"Is Pluto a Planet?" fact sheet available online

newmoon · Dec 15, 2006

A free PDF file is available at this site, giving arguments for and against Pluto's planethood, along with a number of facts about Pluto and other objects (e.g., Mercury, Titan, Ganymede, etc.). It takes 1 to 2 minutes to download.

MeteorWayne · Dec 15, 2006

Since this pdf file is promoting a book, this is borderline spam. This issue has been discussed for months here, and I assure you ALL aspects of the arguments have been addressed <img src="/images/icons/smile.gif" /> Multiple times. In fact the pdf summary has several innaccuracies, and just skims the surface of the full discussion. We've had much more fun than that here <img src="/images/icons/smile.gif" /> <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>

newmoon · Dec 15, 2006

I didn't see any inaccuracies. Of course, it does present opinions on both sides of the Pluto issue, and one may disagree with one opinion or the other; but what factual errors does the document have? Again, I didn't notice any.

MeteorWayne · Dec 16, 2006

Omission: YES: "Pluto is 2 1/2 times the diameter of Ceres" No mention of the KBO Eris here, which is larger than Pluto, although it is mentioned later in another debate point. NO:"Pluto is just an ice ball" I have never heard anyone make that claim. YES/NO Concerning pluto as the largest KBO, no mention of the fact that it is one of 30 Plutinos (locked in 2:3 resonance with Neptune) larger than 300 km. This is a specific subset of the KBO's. This ignores the best argument for calling Pluto a plutino rather than a planet. If you're interested in my views, see Pluto Perspectives parts 1-4 from a few months ago in this forum. We had a lot of fun debating it, and all issues were discussed thoroughly <img src="/images/icons/smile.gif" /> A few views were changed, but I suspect not many. MW <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>

newmoon · Dec 16, 2006

<blockquote>In reply to:<hr />Omission: YES: "Pluto is 2 1/2 times the diameter of Ceres" No mention of the KBO Eris here, which is larger than Pluto, although it is mentioned later in another debate point. <hr /></blockquote> I don't consider that either an error or an omission. The fact sheet was clearly written for kids and their teachers--one point at a time. As you note, the fact sheet DOES give and compare the diameters of Pluto and Eris. <blockquote>In reply to:<hr />NO:"Pluto is just an ice ball" I have never heard anyone make that claim.<hr /></blockquote> I have. Michio Kaku has called it an ice ball on his radio show. Also, Rick Fienberg called it an ice ball on page 8 of the November 2006 issue of Sky & Telescope. In addition, I've heard a lot of ordinary people say that Pluto is mostly ice. In fact, as the fact sheet notes, it's mostly rock. (Frankly, I don't think Pluto's composition matters at all. After all, if Jupiter and Saturn, made mostly of hydrogen and helium, can be planets, why can't an ice ball? But the fact is, Pluto is NOT an ice ball.) <blockquote>In reply to:<hr />YES/NO Concerning pluto as the largest KBO, no mention of the fact that it is one of 30 Plutinos (locked in 2:3 resonance with Neptune) larger than 300 km. This is a specific subset of the KBO's. This ignores the best argument for calling Pluto a plutino rather than a planet.<hr /></blockquote> My understanding is that there are HUNDREDS of Plutinos--but they are all much smaller than Pluto. The fact sheet DOES address this point when it says that Pluto is an abnormally LARGE member of the Edgeworth-Kuiper belt. In fact, as noted there, Pluto is larger than more than 99.9 percent of all Edgeworth-Kuiper belt objects, including all Plutinos. Only Eris is bigger than Pluto. <blockquote>In r</blockquote>

MeteorWayne · Dec 16, 2006

Ok, we'll have to agree to disagree on most points, but... It really bothers me about not mentioning the Plutino class of KBO's. They are clearly a specific subset. FOI, as of 2 months ago, here are the plutino diameters: 2306- Pluto 1000- Orcus 730- 2003AZ84 636- 2003VS2 505 505 500- Ixion 480- Huya 440 383 379 363 350 350 334 319 319 304 304 278 265 253 253 These are only the ones listed before 9/22/06. <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>

newmoon · Dec 16, 2006

OK, so the biggest Plutino--Orcus--is only the size of Ceres. I don't consider that a threat to Pluto's planethood. To me, trans-Neptunian objects bigger than half Pluto's diameter, such as Sedna and Quaoar, are greater threats.

MeteorWayne · Dec 16, 2006

The biggest Plutino OTHER than Pluto <img src="/images/icons/wink.gif" /> <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>

newmoon · Dec 16, 2006

<blockquote>In reply to:<hr />The biggest Plutino OTHER than Pluto.<hr /></blockquote> I wonder: Is it really correct to call Pluto a plutino? "Plutino" means "little Pluto"; thus, a strict interpretation of this phrase implies that Pluto can't be a plutino, just as I can't be my little brother--and a neutrino isn't a neutron. Perhaps this is one semantic debate we shouldn't have.... <img src="/images/icons/smile.gif" />

MeteorWayne · Dec 16, 2006

Actually Plutino refers to KBO objects in 2:3 resonance with Neptune. <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>

MeteorWayne · Dec 16, 2006

"A "planet" is a sun orbiting body at least as large as Pluto, regardless of its orbital characteristics (eccentric or not) or within the plane of the ecliptic by about 10 degrees or so" Which of course does not apply to Pluto at 17 degrees. <img src="/images/icons/smile.gif" /> <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>

MeteorWayne · Dec 16, 2006

I'm not having trouble reading. YOU brought up within 10 degrees or so, then dismissed it with "regardless". I submit such dimissal is not justified. My opinion, which is as good as yours. Pluto's inclination is 17 degrees. One always seems to have a problem dealing with facts that are disputed but true. And I still say that Pluto's orbital charachteristics can not be dismissed with "regardless" since those are the primary things that set it up as the King of the Underworld AND the Plutinos. The Plutinos are an easily (for most) identifiable class of trans Neptunian objects, that I think should be grouped together. That's just my opinion, but clearly it was the basis for the IAU's dynamicists that pushed the poorly worded resolution. As you've stated, this definition will only last till the next IAU General Assembly, when it will be refined or scrapped in favor of something completely different. I was not attacking your post (one ALWAYS seems to think that everything is an attack) just pointing out that Pluto's inclination is 10 degrees MORE than the next most inclined planet. <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>

MeteorWayne · Dec 16, 2006

In My Opinion, Plutinos ARE relevant. Orbital resonances are what define plutinos. THAT is a fact. <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>

robnissen · Dec 18, 2006

"A "planet" is a sun orbiting body at least as large as Pluto, regardless of its orbital characteristics (eccentric or not) or within the plane of the ecliptic by about 10 degrees or so." Since the "OR" in your definition states that anything that orbits the sun within 10 degrees of the ecliptic is a planet REGARDLESS of size, you have just just defined THOUSANDS (tens of thousands) of tiny asteroids which orbit in the plane of ecliptic as planets. That is ridiculous. IMO, the definition of planet is: "Any body that orbits its star that is the size of Mercury or larger but not so large as to support nuclear fusion." Simple, manageable numbers, historically accurate and works with all stars. Indeed, it was only an historic mistake on the size of Pluto that ever caused it to be a planet in the first place.

MeteorWayne · Dec 18, 2006

There's an excellent article in the latest Scientific American discussing the issue. The author suggests a refinement to the current poorly worded IAU definition which makes sense to me. I will see if there's a link or excerpt I can include. If not I'll summarize the points. Also last week's Science News also discussed the issue. I would imagine as "News of 2006" summaries arrive, it will also reocuur. So I guess the horse ain't dead yet <img src="/images/icons/smile.gif" /> <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>

newmoon · Dec 19, 2006

I don't understand why a planet's orbital inclination should matter. Computer simulations suggest that Pluto and Eris were born in the plane of the solar system, with orbital inclinations around 0 degrees; then, due to encounters with the giant planet Neptune, Pluto and Eris got thrown away from the ecliptic. As a result, today Pluto has an orbital inclination of 17 degrees and Eris has an orbital inclination of 44 degrees. But imagine if Venus had been born with the mass of Jupiter. I suspect the Earth would have gotten perturbed into an orbit with a higher inclination. But I would still consider the Earth a planet. Also, I don't understand why the 3:2 resonance between Neptune and Pluto disqualifies the latter from being a planet. There's an odd dance between Venus and Earth, too--that's why Venus's position in the sky tonight is almost exactly its position eight years from now--yet we all consider Venus and Earth to be planets.

MeteorWayne · Dec 20, 2006

I'm not sure you are correct regarding Eris. There are a number of theories, including that it was once a Trojan of Neptune, but I'd say the resolution of that question is still in dispute. It's not just the 2:3 resonance, it's that Neptune is 50,000 times as massive as all of the Plutinos, including Pluto, combined. They are tiny grains of sand, captured and controlled by the king of that orbital zone. This gets back to the poorly worded IAU resolution. I think they had the right idea, but badly botched the wording. With other planetary resonances, it's a mutual thing, with both objects influencing the other. In the case out there in the outer solar system, Pluto's effect on Neptune is insignificant. that's my 2c worth <img src="/images/icons/smile.gif" /> <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>

MeteorWayne · Dec 20, 2006

The choice of a cutoff at Pluto's size is not supported by the data. Mercury is 14X the mass of Eris, which is 1.6 X the mass of Pluto. So Mercury is 22X the mass of Pluto, whereas Pluto is only 3.6X the mass of the next largest sun orbiting solar system object that has been discovered SO FAR. Surely that ratio will fall in the next few years. See my Pluto Perspectives post on mass here <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>

newmoon · Jan 3, 2007

I don't think mass is a wise criterion--it's much too hard to measure. If an object doesn't have a moon, it's impossible to measure the mass until a spacecraft gets there. Diameter is an easier measurement and thus a better criterion. Absolute magnitude is easiest of all--and some people have proposed that be used to divide planets from nonplanets, though it poses some problems.

MeteorWayne · Jan 3, 2007

Fine, Mercury is almost twice the diameter of Eris and Pluto. They are only 50% larger than the next largest objects discovered so far, and that gap will likely be filled in during the next decade. <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>

newmoon · Jan 19, 2007

I agree with you that the IAU vote was a joke. HOWEVER, extremists like Stern share part of the blame. Had the Gingerich committee come up with a moderate, sensible definition of planet--e.g., something that's Pluto-sized or bigger, and that goes around the Sun--then most people could have lived with it. This is, after all, the common sense definition of planet in the popular mind. Also, there are many astronomers who support it. Others would support it as a compromise. A few would have opposed it. Instead, the Gingerich committee came up with a ridiculous and extreme definition that even many who favor Pluto's planethood would have rejected. For example, under that proposal, Pluto's biggest moon, Charon, would have been considered a planet. How's that for a slap in the face to all those who are already a little queasy about Pluto's planethood: call something HALF the size of Pluto a planet!

"Is Pluto a Planet?" fact sheet available online

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