Pluto

[rhm3]

My new personal idea on this:<br /><br /><br /><b>CLASSIFICATION SCHEME FOR SUBSTELLAR OBJECTS</b><br /><br /><b><i>Planemo</i></b> – a spheroid non-fusor<br />• <b>Planet</b> – a planemo directly in orbit around a star<br />o Giant Planet – a planet lacking a crust, large enough to sustain a fluid mantle and atmosphere<br />o Terrestrial Planet – a planet with solid crust, large enough to sustain atmosphere from the hill sphere<br />o Dwarf Planet – a planet with solid crust, large enough to be spheroidal <br />• <b>Moon </b>– a planemo in orbit around a planet or rogue<br />• <b>Rogue </b>– a planemo not in orbit around a star or planemo<br /><br /><b><i>Subplanemo</i></b>– a non-spheroidal non-fusor<br />• <b>Planetoid </b>– a subplanemo in orbit around a star<br />o Asteroid – a subplanemo largely composed of rock, found in the solar system in a region between Mars and Jupiter<br />o Kuiperoid – a subplanemo largely composed of ice and volatiles, found in the solar system in a region between Neptune and the Oort Cloud<br />o Oortoid – a subplanemo largely composed of ice and volatiles, found in the solar system in the Oort Cloud<br />o Comet – a subplanemo largely composed of ice and volatiles in an eccentric enough orbit to display outgassing<br />• <b>Moonoid </b>– a subplanemo in orbit around a planet, rogue, planetoid, or rogueoid<br />• <b>Rogueoid </b>– a subplanemo not in orbit around a star or planemo<br /><br /><b><i>Miscellaneous Clarifications</i></b><br />• <b>Binary System</b> – two substellar objects orbitally locked with a barycenter outside of either object<br />• <b>Satellite</b> – a substellar object in orbit around another object<br /><br /><br /><b>GENERAL NOTES</b><br /><br />There are a few changes in this scheme as opposed to how bodies are currently classified. First off, Pluto-Charon is a binary system (though Earth and Luna remain a planet and moon, respectively). Furthermore, Ceres, Vesta, and all the spheroidal objects in the Kuiper Belt/Oort Cloud are dwarf plan

 

[ittiz]

I like you're definitions. Except the atmosphere part. I used to think it would be a good way but after I did the math I found that it's not so good. I found that almost any body that is round due to it's own gravity can hold an atmosphere of some sort depending on temperature. For instance if CO2 was a gas at the cold temps of Pluto it would probably have a moderate CO2 atmosphere. I made a graph in excel that shows the rough values of which escape velocities and temperatures gases can be retained at. The moon could retain and atmosphere of the inert gas SF6 for instance, which is heavier than even Xenon gas.<br /><br />For these reasons I thought the differentiated interior was a better line for the dwarf and terrestrial planet.

 

[silylene old]

Well this thread about definition of a planet lives on like Lazarus.<br /><br />Since here we go again, here is a link to the best thread we had on this subject (post SDC wipe), and my definition:<br /><br />planet definition thread<br /><br />Anyways, my simple definition, which I still think is the best.<br /><font color="yellow">We did this before in a nice thread before the SDC meltdown. But time to do it again... <br /><br />1) A planet circles a star or stars. If it does circle another planet, it is also considered a planet if the barycenter is above the surface of both objects ('double planets'). <br /><br />2) The maximum mass is below the threshold to sustain deuterium fusion, which is about 13x mass of Jupiter. <br /><br />3) A planet's is largely composed of 'normal' matter. It is not a mini-black hole, nor a mini neutron-object, etc. (not that any of these are possible anyways). This is actually a tough definition, for as the mass exceeds about 2x Jupiter, Coulombic forces between atoms in the object core will be inadequate to prevent atomic nuclei from compressing enough to form "electron degenerate matter" (when electron degeneracy pressure exceeds coulonbic repulsion). Adding additional mass to an object between 2x Jupiter and 13x Jupiter actually makes the object's radius get smaller due to forming additional electron degenerate matter in the core. As a result, masses between 2x Jupiter and 13x Jupiter are partially composed of not 'normal' matter. <br /><br />4) A planet has enough mass to gravitationally assume a spherical or ellipsoidal shape. <br /><br />5) A planet is at least as big as Pluto. This is arbitrary, cultural and controversial. </font><br /><br />Read the entire older thread. It had a very healthy debate and discussion. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[alokmohan]

http://news.yahoo.com/news?tmpl=story&cid=624&e=1&u=/ap/20060813/ap_on_sc/planet_spat.Its about plutos demotion.

 

[rhm3]

My idea for the atmosphere limit is the ability to form an atmosphere from the <b>hill sphere</b>. <br /><br />From Wikipedia... <i>"A Hill sphere approximates the gravitational sphere of influence of one astronomical body in the face of perturbations from another heavier body around which it orbits."</i><br /><br />To my knowledge, when an object reaches ~10^23kg in mass, it is able to gravitationally attract gas from its hill sphere and form an atmosphere. Yes, I am aware objects less massive than this have thin atmospheres (Pluto, Triton) but they formed their atmospheres in different manners. They do not have the mass to pull gas from their hill sphere.<br /><br />I did consider using differentiated interior as a dividing line between dwarf and terrestrial planet. However, that seems to vary a lot in size. For instance, there are small objects such as Ceres and Enceladus that may have differentiated interiors, whereas objects as large as Callisto can be totally homogeneous. Furthermore, the interiors of most KBOs and exosolar objects are unknown and will probably remain unknown for a while. <br /><br />Thus, I prefer using a mass limit (based on the ability to form atmosphere from the hill sphere) as a dividing line as opposed to internal structure. The mass limit is a constant, as opposed to differentiation which varies depending on how active the body is. Another benefit is that the mass of any distant object is generally estimated long before ideas about the interior arise.

 

[MeteorWayne]

Some interesting ideas RHM3.<br />The big problem I see is the arbitrariness of the categories in subplanemo.<br />(PS, I don't think the term planemo is going to be acceptable...too unwieldy, but that's for another reply).<br />You provide definitions for asteroid and comet that reflect an assumed amount of rock and ice/volitiles and location. Since we don't know what the contents are, how can we make that choice?<br /><br />Recent observations suggest that there is a continuum of rock to ice ratios. How would you define the 3 comets just discovered in the asteroid belt?<br /><br />Some asteroids are differentiated, that's how we wind up the iron meteorites, from the core of a differentiated asteroid.<br /><br />Where's the line between the K-E belt and the Oort cloud.<br /><br />Comet Tempel 1 was revealed to have much less ice than we probably would have predicted. <br />Most of what was ejected was silicates.<br /><br />Like I said, some good ideas, but categorizing is a difficult problem when there are so many exceptions. That doesn't mean it's not worth trying <img src="/images/icons/smile.gif" /><br /><br />Should be interesting to see what the IAU comes up with on Wednesday.<br /><br />MW<br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[silylene old]

RHM3:<br /><br />Interesting ideas, but too many categories. I think it should be simply "planet" or "not planet"...not four: planemos, subplanemos, binary and satellites.<br /><br />Your planemo needs to include ellipsoidal shapes (you said "spheroidal"). A spheroid is a subcategory of ellipsoid, not the other way around (just as a square is a subcategory of rectangle). Saturn, for example, has a noticably flattened ellipsoid shape.<br /><br />I do think that "planets" primarily made of exotic matter which are non-fusors (e.g. mini black holes, antimatter, electron degenerate matter, 'dark matter' or whatever yet-to-be discovered form of matter) should be excluded from the definition of planet. [Interestingly, masses between 2xJupiter and 13xJupiter are at least partially composed of degenerate matter.] <br /><br />This set of simple rules still works best, IMO:<br /><font color="yellow">1) A planet circles a star or stars. If it does circle another planet, it is also considered a planet if the barycenter is above the surface of both objects ('double planets'). <br /><br />2) The maximum mass is below the threshold to sustain deuterium fusion, which is about 13x mass of Jupiter. <br /><br />3) A planet's is largely composed of 'normal' matter. It is not a mini-black hole, nor a mini neutron-object, etc. (not that any of these are possible anyways). This is actually a tough definition, for as the mass exceeds about 2x Jupiter, Coulombic forces between atoms in the object core will be inadequate to prevent atomic nuclei from compressing enough to form "electron degenerate matter" (when electron degeneracy pressure exceeds coulonbic repulsion). Adding additional mass to an object between 2x Jupiter and 13x Jupiter actually makes the object's radius get smaller due to forming additional electron degenerate matter in the core. As a result, masses between 2x Jupiter and 13x Jupiter are partially composed of not 'normal' matter. <br /><br />4) A planet has enough mass to gravitati</font> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[rhm3]

<blockquote><font class="small">In reply to:</font><hr /><p>(PS, I don't think the term planemo is going to be acceptable...too unwieldy, but that's for another reply). <p><hr /></p></p></blockquote><br /><br />I've seen it used more frequently in recent articles, so perhaps it's catching on. It's not the best word I admit but it makes sense to be the word for...well...planetary mass objects. <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>You provide definitions for asteroid and comet that reflect an assumed amount of rock and ice/volitiles and location. Since we don't know what the contents are, how can we make that choice? <p><hr /></p></p></blockquote><br /><br />Admittedly, this is gray area. We're talking about irregular, <400km objects found throughout the solar system. I feel we should account for and distinguish between the two main belts...and the idea that asteroids are in the Asteroid Belt and kuiperoids are in the Kuiper Belt is a simple concept for even the average joe to understand. Yes, there are unknowns about composition, but I think we can use logic based on orbit. If object in question is closer to the Kuiper Belt, it's a kuiperoid unless proven otherwise...if it's closer to the Asteroid Belt, it's an asteroid unless proven otherwise. Objects dead in the middle and uncertain should be referred to as a planetoids until more information is found. <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Recent observations suggest that there is a continuum of rock to ice ratios. How would you define the 3 comets just discovered in the asteroid belt?<br /><p><hr /></p></p></blockquote><br /><br />Good point, I forgot about those. I define comet as any sub-planemo displaying outgassing, so yes those are comets. I should take out the part about being composed of ice/volatiles and eccentric enough orbit.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Some asteroids are differentiated, that's how we wind up the iron meteorites, from the co</p></blockquote>

 

[rhm3]

<blockquote><font class="small">In reply to:</font><hr /><p>Interesting ideas, but too many categories. I think it should be simply "planet" or "not planet"...not four: planemos, subplanemos, binary and satellites. <p><hr /></p></p></blockquote><br /><br />Well, in a nutshell it is. Planemo is just a broad term to incorporate moons and rogues. Binaries and satellites are extra clarifications, they aren't seperate identities in themselves. A binary planet system still consists of two planets. My definition of satellite is exactly how it is today (Earth is a satellite of the Sun, Titan is a satellite of Saturn, etc), so that's not a big deal.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Your planemo needs to include ellipsoidal shapes (you said "spheroidal"). A spheroid is a subcategory of ellipsoid, not the other way around (just as a square is a subcategory of rectangle). Saturn, for example, has a noticably flattened ellipsoid shape. <p><hr /></p></p></blockquote><br /><br />Good point. That's what I tried to imply by spheroidal (as opposed to spherical), but, you're right. <img src="/images/icons/wink.gif" /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>I do think that "planets" primarily made of exotic matter which are non-fusors (e.g. mini black holes, antimatter, electron degenerate matter, 'dark matter' or whatever yet-to-be discovered form of matter) should be excluded from the definition of planet. [Interestingly, masses between 2xJupiter and 13xJupiter are at least partially composed of degenerate matter.] <p><hr /></p></p></blockquote><br /><br />I didn't even think of that, but you're right. <br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>3) A planet's is largely composed of 'normal' matter. It is not a mini-black hole, nor a mini neutron-object, etc. (not that any of these are possible anyways). This is actually a tough definition, for as the mass exceeds about 2x Jupiter, Coulombic forces between atoms in the object core will be</p></blockquote>

 

[MeteorWayne]

RHM3,<br />Regarding planemo, I agree it makes a lot of sense, and it is used in the scientific literature. Still think the public will upchuck on that <img src="/images/icons/tongue.gif" /><br /><br />Regarding planemos as asteroids or comets, etc:<br /><blockquote><font class="small">In reply to:</font><hr /><p>Admittedly, this is gray area. We're talking about irregular, <400km objects found throughout the solar system. I feel we should account for and distinguish between the two main belts...and the idea that asteroids are in the Asteroid Belt and kuiperoids are in the Kuiper Belt is a simple concept for even the average joe to understand. Yes, there are unknowns about composition, but I think we can use logic based on orbit. If object in question is closer to the Kuiper Belt, it's a kuiperoid unless proven otherwise...if it's closer to the Asteroid Belt, it's an asteroid unless proven otherwise. Objects dead in the middle and uncertain should be referred to as a planetoids until more information is found <p><hr /></p></p></blockquote><br /><br />No problem here, makes sense. The term Kuiperoid is logical for all that stuff out there. Still the Asteroid/comet thing (not only your suggestion) is a real nasty problem that seems like it will pop up often during the next decade or so. I like the "until proven otherwise" though. Then we get into how much outgassing is enough to be a comet.... <img src="/images/icons/smile.gif" /><br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Mine:Some asteroids are differentiated, that's how we wind up the iron meteorites, from the core of a differentiated asteroid.<br />Yours:That's another reason why I don't want to use differentiation as any type of requirement. <p><hr /></p></p></blockquote><br /><br />Sorry, my bad. I attributed a previous comment to you. You did not include differentiation.<br /><br />Regarding K-E/Oort line:<br /><blockquote><font class="small">In reply to:</font><hr /><p>There very well may not be. That remains to be seen, r</p></blockquote> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[paulanderson]

Some other links as well about the current IAU meeting:<br /><br />http://www.space.com/includes/iab.html?url=/scienceastronomy/060814_pluto_fate.html<br />http://www.spacedaily.com/2006/060814135750.8jf0qxla.html<br />http://www.npr.org/templates/story/story.php?storyId=5631291<br />http://news.bbc.co.uk/2/hi/science/nature/4789531.stm

 

[silylene old]

<font color="yellow">In reply to:<br />--------------------------------------------------------------------------------<br /><br />3) A planet's is largely composed of 'normal' matter. It is not a mini-black hole, nor a mini neutron-object, etc. (not that any of these are possible anyways). This is actually a tough definition, for as the mass exceeds about 2x Jupiter, Coulombic forces between atoms in the object core will be inadequate to prevent atomic nuclei from compressing enough to form "electron degenerate matter" (when electron degeneracy pressure exceeds coulonbic repulsion). Adding additional mass to an object between 2x Jupiter and 13x Jupiter actually makes the object's radius get smaller due to forming additional electron degenerate matter in the core. As a result, masses between 2x Jupiter and 13x Jupiter are partially composed of not 'normal' matter. <br /><br /><br /><br />--------------------------------------------------------------------------------<br /><br /><br /><br />Agree, though would it be problematic if those particular Jupiter 2x-13x objects were allowed and not those others clearly un-planetlike objects? </font><br /><br />I agree. I have a problem with calling these bodies "planets". Somewhere between these limits, the object will be more than 50% by mass of degenerate matter, not ordinary matter.<br /><br />However, it seems to be a common practice to ignore this fine distinction, and simply call it a planet. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[vandivx]

why would "mini-black hole, nor a mini neutron-object, etc." not be a planet? because they didn't form in usual way that planets are formed - by acretion from dust cloud spining around stars (cloud that remained after star formed) - but are actually former stars in their distant past beginings, that's what I think is the reason why one wouldn't call them planets even if they got captured into orbit around some star (they might have been binary star companions of that star)<br /><br />IMO planets should be called all objects that formed the way I describe above even if some planet formed that way somehow left its star and got captured into orbit around another, what matters is the mode of creation here, its past, i.e, not as going through former star stage<br />then in adition there should be those requirements like that spherical shape due to gravitation and so on<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>I agree. I have a problem with calling these bodies "planets". Somewhere between these limits, the object will be more than 50% by mass of degenerate matter, not ordinary matter. <p><hr /></p></p></blockquote><br />I would think those would still be called planets but with a 'qualifier', like gas giant planets or something like that<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

Any mini black hole discovered?Is there any such thing really or bit Hawkings pet?Why none is using TNO?Dont think they are reality?

 

[harmonicaman]

<b>Alokmohan -</b><br /><br /><br />I don't think they really exist either, or there would be a lot of them and we would have detected some strange star behaviors; especially during the ongoing search for Extrasolar planets...<br /><br />An object with so much mass would make for some pretty peculiar star wobbling!

 

[robnissen]

No, it depends on the size. A miniBH the size of earth, would have no more wobble than would earth. A stellar mass BH would look just like a normal binary star system, as long it was far enough apart to not suck gas from the other star. Basically, as long as the BH, whatever its size, is not close enough to suck mass from the star it is circling, it will show no strange effects that we could possibly monitor. It will merely display the gravitational force of an object with its mass. If its mass is planet-sized, we would have no way of telling that it was a black hole, rather than a planet, orbiting its star.

 

[alokmohan]

I dont think they actually exist.

 

[silylene old]

But if a black hole with a mass less than 13 x Jupiter was discovered orbiting a star, should it be called a planet? Or for that matter, any object composed of some type of exotic matter?<br /><br />And if a black hole with 14x Jupiter mass was circling a star, is it a planet? It isn't undergoing fusion as we know it. What about a black hole that is 100x mass of Jupiter? What's the cutoff?<br /><br />And if we exclude fusors (i.e. degenerate matter undergoing some level of fusion; 13x Jupiter), why would we include a slightly lower mass object composed of degenerate matter not undergoing some level of fusion (12x Jupiter)? This is as arbitrary as any other designation.<br /><br />Personally, I would prefer excluding all objects made of any exotic matter, including degenerate matter, whether or not they are currently supporting fusion. This would put the upper limit to a 'planet' at about 2x to 3x Jupiter. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[brellis]

Some comments from laypeople... <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>

 

[harmonicaman]

More comments and another item.

 

[3488]

Looks like Pluto has been saved. 2003 UB313 has now attained planetary status (lets give it a proper name, not some braindead TV cartoon character), 2005 FY, 2004 DW (Orcus), Sedna, Quaoar, 1 Ceres, 2 Pallas & 4 Vesta, are also to be uprated. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[qso1]

Anyone know if Pallas, Vesta, and Juno meet the roundness criteria. We have no unmanned probe images of them. Ceres IIRC we have a radar image of that kind of established its roundness. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[alokmohan]

Fusors :your own naming or name given by astronomers?

 

[mikeemmert]

Vesta:

 

[cuddlyrocket]

There are 12 planets in the IAU draft definition - The nine we have now, plus Ceres, Charon and 'Xena'.<br /><br />There are some candidate planets as well, their status to be determined by observation.<br /><br />People may quibble with the definition, but I think it will probably pass - most astronomers want the thing settled one way or another.