A new planet?

[bonzelite]

right. Ganymede is larger than Mercury. <br /><br />this planet issue is a dead horse. <br />

 

[dark_energy]

How about...<br /><br />1.) Object must be bigger than Ganymede.<br /><br />and/or<br /><br />2.) Object must be on the same plane as the rest of the planets. <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

Because that doesn't work either. Every planet or other sun-orbiting object has its own orbital inclination, so each is on its own unique plane.<br /><br />Now, I could say that Ganymede shouldn't be the standard, because a large chunk of Ganymede is just ice, not rocky core, mantle, or crust, so only the rocky core diameter of Ganymede should be counted as "planetary diameter". If its rocky core isn't big enough too bad.<br /><br />I don't think that Ganymede should be kept out of the planet game either. Any gravitationally formed spherical object can be a planet, including Ganymede, Ceres, Mercury, and Pluto.

 

[mikeemmert]

I think we're losing sight on this topic of the fact that we are now finding extrasolar planets. Any planet definition will be applicable to these new objects.<br /><br />In this light, the moons of gas giants/brown dwarves may very well get some renewed attention. It now appears likely that we will find moons of gas giants that will be orbiting in a habitable zone of some star (don't forget the heat from the gas giant/brown dwarf).<br /><br />So what do we call that? From what we <i>know</i> now, and there <i>is</i> tremendous observational bias, such an arrangement will be the most likely place for extraterrestrial life to evolve.<br /><br />I think ice and gas count.<br /><br />Of course, life could develop on a moon, too, and you could still call it a moon. Chances look pretty slim for Titan, but I wouldn't rule out life altogether there. It might be so primitive that we will have to go all through this definition thing all over again!

 

[mlorrey]

Excellent points. If a moon of Jupiter or Saturn can be as big as Ganymede or Titan, then any of the superjovians we are finding around other stars could easily have Earth-sized moons with atmospheres and if in a habitable zone, life and even intelligent civilizations. And what do you call an object that orbits a brown dwarf? A planet or a moon? What do you call an object that orbits a moon of a planet? A twomoon? Moon^2? a MMoonn?

 

[bonzelite]

dead horse. <br /><br />planet is a round world. <br />moon is an object orbiting a planet. <br />distance from sun is irrelevant. <br />orbital plane or shape is irrelevant.<br />composition is irrelevant. <br /><br />some planets may now be moons captured by other planets.<br /><br />if it's a miniplanet, microplanet, macroplanet, exoplanet, endoplanet, ectoplanet, mesoplanet, gas planet, rocky planet, ice planet, up planet, down planet, charm planet, queer planet, bacon and egg planet ---who cares. they're all planets. <br /><br /> <br />

 

[silylene old]

We are rehashing old territory.<br /><br />Anyways, here is my comprehensive definition:<br /><br /><b>To be a planet: <br />1. object has to orbit a star or stars, and not be a satellite of an object orbiting a star(s) <br />2. has to have a persistent orbit <br />3. has to be massive enough to be rotationally symmetrical if rotated through the polar axis (i.e. ellipsoidal, e.g. Saturn is distinctly non-spherical) <br />4. cannot be so massive as to support fusion <br />5. has to be composed of normal matter (exotic matter such as a micro black hole, or a mini-neutron star cannot be a planet)<br />6. has to be considered a planet by popular acclimation. I know, this is a ridiculous non-technical requirement, but that's the way it is (just like a tomato is a vegetable and not a fruit). Thus Pluto is a planet and Ceres is not.</b><br /><br />http://uplink.space.com/showthreaded.php?Cat=&Board=sciastro&Number=96676&page=&view=&sb=&o= <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>

 

[dark_energy]

A tomato has seeds, a tomato is a fruit! <div class="Discussion_UserSignature"> </div>

 

[silylene old]

Of course a tomato is a fruit. But it has been popularly defined as a vegetable, and so it is (even if that is incorrect). <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>

 

[dark_energy]

How comical. I suggest we strip Pluto of its planethood. <div class="Discussion_UserSignature"> </div>

 

[bonzelite]

tar and feathers for you! <img src="/images/icons/wink.gif" /><br /><br /><br />i agree w/sily's post. i should have specified composition to be non-star. but we basically have said the same things.

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>if it's a miniplanet, microplanet, macroplanet, exoplanet, endoplanet, ectoplanet, mesoplanet, gas planet, rocky planet, ice planet, up planet, down planet, charm planet, queer planet, bacon and egg planet ---who cares. they're all planets.<p><hr /></p></p></blockquote><br /><br />Well said. <img src="/images/icons/wink.gif" /><br /><br />Of course, I like to call *anything* orbiting the Sun a planet -- even if it's not round. But those small, lumpy ones I call "minor planets". So do most astronomers. Unfortunately, it doesn't completely settle the debate, because then instead of arguing whether Pluto is a planet, they argue whether or not it's a major planet.... <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[bonzelite]

thanks.<br /><br />they're planets as long as they're not clearly something else, like a comet or an asteroid. these are more like lumps of rock. ceres, despite it's size, is more like a chunk of rock than a planet. even if an asteroid has a moon, it is not a planet. otherwise, we're back to using "mesoplanet, planetoid, bacon planet..." ---it's a damn lump of rock. it ain't a round world.<br /><br />and yes, one could argue that issue forever. but there comes a point when you just say " look, it's a comet. it's not a planet." "it's a space rock." "it's a piece of debris, a meteor." <br /><br />otherwise, we get into "genus" and "species" zoology of celestial bodies.

 

[Philotas]

<font color="yellow">1. object has to orbit a star or stars,</font><br /><br />Out of curiousity, what about free-floating objects that would fit into your planetary definition if they had been orbiting a star?<br /><br /><font color="yellow">4. cannot be so massive as to support fusion <br />5. has to be composed of normal matter (exotic matter such as a micro black hole, or a mini-neutron star cannot be a planet)</font><br /><br />AFAIK, the fusion limit is at 13x the mass of Jupiter; and should make point 5 obsolete. Nitpicking maybe..<br /> <div class="Discussion_UserSignature"> </div>

 

[silylene old]

<font color="yellow">4. cannot be so massive as to support fusion <br />5. has to be composed of normal matter (exotic matter such as a micro black hole, or a mini-neutron star cannot be a planet) <br /><br />AFAIK, the fusion limit is at 13x the mass of Jupiter; and should make point 5 obsolete. Nitpicking maybe.. </font><br /><br />No, this is a rational extra requirement.<br /><br />It is possible that a small black hole could be orbiting a star. Black holes do not support fusion. But I wouldn't consider them to be a planet!<br /><br />In addition, I will repost myself from another old post of mine from about July2005:<br /><i>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 coulombic 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. </i> <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>

 

[Philotas]

Yeah, but would a mini-black hole have less mass than 13x that of Jupiter? A requirement for a star to become a black hole is to have several times greater mass than the <i>Sun</i>. Sure, a lot of mass may be lost during explosions. <div class="Discussion_UserSignature"> </div>

 

[bonzelite]

a requirement for a star to become a black hole is to have enough belief and faith in theoretically untenable mathematical models. planets actually orbit stars <img src="/images/icons/smile.gif" />

 

[mlorrey]

A black hole could become that light through evaporation, provided it does not absorb as much new material as equals the radiation and charge lost. This would seem to require that it live in a pretty empty solar system, and orbit far enough away from a companion that it doesn't suck any of its material up. It may need to be a wanderer in interstellar space for a while, as I'm not sure whether solar wind would provide sufficient mass to negate the evaporative effects.

 

[twocanntwo]

I think that since the large rock has a moon and It`s estimated at about 20% larger then Pluto,It should be called a planet.I don`t see what all the fuss is all about.

 

[silylene old]

Philotas, I doubt there are many low mass black holes simply because theory does not have a good mechanism for forming one. But if there were, somewhere ni the universe, a low mass black hole orbiting a star, I wold be hesitant to label it a planet.<br /><br />Also, the second half of my statement, which you declined to address after I called your 'nitpick' to task was to question whether low-mass bodies composed of other forms of non-ordinary matter orbiting a star should be called a planet. Bodies with masses between 2 and 13x Jupiter are composed of 'degenerate matter'. Should one of these be considered a planet as we understand that term now? I doubt it. <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>

 

[Philotas]

<font color="yellow">Philotas, I doubt there are many low mass black holes simply because theory does not have a good mechanism for forming one. But if there were, somewhere ni the universe, a low mass black hole orbiting a star, I wold be hesitant to label it a planet.</font><br /><br />I thought such holes were completely impossible; but ok, no point to discuss it any further.<br /><br /><br /><font color="yellow">Also, the second half of my statement, which you declined to address after I called your 'nitpick' to task was to question whether low-mass bodies composed of other forms of non-ordinary matter orbiting a star should be called a planet. Bodies with masses between 2 and 13x Jupiter are composed of 'degenerate matter'. Should one of these be considered a planet as we understand that term now? I doubt it. .</font><br /><br />Ok.<br /><br />Might set a criteria that a planet must consist of roughly />51% normal matter, and then it`s a brown dwarf above that. Would decrease the amount of extrasolar planets discovered, oh well. <br />Alternatively you just call anything above 2x Jupiter brown dwarfs , wich is more scientific. <div class="Discussion_UserSignature"> </div>

 

[mikeemmert]

<blockquote><font class="small">In reply to:</font><hr /><p>Might set a criteria that a planet must consist of roughly >51% normal matter, and then it`s a brown dwarf above that. Would decrease the amount of extrasolar planets discovered, oh well. <br />Alternatively you just call anything above 2x Jupiter brown dwarfs , wich is more scientific.<p><hr /></p></p></blockquote>No, an object with 13x the mass of Jupiter will ignite fusion in it's core. Therefore it is a star. It doesn't matter if the fuel (deuterium, beryllium 7, lithium) is in short supply, it's a star. When it runs out of fuel, it is a dead star.<br /><br />Since most brown dwarves are dead, the term should mean a dead brown dwarf, or if you're talking about populations, then either live or dead ones. The prefix "live" would be reserved for brown dwarves that are still active, since they are a minority.<br />

 

[Philotas]

Oh, yeah. Anything above but 2x Jupiter but also below 13x Jupiter. I didn`t type it in. <div class="Discussion_UserSignature"> </div>

 

[moonprincess83]

I read in the Washington Post , Parade Magzine. There are 2 new Planets. Is That true?

 

[harmonicaman]

Several new objects have been discovered and there is a debate concerning how they will be identified. They may be named as new planets or merely KBO's or Oort Cloud objects -- and the jury (IAU) is still out...<br /><br />...and Pluto may be demoted to a KBO too!<br /><br />Welcome to the discussion!