Plutarchians for a Planet Pluto

Plutarch was a bright dude. If he was around today, I know he would be championing Pluto’s cause, if for nothing other than the plentiful alliterations which it plovides us to play with.

Since this blog is positively starving for reader comments. Imagine my glee this afternoon when I received a 480-word response to my 270-word post about Pluto. There it was finally, proof! One of the things I love about this technology, is that I believe there are people out there who care enough to learn and inform others about seemingly everything. And so it is dear readers that Pluto, and it’s place among the planets, has an advocate.

As such, my 1 day fling with thinking of Pluto as something less than a planet, questioning it’s planethood in effect, is over. See the original post about Pluto in the Blog for Highland Park. In addition, please see the petition protesting the IAU’s irresponsible actions.

All Planet Pluto comments which in appeared in the comments section of the earlier Pluto blog post, are copied in full at end of this post.

Laurel Kornfeld in the Blog for Highland Park

Pluto IS a planet because unlike most objects in the Kuiper Belt, it has attained hydrostatic equilibrium, meaning it has enough self-gravity to have pulled itself into a round shape. When an object is large enough for this to happen, it becomes differentiated with core, mantle, and crust, just like Earth and the larger planets, and develops the same geological processes as the larger planets, processes that inert asteroids and most KBOs do not have.

Not distinguishing between shapeless asteroids and objects whose composition clearly makes them planets is a disservice and is sloppy science.

As of now, there are three other KBOs that meet this criterion and therefore should be classified as planets—Haumea, Makemake, and Eris. Only one KBO has been found to be larger than Pluto, and that is Eris.

The IAU definition makes no linguistic sense, as it states that dwarf planets are not planets at all. That’s like saying a grizzly bear is not a bear. Second, it defines objects solely by where they are while ignoring what they are. If Earth were placed in Pluto’s orbit, by the IAU definition, it would not be a planet. That is because the further away an object is from its parent star, the more difficulty it will have in clearing its orbit.

Significantly, this definition was adopted by only four percent of the IAU, most of whom are not planetary scientists. No absentee voting was allowed. It was done so in a highly controversial process that violated the IAU’s own bylaws, and it was immediately opposed by a petition of 300 professional astronomers saying they will not use the new definition, which they described accurately as “sloppy.” Also significant is the fact that many planetary scientists are not IAU members and therefore had no say in this matter at all.

Many believe we should keep the term planet broad to encompass any non-self-luminous spheroidal object orbiting a star.

We can distinguish different types of planets with subcategories such as terrestrial planets, gas giants, ice giants, dwarf planets, super Earths, hot Jupiters, etc.

We should be broadening, not narrowing our concept of planet as more objects are being discovered in this and other solar systems.
In a 2000 paper, Dr. Alan Stern and Dr. Hal Levison distinguish two types of planets—the gravitationally dominant ones and the smaller ones that are not gravitationally dominant. However, they never say that objects in the latter category are not planets.

I attended the Great Planet Debate, which actually took place in August 2008, and there was a strong consensus there that a broader, more encompassing planet definition is needed. I encourage anyone interested to listen to and view the conference proceedings at You can also read more about this issue on my blog at

You can find the petition of astronomers who rejected the demotion of Pluto here:

January 12, 2009 4:42 PM

About Jorge Costales

- Cuban Exile [veni] - Raised in Miami [vidi] - American Citizen [vici]
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1 Response to Plutarchians for a Planet Pluto

  1. I’m thrilled that I’ve been able to bring a smile to your face. For two years, I have been fighting the demotion of Pluto, which as you can see, I believe was just plain wrong on many levels. At this point, some professional astronomers are even questioning whether the International Astronomical Union should continue to be unquestioned as the “ruling body” in astronomy and are considering forming a rival planetary scientists organization.Meanwhile, you can advocate for Pluto by contacting the IAU, which holds its triennial General Assembly this August. Contact information can be found at , a site organized by Siobhan Elias, another Pluto supporter and friend of mine. She lives in Streator, Illinois, the town where Pluto discoverer Clyde Tombaugh was born in 1906.

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