http://www.pbs.org/wgbh/nova/pluto/
Is Pluto a planet?
Well, it all depends on what is meant by "planet." I define planet very broadly, as a spherical object (or objects) that orbits a star. This definition is very broad, much broader than the IAU definition. But since my definition is so broad, it is usually more helpful to refer to sub-classes within the planets when I talk about celestial objects.
I label Mercury, Venus, Earth, and Mars as Terrestrial Planets. These objects are about 5,000-10,000km in diameter and have a rocky surface.
I label Jupiter, Saturn, Uranus, and Neptune as Gas Giants. These objects are over 50,000km (100,000+ for Hot Giants!) in diameter, have rings, and have a gassy surface.
And lastly, I label Ceres, Pluto-Charon, Eris, Makemake, and Haumea as Dwarf Planets. They are less than 2,500km in diameter, have a rocky surface, and have not cleared their orbits from other surrounding objects. (note: I do not recognize Charon as a moon, but rather as half of a binary planet system. I recognize Nix and Hydra as moons of the Pluto-Charon system.)
So, to answer the question: Yes, I technically consider Pluto a planet. But probably not in the sense most people use the word "planet."
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These definitions are always subject to new information. I fully expect more dwarf planets to be discovered in the Kuiper belt.
And New Horizons will provide much more information about Pluto-Charon in 2015, which could easily change things around.
And yes, I can hear the sighs when I start a sentence with, "Well, it all depends on your definition..."
I think I will always consider Pluto a planet.
Remember the saying "My Very Excellent Mother Just Served Us Nine Pizzas" (or something similar)? It wouldn't flow without Pluto. Nine what?!?! Pluto has to be one of the planets!
Along with that fantastic assertion as to why Pluto should be a planet, I'm less scientific about the meaning of a planet. Does it orbit the sun (star)? Does it look like a planet? If it walks like a duck and talks like a duck...it's a fucking duck.
I'm with you.
If you include Pluto as a planet, do you also include Eris, Makemake, etc.? Do you include Charon?
My Very Excellent Mother Just Served Us Nachos is the new mnemonic device. But if you include Pluto as a planet you have to at least include Eris (which is bigger) Either way, the mnemonic device has to change...
What do you mean "looks like a planet?" Just that it's spherical?
I would argue that Pluto does not look like a prototypical "planet." Compared to the other 8, its orbit is highly elliptical (it even crosses paths with Neptune!) and off-axis. It's a lot smaller than even Mercury, so small that it doesn't have enough gravity to clear out other objects in its vicinity. It also has a "moon" that pulls the rotational center of gravity between them outside of Pluto!
From a quick glance, Pluto looks more like a large asteroid than a planet.
Haha, even at 5 in the morning I had a feeling you'd pick apart what I said =).
Yes, when I say looks like a planet, I do mean spherical. Type in "Pluto" in Google Images. Sift through the ones of Pluto the dog, and yep, looks like a planet I'm used to seeing! Like I said, I'm not being very scientific here.
And so what if it's orbit is elliptical? Does it orbit the sun? Okay then!
AND I am on your side!!! I'm with you!!! Why are you arguing against me?!?! Same team, same team!!!
Haha, I'm not even really arguing with you (yet), I'm still just trying to understand your position! You say you're on my side, but I think when I say "Pluto is a planet" and you say "Pluto is a planet" we mean two different things.
I mention Pluto's elliptical orbit because it's markedly different than the orbits of the traditional planets. If you're trying to decide if Pluto is a planet by comparing it to the traditional 8, it doesn't hold up. It's not "walking like a duck."
..it's almost like you think astronomical nomenclature is irrelevant to our lives. It's almost like you don't have a strong, well-researched opinion on classifications of Kuiper Belt objects at all...
Hahaha, yeah, it's kind of like I don't!
Hey, just because Pluto's orbit isn't like the rest doesn't mean it's not walking like a duck! Ducks come in all shapes and sizes, and have varying styles of waddles. Pluto, I suppose, is the ugly duckling of our solar system.
Or the retarded planet that walks funny.
Right. But the ugly duckling is a swan trying to act like a duck, he's not actually a duck at all.
But the point is they are both birds. "Planet" to me is like the generic term "bird." The traditional 8 planets are two species of bird, say ducks (terrestrial) and geese (gas giants), while dwarf planets are like swans.
So if you're saying Pluto is a bird I agree with you. But if you're saying Pluto is a duck I disagree.
Here is my new mnemonic device for all planets in the solar system in order:
My Very Excellent Mother Can Just Serve Us Nine Pina-Coladas. Handy Mother, Eh?
(Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto-Charon, Haumea, Makemake, Eris.)
Haha, I like it.
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