Get over it. Get a life. Pluto itself doesn’t care. It just continues along, doing as it always has done..

I don’t really understand this crusade, it seems very emotion based. If you want Pluto to be a planet so badly, then you really ought to be demanding that other Kuiper belt objects be classified as planets as well.

“if we discover a Jupiter sized object in the outer reaches of the solar system (which is entirely possible)”

Really? Well, it can’t have formed out there, so it must have migrated, which means there must have been some noncentral object way more massive to throw it out there (like the Oort Cloud is populated), and… oh wait, that doesn’t make any sense, because there is no such object to scatter it.

“The easiest (and most correct) way to do this would be to create a spectrum definition”

Um, no. Easy for stars – to first order they’re blackbodies, and to second order they have spectral lines that are just temperature dependent (metallicity contributes, though not as much – for the hotter stars, the atmospheric opacity is mostly hydrogen anyway).

But planets? With spectral lines that just for terrestrial planets depend on, oh, the age of the planet, geological activity, the presence of life, proximity to their star… that sounds nuts.

I might be totally wrong with all this. After all, I study the IGM, not planet formation. But… I kinda think the IAU definition, flawed though it may be, makes a hell of a lot more sense than anything you’re saying, gopher65.

Nobody should “let go,” “get over it,” or blindly accept the controversial IAU definition, which does not even make scientific sense. The notion that Pluto is a planet–in the same broad category as the larger eight objects–will NOT die with those who learned it in school; in fact, many are still learning it in school today. Only four percent of the IAU voted on this, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. Stern and like-minded scientists favor a broader planet definition that includes any non-self-luminous spheroidal body in orbit around a star. The spherical part is important because objects become spherical when they attain a state known as hydrostatic equilibrium, meaning they are large enough for their own gravity to pull them into a round shape. This is a characteristic of planets and not of shapeless asteroids and Kuiper Belt Objects. Pluto meets this criterion and is therefore a planet. Under this definition, our solar system has 13 planets: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.

Pluto is a planet; it is just one of a third subcategory of planets, the dwarf planets (in spite of the nonsensical IAU decree), in addition to the terrestrial and jovian planets.

I wish I could have attended this demonstration, but I live on the other side of the country, and the trip is expensive. Maybe next year.

Pluto is a planet; it is just one of a third subcategory of planets, the dwarf planets (in spite of the nonsensical IAU decree), in addition to the terrestrial and jovian planets.

By the same logic, I could formulate the sentence:

153 Hilda is a planet, it is just one of a fourth subcategory of planets, the minor planets (in spite of the nonsensical IAU decree), in addition to the terrestrial, jovian, and dwarf planets.

There is nothing inherently wrong with either statement. I agree with you that hydrostatic equilibrium is an important characteristic to consider. But nothing in the IAU’s decision suggests that they don’t consider it. They simply chose to appropriate the word “planet” to the big eight rather than to every round object directly orbiting the sun.

Now, obviously you and Dr. Stern have a different opinion. But at this point we’re talking about aesthetics, not facts, and honestly I have a different aesthetic preference than you do. Personally I think that the terms “planets” and “dwarf planets” are less confusing term than Stern’s own “überplanets” and “unterplanets”, but then again, I’m not a Germanophile.

In the end, we’re drawing a line in the sand that nature doesn’t heed in its actions. The point of these categories is for our own analysis. So there will be border cases that aren’t clear regardless of where we set the boundaries. You think that hydrostatic equilibrium should be the defining category, fine. You still have to deal with 4 Vesta, which doesn’t really qualify as what you termed as a “shapeless asteroid”, but isn’t truly in hydrostatic equlibrium either.

Aesthetically, I like the fact that the term “planets” refers to the largest objects that dominate the solar system. Is it inconsequential that Pluto’s orbit is stable specifically because it avoids that of Neptune? Or that it’s less than 1/50 the mass of Earth’s moon? Or that these two characteristics are interrelated?

Now, I say that the notion that Pluto is in the same category as the eight most massive non-stellar objects in our solar system because it’s true. As a child learning about the solar system, I was always struck by the incongruence of Pluto with respect to the other planets. Here we had a planet that was much smaller than Earth’s moon (as well as six other moons) and had an eccentric orbit crossing that of the much larger Neptune. It was an outlier.

Now, we know that it wasn’t so much of an outlier as it seemed at the time. But that further emphasizes the point. There are a swarm of objects that are like Pluto. Don’t get me wrong, it’s toward the big end of the spectrum, but

It’s much easier for a schoolchild to digest a view of the solar system dominated by eight planets than one where every round object that orbits the sun has spotlight significance. You claim that there are 13…there are 13 that have been recognized as such, but there are likely many more that will be recognized in the coming years. Pluto is an interesting body…but I don’t see it as being in the same league as the big eight (which one could break down further into terrestrial and jovian, or rock, gas, and ice according to one’s preferences). Having the big eight as planets makes for a much easier gateway to learning about the full array of interactions in the solar system than does starting out with the whole swarm.

Ultimately, this strong-emotioned political movement over the naming of categories is silly and will be looked at as quaint by future generations.

Pluto is a planet. A dwarf planet, but that’s still got “planet” in it. So what if it’s also a Kuiper Belt object?

If people want Pluto to be a planet so badly, I suggest they start funding space research something fierce and go out there and clear it’s orbit.

Squish together Pluto, Eris, Make-Make, that Q-thingie and the rest of the Kuiper Belt. Then you’ll have a planet.

People keep saying that if we discover an ‘earth’ in the KB it won’t be a planet. Hvis og hvis min røv var spids …. Has anyone actually bothered to model it? Will an earth be able to exist out there without clearing its orbit?

I didn’t say “spectral” definition, I said “spectrum” definition. The latter is being used in the conventional sense of the word, not in the astronomical sense (although I can see how you’d have thought that). Spectrum definition as in “a definition that is spread across a range of values”; “continuum definition” would be a less confusing way to describe it.

In other words you have a definition that starts with a single grain of dust (or maybe even a single free flying proton), goes up to a lump of dust, then a little rock, then a big rock, then a round rock, then an object with an atmosphere, then an object that is mostly atmosphere, then an object that can sustain tritium fusion, then an object that can sustain deuterium fusion, then an object that can sustain hydrogen fusion. There is no break between any of those points, because there are hybrid objects that would, in a classical definition scheme, fall into more than one category (or into none). The definition therefore is continuous, and flows from one object class into another.

The definition can have new branches placed at any point along its length as new types of objects are discovered. It’s a versatile way to define a set of objects.

In such a definition there is no clear (but arbitrarily placed) cutoff point between “rock” and “planet”, or between “planet” and “star”. The definition is based entirely on the physical properties of the object, rather than on a bunch of arbitrarily drawn lines in the sand.

The main issue I have with the reclassification is that schools, textbooks, museums, movies, documentaries the world over have simply shortened the list of planets, so millions of kids have no idea there is anything like a “dwarf planet”, let alone that Pluto ever existed. They are shown a list of 8 objects and that’s it for the Solar System as far as they are concerned.

For better or worse, the IAU has ended up furthering the cause of scientific ignorance. Think instead how rich their cosmos could be, were they to be told about Sedna, Eris, Makemake as a matter of course.

Regarding #14 Sili “clear its orbit”: Pluto’s orbit is clear. There is no a chance in a billion years it will collide with anything, and it’s unlikely there is anything like a “Trojan asteroid” for Pluto either.

Here’s an example of what I am talking about…the BBC using the term “humiliated” regarding Pluto’s “demotion”…

http://bit.ly/dviZpd

And here’s the New York Times talking about Pluto’s “demotion”
http://nyti.ms/dq7Sc9

“demotion”=lesser rank=lesser importance=incentive to schools, museums, etc to avoid talking about Pluto. And that’s exactly what they’ve been doing.

Mercury has no moon. Pluto does, and a big one, too. In any event, the controversy helps keep kids interested in astronomy and makes the IAU look like old crones from a Dickens’ novel. Once you demote Pluto, teachers will stop even mentioning its existence to kids because it’s not “even” a planet. What a great way to educate children.

Lets agree to disagree. There are 8 1/2 planets in the solar system.

How ironic that a group of protestors rallying in support of the planetary status of Pluto
should end their march … at Neptune.

We managed to image Pluto in september 2008.The picture came across exceptionaly clear.It looked almost perfectly round.
Then last march we took another shot of it and that was a
shocker.There’s a giant mountain on the equator that casts a colossal triangular shadow to the right.
We showed it to the IAU by their trianual general assembly in august.The president for planetary studies,Monsieur Regis Courtin,was intrigued but could’nt
confirm the discovery for lack of another independent source for verification.
The mountain in its various subsequent positions can be seen on http://www.spacenow.com.br/.
Pluto might be a dwarf Planet now,but we know that it hosts the most striking surface feature in the solar system.