The next great planet debate

Alex, Louisville, Kentucky — Wed, 20 Feb 2008 20:57:16 GMT

The definition of a planet needs reform, and I would like to see Pluto reinstated as a planet because I am traditional, though I'm still not sure it qualifies. The orbital path alone makes for a questionable debate. As for Morrison's statement, I think dictionary definitions have to come from somewhere; who better to define than the experts?

The next great planet debate

Daniel Fischer, Königswinter, Germany — Wed, 20 Feb 2008 20:59:45 GMT

It's now 1 1/2 years since "Prague", and around the world - with the exception of one certain country - the new (and first-ever 'official') definition of 'planet' has been accepted and is being taught: One many levels people feel that the dynamical definition is a good one. And not just because it can be explained so easily (esp. when compared to most alternatives): The resulting small total number of planets and the stability of that number on a timescale of centuries satisfy the fundamental expectation that a 'planet', a term associated with the gods of antiquity, has to be something very special in our solar system. Before fiddling around with the status quo (and fantasizing about "a growing consensus" on an opposing view where there is none), I'd rather recommend re-reading http://www.thespacereview.com/article/703/1 ...

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Tim Briggs, Katy, Texas — Wed, 20 Feb 2008 21:24:07 GMT

I grew up my entire life thinking there were nine planets; and now you tell me there are more (or less). The next thing you are going to tell me is that there is no Easter Bunny!

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Thomas Ashby, Calgary — Wed, 20 Feb 2008 21:25:07 GMT

I agree totally with involking roundness in the definition and orbits a star and is not a moon.

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Kevin Brown, Mississauga, Ontario — Wed, 20 Feb 2008 21:33:53 GMT

I think Mark Sykes from the Planetary Research Institute has come up with a great definition. I think haveing sub-catagories, like "dwarf planet", will eventualy become a problem. I'm sure there are planets out there that would make Jupiter look like a dwarf.

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Guy S. Newell — Wed, 20 Feb 2008 21:34:08 GMT

I agree. The IAU can't win on this one. They're first attempt made scientists look like a bunch of confused, muddle minded, would-be lexographers.

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LPClark, Englwood Cliffs NJ — Wed, 20 Feb 2008 21:36:35 GMT

All of you are so full of yourselves it is amazing you can get from room to room or that two of you can fit in the same room. We are on a tiny ball spinning in a vast universe. We are microscopic in comparison to the size of the universe, and you have the unmitigated gall to "decide" what should be called a planet? Your collective egos are astounding and you should all be ashamed of yourselves. We certainly do not need you to define the universe for us.

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Joe N, New York, NY — Wed, 20 Feb 2008 21:40:01 GMT

As with any other scientific definition, I don't believe that any one body of people should have the right to place a solid operating procedure on what defines a "planet" in the first place. Everything doesn't necessarily require an end-all answer. We should leave the labelling up to the people that discover or research these bodies and not overthink the subject.

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John Charles Webb, Jr. Maui, Hawaii — Wed, 20 Feb 2008 21:44:33 GMT

How about if we define 'astronomer' as .....
"A person who defines a 'planet' is an object orbiting a star that has mass sufficient to maintain a gravity-determined (hydrostatic equilibrium) shape."

That will settle the entire issue!

.

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Paul M., E. Berlin, CT — Wed, 20 Feb 2008 21:59:25 GMT

If it's round and orbits a star... it's a planet. Why the need to complicate things?

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Brian Hufe, Newark, DE — Wed, 20 Feb 2008 22:04:34 GMT

I think there are two major definitions almost everyone can agree on, and possibly a third.

1) The object must orbit a start (not another planet, making it a moon)

2) The object should be rounded under its own gravity (hydrostatic equilibrium).

The third possible one is, that if the object has a moon, the center of mass of the planet and moon system should lie within the planet. Whether this be a necessity of the definition of a planet, or the definition of a moon, I don't know. But it avoids a debate in the situation (however rare it may be) when two objects of almost equal mass orbit eachother. In that situation it would be hard to call either one a moon or a planet, and would have to be designated a "planetary doublet" or something.

I think the requirement under the current definition that the planet should the neighborhood surrounding its orbit is a little contrived. I mean, what if a planet shared its orbit with a second planet that was half a period out of phase with the first. Or for that matter, how many moons does a planet need before it hasn't "cleared it's neighborhood"

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gerrit westervoorde grants pass oregon — Wed, 20 Feb 2008 22:08:02 GMT

i think pluto should be a planet

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Gordon, Charleston, SC — Wed, 20 Feb 2008 22:08:05 GMT

To paraphase the topic of trash/treasures, one could say that one man's planet is another man's asteriod. There will never be a "final" decision. I like the idea of categories. Rocky, Gaseous,etc. Leave size out of the equation.

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Biff Laser — Wed, 20 Feb 2008 22:08:27 GMT

Tell the IAU to stuff it. I'm teaching my kids that Pluto is the 9th planet in our solar system.

Pluto '08

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Byron Raum, Beverly Hills, CA — Wed, 20 Feb 2008 22:08:59 GMT

The definition 'A planet is an object orbiting a star that has mass sufficient to maintain a gravity-determined (hydrostatic equilibrium) shape' would cover both members in many a binary system, including white dwarfs, neutron stars and even black holes. Isn't it gravity that determines a black hole's shape?

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Melint, MN — Wed, 20 Feb 2008 22:32:31 GMT

Nuke Pluto.

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Joseph Basile, Worcester MA — Wed, 20 Feb 2008 22:43:15 GMT

Certainly planets differ in size and composition, but I still disagree with the current definition. I think that to exclude Ceres, Pluto, and Eris from true planethood stands only to obstruct the public education process on scientific topics.

Is it better to teach children about 8 planets, or 11?

Also, such a specialized definition as the current one will certainly cause problems as we expand our knowlege base about exoplanets and attempt to classify them. We should also reconsider the "double planet" definition (i.e. Pluto/Charon). I'm comfortable with the idea of the Earth/Moon system becoming a double planet one day (As the Moon's orbit enlarges over time).

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Phil Barbe — Wed, 20 Feb 2008 23:08:23 GMT

This debate is a waste of time and resources, and only makes science for children allthemore confusing. We Grew up with the knowledge that there were nine planets, by classifying them and diminishing their value does nothing to make children want to study them. This group of self-important eggheads need to realize that it doesnt matter if Pluto's a planet or not, just that you need to make astronomy and other sciences more interesting to hold the interest of future scientist. Quit Quibbeling!

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Scott — Wed, 20 Feb 2008 23:35:53 GMT

Here's my definition of a planet...

Any gaseous or rocky spherical object that orbits a star, is not a moon or satellite, regardless of size, chemical makeup, or distance from it's host star should be considered a planet. I don't think we need more than one type of planet, ie, dwarf planets etc. A planet is a planet.

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mike d. milwaukee wi. — Wed, 20 Feb 2008 23:41:24 GMT

before we start telling the world about our solar system planets we should have explored these orbs first than say if it is a planet

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Deric C., Los Angeles, CA — Thu, 21 Feb 2008 00:19:43 GMT

I think it will come down to lots of categories of planets (rocky, gas, giant, dwarf, etc.) But there still remains the basic "counting" question. It's not always easily defined, but what about identifying the major planets that orbit more or less in the formation plane and calling them "Main Sequence" planets or something.. Just a thought (although i'm sure there's lots of "what if's" that come with that and it won't account for the large variety that we will inevitably see out there.

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Steven F. Durst — Thu, 21 Feb 2008 00:20:53 GMT

Who are these people? Do they think just because they say so, that an orb in orbit around the sun is no longer considered an orb? Just because "THEY" say so? Gee there has to be important activities for the scientific community to be working on and pondering other than this nonsense. Pluto is and will remain a planet in my opinion. So also are the larger ones that have been found farther out. They are still locked in an orbit around our sun they are a round object with gravity and some have moons around them. You know like a planet......

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Delmar Fairchild, Barron, WI — Thu, 21 Feb 2008 00:28:11 GMT

I would think that they could be classified by the "inner life circle zone" of rocky planets that on the outer edge may support water and mobile natural life forms (like we have); then the gas zone that may only harbor primitive life in the outer film (like a mini solar system but where the "planets" would be the living entities); and finally the frozen zone which may harbor life locked in under the surface or none at all.
The last zone being a storage depot for the other two zones,once we learn how to get out there and back with the goods (water, methane, minerals).

I believe that all solar systems throughout the universe would follow this set up for their planets seeing as all Hydrogen and Helium atoms were made during the big bang and a star's gravitational forces make all the other elements resulting from Hydrogen and Helium fusion.
You may have an odd mini solar system area like Jupiter where a moon may have life forms due to its own volcanic activity or influence by the mother gas giant or even in the atmosphere of the gas giant itself, but they will still be classified within the gas zone.

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Fritz Radke, Lebanon, Pennsylvania — Thu, 21 Feb 2008 00:32:52 GMT

Because of all the variables and diversities of our solar bodies, why don't we make the definition of planets as simple as this, any solar componant greater in volumn than the largest moon orbiting any planet would be a planet. Any smaller would not be.

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Karen Ramirez, La Puente, California — Thu, 21 Feb 2008 00:41:34 GMT

WHY ARE YOU GUYS GOING TO DEBATE ABOUT ANOTHER PLANET?? THEY ALREADY TOOK PLUTO AWAY FROM US NOW JUPITER? WHAT IS WRONG WITH JUPITER? I MYSELF STILL THINK PLUTO AS A PLANET EVEN THOUGH THOSE "SCIENTIST" SAY PLUTO ISN'T A PLANET AND IF THEY SAY JUPITER IS NOT A PLANET I WILL STILL CONSIDER IT A PLANET!

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Amber,Fontenot, Louisiana, lafayette — Thu, 21 Feb 2008 00:54:19 GMT

I believe that planets should be further studied and talked about in a respectable matere. I have no further doubt what scientist might discover.

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Dennis McClain-Furmanski, Dalworthington Gardens, TX — Thu, 21 Feb 2008 00:57:24 GMT

We have star names that are over a thousand years old. We have constellations that represent things similarly ancient and have little relation to present day culture. If we can retain these for this long with no justification other than tradition, we can do the same for Pluto. It has almost 70 years of history as a planet, and was defined within our culture. If not, we should look at redrawing the sky atlases for more relevant constellations and issuing new star names.

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John Scoblic, Anchorage, AK — Thu, 21 Feb 2008 01:53:52 GMT

Moral of the Poem: "Blindmen and the Elephant".

So oft in theologic wars,
The disputants, I ween,

Rail on in utter ignorance
Of what each other mean,

And prate about an Elephant
Not one of them has seen!

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bah — Thu, 21 Feb 2008 01:57:42 GMT

does it really matter? Who will benefit from us NOT calling Jupiter and Pluto a planet???

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Steve Z., Doylestown, PA — Thu, 21 Feb 2008 02:22:07 GMT

Let's keep this simple for a change! Planets are like apples; there are many different varieties but they are all still apples. Why not have subcategories of planets but call them and count them as planets?! Let's move on.

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Kevin Danson, San Clemente California — Thu, 21 Feb 2008 02:39:02 GMT

I think its great that the IAU is getting together to discuss this. Jupiter is known to emit thermal and other forms of electromagnetic radiation and has been referred to as a "near star".

Other solar systems are known to have two stars in which a smaller star may orbit the larger star much like Jupiter orbits our sun.

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John Ducmanh, NYC — Thu, 21 Feb 2008 03:15:40 GMT

If Pluto is considered to a 'minor' planet, why not the Earth, Mars, Venus and Mercury as well? Compared to the gas giants in our solar system and in the extrasolar systems discovered so far, none of the inner, rocky planets is worth mentioning--except for our fixation on potentially inhabitable worlds.

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Brad Berg, Eau Claire, WI — Thu, 21 Feb 2008 03:22:04 GMT

I think the two keys to a definition of planet are the hydrostatic equillibrium and the fact that they orbit a star. If a body happens to primarily orbit a planet, instead of the star, then it is a moon. To have bumped Pluto reduces our ideas of the diversity of our own solar system when it becomes increasingly clear that there is so much more to our solar system than just the sun and the bodies we have accepted as planets. I'd love to see the view of the solar system increased than to take away what has for so long been an established order of planets.

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Ryan Walker, Days Creek, Oregon — Thu, 21 Feb 2008 03:44:42 GMT

I hope that the definition of a planet is changed. We were robbed of Pluto and I don't want other planets to be reclassified. I grew up knowing there were nine planets and I STILL believe that there are NINE.

As we learn more about solar systems in our galaxy and other galaxies the issue may need to be addressed again. For now things should remain how they were before the IAU stuck it’s “nose” in the business. I agree with Mr. Boyle, “the IAU should just drop it”. I am afraid that if astronomers over analyze the planets there will be more categories than there are planets.

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Josh Levin, Cherry Hill, NJ — Thu, 21 Feb 2008 03:46:09 GMT

Even the term "gas giant" is subject to controversy. Some astronomers prefer to call Uranus and Neptune "ice giants". See http://en.wikipedia.org/wiki/Gas_giant#Terminology

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Bob Dean — Thu, 21 Feb 2008 03:49:16 GMT

Why doesn't the IAU go and watch the old Star Trek series and adopt how Starfleet classified planets.

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Mike Barrier, Bingen, Washington — Thu, 21 Feb 2008 03:55:25 GMT

A ROSE BY ANY OTHER WOULD STILL SMELL THE SAME.

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Davis — Thu, 21 Feb 2008 03:58:19 GMT

IAU delegates should come up with a definition, with the understanding that it would periodically reviewed.
I think that is the scietific method.

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Looey Munn, R9oundup, MT — Thu, 21 Feb 2008 04:07:26 GMT

The Sykes 3-part definition sounds good to me, so far.

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Wade El Paso, TX — Thu, 21 Feb 2008 04:39:49 GMT

Just like species, orders, etc. of animals and plants, maybe it is a good idea to more precisely classify objects in space as well. It will eventually be needed, the more we learn about other systems.

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david turner,alberta,canada — Thu, 21 Feb 2008 05:11:58 GMT

ok..theres a thing it circles our star..its round and has an orbit..soooooo di we need to waste everynes time by saying that they arent planets? what are they moons? scientists need to discover something new..they are getting bored..maybe find thier .never mind that wont get printed..is the sun a sun? who knows..maybe its just a really bright star..

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Trish - Glyndon MD — Thu, 21 Feb 2008 05:22:43 GMT

As an astrologer, it doesn't matter WHAT they call little Pluto. It still has a TREMENDOUS effect on our lives.....and possibly one of the most powerful.

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meow meow, planet earth — Thu, 21 Feb 2008 05:28:42 GMT

I have always thought that it was wrong to downgrade Pluto. Hopefully the Astrobiology dept. will see the interstellar light and reverse the aformentioned demotion of Pluto.

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Rob Seiders, West Reading, PA — Thu, 21 Feb 2008 05:39:50 GMT

i just love the fact that i am 26 years old, and, i learned about the "9" planets in our solar system. now i have a 5 year old daughter and 13 month old son and when it comes time for them to learn of our solar system and planets i am going to have to re-educate myself. why do we over analyze everything? next thing you will tell me is the south won, hitler was a diplomat and elvis is alive. how about we start worrying about the things that matter. EARTH?!?!? sorry... just like to vent about stupidity!

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JB, Kenmore, WA — Thu, 21 Feb 2008 05:56:12 GMT

I realize this story was probably dictated and typed out by someone other than the author, but "axly"? Did no editor read this, to correct to "actually"?

[Alan adds: Yeouch! I was rushed a bit with this item, and that abbreviation unfortunately slipped through. I also mistakenly referred to Sykes' organization as the "Planetary Research Institute" rather than the Planetary Science Institute. I've made correx for both mstks.]

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Tyrus Lytton, Athens Georgia — Thu, 21 Feb 2008 05:59:08 GMT

While being able to classify and organize things are in the realm of science- taxonomy has always been disputed in the animal world. How should things be organized? What latin phrasing should we use to designate this animal into this kingdom or that order. At a certain point the names are arbitrary. Lets just nip it in the bud and provide a full dull detailed analysis of the object instead of an abreviation. i.e. instead of Earth, we'll say "a spherical mass that is comprised mostly of water, with a surface area of..." Names are supposed to make things easier, so the only thing that is making things difficult are people who don't like what things are called. Calling a zebra a brazier doesn't change the fact that it has stripes. And if someday we discover more equine-esque animals with larger stripes then a zebra a zebra will still be called a zebra. These people should choose one way and go with it. I say if the IAU wants to mess around with renaming celestial bodies then they should organize them by how they are formed. As an interesting side, in the following I've repleaced plant with planet from the website, www.rbg.ca
"Communication about planets requires that individual planets be grouped into species, and in many diverse situations communication further requires the recognition of higher-level units of classification.

Communication also requires that planets have widely accepted and recognized scientific names that reflect their positions in the hierarchy of classification. Anyone with a special interest in a planet specifiction for any reason must be assured of the identity of the planets in question.

And, of course, preservation of planet diversity depends on taxonomy, because measures cannot be taken to preserve a specific planet until its existence is known, until it can be distinguished from other planets, and until it can be referred to by name".

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Rich Burke Flushing NY — Thu, 21 Feb 2008 06:52:15 GMT

Pluto and Charon should be reinstated as a double planet, Because it has been proven they both orbit each other. However, That being said if Pluto were brought into the inner part of our solar system it would warm up and grow a tail! Now what kind of behavior is that for a planet? That would just be embarresing

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Miya, Colorado — Thu, 21 Feb 2008 06:53:24 GMT

I like the traditional use of the 9 planets(if there are more, wonderful). They revolve around the sun and renaming planets because they're not technically rock will just confuse a lot of people. Even if they do change the names and classifications, I think people will just keep using the old ones.

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Brett — Thu, 21 Feb 2008 07:10:57 GMT

It seems simple to me. A planet is any round object whose primary orbital relationship is to it's star.

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Michael Robb, Sedona, AZ — Thu, 21 Feb 2008 07:44:46 GMT

Pluto was discovered while searching for a new "planet", found in the area predicted it became the ninth planet. Pluto and its moon Charon combined have only about 5% the mass of Mercury. Since Mercury is commonly considered a small planet, what does that make Pluto?

People have a strong response to Pluto's demotion from planet status, but how would we classify Pluto if discovered today? The first trans-Neptunian object? or nearest Kuiper belt body? Pluto may not even be the largest of these remote members of our solar system.

To the average person the IAU created an incomprehensible mess with the new definitions. Maybe Pluto should just be "grandfathered" in as a planet and the IAU can ignore it while coming up with the new definitions.

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Pluto Ambassador to IAU — Thu, 21 Feb 2008 07:46:36 GMT

I think Pluto should be considered a regular planet, get rid of these stupid categories like "dwarf planet."

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John Klein, Springfield Missouri — Thu, 21 Feb 2008 08:42:08 GMT

I have pondered upon the definition of a planet, the original definition is "wandering star" which is obsolete but has been adopted to new science fact. then three planets where added, Ceres was added in 1801 then dropped,Pluto was added then dropped. The current definition of a planet can never be black and white to modern science because of obvious reasons, I agree with the previous blog regarding planet "species". if it orbits a star its a planet, there are countless planets in our solar system, very different shapes, sizes, compositions(comets), lifespans(comets) and orbits. when we point new telescopes at the stars we are going to find millions of these, as well as unconceivable objects, one of a kind objects, that will have us scratching our heads. We shouldn't subject our time trying to categorize objects that blur between definitions originating from prehistoric references that where not understood at that time nor should we call an object one thing and not another. a new word should be given to a new definition of a planet. I think a new concept should be adopted for planetary systems, the ten largest bodies in any given star system should be given this definition, the ten largest moons around a planet another definition no matter the size, if it is so small it has no useful value it does not have to be given a formal name per vote, sizes 11 through 1000 another definition, and so on, brown dwarfs don't get any part of the sizing. brown dwarfs have the new moon definition for bodies orbiting it, and can have a definition for moon of a moon, brown dwarfs and other non nuclear bodies not orbiting a star are the replacement definitions for planets not orbiting stars. the new definitions can keep going, requires a little traditional sacrifice but will clear up the confusion when we need to reference 1 planet out of a million others. to close the book on the issue end the use of the term "planet" as we know it by giving back Pluto its planethood give Iris Planethood, give the 8 other planets catalog numbers like asteroids and everything else has, then you will have ten "planets" never add another planet to the Planethood, just start using the new defined words for the rest of the millions of bodies out there and these ten as well. the current species of worlds like comets, asteroids, ice Giants and many others can stay, but should be considered attributes to the new founded definitions.

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Daniel Carmona; Osaka, Japan — Thu, 21 Feb 2008 09:09:45 GMT

Are scientists and astronomers at the IAU truly so desperate to prove something ground-breaking within their own life times that they feel the need to start disproving something is what is by saying what it isn’t? How childish is that? Brian Hufe (Newark, DE), Byron Raum (Beverly Hills, CA), and Scott (???), as well as many others, give great definitions of a planet, which are widely accepted by many. Given those definitions, to say that Pluto and its moon Charon are only two hunks of rock that happen to be stuck in our suns gravitational pull smells of hypocrisy to me. That's like saying our coccyx is only the end of our spines and wasn't once the beginning of our tails. If it is possible that we once had tails, then maybe Pluto had a greater atmosphere eons go. There is clearly ice on the planet at the present, and when it nears the Sun, a thicker atmosphere of nitrogen, methane and carbon monoxide are apparent. This may not be my field of research, but all of the above sure sounds like characteristics of a planet to me. To proceed to adjust the definition of a word—or to basically bandy words about—just for the sole purpose of fluffing ones own ego and status in their respected field is poor research indeed. Poor Pluto…why don’t they leave him alone and pick on a planet their own size?

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John Martinsburg, WV. — Thu, 21 Feb 2008 09:11:48 GMT

A scientist is an entity that circles a central idea and clears its area of all common sense. Those entities who have not cleared their area of all common sense are "dwarf" scientists. Seems logical to me.

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Richard Boswell, Washington, D.C. — Thu, 21 Feb 2008 11:09:20 GMT

Given the criteria, does this mean that we can classify Rush Limbaugh as a "gas-giant"?

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Dale Bills, Carencro, Louisiana — Thu, 21 Feb 2008 11:13:23 GMT

It has to orbit a star to be a planet? Binary systems and systems with their gas giants close to their star will likely have ejected their rocky planets and smaller gas giants into interstellar space. There may be as many, or more, of these objects than planets orbiting a star. Talk about a hazard to navigation for starships and a really bad day for the Earth if we got hit. But they would still be planets, frozen to three degrees Kelvin, floating out there between the stars. Even gas giants would eventually, after billions of years, freeze solid with only a thin ocean of liquid helium on their surfaces. These would neither be giants, nor gaseous, yet have a composition like Jupiter. What would you call them? Dwarf Gas Giants? Popsicles?

The only workable definition would be a round object that achieved and maintains its roundness from gravity
AND has never sustained a thermonuclear reaction. This leaves out white dwarfs and neutron stars. They once sustained fusion until their fuel ran out. Black holes would never qualify because a singularity does not have roundness, it is a mathematical point.
The event horizon of a black hole is not a surface
(common mistake of non-scientists and even undergrad physics students).

This leaves Pluto as a planet and unfortunately there
could be thousands more out there in the Oort cloud or further out, bound to the sun. Children would still learn the traditional nine. What is important is they know there are many more after that, including Ceres and Vega in the asteroid belt. If they want they can learn more if they are interested in astronomy.

I am sure there are some whoppers out there beyond Pluto that are as large as the earth or bigger. They could sell the naming right to those to large corporations. Staples? Sears? Ford? NFL, anyone? Just kidding.

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Roger Kohn, Tucson, AZ — Thu, 21 Feb 2008 12:34:27 GMT

The debate about the definition of a planet is useful, the outcome of that debate less so. Regardless of what emerges from this meeting in Rio, someday it will be challenged, and rightly so. As others have stated, science is a process... and sometimes that process is messy.

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cyrano, Iraq, bagdad — Thu, 21 Feb 2008 12:45:11 GMT

I completely agree that we discuss these issues. But, since none of us in our lifetime will every see Pluto surface, nor will we (in our lifetime) visit Pluto or any of these planets, you have to wonder if these scientists have nothing better to do currently. If these scientist put this much effort into addressing more immediate concerns (polution, overpopullation, destruction of our environment, and possibly global warmth) we might have better solutions. I am very dissapointed that many of our so called brilliant minds waste their time doing this trivial task. It just proves a point further that we are heading down a road that is going nowhere. If the brightest minds in our world are not going to concentrate on important issues; then we truly are going down the road to our own extinction. The dinosaurs did not see their demise. We should just live it up, party, and at the end of the night it will be our children and future offspring who will pick up the check. Sad

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Scott Potter, Lexington, KY — Thu, 21 Feb 2008 13:13:02 GMT

This whole definition thing is really just mental masturbation. Simply look at the etymology. Planet comes from the Greek for "wanderer." This was all before anyone really knew how they moved. Given the apparent looping motion of mars as seen from the earth, the sky was populated only with fixed stars and wanderers. Basically, anything orbiting a star other than a satellite is a wanderer, and even more appropriately, rogue bodies orbiting nothing are wanderers, irrespective of mass and shape.

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Andy La Plata, MD — Thu, 21 Feb 2008 13:35:35 GMT

Why not do away with "planet" altogether? Why not just describe every "object" that orbits a star by its name (if it has one), physical characteristics (spherical, irregular, gaseous, rocky), the details of its orbit (ellipticity, mean distance from the star, inclination to the ecliptic, and etc.) and the presence or absence of moons? This could be used to describe any object orbiting any star. You don't need the word planet to talk about an orbiting body in a meaningful way. It may be convenient but it certainly isn't essential.

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ted spriggs, Orange, CA — Thu, 21 Feb 2008 13:37:06 GMT

I vote that Pluto be reinstated as a planet and that the definition of a planet include "roundness" which implies the somewhat uniform characteristics compatible with gravity induced form, etc. All the other known space objects have irregular shapes.

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Thomas Lee Elifritz — Thu, 21 Feb 2008 13:44:02 GMT

The 'Meghar Scale of Planetary Mass Classification' is already well established in the literature, and is well adapted to comparing extrasolar planets to solar system planets. I have added the lunar class planets (Moon) and the asteroid planets (Ceres), and further an ice moon class planet to the scale (Enceladus) :

http://www.astronomy-chat.net/astronomy/Planetary_Classification_Systems_739130.html

You can clearly see this scale in action here :

http://en.wikipedia.org/wiki/Image:Graph_showing_relative_masses_2.png

and I have blogged this extensively, as it is now widely accepted in the scientific community :

http://cosmic.lifeform.org/?p=166 (offline)

The 'sphericity' issue still applies here as well, and it extends well into, gas giants, super giants, brown dwarfs and stellar masses, measured in Jupiter masses.

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Ron, Pierre SD — Thu, 21 Feb 2008 14:20:28 GMT

The IAAU (International Amateur Astronomical Union) which Boast over half a million members world wide would like to denounce The IAU planet definition as Vague and Arbitrary.

The IAAU voted yesterday to denounce the definition with a unanimous decision, 4-0.
Membership includes any amateur that (1) owns a Telescope or pair of binoculars and
(2) Actually wants to be a member. Acceptance into the Union is free and automatic from The time the individual stats, 'Hey, I want to belong to the IAAU."

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Betty Agnew, Virginia Beach, VA — Thu, 21 Feb 2008 14:26:43 GMT

AAAAAAAAAH!! Does this mean I have to change the planet song I've known since kindergarden! I think Pluto is a planet. It's just small.

The next great planet debate

Doug Fingles, Warner Robins, GA — Thu, 21 Feb 2008 14:48:28 GMT

I agree with Brian and Brad; a planet should be in a primary orbit around a star. If it orbits another object that orbits a star, it is a moon, not a planet. The definition should be updated to be that precise, otherwise some yahoo will point out that everything in the solar system "orbits" the Sun in one fashion or another, and we'll be off to the debates once again.

The next great planet debate

Thought Shaman — Thu, 21 Feb 2008 15:44:49 GMT

Ah! another planet debate. Here is a link to one that is a year old: http://www.earthsky.org/blog/50966/who-else-wants-pluto-to-be-a-planet-again

I am repeating my last post on this topic from the above discussion. "Planet as a round body and *not* a moon" people might find it especially interesting.

---------------------------------------
Feb 17, 2007 02:31 PM #

Thought Shaman says:
Bob you are quite right in that there are two camps.

However, it is not the case that they are talking across each other. One camp has a typical case of what Stephen Colbert terms “truthiness.” They want to hold on to their positions regardless of what the facts are.

I disagree with your implication that it is the traditionalists that are comfortable with ambiguity. In fact, it is those who are willing to consider Pluto et al., to not be planets, who are attempting to look at the facts of the domain, and are comfortable with a not so precise “formulation” for classification (insofar as the “principles” are sound) who are being open.

It is sad that some people do not seem to understand their own principles for classification.

I have pointed out that hydrostatic equilibrium is simply a formulation for an object being sufficiently big, yet people keep complaining about it. The size criterion is a carry over from the traditional way of thinking.

The other point of dominance is also a carry over from the traditional way of thinking. The reason Titan and Ganymede are not considered planets is because Saturn and Jupiter respectively so dominate their orbits that they have captured the two smaller bodies and forced them into orbit around themselves.

Note that “orbits” is a transitive property. If Y orbits X, and if Z orbits Y, Z also orbits X.

Location obiviously matters regardless of size in traditional classification. If Titan and Ganymede were elsewhere in space they would likely be planets even in the traditional view.

Therefore, size and dominance are the two traditional criteria that form the basis for the classification of a planet.

All I ask is that people apply the classifier to the entire domain consistently.

It is inconsistent to reduce the domain to only those bodies that directly orbit the star(s) and then claim there is no concept of dominance. Especially since the concept of dominance was applied to reduce the domain by eliminating the satellites (moons) in the first place.

As far as the view of Pluto’s size being proposed as the cut-off, it is simply classifying by fiat, and is not good science. As I mentioned in a previous post, in science a better classification tends to supplant an earlier one with arbitrary formulations. Further, if we are using this view then we can equally well pick Mercury, or the much smaller Varuna.

The historical argument for Pluto being the cut-off doesn’t hold either simply because it is the historical “inaccuracy” of Pluto that is point people are trying to correct.

I agree with Bob that it may be possible to have two definitions, one colloquial and one scientific. However, this could be a little strange as we’d have to teach them both to the populace. I can imagine a quiz question on the number of planets being answerable both ways causing some mayhem.

The other approach is to simply designate that a planet is a cultural body of interest (from a scientific perspective, the absence of definition of planet will not affect the process of enquiry). In this case, we can simply vote as to which bodies we consider to be planets periodically, say every 5 years or so. Just imagine the fun people can have gathering votes for Pluto or poor little Varuna :).

Bob, I don’t think one has to be an astronomer or a member of the IAU to present views and thoughts. I thank you for yours and thanks to Magenta, Bruce, and others as well.

The next great planet debate

Dennis, Richmond VA — Thu, 21 Feb 2008 15:49:16 GMT

I agree with the roundness, but I disagree with the orbit. If Mars were to be thrown out of it's orbit and leave the solar system, would it cease being a planet? What if we find an object the size and composition of Earth in orbit around a gas giant? Not a planet? And if the gas giant then ignites to become a small star, the Earth sized moon then becomes a planet? I don't like names that can change when the object named does not. A planet is something big enough to be round, but not so big that it becomes a star. In between we have several sizes of giant planets, both gas and ice, we have terrestrial planets, small planets without atmospheres, and dwarf planets. Things that are almost planets but not quite, or are in dispute might be called planetoids. Planets that orbit other planets are also moons. Planets that have not yet cleared out their orbit are called planets that have not yet cleared out their orbit.

The next great planet debate

Dennis, Richmond VA — Thu, 21 Feb 2008 15:56:13 GMT

Oh, and one more thing, if you believe Pluto is a planet, then Eris must also be one, since it is bigger than Pluto. So however you think about it, there are not NINE. Ten. Eris would make ten planets. It's what started the whole thing in the first place.

The next great planet debate

Greg, Monroe, Michigan — Thu, 21 Feb 2008 16:01:51 GMT

Personally I think that to place this much emphasis on the definition of a planet is rather moot. Most of the laypeople especially those that were raised in the 80's and 90's are going to call Pluto a planet. I personally am not going to waste the time to make the distinction that Pluto is a dwarf planet. If it doesn't affect the well being of man kind we really are just wasting a huge amount of time and energy.

The next great planet debate

Ross McLaurin — Thu, 21 Feb 2008 16:02:40 GMT

Pluto is a planet! I shall not lie to my grandchildren. Why is it, "O Great OZ of science", that you can discover new planets within our solar system, within the sientific definition of a planet, get all excited about it and then, "BANG" simply discard time accepted parameters of the definition.
Guess this explains THE BIG BANG theory.
Get a life or better yet, don't!

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Ross McLaurin — Thu, 21 Feb 2008 16:04:37 GMT

PLANET PLUTO.........FOREVER!

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Allan, Auckland, New Zealand — Thu, 21 Feb 2008 16:36:23 GMT

Keep science consistent! Use the 7-level scientific nomenclature standards they use for biology (..., Genus, Species.) to describe all heavenly bodies.

The next great planet debate

Janitor, San Diego — Thu, 21 Feb 2008 16:59:01 GMT

on a response to LPClark, If we do not define the universe, then we are lost in the universe, ill give you another example, If we dont define LPClark then LPClark doesent exist... LOL. <-Sarcasm. By the way defining planets, stars, possible alien lifeforms as well as earthly animals and diseases has and will continue to help our world and us in everyway for the rest of time. [...] simply by looking at this messege you are judging/defining it, We certainly do not need you to define it for us.

The next great planet debate

Brian Shaw, Kalamazoo, Michigan — Thu, 21 Feb 2008 17:01:42 GMT

Who's more "self-absorbed:" the "eggheads" who get together to consider informed arguments, or people who insist Pluto is a planet--even though they've never actually seen it nor know much about it--just because they learned in fourth grade that it was?

If it's "stupid" to reconsider old ideas, I guess we'd better get rid of ALL science--come to think of it, there are plenty of people in this country (including its president) who would probably like that.

The next great planet debate

OneVoice, Frederick, MD — Thu, 21 Feb 2008 17:06:08 GMT

I don't understand the dynamicists position. If the influence a body causes is part of the reason to call it a planet then shouldn't the influence Pluto has on its one...er I mean 3 moons be sufficient to call it a planet. While we're at it doesn't the definition of a moon mean that it orbits a planet. What do we call Charon and her 2 recently discovered siblings?

The next great planet debate

Wayne, Alamogordo, NM — Thu, 21 Feb 2008 17:15:31 GMT

I agree with Davis. Since the IAU has declared themselves keepers of astronomical definitions, let's put the burden of maintaining their definitions directly on their shoulders. It's up to the scientific community to as a whole to force the IAU to adjust definitions, as needed, so that some kind of consensus can be reached, especially when the IAU decisions are in the minority. And for those of you who think precisely defining something is a wasted effort, remember, science is about measurements, and accurate measurements can't be made without accurate definitions of what is being measured and how it is being measured.

The next great planet debate

Tom Carter — Thu, 21 Feb 2008 17:23:18 GMT

Planet or not pluto's not going to up and disappear just because we reclassify it. Quoting the "9 planets" to children certainly won't do them any harm.

Trying to classify bodies in space is always tricky because unlike biology the gross distinction of objects in the cosmos is pretty clearly in 3 catagories: Things undergoing fusion, Things not undergoing fusion that were not at some point undergoing fusion, Things that were formerly undergoing fusion. Everything from space dust to Gas Giants to frozen canned monkeys comes under catagory 2. Besides, when we finally get a really good look at annother solar system are we really going to bicker about how many planets it has or are we going to study every single thing that comes infront of our lenses?

The next great planet debate

City of San Diego — Thu, 21 Feb 2008 17:23:22 GMT

"All of you are so full of yourselves it is amazing you can get from room to room or that two of you can fit in the same room. We are on a tiny ball spinning in a vast universe. We are microscopic in comparison to the size of the universe, and you have the unmitigated gall to "decide" what should be called a planet? Your collective egos are astounding and you should all be ashamed of yourselves. We certainly do not need you to define the universe for us."
LPClark, Englwood Cliffs NJ (Sent Wednesday, February 20, 2008 4:36 PM)

I take the following as an attack on a comment of another.

PLEASE READ: All comments must be approved before appearing in the thread; time and space constraints prevent all comments from appearing. We will only approve comments that are directly related to the blog, use appropriate language and are not attacking the comments of others.

[Alan adds: Yes, it's often a judgment call about what separates permitted debate from an impermissible attack, and sometimes I have to question my own judgment on this. I'm usually less comfortable with comments that go after one person in particular, especially comments directed at the person rather than the information put out by that person ... I'm also very uncomfortable about certain words, such as "morons," etc. I'm more comfortable with comments that address a point of view (e.g., talking about evolution's defenders or Darwin's detractors rather than a specific person, particularly a specific poster). But again, it's a judgment call, and I apologize for any cases in which a person feels unduly attacked.

The next great planet debate

Mickey, Orlando, FL — Thu, 21 Feb 2008 17:26:01 GMT

I thought Pluto was my dog?

The next great planet debate

Robert Murdock — Thu, 21 Feb 2008 17:29:51 GMT

I believe if an object is round it should be classifed as a planet, whether or not it is also a moon. To simplify matters though why not just call everything outside the orbit of Mars as either an asteroid or comet, that is if it is predominately rock it's an asteroid, if it's predominately gas or ice it,s a comet.

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David Lincoln, Gaithersburg, Maryland. — Thu, 21 Feb 2008 17:40:52 GMT

I agree with the 'gravity determined shape' definition for planets. As already stated in the blog, it recognizes a dichotomy which appears to be quite fundamental, that between the round objects and the irregulars. This would provide a useful framework for solar system studies. For those who don't want to use it, that's ok too.

The next great planet debate

Mathew, Bellevue, WA — Thu, 21 Feb 2008 17:45:39 GMT

For those of you that say Pluto is a planet, then there are millions more just like it in the Kuiper belt and Oort cloud. That being said, it is my belief that the definition of a planet should include 2 things:
1) That it was formed by accretion during the early stage of the solar system.
2) That it orbits the sun along the ecliptic

This would solidify 8 planets in our solar system and disclude and captured objects (one could argue that planets could be captured by a solar system, but it is my belief that those should be classified seperately)

The reason that this is an important topis is that we can move forward with a stable, accepted definition to progress in the area of planetary science.

The next great planet debate

KConod — Thu, 21 Feb 2008 17:53:21 GMT

Problem with this alternative definition is that the number of planets in the solar system would drop to zero! The Earth and just about every planet I can think of is not a perfect sphere - its an oblate spheroid - so how round is round? I don't think that definition solves anything at all!

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Eric, Concord NH — Thu, 21 Feb 2008 18:01:58 GMT

Larger than the largest moon not only continues to oust Pluto (as any planet definition should), but it also ousts Mercury which is smaller than Ganymede.
I like the definition above that planets should orbit at or near the plane of formation (aka ecliptic plane).
This keeps comets that have not approached close enough to the sun (like Pluto) out of the mix.
I find it funny how many people ask the question "Who are scientists to define scientific terms?" Well, ummm, they're scientists. Scientific terms define their occupation. If anyone is qualified, a scientist or group thereof, should get the nod.
Doctors don't use a public consensus on what they call th next virus. Why should scientists?

BTW, tradition has never been used to "keep" a name in astronomy. If it were, The Andromeda Galaxy would still be called Andromeda Nebula...as were the Large and Small Megallanic Clouds or any other galaxy discovered before the 1900's.

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Joe, Minneapolis, MN — Thu, 21 Feb 2008 18:08:13 GMT

I agree with the decision to add additional categories to the existing definition of planets. Considering the fact that many of the extra-solar planets discovered have different compositions, densities, and sizes, we cannot just restrict the definition of a planet to a mere "It is round and orbits a star."

The next great planet debate

Adam, New Jersey — Thu, 21 Feb 2008 18:09:38 GMT

I have to admit, I found Mr. Daniel Fischer comments rather insulting and his article to be very biased. I spent a year living in his neck of the woods, and regularly keep in touch with the friends that I made in both Germany and Denmark. Several of them being the american equivalent of Elementary school teachers. When the planet debate came up in 2006, and pluto was demoted to dwarf status many of them said (and still are) teaching that there are 9 planets in the solar system. It is very obviouse to me that Mr. Fischer did not do his homework on this.
And by the way Mr. Fischer, it wasn't just American Scientists who were vocal, it was also Japanese, English, GERMAN, and Canadian. Before you start flapping your gums, or your fingers in this case, get your facts right and actually interview people. I don't appreciate when journalist doesn't get their facts right.

The next great planet debate

David Crosby Burns, OR — Thu, 21 Feb 2008 18:23:17 GMT

Funny thing is that science tends to be re-written every so often which makes the current theory just one more waiting to be shelved as obsolete. Why can't they do something productive, like, save the planet? They act like they actually were here during the big bang. Doe's to much education make one stupid?

The next great planet debate

BH, Studio City, CA — Thu, 21 Feb 2008 18:33:14 GMT

I'd have to agree with a previous poster: instead of "demoting" or "removing" a planet, use a classification system similar to that used on Star Trek.
http://memory-alpha.org/en/wiki/Planetary_classification

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Tiffany Allen, Kingston, Ontario — Thu, 21 Feb 2008 18:52:02 GMT

I think Pluto is a planet, I think Jupiter is a planet. End of story. Why there needs to be a great debate about it is beyond me.

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Dick Thurstan — Thu, 21 Feb 2008 19:02:42 GMT

Guys - the solution is so simple. Seeing is believing, right? So Mr NASA, design a craft to take these armchair space wisecrackers on a fact finding mission to observe these terestial bodies. In the meantime leave the textbooks as they are. By the time they come back (so long as the US Navy doesnt identify them as a falling defunct satellite)it will be 30 years on so who cares?

The next great planet debate

Buu Truong, Blaine, MN — Thu, 21 Feb 2008 19:20:09 GMT

I don't know much but here is my two cents. Long ago, I learned that there are 108 elements on earth. Now, there are 118 and more are defined everyday. Those latest have funny names Uuq, Uup, Uuh, Uus, Uuo. They me be synthesized or may only be exist for a millioned of a second. So what? We call that science, and progress. More and more knowledges are found everyday. Certainly, God knows the rules and we don't have the capacity yet to know it all. Like two boys in the same household, each one always think he is more right than the other. Let's ask the people who were kids in the early 20th century to ask them if they mind at all when the 9th planet Pluto was found. Convention calls us to believe it's 9. There are more discoveries, certainly for years to come. I like categories better, and leave them wide open. WHen we find another one, put them in that category. Don't be too concern much about number.

The next great planet debate

Dennis, Richmond VA — Thu, 21 Feb 2008 20:35:39 GMT

Eris should be the 11th planet... (Yes, we should count Ceres as a planet)

Dwarf Planets are Planets too!

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Wayne — Thu, 21 Feb 2008 21:33:25 GMT

How about this. If it's round and floating in space, it's a planet. If it's exploding in place, a star. Lumpy and just an unpleasant place to be, call it an asteroid or whatever. Just let it go for Pete's sake...there are bigger, better things to do with your minds...

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Chris House — Thu, 21 Feb 2008 23:28:06 GMT

Oh my, we're wading back into this debate again... well I suppose it's inevitable that we will periodically rehash this until a real workable one (i.e. one that will keep working as we find more and more extrasolar bodies and other minor bodies in our system).

I've read practically every sort of idea out there, and some make a lot of sense in some areas but leave gaping voids in others.

The only type I believe that would be able to take account for a variety of scenarios would be one similar to that used in the 'Star Trek' series.

They seem to use the term planet to refer to most things that we would think of as 'round balls', but instead of assigning some long and confusing name to each group, each major type is given a letter category.

Earth is considered a 'class M planet'. Mars and Venus without breathable atmospheres would be tucked into a different class... although if terraformed, their class designation would shift over time to reflect the increased habitability of the world.

Smaller bodies are also assigned categories, but they're not referred to as 'planets'... moon, asteroid and comets have all been shown - and as those are all perfectly good names as is, no need to change.

Obvoiusly even the Star Trek categories were limited to known or theorized types of stellar bodies and smaller objects - although of course we can add in new classes/types of objects as they are discovered.

If we think of 'Planet' with a capital P, then I don't think Pluto fits... our own moon Luna is considerably larger. Even though Pluto currently orbits the sun as an independent object, who really knows how long the 'current' orbit has been stable.

It could be a great joke of cosmic irony, if it was later learned that Pluto didn't even form in our solar system - but that its tiny moon Charon did. This could put us in the odd position of promoting Charon to full planethood and demoting Pluto to being simply a temporary/guest body in our system.

I don't care whether they call Pluto a planet once it's all said and done - however the IAU needs to being the process of setting up a specific series of categories for planets and other bodies; from the smallest to the largest.

Each of those categories also should have subcategories that indicate surface/atmospheric conditions or chemical composition.

With the advances we've see in interferometry (connecting a series of telescopes together to increase imaging power), solar spectroscopy studies (looking for difference in spectrum as planet transits in front of the sun), and with the upcoming satellite based observatories, we will be finding not just 'hot Jupiters' around other worlds soon - but rocky worlds with atmospheres.

It would be nice to have a place to sort them agreed on and ready to go well before we get the inevitable surge of hundreds of newly discovered terrestrial worlds to try to deal with (as far as data goes).

The next great planet debate

M_planets, Flintridge, CA — Fri, 22 Feb 2008 05:24:02 GMT

I agree; Pluto should be "grandfathered" in as a planet. The darn thing has 3 moons ! and in a very orderly system. It behaves just like a planet. On this basis, Sedna, Quaoar, and EL61 should also be planets. Pluto will always be the 9th planet.
..Support Pluto's planethood:
http://www.tritonfun.com/custom.em?pid=547283

Oh, and let's not forget Eris in this list, as well
(or should we say, "Xena"...)

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Jerry Jordan,Ft. Worth ,Tx. — Sat, 23 Feb 2008 19:07:39 GMT

If mars were to be pulled into an orbit around Jupiter,would it then be just a moon?
If the moon orbited mercury then would they be like Pluto and Charon?
I think there are many different types of planets and should be listed in different categories.
As they discover more,they will see that there are many different sizes and makeups.

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JC, Fairbanks, AK — Mon, 25 Feb 2008 04:19:24 GMT

Tradition is fine as long as it isn't a ball and chain around one's leg. The best example I can think of is many people's insistence on use of the English sysem of units (pounds, feet, hectares per fortnight . . . ). This is bad enough in everyday life, but is unacceptable in scientific fields (students in classes I have taught lose serious points on any work not turned in in metric units). This definition of a planet business is another good example. Here's a simple fact: whatever some people may want to call it, in scientific circles Pluto is not, and is highly unlikely to be, considered I planet. Period.

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JC, Fairbanks, AK — Mon, 25 Feb 2008 04:50:14 GMT

Also, keep in mind that it makes no sense to call Pluto a planet, and not the rest of the Kuiper Belt objects. Do we really want to have *tens of thousands* of 'planets'?

Ultimately it doesn't matter what is said here and elsewhere. The IAU is GOING to define the term 'planet', and that's the end of it. Doen't matter one whit who likes it or not.

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Forest Roberts, Kettering, Ohio — Tue, 26 Feb 2008 16:55:51 GMT

A massive Spherical body orbiting a star whose orbit remains constant and within a mimimal tolerance, and remaining equal distant to the star due to it's gravitational attraction to the star, should be concidered a planet. Size and/or makeup of such a body should not negate it's status unless critically acted upon by a larger massive body altering it's current course.

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Tina Chen — Fri, 29 Feb 2008 01:03:08 GMT

The next great planet debate

Rodney Sibert, Trussville, Alabama — Thu, 06 Mar 2008 05:07:50 GMT

Guys, guys, guys...

Look, a planet does not have a tail when it orbits a star correct?

Think about a comet for a moment... It has a tail, it's not a planet.
I don't care it the comet is a perfect sphere. It's still not a planet.
I don't care if the comet is the size of Pluto, it's still not a planet.

Are you still with me?

If you were to move Pluto and Charon closer to the Sun (like maybe the distance of Earth) both Pluto and Charon would have a tail, I would think probably a combined tail.
Therefore, Pluto and Charon, and Eris, and Ceres, and all the other larger bodies that are in the ort cloud that we haven't discovered yet, are not planets.

Why do we even need to define a planet?
I almost wrote good question. Bad question.
Why define anything. Why not just move around aimlessly and give things our own name that we want. Then we could each have our own language. And we could each teach our kids what we think is correct. And we could evolve into superior humans with the complete understanding of how to set the clocks on our VCRs. Just see the instruction manual, it's in 6,679,493,900 different languages.

Come on people, your smart enough to log onto the internet, this shouldn't be that difficult.

I still love all of you though.

Peace...

:-)

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Rodney Sibert, Trussville, Alabama — Thu, 06 Mar 2008 07:33:56 GMT

Jupiter -
Ok, there's a good one. It could be considered a failed star. Basically it is, with other planets (moons) orbiting it. Kinda like another solar system. You take Ganymede out of Jupiters orbit, put it between the Earth and Mars, and it's now a planet.

We do need a clear definition.

Again to Pluto-

Just because we hurried to classify it a planet when we found it, does not mean we were correct.
Just because we used to be allowed to roam around in the back seat while Mom and Dad drove us somewhere doesn't make it right (By the way, I am against ticketing for not wearing a seatbelt. All 47 of my tickets I paid, and I'm still passionately against it).

If your going to teach something you need to teach updated material. Otherwise, everyone is arguing that they are correct cause that's what they learned.

Example - A day is 24 hours.
A day is not exactly 24 hours.
A day is 23 hours, 56 minutes, and 4.1 seconds.

Yes, it matters.

:-)

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Doc — Mon, 24 Mar 2008 18:14:24 GMT

As a teacher, I told one of my classes that Pluto was no longer a planet. One immediately asked: "Is it missing?" My bad grammar, I suppose. Historically Pluto has been a planet, and tradition says it still should be - let it be the exception to the rule because of its history.

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A Rae, Scotland — Fri, 28 Mar 2008 00:55:59 GMT

I would put forward a somewhat different classification. Taking the galaxy as a whole I would classify each spherical body according to its orbit and not so much on its physical characteristics, most of which are dependent on mass and form a continuum anyway. For example where do you draw the line between Brown Dwarfs and Giant planets. There are always going to be grey areas. Whereas what any particular body orbits is pretty straightforward:

1) Primary objects orbit the galactic core - stars, white dwarfs, pulsars, rogue planets etc

2) Secondary objects orbit a primary object e.g. Jupiter, Ceres, Sirius B, smaller stars in binary systems etc

3) Tertiary objects orbit a secondary object e.g. the Moon, Io, Titan etc

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JC, Fairbanks, AK — Thu, 15 May 2008 22:35:43 GMT

Yes Rodney of AL, that will soon be up to open debate as well. Things not much bigger than Jupiter are being classified as 'brown dwarf' stars nowdays.... But I think people are getting way to exercised about the whole thing.

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Siobhan, Streator, IL — Fri, 08 Aug 2008 13:55:52 GMT

I don't agree with what the IAU came up with for their definition of a planet. Another problem that no one seems to be addressing is the fact that they don't apply their definition evenly amongst all the "planets". The only planet they excluded was Pluto, when in fact, if you go by their own definition- half the planets in our solar system should be excluded.....

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Laurel Kornfeld, Highland Park, NJ — Wed, 27 Aug 2008 18:15:13 GMT

I attended the Great Planet Debate and personally believe Sykes' definition makes far more sense than the IAU's definition. The latter defines objects solely by where they are while ignoring what they are and makes no linguistic sense by saying dwarf planets are not planets at all. Changing this one statement would go a long way toward incorporating both dynamics and geophysical properties in defining the term planet. Why is the IAU so determined to keep the number of planets in our solar system artificially small? The discovery of Eris doesn't mean Pluto and Eris aren't planets; it means there is yet a new subcategory of planets--the ice dwarves--for which we have not previously accounted. The best idea is to keep the term planet broad and then use subcategories to distinguish types of planets, ie, terrestrial planets, gas giants, ice giants, dwarf planets, super Earths, hot Jupiters, etc. with many more likely to come.

Also significant is that most IAU members are not planetary scientists while most planetary scientists are not members of the IAU. Maybe we need a new organization of scientists who study planets to do a better job in crafting a planet definition.

Daniel Fischer is not correct when he says the IAU definition is now being accepted and taught in every country but the US. This is a straw man argument intended to discredit those who oppose the IAU decision by arguing their views are based on nationality, namely being American. That is absolutely not true. Astronomy educators in many countries have reported resistance to the IAU definition. And there is a case to be made that the initial demotion of Pluto was motivated by anti-American sentiment among European astronomers.