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August 28, 2006



Thanks for reminding the readers that dwarf humans are still humans (seeing as I've been a Pseudoachondroplastic dwarf human since conception, as have members of my family for 3 generations). A "little" more off topic info, ranks of Catholic dwarfs can claim a blessed (Bl. Margaret) and Saint (St. John the Dwarf).


I disagree with the statement that, "what an object is is more important than where it is if you want to talk about its nature."

Mt Everest, so long as it is planted on earth, is a mountain. However, is we somehow managed to blast it free and set it loose to drift in outer space, it would no longer be a mountain. what it is has not changed. It is still a big ol' rock. However, where it is--drifting in space--means it can no longer be called a mountain.


I come with non-planetary news. I just noticed that you're among the top 25 Catholic websites in the world. Kudos!

I feel compelled to start the B.P.B. (Bring Pluto Back) Society! Who's with me?

J.R. Stoodley

Dwarfs of Kage's sort are humans of course. Dwarfs or Dwarves of mythology or fantasy are not. Since planets are named after mythological deities, it is not clear to me which meaning of the word "dwarf" is meant.

Ed Peters

Just as long as Pluto is not a planet.

J.R. Stoodley

Ry makes a good point about Mt. Everest.

Another example:

Two protons and two neutrons is a helium nucleus if it is orbited by two electrons. Without these electrons, it is an alpha particle. One is the main componant of the gas that fills balloons and makes people speak like Micky Mouse, another is a potentially deadly form of nuclear radiation.

I don't know about the philisophical definition of a nature, but science needs to be more practical than that. If a big rock rests on a planet it is a boulder. If it circles a star it is an asteroid. If it circles a planet it is a satellite (moon). It matters not only what it is but where it is and what it is doing.


While I agree with much of what you write, at some level a body's relationship to the rest of the solar system must come into play. Why not mention the planets of Io, Ganymede, and Europa? These earth-sized bodies fit your definition of a planet based on "what" they are, and would be considered planets if they fell in a different orbital plane. However, it is precicely their relationship to Jupiter that makes them satellites rather than planets.

In fact, one of the reasons I maintain that Pluto should be considered a full-fledged planet is that it has a moon of its own.


I'm not saying the IAU's decision is perfectly sensible, but "what" is going to be darn near impossible to use. Ultimately, astronomers would like a definition that has to do with how the darn thing formed. That would be a definition of its nature - central mass of starbirth cloud, or debris. But we can only observe what is now the case, and make some extrapolations. This leads to awkward questions, e.g.: if an exoplanet were actually captured, is it still a planet?

I recommend a nice review: www.arxiv.org/abs/astro-ph/0608417 (link to the abstract, available to the public, but as PDF). It's almost layman's level. It discusses mass and orbital properties that can distinguish astronomical bodies, in terms of the "planet" discussion.

They also note the cultural context - "planet" seems to mean the most important bodies around a star that aren't other stars or orbiting a planet. If there are dozens or hundreds of planets (and we really haven't evaluated anywhere near everything at the edge of our solar system), "planet" ceases to be a very meaningful category. It's not unreasonable to include orbital context - Ceres was downgraded pretty quickly when they realized it wasn't special - it was just a bit bigger than a bunch or rocks out in the asteroid belt.

I'll note the movie Serenity's setup: "We found a system with dozens of planets and hundreds of moons". If each planet were just a big asteroid, it would have been a very different scifi colonization scenario.

I'll also note that saying anything that's big enough to slump down to a spherelike shape is a planet leads to ambiguity: how close to a sphere? and why does it have to be bigger for stiffer material?

Sorry, long post. It's just that I keep getting asked about this, even though it's not my area of astronomy.

J.R. Stoodley

About clearing, it seems certain that by the current definition Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune have all sufficiently cleared their orbits to fit the modern definition of (non-dwarf) planet, and Pluto has not. I imagine the clearing thing is related to size just like the spherical shape requirement. Both these requirements have fairly fuzzy bounderies that must be fairly arbitrarily decided, in a way that makes sense. If this is so, why object to the one requirement but accept the other?

Old Zhou

I think they should also add that a "real" planet has to have a real, significant, persistent atmosphere.
And then vote Mercury off the island.
Seven planets...just like the old days!


But I think Pluto has an atmosphere, which would put it back on the list. (As Mr. Chekov said: "I think I'm getting space-sick").

J.R. Stoodley

But Mercury was one of those original planets. I would hope the origial seven planets would all be retained in any redefinition. Mercury does have a bit of an atmosphere too, and has a nice near-circular orbit, and spherical shape.

What we need to do is find another dwarf planet, so we can have 12 planets, three types with four members each. It don't get much more Trinitarian than that!

J.R. Stoodley


I'm pretty sure Pluto does not have any atmosphere. I'd have to check though.

J.R. Stoodley

Astronomers need to develope a specialized field of astronomical taxonomy, and found a taxonomic association like the ones we have in biology to force one system on everyone. Then you wouldn't have these crazy conferences where people quiestion the outcome, just an official International Association for Astronomical Taxonomy coming out with the current definitions.

francis 03

Seems to me that by Jimmy's proposed definition we'd have 29 or so planets, as of now. To wit: Mercury, Venus, Earth, Luna (or whatever we'd call the Moon), Mars, Ceres, Jupiter, Io, Europa, Ganymede, Callisto, Saturn, Mimas, Enceladus, Dione, Tethys, Rhea, Titan, Uranus, Miranda, Ariel, Umbriel, Titania, Oberon, Neptune, Triton, Pluto, Charon, and "Xena."

You can quibble about some of the bodies that would be at the very margin, but there's no escaping that this would involve adding roughly 20 objects currently classed as moons or asteroids to the list of planets, including Earth's Moon, four Jovian satellites, six (!) moons of Saturn, five of Uranus, and one each for Neptune and Pluto. And all this is without considering what are likely to turn out to be dozens more as-yet-undiscovered Kuiper-Belt and Oort-Cloud objects. Is this really what anyone wants to do with such a treasured appellation?

Further, the distinction raised by this post between "what something is" and "how something relates to others" makes me raise my eyebrows. I don't think you can divide those categories so neatly. After all, isn't how things relate to others an important characteristic of what they are? Physicists can put it much more elegantly, I'm sure, but when we say someone is "a doctor" we often mean not just that he holds an M.D., but also that he has an office and sees patients by appointment. This describes both the attributes of the person and his relationships with others.

francis 03

I like that, Bill. Failing that proposition, how about we find four more dwarf planets, and then name them Happy, Dopey, Sleepy, Sneezy, Grumpy, Doc, and . . . um . . . Alito!


Pluto has an atmosphere (barely), at least when it's closer-in. I vaguely remember the disappointment with a delay in getting a Pluto mission going, because it wouldn't pass by during the atmospheric freezeout (or the expected peak of the freezeout?)

see http://www.windows.ucar.edu/tour/link=/pluto/lower_atmosphere.html&edu=elem

Also, while I was taught Charon-as-Pluto's -Moon in school, that's not true in the same sense that the Moon is a satellite of the Earth. Pluto and Charon are close in size and each orbits about the center of mass point of the two bodies - which isn't in either Pluto or Charon. So here's more fuzziness - moon vs. double-"dwarf planet".

Maybe one day the IAU will have to solidify the definition of "moon"

Old Zhou

Did anyone else enjoy Jane Spencer's column about Pluto last Friday in the Wall Street Journal?

Some choice bits:

"The ruling by the world's top astronomers to boot Pluto from the planet category is sending shock waves through another set of dedicated stargazers: the world of astrologers, who are already mulling how this turn of events will affect our moods, our lucky numbers and our chances of getting a date on Saturday night."

"Whether he's a planet, an asteroid, or a radioactive matzo ball, Pluto has proven himself worthy of a permanent place in all horoscopes," says Shelley Ackerman, columnist for the spirituality Web site Beliefnet.com. Ms. Ackerman criticized the IAU for not including astrologers in its decision.

Radioactive matzo ball?


So Pluto and Charon revolve around each other, just a the Romulans' home planets do...Uhoh.


Don't forget the Centaurs, and the two or three other bodies in the asteroid belt which are spherical (though damaged out of round). There are quite a few KBOs larger than Charon, Many with silly names (people working with them can't keep saying 'ub313' over and over.

I would propose a nomenclature based on what they are, and a second nomenclature based upon orbit.

Luna is a dwarf planet which is the primary moon of Earth.

Could we bring in words like 'globe' or 'world', and use 'planet' for a nonstellar, spherical body, which orbits a star (fusor).

Many small, irregular asteroids (I prefer planetismals) have moonlets.


As an amateur astronomer, I always liked the term "planetoid". Rather ambiguous to some...but it denotes an object too large to classify as an asteroid, but too small to be with the "big boys"...I've called Pluto a planetoid for years, and now I feel justified :-)


1) A "planet" [1] is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit

So how much space junk do we have to put up before the earth can no longer be classified as a planet?


Old Zhou,

I also read the article from the WSJ about the astrologers. You missed some of the funnier parts. One, since this IAU has declared that Pluto isn't a planet, that also wipes it off of the astrological charts. If it has so much "energy" to "affect our lives", why does it matter *who* says *what* it is. Two, they are pleased about the addition of the new "feminine" planets (as determined by their names, given by different folks), because we need a more "nurturing influence" in our solar system. Good thing I had my tinfoil hat firmly on my head while reading this.


I like planetoid, too. Maybe it will become common parlance for the "dwarf planets"

As for planet=nonstar orbiting a star, that will engender some fuzziness.

First, the clear demarcation of star/brown dwarf.

Does it matter if it's orbiting a "pre-star"? Lots of stars form in tight groups, and if one hasn't yet grabbed enough gas to start fusion, but gets a planet captured from another system (planet ejection is likely given the wild orbits seen in some exoplanet survivors), is that captured wanderer a planet anymore?

What about a non-fusor star (I don't think we can define star to be anything which ever was a star - black holes are a quite different beast). A neutron star isn't fusing and isn't a "star" in that conventional sense. Yet I don't think we're going to downgrade the "few Earth"-sized pulsar planets (the first exoplanets discovered!). The pulsar planets almost certainly didn't even form around the star that was there before dying into a pulsar form. They would have formed from debris afterwards.


BTW, you may be interested to know that an astronomers-only petition is circulating, to ask the IAU to reconsider.

J.R. Stoodley

Dwarf planet suggests, as Jimmy says, a true planet of a particular kind. Planetoid suggests something similar to a planet that is not one. I perfer dwarf planet and seriously think they should be named after Eddic dwarves, but planetoid seems more in keeping with the meaning the IAU wants.


Does that mean i have to relearn the Solar System?


Does that mean i have to relearn the Solar System?


Sorry for the double post. Anyways, would this be a sign that the Universe is larger than we thought?

Jared Weber

Time out, people. (I know I don't have the power to call that, but what the heck.)

Why does everyone keep putting Xena in quotation marks?


I think we need more planets, & am still holding out for 153.That was the number suggested by a friend,& I like it. (Imagine a silly cockeyed smiley hitting herself in the head with a wooden mallet here).


Why 153? To correspond with the number of fishes caught by St. Peter? At least We can now set forth and try to find another Planet to settle in case of the Earth being destroyed. Mars is no longer the only fit candidate for 'A New Earth'.


Patrick: That's as good a reason as any....Nice & biblical!!
Since she & I both had to memorize the planets, in order, I think she was just shooting for too many for her grandkids to be made to reel them all off.


"Xena" is in "quotation marks" because it's only the "unofficial name" for the "dwarf planet" underdiscussion. Its "real name" (for now) is just a "string" of "letters and numbers."


Well, so much for the 'My Very Excellent Mother' mnemonic. I pray they change the new planet's name from 'Xena,' though; I'd hate for us to be a laughingstock for future generations...
On the other hand, maybe it's too late to be worrying about that.


Since "Xena" has a moon named "Gabrielle", I think we may be sure that people of the future will be saying: "What were they thinking?"

Brian John Schuettler

"Well, so much for the 'My Very Excellent Mother' mnemonic. I pray they change the new planet's name from 'Xena,' though; I'd hate for us to be a laughingstock for future generations...
On the other hand, maybe it's too late to be worrying about that."

If we survived Uranus...we can survive Xena.
If you were able to look into a clear autumnal sky and see a heavenly body, which would you choose...Xena or Uranus?
Besides, what 'future" generations?


As for "Xena"'s real name, I propose that Scientists should come together to discuss this. After their discussion,(Which shall hereby be called the Scientific Council of [insert placename here]) They'll release the proceedings. 'If anyone does not believe that the Planet formerly named 'Xena' is a planet, Let him be Anathema (scientific-wise).'


That reminds me. Over there in America is August 29, The feast of the beheading of St. John the Baptist. (sorry if this is off-topic)

francis 03

Favorite newspaper headline (from a few years ago):

Is There a Ring of Debris Around Uranus?


It seems that this redefinition has generated a lot of discussion, but I would like to pick up a thread that francis 03 started regarding relational properties.

quoting francis 03:

the distinction raised by this post between "what something is" and "how something relates to others" makes me raise my eyebrows.

Mine also. Mr. Akin apparently has a certain philosophical view that there are these things called "natural kinds", which I take to be a sort of essence, and it is the business of science to discover them. Also, these natural kinds contain only non-relational, or intrinsic properties. I believe the view goes back to Aristotle.

First, it seems that relational properties are often involved in many concepts, as J.R. Stoodley pointed out:

quoting J.R. Stoodley:

It matters not only what it is but where it is and what it is doing

An example might be "school principal". How could you explain what a school principal is without using relational properties? Surely, we can't determine whether or not a person was a school principal by physical autopsy! (Although some might want to try anyway.) Yet, school principals surely exist. Perhaps then Mr. Akin might counter that "school principal" isn't a fit term for science.

The trouble is that "planet", intuitively, seems to have a relational aspect. What are planets? They are things that go around stars. (We all believe, and we're right.) (This does NOT mean that everything that goes around the sun is a planet.)

Secondly, Mr. Akin's assumptions, even if they aren't wrong-- and I think they might be-- are BIG assumptions. The assumptions are

(1) There are natural kinds.


(2) It is the business of science to find natural kinds.

Concerning (1):

Are there such things as natural kinds? Or, for that matter, essences? Do all meaningful and useful terms have definitions of that sort? Might some terms be incapable of definition of this sort? (Maybe they are definable using a set of "family resemblances" a la Wittgenstein, but maybe there is no essence to find.)

Concerning (2): Is that what science is really all about? I'd like to believe that, but maybe that's just too lofty a goal for science. Perhaps a more humble view is more realistic: maybe science is just a tool for generating useful predictions. Or maybe science is a bundle of different goals and methods; maybe it isn't all natural kind finding.


on the lighter side concerning Pluto: does anyone remember the fungus creatures from Pluto in Lovecraft's stories? Maybe we should ask them. (Or maybe not!)

Jamie Beu

BTW, I didn't see anybody mention this already, but Pluto does have an atmosphere. The problem is that it does not have its own atmosphere. Pluto's moon, Charon, is so close to Pluto, that it is actually a "shared atmosphere".

As for future generations laughing, how many schoolchildren have laughed about a (former) planet named after Mickey Mouse's dog?

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