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Thomas Ashby, Calgary — Tue, 12 Aug 2008 15:30:42 GMT

I sure agreee with the roundness property. Instead of minor planets, why not just class or type 1,2,3 planets. A minimum requirement for roundness would mean that the object has experienced the same planet building process as any other planet. Just because accretion ceased much earlier than others shouldn't take away from holding planet status.

I remember as a young kid seeing representations of ceres in space books and thinking, "hey that looks like a planet but they call it an asteroid."

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Eric Smith, London, Ontario Canada — Tue, 12 Aug 2008 15:32:55 GMT

"clear the neighborhood around its orbit,"

Technically, this characteristic disqualifies Earth from the definition does it not? Shouldn't we at least have a set of characteristic that Earth falls within?

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Michael Mealling, Atlanta, GA — Tue, 12 Aug 2008 15:33:47 GMT

Here's another way of looking at it: Anything that orbits a star that hasn't undergone stellar ignition is a planet. Planets are classified by mass only. Each class begins at the midpoint between classes :

milliplanet class: Pluto,Ceres (.0021)
centiplanet class: Mercury at .055
deciplanet class: Mars at .107
planet class: Earth (1), Venus (.6)
dekaplanet class: Neptune (17.147)
hectoplanet class: Saturn & Jupiter
kiloplanet class: Upsilon Andromedae d (1,248)

The brown dwarf limit is 4,131 planets, or 4.1 kiloplanets.

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Tim Rommes, Washington, UT — Tue, 12 Aug 2008 15:36:03 GMT

Are there plans for a podcast or some such? Better quality, rewind and review, listen when I have time available.

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Ian McGuigan — Tue, 12 Aug 2008 15:43:39 GMT

We should be basing this on Mass and not on Roundness or "clearing space" or other factors. A low point for Mass would eliminate the majority of these issues. While it may mean that some Moons become planets, if a moon had enough mass to be a planet but got captured by a gas giant then it should still be considered a planet.

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Josh Levin, Marlton, NJ — Tue, 12 Aug 2008 15:57:32 GMT

I would like to comment on the concept of "double planets". I'm raising a bunch of questions, hoping that the other bloggers will debate the answers.

The center of gravity of the Earth-Moon system is almost 1000 miles below the surface of the Earth, so Moon is definitely a satellite of the Earth.

Wikipedia states "The center of mass (barycenter) of the Pluto-Charon system lies outside either body." This implies that Pluto and Charon form a double system, being "dual dwarf planets". Note that the other two satellites, Nix and Hydra, orbit around the Pluto-Charon system.

Now, consider the Sun-Jupiter system. The center of gravity is actually above the visible "surface" of the Sun. Again, from Wikipedia, "Jupiter is 2.5 times more massive than all the other planets in our Solar System combined — this is so massive that its barycenter with the Sun actually lies above the Sun's surface . . . ." (A possible exception to this statement is that both bodies are gas bodies. The Sun has no solid surface, and Jupiter's, if it exists, is deep below the visible surface. How do you define the surface of a gas body, when the gas simply becomes less and less dense as you move away from the center of the body? Conventionally, we use the "visible" surface, which is what we can see within the spectrum that our eyes happen to be sensitive to.)

Also note that Mercury, Venus, Earth, Mars, and numerous asteroids orbit the Sun within Jupiter's orbit. Are then these bodies "satellites" of the Sun, while the outer planets are "satellites" of the Sun-Jupiter system?

Let the debates begin!

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Mike R. in Reston, VA — Tue, 12 Aug 2008 16:09:17 GMT

A simple definition was proposed 2 years ago and rejected. It still seems to me to be the best.

A Planet is a round body in an independant orbit around the sun.

A moon is a body (round or irregular) orbiting a round object (a Planet) in orbit around the sun.

An asteroid is an irregular body in orbit around the sun.

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Brad, Eau Claire, WI — Tue, 12 Aug 2008 17:00:56 GMT

GO PLUTO-HUGGERS! When I read of the demotion of Pluto (and consequently) the exclusion of Eris, Ceres, Charon and others, I thought how boring the IAU just made our view of the solar system. I like the idea of having exotic components - double planets, 12 or more, etc. It adds a spice to the system and makes us look at it with fresh eyes instead of dulling them down.

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Brian Hufe, Newark DE — Tue, 12 Aug 2008 17:18:06 GMT

Planet should be defined as something round that orbits a star. That's how common knowledge has basically defined it. The star part is important because it separates moons from planets. The round part is important because it separates asteroids from planets. The "clearing the neighborhood" part of the existing definition is pretty arbitrary because it means you are defining an object based on its surroundings. Not to mention, just how "clear" does the neighborhood have to be? I think the definition should be worded such that the object only had to be under hydrostatic equilibrium at some point in time. If you take a big chunk out of a planet, it becomes a planet and a chunk of a planet, not a completely new thing. Unless of course the planet shatters into tons of tiny pieces.

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Dave Mosher, New York, NY — Tue, 12 Aug 2008 17:18:42 GMT

Great post Alan.
I just chatted with Tyson today, and he told me his basic schtick is this: Stuff in our solar system - and now other solar systems - needs a biology-like calssification system (you know, kingdom phylum class order family genus species). He says we're learning way too much about the universe to stick with an outdated system that could limit the way scientists think. We need something more... well, scientific!
Suffice to say I'm curious to see how this thing evolves :)

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Derek Meche — Tue, 12 Aug 2008 17:48:57 GMT

I have a suggestion for the definition of a planet. If it is round, orbits the sun independent of being a partner with a larger body, and has a minimum circumference equal to or greater than Pluto, it is a planet.

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g rimkus — Tue, 12 Aug 2008 17:49:19 GMT

a solar system will have planets orbiting a sun at calculated distances based on the mass of that sun.
The planets are like energy levels of protons of different atoms having specific orbitals. The confiruration of each solar system then is different because of different opposing masses of each planet & its distance of a given mass of an opposing sun. In summary ..each planet has a specific space to be filled like a open puzzel piece.

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Plutocrat, Roswell, N.M. — Tue, 12 Aug 2008 17:50:05 GMT

Pluto is a planet. It has been for over half a century and should remain so. The new wave of planetary chauvinism is ridiculous. Hey, you guys, get back to work looking for life on other PLANETS and leave Pluto alone. Go pick on someone your own size.

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vanderghast — Tue, 12 Aug 2008 17:50:56 GMT

The moon is round, so will it be a planet too?

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S.B. Stein E.B. NJ — Tue, 12 Aug 2008 18:03:41 GMT

I would have to say that Pluto should be considered a full planet. It is mainly for historical reason; I know that I grew up believing that Pluto is a planet.

As for something more scientific; I would have to say that something that has an orbit around the sun and a good chance of having an atmosphere should be (but not always) be a planet. If a body also has satelites in orbit around it, that should also be a consideration.

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Tom Hauer, Post Falls, Idaho — Tue, 12 Aug 2008 18:05:03 GMT

What a waste of time! I hope my tax dollars aren't being funnelled into this "understanding of why we think the way we do". Too many scientists enjoy aguing for arguemnts sake.

Why not have a spectrum of definitions for 'orbiting bodies'? Sort of like stars' H/R diagram? Then you could have representative examples along the way.

We don't need to have specific definitions until space lawyers eventually get involved (and they will), to decide if 'planets' or 'plotinos' get government aid.

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Shuntrell L. Surry, Uijeongbucity, South Korea — Tue, 12 Aug 2008 18:10:18 GMT

Hey though little guys out have just as much of a right to be a planet. people think that they have to be a just the right size or clear it's orbit. I say just add them all as planets even the newly found ones. It would be truely great to have a duo planetary system of our own and new world to study and make books about them. We want to know whats is in our solar family.

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Rick — Tue, 12 Aug 2008 18:13:10 GMT

From the article: Are 'planets' passé?

Yes, the concept of classifying every bit of rock in the system is. Just refer to them by their common name. After all, does anyone care how many cities there are in the world and categorize them? No, they don't. Just differentiate them by name and be done with it.

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Brad, St Louis MO — Tue, 12 Aug 2008 18:50:34 GMT

I think that the problem is being looked at in the wrong light, and in many ways agree with Tyson. The term "planet" may well simply be to simplistic to continue in scientific parlance. My own field is archaeology, and calling something a planet is akin to calling something a pot or a lithic. In the end, it just doesn't tell you much about the object.

Orbital objects need a classification scheme which embodies whether they orbit the sun or another orbital object, their mass, roundness, and composition. Such a classification scheme would be useful for science. As for the term planet, I prefer to call them the "Classic Planets" which are the nine historically identified planets. Useful for the elementary school classroom, but not for scientific study.

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Alan Stern — Tue, 12 Aug 2008 19:48:29 GMT

Interesting that Neil and other defenders of the IAU definition have, under severe technical criticism by planetary scientists, retreated to the stance that well, 'definitions don't matter' anyway. It's telling.

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KSW, Newport News, VA — Tue, 12 Aug 2008 20:56:16 GMT

I still think that Pluto is a planet. It is spherical and orbits the sun. Right there, it meets the first two criteria for gain planet status. The third says that it is a dominant in that part of space. People site the fact that Pluto comes within the orbit of Neptune. Others debate about its closeness to Charon. First, it only spends a brief time within Neptune's orbit. So 99 % of the time or so, it is a planent. A very small pecntage of the time it is not. I would say the majority of the time it is a planet so it has earned the right to be called a planet. For those, people who argue about Charon relationship to Pluto which keeps it from being a planet, I would say that people who call both a double planet would describe this relationship. Again, Pluto reverts to its planet status. I would like the IAU to consider this and the upcoming conference to work to reinstate Pluto as a planet.

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Ryan, Rochester, NY — Tue, 12 Aug 2008 22:03:10 GMT

I don't see why astronomers are afraid to rewrite the textbooks. We, as a species, have only been aware of 9 planets in our solar system for so long that when we started to discover these new elusive worlds, astronomers didnt know how to change. "We can't add new planets to our model, so we need to take the oddball (Pluto) away, so we dont have to add new planets." Hey, I wish we had 100 planets in our solar system.

I'm not sure who it was that suggested a new way of looking at things. Some scientist type. I believe he had three calssifications. Rocky planets, Gas giants, and Ice worlds. Please do not quote me on the terminology. However, I think this sytem is simple and effective. It will account for all planets that we discover in this solar system and the next.

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William Hanson, Carlisle, PA — Tue, 12 Aug 2008 22:41:56 GMT

I agree most closely with the definition: "A planet is a round object (in hydrostatic equilibrium) orbiting a star." although I would suggest it be modified to "A planet is a spheroid or oblate spheroid in hydrostatic equilibrum." One of the problems with this definition being so concise is that a planet which is very hot could form a highly oplate spheroid much thinner at the poles but still be in hydrostatic equilibrum - ref Saturn moon Iapetus.

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Laurel Kornfeld — Tue, 12 Aug 2008 22:54:36 GMT

I plan to personally attend the entire conference--I'm leaving tomorrow--and the first thing for which I want to commend the organizers is opening this conference to the public. This shows an interest in hearing public concerns and valuing input from multiple sources, something not shown by the IAU in its decision process.

I agree with Sykes that planet should remain a broad term for objects in hydrostatic equilibrium that orbit stars (or once orbited stars but have since been ejected from those orbits, such as rogue planets). And I think astronomers should welcome rather than ridicule public sentiment over Pluto. If people feel strongly, that means they are interested and paying attention. Don't astronomers want people to be excited by their field as opposed to apathetic? Interest in even one object or aspect can spark broader interest in astronomy as a whole.

As we discover more objects and more diverse ones in this solar system and others, we should be keeping the term planet as broad as possible to incorporate what may end up being many new categories. We can distinguish types of planets under subcategories such as terrestrial planets, gas giants, ice giants, dwarf planets, hot Jupiters, super Earths, etc. Moons in a state of hydrostatic equilibrium could be classified as secondary planets, as they were during the 19th century.

We know that in 2015, only seven years from now, we will receive a wealth of information on both Ceres and Pluto from the Dawn and New Horizons missions. Knowing this new data is coming, we should leave the debate open. There is nothing wrong with teaching children that there are multiple schools of thought on an issue, that different people can look at the same facts and come up with different interpretations. That is a lesson in and of itself.

I will be blogging about the Great Planet Debate from my web site at http://laurele.livejournal.com

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Ray Hernandez — Tue, 12 Aug 2008 22:59:08 GMT

as humans we make things a bit difficult sometimes. easiest way to see if pluto is a planet is to see what constitutes a planet. say if there are 10 things that we look at to make a body a planet, then that is that. pluto was a planet. what changed that? also we are taking ourselves too seriously here. now say, pluto gets hit by a monstrous body, gets cut in half, what will it be classified then.

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Steven F. Durst, Bayard,WV — Tue, 12 Aug 2008 23:01:44 GMT

Nothing new from me. I have always thought that the IAU are a buch of dimwits for even bringing up the issue. Planet....all the objects in orbit around this star are still and will remain an object in orbit around this star. Even if the IAU says otherwise.
as we are more able to find other planets in orbit around our star why wouldn't they be planets? To say otherwise is just,well, stupid. To say that the first 8 planets found with crude telescopes are the only objects to be classiffied as planets is like saying the old world was flat until the "New" world was found. But that the new world doesn't actualy count when compared to the old.
Sound stupid? Well it is stupid of the IAU to ignore the facts that planet sized objects with moons orbiting them are out there orbiting our star. Pluto and Eris and more yet discovered are still planets.
I read or heard a story where some of these outter ice planets have more heat than they should??? Should by what? By what we know of planets? These brains at the IAU can't even understand what a planet is, so what makes them think they know anything about them.
Our technology has come a long way since the dark ages but the mentality of experts hasn't changed one bit.

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Wayne — Tue, 12 Aug 2008 23:31:03 GMT

OMG, it's round, it floats in space, and is large enough to commercialize and exploit its resources, it's a planet. This is simply silly to me, and I really don't see the point in calling pluto a planet or not. Does it really matter THAT much?

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Michael Smith, Portland Oregon — Tue, 12 Aug 2008 23:32:13 GMT

This is a little like wondering how many angels can dance on the head of a pin. What difference does it really make? In the simplest terms, a planet revolves around a star, and moons revolve around planets. The obvious problem with this is the asteroids, comets and what other objects dwell in the ort belt. How are they different? What sets them apart from planets and moons in a way which is unambiguous and does not unduely cloud the previous definitions?

It seems to me that planets are basically two-body dynamic systems with perturbations from moons and other planets. Asteroids within the asteroid belt or even the ort cloud might be more properly thought of as many body problems, whose motions are equally determined by both sun, other planets and one another...

Of course, this still leaves unresolved the issue of how one classifies non-spherical bodies... I suggest that we reject the name 'planet' for these bodies because it disturbs our sense of symmetry in the universe... planets should be round...

Either way, whether you decide that planets are round, or have some lower bound to the size necessary to be considered a 'planet' it is utterly inescapable that one will have classes of objects which are difficult to classify.

Why not just classify anything in this grey area as higher order planetoid objects and be done with it? It seems to me that anything else is a waste of time.

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Paul White, Raleigh, North Carolina — Wed, 13 Aug 2008 00:32:37 GMT

Here is one solution:

There are exactly four planets;
Jupiter, Saturn, Uranus, and Neptune.

Everything else is rubble!

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John Doe, Seattle, Wash. — Wed, 13 Aug 2008 01:17:20 GMT

what the hell? Why isn't pluto a planet that is all I want to know not all the rest of this rubbish!

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Mike, Foreman, Ark. — Wed, 13 Aug 2008 01:50:36 GMT

I just have to say it. If you can't define something so a smart 5 year old has a good idea what you're talking about, then you don't understand what you're talking about very well.

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Jon Wiest, Winnipeg, Canada — Wed, 13 Aug 2008 03:04:52 GMT

IMHO the debate is silly, using outmoded taxonomies more important to astrology than astronomy. Clearly "planet" is no longer a useful word, if it ever was. Once we start viewing the orbiting bodies of other stellar systems I think this will become clear. We should find new classifications and naming conventions, some of which might include composition (rocky, gaseous), size, orbital regularity, etc. If we must use the word "planet", perhaps it should be reserved for those bodies which are the largest and share orbital regularity with their peers...in which case Pluto is not a planet.

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The cool guy — Wed, 13 Aug 2008 03:17:39 GMT

Just a thought...

A planet could be defined as, "A spherical object with an independent orbit that posseses an atmosphere."

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neil richmond va — Wed, 13 Aug 2008 03:24:35 GMT

thank you Mr. Boyle. Good stuff.

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Rodney Sibert, Trusssville, AL — Wed, 13 Aug 2008 04:32:10 GMT

I don't think of Pluto as a planet. Planets do not have tails when orbiting close to a star (the sun). However, it doesn't bother me that others do.
I applaud the scientist for trying to get a more define description of what a planet really is. Just because we considered it a planet in the past, doesn't mean we can't change our minds now. We know allot more today than we did 50 years ago. And hopefully we will know more 50 years from now than we do today.
You can't just think of a huge round body orbiting a star as a planet. If you take Saturn's moon Titan, move it away from Saturn and closer in with the other terrestrial planets, you will have to classify it as a planet. It has several characteristics similar to Earth. Pluto has almost none. But then Titan is orbiting Saturn while Saturn orbits the Sun.
Saturn, Jupiter, Uranus, and Neptune are more like failed stars, comprised mostly of gasses. I wouldn't have a problem with their classification changing as well. These gas giants are more like mini solar systems inside of our own.
Whatever the final decision is, we'll get used to it. Let's just not vote every couple of years, then recount the ballots... lol...
Rodney... :-)

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Scott, Hesperia, Ca. — Wed, 13 Aug 2008 04:48:33 GMT

Here's my take. If it's spherical, orbits a star, is not a moon, asteroid or comet an object should be classified as a planet. There are many different types of stars yet we call them all stars so I'm not understanding the confusion on this. :)

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Matt, San Diego, CA — Wed, 13 Aug 2008 05:24:08 GMT

I'd say any body in our universe that has a gravitational pull equal or greater then our moon, has even the weakest of atmospheres, is a gaseous or rocky mass, has a consistent elliptical or circular orbit around the sun, and is greater in diameter then 30 miles could be considered a planet. Since this hasnt really been thouroughly discussed by scientists until recently, how can they claim to know exactly what constitutes a planet? More importantly, what does it matter if pluto, a gaseous planet many times the size of our moon, is considered a planetoid, or a planet.

Asteroids and meteors/meteorites, to me, should be called such if they are free-flying objects, constantly colliding and smashing into eachother in either an asteroid belt, or a random orbit.

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Steve Matusch, Sudbury, Ontario — Wed, 13 Aug 2008 10:18:13 GMT

This whole debate about definitions seems rather silly and a waste of bright talented people.

Pluto is pluto, and there are a bunch of similar objects out there with likely similar origins and characteristics. Isn't it more interesting and worthwhile to do real research than to yip-yap and play politics about what to name them?

I can't find the name of the author or the quote but doesn't it go something like "learn the name of something and you have learned something about people - but nothing about the thing itself"

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David Stever, Cochituate, Massachusetts — Wed, 13 Aug 2008 13:04:04 GMT

Just as a clarification, Charon would be a planet because in the Pluto-Charon orbital dynamic, the center of pair is beyond the surface of Pluto. In the similar Earth-Luna orbital dynamic, the center is under the Earth's surface. From this, Luna is a moon, and Charon is a planet.

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Geoff, Lancaster, South Carolina — Wed, 13 Aug 2008 13:09:12 GMT

My definition of a planet:
A spherical body, icy, rocky or gaseous, that orbits ANY star, even if that orbit is circular or elliptic, in the plane of the ecliptic or not. Exception: Ceres, which is in the asteroid belt, could be considered a proto-planet, and may be a planet in several billion years. (Like, we'll be around to see it!)
Therefor, Pluto is a planet, and so are all those other bodies beyond Pluto that meet my definition above.
Also, moons. A spherical body that orbits a planet, whether icy, rocky or gaseous. By this definition, Mars has no moons, only captured asteroids.

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Dave- PA. — Wed, 13 Aug 2008 13:29:02 GMT

Does it really matter? Do you think the people of Pluto increased the planet's use of anti-depressants the day Earth kicked them out of the planet club. No! Why? Cause nobody lives there. Debate or no debate we spend hours,days, and years debating things in our society that we can't change but for some people their fun to talk to about. Why? The solar system will go on whether Pluto gets it's designation as a planet back or not. Does it serve any purpose here? Does making this ice covered rock at the end of our planetary solar system in any way enhance life here on Earth? No! Not at all. I think we need to spend more time and money if needed to study the stars to be certain no floating baked potato doesn't decide the time is right to give our world another hole in the ground. We have some of the most brightest minds in the world in aerospace engineering,physics,etc. debating on the status of planets to be or not be. How about finding a way to get free cable from Venus or unlimited minutes on weekends to Neptune. If they keep messing around the peolpe on Saturn and Mercury are gonna file suit for coyright infringement for naming cars after them. We already have a Pluoto. He's at Disney!

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Midge Baker, Prescott, AZ — Wed, 13 Aug 2008 13:35:40 GMT

Forget size, roundness, etc. Keep it simple:

A "planet" orbits a star, in a stable orbit which does notintersect the orbit of any other planet. A "moon" orbits a planet.
Two or more objects which orbit each other while the unit orbits a star is a multiplanet system.

Why the big controversy? Lol - or are you just trying to drive us laymen nuts?

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J Quinlan — Wed, 13 Aug 2008 13:43:22 GMT

leave poor little Pluto alone. The little guy should be grandfathered in for crying out loud ! " Marys Violet Eyes Makes John Stay Up Nights PERIOD. " That's how everyone taught their kids the sequence ! They are all in their twenties now and they still remember it. Shame on the people who demoted poor little Pluto ! Shame on you...............

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Buddy, Phoenix Arizona — Wed, 13 Aug 2008 13:47:58 GMT

Please, we have had enough of the prattling of an effite corp of impudent snobs who would rob us of our beloved Pluto's status as a planet.
There is nothing compelling anyone to make such a change. Pluto has an atmosphere and a moon and Pluto has a rich hitory in our shared human experience.

Asteroids are not planets and as to the other celestial body mentioned as a possible new member of the heavenly spheres; Eris? Let the grown ups, the Cardinals of the Astronomical SEE, convene and with grave, sober thought , fully cognizant of the gravity of the situation let them decide if we open the books on new planetary membership in our solar system.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. So say we.

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Dan, traverse city, Mi — Wed, 13 Aug 2008 14:10:41 GMT

I like the idea of paired planets. And, round seems like a decent definition, but I would not want a bb pellet to be considered a planet. Therefore, I believe that there should be some consideration of how tightly bound the body is to its host star. How much energy would it take to dislodge it. That way the further an object was from the sun the larger it would need to be in order to be considered sufficiently bound to the system.

just a small proposal...

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Huey, Temple, TX — Wed, 13 Aug 2008 14:37:16 GMT

Why not include Makemake as a planet? It is in hydrostatic equilibrium and larger than Ceres.

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Shane Swinning, Kernersville, North Carolina — Wed, 13 Aug 2008 15:11:39 GMT

Why not take on Tyson's approach and designate seperate classifications for all celestial bodies. We already differentiate the solar system's inner 4 planets from the outer 5 (or 4 depending on your view of pluto). At least we would be able to get a good idea of the makeup of a celestial body by its classification instead of walking around calling any arbitrary round object a planet.

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Jeff, Port Lavaca, TX — Wed, 13 Aug 2008 15:30:50 GMT

Why should what is around an object affect how we define that object? Is the presence or absence of other ducks necessary to define what a duck is? Would a duck cease to be a duck if we moved it somewhere else? Definitions should, as much as is reasonable, clearly delineate that class of object from others. That a planet must have enough mass to maintain hydrostatic equilibrium is very clear and easy to determine. Clearing the neighborhood around its orbit is much less clear. How many and what size objects are allowed in a planet’s orbit in order for it to be classified as a planet? Earth’s orbit still has thousands of orbit crossing objects. At what point would the amount of asteroids and other celestial debris cause Earth to be demoted from its planet status? I think Ceres, Pluto, and Eris should be classified as planets.
The other element of a planet’s definition should be that it primarily orbits a star. Charon should be classified as a moon as it primarily orbits its larger neighbor. If we allow Charon to be a planet, then wouldn’t the Moon also be a planet? The Moon’s orbit around the Sun never curves away from the Sun. It also orbits a common center of gravity with its larger neighbor,
We need a simple and clear definition of a planet so that, as more new objects are discovered around other stars, we do not need a vote by an arcane institution to determine its classification. Having a definition dependent on the object's evolutionary history or the presence of undetectable objects in its orbit will be untenable as we identify planets in other star systems.

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Len Rowe, Lakewood, CO — Wed, 13 Aug 2008 16:07:56 GMT

The word Planetoid:

How about some boundaries for defining what a "pre-evolved" planetary object and an "evolved" planetary object consists of to start with when considering where a planetoid fits in as a unique and seperate entity? What are the characteristics that are primarily "planet" in nature as we currently define a planet "Earth-like" that revolves around the sun? Does the word planetoid contribute to any scientific merit to the exploration of space? Fact is that all celestial objects are all satellites to other gravitational forces; even our sun; just in different capacities. Yet we define the difference between the galaxies, suns, planets, planetoids and moons for the context in which those words are used. All seem to be in relationship to the mass of those objects and what the characteristics are within that relate to what we know all the way down to the electron orbiting the neutron. It’s all symbiotically integrated and dependent regardless of our understanding.

I think that Earth should be the basis of origin for the most known "evolved" planet because it supports a biosphere and evolution; perhaps even "post-evolved" with the breath of consciousness; no other celestial object we know of can compare to sustain us.
This objection by Sykes to the word planetoid is about the positioning of planets as some sort of a pecking order. As the issue for the word then remains a size / mass comparison to Earth then I would conclude that Sykes may be missing the point. I fail to understand the scientific merit of this sub-planet word until there is some context to compare with that is scientifically interesting.

Someday, that may require the evolution of the word planet itself, but is it time? Do we know enough yet? Were not all celestial objects with retro movement in the 1800's considered planets based on the fact they also rotate around the same star? Would those astronomers have invented or used modified words to be more specific and detail in there findings had they had the Hubble Space Telescope?
I'm thinking yes to most of the above.

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Onevoice, Frederick MD — Wed, 13 Aug 2008 16:47:28 GMT

I agree with Sykes - and it doesn't matter if there are 10, 12 or 50 planets discovered a decade from now. Roundness (or mass) and orbiting a star or another palent seem to be logical distinctions between planets, moons and astroids just as internal temperatures are used as the primary distinction between planets and stars. Its exact location within the solar system, its path being clear and whether its in a solitary or binary relationship don't seem to be relevant. If Pluto's orbit becomes more rounded in the future by a chance encounter with another object, would we then have to reclasify it as a real planet?

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Stephen Wilson, Tempe, Arizona — Wed, 13 Aug 2008 16:50:22 GMT

Until the 2015 mission flyby to Pluto and beyond where we will have a much better idea of what's out there, I believe it is foolish for the international scientific community to vote on what constitutes a planet in Kaiper belt region. We just don't have all the facts yet. Since we don't typically discriminate among the objects found in the asteroid belt located between Mars and Jupiter, likewise we should be content in not classifying stuff in the Kaiper belt region until the hard facts come in! The rush to classify everything prematurely also takes the fun and mystery out of it all!

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Dennis Walschinski, Milwaukee, WI — Wed, 13 Aug 2008 17:34:19 GMT

Pluto should be a planet along with Charon and Eris.
Second class astronomers don't know what a planet is even after it bites them in the butt.

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Ray Belanger, Las Vegas, N.V. — Wed, 13 Aug 2008 19:03:47 GMT

I have to agree with Tyson, basically "things Happen" tryig to "fix" subjective order with a lable is certainly nothing to argue about, other classifications would be more informative to students, such as size shape and composition, and distance from earth, speed, orbit. they should be "named" with numbers only, not names like Earth, Mars, or Pluto. [Earth would be 3]

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Dan, Toronto, Ohio — Wed, 13 Aug 2008 20:03:09 GMT

It seems to me that we have already classified planets in our search for them around other stars. They have all these types of planets already classified:
1. Gas Giants (similar to Jupiter and Saturn)
2. Earth Like (such as Venus and of course, Earth)
3. Dwarf Planets (such as Pluto and Ceres)
4. Rogue Planets (a planet that has escaped its orbit around a star).
In all these cases, it is still called a planet. First, let us declare what a 'Moon' is. This is an object in space who’s shape does not have to be round, but can be round, that rotates around a planetary object where the center of rotation is always within the planetary object. This is called a moon of the planetary object. Also, a moon may be large enough to have an atmosphere, and a moon of its own.
The definition of a planet is that it has enough gravity to make itself round and does NOT rotate around another planetary object where the center of rotation is always within the other planetary object. But if the center of rotation between two round planetary objects is between the two objects, or oscillates from within one and goes outside of it now and then, or if it is determined that someday the center of rotation will exit the planetary object, then they are both classified as a planet, such as Pluto and Charon. A planet does not have to rotate around a star, since rogue planets will be found.

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Loren, SF Bay Area, CA — Wed, 13 Aug 2008 23:27:21 GMT

With all the problems we have here on Earth, isn't it a little silly for people to get into heated arguments about whether Pluto is a planet or not?

My favorite T-shirt this month reads, "Don't worry, Pluto; I'm not a planet either."

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Sam, Oakland, CA — Thu, 14 Aug 2008 00:05:07 GMT

Oh come on already... eight's enough. We need to draw the line somewhere. Satellites/Moons, Plutoids / Dwarf Planets, Asteroids shouldn't be called planets, regardless of whatever geologic / internal processes. What comes next - comets as a new class of 'planet?' Pluto isn't a planet, it was the first outer belt (ie Kuiper Belt) object to be detected. There's possibly thousands more like it out there. They can't all be considered planets.

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Kip Portland, Or — Thu, 14 Aug 2008 00:41:05 GMT

In my humble opinion, a planet should be defined by the following:
It's gravity should make the object round. It's gravity should clear it's orbit of debris. It should orbit around it's star (if it orbits another object around the star then it's a moon). It's orbit should be no more than 20 degrees off the planar axis (then it's an asteriod/comet).

I do like the idea of calling Pluto/Charon a binary planet as their respective masses and proximity does cause them to orbit each other as they orbit the sun.

A simple definition like this would clear the air and let scientist get back to discovering things instead of squabbling like schoolgirls.

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ken, fort worth, tx — Thu, 14 Aug 2008 02:57:20 GMT

Our current understanding is that Planets and Star Systems abound in the known Universe, while discovery of our own Solar System is still a work in progress. Aided initially by the early telescopes our neighboring planets presented themselves. The fainter, more distant orbs defied detection, but clever methods yielded the newer discoveries. With more observation of our planetary system, we have tracked orbits, and measured features, including axial rotation, atmospheres, magnetism, surface pressures and temperatures and their roundness. Oh the roundness!

Can we decide what is planetary by virtue of roundness, orbital inclination or elliptical orbit, when we have not fully discovered all that surrounds our own Sun, our own Galaxy and our celestial neighbors? What if such an oddity as a Plutoid, albeit in a distant Sun’s entourage, but in more temperate zone, harbored life? Would we then have the temerity to declare a foul? I think not.

Any discussion of what is, or is not a planet, should not be limited to our current understanding of this puny corner of the Milky Way. We should aim to permit acceptance of new discoveries, while allowing duplicity if practical to not discount any reasonable explanation of the condensate formations around a distant Sun. Pragmatism sucks.

Would that Sagan could elevate the discussion. Would he lapse into ‘a Pale Purple Dot’ a study of the oddity that’s Pluto? My 10 cents: decide what’s planetary if you must, but do so in a manner which is inclusive.

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Michael Wood — Thu, 14 Aug 2008 04:18:33 GMT

I’ve been watching the discussion over Pluto with quite a bit of interest. Personally, I think Pluto should be a planet. Still, I have to agree with Tyson that "an irrational sway over our hearts and minds" exists when it comes to defining the word planet. I don’t think that’s a bad thing, however. Irrationality implies passion, dedication, and drive; I would argue that most scientists entered their chosen field of study based upon some irrationality at some point in time. Tyson’s own suggestion belies this as well, when he notes “Suppose other properties are what matter to you.”

That being said, I’m very much a fan of the scheme where a planet is a round object that orbits a star. This definition still allows for the investigation of all the individual properties that fascinate Tyson, while still being simple enough to be applied to any system imaginable. The problem with defining a planet as an object that has cleared the neighbor around its orbit is that it is not a very, well, clear definition. What is the “neighborhood?” How far does one have to go? How clear does it have to be? Round could have similar problems, but let’s be reasonable (or rational?) for a moment—if you say that a planet is round and orbits a star, most fifth graders can grasp the concept and come up with a correct answer. However, most astronomers still can’t fully answer when the neighborhood is clear, at least not without quite a bit of irrelevant discussion.

Let’s face it; we all know what a planet is, more or less. We live on one, and we have several in our system. They’re round things that orbit stars. They have several other interesting characteristics, but they’re all pretty much the same in that respect. We also are learning that there are lots of planets outside of our system…we might not know for sure that they’ve “cleared their neighborhood,” but they’re big, probably round, and very interesting objects to study.

Oh, and Pluto is a planet.

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Michael Kent, Ohio — Thu, 14 Aug 2008 13:30:20 GMT

That does actually raise some interesting points with orbits. Double planets seem reasonable. I guess the definition would define a double planet where the cm lies outside the bodies,and a planet-moon situation where it lies inside one.

It seems to me that the solution is to first define a Planet as one of those nine bodies which were historically known as planets.These are "The Planets" This of course includes pluto. Then admit this is not really a scientific definition,but one based on the old conventions. This is similar to the way some chemicals are named. Toluene is still known by that name,rather than methy-benzene. Similarly a new system for classifying bodies in the solar system should be developed that logically classifies objects.

Off the top of my head,there are bodies like the earth and mars,like Jupiter,and like Pluto,as well as asteroids. These are all very different things and obviously should have different designations. The problem with defining a planet is that if you try to include only some of these arbitrarily,you end up with something that does not work.

Once we have abandoned the term planets you can come up with definitions that work. (using the word planet of course is allowed) You can have earth like planets ("terramorphic planet"?) ,Jupiter like planets etc.Each can be given a nice descriptive name. Objects like Pluto seem to be quite common. While Pluto is one of "The Planets" due to its historical significance,its actually a member of a class of objects that are quite common. Classification of these have not been a problem. The real problem was trying to classify these and have Pluto not be included.

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Josh Levin, Marlton, NJ — Thu, 14 Aug 2008 13:32:13 GMT

The definition of a "planet" has changed before.

In ancient days, the seven planets were the seven "wandering stars", those that did not seem to stay in a fixed spot on the celestial firmament. These did not include the Earth, but did include the Sun and the Moon, plus Mercury, Venus, Mars, Jupiter, and Saturn. The Pantheon ("all gods") temple in Rome was dedicated to the corresponding seven gods and goddesses.

"ken, fort worth, tx" used the term "orbs". I think this is a good catch-all term for celestial bodies, whether round or irregular, luminous or not, gaseous or icy or rocky.

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Michael Kent, Ohio — Thu, 14 Aug 2008 13:41:14 GMT

<<<<<<<
Why should what is around an object affect how we define that object? Is the presence or absence of other ducks necessary to define what a duck is? Would a duck cease to be a duck if we moved it somewhere else?
>>>>>>>>
Is a doorknob still a doorknob if its mounted on drawer and used to open that drawer. In a sense it is. If it broke and we wanted an identical replacement,we would go look in doorknobs at the hardware store.However,in another sense,we would call it a drawer handle,because that describes whats its doing. If someone asked you ,does that drawer have a handle,your answer would be yes.

>>>>> The other element of a planet’s definition should be that it primarily orbits a star. Charon should be classified as a moon as it primarily orbits its larger neighbor.
If we allow Charon to be a planet, then wouldn’t the Moon also be a planet? The Moon’s orbit around the Sun never curves away from the Sun.

>>>>>>>

as someone else mentioned,the cm of the earth moon system is inside the earth,while the cm of the Pluto Charon system is inside neither. We have to define what it means to say A orbits B. If it means the cm of the AB system is closer to A then Charon is a moon. What about complex many body systems where the cm is moving.

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Tim Rommes, Washington, UT — Thu, 14 Aug 2008 15:09:33 GMT

Eric Smith,
Why would Earth be disqualified as not clearing it’s orbit?

Micheal Mealling,
Then we have picoplanets, maybe most shooting stars would be Planck Planets. All this does is describe mass. If that were to be the only part of the definition then we are not further classifying but instead unclassifying asteroids.

Josh Levin,
Quite excellent! The “surface” of a gas giant is indeed difficult to define. One way to define the size of a gas giant would be the radius at which gravity begins to decrease. Well away from the planet it’s gravitational pull increases as you get closer. Entering it’s atmosphere gravitational density continues to increase as you go down, much like with our planet. By the time you reach the center it has no gravitational density, or rather it all cancels each other out. At some point it’s at a maximum, with any planet, although there are more variations on solid planets owing to the structure provided by solid stuff. At the base of it, all mass is effecting all other mass. So to an extent they were right hundreds of years back, the entire universe does revolve around us. Just not as much as it revolves around our sun, and that not as much as it revolves around the local black hole, and that not as much as it revolves around our galaxy, … With increasing mass the effect is more evident, it is a popularity contest. Saying what orbits what is, to a degree, arbitrary. It’s kind of like saying when dinner is hot and when it got cold because you wouldn’t get off the computer. By midnight dinner is definitely cold, Mercury definitely orbits the Sun. Whether it a planet/moons, double planets/moons, triple planets/moons, etc., is less important, to me, than the fact that it’s a barycenter in orbit around something else. You can identify a system. All the planets could be said to orbit the moving, relative, barycenter of the whole system. In the ‘80’s(?) all the planets lined up on one side of the Sun, the barycenter would be as far from the sun’s cetner as it will ever be, at some point the planets may align so that it’s right at the sun’s center. Clearly the most dominant contributor over time is the sun.

Vanderghast,
Absolutely. Or not. It will forever have an asterisk in it’s stats. *orbits the Earth as part of it’s system.

Wayne,
I hate to think that classification as a planet or not would depend on our ability to exploit (read ruin) it. But there is some despicable truth to that. The importance of correctly classifying things for purposes of scientific study / understanding / advancement of knowledge: Is that pet you have a mammal or a bird or a plant? Screw it, doesn’t matter, who cares, what difference do those things make?

FYI:
Round here means hydrostatic equilibrium. It’s just easier to spell. If we were to find a liquid planet with a high rate of spin so that it’s long axis (at the equator) was 10x it’s short axis (pole to pole) it would still be our “round.”
Material composition then comes into play because of structure. A huge potato shaped chunk of iron has way more mass than enough moon dust that is able to pull itself into round. The round moon dust would be “round” and the iron potato would not be. Half the iron potato with enough liquid around it, less mass than the full iron potato, falls into “round.”
If we sent a robot into the asteroid belt to chisel a large asteroid into a perfect sphere and then expel all the other asteroids from that orbital neighborhood we should not call that a planet. If we sent a robot into the asteroid belt to assemble all the asteroids into one body, and that body has enough mass to pull into round, and enough mass to (be able to) clear it’s local orbit, then it’s a(n artificial) planet.
Clearing the neighborhood is reminiscent of whether or not you’re sick. All kinds of bad ju running through my system right now, but I’m pretty clear. I think essentially, if the object would capture the debris upon crossing it, or if the debris is locked by the objects gravity then it’s a no brainer to call the orbit cleared. Fast movers, while in the orbital area, that are in more elliptical orbits or in different orbital planes that cross discretely should probably not count, but then where do we draw those lines?

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Jason Bontrager, Brenham, TX — Thu, 14 Aug 2008 18:00:16 GMT

Why the fascination with orbits? Only one commenter (AFAICT) has mentioned Rogue Planets. Since we're all throwing our personal definitions around I'll offer mine.

Planet: an object in hydrostatic equilibrium with a spherical or oblate shape that is insufficiently massive to induce nuclear fusion due to self-gravitation.

Classes of Planets:
Class 1: A planet that doesn't orbit another discrete body. AKA a "Rogue Planet"
Class 2: A planet in orbit around a star.
Class 3: A planet in orbit around another planet.
Class 3a: A planet in orbit around a Class 1 Planet.

That's pretty much it. Objects that are no longer undergoing fusion might be classified as Post Stellar Objects (White Dwarfs, Black Holes, Planetary Nebulae, etc).

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P. Michael Hutchins, Carlisle, MA — Thu, 14 Aug 2008 21:16:48 GMT

Interesting Rorschach test!

The real issue is what's the point of definitions - or rather, concepts.

We need to ask that of the concept "planet".

Does it have any scientific utility whatsoever?
(I don't know.)

...or are we confounding that with colloquial speech..

..and worse, going on from there to see scientists as just another kind of authority, and therefore expecting them to come out with a stone tablet on the matter

..and /worse/, their accepting that!

Children of a certain age span, who have ~learned~ that Pluto is a planet, need not be subjected to the emotional traumatization of being told that it is so no longer; people older than that should learn enough about epistemology to understand the above; children younger than that need never care (just as most of us don't spend time pining about the demise of the dinosaurs - and, I suggest, psychologically healthy people in the somewhat-distant future won't tear down the quality of their lives by bemoaning the extinction of the blue-spotted redbellied swamp crawler, or whatever.

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Marcia — Fri, 15 Aug 2008 04:40:01 GMT

What about Eris? It is considered to also be a dwarf planet. As it should be. As far as I'm concerned Triton and Enceladus would be dwarf planets as well since they seem to have similar chemical compositions, round... captured sphered or not.

[The object found to orbit between the Kuiper Belt and the Oort Cloud? The dwarf planet is the most distant object ever seen in orbit around the sun, even more distant than Sedna, the planetoid discovered almost 2 years ago. It is almost 10 billion miles from the sun and more than 3 times more distant than the next closest planet, Pluto and takes more than twice as long to orbit the sun as Pluto.]

http://www.gps.caltech.edu/~mbrown/planetlila/index.html

Amazingly cool.

Roundness doesn't always count, but it's where they came from and even if they were captured objects as Triton and Enceladus seem to be.

MHO

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Another Brad from St. Louis — Fri, 15 Aug 2008 21:09:58 GMT

I think it'd be really kewl to have 13 planets and counting. The big thing that the IAU fails to understand is that "new" discoveries are exciting. Subtraction or reclassification is not exciting, it's boring. So while the IAU may be great scientists, their PR skills, well, they ain't so good.

Look, at the end of the day, we just need a basic term for these bodies with a very basic name. Think animal, vegetable, mineral.

Simple definitions:

If it creates energy through nuclear fusion and anchors a solar system, it's a star.

If it's made up of anything, orbits a star, and has hydrostatic equilibrium, it's a planet.

If it's made up of anything and orbits a planet, it's a moon.

If it's made of rock or ore, orbits a star, and doesn't have hydrostatic equilibrium, it's an asteroid.

If it's made up of ice, orbits a star, and doesn't have hydrostatic equilibrium, it's a comet.

This idea of having different classifications for planets is all fine for people who really get into this subject (like me). I have no problem with calling a planet a terrestrial planet, a gas giant, an ice giant, etc. But give the public a new discovery, not a new genus.

Last time I checked, astronomers make their living off grants and donations. Isn't it smarter to make the people with the money get excited about being a part of new discoveries than to have them to realize their money's going towards "reclassifications"?

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Tim Rommes, Washington, UT — Sat, 16 Aug 2008 08:26:20 GMT

Another Brad,
Very true, but very much a political answer to a scientific problem. For the sake of the science stuff like this should be handled in house, shielded from public view so as not to distract Daddy Warbucks so he can stay focused on those new discoveries. Of course, there's not much of a house to keep this in.

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Dennis, Richmond VA — Sun, 17 Aug 2008 16:53:11 GMT

I really don't care what the final definition is as long as it is not specific to our solar system. The current definition means that if mars orbited abother star, it would not be defined as a planet. The whole plutiod definition only applies to our one solar system, and so is unworkable.

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Will Davis — Mon, 18 Aug 2008 06:12:07 GMT

We already call Jupiter, Saturn, Uranus and Neptune "Gas Giants". We call the four inner planets "Rocky Planets". I suppose Pluto just got the short end of the stick!

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Kirk Nichols, Traverse City, MI — Mon, 18 Aug 2008 17:11:07 GMT

What's the difference if we humans choose to call Pluto a planet or a dwarf planet? It certainly doesn't make any difference to Pluto, and takes nothing away from those who discovered it and have studied it.

The term "planet" has been used for thousands of years to describe a "star" that wanders, as opposed to stars that do not. With our modern understanding of the solar system and the universe, it might be time to come up with some new terminology. Earth and Jupiter are both classified as planets because they both fit the techinical definition, but apart from both orbiting the sun, they don't have much else in common. I think it's high time that we came up with a totally new system for classifying celestial bodies within our solar system, and stop arguing about things that don't really matter.

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jerry starkey, muskogee, oklahoma — Tue, 19 Aug 2008 15:51:39 GMT

was there not a way to determine distance for solar? like AU, why not use the same determination for planets...example earth would be a 1.0 planet based on mass or roundness or habitablity. then you could determine that the next planet would be + on - percentage wise of whatever was chosen as the new standard.just a thought...

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Yvan Schmidt, Placentia, CA — Tue, 19 Aug 2008 20:19:54 GMT

The gravity-clearing concept should be excluded from the definition of a planet, because that concept is absolutely biased towards near-sun objects at the expense of far-sun objects.

In our own solar system, it would appear obvious that part of the reason there are a number of dwarf planets (or whatever you want to call them) outside of the Neptune/Uranus orbit pattern is because the density of mass in such an outer layer is so much lower than at the orbital distance of, say, Venus. In theory, there should be a "solid mass" in the Pluto orbital comparable to any of the other solid planet orbitals, but because the volume of space that this mass is enclosed in is SO MUCH larger than in an inner orbital, there is not enough gravity associated with the larger clumps of mass in that orbital to make all the solid mass congeal as one planet.

On the subject of planets versus moons, it would seem that the issue is one of orbits, and not just definitions. Would you consider a round moon (Titan, Triton, our Moon, etc) a planet, or a moon. Triton would be particularly interesting, because I think it would be easy to make an argument that Triton is/was a planet, or at least a dwarf planet/KBO, which got caught-up in the gravitational pull of a larger object (Neptune). Does this make it a moon, or a captured planet?

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Frank, Dallas, TX — Tue, 19 Aug 2008 22:29:48 GMT

"Planet" is an anachronism from the ancient Greeks that means "wanderer", and was meant to apply only to the wandering celestial bodies that are visible with an unaided eye. We need a whole new word to define another world. How about "world"? "Globe" could be a good one if the roundness thing sticks. Maybe we just need to be more organized in classification - planet, globe, world, body, could be terms sort of like genus, phylum, species, order... well, you can see I'm not a biologist!

I think Pluto never should have been a planet in terms of being a planet like the other eight - its orbit is too eccentric.

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Delmar Fairchild, Barron, WI — Tue, 19 Aug 2008 23:40:05 GMT

Trying to put a group of heavenly bodies in a catagory by themselves is "trying".

Just give a name to each "object" and be done with it. There will be times when an object will not fit in the molds we design, so we have to shelve it and call it "something else" while it sits there. If everything is an object, we can get on with discovering more "Objects".

In our future endeavors, one may hear on the news or read in a paper, "We have an object named YYYY revolving around the sun XXXX at "such and such" distance in galaxy AAAA. It is ZZZZ big and may (or not) be in the position to where our type life can be supported."
Planets, comets and other Objects in space were named in the past because we were too small to see the big picture. Now we are big boys (& girls)so we will be finding more than what our minds can collate.

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Tim Rommes, Washington, UT — Wed, 20 Aug 2008 12:39:30 GMT

Yvan Schmidt,
Point, or actually points, well taken. Here are my non-authoritative replies.
“at the expense of far-sun objects” This is an argument against calling Michael Jordan a great basketball player because we don’t call me one. And nobody calls me one. What about another object in a different area of space that just didn’t have enough mass available to bulk up to planetary standards? Or one that had enough mass available but didn’t get it before a competing object did? They’d be planets if they had more mass available, but they didn’t. This has to be accomplishment based. Maybe at such slow orbital speeds the far out regions are in the planet forming process. Maybe in other systems with large stars that is the case also but those planets won’t have time to form. The definition of band clearing should be closely looked at, though.

IMHO the planet determination should come first. Then primary orbit. That way it’s either a planet or not, then is that planet a moon, a moon just meaning it’s in a secondary (or tertiary, …) orbit. And I don’t go for the “rouge planet” idea. Planets are objects captured in a star system, not interstellar objects. Whether it’s a planet or a moon carries less intrigue for me as whether or not the other body has a tidal influence. Our moon presents the same face to our planet all the time. A moon that spins relative to it’s host planet is a much more exciting thing to me.

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Laurel Kornfeld, Highland Park, NJ — Thu, 21 Aug 2008 19:04:25 GMT

Tim, the problem with the dynamical definition is that an object of the same mass and size can in one location (closer to the sun) be considered a planet and in another location not be considered a planet (eg, if it orbits in the Kuiper Belt). A good definition must take into account both where an object is and what that object is. The comparison with calling Michael Jordan a great basketball player doesn't hold, mainly because in that instance the sole criteria for comparison are the two individuals themselves, not where the two individuals (you and Jordan)are. That's in addition to the fact that the phrase "great basketball player" is itself far more subjective than the term planet. I do agree that round moons of planets should be considered secondary planets, a term often used during the 19th century to define them. In fact, when Galileo first spotted the moons of Jupiter, he referred to them as planets. The issue with a rogue planet is this: these are objects that were part of some system--either a star system or a pulsar,etc.--and then were somehow ejected from their orbits. Do they stop being planets once they are thrown out of their orbits? Again, that means defining them solely by where they are as opposed to what they are. Since at this point in time we do not have the technology to detect the composition of rogue planets due to their distance, I don't think we are in a position to make any more than tentative classifications of these objects.

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Tim Rommes, Washington, UT — Fri, 22 Aug 2008 09:32:04 GMT

Laurel,
I think the term planet is very subjective. For instance(s): I think a planet is an object that is part of a system so, yes, we stop calling rogue planets planets. I also think that clearing their neighborhood is important. If it would be a planet in our orbit but it's a KBO then it's not finished. For me a planet is an object that only interacts with rogues, things on crossing orbits, or things in it's gravitational hold. Obviously, other people feel quite differently on both counts.