosmogony or circumstance). It has been suggested that since deuterium fusion is not really a significant long-term source of luminosity, distinctions based on it are forced. Astrophysically that is reasonable, although it is often the case that objects very near the boundary of classes are harder to differentiate than those well away from the boundary. But the importance of the fusion/non-fusion boundary is another example of a strong "cultural" influence (that stars have fusion and planets don&#39;t). Because of that, it may make sense to coin new terms, say "fusor" and "non-fusor", to make this distinction explicit (without additional baggage). Such terms would take much of the heat out of several of the current disagreements.
We can see that defining objects purely on the basis of mass has its problems. It would be nice if the degeneracy boundary coincided with fusion boundaries at both ends, but it does not. There is a mismatch at high masses between the end of stable hydrogen burning (the main sequence), and the actual hydrogen-burning limit (the latter term is often confused with the former condition). The problematic objects for our purposes are degenerate non-fusors. As regards the definition of "planet", of course, the other question is whether one is willing to use a purely mass-based definition, or must consider cosmogony and circumstance as well. Finally, to do something about the low mass limit for planets, the best choice seems to be a requirement that they have sufficient mass for gravity to force a spherical shape.


III. Circumstance

I pointed out in the Introduction that the cultural definition of planet generally includes the necessity of being "in orbit about a star". We can therefore agree that if "circumstance" is to be included in the formal definition, this is a minimal requirement. Our Solar System suggests that planets should furthermore be found in circular orbits, and this was thought to be a natural consequence of the fact that planets form in disks. Indeed, as the first extrasolar planets were found, their eccentric orbits caused some to doubt that they are really "planets". As more systems were found, however, they inspired theoretical work that makes it likely that planets can indeed inhabit eccentric orbits (even planets which formed just as Jupiter did). We realized that if one has several massive planets, it is quite easy for them to disturb each other&#39;s orbits. We further realized that disks can move planets from their birth orbits (in the most extreme cases, dumping them into the star itself). Interactions between the planet and disk can also damp or excite eccentricity, depending on the particulars. Thus, even if planets built from planetesimals really must form in circular orbits, that is not how we may find them. Furthermore, planet formation may be influenced by mergers with smaller planets, or may occur instead by direct formation through disk instabilities (see section on cosmogony); either of which might generate eccentric orbits. It now seems unwise to use a circumstance based on orbital eccentricity in a definition of "planet".
The next question is what sort of object a planet must be orbiting. This seems relatively uncontroversial; it is generally agreed that the object being orbited should be a fusor. My experience is that few raise objections if it is a brown dwarf (so long as that is defined so only fusors are brown dwarfs). The only uncertainty comes if the "central" object is a degenerate non-fusor. Both objects may be like that, or at a minimum the center of mass may be well outside either of them. Such a configuration may be hard (especially if the secondary is too massive) to differentiate from a "binary planet", so it seems safer to demand that the primary be a fusor.
The object may not be the only one in orbit about the central fusor. Indeed, it is more convincing to have several objects in a system in "planetary" orbits (meaning they at least vaguely resemble those in the Solar System), since then the system more closely resembles ours. A single object in an eccentric orbit is uncomfortably similar to a binary stellar system (though this may just reflect our Solar System bias). Nonetheless, if all the objects in the Solar System were removed, leaving only the Sun and Jupiter, it is unlikely that anyone would wish to revoke Jupiter&#39;s planetary status.
On the other hand, having too many other similar objects in similar orbits has already been fatal to an object&#39;s planetary status. Ceres was originally designated a planet (and found in the position anticipated by Bode&#39;s Law, between Mars and Jupiter). It lost its status when several objects somewhat smaller than it, and in similar orbits, were discovered. Precisely the same situation has now arisen with Pluto. If we were historically consistent, there would be no question about the demotion of Pluto to "minor planet". In Pluto&#39;s case, another strike against it is that it crosses inside Neptune&#39;s orbit. If "major" planets do that, they will inevitably perturb each other into new orbits. Stable planetary systems must have all the major planets in non-crossing orbits (by the very definition of "stable"). It is a matter of taste whether one wants to include this requirement in a definition of "planet", but it seems to make sense to call small objects in crossing orbits "minor planets" by default.
Finally, we must deal with an object which is not in orbit about a more massive object at all. Given the cultural understanding of "planet" it would seem at first that, in a discussion of circumstance, this case cannot be included in the definition of "planet". We must, however, consider the instance where an object that is born as an acceptable planet is later ejected from the system. Turning the reasoning in the previous paragraph around, if Jupiter were suddenly lost from the Solar System, would we then consider it no longer a planet? That is again a matter of opinion, but I doubt that many would consider ejection grounds to revoke its status. It should be pointed out that smaller planets are even more likely to be thrown out (witness the vast number of Oort cloud comets). An ejected Earth would certainly still be considered a planet (what else could it be?). An attractive option is to append an adjective to reflect the new situation, such as "ejected" or "free-floating", to planet. The problem here is in determining whether a free-floating object has a history like this, or was formed without a primary. If the latter is true, a clear majority prefers not to call the object a planet. Those who would like to do so don&#39;t want circumstance considered in the definition at all, and insist on a definition based purely on characteristics.


IV. Cosmogony
One of the most fundamental properties of our Solar System, the one which best evokes its origin, is the fact that it is arrayed in a disk around the Sun, with all the major angular momentum vectors in (almost) the same direction. This allowed Laplace to state his "nebular hypothesis", the modern form of which is now universally accepted. This scenario is strongly supported by the ample evidence of commonly occurring disks around newly forming stars. These disks have been shown to often contain sufficient material to produce a system like ours (at least in principle). The theory of star formation, furthermore, demands that such disks should form early in the construction of the star; it is a fundamental property of the molecular cloud cores which produce stars that they have far more angular momentum than we see ends up in stars.
Thus, it is often stated that a fundamental property of planets is that they "formed in a disk". This is offered in contra-distinction to "stars" which form by "direct collapse of a molecular cloud core". I would first like to argue that this is an aspect of cosmogony that is not useful as commonly stated (I will replace it with a useful statement in the same spirit afterwards). The fact is that stars form in disks as inevitably as planets. One may immediately object that even if that is so, stars form at the centers of disks but planets form in the disks around stars. This viewpoint is misleading as well. The majority of stars actually form in multiple systems. In that case, there is typically a circumstellar disk centered on each star. When the separation of the stars is on solar system dimensions, there is often a circumbinary disk as well. From the point of view of the circumbinary disk, neither star is at its center (the center of mass is).
This may still seem like quibbling, until one goes through the exercise of shrinking one of the stars (increasing the mass ratio of the binary). Now there is a circumstellar disk around the primary, whose size is determined by the binary separation. There is one around the secondary, which decreases in size and mass along with the mass of the secondary. And there is a circumbinary disk that increases in importance relative to the primary&#39;s disk as the binary separation decreases. Eventually, the secondary and its disk become small enough compared to the primary and circumbinary disk that we begin to speak of a purely circumstellar disk around the primary, with a "gap" in it at the location of the secondary, and a small secondary disk. There is a smooth changeover from one point of view to the other, with no qualitative difference between them. In fact, Jupiter seems to have had a disk around it (as evidenced by the compositional gradient of the Galilean moons with distance from Jupiter), and so is equivalent to a very small secondary in a 5 AU binary system, at least from the point of view of whether it "formed in a disk". With low mass fusor primaries and high mass non-fusor secondaries, the configuration looks even more like a stellar binary.
We can save the conceptual importance of disks to planet formation, while evading the above criticism, if we look a little deeper. The principle behind using "formation in a disk" as a criterion for planets should not concentrate on the disk itself, but the way in which the disk makes planets. A much more powerful and justifiable distinction to be drawn between the formation of planets and stars could be a requirement that planets form through mechanisms which require the prior formation of planetesimals. These might be defined as macroscopic bodies too small to be forced into spheres by their own gravity, which are composed of solids, liquids, and/or ices. Current theory supposes that one will not produce such bodies except as a consequence of settling and agglomeration of dust and frozen gas in a disk (though even that is not indisputable).
For all we know, such bodies may form at the early core of an incipient star as well, but they are not required for its subsequent formation. They certainly seem to be required for the construction of the terrestrial planets, and also for any spherical icy bodies further out (which can include planets, moons, and other cases). The current favored theory for the formation of the gas giant planets in our Solar System posits as an initial step the construction of a rock/ice core of 10-15 earth masses, which would be built by planetesimal/planet mergers. The predominant gas component of Jupiter and Saturn can then be accreted directly from the gas disk by this core. Uranus and Neptune appear to be cases where the core is present but the gas accretion process was terminated before it went as far, perhaps by the disappearance of the gas disk while they formed (more slowly). It was thought that this mode of origin must result in circular orbits, but we now realize that they need not stay that way (see the section on "circumstance"). It was also thought that this mode of formation can only operate beyond the "ice boundary" where icy planetesimals are numerous; it is unclear in light of the exoplanets whether that idea is still valid (though it might be if their current orbits are greatly modified from birth).
Originally it was thought that this mode of formation could not produce objects greater than about 2 jupiters, because of the large tidal gap they open in the disk. If this is the case, then there is a natural congruence between the lower mass limit for degenerate objects and a formation modal boundary. Lately, however, it has become clear that accretion can occur across even the gaping tidal gaps in stellar binary systems. It is currently unclear how large an object the runaway gas accretion mode can produce.
It has now been proposed that there may be a third mode of planet formation. Due to gravitational instabilities in a sufficiently dense and cold disk, one might force disk material (both gas and dust, and any nearby planetesimals) to collapse directly into an object whose mass is a few jupiters (the mass limits for this process are not known). This might occur by itself in the right kind of mixed disk, or it might be promoted by the settling of dust to the midplane within a gas disk. The result could be what most people would be comfortable calling "gas giants", as well as more massive objects (including most of the current "exoplanets"), up to what people would be comfortable calling "brown dwarfs". It is unclear whether this is also the mode of formation for (some) stellar binaries; that has to do with whether the "fragmentation" of the original material occurs before or after it is forced into a disk (which we don&#39;t really know). It is possible that disk instabilities work for both fusors and non-fusors. There may or may not be a good boundary based on cosmogenesis near in mass to the lower fusion boundary.
If disk instabilities are the mode of formation for the inner massive exoplanets, it might explain why they have orbits that more closely resemble stellar binary systems. The question is whether the objects this mode produces should be called "planets". That is a matter of opinion, but it is interesting to note that the rock/ice core we expect to find in Jupiter seems to be absent, down to a current upper limit of 5 earth masses. Those who would like to exclude a "direct" mode of formation for "planets" may end up having to argue that Jupiter is not really a planet (or, more likely, having to change their definition).
The justification for excluding directly collapsed objects is also more problematic now that a system in which there are several massive objects arrayed in "planetary" orbits around a star has been found (HD 168443). We know of no stellar multiple systems that look like it. Stellar triples are all hierarchical, with a close inner pair and a distant companion. At first glance one might also claim this one is too (the outer orbit is 10 times further than the inner orbit). But in stellar cases, the outer object is always the least massive. Furthermore, since the massive fusor companion is at 3 AU, it is hard to imagine that the inner (probably non-fusor) companion&#39;s core formed from the agglomeration of icy planetesimals, or obtained most of its (quite substantial) mass by late gas accretion in its very restricted inner chunk of the disk. With such massive objects, it is unlikely that disk accretion could shrink their orbits a great deal, and also difficult to arrange a transfer of angular momentum to other objects to get them both where they are.
At this point, it probably only makes sense to insist that directly collapsed objects are not planets as a matter of taste: they are not planets because one does not wish them to be. However, there is no general agreement that the circumstantial or theoretical case for directly collapsing planets is fully made, nor that the direct mechanism can produce objects as light as Jupiter. This will clearly be a fertile area for theorists and observers for the next decade or two. Perhaps the most telling point is that almost nobody would care which mode it turns out Jupiter formed with; we would still insist it is a planet&#33;
Finally there is the question of the "free-floating planets". There are two possibilities for their formation. One is that they formed in planetary systems around stars (by whatever mechanisms are allowed to planets), and were subsequently ejected from the system by interaction with other massive bodies in the system (these could be planets or stars). Here the cosmogony question conflicts with the "circumstance" criterion; does a "properly generated" planet cease being a planet because of its circumstances?
The other possibility is that these objects formed in isolation, or at least were not originally bound to a star. If they form at the center of their own disk, and there is no circumbinary disk encompassing them and a fusor, most would agree that their cosmogony was "star-like". A majority takes this as sufficient reason to exclude such objects from the class of planets. Even here, however, the situation is somewhat muddled. Suppose (as already happens in numerical simulations) a binary star system is forming. The interaction between the stars, their circumstellar disks, and the circumbinary disk, produces various instabilities, shocks, and pile-ups in or between the disks. One of these collapses to form a non-fusor surrounded by its own little disk. It is not in a stable orbit, and is eventually ejected from the stellar system. Is this a planet? Does it matter whether it was first in one of the circumstellar disks, in the circumbinary disk, or had no real identifiable locus of "origin"? This problem disappears if "direct" objects are not allowed to be called planets, but otherwise it is rather confusing. Perhaps we should call such objects "confusors" (just kidding).
The problem is, as it was with runaway gas accretion onto a core, that it is very difficult to determine observationally what the cosmogony of these free-floating objects was. Whether they form in isolation or are ejected from a system leaves few lasting or easily observed traces. It is possible in principle that their current motion might provide such information; a young object seen in a cluster with much greater than the cluster escape velocity would be the best case. There are no current examples of objects that are known to have been ejected from planetary systems. We also have only glimmerings of the mass function for non-fusors that form "like stars". It is unclear what their minimum mass might be, what the true number of such objects is, or how it compares with the number of ejected objects.
We thus come to the primary difficulty with using cosmogony at all as a basis for defining planets. The truth is that we don&#39;t really know very much about the details of planet formation, and have rather few observational diagnostics for it. The situation is not entirely in hand even in the Solar System, and certainly not for the increasing zoo of extrasolar planetary systems and other substellar objects. Without an orbiting spacecraft, it is extremely difficult to ascertain the presence or absence of a rock/ice core in a massive gas giant (even with a spacecraft its tough). This problem gets harder the greater the mass of gas that overlies the core. We also no longer feel able to argue that the semimajor axis or eccentricity of an orbit is a firm piece of evidence for the cosmogony of the object; it is clear that orbits can be modified. Part of the problem has been that without firm theories or confirming observations, the discussion on cosmogony comes down on the wrong side of the border between science and religion (and has some of the heat inherent in that as well). I feel it is currently unproductive to use it as even a partial basis for a definition of planets, yet am finally compelled to include a bit of it for "cultural" reasons.

V. A Proposed Definition for "Planet"

"That&#39;s a great deal to make one word mean", said Alice.
"When I make a word do a lot of work like that", said Humpty-Dumpty, "I always pay it extra."
Lewis Carroll in Alice Through the Looking Glass (1872)

Given all the above considerations, it seems difficult to compose a definition that would satisfy the many conflicting constraints (cultural and astrophysical), deal with the three arenas, and encompass our new knowledge. But here is an attempt that may qualify (without even having to pay the word exorbitant wages):
"A planet is an object that is spherical due to its own gravity, that is never capable of core fusion, and which is formed in orbit around an object in which core fusion occurs at some time". Or more succinctly: "A planet is a spherical non-fusor born in orbit around a fusor".
This captures the two clearest cultural imperatives (that a planet be in orbit, and not be a fusor). It avoids the difficulties associated with our ignorance (both observationally and theoretically) of cosmogenetic issues, and allows planets to form as they will. There is increasing evidence from the current mass distribution of "exoplanets" that a different formation mode operates below the deuterium-burning limit (or something close to it) than for more massive substellar objects, at least in proximity to solar-type stars. This definition does not conflict with that evidence. It is not so specific that it excludes any of the current objects that most would agree are planets. The definition does not include non-fusors that form "like stars" by themselves (but it is fair to say that such objects have "planetary masses"). I have modified my own previous stance on the definition (which was purely mass-based) as a concession to thinking about the overall problem in the cultural context. To apply the definition requires observations of the mass and environment of an object (or inferring these from a combination of observations and well-accepted modeling).
As an example let us take the example of HD 168443 (a solar-type star). At 3 AU there is an object which is indisputably well above the fusion boundary (with a lower mass limit of 17 jupiters). At 0.3 AU there is an object above 7 jupiters. This could also be above the fusion limit if the orbital inclination is low enough, but there is evidence from Hipparcos which makes that relatively unlikely. There is certainly no need to speculate on what to call the outer massive object it is very clearly a brown dwarf. The identity of the inner object is also easy (subject to determination of the true orbital inclination): it nicely fits my definition of "planet". It should be pointed out that there may well be other "stellar" close binaries with inner giant planets; the Doppler searchers have quite purposefully avoided examining this question by avoiding close stellar binaries as targets. At any rate, the identity of objects in this system are only puzzling to those who insist on cosmogenetic preconceptions as defining characteristics.
To the basic definition one is encouraged to add adjectives that make it clearer what one is talking about. For our Solar System, one can refer to "historical" planets (which include Pluto). As regards characteristics, one can speak of "ordinary" or "degenerate" planets (perhaps the latter could be called "superplanets" in deference to their mass). As regards circumstance, one can refer to planets as "minor" or "major" depending on whether they are in unique, non-crossing orbits or not. This may also depend on how many similar objects there are in the system. This paper does not address the question of exactly how to make this distinction. For cosmogony, one can apply adjectives for each mode of formation (once it is theoretically well-accepted and can be justified observationally). These might include "agglomerated", "core-accretion", "direct", or different and/or additional other terms.
My proposed definition has the intended "flaw" that it includes ejected planets; those subject to the following sad fate (with apologies to Gilbert and Sullivan&#39;s 1885 Mikado)

In an inner stable orbit, round a warm and yellow sun,
with an outer fellow planet that&#39;s a huge and gaseous one.
Which will migrate ever closer, wielding gravity&#39;s sharp kicks,
whose result is cold careening to the interstellar "sticks".

To confirm such a history may be difficult in most cases. The class of "non-fusors" is therefore, however, not congruent with "planets", because of the possibility that non-fusors may be also be formed as isolated free-floaters. Such objects should in principle be given a "stellar" sort of name (such as the recently proposed "grey dwarf") to distinguish them from ejected planets. As a practical matter, it will be difficult to attach the proper label to a given object (although "free-floating non-fusor" is indisputable if the mass is known, since a fusor companion would always be found if a non-fusor has been detected). I think it worth living with this difficulty, because it is likely that many ejected analogs of our local terrestrial and gas giant planets are floating out between the stars. They deserve to be called planets despite their misfortune. Even accepting this, the difficulty of confirmation once again reinforces the problem with including any cosmogony in the definition. An easy way out would be to drop "born" from the definition (and abandon ejected planets as worthy of the name).
One must eventually deal with the question of planets versus moons, and other binary or multiple configurations. For two non-fusors in orbit about each other, it has been suggested that one differentiate between a "binary companion" and a "satellite" by demanding that the center of mass for the objects be outside both of them for the term "binary" to be appropriate. I further suggest that this be independent of the masses involved. Thus, a bound pair of objects with 9 and 11 jupiter masses would be a "binary planet", so long as the pair were born in orbit around a fusor (also independent of its mass). If they were by themselves, they would be "binary grey dwarfs" (or whatever term applies to isolated non-fusors). A substantial disadvantage with this proposed definition is that it is very "circumstantial" - to the extent that our own Moon would become a planet if it recedes sufficiently far from us. For the purpose of this paper, it is probably better to duck this issue altogether. This problem makes explicit the difficulty of the role which circumstance can play if used in the identity of objects. It is this which leads some to suggest that a purely "characteristics-based" definition makes more sense. It seems, however, that most are not ready for that conceptual change. A circumstantial component is required if we are to retain the cultural imperative of being "in orbit around a fusor" for planets.
Thus, in the end, I think it is possible to fashion a formal definition of "planet" that will accomplish the astrophysical point of having such a word. It can also fit in well with our cultural preconceptions (these are unavoidable given that we live on a planet, in a planetary system), but at some cost. This definition should be able to survive subsequent discoveries and understandings about the characteristics, circumstances, origin, and evolution of planets, and the many undiscovered configurations that Nature has probably produced, which will delight new generations of astronomers. Perhaps, as the general public becomes familiar with the new astrophysical context in which "planets" are discussed, the cultural imperatives surrounding the word will eventually change.

I welcome discussion on this paper; please send email to basri@astro.berkeley.edu

Source:
http://astron.berkeley.edu/~basri/definepl...net/Mercury.htm (http://astron.berkeley.edu/~basri/defineplanet/Mercury.htm)

For a simplified, more layman discussion of this criterion, one can visit the following URL:
http://astron.berkeley.edu/~basri/definepl...hatsaplanet.htm (http://astron.berkeley.edu/~basri/defineplanet/whatsaplanet.htm)



Hope this helps&#33;

:P

rajasun
2003-Dec-18, 07:23 AM
Personally, I am one of those who thinks that Pluto is BOTH a planet and a KBO. It is a planet because it is definitely in orbit around a lighted FUSOR (i.e. the Sun) and it is above 700 km in radius and thus has a stable spherical shape. It is a KBO because it is INDEED found in the Edgeworth-Kuiper Belt (EKB).

:P

rajasun
2003-Dec-18, 07:34 AM
BTW just to correct a MISCONCEPTION - a body of planetary mass orbited by another body of a similar mass does NOT qualify it instantly to be a planet. Yes, Pluto has a moon in Charon BUT MANY KBOs are known to be binary in nature also i.e. many KBOs have their own satellites/moons too&#33;

E.g.
http://www.solarviews.com/eng/kuiper2.htm
"Hubble Hunts Down Binary Objects at the Fringe of Our Solar System"

http://unisci.com/stories/20022/0418024.htm
"Some Kuiper Belt Objects Turn Out To Be Binary Pairs"

http://www-int.stsci.edu/~stephens/00CF105.html
"00CF105, A binary kbo"

http://opostaff.stsci.edu/~griffin/binary.html
"The Binary Kuiper Belt Object 1998 WW31"

http://opostaff.stsci.edu/~griffin/KBO_2.jpg

http://www.aas.org/publications/baas/v34n3...dps2002/337.htm (http://www.aas.org/publications/baas/v34n3/dps2002/337.htm)
"Dynamics of the Binary KBO 1998 WW31 and Predictions of Mutual Eclipses"

Hope this helps&#33;
:P

TheThorn
2003-Dec-18, 06:59 PM
A very interestng article, rajasun.

From the article in your first note: "A planet is a spherical non-fusor which is born in orbit around a fusor."

Under that definition, Pluto is clearly a planet, as you pointed out in your second note: "Personally, I am one of those who thinks that Pluto is BOTH a planet and a KBO. It is a planet because it is definitely in orbit around a lighted FUSOR (i.e. the Sun) and it is above 700 km in radius and thus has a stable spherical shape. It is a KBO because it is INDEED found in the Edgeworth-Kuiper Belt (EKB)."

The interesting side consequence of adopting this definition is that at least one asteroid (Ceres) would also qualify as a planet, as would a number of other KBOs (Quaoar, Ixion, Varuna, 2002 AW197, and probably many more).

I think more people would have trouble with "promoting" Ceres than are having trouble with "demoting" Pluto.

But at least it is a clear, unambiguous definition of the term. Of course, accepting any clear, unambigous definition of the term will abruptly end this discussion ;)

zephyr46
2003-Dec-18, 11:59 PM
I love this debate. I don&#39;t know if I can keep up with it.

The Minor Planets Center (http://cfa-www.harvard.edu/iau/lists/OuterPlot.html)

This link is to the Outer Solar system plot. If we are talking about Pluto as a planet, what are the Plutinos ? Co-orbitals? Resonant Co-Orbitals?

I would ask, what place does an atmosphere play in determining a planet and a Coma (in the case of Chiron) ?

Very diplomatic suggestion, that Pluto is both KBO and Planet. I like to think of pluto as a planet, (we have so few in our solar system as it is, the Idea of loosing one :( &#33;&#33;). But is Pluto not to Plutinos as Aten and Apollo are to Atens and Apollos (http://szyzyg.arm.ac.uk/~spm/neo_map.html) (reference from Bill Allen (http://www.hohmanntransfer.com/news.htm) ?

rajasun
2003-Dec-19, 12:13 AM
Hiya TheThorn. Glad that you find that article and my posts interesting. While Prof. Basri has more or less devised IMHO a most comprehensive set of guidelines on planethood, I&#39;m NOT hopeful that astronomers will all swiftly come to an agreement anytime soon, maybe even never. We have only to look at the number of different measures we have for celestial distances e.g. km, miles, AU, parsec (pc), etc. Different astronomer has his or her own preference.

I agree that Pluto is NOT an UNIQUE case. There are the KBOs you mentioned e.g. Ixion as well as the largest asteroid of them all - Ceres, all of whom will qualify under Prof. Basri&#39;s Criterion to become planets. I recall coming across a discussion or was it an article where Prof. Basri unreseservedly declare there are something like 12 or 14 planets in the Solar System NOT 9.

Admittedly, Pluto does have a special place in my heart. Currently, it represents the furthest KNOWN "MAJOR" outpost of the Sun. Its orbital evolution and history along with those of the other KBOs (e.g. Classical KBOs and Scattered Disk Objects (SDOs)) is a subject of intense interest to me. In the course of the next few weeks and months, all will see soon enough as to why this is so.

Matthew
2003-Dec-19, 12:31 AM
We have only to look at the number of different measures we have for celestial distances e.g. km, miles, AU, parsec (pc), etc. Different astronomer has his or her own preference.


Those all have different purposes.

I think deciding on what is a planet should be decided when we have more data on planets belonging to other stars.

Littlemews
2003-Dec-19, 12:53 AM
http://pluto.jhuapl.edu/
I guess you guyz should check out this website....

Pluto is a planet, as we know (well I should go along with the entire group)..I agree with that too.
As I read those article about pluto, let said 45% of them saying Pluto is KBO object, and charon as well...but 51% of them agree Pluto is an planet and Charon is the moon (Like our Moon, never get an chance to see the backside) and 4% is unknow <_< We cant tell whether that its a planet or not, I mean lets just assume that its a SubPlanet....but lets wait till 2015 and see what happen ><

rajasun
2003-Dec-19, 12:59 AM
Matthew, it is true that distance measures do by and large have different purposes. BUT it is NOT difficult to find within a common frame of reference e.g. the confines of our known planetary system (i.e. distance out to Pluto), different astronomers, books, journals (e.g. AJ, ApJ, AAS, Icarus, MNRAS) adopt different measures to some common object. Another area where astronomers cannot agree on is how and what to expressed Stellar Mass in. i.e. the 2 most commonly expression are in terms of kg or in terms of solar masses. Some astronomers I know prefer to keep things simple by expressing a star&#39;s mass in terms of solar masses (i.e. x Msun) and generally do NOT have much good things to say about those who prefer kg (somehow you detect some animosity between the 2 groups i.e. the astrophysicists and the other group i.e. the other astronomers (e.g. atmospheric modellers, infrared astronomers)).

In private correspondence with Prof. Basri, Prof. John J. Matese, Dr. J. D. Kirkpatrick, Dr. Peter Bodenheimer, etc, they do NOT think it will be anytime soon that we come to a all encompassing and universal definition that each and everyone will abide by. Some of them actually believe such a time will NEVER ever come&#33;

zephyr46
2003-Dec-19, 01:29 AM
rajasun, my favorite Astronomical unit of measurement is the LD
Lunar Distence Space weather (http://www.spaceweather.com/) demonstrates the use :)


I agree that Pluto is NOT an UNIQUE case. There are the KBOs you mentioned e.g. Ixion as well as the largest asteroid of them all - Ceres, all of whom will qualify under Prof. Basri&#39;s Criterion to become planets

In regions of minor planets / asteroids, I think Ceres is an Asteroid, as it lacks an atmosphere, whereas Pluto has one :)

TheThorn
2003-Dec-19, 01:34 AM
Hi, Zephyr.

"I love this debate. I don&#39;t know if I can keep up with it."

It is an interesting subject, and there seems to be some emotion in it too.

"If we are talking about Pluto as a planet, what are the Plutinos ? Co-orbitals? Resonant Co-Orbitals?"

A good question. Pluto and the other Plutinos all have a 3/2 resonance with Neptune. Their orbits appear to vary quite a bit in eccentricity and inclination. The only thing they have in common is their orbital period. So they&#39;re not co-orbital, and they&#39;re not resonant with each other either.

"But is Pluto not to Plutinos as Aten and Apollo are to Atens and Apollos (reference from Bill Allen ?"

That&#39;s one way to look at it. But Aten and Apollo are only first in their respective groups in terms of date of discovery. Pluto is first in size as well.

rajasun
2003-Dec-19, 01:44 AM
zephyr46 possession of an atmosphere is NOT listed as "MUST HAVE" requirement for planethood under BOTH the IAU Working Group on Extrasolar Planets as well as Prof. Gibor Basri&#39;s proposed scheme. Mercury has NO atmosphere (at least NOT a permanent one) and yet it is a planet, so I do nOT see why an atmosphere is a necessity, so long as the body under consideration is of a spherical shape above 700 km in size and is in orbit around a fusor (i.e. includes objects orbiting stars, brown dwarfs, white dwarfs, neutron stars/pulsars, black holes)

Check them out below or near foot of the previous page of this thread...

http://www.ciw.edu/IAU/div3/wgesp/


http://astron.berkeley.edu/~basri/definepl...net/Mercury.htm (http://astron.berkeley.edu/~basri/defineplanet/Mercury.htm)


http://astron.berkeley.edu/~basri/definepl...hatsaplanet.htm (http://astron.berkeley.edu/~basri/defineplanet/whatsaplanet.htm)

I would prefer recognizing Ceres as a Main Belt Asteroid as well as a planet in the spirit of calling Pluto a KBO as well as a planet.

:P

TheThorn
2003-Dec-19, 01:50 AM
Hi rajasun.

"While Prof. Basri has more or less devised IMHO a most comprehensive set of guidelines on planethood, I&#39;m NOT hopeful that astronomers will all swiftly come to an agreement anytime soon, maybe even never."

One of the criteria that might be worthy of another look is the "spherical" one. It puts a lower limit on size at about 700km. That seems a little low, given current usage of the term "planet", and is what results in the inclusion of objects like Ceres. I think Ceres is a real problem for this definition, because we&#39;ve known about it for 200 years, and decided through that period that it is not a planet. I think for any definiition to find wide acceptance, it would have to respect that.

Here&#39;s a suggestion for an alternate. Instead of having to be big enough to have a stable spherical shape, make that criterion being big enough to have differentiated internally - i.e. that the core would be different than the surface. That certainly applies to all the planets (with the possible exception of Pluto?) and doesn&#39;t apply to the asteroids and comets. Or does it work for Ceres - I&#39;ve hit the limits of my knowlege here. Heck, I was just thinking out loud
:rolleyes: .

"Its orbital evolution and history along with those of the other KBOs (e.g. Classical KBOs and Scattered Disk Objects (SDOs)) is a subject of intense interest to me. In the course of the next few weeks and months, all will see soon enough as to why this is so."

Are you involved in some research that is about to be published or something?

rajasun
2003-Dec-19, 01:54 AM
Originally posted by TheThorn@Dec 19 2003, 01:34 AM
Hi, Zephyr.

"I love this debate. I don&#39;t know if I can keep up with it."

It is an interesting subject, and there seems to be some emotion in it too.

"If we are talking about Pluto as a planet, what are the Plutinos ? Co-orbitals? Resonant Co-Orbitals?"

A good question. Pluto and the other Plutinos all have a 3/2 resonance with Neptune. Their orbits appear to vary quite a bit in eccentricity and inclination. The only thing they have in common is their orbital period. So they&#39;re not co-orbital, and they&#39;re not resonant with each other either.

"But is Pluto not to Plutinos as Aten and Apollo are to Atens and Apollos (reference from Bill Allen ?"

That&#39;s one way to look at it. But Aten and Apollo are only first in their respective groups in terms of date of discovery. Pluto is first in size as well.
Perhaps some of these articles/papers below may help one understand the lightweight residents that inhabit the nether fringes of our known planetary system better...

http://www.ifa.hawaii.edu/faculty/jewitt/k...kb/plutino.html (http://www.ifa.hawaii.edu/faculty/jewitt/kb/plutino.html)

http://www.ifa.hawaii.edu/faculty/jewitt/k...-classical.html (http://www.ifa.hawaii.edu/faculty/jewitt/kb/kb-classical.html)

http://www.ifa.hawaii.edu/faculty/jewitt/k...-scattered.html (http://www.ifa.hawaii.edu/faculty/jewitt/kb/kb-scattered.html)

http://www.ifa.hawaii.edu/faculty/jewitt/k...b/binaries.html (http://www.ifa.hawaii.edu/faculty/jewitt/kb/binaries.html)


http://arxiv.org/pdf/astro-ph/0308467

The Size Distribution of Trans-Neptunian Bodies
Authors: G. M. Bernstein, D. E. Trilling, R. L. Allen, M. E. Brown, M. Holman, R. Malhotra

[Condensed] We search 0.02 deg^2 for trans-Neptunian objects (TNOs) with m<=29.2 (diameter ~15 km) using the ACS on HST. Three new objects are discovered, roughly 25 times fewer than expected from extrapolation of the differential sky density Sigma(m) of brighter objects. The ACS and other recent TNO surveys show departures from a power law size distribution. Division of the TNO sample into ``classical Kuiper belt&#39;&#39; (CKB) and ``Excited&#39;&#39; samples reveals that Sigma(m) differs for the two populations at 96% confidence. A rolling-index or double power law adequately fits all data. Implications include: The total mass of the CKB is ~0.010 M_Earth, only a few times Pluto&#39;s mass, and is predominately in the form of ~100 km bodies. The mass of Excited objects is perhaps a few times larger. The Excited class has a shallower bright-end size distribution; the largest objects, including Pluto, comprise tens of percent of the total mass whereas the largest CKBOs are only ~2% of its mass. The predicted mass of the largest Excited body is close to the Pluto mass; the largest CKBO is ~60 times less massive. The deficit of small TNOs occurs for sizes subject to disruption by present-day collisions, suggesting extensive depletion by collisions. Both accretion and erosion appearing to have proceeded to more advanced stages in the Excited class than the CKB. The absence of distant TNOs implies that any distant (60 AU) population must have less than the CKB mass in the form of objects 40 km or larger. The KBO populations are far sparser than theoretical estimates of the required precursor population for short period comets.


http://www.ifa.hawaii.edu/~jewitt/papers/C...12k/CJL2001.pdf (http://www.ifa.hawaii.edu/~jewitt/papers/CFHT12k/CJL2001.pdf)


Hope this helps&#33;

:P

Matthew
2003-Dec-19, 02:19 AM
Here&#39;s a suggestion for an alternate. Instead of having to be big enough to have a stable spherical shape, make that criterion being big enough to have differentiated internally - i.e. that the core would be different than the surface. That certainly applies to all the planets (with the possible exception of Pluto?) and doesn&#39;t apply to the asteroids and comets. Or does it work for Ceres - I&#39;ve hit the limits of my knowlege here. Heck, I was just thinking out loud
.

Well if Ceres did have a different inside then you might call it a planet. But all the "9" planets have a structure, with different layers. But I think that all planets should have enough gravity to have a spherical shape.

rajasun
2003-Dec-19, 02:19 AM
SHARP observations and a good suggestion TheThorn...

Here&#39;s a suggestion for an alternate. Instead of having to be big enough to have a stable spherical shape, make that criterion being big enough to have differentiated internally - i.e. that the core would be different than the surface. That certainly applies to all the planets (with the possible exception of Pluto?) and doesn&#39;t apply to the asteroids and comets. Or does it work for Ceres - I&#39;ve hit the limits of my knowlege here. Heck, I was just thinking out loud

Very thought provoking BUT I see one problem i.e. how do we know for sure the MINIMUM mass a body needs to possess before it can acquire some degree of internal differentiation? Are there unique conditions that may render differentiation of a body&#39;s interior difficult? IF so, what should we then call such a body? hmmm...


Are you involved in some research that is about to be published or something?

Hehe I&#39;m NOT sure if ANY of the journals will accept what I am in the process of writing up. Perhaps it will appear on some websites, things are still kinda fluid at the moment. I&#39;m in contact with astronomers and astrophysicists in various fields of research e.g. the Edgeworth-Kuiper Belt (EKB), Oort Cloud, Brown dwarf (BD) evolution and theoretical studies, celestial mechanics, radio astronomers, High Energy astrophysics, Microlensing experts, etc. My research focuses on the ODDBALL behavior present in the outer regions of our Solar System, in particular, the MISSING MASS in the EKB, Scattered Disk, Oort Cloud, relative absence in return of the Long Period Comets (LPCs) from the Oort Cloud and the abrupt "truncation" of the Classical Kuiper Belt (CKB) at ~50 AU.

A hypothesis has been formulated BUT it NEEDS compiling into a COMPACT piece as well as further fine tuning. All that i can say at the moment is that there is something VERY BIZZARE that is out there, something MASSIVE BUT DIM. Stay tune&#33;

:rolleyes:

Matthew
2003-Dec-19, 09:35 AM
There was a conversation that started in this thread about a Brown Dwarf apart of the solar system. This has know been moved to Brown Dwarf Apart of the Solar System... (http://www.universetoday.com/forum/index.php?showtopic=1489) which can be found in the "Everything Else in the Universe" (http://www.universetoday.com/forum/index.php?showforum=8) section of the forum.

rajasun
2003-Dec-19, 09:43 AM
Originally posted by matthew@Dec 19 2003, 09:35 AM
There was a conversation that started in this thread about a Brown Dwarf apart of the solar system. This has know been moved to Brown Dwarf Apart of the Solar System... (http://www.universetoday.com/forum/index.php?showtopic=1489) which can be found in the "Everything Else in the Universe" (http://www.universetoday.com/forum/index.php?showforum=8) section of the forum.
Okie dokie Matt, I do see the rational behind it...many thanks for doing so&#33; B)

TheThorn
2003-Dec-20, 06:38 PM
Hi rajasun.

"BUT I see one problem i.e. how do we know for sure the MINIMUM mass a body needs to possess before it can acquire some degree of internal differentiation? Are there unique conditions that may render differentiation of a body&#39;s interior difficult? IF so, what should we then call such a body? hmmm..."

Yeah, that occurred to me as I was typing. Like I said I was just thinking out loud.

My motivation for the suggestions was that the inclusion of Ceres and some of the larger KBOs as planets (especially Ceres) will make acceptance of that definition controversial. The problem is that the lower limit on size (700km) is too small. Ideally what is needed is a lower limit between 1200km and 2000km or so.

The lower limit in the definition comes from the requirement of spherical shape, so that&#39;s the criterion that needs to be examined. Just replacing it with a 1500km limit would work, but it would be too arbitrary for my tastes. So I started thinking about what else differentiates planets from rocks, and the internal structure popped into my head.

But even while I was typing I realized that a) I don&#39;t know whether Ceres is (or Pluto isn&#39;t) internally differentiated, so my suggested criterion might be no better than the original and B) it might be difficult to tell from a distance what an object is like internally, so my criterion might be difficult to apply.

It was just a thought, and not a very good one I guess.

damienpaul
2003-Dec-20, 08:25 PM
i second the seconding of the motion.... :P

damienpaul
2004-Jan-06, 01:45 AM
i further second your motion, the orbits of pluto and charon intrigue can anyone shed some light on it?

ebbixx
2004-Feb-25, 07:25 AM
Originally posted by DippyHippy@Dec 1 2003, 02:15 AM
I guess, technically, it&#39;s a KBO then but I think it will always be a planet as far as I&#39;m concerned. Why can&#39;t we just make an exception in this case anyway? Why must we re-classify it at all?

I believe the point of reclassification is to clarify its relationship to other Kuiper Belt objects. Also, I suspect (tongue-in-cheek) that astro. academics would rather not have the profession "embarassed" by some eventual discovery of one or more larger KBOs.

In the vernacular, Pluto will probably long continue to be regarded as a "planet" out of respect for Tombaugh&#39;s persistence, if nothing else, or perhaps just for sentimentality&#39;s sake, and the fact so many living today first learned of it as a planet. However, where science education is concerned, it seems like a very good idea henceforth to teach both about its discovery as a "planet" and about (presumed) more proper classification as a KBO.

This, of course,presumes that future findings do not in turn revise Pluto&#39;s status further. To me, though, the value of teaching both aspects of Pluto&#39;s history, is in teaching how science progresses, and how it remains always open to constant revision, at least under optimal conditions, as new data and observations require such revisions to be made.