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Now I know what a planet is August 25, 2006

Posted by dr. gonzo in Science, Space.
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The astronomical community chose to downgrade Pluto to a dwarf planet instead of going with their original draft proposal. Clyde Tombaugh is rolling in his grave and millions of school children worldwide will now recite an incomplete sentence trying to remember the name of the nine–ahem–eight planets.

Hey, what’re you gonna do? So Pluto’s not a planet, no big deal–psst–it never really was. As exciting as it would have been to have a star system with scores of “planets,” it really won’t matter. Most people will think of Pluto as a planet. I still think of U.S. Cellular Field as Comiskey Park (II). You can’t change minds with arbitrary definition changes or name changes.

Either way, the point is, this was never and never will be up to astronomers. The public decides what is a planet around these here parts compadre. Pluto has a permanant “Don’t Mess” sign adhered to its icy surface.

The definition is still vaguely similar to one I thought up a couple months back. The defintion resolution establishes three categories for celestial objects.

First it says:

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

The superscript added this resolution:

RESOLUTION 5B
Insert the word “classical” before the word “planet” in Resolution 5A, Section (1), and footnote 1. Thus reading:

(1) A classical planet(1) is a celestial body . . .

and
——————————————————————————–

1The eight classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

The other two categories, to one of which Pluto, 2003 UB313 and Ceres now belong, include Dwarf Planets and Small Solar System Bodies.

The Resolution as voted on defines Dwarf Planet:

A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

This is all very interesting to astronomers I am sure. The public will disregard it and astronomers may choose to define planet with their own de facto defintion in the face of the IAUs decision through sheer popular will. The rest of the resolution specifically says that Pluto is demoted to Dwarf Planet status.

This, despite earlier IAU assertions and measures to ensure Pluto was not demoted. The IAU made sure there will be no tenth planet (or 57th planet for that matter) and virtually ensured that no other planets will be discovered in our solar system.

Interestingly this definition only applies to our solar system, so in reality the definition of the word for the majority of objects in our galaxy is still up in the air.

At least this debate is over with, for now. Also, Neptune will now always be the solar system’s most distant planet.

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Comments»

1. Daniel H. - August 25, 2006

Actually, according to comments from his widow in this article:
http://www.wtop.com/?nid=220&sid=892546

Clyde Tombaugh probably isn’t rolling in his grave. Though he’d still be disappointed.

2. dr. gonzo - August 25, 2006

I saw that. But what does she know, she’s 93.

3. Matt - August 28, 2006

“Either way, the point is, this was never and never will be up to astronomers. The public decides what is a planet around these here parts compadre. Pluto has a permanant “Don’t Mess” sign adhered to its icy surface.”

Oh, ok. As long as we’re making sensible arguments, and what not.

4. dr. gonzo - August 30, 2006

You don’t find that sensible?

5. Matt - September 2, 2006

People who have no education or background in astronomy deciding best what a planet is, instead of people who do? No, I don’t find that sensible.

That would be like someone who’s had no medical training aside from CPR saying, “The point is, how to do open heart surgery has never and never will be up to doctors and surgeons. The public decides how to perform open heart surgery.”

Um…. yeah.

6. dr. gonzo - September 2, 2006

It’s a semantics debate really. The definition is arbitrary and unscientific. Clear the orbit? What? Earth, Mars, Jupiter and Neptune haven’t cleared their orbits. Each planet is shadowed by thousands of asteroids.

I don’t think astronomers are any more qualified than anyone else. Given the small percentage that think this is a good definition I would say they are with the public on this one. My point is that no amount of officially defining terms that are almost indefinable will ever change public perception. Planet is a cultural term not a scientific one. That’s my point.

7. Lenoxus - October 7, 2006

I agree with “gonzo” re comment 5 — after all, the definition of a planet certinaly isn’t a life-or-death issue, at least not right now.


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