Why Is Neptune Still A Planet?

edwingene · Aug 25, 2006

Pluto is supposedly not a planet because it doesn't meet the third of the new criteria for a planet, in that since it crosses Neptune's orbit it doesn't "clear its orbital neighborhood". Well, if Pluto doesn't "clear its orbital neighborhood" because it Neptune crosses its orbit, can't you say the same thing about Neptune? Neptune doesn't "clear its orbital neighborhood" because Pluto crosses ITS orbit, doesn't it? In fact, wouldn't you have even more expectation that Neptune would "clear its orbital neighborhood" of Pluto, since Neptune is so much larger than Pluto? If Pluto cannot be defined as a planet because it doesn't satisfy the third criteria, then Neptune can't be classified as a planet because it also doesn't satisfy the third criteria.

MeteorWayne · Aug 25, 2006

Welcome to SDC! I think the general answer is that Neptune has cleared i out sizeable objects in it's orbit. Pluto is a tiny object (mass-wise) The Plutinos (such as Pluto) only remain there because there are in resonant orbits with Neptune. Otherwise, they'd be ejected, or thrown into the sun. (which could be an ouchy for earth) <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

edwingene · Aug 25, 2006

You're right. Pluto is a tiny object (mass-wise), but that's not one of the planet-criteria. The article I read said that since Neptune crosses Pluto's orbit, that Pluto has not "cleared its orbital neighborhood". But can't you say the same thing about Neptune? Since Pluto crosses Neptune's orbit, Neptune has not cleared ITS orbital neighborhood, either. If Pluto is not a planet because it doesn't satisfy the third criteria, the Neptune cannot be a planet for the same reason. If one is a planet, then the other must be. If one is not a planet then the other cannot be, also.

harmonicaman · Aug 25, 2006

Obviously the imperfect structure of the Solar System disproves the Intelligent Design theory.

MeteorWayne · Aug 25, 2006

You're right. Pluto is a tiny object (mass-wise), but that's not one of the planet-criteria. Yes, I believe it is, although the size/volume/mass ratio is not well defined in the IAU resolution this link has been referred to, but I don't see it in the IAU resolution. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

edwingene · Aug 25, 2006

I don't have the criteria in front of me but, if I remember correctly, one of the criteria was that (paraphrasing here) the obect must have enough mass to have enough gravity to overcome external inertia and form itself into a spherical object. Pluto certainly has done that, so its size/volume/mass ratio is definitely enough to be defined as a planet.

MeteorWayne · Aug 25, 2006

The ratio I'm referring to is the Neptune to Pluto mass/volume ratio. I'll see if I can find which thread that was in (There are at least a dozen Pluto threads running right now. It's hard to keep track) <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

edwingene · Aug 25, 2006

OK. But I don't remember that relative size to another planet was one of the three planet definition criteria. And, if Pluto is so much smaller that Neptune, shouldn't Neptune have cleared Pluto out of its "orbital neighborhood" by now? Since Neptune hasn't done that, how can Neptune be said to satisfy all three planet definition criteria? All I'm asking for is an objective set of criteria that is applied to all "planets" objectively. If Pluto is not a Planet, then Neptune cannot be a planet. If Neptune is a planet, then Pluto must be a planet.

MeteorWayne · Aug 25, 2006

Pluto (and the other plutinos) are locked into their current obits by Neptune. Thay can't escape (in the short term, anyway) <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

edwingene · Aug 25, 2006

MeteorWayne: "Pluto (and the other plutinos) are locked into their current obits by Neptune. Thay can't escape (in the short term, anyway)" Not one of the three planet definition criteria, if I remember right. Unless that means that Pluto (and other plutinos) are, in a general sense, satellites of Neptune. It doesn't bother me that Pluto is no longer classified as a planet, but until I can see that the planet definition criteria is objectively applied to all "planets" then I will just have to conclude that "planet" is still a subjective definition.

MeteorWayne · Aug 25, 2006

Hey listen, you may be right. But at least now there's an actual definition we can argue about. That definition will probably improve in the future as we all continue to think about the issue. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

Saiph · Aug 25, 2006

well...Neptune is ~17x the mass of earth, while pluto is ~0.002x the mass of earth. The masses are ~1x10^27 kg for Neptune, and 1.25x10^22 kg for Pluto. I.e. Neptune has swept it's orbit clean of any compariable body, as Pluto, the largest object that's in neptunes orbital region, is 8500x smaller than Neptune (mass wise). However, looking at it from the other perspective, Pluto's orbital region is littered with objects that are within several percent of it's mass, and then there's Neptune which is several thousand times larger... <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

halcyondays · Aug 25, 2006

Also, couldn't you say that in fact the orbits of Neptune and Pluto don't intersect because they have such differing angles of orbital inclination ? They never really get THAT close, and their orbits only cross each other in two dimensions, so we're justified in saying Nepture has indeed cleared its path of other bodies.....

vogon13 · Aug 25, 2006

Although largish, Pluto is in a resonant relationship with Neptune of 2:3. As I am fond of pointing out, even earth has few 'resonant siblings', such as Toro and Cruithne. IIRC, the resonance for Toro is 8:5 (or was it 13:8?). The solar system is an inherently 'messy' place, and the intersection of Pluto and Neptune is actually not that big a deal. BTW, with an atmosphere, climate, 3 moons, and probable continuing geological activity, Pluto is clearly a planet. <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

vogon13 · Aug 26, 2006

You might want to ask why earth is still considered a planet, too. The following objects: 3200 Phaethon 1566 Icarus 2212 Hephaistos 2101 Adonis 2340 Hathor 2100 Ra-Shalom 3362 Khufu 1864 Daedalus 1865 Cerberus 1981 Midas 2201 Olijato 1862 Apollo 2063 Bacchus 1685 Toro 2062 Aten 2135 Aristaeus 2320 Orthos 1620 Geographos 1866 Sisyphus 1863 Antinous 2102 Tantalus and numerous others, all remain to be cleared out of earth's territory. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

MeteorWayne · Aug 26, 2006

All are rubble compared to our bigger chunk of the rubble. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

vogon13 · Aug 26, 2006

{I put a <img src="/images/icons/smile.gif" /> on it, a previous post of mine indicates I do, in fact, support planetary status for Pluto. Even Ceres. But not Charon.} <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

bdewoody · Aug 28, 2006

I believe the definition was specifically tailored to exclude Pluto from planetary status and that they goofed. <div class="Discussion_UserSignature"> Bob DeWoody </div>

Saiph · Aug 28, 2006

well vogon, it's simple: Those objects orbits are dictated by the earth, or so can be so heavily influenced by it as to completely change them. If I ask you to clear a room, you get the people out, you don't worry about the dust bunnies. Take a look at the links I provided in other links (like new planet definition thread) to the wikipedia article discussing the analytical approach (i.e. how the measure this). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

vogon13 · Aug 28, 2006

{I put a <img src="/images/icons/smile.gif" /> on that one too} <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

olivebird111 · Sep 1, 2006

jezz you guys the title says why is neptune still a planet... i will make a

damian_d · Sep 12, 2006

I agree with EdwinGene. We can all come up with caveats that make Neptune a planet and Pluto not a planet, but the point is, the current definition is simply not specific enough to deal with this ambiguity. No where does it say planet X needs to be Y times bigger than all objects "in it's path". And it doesn't say it's okay if objects are in resonant orbits, etc. Saiph: "If I ask you to clear a room, you get the people out, you don't worry about the dust bunnies." This is a clear metaphore as to how subjective this definition is. If you ask me to clear a room, sure, I might think of getting the people out. But if you ask a furniture mover to clear a room, he/she might think the furniture counts. It's too open for interpretation. On a side note, I think it's too bad that this symantics debate may lead some people to consider some objects unimportant because they don't have a coveted planetary status.

MeteorWayne · Sep 12, 2006

Welcome to SDC. Just because Pluto is now the largest member of a significant class of objects, in no way affects it's importance. In my opinion, there's too much useless screaming and yelling about it's "demotion". To me the facts speak for themselves, and I have my opinion as to it's "planetary" status, but it changes nothing about it's value. That seems to be a point that all the hysterical defenders of both points of view have missed. It is, and will continue to be a fascinating object worthy of it's upcoming investigation. So what if it's a Plutino, a Dwarf Planet, or a Planet? It's only taxonomy, not life or death. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

badspeller · Sep 12, 2006

My problem with this theory has nothing to do with Pluto's demotion. (Afterall, I've thought it needed to be demoted for about five years now.) My problem with the theory is that when you look at the debates, when you look at the language used, it becomes apparent that the astronomers involved had no interest in defineing the word "planet." All they wanted was to demote Pluto and they were going to demote Pluto, no matter what.

badspeller · Sep 12, 2006

And I just realized that I used the word "Theory" When I meant to use the word "debate." *chuckle* My appologies.

Why Is Neptune Still A Planet?

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